diff --git a/bootstat/Android.bp b/bootstat/Android.bp
index 545a06f..ca59ef3 100644
--- a/bootstat/Android.bp
+++ b/bootstat/Android.bp
@@ -35,7 +35,7 @@
         "libcutils",
         "liblog",
     ],
-    static_libs: ["libgtest_prod"],
+    header_libs: ["libgtest_prod_headers"],
 }
 
 // bootstat static library
diff --git a/cpio/Android.bp b/cpio/Android.bp
index 16af079..cd2a624 100644
--- a/cpio/Android.bp
+++ b/cpio/Android.bp
@@ -8,7 +8,11 @@
     name: "mkbootfs",
     srcs: ["mkbootfs.c"],
     cflags: ["-Werror"],
-    shared_libs: ["libcutils"],
+    static_libs: [
+        "libbase",
+        "libcutils",
+        "liblog",
+    ],
     dist: {
         targets: ["dist_files"],
     },
diff --git a/debuggerd/debuggerd_test.cpp b/debuggerd/debuggerd_test.cpp
index 144faee..93725b9 100644
--- a/debuggerd/debuggerd_test.cpp
+++ b/debuggerd/debuggerd_test.cpp
@@ -274,7 +274,7 @@
   }
 
   if (signo == 0) {
-    ASSERT_TRUE(WIFEXITED(status));
+    ASSERT_TRUE(WIFEXITED(status)) << "Terminated due to unexpected signal " << WTERMSIG(status);
     ASSERT_EQ(0, WEXITSTATUS(signo));
   } else {
     ASSERT_FALSE(WIFEXITED(status));
diff --git a/debuggerd/seccomp_policy/crash_dump.arm64.policy b/debuggerd/seccomp_policy/crash_dump.arm64.policy
index 1585cc6..21887ab 100644
--- a/debuggerd/seccomp_policy/crash_dump.arm64.policy
+++ b/debuggerd/seccomp_policy/crash_dump.arm64.policy
@@ -24,7 +24,7 @@
 rt_sigprocmask: 1
 rt_sigaction: 1
 rt_tgsigqueueinfo: 1
-prctl: arg0 == PR_GET_NO_NEW_PRIVS || arg0 == 0x53564d41
+prctl: arg0 == PR_GET_NO_NEW_PRIVS || arg0 == 0x53564d41 || arg0 == PR_PAC_RESET_KEYS
 madvise: 1
 mprotect: arg2 in 0x1|0x2
 munmap: 1
diff --git a/debuggerd/seccomp_policy/crash_dump.policy.def b/debuggerd/seccomp_policy/crash_dump.policy.def
index cd5aad4..90843fc 100644
--- a/debuggerd/seccomp_policy/crash_dump.policy.def
+++ b/debuggerd/seccomp_policy/crash_dump.policy.def
@@ -34,7 +34,12 @@
 rt_tgsigqueueinfo: 1
 
 #define PR_SET_VMA 0x53564d41
+#if defined(__aarch64__)
+// PR_PAC_RESET_KEYS happens on aarch64 in pthread_create path.
+prctl: arg0 == PR_GET_NO_NEW_PRIVS || arg0 == PR_SET_VMA || arg0 == PR_PAC_RESET_KEYS
+#else
 prctl: arg0 == PR_GET_NO_NEW_PRIVS || arg0 == PR_SET_VMA
+#endif
 
 #if 0
 libminijail on vendor partitions older than P does not have constants from <sys/mman.h>.
diff --git a/fastboot/Android.bp b/fastboot/Android.bp
index 43b2ddd..2c70778 100644
--- a/fastboot/Android.bp
+++ b/fastboot/Android.bp
@@ -183,7 +183,7 @@
     ],
 
     static_libs: [
-        "libgtest_prod",
+        "libc++fs",
         "libhealthhalutils",
         "libsnapshot_cow",
         "libsnapshot_nobinder",
@@ -192,6 +192,7 @@
 
     header_libs: [
         "avb_headers",
+        "libgtest_prod_headers",
         "libsnapshot_headers",
         "libstorage_literals_headers",
     ],
diff --git a/fastboot/device/flashing.cpp b/fastboot/device/flashing.cpp
index 333ca50..ee0aa58 100644
--- a/fastboot/device/flashing.cpp
+++ b/fastboot/device/flashing.cpp
@@ -27,6 +27,7 @@
 
 #include <android-base/file.h>
 #include <android-base/logging.h>
+#include <android-base/properties.h>
 #include <android-base/strings.h>
 #include <ext4_utils/ext4_utils.h>
 #include <fs_mgr_overlayfs.h>
@@ -162,7 +163,9 @@
                 partition_name == "boot_b")) {
         CopyAVBFooter(&data, block_device_size);
     }
-    WipeOverlayfsForPartition(device, partition_name);
+    if (android::base::GetProperty("ro.system.build.type", "") != "user") {
+        WipeOverlayfsForPartition(device, partition_name);
+    }
     int result = FlashBlockDevice(handle.fd(), data);
     sync();
     return result;
diff --git a/fastboot/fastboot.cpp b/fastboot/fastboot.cpp
index 700d4bd..e5319a5 100644
--- a/fastboot/fastboot.cpp
+++ b/fastboot/fastboot.cpp
@@ -411,6 +411,13 @@
             " gsi wipe|disable           Wipe or disable a GSI installation (fastbootd only).\n"
             " wipe-super [SUPER_EMPTY]   Wipe the super partition. This will reset it to\n"
             "                            contain an empty set of default dynamic partitions.\n"
+            " create-logical-partition NAME SIZE\n"
+            "                            Create a logical partition with the given name and\n"
+            "                            size, in the super partition.\n"
+            " delete-logical-partition NAME\n"
+            "                            Delete a logical partition with the given name.\n"
+            " resize-logical-partition NAME SIZE\n"
+            "                            Change the size of the named logical partition.\n"
             " snapshot-update cancel     On devices that support snapshot-based updates, cancel\n"
             "                            an in-progress update. This may make the device\n"
             "                            unbootable until it is reflashed.\n"
@@ -673,7 +680,7 @@
     return fd;
 }
 
-static void CheckRequirement(const std::string& cur_product, const std::string& var,
+static bool CheckRequirement(const std::string& cur_product, const std::string& var,
                              const std::string& product, bool invert,
                              const std::vector<std::string>& options) {
     Status("Checking '" + var + "'");
@@ -685,7 +692,7 @@
             double split = now();
             fprintf(stderr, "IGNORE, product is %s required only for %s [%7.3fs]\n",
                     cur_product.c_str(), product.c_str(), (split - start));
-            return;
+            return true;
         }
     }
 
@@ -694,7 +701,7 @@
         fprintf(stderr, "FAILED\n\n");
         fprintf(stderr, "Could not getvar for '%s' (%s)\n\n", var.c_str(),
                 fb->Error().c_str());
-        die("requirements not met!");
+        return false;
     }
 
     bool match = false;
@@ -714,7 +721,7 @@
     if (match) {
         double split = now();
         fprintf(stderr, "OKAY [%7.3fs]\n", (split - start));
-        return;
+        return true;
     }
 
     fprintf(stderr, "FAILED\n\n");
@@ -724,7 +731,7 @@
         fprintf(stderr, " or '%s'", it->c_str());
     }
     fprintf(stderr, ".\n\n");
-    die("requirements not met!");
+    return false;
 }
 
 bool ParseRequirementLine(const std::string& line, std::string* name, std::string* product,
@@ -788,7 +795,7 @@
     }
 }
 
-static void CheckRequirements(const std::string& data) {
+static void CheckRequirements(const std::string& data, bool force_flash) {
     std::string cur_product;
     if (fb->GetVar("product", &cur_product) != fastboot::SUCCESS) {
         fprintf(stderr, "getvar:product FAILED (%s)\n", fb->Error().c_str());
@@ -812,7 +819,14 @@
         if (name == "partition-exists") {
             HandlePartitionExists(options);
         } else {
-            CheckRequirement(cur_product, name, product, invert, options);
+            bool met = CheckRequirement(cur_product, name, product, invert, options);
+            if (!met) {
+                if (!force_flash) {
+                  die("requirements not met!");
+                } else {
+                  fprintf(stderr, "requirements not met! but proceeding due to --force\n");
+                }
+            }
         }
     }
 }
@@ -1405,7 +1419,8 @@
 
 class FlashAllTool {
   public:
-    FlashAllTool(const ImageSource& source, const std::string& slot_override, bool skip_secondary, bool wipe);
+    FlashAllTool(const ImageSource& source, const std::string& slot_override, bool skip_secondary,
+                 bool wipe, bool force_flash);
 
     void Flash();
 
@@ -1421,16 +1436,19 @@
     std::string slot_override_;
     bool skip_secondary_;
     bool wipe_;
+    bool force_flash_;
     std::string secondary_slot_;
     std::vector<std::pair<const Image*, std::string>> boot_images_;
     std::vector<std::pair<const Image*, std::string>> os_images_;
 };
 
-FlashAllTool::FlashAllTool(const ImageSource& source, const std::string& slot_override, bool skip_secondary, bool wipe)
+FlashAllTool::FlashAllTool(const ImageSource& source, const std::string& slot_override,
+                           bool skip_secondary, bool wipe, bool force_flash)
    : source_(source),
      slot_override_(slot_override),
      skip_secondary_(skip_secondary),
-     wipe_(wipe)
+     wipe_(wipe),
+     force_flash_(force_flash)
 {
 }
 
@@ -1478,7 +1496,7 @@
     if (!source_.ReadFile("android-info.txt", &contents)) {
         die("could not read android-info.txt");
     }
-    ::CheckRequirements({contents.data(), contents.size()});
+    ::CheckRequirements({contents.data(), contents.size()}, force_flash_);
 }
 
 void FlashAllTool::DetermineSecondarySlot() {
@@ -1598,14 +1616,15 @@
     return unzip_to_file(zip_, name.c_str());
 }
 
-static void do_update(const char* filename, const std::string& slot_override, bool skip_secondary) {
+static void do_update(const char* filename, const std::string& slot_override, bool skip_secondary,
+                      bool force_flash) {
     ZipArchiveHandle zip;
     int error = OpenArchive(filename, &zip);
     if (error != 0) {
         die("failed to open zip file '%s': %s", filename, ErrorCodeString(error));
     }
 
-    FlashAllTool tool(ZipImageSource(zip), slot_override, skip_secondary, false);
+    FlashAllTool tool(ZipImageSource(zip), slot_override, skip_secondary, false, force_flash);
     tool.Flash();
 
     CloseArchive(zip);
@@ -1630,8 +1649,9 @@
     return unique_fd(TEMP_FAILURE_RETRY(open(path.c_str(), O_RDONLY | O_BINARY)));
 }
 
-static void do_flashall(const std::string& slot_override, bool skip_secondary, bool wipe) {
-    FlashAllTool tool(LocalImageSource(), slot_override, skip_secondary, wipe);
+static void do_flashall(const std::string& slot_override, bool skip_secondary, bool wipe,
+                        bool force_flash) {
+    FlashAllTool tool(LocalImageSource(), slot_override, skip_secondary, wipe, force_flash);
     tool.Flash();
 }
 
@@ -2179,9 +2199,9 @@
         } else if (command == "flashall") {
             if (slot_override == "all") {
                 fprintf(stderr, "Warning: slot set to 'all'. Secondary slots will not be flashed.\n");
-                do_flashall(slot_override, true, wants_wipe);
+                do_flashall(slot_override, true, wants_wipe, force_flash);
             } else {
-                do_flashall(slot_override, skip_secondary, wants_wipe);
+                do_flashall(slot_override, skip_secondary, wants_wipe, force_flash);
             }
             wants_reboot = true;
         } else if (command == "update") {
@@ -2193,7 +2213,7 @@
             if (!args.empty()) {
                 filename = next_arg(&args);
             }
-            do_update(filename.c_str(), slot_override, skip_secondary || slot_all);
+            do_update(filename.c_str(), slot_override, skip_secondary || slot_all, force_flash);
             wants_reboot = true;
         } else if (command == FB_CMD_SET_ACTIVE) {
             std::string slot = verify_slot(next_arg(&args), false);
diff --git a/fs_mgr/fs_mgr.cpp b/fs_mgr/fs_mgr.cpp
index 6952cdf..ea9d333 100644
--- a/fs_mgr/fs_mgr.cpp
+++ b/fs_mgr/fs_mgr.cpp
@@ -264,12 +264,12 @@
                 F2FS_FSCK_BIN, "-f", "-c", "10000", "--debug-cache", blk_device.c_str()};
 
         if (should_force_check(*fs_stat)) {
-            LINFO << "Running " << F2FS_FSCK_BIN << " -f -c 10000 --debug-cache"
+            LINFO << "Running " << F2FS_FSCK_BIN << " -f -c 10000 --debug-cache "
                   << realpath(blk_device);
             ret = logwrap_fork_execvp(ARRAY_SIZE(f2fs_fsck_forced_argv), f2fs_fsck_forced_argv,
                                       &status, false, LOG_KLOG | LOG_FILE, false, FSCK_LOG_FILE);
         } else {
-            LINFO << "Running " << F2FS_FSCK_BIN << " -a -c 10000 --debug-cache"
+            LINFO << "Running " << F2FS_FSCK_BIN << " -a -c 10000 --debug-cache "
                   << realpath(blk_device);
             ret = logwrap_fork_execvp(ARRAY_SIZE(f2fs_fsck_argv), f2fs_fsck_argv, &status, false,
                                       LOG_KLOG | LOG_FILE, false, FSCK_LOG_FILE);
@@ -647,6 +647,46 @@
     return sb == cpu_to_le32(F2FS_SUPER_MAGIC);
 }
 
+static void SetReadAheadSize(const std::string& entry_block_device, off64_t size_kb) {
+    std::string block_device;
+    if (!Realpath(entry_block_device, &block_device)) {
+        PERROR << "Failed to realpath " << entry_block_device;
+        return;
+    }
+
+    static constexpr std::string_view kDevBlockPrefix("/dev/block/");
+    if (!android::base::StartsWith(block_device, kDevBlockPrefix)) {
+        LWARNING << block_device << " is not a block device";
+        return;
+    }
+
+    DeviceMapper& dm = DeviceMapper::Instance();
+    while (true) {
+        std::string block_name = block_device;
+        if (android::base::StartsWith(block_device, kDevBlockPrefix)) {
+            block_name = block_device.substr(kDevBlockPrefix.length());
+        }
+        std::string sys_partition =
+                android::base::StringPrintf("/sys/class/block/%s/partition", block_name.c_str());
+        struct stat info;
+        if (lstat(sys_partition.c_str(), &info) == 0) {
+            // it has a partition like "sda12".
+            block_name += "/..";
+        }
+        std::string sys_ra = android::base::StringPrintf("/sys/class/block/%s/queue/read_ahead_kb",
+                                                         block_name.c_str());
+        std::string size = android::base::StringPrintf("%llu", (long long)size_kb);
+        android::base::WriteStringToFile(size, sys_ra.c_str());
+        LINFO << "Set readahead_kb: " << size << " on " << sys_ra;
+
+        auto parent = dm.GetParentBlockDeviceByPath(block_device);
+        if (!parent) {
+            return;
+        }
+        block_device = *parent;
+    }
+}
+
 //
 // Prepare the filesystem on the given block device to be mounted.
 //
@@ -667,6 +707,11 @@
     }
     mkdir(mount_point.c_str(), 0755);
 
+    // Don't need to return error, since it's a salt
+    if (entry.readahead_size_kb != -1) {
+        SetReadAheadSize(blk_device, entry.readahead_size_kb);
+    }
+
     int fs_stat = 0;
 
     if (is_extfs(entry.fs_type)) {
diff --git a/fs_mgr/fs_mgr_fstab.cpp b/fs_mgr/fs_mgr_fstab.cpp
index ad48dd1..42bf356 100644
--- a/fs_mgr/fs_mgr_fstab.cpp
+++ b/fs_mgr/fs_mgr_fstab.cpp
@@ -255,6 +255,13 @@
             } else {
                 entry->reserved_size = static_cast<off64_t>(size);
             }
+        } else if (StartsWith(flag, "readahead_size_kb=")) {
+            int val;
+            if (ParseInt(arg, &val, 0, 16 * 1024)) {
+                entry->readahead_size_kb = val;
+            } else {
+                LWARNING << "Warning: readahead_size_kb= flag malformed (0 ~ 16MB): " << arg;
+            }
         } else if (StartsWith(flag, "eraseblk=")) {
             // The erase block size flag is followed by an = and the flash erase block size. Get it,
             // check that it is a power of 2 and at least 4096, and return it.
diff --git a/fs_mgr/fs_mgr_overlayfs.cpp b/fs_mgr/fs_mgr_overlayfs.cpp
index 1134f14..cb09383 100644
--- a/fs_mgr/fs_mgr_overlayfs.cpp
+++ b/fs_mgr/fs_mgr_overlayfs.cpp
@@ -116,6 +116,8 @@
 void MapScratchPartitionIfNeeded(Fstab*, const std::function<bool(const std::set<std::string>&)>&) {
 }
 
+void CleanupOldScratchFiles() {}
+
 void TeardownAllOverlayForMountPoint(const std::string&) {}
 
 }  // namespace fs_mgr
diff --git a/fs_mgr/include_fstab/fstab/fstab.h b/fs_mgr/include_fstab/fstab/fstab.h
index 8ecf41b..2704e47 100644
--- a/fs_mgr/include_fstab/fstab/fstab.h
+++ b/fs_mgr/include_fstab/fstab/fstab.h
@@ -47,6 +47,7 @@
     int max_comp_streams = 0;
     off64_t zram_size = 0;
     off64_t reserved_size = 0;
+    off64_t readahead_size_kb = -1;
     std::string encryption_options;
     off64_t erase_blk_size = 0;
     off64_t logical_blk_size = 0;
diff --git a/fs_mgr/libdm/dm_target.cpp b/fs_mgr/libdm/dm_target.cpp
index ef46eb9..b0639e6 100644
--- a/fs_mgr/libdm/dm_target.cpp
+++ b/fs_mgr/libdm/dm_target.cpp
@@ -95,7 +95,9 @@
 }
 
 void DmTargetVerity::SetVerityMode(const std::string& mode) {
-    if (mode != "restart_on_corruption" && mode != "ignore_corruption") {
+    if (mode != "panic_on_corruption" &&
+        mode != "restart_on_corruption" &&
+        mode != "ignore_corruption") {
         LOG(ERROR) << "Unknown verity mode: " << mode;
         valid_ = false;
         return;
diff --git a/fs_mgr/libfs_avb/avb_util.cpp b/fs_mgr/libfs_avb/avb_util.cpp
index 2288674..31494c1 100644
--- a/fs_mgr/libfs_avb/avb_util.cpp
+++ b/fs_mgr/libfs_avb/avb_util.cpp
@@ -61,7 +61,9 @@
 
     // Converts veritymode to the format used in kernel.
     std::string dm_verity_mode;
-    if (verity_mode == "enforcing") {
+    if (verity_mode == "panicking") {
+        dm_verity_mode = "panic_on_corruption";
+    } else if (verity_mode == "enforcing") {
         dm_verity_mode = "restart_on_corruption";
     } else if (verity_mode == "logging") {
         dm_verity_mode = "ignore_corruption";
diff --git a/fs_mgr/libsnapshot/Android.bp b/fs_mgr/libsnapshot/Android.bp
index e28cfd4..adfb56c 100644
--- a/fs_mgr/libsnapshot/Android.bp
+++ b/fs_mgr/libsnapshot/Android.bp
@@ -265,6 +265,7 @@
         "android.hardware.boot@1.0",
         "android.hardware.boot@1.1",
         "libbrotli",
+        "libc++fs",
         "libfs_mgr",
         "libgsi",
         "libgmock",
@@ -298,6 +299,7 @@
     ],
     static_libs: [
         "libbrotli",
+        "libc++fs",
         "libfstab",
         "libsnapshot",
         "libsnapshot_cow",
@@ -327,6 +329,7 @@
         "power_test.cpp",
     ],
     static_libs: [
+        "libc++fs",
         "libsnapshot",
         "update_metadata-protos",
     ],
@@ -356,6 +359,7 @@
     static_libs: [
         "libbase",
         "libbrotli",
+        "libc++fs",
         "libchrome",
         "libcrypto_static",
         "libcutils",
@@ -418,6 +422,7 @@
         "snapuserd.cpp",
         "snapuserd_daemon.cpp",
 	"snapuserd_worker.cpp",
+	"snapuserd_readahead.cpp",
     ],
 
     cflags: [
diff --git a/fs_mgr/libsnapshot/android/snapshot/snapshot.proto b/fs_mgr/libsnapshot/android/snapshot/snapshot.proto
index 1ebc29f..92aa55c 100644
--- a/fs_mgr/libsnapshot/android/snapshot/snapshot.proto
+++ b/fs_mgr/libsnapshot/android/snapshot/snapshot.proto
@@ -139,7 +139,28 @@
     Cancelled = 7;
 };
 
-// Next: 7
+// Next 14:
+//
+// To understand the source of each failure, read snapshot.cpp. To handle new
+// sources of failure, avoid reusing an existing code; add a new code instead.
+enum MergeFailureCode {
+    Ok = 0;
+    ReadStatus = 1;
+    GetTableInfo = 2;
+    UnknownTable = 3;
+    GetTableParams = 4;
+    ActivateNewTable = 5;
+    AcquireLock = 6;
+    ListSnapshots = 7;
+    WriteStatus = 8;
+    UnknownTargetType = 9;
+    QuerySnapshotStatus = 10;
+    ExpectedMergeTarget = 11;
+    UnmergedSectorsAfterCompletion = 12;
+    UnexpectedMergeState = 13;
+};
+
+// Next: 8
 message SnapshotUpdateStatus {
     UpdateState state = 1;
 
@@ -160,9 +181,12 @@
 
     // Merge phase (if state == MERGING).
     MergePhase merge_phase = 6;
+
+    // Merge failure code, filled if state == MergeFailed.
+    MergeFailureCode merge_failure_code = 7;
 }
 
-// Next: 9
+// Next: 10
 message SnapshotMergeReport {
     // Status of the update after the merge attempts.
     UpdateState state = 1;
@@ -188,4 +212,7 @@
 
     // Time from sys.boot_completed to merge start, in milliseconds.
     uint32 boot_complete_to_merge_start_time_ms = 8;
+
+    // Merge failure code, filled if state == MergeFailed.
+    MergeFailureCode merge_failure_code = 9;
 }
diff --git a/fs_mgr/libsnapshot/cow_api_test.cpp b/fs_mgr/libsnapshot/cow_api_test.cpp
index 5d63220..b75b154 100644
--- a/fs_mgr/libsnapshot/cow_api_test.cpp
+++ b/fs_mgr/libsnapshot/cow_api_test.cpp
@@ -25,6 +25,10 @@
 #include <libsnapshot/cow_reader.h>
 #include <libsnapshot/cow_writer.h>
 
+using testing::AssertionFailure;
+using testing::AssertionResult;
+using testing::AssertionSuccess;
+
 namespace android {
 namespace snapshot {
 
@@ -781,6 +785,202 @@
     ASSERT_TRUE(reader.Parse(cow_->fd));
 }
 
+AssertionResult WriteDataBlock(CowWriter* writer, uint64_t new_block, std::string data) {
+    data.resize(writer->options().block_size, '\0');
+    if (!writer->AddRawBlocks(new_block, data.data(), data.size())) {
+        return AssertionFailure() << "Failed to add raw block";
+    }
+    return AssertionSuccess();
+}
+
+AssertionResult CompareDataBlock(CowReader* reader, const CowOperation& op,
+                                 const std::string& data) {
+    CowHeader header;
+    reader->GetHeader(&header);
+
+    std::string cmp = data;
+    cmp.resize(header.block_size, '\0');
+
+    StringSink sink;
+    if (!reader->ReadData(op, &sink)) {
+        return AssertionFailure() << "Failed to read data block";
+    }
+    if (cmp != sink.stream()) {
+        return AssertionFailure() << "Data blocks did not match, expected " << cmp << ", got "
+                                  << sink.stream();
+    }
+
+    return AssertionSuccess();
+}
+
+TEST_F(CowTest, ResumeMidCluster) {
+    CowOptions options;
+    options.cluster_ops = 7;
+    auto writer = std::make_unique<CowWriter>(options);
+    ASSERT_TRUE(writer->Initialize(cow_->fd));
+
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 1, "Block 1"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 2, "Block 2"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 3, "Block 3"));
+    ASSERT_TRUE(writer->AddLabel(1));
+    ASSERT_TRUE(writer->Finalize());
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 4, "Block 4"));
+    ASSERT_EQ(lseek(cow_->fd, 0, SEEK_SET), 0);
+
+    writer = std::make_unique<CowWriter>(options);
+    ASSERT_TRUE(writer->InitializeAppend(cow_->fd, 1));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 4, "Block 4"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 5, "Block 5"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 6, "Block 6"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 7, "Block 7"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 8, "Block 8"));
+    ASSERT_TRUE(writer->AddLabel(2));
+    ASSERT_TRUE(writer->Finalize());
+    ASSERT_EQ(lseek(cow_->fd, 0, SEEK_SET), 0);
+
+    CowReader reader;
+    ASSERT_TRUE(reader.Parse(cow_->fd));
+
+    auto iter = reader.GetOpIter();
+    size_t num_replace = 0;
+    size_t max_in_cluster = 0;
+    size_t num_in_cluster = 0;
+    size_t num_clusters = 0;
+    while (!iter->Done()) {
+        const auto& op = iter->Get();
+
+        num_in_cluster++;
+        max_in_cluster = std::max(max_in_cluster, num_in_cluster);
+
+        if (op.type == kCowReplaceOp) {
+            num_replace++;
+
+            ASSERT_EQ(op.new_block, num_replace);
+            ASSERT_TRUE(CompareDataBlock(&reader, op, "Block " + std::to_string(num_replace)));
+        } else if (op.type == kCowClusterOp) {
+            num_in_cluster = 0;
+            num_clusters++;
+        }
+
+        iter->Next();
+    }
+    ASSERT_EQ(num_replace, 8);
+    ASSERT_EQ(max_in_cluster, 7);
+    ASSERT_EQ(num_clusters, 2);
+}
+
+TEST_F(CowTest, ResumeEndCluster) {
+    CowOptions options;
+    int cluster_ops = 5;
+    options.cluster_ops = cluster_ops;
+    auto writer = std::make_unique<CowWriter>(options);
+    ASSERT_TRUE(writer->Initialize(cow_->fd));
+
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 1, "Block 1"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 2, "Block 2"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 3, "Block 3"));
+    ASSERT_TRUE(writer->AddLabel(1));
+    ASSERT_TRUE(writer->Finalize());
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 4, "Block 4"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 5, "Block 5"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 6, "Block 6"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 7, "Block 7"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 8, "Block 8"));
+    ASSERT_EQ(lseek(cow_->fd, 0, SEEK_SET), 0);
+
+    writer = std::make_unique<CowWriter>(options);
+    ASSERT_TRUE(writer->InitializeAppend(cow_->fd, 1));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 4, "Block 4"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 5, "Block 5"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 6, "Block 6"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 7, "Block 7"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 8, "Block 8"));
+    ASSERT_TRUE(writer->AddLabel(2));
+    ASSERT_TRUE(writer->Finalize());
+    ASSERT_EQ(lseek(cow_->fd, 0, SEEK_SET), 0);
+
+    CowReader reader;
+    ASSERT_TRUE(reader.Parse(cow_->fd));
+
+    auto iter = reader.GetOpIter();
+    size_t num_replace = 0;
+    size_t max_in_cluster = 0;
+    size_t num_in_cluster = 0;
+    size_t num_clusters = 0;
+    while (!iter->Done()) {
+        const auto& op = iter->Get();
+
+        num_in_cluster++;
+        max_in_cluster = std::max(max_in_cluster, num_in_cluster);
+
+        if (op.type == kCowReplaceOp) {
+            num_replace++;
+
+            ASSERT_EQ(op.new_block, num_replace);
+            ASSERT_TRUE(CompareDataBlock(&reader, op, "Block " + std::to_string(num_replace)));
+        } else if (op.type == kCowClusterOp) {
+            num_in_cluster = 0;
+            num_clusters++;
+        }
+
+        iter->Next();
+    }
+    ASSERT_EQ(num_replace, 8);
+    ASSERT_EQ(max_in_cluster, cluster_ops);
+    ASSERT_EQ(num_clusters, 3);
+}
+
+TEST_F(CowTest, DeleteMidCluster) {
+    CowOptions options;
+    options.cluster_ops = 7;
+    auto writer = std::make_unique<CowWriter>(options);
+    ASSERT_TRUE(writer->Initialize(cow_->fd));
+
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 1, "Block 1"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 2, "Block 2"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 3, "Block 3"));
+    ASSERT_TRUE(writer->AddLabel(1));
+    ASSERT_TRUE(writer->Finalize());
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 4, "Block 4"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 5, "Block 5"));
+    ASSERT_TRUE(WriteDataBlock(writer.get(), 6, "Block 6"));
+    ASSERT_EQ(lseek(cow_->fd, 0, SEEK_SET), 0);
+
+    writer = std::make_unique<CowWriter>(options);
+    ASSERT_TRUE(writer->InitializeAppend(cow_->fd, 1));
+    ASSERT_TRUE(writer->Finalize());
+    ASSERT_EQ(lseek(cow_->fd, 0, SEEK_SET), 0);
+
+    CowReader reader;
+    ASSERT_TRUE(reader.Parse(cow_->fd));
+
+    auto iter = reader.GetOpIter();
+    size_t num_replace = 0;
+    size_t max_in_cluster = 0;
+    size_t num_in_cluster = 0;
+    size_t num_clusters = 0;
+    while (!iter->Done()) {
+        const auto& op = iter->Get();
+
+        num_in_cluster++;
+        max_in_cluster = std::max(max_in_cluster, num_in_cluster);
+        if (op.type == kCowReplaceOp) {
+            num_replace++;
+
+            ASSERT_EQ(op.new_block, num_replace);
+            ASSERT_TRUE(CompareDataBlock(&reader, op, "Block " + std::to_string(num_replace)));
+        } else if (op.type == kCowClusterOp) {
+            num_in_cluster = 0;
+            num_clusters++;
+        }
+
+        iter->Next();
+    }
+    ASSERT_EQ(num_replace, 3);
+    ASSERT_EQ(max_in_cluster, 5);  // 3 data, 1 label, 1 cluster op
+    ASSERT_EQ(num_clusters, 1);
+}
+
 }  // namespace snapshot
 }  // namespace android
 
diff --git a/fs_mgr/libsnapshot/cow_reader.cpp b/fs_mgr/libsnapshot/cow_reader.cpp
index 7199b38..35a02e6 100644
--- a/fs_mgr/libsnapshot/cow_reader.cpp
+++ b/fs_mgr/libsnapshot/cow_reader.cpp
@@ -94,11 +94,6 @@
                    << "Expected: " << kCowMagicNumber;
         return false;
     }
-    if (header_.header_size != sizeof(CowHeader)) {
-        LOG(ERROR) << "Header size unknown, read " << header_.header_size << ", expected "
-                   << sizeof(CowHeader);
-        return false;
-    }
     if (header_.footer_size != sizeof(CowFooter)) {
         LOG(ERROR) << "Footer size unknown, read " << header_.footer_size << ", expected "
                    << sizeof(CowFooter);
@@ -123,8 +118,7 @@
         return false;
     }
 
-    if ((header_.major_version != kCowVersionMajor) ||
-        (header_.minor_version != kCowVersionMinor)) {
+    if ((header_.major_version > kCowVersionMajor) || (header_.minor_version != kCowVersionMinor)) {
         LOG(ERROR) << "Header version mismatch";
         LOG(ERROR) << "Major version: " << header_.major_version
                    << "Expected: " << kCowVersionMajor;
@@ -137,10 +131,25 @@
 }
 
 bool CowReader::ParseOps(std::optional<uint64_t> label) {
-    uint64_t pos = lseek(fd_.get(), sizeof(header_), SEEK_SET);
-    if (pos != sizeof(header_)) {
-        PLOG(ERROR) << "lseek ops failed";
-        return false;
+    uint64_t pos;
+
+    // Skip the scratch space
+    if (header_.major_version >= 2 && (header_.buffer_size > 0)) {
+        LOG(DEBUG) << " Scratch space found of size: " << header_.buffer_size;
+        size_t init_offset = header_.header_size + header_.buffer_size;
+        pos = lseek(fd_.get(), init_offset, SEEK_SET);
+        if (pos != init_offset) {
+            PLOG(ERROR) << "lseek ops failed";
+            return false;
+        }
+    } else {
+        pos = lseek(fd_.get(), header_.header_size, SEEK_SET);
+        if (pos != header_.header_size) {
+            PLOG(ERROR) << "lseek ops failed";
+            return false;
+        }
+        // Reading a v1 version of COW which doesn't have buffer_size.
+        header_.buffer_size = 0;
     }
 
     auto ops_buffer = std::make_shared<std::vector<CowOperation>>();
@@ -360,13 +369,7 @@
     //                        Replace-op-4, Zero-op-9, Replace-op-5 }
     //==============================================================
 
-    for (uint64_t i = 0; i < ops_->size(); i++) {
-        auto& current_op = ops_->data()[i];
-        if (current_op.type != kCowCopyOp) {
-            break;
-        }
-        num_copy_ops += 1;
-    }
+    num_copy_ops = FindNumCopyops();
 
     std::sort(ops_.get()->begin() + num_copy_ops, ops_.get()->end(),
               [](CowOperation& op1, CowOperation& op2) -> bool {
@@ -377,6 +380,23 @@
         CHECK(ops_->size() >= header_.num_merge_ops);
         ops_->erase(ops_.get()->begin(), ops_.get()->begin() + header_.num_merge_ops);
     }
+
+    num_copy_ops = FindNumCopyops();
+    set_copy_ops(num_copy_ops);
+}
+
+uint64_t CowReader::FindNumCopyops() {
+    uint64_t num_copy_ops = 0;
+
+    for (uint64_t i = 0; i < ops_->size(); i++) {
+        auto& current_op = ops_->data()[i];
+        if (current_op.type != kCowCopyOp) {
+            break;
+        }
+        num_copy_ops += 1;
+    }
+
+    return num_copy_ops;
 }
 
 bool CowReader::GetHeader(CowHeader* header) {
@@ -470,7 +490,7 @@
 
 bool CowReader::GetRawBytes(uint64_t offset, void* buffer, size_t len, size_t* read) {
     // Validate the offset, taking care to acknowledge possible overflow of offset+len.
-    if (offset < sizeof(header_) || offset >= fd_size_ - sizeof(CowFooter) || len >= fd_size_ ||
+    if (offset < header_.header_size || offset >= fd_size_ - sizeof(CowFooter) || len >= fd_size_ ||
         offset + len > fd_size_ - sizeof(CowFooter)) {
         LOG(ERROR) << "invalid data offset: " << offset << ", " << len << " bytes";
         return false;
diff --git a/fs_mgr/libsnapshot/cow_snapuserd_test.cpp b/fs_mgr/libsnapshot/cow_snapuserd_test.cpp
index 045d9db..313eb64 100644
--- a/fs_mgr/libsnapshot/cow_snapuserd_test.cpp
+++ b/fs_mgr/libsnapshot/cow_snapuserd_test.cpp
@@ -96,6 +96,7 @@
 class CowSnapuserdTest final {
   public:
     bool Setup();
+    bool SetupCopyOverlap();
     bool Merge();
     void ValidateMerge();
     void ReadSnapshotDeviceAndValidate();
@@ -114,6 +115,7 @@
     void StartMerge();
 
     void CreateCowDevice();
+    void CreateCowDeviceWithCopyOverlap();
     void CreateBaseDevice();
     void InitCowDevice();
     void SetDeviceControlName();
@@ -191,6 +193,24 @@
     return setup_ok_;
 }
 
+bool CowSnapuserdTest::SetupCopyOverlap() {
+    CreateBaseDevice();
+    CreateCowDeviceWithCopyOverlap();
+
+    SetDeviceControlName();
+
+    StartSnapuserdDaemon();
+    InitCowDevice();
+
+    CreateDmUserDevice();
+    InitDaemon();
+
+    CreateSnapshotDevice();
+    setup_ok_ = true;
+
+    return setup_ok_;
+}
+
 void CowSnapuserdTest::StartSnapuserdDaemon() {
     pid_t pid = fork();
     ASSERT_GE(pid, 0);
@@ -255,6 +275,49 @@
     ASSERT_EQ(memcmp(snapuserd_buffer.get(), (char*)orig_buffer_.get() + (size_ * 3), size_), 0);
 }
 
+void CowSnapuserdTest::CreateCowDeviceWithCopyOverlap() {
+    std::string path = android::base::GetExecutableDirectory();
+    cow_system_ = std::make_unique<TemporaryFile>(path);
+
+    CowOptions options;
+    options.compression = "gz";
+    CowWriter writer(options);
+
+    ASSERT_TRUE(writer.Initialize(cow_system_->fd));
+
+    size_t num_blocks = size_ / options.block_size;
+    size_t x = num_blocks;
+    size_t blk_src_copy = num_blocks - 1;
+
+    // Create overlapping copy operations
+    while (1) {
+        ASSERT_TRUE(writer.AddCopy(blk_src_copy + 1, blk_src_copy));
+        x -= 1;
+        if (x == 0) {
+            ASSERT_EQ(blk_src_copy, 0);
+            break;
+        }
+        blk_src_copy -= 1;
+    }
+
+    // Flush operations
+    ASSERT_TRUE(writer.Finalize());
+
+    // Construct the buffer required for validation
+    orig_buffer_ = std::make_unique<uint8_t[]>(total_base_size_);
+
+    // Read the entire base device
+    ASSERT_EQ(android::base::ReadFullyAtOffset(base_fd_, orig_buffer_.get(), total_base_size_, 0),
+              true);
+
+    // Merged operations
+    ASSERT_EQ(android::base::ReadFullyAtOffset(base_fd_, orig_buffer_.get(), options.block_size, 0),
+              true);
+    ASSERT_EQ(android::base::ReadFullyAtOffset(
+                      base_fd_, (char*)orig_buffer_.get() + options.block_size, size_, 0),
+              true);
+}
+
 void CowSnapuserdTest::CreateCowDevice() {
     unique_fd rnd_fd;
     loff_t offset = 0;
@@ -707,17 +770,17 @@
 
             de = reinterpret_cast<struct disk_exception*>((char*)buffer + offset);
             ASSERT_EQ(de->old_chunk, 21);
-            ASSERT_EQ(de->new_chunk, 537);
+            ASSERT_EQ(de->new_chunk, 536);
             offset += sizeof(struct disk_exception);
 
             de = reinterpret_cast<struct disk_exception*>((char*)buffer + offset);
             ASSERT_EQ(de->old_chunk, 22);
-            ASSERT_EQ(de->new_chunk, 538);
+            ASSERT_EQ(de->new_chunk, 537);
             offset += sizeof(struct disk_exception);
 
             de = reinterpret_cast<struct disk_exception*>((char*)buffer + offset);
             ASSERT_EQ(de->old_chunk, 23);
-            ASSERT_EQ(de->new_chunk, 539);
+            ASSERT_EQ(de->new_chunk, 538);
             offset += sizeof(struct disk_exception);
 
             // End of metadata
@@ -757,6 +820,23 @@
     harness.ValidateMerge();
     harness.Shutdown();
 }
+
+TEST(Snapuserd_Test, Snapshot_COPY_Overlap_TEST) {
+    CowSnapuserdTest harness;
+    ASSERT_TRUE(harness.SetupCopyOverlap());
+    ASSERT_TRUE(harness.Merge());
+    harness.ValidateMerge();
+    harness.Shutdown();
+}
+
+TEST(Snapuserd_Test, Snapshot_COPY_Overlap_Merge_Resume_TEST) {
+    CowSnapuserdTest harness;
+    ASSERT_TRUE(harness.SetupCopyOverlap());
+    harness.MergeInterrupt();
+    harness.ValidateMerge();
+    harness.Shutdown();
+}
+
 }  // namespace snapshot
 }  // namespace android
 
diff --git a/fs_mgr/libsnapshot/cow_writer.cpp b/fs_mgr/libsnapshot/cow_writer.cpp
index 59f6d6f..51c00a9 100644
--- a/fs_mgr/libsnapshot/cow_writer.cpp
+++ b/fs_mgr/libsnapshot/cow_writer.cpp
@@ -94,6 +94,7 @@
     header_.block_size = options_.block_size;
     header_.num_merge_ops = 0;
     header_.cluster_ops = options_.cluster_ops;
+    header_.buffer_size = 0;
     footer_ = {};
     footer_.op.data_length = 64;
     footer_.op.type = kCowFooterOp;
@@ -139,12 +140,6 @@
     return true;
 }
 
-void CowWriter::InitializeMerge(borrowed_fd fd, CowHeader* header) {
-    fd_ = fd;
-    memcpy(&header_, header, sizeof(CowHeader));
-    merge_in_progress_ = true;
-}
-
 bool CowWriter::Initialize(unique_fd&& fd) {
     owned_fd_ = std::move(fd);
     return Initialize(borrowed_fd{owned_fd_});
@@ -172,7 +167,7 @@
 }
 
 void CowWriter::InitPos() {
-    next_op_pos_ = sizeof(header_);
+    next_op_pos_ = sizeof(header_) + header_.buffer_size;
     cluster_size_ = header_.cluster_ops * sizeof(CowOperation);
     if (header_.cluster_ops) {
         next_data_pos_ = next_op_pos_ + cluster_size_;
@@ -196,6 +191,10 @@
         return false;
     }
 
+    if (options_.scratch_space) {
+        header_.buffer_size = BUFFER_REGION_DEFAULT_SIZE;
+    }
+
     // Headers are not complete, but this ensures the file is at the right
     // position.
     if (!android::base::WriteFully(fd_, &header_, sizeof(header_))) {
@@ -203,7 +202,27 @@
         return false;
     }
 
+    if (options_.scratch_space) {
+        // Initialize the scratch space
+        std::string data(header_.buffer_size, 0);
+        if (!android::base::WriteFully(fd_, data.data(), header_.buffer_size)) {
+            PLOG(ERROR) << "writing scratch space failed";
+            return false;
+        }
+    }
+
+    if (!Sync()) {
+        LOG(ERROR) << "Header sync failed";
+        return false;
+    }
+
+    if (lseek(fd_.get(), sizeof(header_) + header_.buffer_size, SEEK_SET) < 0) {
+        PLOG(ERROR) << "lseek failed";
+        return false;
+    }
+
     InitPos();
+
     return true;
 }
 
@@ -232,15 +251,11 @@
     // Free reader so we own the descriptor position again.
     reader = nullptr;
 
-    // Remove excess data
-    if (!Truncate(next_op_pos_)) {
-        return false;
-    }
     if (lseek(fd_.get(), next_op_pos_, SEEK_SET) < 0) {
         PLOG(ERROR) << "lseek failed";
         return false;
     }
-    return true;
+    return EmitClusterIfNeeded();
 }
 
 bool CowWriter::EmitCopy(uint64_t new_block, uint64_t old_block) {
@@ -319,6 +334,14 @@
     return WriteOperation(op);
 }
 
+bool CowWriter::EmitClusterIfNeeded() {
+    // If there isn't room for another op and the cluster end op, end the current cluster
+    if (cluster_size_ && cluster_size_ < current_cluster_size_ + 2 * sizeof(CowOperation)) {
+        if (!EmitCluster()) return false;
+    }
+    return true;
+}
+
 std::basic_string<uint8_t> CowWriter::Compress(const void* data, size_t length) {
     switch (compression_) {
         case kCowCompressGz: {
@@ -379,6 +402,21 @@
     auto continue_num_ops = footer_.op.num_ops;
     bool extra_cluster = false;
 
+    // Blank out extra ops, in case we're in append mode and dropped ops.
+    if (cluster_size_) {
+        auto unused_cluster_space = cluster_size_ - current_cluster_size_;
+        std::string clr;
+        clr.resize(unused_cluster_space, '\0');
+        if (lseek(fd_.get(), next_op_pos_, SEEK_SET) < 0) {
+            PLOG(ERROR) << "Failed to seek to footer position.";
+            return false;
+        }
+        if (!android::base::WriteFully(fd_, clr.data(), clr.size())) {
+            PLOG(ERROR) << "clearing unused cluster area failed";
+            return false;
+        }
+    }
+
     // Footer should be at the end of a file, so if there is data after the current block, end it
     // and start a new cluster.
     if (cluster_size_ && current_data_size_ > 0) {
@@ -403,6 +441,17 @@
         return false;
     }
 
+    // Remove excess data, if we're in append mode and threw away more data
+    // than we wrote before.
+    off_t offs = lseek(fd_.get(), 0, SEEK_CUR);
+    if (offs < 0) {
+        PLOG(ERROR) << "Failed to lseek to find current position";
+        return false;
+    }
+    if (!Truncate(offs)) {
+        return false;
+    }
+
     // Reposition for additional Writing
     if (extra_cluster) {
         current_cluster_size_ = continue_cluster_size;
@@ -445,12 +494,7 @@
         if (!WriteRawData(data, size)) return false;
     }
     AddOperation(op);
-    // If there isn't room for another op and the cluster end op, end the current cluster
-    if (cluster_size_ && op.type != kCowClusterOp &&
-        cluster_size_ < current_cluster_size_ + 2 * sizeof(op)) {
-        if (!EmitCluster()) return false;
-    }
-    return true;
+    return EmitClusterIfNeeded();
 }
 
 void CowWriter::AddOperation(const CowOperation& op) {
@@ -492,24 +536,6 @@
     return true;
 }
 
-bool CowWriter::CommitMerge(int merged_ops) {
-    CHECK(merge_in_progress_);
-    header_.num_merge_ops += merged_ops;
-
-    if (lseek(fd_.get(), 0, SEEK_SET) < 0) {
-        PLOG(ERROR) << "lseek failed";
-        return false;
-    }
-
-    if (!android::base::WriteFully(fd_, reinterpret_cast<const uint8_t*>(&header_),
-                                   sizeof(header_))) {
-        PLOG(ERROR) << "WriteFully failed";
-        return false;
-    }
-
-    return Sync();
-}
-
 bool CowWriter::Truncate(off_t length) {
     if (is_dev_null_ || is_block_device_) {
         return true;
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/cow_format.h b/fs_mgr/libsnapshot/include/libsnapshot/cow_format.h
index 797b8ef..000e5e1 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/cow_format.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/cow_format.h
@@ -21,15 +21,22 @@
 namespace snapshot {
 
 static constexpr uint64_t kCowMagicNumber = 0x436f77634f572121ULL;
-static constexpr uint32_t kCowVersionMajor = 1;
+static constexpr uint32_t kCowVersionMajor = 2;
 static constexpr uint32_t kCowVersionMinor = 0;
 
+static constexpr uint32_t kCowVersionManifest = 2;
+
+static constexpr uint32_t BLOCK_SZ = 4096;
+static constexpr uint32_t BLOCK_SHIFT = (__builtin_ffs(BLOCK_SZ) - 1);
+
 // This header appears as the first sequence of bytes in the COW. All fields
 // in the layout are little-endian encoded. The on-disk layout is:
 //
 //      +-----------------------+
 //      |     Header (fixed)    |
 //      +-----------------------+
+//      |     Scratch space     |
+//      +-----------------------+
 //      | Operation  (variable) |
 //      | Data       (variable) |
 //      +-----------------------+
@@ -68,6 +75,9 @@
 
     // Tracks merge operations completed
     uint64_t num_merge_ops;
+
+    // Scratch space used during merge
+    uint32_t buffer_size;
 } __attribute__((packed));
 
 // This structure is the same size of a normal Operation, but is repurposed for the footer.
@@ -144,11 +154,31 @@
 static constexpr uint8_t kCowCompressGz = 1;
 static constexpr uint8_t kCowCompressBrotli = 2;
 
+static constexpr uint8_t kCowReadAheadNotStarted = 0;
+static constexpr uint8_t kCowReadAheadInProgress = 1;
+static constexpr uint8_t kCowReadAheadDone = 2;
+
 struct CowFooter {
     CowFooterOperation op;
     CowFooterData data;
 } __attribute__((packed));
 
+struct ScratchMetadata {
+    // Block of data in the image that operation modifies
+    // and read-ahead thread stores the modified data
+    // in the scratch space
+    uint64_t new_block;
+    // Offset within the file to read the data
+    uint64_t file_offset;
+} __attribute__((packed));
+
+struct BufferState {
+    uint8_t read_ahead_state;
+} __attribute__((packed));
+
+// 2MB Scratch space used for read-ahead
+static constexpr uint64_t BUFFER_REGION_DEFAULT_SIZE = (1ULL << 21);
+
 std::ostream& operator<<(std::ostream& os, CowOperation const& arg);
 
 int64_t GetNextOpOffset(const CowOperation& op, uint32_t cluster_size);
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/cow_reader.h b/fs_mgr/libsnapshot/include/libsnapshot/cow_reader.h
index 552fd96..9ebcfd9 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/cow_reader.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/cow_reader.h
@@ -141,18 +141,21 @@
 
     bool GetRawBytes(uint64_t offset, void* buffer, size_t len, size_t* read);
 
-    void UpdateMergeProgress(uint64_t merge_ops) { header_.num_merge_ops += merge_ops; }
-
     void InitializeMerge();
 
     void set_total_data_ops(uint64_t size) { total_data_ops_ = size; }
 
     uint64_t total_data_ops() { return total_data_ops_; }
 
+    void set_copy_ops(uint64_t size) { copy_ops_ = size; }
+
+    uint64_t total_copy_ops() { return copy_ops_; }
+
     void CloseCowFd() { owned_fd_ = {}; }
 
   private:
     bool ParseOps(std::optional<uint64_t> label);
+    uint64_t FindNumCopyops();
 
     android::base::unique_fd owned_fd_;
     android::base::borrowed_fd fd_;
@@ -162,6 +165,7 @@
     std::optional<uint64_t> last_label_;
     std::shared_ptr<std::vector<CowOperation>> ops_;
     uint64_t total_data_ops_;
+    uint64_t copy_ops_;
 };
 
 }  // namespace snapshot
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h b/fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h
index 6ffd5d8..f43ea68 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h
@@ -36,6 +36,8 @@
 
     // Number of CowOperations in a cluster. 0 for no clustering. Cannot be 1.
     uint32_t cluster_ops = 200;
+
+    bool scratch_space = true;
 };
 
 // Interface for writing to a snapuserd COW. All operations are ordered; merges
@@ -100,13 +102,12 @@
     bool InitializeAppend(android::base::unique_fd&&, uint64_t label);
     bool InitializeAppend(android::base::borrowed_fd fd, uint64_t label);
 
-    void InitializeMerge(android::base::borrowed_fd fd, CowHeader* header);
-    bool CommitMerge(int merged_ops);
-
     bool Finalize() override;
 
     uint64_t GetCowSize() override;
 
+    uint32_t GetCowVersion() { return header_.major_version; }
+
   protected:
     virtual bool EmitCopy(uint64_t new_block, uint64_t old_block) override;
     virtual bool EmitRawBlocks(uint64_t new_block_start, const void* data, size_t size) override;
@@ -115,6 +116,7 @@
 
   private:
     bool EmitCluster();
+    bool EmitClusterIfNeeded();
     void SetupHeaders();
     bool ParseOptions();
     bool OpenForWrite();
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot.h b/fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot.h
index 1cb966b..94d5055 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot.h
@@ -27,6 +27,7 @@
     MOCK_METHOD(bool, CancelUpdate, (), (override));
     MOCK_METHOD(bool, FinishedSnapshotWrites, (bool wipe), (override));
     MOCK_METHOD(void, UpdateCowStats, (ISnapshotMergeStats * stats), (override));
+    MOCK_METHOD(MergeFailureCode, ReadMergeFailureCode, (), (override));
     MOCK_METHOD(bool, InitiateMerge, (), (override));
 
     MOCK_METHOD(UpdateState, ProcessUpdateState,
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot_merge_stats.h b/fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot_merge_stats.h
index ac2c787..067f99c 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot_merge_stats.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot_merge_stats.h
@@ -34,11 +34,13 @@
     MOCK_METHOD(void, set_estimated_cow_size_bytes, (uint64_t), (override));
     MOCK_METHOD(void, set_boot_complete_time_ms, (uint32_t), (override));
     MOCK_METHOD(void, set_boot_complete_to_merge_start_time_ms, (uint32_t), (override));
+    MOCK_METHOD(void, set_merge_failure_code, (MergeFailureCode), (override));
     MOCK_METHOD(uint64_t, cow_file_size, (), (override));
     MOCK_METHOD(uint64_t, total_cow_size_bytes, (), (override));
     MOCK_METHOD(uint64_t, estimated_cow_size_bytes, (), (override));
     MOCK_METHOD(uint32_t, boot_complete_time_ms, (), (override));
     MOCK_METHOD(uint32_t, boot_complete_to_merge_start_time_ms, (), (override));
+    MOCK_METHOD(MergeFailureCode, merge_failure_code, (), (override));
     MOCK_METHOD(std::unique_ptr<Result>, Finish, (), (override));
 
     using ISnapshotMergeStats::Result;
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/snapshot.h b/fs_mgr/libsnapshot/include/libsnapshot/snapshot.h
index 7e74fac..195b6f2 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/snapshot.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/snapshot.h
@@ -167,6 +167,10 @@
     virtual UpdateState ProcessUpdateState(const std::function<bool()>& callback = {},
                                            const std::function<bool()>& before_cancel = {}) = 0;
 
+    // If ProcessUpdateState() returned MergeFailed, this returns the appropriate
+    // code. Otherwise, MergeFailureCode::Ok is returned.
+    virtual MergeFailureCode ReadMergeFailureCode() = 0;
+
     // Find the status of the current update, if any.
     //
     // |progress| depends on the returned status:
@@ -332,6 +336,7 @@
     bool CancelUpdate() override;
     bool FinishedSnapshotWrites(bool wipe) override;
     void UpdateCowStats(ISnapshotMergeStats* stats) override;
+    MergeFailureCode ReadMergeFailureCode() override;
     bool InitiateMerge() override;
     UpdateState ProcessUpdateState(const std::function<bool()>& callback = {},
                                    const std::function<bool()>& before_cancel = {}) override;
@@ -381,6 +386,7 @@
     FRIEND_TEST(SnapshotTest, MapPartialSnapshot);
     FRIEND_TEST(SnapshotTest, MapSnapshot);
     FRIEND_TEST(SnapshotTest, Merge);
+    FRIEND_TEST(SnapshotTest, MergeFailureCode);
     FRIEND_TEST(SnapshotTest, NoMergeBeforeReboot);
     FRIEND_TEST(SnapshotTest, UpdateBootControlHal);
     FRIEND_TEST(SnapshotUpdateTest, DaemonTransition);
@@ -493,6 +499,9 @@
     // Unmap a COW image device previously mapped with MapCowImage().
     bool UnmapCowImage(const std::string& name);
 
+    // Unmap a COW and remove it from a MetadataBuilder.
+    void UnmapAndDeleteCowPartition(MetadataBuilder* current_metadata);
+
     // Unmap and remove all known snapshots.
     bool RemoveAllSnapshots(LockedFile* lock);
 
@@ -529,7 +538,8 @@
     // Interact with /metadata/ota/state.
     UpdateState ReadUpdateState(LockedFile* file);
     SnapshotUpdateStatus ReadSnapshotUpdateStatus(LockedFile* file);
-    bool WriteUpdateState(LockedFile* file, UpdateState state);
+    bool WriteUpdateState(LockedFile* file, UpdateState state,
+                          MergeFailureCode failure_code = MergeFailureCode::Ok);
     bool WriteSnapshotUpdateStatus(LockedFile* file, const SnapshotUpdateStatus& status);
     std::string GetStateFilePath() const;
 
@@ -538,12 +548,12 @@
     std::string GetMergeStateFilePath() const;
 
     // Helpers for merging.
-    bool MergeSecondPhaseSnapshots(LockedFile* lock);
-    bool SwitchSnapshotToMerge(LockedFile* lock, const std::string& name);
-    bool RewriteSnapshotDeviceTable(const std::string& dm_name);
+    MergeFailureCode MergeSecondPhaseSnapshots(LockedFile* lock);
+    MergeFailureCode SwitchSnapshotToMerge(LockedFile* lock, const std::string& name);
+    MergeFailureCode RewriteSnapshotDeviceTable(const std::string& dm_name);
     bool MarkSnapshotMergeCompleted(LockedFile* snapshot_lock, const std::string& snapshot_name);
     void AcknowledgeMergeSuccess(LockedFile* lock);
-    void AcknowledgeMergeFailure();
+    void AcknowledgeMergeFailure(MergeFailureCode failure_code);
     MergePhase DecideMergePhase(const SnapshotStatus& status);
     std::unique_ptr<LpMetadata> ReadCurrentMetadata();
 
@@ -570,14 +580,22 @@
                                  const SnapshotStatus& status);
     bool CollapseSnapshotDevice(const std::string& name, const SnapshotStatus& status);
 
+    struct MergeResult {
+        explicit MergeResult(UpdateState state,
+                             MergeFailureCode failure_code = MergeFailureCode::Ok)
+            : state(state), failure_code(failure_code) {}
+        UpdateState state;
+        MergeFailureCode failure_code;
+    };
+
     // Only the following UpdateStates are used here:
     //   UpdateState::Merging
     //   UpdateState::MergeCompleted
     //   UpdateState::MergeFailed
     //   UpdateState::MergeNeedsReboot
-    UpdateState CheckMergeState(const std::function<bool()>& before_cancel);
-    UpdateState CheckMergeState(LockedFile* lock, const std::function<bool()>& before_cancel);
-    UpdateState CheckTargetMergeState(LockedFile* lock, const std::string& name,
+    MergeResult CheckMergeState(const std::function<bool()>& before_cancel);
+    MergeResult CheckMergeState(LockedFile* lock, const std::function<bool()>& before_cancel);
+    MergeResult CheckTargetMergeState(LockedFile* lock, const std::string& name,
                                       const SnapshotUpdateStatus& update_status);
 
     // Interact with status files under /metadata/ota/snapshots.
@@ -738,6 +756,10 @@
     // Helper of UpdateUsesCompression
     bool UpdateUsesCompression(LockedFile* lock);
 
+    // Wrapper around libdm, with diagnostics.
+    bool DeleteDeviceIfExists(const std::string& name,
+                              const std::chrono::milliseconds& timeout_ms = {});
+
     std::string gsid_dir_;
     std::string metadata_dir_;
     std::unique_ptr<IDeviceInfo> device_;
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stats.h b/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stats.h
index e617d7a..4ce5077 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stats.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stats.h
@@ -34,11 +34,13 @@
     virtual void set_estimated_cow_size_bytes(uint64_t bytes) = 0;
     virtual void set_boot_complete_time_ms(uint32_t ms) = 0;
     virtual void set_boot_complete_to_merge_start_time_ms(uint32_t ms) = 0;
+    virtual void set_merge_failure_code(MergeFailureCode code) = 0;
     virtual uint64_t cow_file_size() = 0;
     virtual uint64_t total_cow_size_bytes() = 0;
     virtual uint64_t estimated_cow_size_bytes() = 0;
     virtual uint32_t boot_complete_time_ms() = 0;
     virtual uint32_t boot_complete_to_merge_start_time_ms() = 0;
+    virtual MergeFailureCode merge_failure_code() = 0;
 
     // Called when merge ends. Properly clean up permanent storage.
     class Result {
@@ -70,6 +72,8 @@
     uint32_t boot_complete_time_ms() override;
     void set_boot_complete_to_merge_start_time_ms(uint32_t ms) override;
     uint32_t boot_complete_to_merge_start_time_ms() override;
+    void set_merge_failure_code(MergeFailureCode code) override;
+    MergeFailureCode merge_failure_code() override;
     std::unique_ptr<Result> Finish() override;
 
   private:
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stub.h b/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stub.h
index cc75db8..a7cd939 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stub.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stub.h
@@ -29,6 +29,7 @@
     bool CancelUpdate() override;
     bool FinishedSnapshotWrites(bool wipe) override;
     void UpdateCowStats(ISnapshotMergeStats* stats) override;
+    MergeFailureCode ReadMergeFailureCode() override;
     bool InitiateMerge() override;
     UpdateState ProcessUpdateState(const std::function<bool()>& callback = {},
                                    const std::function<bool()>& before_cancel = {}) override;
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/snapuserd_kernel.h b/fs_mgr/libsnapshot/include/libsnapshot/snapuserd_kernel.h
index 2b6c8ef..6bb7a39 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/snapuserd_kernel.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/snapuserd_kernel.h
@@ -47,9 +47,6 @@
 static constexpr uint32_t CHUNK_SIZE = 8;
 static constexpr uint32_t CHUNK_SHIFT = (__builtin_ffs(CHUNK_SIZE) - 1);
 
-static constexpr uint32_t BLOCK_SZ = 4096;
-static constexpr uint32_t BLOCK_SHIFT = (__builtin_ffs(BLOCK_SZ) - 1);
-
 #define DIV_ROUND_UP(n, d) (((n) + (d)-1) / (d))
 
 // This structure represents the kernel COW header.
diff --git a/fs_mgr/libsnapshot/inspect_cow.cpp b/fs_mgr/libsnapshot/inspect_cow.cpp
index 453b5c6..4a84fba 100644
--- a/fs_mgr/libsnapshot/inspect_cow.cpp
+++ b/fs_mgr/libsnapshot/inspect_cow.cpp
@@ -38,7 +38,8 @@
 static void usage(void) {
     LOG(ERROR) << "Usage: inspect_cow [-sd] <COW_FILE>";
     LOG(ERROR) << "\t -s Run Silent";
-    LOG(ERROR) << "\t -d Attempt to decompress\n";
+    LOG(ERROR) << "\t -d Attempt to decompress";
+    LOG(ERROR) << "\t -b Show data for failed decompress\n";
 }
 
 // Sink that always appends to the end of a string.
@@ -59,7 +60,25 @@
     std::string stream_;
 };
 
-static bool Inspect(const std::string& path, bool silent, bool decompress) {
+static void ShowBad(CowReader& reader, const struct CowOperation& op) {
+    size_t count;
+    auto buffer = std::make_unique<uint8_t[]>(op.data_length);
+
+    if (!reader.GetRawBytes(op.source, buffer.get(), op.data_length, &count)) {
+        std::cerr << "Failed to read at all!\n";
+    } else {
+        std::cout << "The Block data is:\n";
+        for (int i = 0; i < op.data_length; i++) {
+            std::cout << std::hex << (int)buffer[i];
+        }
+        std::cout << std::dec << "\n\n";
+        if (op.data_length >= sizeof(CowOperation)) {
+            std::cout << "The start, as an op, would be " << *(CowOperation*)buffer.get() << "\n";
+        }
+    }
+}
+
+static bool Inspect(const std::string& path, bool silent, bool decompress, bool show_bad) {
     android::base::unique_fd fd(open(path.c_str(), O_RDONLY));
     if (fd < 0) {
         PLOG(ERROR) << "open failed: " << path;
@@ -107,6 +126,7 @@
             if (!reader.ReadData(op, &sink)) {
                 std::cerr << "Failed to decompress for :" << op << "\n";
                 success = false;
+                if (show_bad) ShowBad(reader, op);
             }
             sink.Reset();
         }
@@ -124,7 +144,8 @@
     int ch;
     bool silent = false;
     bool decompress = false;
-    while ((ch = getopt(argc, argv, "sd")) != -1) {
+    bool show_bad = false;
+    while ((ch = getopt(argc, argv, "sdb")) != -1) {
         switch (ch) {
             case 's':
                 silent = true;
@@ -132,6 +153,9 @@
             case 'd':
                 decompress = true;
                 break;
+            case 'b':
+                show_bad = true;
+                break;
             default:
                 android::snapshot::usage();
         }
@@ -143,7 +167,7 @@
         return 1;
     }
 
-    if (!android::snapshot::Inspect(argv[optind], silent, decompress)) {
+    if (!android::snapshot::Inspect(argv[optind], silent, decompress, show_bad)) {
         return 1;
     }
     return 0;
diff --git a/fs_mgr/libsnapshot/snapshot.cpp b/fs_mgr/libsnapshot/snapshot.cpp
index a0a1e4f..8f3926a 100644
--- a/fs_mgr/libsnapshot/snapshot.cpp
+++ b/fs_mgr/libsnapshot/snapshot.cpp
@@ -21,6 +21,7 @@
 #include <sys/types.h>
 #include <sys/unistd.h>
 
+#include <filesystem>
 #include <optional>
 #include <thread>
 #include <unordered_set>
@@ -587,8 +588,7 @@
 bool SnapshotManager::UnmapSnapshot(LockedFile* lock, const std::string& name) {
     CHECK(lock);
 
-    auto& dm = DeviceMapper::Instance();
-    if (!dm.DeleteDeviceIfExists(name)) {
+    if (!DeleteDeviceIfExists(name)) {
         LOG(ERROR) << "Could not delete snapshot device: " << name;
         return false;
     }
@@ -746,32 +746,35 @@
         return false;
     }
 
-    bool rewrote_all = true;
+    auto reported_code = MergeFailureCode::Ok;
     for (const auto& snapshot : *merge_group) {
         // If this fails, we have no choice but to continue. Everything must
         // be merged. This is not an ideal state to be in, but it is safe,
         // because we the next boot will try again.
-        if (!SwitchSnapshotToMerge(lock.get(), snapshot)) {
+        auto code = SwitchSnapshotToMerge(lock.get(), snapshot);
+        if (code != MergeFailureCode::Ok) {
             LOG(ERROR) << "Failed to switch snapshot to a merge target: " << snapshot;
-            rewrote_all = false;
+            if (reported_code == MergeFailureCode::Ok) {
+                reported_code = code;
+            }
         }
     }
 
     // If we couldn't switch everything to a merge target, pre-emptively mark
     // this merge as failed. It will get acknowledged when WaitForMerge() is
     // called.
-    if (!rewrote_all) {
-        WriteUpdateState(lock.get(), UpdateState::MergeFailed);
+    if (reported_code != MergeFailureCode::Ok) {
+        WriteUpdateState(lock.get(), UpdateState::MergeFailed, reported_code);
     }
 
     // Return true no matter what, because a merge was initiated.
     return true;
 }
 
-bool SnapshotManager::SwitchSnapshotToMerge(LockedFile* lock, const std::string& name) {
+MergeFailureCode SnapshotManager::SwitchSnapshotToMerge(LockedFile* lock, const std::string& name) {
     SnapshotStatus status;
     if (!ReadSnapshotStatus(lock, name, &status)) {
-        return false;
+        return MergeFailureCode::ReadStatus;
     }
     if (status.state() != SnapshotState::CREATED) {
         LOG(WARNING) << "Snapshot " << name
@@ -780,8 +783,8 @@
 
     // After this, we return true because we technically did switch to a merge
     // target. Everything else we do here is just informational.
-    if (!RewriteSnapshotDeviceTable(name)) {
-        return false;
+    if (auto code = RewriteSnapshotDeviceTable(name); code != MergeFailureCode::Ok) {
+        return code;
     }
 
     status.set_state(SnapshotState::MERGING);
@@ -795,26 +798,26 @@
     if (!WriteSnapshotStatus(lock, status)) {
         LOG(ERROR) << "Could not update status file for snapshot: " << name;
     }
-    return true;
+    return MergeFailureCode::Ok;
 }
 
-bool SnapshotManager::RewriteSnapshotDeviceTable(const std::string& name) {
+MergeFailureCode SnapshotManager::RewriteSnapshotDeviceTable(const std::string& name) {
     auto& dm = DeviceMapper::Instance();
 
     std::vector<DeviceMapper::TargetInfo> old_targets;
     if (!dm.GetTableInfo(name, &old_targets)) {
         LOG(ERROR) << "Could not read snapshot device table: " << name;
-        return false;
+        return MergeFailureCode::GetTableInfo;
     }
     if (old_targets.size() != 1 || DeviceMapper::GetTargetType(old_targets[0].spec) != "snapshot") {
         LOG(ERROR) << "Unexpected device-mapper table for snapshot: " << name;
-        return false;
+        return MergeFailureCode::UnknownTable;
     }
 
     std::string base_device, cow_device;
     if (!DmTargetSnapshot::GetDevicesFromParams(old_targets[0].data, &base_device, &cow_device)) {
         LOG(ERROR) << "Could not derive underlying devices for snapshot: " << name;
-        return false;
+        return MergeFailureCode::GetTableParams;
     }
 
     DmTable table;
@@ -822,10 +825,10 @@
                                     SnapshotStorageMode::Merge, kSnapshotChunkSize);
     if (!dm.LoadTableAndActivate(name, table)) {
         LOG(ERROR) << "Could not swap device-mapper tables on snapshot device " << name;
-        return false;
+        return MergeFailureCode::ActivateNewTable;
     }
     LOG(INFO) << "Successfully switched snapshot device to a merge target: " << name;
-    return true;
+    return MergeFailureCode::Ok;
 }
 
 enum class TableQuery {
@@ -897,20 +900,20 @@
 UpdateState SnapshotManager::ProcessUpdateState(const std::function<bool()>& callback,
                                                 const std::function<bool()>& before_cancel) {
     while (true) {
-        UpdateState state = CheckMergeState(before_cancel);
-        LOG(INFO) << "ProcessUpdateState handling state: " << state;
+        auto result = CheckMergeState(before_cancel);
+        LOG(INFO) << "ProcessUpdateState handling state: " << result.state;
 
-        if (state == UpdateState::MergeFailed) {
-            AcknowledgeMergeFailure();
+        if (result.state == UpdateState::MergeFailed) {
+            AcknowledgeMergeFailure(result.failure_code);
         }
-        if (state != UpdateState::Merging) {
+        if (result.state != UpdateState::Merging) {
             // Either there is no merge, or the merge was finished, so no need
             // to keep waiting.
-            return state;
+            return result.state;
         }
 
         if (callback && !callback()) {
-            return state;
+            return result.state;
         }
 
         // This wait is not super time sensitive, so we have a relatively
@@ -919,36 +922,36 @@
     }
 }
 
-UpdateState SnapshotManager::CheckMergeState(const std::function<bool()>& before_cancel) {
+auto SnapshotManager::CheckMergeState(const std::function<bool()>& before_cancel) -> MergeResult {
     auto lock = LockExclusive();
     if (!lock) {
-        return UpdateState::MergeFailed;
+        return MergeResult(UpdateState::MergeFailed, MergeFailureCode::AcquireLock);
     }
 
-    UpdateState state = CheckMergeState(lock.get(), before_cancel);
-    LOG(INFO) << "CheckMergeState for snapshots returned: " << state;
+    auto result = CheckMergeState(lock.get(), before_cancel);
+    LOG(INFO) << "CheckMergeState for snapshots returned: " << result.state;
 
-    if (state == UpdateState::MergeCompleted) {
+    if (result.state == UpdateState::MergeCompleted) {
         // Do this inside the same lock. Failures get acknowledged without the
         // lock, because flock() might have failed.
         AcknowledgeMergeSuccess(lock.get());
-    } else if (state == UpdateState::Cancelled) {
+    } else if (result.state == UpdateState::Cancelled) {
         if (!device_->IsRecovery() && !RemoveAllUpdateState(lock.get(), before_cancel)) {
             LOG(ERROR) << "Failed to remove all update state after acknowleding cancelled update.";
         }
     }
-    return state;
+    return result;
 }
 
-UpdateState SnapshotManager::CheckMergeState(LockedFile* lock,
-                                             const std::function<bool()>& before_cancel) {
+auto SnapshotManager::CheckMergeState(LockedFile* lock, const std::function<bool()>& before_cancel)
+        -> MergeResult {
     SnapshotUpdateStatus update_status = ReadSnapshotUpdateStatus(lock);
     switch (update_status.state()) {
         case UpdateState::None:
         case UpdateState::MergeCompleted:
             // Harmless races are allowed between two callers of WaitForMerge,
             // so in both of these cases we just propagate the state.
-            return update_status.state();
+            return MergeResult(update_status.state());
 
         case UpdateState::Merging:
         case UpdateState::MergeNeedsReboot:
@@ -963,26 +966,26 @@
             // via the merge poll below, but if we never started a merge, we
             // need to also check here.
             if (HandleCancelledUpdate(lock, before_cancel)) {
-                return UpdateState::Cancelled;
+                return MergeResult(UpdateState::Cancelled);
             }
-            return update_status.state();
+            return MergeResult(update_status.state());
 
         default:
-            return update_status.state();
+            return MergeResult(update_status.state());
     }
 
     std::vector<std::string> snapshots;
     if (!ListSnapshots(lock, &snapshots)) {
-        return UpdateState::MergeFailed;
+        return MergeResult(UpdateState::MergeFailed, MergeFailureCode::ListSnapshots);
     }
 
     auto other_suffix = device_->GetOtherSlotSuffix();
 
     bool cancelled = false;
-    bool failed = false;
     bool merging = false;
     bool needs_reboot = false;
     bool wrong_phase = false;
+    MergeFailureCode failure_code = MergeFailureCode::Ok;
     for (const auto& snapshot : snapshots) {
         if (android::base::EndsWith(snapshot, other_suffix)) {
             // This will have triggered an error message in InitiateMerge already.
@@ -990,12 +993,15 @@
             continue;
         }
 
-        UpdateState snapshot_state = CheckTargetMergeState(lock, snapshot, update_status);
-        LOG(INFO) << "CheckTargetMergeState for " << snapshot << " returned: " << snapshot_state;
+        auto result = CheckTargetMergeState(lock, snapshot, update_status);
+        LOG(INFO) << "CheckTargetMergeState for " << snapshot << " returned: " << result.state;
 
-        switch (snapshot_state) {
+        switch (result.state) {
             case UpdateState::MergeFailed:
-                failed = true;
+                // Take the first failure code in case other failures compound.
+                if (failure_code == MergeFailureCode::Ok) {
+                    failure_code = result.failure_code;
+                }
                 break;
             case UpdateState::Merging:
                 merging = true;
@@ -1013,8 +1019,10 @@
                 break;
             default:
                 LOG(ERROR) << "Unknown merge status for \"" << snapshot << "\": "
-                           << "\"" << snapshot_state << "\"";
-                failed = true;
+                           << "\"" << result.state << "\"";
+                if (failure_code == MergeFailureCode::Ok) {
+                    failure_code = MergeFailureCode::UnexpectedMergeState;
+                }
                 break;
         }
     }
@@ -1023,24 +1031,25 @@
         // Note that we handle "Merging" before we handle anything else. We
         // want to poll until *nothing* is merging if we can, so everything has
         // a chance to get marked as completed or failed.
-        return UpdateState::Merging;
+        return MergeResult(UpdateState::Merging);
     }
-    if (failed) {
+    if (failure_code != MergeFailureCode::Ok) {
         // Note: since there are many drop-out cases for failure, we acknowledge
         // it in WaitForMerge rather than here and elsewhere.
-        return UpdateState::MergeFailed;
+        return MergeResult(UpdateState::MergeFailed, failure_code);
     }
     if (wrong_phase) {
         // If we got here, no other partitions are being merged, and nothing
         // failed to merge. It's safe to move to the next merge phase.
-        if (!MergeSecondPhaseSnapshots(lock)) {
-            return UpdateState::MergeFailed;
+        auto code = MergeSecondPhaseSnapshots(lock);
+        if (code != MergeFailureCode::Ok) {
+            return MergeResult(UpdateState::MergeFailed, code);
         }
-        return UpdateState::Merging;
+        return MergeResult(UpdateState::Merging);
     }
     if (needs_reboot) {
         WriteUpdateState(lock, UpdateState::MergeNeedsReboot);
-        return UpdateState::MergeNeedsReboot;
+        return MergeResult(UpdateState::MergeNeedsReboot);
     }
     if (cancelled) {
         // This is an edge case, that we handle as correctly as we sensibly can.
@@ -1048,16 +1057,17 @@
         // removed the snapshot as a result. The exact state of the update is
         // undefined now, but this can only happen on an unlocked device where
         // partitions can be flashed without wiping userdata.
-        return UpdateState::Cancelled;
+        return MergeResult(UpdateState::Cancelled);
     }
-    return UpdateState::MergeCompleted;
+    return MergeResult(UpdateState::MergeCompleted);
 }
 
-UpdateState SnapshotManager::CheckTargetMergeState(LockedFile* lock, const std::string& name,
-                                                   const SnapshotUpdateStatus& update_status) {
+auto SnapshotManager::CheckTargetMergeState(LockedFile* lock, const std::string& name,
+                                            const SnapshotUpdateStatus& update_status)
+        -> MergeResult {
     SnapshotStatus snapshot_status;
     if (!ReadSnapshotStatus(lock, name, &snapshot_status)) {
-        return UpdateState::MergeFailed;
+        return MergeResult(UpdateState::MergeFailed, MergeFailureCode::ReadStatus);
     }
 
     std::unique_ptr<LpMetadata> current_metadata;
@@ -1070,7 +1080,7 @@
         if (!current_metadata ||
             GetMetadataPartitionState(*current_metadata, name) != MetadataPartitionState::Updated) {
             DeleteSnapshot(lock, name);
-            return UpdateState::Cancelled;
+            return MergeResult(UpdateState::Cancelled);
         }
 
         // During a check, we decided the merge was complete, but we were unable to
@@ -1081,11 +1091,11 @@
         if (snapshot_status.state() == SnapshotState::MERGE_COMPLETED) {
             // NB: It's okay if this fails now, we gave cleanup our best effort.
             OnSnapshotMergeComplete(lock, name, snapshot_status);
-            return UpdateState::MergeCompleted;
+            return MergeResult(UpdateState::MergeCompleted);
         }
 
         LOG(ERROR) << "Expected snapshot or snapshot-merge for device: " << name;
-        return UpdateState::MergeFailed;
+        return MergeResult(UpdateState::MergeFailed, MergeFailureCode::UnknownTargetType);
     }
 
     // This check is expensive so it is only enabled for debugging.
@@ -1095,29 +1105,30 @@
     std::string target_type;
     DmTargetSnapshot::Status status;
     if (!QuerySnapshotStatus(name, &target_type, &status)) {
-        return UpdateState::MergeFailed;
+        return MergeResult(UpdateState::MergeFailed, MergeFailureCode::QuerySnapshotStatus);
     }
     if (target_type == "snapshot" &&
         DecideMergePhase(snapshot_status) == MergePhase::SECOND_PHASE &&
         update_status.merge_phase() == MergePhase::FIRST_PHASE) {
         // The snapshot is not being merged because it's in the wrong phase.
-        return UpdateState::None;
+        return MergeResult(UpdateState::None);
     }
     if (target_type != "snapshot-merge") {
         // We can get here if we failed to rewrite the target type in
         // InitiateMerge(). If we failed to create the target in first-stage
         // init, boot would not succeed.
         LOG(ERROR) << "Snapshot " << name << " has incorrect target type: " << target_type;
-        return UpdateState::MergeFailed;
+        return MergeResult(UpdateState::MergeFailed, MergeFailureCode::ExpectedMergeTarget);
     }
 
     // These two values are equal when merging is complete.
     if (status.sectors_allocated != status.metadata_sectors) {
         if (snapshot_status.state() == SnapshotState::MERGE_COMPLETED) {
             LOG(ERROR) << "Snapshot " << name << " is merging after being marked merge-complete.";
-            return UpdateState::MergeFailed;
+            return MergeResult(UpdateState::MergeFailed,
+                               MergeFailureCode::UnmergedSectorsAfterCompletion);
         }
-        return UpdateState::Merging;
+        return MergeResult(UpdateState::Merging);
     }
 
     // Merging is done. First, update the status file to indicate the merge
@@ -1130,18 +1141,18 @@
     // snapshot device for this partition.
     snapshot_status.set_state(SnapshotState::MERGE_COMPLETED);
     if (!WriteSnapshotStatus(lock, snapshot_status)) {
-        return UpdateState::MergeFailed;
+        return MergeResult(UpdateState::MergeFailed, MergeFailureCode::WriteStatus);
     }
     if (!OnSnapshotMergeComplete(lock, name, snapshot_status)) {
-        return UpdateState::MergeNeedsReboot;
+        return MergeResult(UpdateState::MergeNeedsReboot);
     }
-    return UpdateState::MergeCompleted;
+    return MergeResult(UpdateState::MergeCompleted, MergeFailureCode::Ok);
 }
 
-bool SnapshotManager::MergeSecondPhaseSnapshots(LockedFile* lock) {
+MergeFailureCode SnapshotManager::MergeSecondPhaseSnapshots(LockedFile* lock) {
     std::vector<std::string> snapshots;
     if (!ListSnapshots(lock, &snapshots)) {
-        return UpdateState::MergeFailed;
+        return MergeFailureCode::ListSnapshots;
     }
 
     SnapshotUpdateStatus update_status = ReadSnapshotUpdateStatus(lock);
@@ -1150,24 +1161,27 @@
 
     update_status.set_merge_phase(MergePhase::SECOND_PHASE);
     if (!WriteSnapshotUpdateStatus(lock, update_status)) {
-        return false;
+        return MergeFailureCode::WriteStatus;
     }
 
-    bool rewrote_all = true;
+    MergeFailureCode result = MergeFailureCode::Ok;
     for (const auto& snapshot : snapshots) {
         SnapshotStatus snapshot_status;
         if (!ReadSnapshotStatus(lock, snapshot, &snapshot_status)) {
-            return UpdateState::MergeFailed;
+            return MergeFailureCode::ReadStatus;
         }
         if (DecideMergePhase(snapshot_status) != MergePhase::SECOND_PHASE) {
             continue;
         }
-        if (!SwitchSnapshotToMerge(lock, snapshot)) {
+        auto code = SwitchSnapshotToMerge(lock, snapshot);
+        if (code != MergeFailureCode::Ok) {
             LOG(ERROR) << "Failed to switch snapshot to a second-phase merge target: " << snapshot;
-            rewrote_all = false;
+            if (result == MergeFailureCode::Ok) {
+                result = code;
+            }
         }
     }
-    return rewrote_all;
+    return result;
 }
 
 std::string SnapshotManager::GetSnapshotBootIndicatorPath() {
@@ -1199,7 +1213,7 @@
     RemoveAllUpdateState(lock);
 }
 
-void SnapshotManager::AcknowledgeMergeFailure() {
+void SnapshotManager::AcknowledgeMergeFailure(MergeFailureCode failure_code) {
     // Log first, so worst case, we always have a record of why the calls below
     // were being made.
     LOG(ERROR) << "Merge could not be completed and will be marked as failed.";
@@ -1216,7 +1230,7 @@
         return;
     }
 
-    WriteUpdateState(lock.get(), UpdateState::MergeFailed);
+    WriteUpdateState(lock.get(), UpdateState::MergeFailed, failure_code);
 }
 
 bool SnapshotManager::OnSnapshotMergeComplete(LockedFile* lock, const std::string& name,
@@ -1252,25 +1266,6 @@
     return true;
 }
 
-static bool DeleteDmDevice(const std::string& name, const std::chrono::milliseconds& timeout_ms) {
-    auto start = std::chrono::steady_clock::now();
-    auto& dm = DeviceMapper::Instance();
-    while (true) {
-        if (dm.DeleteDeviceIfExists(name)) {
-            break;
-        }
-        auto now = std::chrono::steady_clock::now();
-        auto elapsed = std::chrono::duration_cast<std::chrono::milliseconds>(now - start);
-        if (elapsed >= timeout_ms) {
-            LOG(ERROR) << "DeleteDevice timeout: " << name;
-            return false;
-        }
-        std::this_thread::sleep_for(400ms);
-    }
-
-    return true;
-}
-
 bool SnapshotManager::CollapseSnapshotDevice(const std::string& name,
                                              const SnapshotStatus& status) {
     auto& dm = DeviceMapper::Instance();
@@ -1326,11 +1321,11 @@
         UnmapDmUserDevice(name);
     }
     auto base_name = GetBaseDeviceName(name);
-    if (!dm.DeleteDeviceIfExists(base_name)) {
+    if (!DeleteDeviceIfExists(base_name)) {
         LOG(ERROR) << "Unable to delete base device for snapshot: " << base_name;
     }
 
-    if (!DeleteDmDevice(GetSourceDeviceName(name), 4000ms)) {
+    if (!DeleteDeviceIfExists(GetSourceDeviceName(name), 4000ms)) {
         LOG(ERROR) << "Unable to delete source device for snapshot: " << GetSourceDeviceName(name);
     }
 
@@ -2083,15 +2078,14 @@
         return false;
     }
 
-    auto& dm = DeviceMapper::Instance();
     auto base_name = GetBaseDeviceName(target_partition_name);
-    if (!dm.DeleteDeviceIfExists(base_name)) {
+    if (!DeleteDeviceIfExists(base_name)) {
         LOG(ERROR) << "Cannot delete base device: " << base_name;
         return false;
     }
 
     auto source_name = GetSourceDeviceName(target_partition_name);
-    if (!dm.DeleteDeviceIfExists(source_name)) {
+    if (!DeleteDeviceIfExists(source_name)) {
         LOG(ERROR) << "Cannot delete source device: " << source_name;
         return false;
     }
@@ -2181,7 +2175,7 @@
         return false;
     }
 
-    if (!DeleteDmDevice(GetCowName(name), 4000ms)) {
+    if (!DeleteDeviceIfExists(GetCowName(name), 4000ms)) {
         LOG(ERROR) << "Cannot unmap: " << GetCowName(name);
         return false;
     }
@@ -2202,7 +2196,7 @@
         return true;
     }
 
-    if (!dm.DeleteDeviceIfExists(dm_user_name)) {
+    if (!DeleteDeviceIfExists(dm_user_name)) {
         LOG(ERROR) << "Cannot unmap " << dm_user_name;
         return false;
     }
@@ -2434,10 +2428,15 @@
     return status;
 }
 
-bool SnapshotManager::WriteUpdateState(LockedFile* lock, UpdateState state) {
+bool SnapshotManager::WriteUpdateState(LockedFile* lock, UpdateState state,
+                                       MergeFailureCode failure_code) {
     SnapshotUpdateStatus status;
     status.set_state(state);
 
+    if (state == UpdateState::MergeFailed) {
+        status.set_merge_failure_code(failure_code);
+    }
+
     // If we're transitioning between two valid states (eg, we're not beginning
     // or ending an OTA), then make sure to propagate the compression bit.
     if (!(state == UpdateState::Initiated || state == UpdateState::None)) {
@@ -2593,11 +2592,10 @@
     return true;
 }
 
-static void UnmapAndDeleteCowPartition(MetadataBuilder* current_metadata) {
-    auto& dm = DeviceMapper::Instance();
+void SnapshotManager::UnmapAndDeleteCowPartition(MetadataBuilder* current_metadata) {
     std::vector<std::string> to_delete;
     for (auto* existing_cow_partition : current_metadata->ListPartitionsInGroup(kCowGroupName)) {
-        if (!dm.DeleteDeviceIfExists(existing_cow_partition->name())) {
+        if (!DeleteDeviceIfExists(existing_cow_partition->name())) {
             LOG(WARNING) << existing_cow_partition->name()
                          << " cannot be unmapped and its space cannot be reclaimed";
             continue;
@@ -2694,8 +2692,18 @@
     AutoDeviceList created_devices;
 
     const auto& dap_metadata = manifest.dynamic_partition_metadata();
-    bool use_compression =
-            IsCompressionEnabled() && dap_metadata.vabc_enabled() && !device_->IsRecovery();
+    CowOptions options;
+    CowWriter writer(options);
+    bool cow_format_support = true;
+    if (dap_metadata.cow_version() < writer.GetCowVersion()) {
+        cow_format_support = false;
+    }
+
+    LOG(INFO) << " dap_metadata.cow_version(): " << dap_metadata.cow_version()
+              << " writer.GetCowVersion(): " << writer.GetCowVersion();
+
+    bool use_compression = IsCompressionEnabled() && dap_metadata.vabc_enabled() &&
+                           !device_->IsRecovery() && cow_format_support;
 
     std::string compression_algorithm;
     if (use_compression) {
@@ -2962,7 +2970,13 @@
                 return Return::Error();
             }
 
-            CowWriter writer(CowOptions{.compression = it->second.compression_algorithm()});
+            CowOptions options;
+            if (device()->IsTestDevice()) {
+                options.scratch_space = false;
+            }
+            options.compression = it->second.compression_algorithm();
+
+            CowWriter writer(options);
             if (!writer.Initialize(fd) || !writer.Finalize()) {
                 LOG(ERROR) << "Could not initialize COW device for " << target_partition->name();
                 return Return::Error();
@@ -3071,6 +3085,10 @@
     CowOptions cow_options;
     cow_options.compression = status.compression_algorithm();
     cow_options.max_blocks = {status.device_size() / cow_options.block_size};
+    // Disable scratch space for vts tests
+    if (device()->IsTestDevice()) {
+        cow_options.scratch_space = false;
+    }
 
     // Currently we don't support partial snapshots, since partition_cow_creator
     // never creates this scenario.
@@ -3626,5 +3644,82 @@
     stats->set_estimated_cow_size_bytes(estimated_cow_size);
 }
 
+bool SnapshotManager::DeleteDeviceIfExists(const std::string& name,
+                                           const std::chrono::milliseconds& timeout_ms) {
+    auto& dm = DeviceMapper::Instance();
+    auto start = std::chrono::steady_clock::now();
+    while (true) {
+        if (dm.DeleteDeviceIfExists(name)) {
+            return true;
+        }
+        auto now = std::chrono::steady_clock::now();
+        auto elapsed = std::chrono::duration_cast<std::chrono::milliseconds>(now - start);
+        if (elapsed >= timeout_ms) {
+            break;
+        }
+        std::this_thread::sleep_for(400ms);
+    }
+
+    // Try to diagnose why this failed. First get the actual device path.
+    std::string full_path;
+    if (!dm.GetDmDevicePathByName(name, &full_path)) {
+        LOG(ERROR) << "Unable to diagnose DM_DEV_REMOVE failure.";
+        return false;
+    }
+
+    // Check for child dm-devices.
+    std::string block_name = android::base::Basename(full_path);
+    std::string sysfs_holders = "/sys/class/block/" + block_name + "/holders";
+
+    std::error_code ec;
+    std::filesystem::directory_iterator dir_iter(sysfs_holders, ec);
+    if (auto begin = std::filesystem::begin(dir_iter); begin != std::filesystem::end(dir_iter)) {
+        LOG(ERROR) << "Child device-mapper device still mapped: " << begin->path();
+        return false;
+    }
+
+    // Check for mounted partitions.
+    android::fs_mgr::Fstab fstab;
+    android::fs_mgr::ReadFstabFromFile("/proc/mounts", &fstab);
+    for (const auto& entry : fstab) {
+        if (android::base::Basename(entry.blk_device) == block_name) {
+            LOG(ERROR) << "Partition still mounted: " << entry.mount_point;
+            return false;
+        }
+    }
+
+    // Check for detached mounted partitions.
+    for (const auto& fs : std::filesystem::directory_iterator("/sys/fs", ec)) {
+        std::string fs_type = android::base::Basename(fs.path().c_str());
+        if (!(fs_type == "ext4" || fs_type == "f2fs")) {
+            continue;
+        }
+
+        std::string path = fs.path().c_str() + "/"s + block_name;
+        if (access(path.c_str(), F_OK) == 0) {
+            LOG(ERROR) << "Block device was lazily unmounted and is still in-use: " << full_path
+                       << "; possibly open file descriptor or attached loop device.";
+            return false;
+        }
+    }
+
+    LOG(ERROR) << "Device-mapper device " << name << "(" << full_path << ")"
+               << " still in use."
+               << "  Probably a file descriptor was leaked or held open, or a loop device is"
+               << " attached.";
+    return false;
+}
+
+MergeFailureCode SnapshotManager::ReadMergeFailureCode() {
+    auto lock = LockExclusive();
+    if (!lock) return MergeFailureCode::AcquireLock;
+
+    SnapshotUpdateStatus status = ReadSnapshotUpdateStatus(lock.get());
+    if (status.state() != UpdateState::MergeFailed) {
+        return MergeFailureCode::Ok;
+    }
+    return status.merge_failure_code();
+}
+
 }  // namespace snapshot
 }  // namespace android
diff --git a/fs_mgr/libsnapshot/snapshot_reader_test.cpp b/fs_mgr/libsnapshot/snapshot_reader_test.cpp
index 4202d22..9373059 100644
--- a/fs_mgr/libsnapshot/snapshot_reader_test.cpp
+++ b/fs_mgr/libsnapshot/snapshot_reader_test.cpp
@@ -150,6 +150,7 @@
     CowOptions options;
     options.compression = "gz";
     options.max_blocks = {kBlockCount};
+    options.scratch_space = false;
 
     unique_fd cow_fd(dup(cow_->fd));
     ASSERT_GE(cow_fd, 0);
diff --git a/fs_mgr/libsnapshot/snapshot_stats.cpp b/fs_mgr/libsnapshot/snapshot_stats.cpp
index 7fcfcea..4a93d65 100644
--- a/fs_mgr/libsnapshot/snapshot_stats.cpp
+++ b/fs_mgr/libsnapshot/snapshot_stats.cpp
@@ -130,6 +130,14 @@
     return report_.boot_complete_to_merge_start_time_ms();
 }
 
+void SnapshotMergeStats::set_merge_failure_code(MergeFailureCode code) {
+    report_.set_merge_failure_code(code);
+}
+
+MergeFailureCode SnapshotMergeStats::merge_failure_code() {
+    return report_.merge_failure_code();
+}
+
 class SnapshotMergeStatsResultImpl : public SnapshotMergeStats::Result {
   public:
     SnapshotMergeStatsResultImpl(const SnapshotMergeReport& report,
diff --git a/fs_mgr/libsnapshot/snapshot_stub.cpp b/fs_mgr/libsnapshot/snapshot_stub.cpp
index 43825cc..1a9eda5 100644
--- a/fs_mgr/libsnapshot/snapshot_stub.cpp
+++ b/fs_mgr/libsnapshot/snapshot_stub.cpp
@@ -135,6 +135,8 @@
     uint32_t boot_complete_time_ms() override { return 0; }
     void set_boot_complete_to_merge_start_time_ms(uint32_t) override {}
     uint32_t boot_complete_to_merge_start_time_ms() override { return 0; }
+    void set_merge_failure_code(MergeFailureCode) override {}
+    MergeFailureCode merge_failure_code() { return MergeFailureCode::Ok; }
 };
 
 ISnapshotMergeStats* SnapshotManagerStub::GetSnapshotMergeStatsInstance() {
@@ -163,4 +165,9 @@
     LOG(ERROR) << __FUNCTION__ << " should never be called.";
 }
 
+auto SnapshotManagerStub::ReadMergeFailureCode() -> MergeFailureCode {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return MergeFailureCode::Ok;
+}
+
 }  // namespace android::snapshot
diff --git a/fs_mgr/libsnapshot/snapshot_test.cpp b/fs_mgr/libsnapshot/snapshot_test.cpp
index 8fae00b..45db7a4 100644
--- a/fs_mgr/libsnapshot/snapshot_test.cpp
+++ b/fs_mgr/libsnapshot/snapshot_test.cpp
@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#include <libsnapshot/cow_format.h>
 #include <libsnapshot/snapshot.h>
 
 #include <fcntl.h>
@@ -327,6 +328,7 @@
 
         auto dynamic_partition_metadata = manifest.mutable_dynamic_partition_metadata();
         dynamic_partition_metadata->set_vabc_enabled(IsCompressionEnabled());
+        dynamic_partition_metadata->set_cow_version(android::snapshot::kCowVersionMajor);
 
         auto group = dynamic_partition_metadata->add_groups();
         group->set_name("group");
@@ -676,6 +678,18 @@
     ASSERT_EQ(test_device->merge_status(), MergeStatus::MERGING);
 }
 
+TEST_F(SnapshotTest, MergeFailureCode) {
+    ASSERT_TRUE(AcquireLock());
+
+    ASSERT_TRUE(sm->WriteUpdateState(lock_.get(), UpdateState::MergeFailed,
+                                     MergeFailureCode::ListSnapshots));
+    ASSERT_EQ(test_device->merge_status(), MergeStatus::MERGING);
+
+    SnapshotUpdateStatus status = sm->ReadSnapshotUpdateStatus(lock_.get());
+    ASSERT_EQ(status.state(), UpdateState::MergeFailed);
+    ASSERT_EQ(status.merge_failure_code(), MergeFailureCode::ListSnapshots);
+}
+
 enum class Request { UNKNOWN, LOCK_SHARED, LOCK_EXCLUSIVE, UNLOCK, EXIT };
 std::ostream& operator<<(std::ostream& os, Request request) {
     switch (request) {
@@ -841,6 +855,7 @@
 
         auto dynamic_partition_metadata = manifest_.mutable_dynamic_partition_metadata();
         dynamic_partition_metadata->set_vabc_enabled(IsCompressionEnabled());
+        dynamic_partition_metadata->set_cow_version(android::snapshot::kCowVersionMajor);
 
         // Create a fake update package metadata.
         // Not using full name "system", "vendor", "product" because these names collide with the
diff --git a/fs_mgr/libsnapshot/snapuserd.cpp b/fs_mgr/libsnapshot/snapuserd.cpp
index 5ef9e29..2ccc750 100644
--- a/fs_mgr/libsnapshot/snapuserd.cpp
+++ b/fs_mgr/libsnapshot/snapuserd.cpp
@@ -47,28 +47,202 @@
 
         worker_threads_.push_back(std::move(wt));
     }
+
+    read_ahead_thread_ = std::make_unique<ReadAheadThread>(cow_device_, backing_store_device_,
+                                                           misc_name_, GetSharedPtr());
     return true;
 }
 
 bool Snapuserd::CommitMerge(int num_merge_ops) {
-    {
-        std::lock_guard<std::mutex> lock(lock_);
-        CowHeader header;
+    struct CowHeader* ch = reinterpret_cast<struct CowHeader*>(mapped_addr_);
+    ch->num_merge_ops += num_merge_ops;
 
-        reader_->GetHeader(&header);
-        header.num_merge_ops += num_merge_ops;
-        reader_->UpdateMergeProgress(num_merge_ops);
-        if (!writer_->CommitMerge(num_merge_ops)) {
-            SNAP_LOG(ERROR) << "CommitMerge failed... merged_ops_cur_iter: " << num_merge_ops
-                            << " Total-merged-ops: " << header.num_merge_ops;
-            return false;
-        }
-        merge_initiated_ = true;
+    if (read_ahead_feature_ && read_ahead_ops_.size() > 0) {
+        struct BufferState* ra_state = GetBufferState();
+        ra_state->read_ahead_state = kCowReadAheadInProgress;
     }
 
+    int ret = msync(mapped_addr_, BLOCK_SZ, MS_SYNC);
+    if (ret < 0) {
+        PLOG(ERROR) << "msync header failed: " << ret;
+        return false;
+    }
+
+    merge_initiated_ = true;
+
     return true;
 }
 
+void Snapuserd::PrepareReadAhead() {
+    if (!read_ahead_feature_) {
+        return;
+    }
+
+    struct BufferState* ra_state = GetBufferState();
+    // Check if the data has to be re-constructed from COW device
+    if (ra_state->read_ahead_state == kCowReadAheadDone) {
+        populate_data_from_cow_ = true;
+    } else {
+        populate_data_from_cow_ = false;
+    }
+
+    StartReadAhead();
+}
+
+bool Snapuserd::GetRABuffer(std::unique_lock<std::mutex>* lock, uint64_t block, void* buffer) {
+    CHECK(lock->owns_lock());
+    std::unordered_map<uint64_t, void*>::iterator it = read_ahead_buffer_map_.find(block);
+
+    // This will be true only for IO's generated as part of reading a root
+    // filesystem. IO's related to merge should always be in read-ahead cache.
+    if (it == read_ahead_buffer_map_.end()) {
+        return false;
+    }
+
+    // Theoretically, we can send the data back from the read-ahead buffer
+    // all the way to the kernel without memcpy. However, if the IO is
+    // un-aligned, the wrapper function will need to touch the read-ahead
+    // buffers and transitions will be bit more complicated.
+    memcpy(buffer, it->second, BLOCK_SZ);
+    return true;
+}
+
+// ========== State transition functions for read-ahead operations ===========
+
+bool Snapuserd::GetReadAheadPopulatedBuffer(uint64_t block, void* buffer) {
+    if (!read_ahead_feature_) {
+        return false;
+    }
+
+    {
+        std::unique_lock<std::mutex> lock(lock_);
+        if (io_state_ == READ_AHEAD_IO_TRANSITION::READ_AHEAD_FAILURE) {
+            return false;
+        }
+
+        if (io_state_ == READ_AHEAD_IO_TRANSITION::IO_IN_PROGRESS) {
+            return GetRABuffer(&lock, block, buffer);
+        }
+    }
+
+    {
+        // Read-ahead thread IO is in-progress. Wait for it to complete
+        std::unique_lock<std::mutex> lock(lock_);
+        while (!(io_state_ == READ_AHEAD_IO_TRANSITION::READ_AHEAD_FAILURE ||
+                 io_state_ == READ_AHEAD_IO_TRANSITION::IO_IN_PROGRESS)) {
+            cv.wait(lock);
+        }
+
+        return GetRABuffer(&lock, block, buffer);
+    }
+}
+
+// This is invoked by read-ahead thread waiting for merge IO's
+// to complete
+bool Snapuserd::WaitForMergeToComplete() {
+    {
+        std::unique_lock<std::mutex> lock(lock_);
+        while (!(io_state_ == READ_AHEAD_IO_TRANSITION::READ_AHEAD_BEGIN ||
+                 io_state_ == READ_AHEAD_IO_TRANSITION::IO_TERMINATED)) {
+            cv.wait(lock);
+        }
+
+        if (io_state_ == READ_AHEAD_IO_TRANSITION::IO_TERMINATED) {
+            return false;
+        }
+
+        io_state_ = READ_AHEAD_IO_TRANSITION::READ_AHEAD_IN_PROGRESS;
+        return true;
+    }
+}
+
+// This is invoked during the launch of worker threads. We wait
+// for read-ahead thread to by fully up before worker threads
+// are launched; else we will have a race between worker threads
+// and read-ahead thread specifically during re-construction.
+bool Snapuserd::WaitForReadAheadToStart() {
+    {
+        std::unique_lock<std::mutex> lock(lock_);
+        while (!(io_state_ == READ_AHEAD_IO_TRANSITION::IO_IN_PROGRESS ||
+                 io_state_ == READ_AHEAD_IO_TRANSITION::READ_AHEAD_FAILURE)) {
+            cv.wait(lock);
+        }
+
+        if (io_state_ == READ_AHEAD_IO_TRANSITION::READ_AHEAD_FAILURE) {
+            return false;
+        }
+
+        return true;
+    }
+}
+
+// Invoked by worker threads when a sequence of merge operation
+// is complete notifying read-ahead thread to make forward
+// progress.
+void Snapuserd::StartReadAhead() {
+    {
+        std::lock_guard<std::mutex> lock(lock_);
+        io_state_ = READ_AHEAD_IO_TRANSITION::READ_AHEAD_BEGIN;
+    }
+
+    cv.notify_one();
+}
+
+void Snapuserd::MergeCompleted() {
+    {
+        std::lock_guard<std::mutex> lock(lock_);
+        io_state_ = READ_AHEAD_IO_TRANSITION::IO_TERMINATED;
+    }
+
+    cv.notify_one();
+}
+
+bool Snapuserd::ReadAheadIOCompleted(bool sync) {
+    if (sync) {
+        // Flush the entire buffer region
+        int ret = msync(mapped_addr_, total_mapped_addr_length_, MS_SYNC);
+        if (ret < 0) {
+            PLOG(ERROR) << "msync failed after ReadAheadIOCompleted: " << ret;
+            return false;
+        }
+
+        // Metadata and data are synced. Now, update the state.
+        // We need to update the state after flushing data; if there is a crash
+        // when read-ahead IO is in progress, the state of data in the COW file
+        // is unknown. kCowReadAheadDone acts as a checkpoint wherein the data
+        // in the scratch space is good and during next reboot, read-ahead thread
+        // can safely re-construct the data.
+        struct BufferState* ra_state = GetBufferState();
+        ra_state->read_ahead_state = kCowReadAheadDone;
+
+        ret = msync(mapped_addr_, BLOCK_SZ, MS_SYNC);
+        if (ret < 0) {
+            PLOG(ERROR) << "msync failed to flush Readahead completion state...";
+            return false;
+        }
+    }
+
+    // Notify the worker threads
+    {
+        std::lock_guard<std::mutex> lock(lock_);
+        io_state_ = READ_AHEAD_IO_TRANSITION::IO_IN_PROGRESS;
+    }
+
+    cv.notify_all();
+    return true;
+}
+
+void Snapuserd::ReadAheadIOFailed() {
+    {
+        std::lock_guard<std::mutex> lock(lock_);
+        io_state_ = READ_AHEAD_IO_TRANSITION::READ_AHEAD_FAILURE;
+    }
+
+    cv.notify_all();
+}
+
+//========== End of state transition functions ====================
+
 bool Snapuserd::IsChunkIdMetadata(chunk_t chunk) {
     uint32_t stride = exceptions_per_area_ + 1;
     lldiv_t divresult = lldiv(chunk, stride);
@@ -93,9 +267,9 @@
         return;
     }
 
-    CowHeader header;
-    reader_->GetHeader(&header);
-    SNAP_LOG(INFO) << "Merge-status: Total-Merged-ops: " << header.num_merge_ops
+    struct CowHeader* ch = reinterpret_cast<struct CowHeader*>(mapped_addr_);
+
+    SNAP_LOG(INFO) << "Merge-status: Total-Merged-ops: " << ch->num_merge_ops
                    << " Total-data-ops: " << reader_->total_data_ops();
 }
 
@@ -175,8 +349,10 @@
     reader_->InitializeMerge();
     SNAP_LOG(DEBUG) << "Merge-ops: " << header.num_merge_ops;
 
-    writer_ = std::make_unique<CowWriter>(options);
-    writer_->InitializeMerge(cow_fd_.get(), &header);
+    if (!MmapMetadata()) {
+        SNAP_LOG(ERROR) << "mmap failed";
+        return false;
+    }
 
     // Initialize the iterator for reading metadata
     cowop_riter_ = reader_->GetRevOpIter();
@@ -258,13 +434,15 @@
         data_chunk_id = GetNextAllocatableChunkId(data_chunk_id);
     }
 
+    int num_ra_ops_per_iter = ((GetBufferDataSize()) / BLOCK_SZ);
     std::optional<chunk_t> prev_id = {};
     std::map<uint64_t, const CowOperation*> map;
-    std::set<uint64_t> dest_blocks;
     size_t pending_copy_ops = exceptions_per_area_ - num_ops;
-    SNAP_LOG(INFO) << " Processing copy-ops at Area: " << vec_.size()
-                   << " Number of replace/zero ops completed in this area: " << num_ops
-                   << " Pending copy ops for this area: " << pending_copy_ops;
+    uint64_t total_copy_ops = reader_->total_copy_ops();
+
+    SNAP_LOG(DEBUG) << " Processing copy-ops at Area: " << vec_.size()
+                    << " Number of replace/zero ops completed in this area: " << num_ops
+                    << " Pending copy ops for this area: " << pending_copy_ops;
     while (!cowop_riter_->Done()) {
         do {
             const CowOperation* cow_op = &cowop_riter_->Get();
@@ -300,41 +478,20 @@
             // Op-6: 15 -> 18
             //
             // Note that the blocks numbers are contiguous. Hence, all 6 copy
-            // operations can potentially be batch merged. However, that will be
+            // operations can be batch merged. However, that will be
             // problematic if we have a crash as block 20, 19, 18 would have
             // been overwritten and hence subsequent recovery may end up with
             // a silent data corruption when op-1, op-2 and op-3 are
             // re-executed.
             //
-            // We will split these 6 operations into two batches viz:
-            //
-            // Batch-1:
-            // ===================
-            // Op-1: 20 -> 23
-            // Op-2: 19 -> 22
-            // Op-3: 18 -> 21
-            // ===================
-            //
-            // Batch-2:
-            // ==================
-            // Op-4: 17 -> 20
-            // Op-5: 16 -> 19
-            // Op-6: 15 -> 18
-            // ==================
-            //
-            // Now, merge sequence will look like:
-            //
-            // 1: Merge Batch-1 { op-1, op-2, op-3 }
-            // 2: Update Metadata in COW File that op-1, op-2, op-3 merge is
-            // done.
-            // 3: Merge Batch-2
-            // 4: Update Metadata in COW File that op-4, op-5, op-6 merge is
-            // done.
-            //
-            // Note, that the order of block operations are still the same.
-            // However, we have two batch merge operations. Any crash between
-            // either of this sequence should be safe as each of these
-            // batches are self-contained.
+            // To address the above problem, read-ahead thread will
+            // read all the 6 source blocks, cache them in the scratch
+            // space of the COW file. During merge, read-ahead
+            // thread will serve the blocks from the read-ahead cache.
+            // If there is a crash during merge; on subsequent reboot,
+            // read-ahead thread will recover the data from the
+            // scratch space and re-construct it thereby there
+            // is no loss of data.
             //
             //===========================================================
             //
@@ -398,14 +555,10 @@
                 if (diff != 1) {
                     break;
                 }
-                if (dest_blocks.count(cow_op->new_block) || map.count(cow_op->source) > 0) {
-                    break;
-                }
             }
             metadata_found = true;
             pending_copy_ops -= 1;
             map[cow_op->new_block] = cow_op;
-            dest_blocks.insert(cow_op->source);
             prev_id = cow_op->new_block;
             cowop_riter_->Next();
         } while (!cowop_riter_->Done() && pending_copy_ops);
@@ -426,6 +579,9 @@
             offset += sizeof(struct disk_exception);
             num_ops += 1;
             copy_ops++;
+            if (read_ahead_feature_) {
+                read_ahead_ops_.push_back(it->second);
+            }
 
             SNAP_LOG(DEBUG) << num_ops << ":"
                             << " Copy-op: "
@@ -453,9 +609,17 @@
             }
 
             data_chunk_id = GetNextAllocatableChunkId(data_chunk_id);
+            total_copy_ops -= 1;
+            /*
+             * Split the number of ops based on the size of read-ahead buffer
+             * region. We need to ensure that kernel doesn't issue IO on blocks
+             * which are not read by the read-ahead thread.
+             */
+            if (read_ahead_feature_ && (total_copy_ops % num_ra_ops_per_iter == 0)) {
+                data_chunk_id = GetNextAllocatableChunkId(data_chunk_id);
+            }
         }
         map.clear();
-        dest_blocks.clear();
         prev_id.reset();
     }
 
@@ -470,6 +634,7 @@
 
     chunk_vec_.shrink_to_fit();
     vec_.shrink_to_fit();
+    read_ahead_ops_.shrink_to_fit();
 
     // Sort the vector based on sectors as we need this during un-aligned access
     std::sort(chunk_vec_.begin(), chunk_vec_.end(), compare);
@@ -484,9 +649,41 @@
     // Total number of sectors required for creating dm-user device
     num_sectors_ = ChunkToSector(data_chunk_id);
     merge_initiated_ = false;
+    PrepareReadAhead();
+
     return true;
 }
 
+bool Snapuserd::MmapMetadata() {
+    CowHeader header;
+    reader_->GetHeader(&header);
+
+    if (header.major_version >= 2 && header.buffer_size > 0) {
+        total_mapped_addr_length_ = header.header_size + BUFFER_REGION_DEFAULT_SIZE;
+        read_ahead_feature_ = true;
+    } else {
+        // mmap the first 4k page - older COW format
+        total_mapped_addr_length_ = BLOCK_SZ;
+        read_ahead_feature_ = false;
+    }
+
+    mapped_addr_ = mmap(NULL, total_mapped_addr_length_, PROT_READ | PROT_WRITE, MAP_SHARED,
+                        cow_fd_.get(), 0);
+    if (mapped_addr_ == MAP_FAILED) {
+        SNAP_LOG(ERROR) << "mmap metadata failed";
+        return false;
+    }
+
+    return true;
+}
+
+void Snapuserd::UnmapBufferRegion() {
+    int ret = munmap(mapped_addr_, total_mapped_addr_length_);
+    if (ret < 0) {
+        SNAP_PLOG(ERROR) << "munmap failed";
+    }
+}
+
 void MyLogger(android::base::LogId, android::base::LogSeverity severity, const char*, const char*,
               unsigned int, const char* message) {
     if (severity == android::base::ERROR) {
@@ -507,11 +704,28 @@
 }
 
 /*
- * Entry point to launch worker threads
+ * Entry point to launch threads
  */
 bool Snapuserd::Start() {
     std::vector<std::future<bool>> threads;
+    std::future<bool> ra_thread;
+    bool rathread = (read_ahead_feature_ && (read_ahead_ops_.size() > 0));
 
+    // Start the read-ahead thread and wait
+    // for it as the data has to be re-constructed
+    // from COW device.
+    if (rathread) {
+        ra_thread = std::async(std::launch::async, &ReadAheadThread::RunThread,
+                               read_ahead_thread_.get());
+        if (!WaitForReadAheadToStart()) {
+            SNAP_LOG(ERROR) << "Failed to start Read-ahead thread...";
+            return false;
+        }
+
+        SNAP_LOG(INFO) << "Read-ahead thread started...";
+    }
+
+    // Launch worker threads
     for (int i = 0; i < worker_threads_.size(); i++) {
         threads.emplace_back(
                 std::async(std::launch::async, &WorkerThread::RunThread, worker_threads_[i].get()));
@@ -522,8 +736,69 @@
         ret = t.get() && ret;
     }
 
+    if (rathread) {
+        // Notify the read-ahead thread that all worker threads
+        // are done. We need this explicit notification when
+        // there is an IO failure or there was a switch
+        // of dm-user table; thus, forcing the read-ahead
+        // thread to wake up.
+        MergeCompleted();
+        ret = ret && ra_thread.get();
+    }
+
     return ret;
 }
 
+uint64_t Snapuserd::GetBufferMetadataOffset() {
+    CowHeader header;
+    reader_->GetHeader(&header);
+
+    size_t size = header.header_size + sizeof(BufferState);
+    return size;
+}
+
+/*
+ * Metadata for read-ahead is 16 bytes. For a 2 MB region, we will
+ * end up with 8k (2 PAGE) worth of metadata. Thus, a 2MB buffer
+ * region is split into:
+ *
+ * 1: 8k metadata
+ *
+ */
+size_t Snapuserd::GetBufferMetadataSize() {
+    CowHeader header;
+    reader_->GetHeader(&header);
+
+    size_t metadata_bytes = (header.buffer_size * sizeof(struct ScratchMetadata)) / BLOCK_SZ;
+    return metadata_bytes;
+}
+
+size_t Snapuserd::GetBufferDataOffset() {
+    CowHeader header;
+    reader_->GetHeader(&header);
+
+    return (header.header_size + GetBufferMetadataSize());
+}
+
+/*
+ * (2MB - 8K = 2088960 bytes) will be the buffer region to hold the data.
+ */
+size_t Snapuserd::GetBufferDataSize() {
+    CowHeader header;
+    reader_->GetHeader(&header);
+
+    size_t size = header.buffer_size - GetBufferMetadataSize();
+    return size;
+}
+
+struct BufferState* Snapuserd::GetBufferState() {
+    CowHeader header;
+    reader_->GetHeader(&header);
+
+    struct BufferState* ra_state =
+            reinterpret_cast<struct BufferState*>((char*)mapped_addr_ + header.header_size);
+    return ra_state;
+}
+
 }  // namespace snapshot
 }  // namespace android
diff --git a/fs_mgr/libsnapshot/snapuserd.h b/fs_mgr/libsnapshot/snapuserd.h
index 87c5528..0a5ab50 100644
--- a/fs_mgr/libsnapshot/snapuserd.h
+++ b/fs_mgr/libsnapshot/snapuserd.h
@@ -17,8 +17,10 @@
 #include <linux/types.h>
 #include <stdint.h>
 #include <stdlib.h>
+#include <sys/mman.h>
 
 #include <bitset>
+#include <condition_variable>
 #include <csignal>
 #include <cstring>
 #include <future>
@@ -29,6 +31,7 @@
 #include <string>
 #include <thread>
 #include <unordered_map>
+#include <unordered_set>
 #include <vector>
 
 #include <android-base/file.h>
@@ -56,6 +59,35 @@
  */
 static constexpr int NUM_THREADS_PER_PARTITION = 4;
 
+/*
+ * State transitions between worker threads and read-ahead
+ * threads.
+ *
+ * READ_AHEAD_BEGIN: Worker threads initiates the read-ahead
+ *                   thread to begin reading the copy operations
+ *                   for each bounded region.
+ *
+ * READ_AHEAD_IN_PROGRESS: When read ahead thread is in-flight
+ *                         and reading the copy operations.
+ *
+ * IO_IN_PROGRESS: Merge operation is in-progress by worker threads.
+ *
+ * IO_TERMINATED: When all the worker threads are done, request the
+ *                read-ahead thread to terminate
+ *
+ * READ_AHEAD_FAILURE: If there are any IO failures when read-ahead
+ *                     thread is reading from COW device.
+ *
+ * The transition of each states is described in snapuserd_readahead.cpp
+ */
+enum class READ_AHEAD_IO_TRANSITION {
+    READ_AHEAD_BEGIN,
+    READ_AHEAD_IN_PROGRESS,
+    IO_IN_PROGRESS,
+    IO_TERMINATED,
+    READ_AHEAD_FAILURE,
+};
+
 class BufferSink : public IByteSink {
   public:
     void Initialize(size_t size);
@@ -76,6 +108,47 @@
 
 class Snapuserd;
 
+class ReadAheadThread {
+  public:
+    ReadAheadThread(const std::string& cow_device, const std::string& backing_device,
+                    const std::string& misc_name, std::shared_ptr<Snapuserd> snapuserd);
+    bool RunThread();
+
+  private:
+    void InitializeIter();
+    bool IterDone();
+    void IterNext();
+    const CowOperation* GetIterOp();
+    void InitializeBuffer();
+
+    bool InitializeFds();
+    void CloseFds() {
+        cow_fd_ = {};
+        backing_store_fd_ = {};
+    }
+
+    bool ReadAheadIOStart();
+    void PrepareReadAhead(uint64_t* source_block, int* pending_ops, std::vector<uint64_t>& blocks);
+    bool ReconstructDataFromCow();
+    void CheckOverlap(const CowOperation* cow_op);
+
+    void* read_ahead_buffer_;
+    void* metadata_buffer_;
+    std::vector<const CowOperation*>::reverse_iterator read_ahead_iter_;
+    std::string cow_device_;
+    std::string backing_store_device_;
+    std::string misc_name_;
+
+    unique_fd cow_fd_;
+    unique_fd backing_store_fd_;
+
+    std::shared_ptr<Snapuserd> snapuserd_;
+
+    std::unordered_set<uint64_t> dest_blocks_;
+    std::unordered_set<uint64_t> source_blocks_;
+    bool overlap_;
+};
+
 class WorkerThread {
   public:
     WorkerThread(const std::string& cow_device, const std::string& backing_device,
@@ -116,12 +189,16 @@
     bool ProcessCopyOp(const CowOperation* cow_op);
     bool ProcessZeroOp();
 
+    bool ReadFromBaseDevice(const CowOperation* cow_op);
+    bool GetReadAheadPopulatedBuffer(const CowOperation* cow_op);
+
     // Merge related functions
     bool ProcessMergeComplete(chunk_t chunk, void* buffer);
     loff_t GetMergeStartOffset(void* merged_buffer, void* unmerged_buffer,
                                int* unmerged_exceptions);
+
     int GetNumberOfMergedOps(void* merged_buffer, void* unmerged_buffer, loff_t offset,
-                             int unmerged_exceptions);
+                             int unmerged_exceptions, bool* copy_op, bool* commit);
 
     sector_t ChunkToSector(chunk_t chunk) { return chunk << CHUNK_SHIFT; }
     chunk_t SectorToChunk(sector_t sector) { return sector >> CHUNK_SHIFT; }
@@ -158,7 +235,10 @@
     bool CommitMerge(int num_merge_ops);
 
     void CloseFds() { cow_fd_ = {}; }
-    void FreeResources() { worker_threads_.clear(); }
+    void FreeResources() {
+        worker_threads_.clear();
+        read_ahead_thread_ = nullptr;
+    }
     size_t GetMetadataAreaSize() { return vec_.size(); }
     void* GetExceptionBuffer(size_t i) { return vec_[i].get(); }
 
@@ -173,16 +253,47 @@
         return p1.first < p2.first;
     }
 
-  private:
-    std::vector<std::unique_ptr<WorkerThread>> worker_threads_;
+    void UnmapBufferRegion();
+    bool MmapMetadata();
 
+    // Read-ahead related functions
+    std::vector<const CowOperation*>& GetReadAheadOpsVec() { return read_ahead_ops_; }
+    std::unordered_map<uint64_t, void*>& GetReadAheadMap() { return read_ahead_buffer_map_; }
+    void* GetMappedAddr() { return mapped_addr_; }
+    bool IsReadAheadFeaturePresent() { return read_ahead_feature_; }
+    void PrepareReadAhead();
+    void StartReadAhead();
+    void MergeCompleted();
+    bool ReadAheadIOCompleted(bool sync);
+    void ReadAheadIOFailed();
+    bool WaitForMergeToComplete();
+    bool GetReadAheadPopulatedBuffer(uint64_t block, void* buffer);
+    bool ReconstructDataFromCow() { return populate_data_from_cow_; }
+    void ReconstructDataFromCowFinish() { populate_data_from_cow_ = false; }
+    bool WaitForReadAheadToStart();
+
+    uint64_t GetBufferMetadataOffset();
+    size_t GetBufferMetadataSize();
+    size_t GetBufferDataOffset();
+    size_t GetBufferDataSize();
+
+    // Final block to be merged in a given read-ahead buffer region
+    void SetFinalBlockMerged(uint64_t x) { final_block_merged_ = x; }
+    uint64_t GetFinalBlockMerged() { return final_block_merged_; }
+    // Total number of blocks to be merged in a given read-ahead buffer region
+    void SetTotalRaBlocksMerged(int x) { total_ra_blocks_merged_ = x; }
+    int GetTotalRaBlocksMerged() { return total_ra_blocks_merged_; }
+
+  private:
     bool IsChunkIdMetadata(chunk_t chunk);
     chunk_t GetNextAllocatableChunkId(chunk_t chunk_id);
 
+    bool GetRABuffer(std::unique_lock<std::mutex>* lock, uint64_t block, void* buffer);
     bool ReadMetadata();
     sector_t ChunkToSector(chunk_t chunk) { return chunk << CHUNK_SHIFT; }
     chunk_t SectorToChunk(sector_t sector) { return sector >> CHUNK_SHIFT; }
     bool IsBlockAligned(int read_size) { return ((read_size & (BLOCK_SZ - 1)) == 0); }
+    struct BufferState* GetBufferState();
 
     std::string cow_device_;
     std::string backing_store_device_;
@@ -197,7 +308,6 @@
     std::unique_ptr<ICowOpIter> cowop_iter_;
     std::unique_ptr<ICowOpReverseIter> cowop_riter_;
     std::unique_ptr<CowReader> reader_;
-    std::unique_ptr<CowWriter> writer_;
 
     // Vector of disk exception which is a
     // mapping of old-chunk to new-chunk
@@ -208,6 +318,21 @@
     std::vector<std::pair<sector_t, const CowOperation*>> chunk_vec_;
 
     std::mutex lock_;
+    std::condition_variable cv;
+
+    void* mapped_addr_;
+    size_t total_mapped_addr_length_;
+
+    std::vector<std::unique_ptr<WorkerThread>> worker_threads_;
+    // Read-ahead related
+    std::unordered_map<uint64_t, void*> read_ahead_buffer_map_;
+    std::vector<const CowOperation*> read_ahead_ops_;
+    bool populate_data_from_cow_ = false;
+    bool read_ahead_feature_;
+    uint64_t final_block_merged_;
+    int total_ra_blocks_merged_ = 0;
+    READ_AHEAD_IO_TRANSITION io_state_;
+    std::unique_ptr<ReadAheadThread> read_ahead_thread_;
 
     bool merge_initiated_ = false;
     bool attached_ = false;
diff --git a/fs_mgr/libsnapshot/snapuserd_client.cpp b/fs_mgr/libsnapshot/snapuserd_client.cpp
index 16d02e4..41ab344 100644
--- a/fs_mgr/libsnapshot/snapuserd_client.cpp
+++ b/fs_mgr/libsnapshot/snapuserd_client.cpp
@@ -113,7 +113,7 @@
 
 bool SnapuserdClient::Sendmsg(const std::string& msg) {
     LOG(DEBUG) << "Sendmsg: msg " << msg << " sockfd: " << sockfd_;
-    ssize_t numBytesSent = TEMP_FAILURE_RETRY(send(sockfd_, msg.data(), msg.size(), 0));
+    ssize_t numBytesSent = TEMP_FAILURE_RETRY(send(sockfd_, msg.data(), msg.size(), MSG_NOSIGNAL));
     if (numBytesSent < 0) {
         PLOG(ERROR) << "Send failed";
         return false;
diff --git a/fs_mgr/libsnapshot/snapuserd_readahead.cpp b/fs_mgr/libsnapshot/snapuserd_readahead.cpp
new file mode 100644
index 0000000..09ee2f2
--- /dev/null
+++ b/fs_mgr/libsnapshot/snapuserd_readahead.cpp
@@ -0,0 +1,460 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "snapuserd.h"
+
+#include <csignal>
+#include <optional>
+#include <set>
+
+#include <libsnapshot/snapuserd_client.h>
+
+namespace android {
+namespace snapshot {
+
+using namespace android;
+using namespace android::dm;
+using android::base::unique_fd;
+
+#define SNAP_LOG(level) LOG(level) << misc_name_ << ": "
+#define SNAP_PLOG(level) PLOG(level) << misc_name_ << ": "
+
+/*
+ * Merging a copy operation involves the following flow:
+ *
+ * 1: dm-snapshot layer requests merge for a 4k block. dm-user sends the request
+ *    to the daemon
+ * 2: daemon reads the source block
+ * 3: daemon copies the source data
+ * 4: IO completion sent back to dm-user (a switch from user space to kernel)
+ * 5: dm-snapshot merges the data to base device
+ * 6: dm-snapshot sends the merge-completion IO to dm-user
+ * 7: dm-user re-directs the merge completion IO to daemon (one more switch)
+ * 8: daemon updates the COW file about the completed merge request (a write syscall) and followed
+ * by a fysnc. 9: Send the IO completion back to dm-user
+ *
+ * The above sequence is a significant overhead especially when merging one 4k
+ * block at a time.
+ *
+ * Read-ahead layer will optimize the above path by reading the data from base
+ * device in the background so that merging thread can retrieve the data from
+ * the read-ahead cache. Additionally, syncing of merged data is deferred to
+ * read-ahead thread threadby the IO path is not bottlenecked.
+ *
+ * We create a scratch space of 2MB to store the read-ahead data in the COW
+ * device.
+ *
+ *      +-----------------------+
+ *      |     Header (fixed)    |
+ *      +-----------------------+
+ *      |    Scratch space      |  <-- 2MB
+ *      +-----------------------+
+ *
+ *      Scratch space is as follows:
+ *
+ *      +-----------------------+
+ *      |       Metadata        | <- 4k page
+ *      +-----------------------+
+ *      |       Metadata        | <- 4k page
+ *      +-----------------------+
+ *      |                       |
+ *      |    Read-ahead data    |
+ *      |                       |
+ *      +-----------------------+
+ *
+ * State transitions and communication between read-ahead thread and worker
+ * thread during merge:
+ * =====================================================================
+ *
+ *   Worker Threads                                 Read-Ahead thread
+ *   ------------------------------------------------------------------
+ *
+ *      |
+ *      |
+ *  --> -----------------READ_AHEAD_BEGIN------------->|
+ *  |   |                                              | READ_AHEAD_IN_PROGRESS
+ *  |  WAIT                                            |
+ *  |   |                                              |
+ *  |   |<-----------------IO_IN_PROGRESS---------------
+ *  |   |                                              |
+ *  |   | IO_IN_PRGRESS                               WAIT
+ *  |   |                                              |
+ *  |<--|                                              |
+ *      |                                              |
+ *      ------------------IO_TERMINATED--------------->|
+ *                                                     END
+ *
+ *
+ * ===================================================================
+ *
+ * Example:
+ *
+ * We have 6 copy operations to be executed in OTA and there is a overlap. Update-engine
+ * will write to COW file as follows:
+ *
+ * Op-1: 20 -> 23
+ * Op-2: 19 -> 22
+ * Op-3: 18 -> 21
+ * Op-4: 17 -> 20
+ * Op-5: 16 -> 19
+ * Op-6: 15 -> 18
+ *
+ * Read-ahead thread will read all the 6 source blocks and store the data in the
+ * scratch space. Metadata will contain the destination block numbers. Thus,
+ * scratch space will look something like this:
+ *
+ * +--------------+
+ * | Block   23   |
+ * | offset - 1   |
+ * +--------------+
+ * | Block   22   |
+ * | offset - 2   |
+ * +--------------+
+ * | Block   21   |
+ * | offset - 3   |
+ * +--------------+
+ *    ...
+ *    ...
+ * +--------------+
+ * | Data-Block 20| <-- offset - 1
+ * +--------------+
+ * | Data-Block 19| <-- offset - 2
+ * +--------------+
+ * | Data-Block 18| <-- offset - 3
+ * +--------------+
+ *     ...
+ *     ...
+ *
+ * ====================================================================
+ * IO Path:
+ *
+ * Read-ahead will serve the data to worker threads during merge only
+ * after metadata and data are persisted to the scratch space. Worker
+ * threads during merge will always retrieve the data from cache; if the
+ * cache is not populated, it will wait for the read-ahead thread to finish.
+ * Furthermore, the number of operations merged will by synced to the header
+ * only when all the blocks in the read-ahead cache are merged. In the above
+ * case, when all 6 operations are merged, COW Header is updated with
+ * num_merge_ops = 6.
+ *
+ * Merge resume after crash:
+ *
+ * Let's say we have a crash after 5 operations are merged. i.e. after
+ * Op-5: 16->19 is completed but before the Op-6 is merged. Thus, COW Header
+ * num_merge_ops will be 0 as the all the ops were not merged yet. During next
+ * reboot, read-ahead thread will re-construct the data in-memory from the
+ * scratch space; when merge resumes, Op-1 will be re-exectued. However,
+ * data will be served from read-ahead cache safely even though, block 20
+ * was over-written by Op-4.
+ *
+ */
+
+ReadAheadThread::ReadAheadThread(const std::string& cow_device, const std::string& backing_device,
+                                 const std::string& misc_name,
+                                 std::shared_ptr<Snapuserd> snapuserd) {
+    cow_device_ = cow_device;
+    backing_store_device_ = backing_device;
+    misc_name_ = misc_name;
+    snapuserd_ = snapuserd;
+}
+
+void ReadAheadThread::CheckOverlap(const CowOperation* cow_op) {
+    if (dest_blocks_.count(cow_op->new_block) || source_blocks_.count(cow_op->source)) {
+        overlap_ = true;
+    }
+
+    dest_blocks_.insert(cow_op->source);
+    source_blocks_.insert(cow_op->new_block);
+}
+
+void ReadAheadThread::PrepareReadAhead(uint64_t* source_block, int* pending_ops,
+                                       std::vector<uint64_t>& blocks) {
+    int num_ops = *pending_ops;
+    int nr_consecutive = 0;
+
+    if (!IterDone() && num_ops) {
+        // Get the first block
+        const CowOperation* cow_op = GetIterOp();
+        *source_block = cow_op->source;
+        IterNext();
+        num_ops -= 1;
+        nr_consecutive = 1;
+        blocks.push_back(cow_op->new_block);
+
+        if (!overlap_) {
+            CheckOverlap(cow_op);
+        }
+
+        /*
+         * Find number of consecutive blocks working backwards.
+         */
+        while (!IterDone() && num_ops) {
+            const CowOperation* op = GetIterOp();
+            if (op->source != (*source_block - nr_consecutive)) {
+                break;
+            }
+            nr_consecutive += 1;
+            num_ops -= 1;
+            blocks.push_back(op->new_block);
+            IterNext();
+
+            if (!overlap_) {
+                CheckOverlap(op);
+            }
+        }
+    }
+}
+
+bool ReadAheadThread::ReconstructDataFromCow() {
+    std::unordered_map<uint64_t, void*>& read_ahead_buffer_map = snapuserd_->GetReadAheadMap();
+    read_ahead_buffer_map.clear();
+    loff_t metadata_offset = 0;
+    loff_t start_data_offset = snapuserd_->GetBufferDataOffset();
+    int num_ops = 0;
+    int total_blocks_merged = 0;
+
+    while (true) {
+        struct ScratchMetadata* bm = reinterpret_cast<struct ScratchMetadata*>(
+                (char*)metadata_buffer_ + metadata_offset);
+
+        // Done reading metadata
+        if (bm->new_block == 0 && bm->file_offset == 0) {
+            break;
+        }
+
+        loff_t buffer_offset = bm->file_offset - start_data_offset;
+        void* bufptr = static_cast<void*>((char*)read_ahead_buffer_ + buffer_offset);
+        read_ahead_buffer_map[bm->new_block] = bufptr;
+        num_ops += 1;
+        total_blocks_merged += 1;
+
+        metadata_offset += sizeof(struct ScratchMetadata);
+    }
+
+    // We are done re-constructing the mapping; however, we need to make sure
+    // all the COW operations to-be merged are present in the re-constructed
+    // mapping.
+    while (!IterDone()) {
+        const CowOperation* op = GetIterOp();
+        if (read_ahead_buffer_map.find(op->new_block) != read_ahead_buffer_map.end()) {
+            num_ops -= 1;
+            snapuserd_->SetFinalBlockMerged(op->new_block);
+            IterNext();
+        } else {
+            // Verify that we have covered all the ops which were re-constructed
+            // from COW device - These are the ops which are being
+            // re-constructed after crash.
+            CHECK(num_ops == 0);
+            break;
+        }
+    }
+
+    snapuserd_->SetTotalRaBlocksMerged(total_blocks_merged);
+
+    snapuserd_->ReconstructDataFromCowFinish();
+
+    if (!snapuserd_->ReadAheadIOCompleted(true)) {
+        SNAP_LOG(ERROR) << "ReadAheadIOCompleted failed...";
+        snapuserd_->ReadAheadIOFailed();
+        return false;
+    }
+
+    SNAP_LOG(INFO) << "ReconstructDataFromCow success";
+    return true;
+}
+
+bool ReadAheadThread::ReadAheadIOStart() {
+    // Check if the data has to be constructed from the COW file.
+    // This will be true only once during boot up after a crash
+    // during merge.
+    if (snapuserd_->ReconstructDataFromCow()) {
+        return ReconstructDataFromCow();
+    }
+
+    std::unordered_map<uint64_t, void*>& read_ahead_buffer_map = snapuserd_->GetReadAheadMap();
+    read_ahead_buffer_map.clear();
+
+    int num_ops = (snapuserd_->GetBufferDataSize()) / BLOCK_SZ;
+    loff_t metadata_offset = 0;
+
+    struct ScratchMetadata* bm =
+            reinterpret_cast<struct ScratchMetadata*>((char*)metadata_buffer_ + metadata_offset);
+
+    bm->new_block = 0;
+    bm->file_offset = 0;
+
+    std::vector<uint64_t> blocks;
+
+    loff_t buffer_offset = 0;
+    loff_t offset = 0;
+    loff_t file_offset = snapuserd_->GetBufferDataOffset();
+    int total_blocks_merged = 0;
+    overlap_ = false;
+    dest_blocks_.clear();
+    source_blocks_.clear();
+
+    while (true) {
+        uint64_t source_block;
+        int linear_blocks;
+
+        PrepareReadAhead(&source_block, &num_ops, blocks);
+        linear_blocks = blocks.size();
+        if (linear_blocks == 0) {
+            // No more blocks to read
+            SNAP_LOG(DEBUG) << " Read-ahead completed....";
+            break;
+        }
+
+        // Get the first block in the consecutive set of blocks
+        source_block = source_block + 1 - linear_blocks;
+        size_t io_size = (linear_blocks * BLOCK_SZ);
+        num_ops -= linear_blocks;
+        total_blocks_merged += linear_blocks;
+
+        // Mark the block number as the one which will
+        // be the final block to be merged in this entire region.
+        // Read-ahead thread will get
+        // notified when this block is merged to make
+        // forward progress
+        snapuserd_->SetFinalBlockMerged(blocks.back());
+
+        while (linear_blocks) {
+            uint64_t new_block = blocks.back();
+            blocks.pop_back();
+            // Assign the mapping
+            void* bufptr = static_cast<void*>((char*)read_ahead_buffer_ + offset);
+            read_ahead_buffer_map[new_block] = bufptr;
+            offset += BLOCK_SZ;
+
+            bm = reinterpret_cast<struct ScratchMetadata*>((char*)metadata_buffer_ +
+                                                           metadata_offset);
+            bm->new_block = new_block;
+            bm->file_offset = file_offset;
+
+            metadata_offset += sizeof(struct ScratchMetadata);
+            file_offset += BLOCK_SZ;
+
+            linear_blocks -= 1;
+        }
+
+        // Read from the base device consecutive set of blocks in one shot
+        if (!android::base::ReadFullyAtOffset(backing_store_fd_,
+                                              (char*)read_ahead_buffer_ + buffer_offset, io_size,
+                                              source_block * BLOCK_SZ)) {
+            SNAP_PLOG(ERROR) << "Copy-op failed. Read from backing store: " << backing_store_device_
+                             << "at block :" << source_block << " buffer_offset : " << buffer_offset
+                             << " io_size : " << io_size << " buf-addr : " << read_ahead_buffer_;
+
+            snapuserd_->ReadAheadIOFailed();
+            return false;
+        }
+
+        // This is important - explicitly set the contents to zero. This is used
+        // when re-constructing the data after crash. This indicates end of
+        // reading metadata contents when re-constructing the data
+        bm = reinterpret_cast<struct ScratchMetadata*>((char*)metadata_buffer_ + metadata_offset);
+        bm->new_block = 0;
+        bm->file_offset = 0;
+
+        buffer_offset += io_size;
+        CHECK(offset == buffer_offset);
+        CHECK((file_offset - snapuserd_->GetBufferDataOffset()) == offset);
+    }
+
+    snapuserd_->SetTotalRaBlocksMerged(total_blocks_merged);
+
+    // Flush the data only if we have a overlapping blocks in the region
+    if (!snapuserd_->ReadAheadIOCompleted(overlap_)) {
+        SNAP_LOG(ERROR) << "ReadAheadIOCompleted failed...";
+        snapuserd_->ReadAheadIOFailed();
+        return false;
+    }
+
+    return true;
+}
+
+bool ReadAheadThread::RunThread() {
+    if (!InitializeFds()) {
+        return false;
+    }
+
+    InitializeIter();
+    InitializeBuffer();
+
+    while (!IterDone()) {
+        if (!ReadAheadIOStart()) {
+            return false;
+        }
+
+        bool status = snapuserd_->WaitForMergeToComplete();
+
+        if (status && !snapuserd_->CommitMerge(snapuserd_->GetTotalRaBlocksMerged())) {
+            return false;
+        }
+
+        if (!status) break;
+    }
+
+    CloseFds();
+    SNAP_LOG(INFO) << " ReadAhead thread terminating....";
+    return true;
+}
+
+// Initialization
+bool ReadAheadThread::InitializeFds() {
+    backing_store_fd_.reset(open(backing_store_device_.c_str(), O_RDONLY));
+    if (backing_store_fd_ < 0) {
+        SNAP_PLOG(ERROR) << "Open Failed: " << backing_store_device_;
+        return false;
+    }
+
+    cow_fd_.reset(open(cow_device_.c_str(), O_RDWR));
+    if (cow_fd_ < 0) {
+        SNAP_PLOG(ERROR) << "Open Failed: " << cow_device_;
+        return false;
+    }
+
+    return true;
+}
+
+void ReadAheadThread::InitializeIter() {
+    std::vector<const CowOperation*>& read_ahead_ops = snapuserd_->GetReadAheadOpsVec();
+    read_ahead_iter_ = read_ahead_ops.rbegin();
+}
+
+bool ReadAheadThread::IterDone() {
+    std::vector<const CowOperation*>& read_ahead_ops = snapuserd_->GetReadAheadOpsVec();
+    return read_ahead_iter_ == read_ahead_ops.rend();
+}
+
+void ReadAheadThread::IterNext() {
+    read_ahead_iter_++;
+}
+
+const CowOperation* ReadAheadThread::GetIterOp() {
+    return *read_ahead_iter_;
+}
+
+void ReadAheadThread::InitializeBuffer() {
+    void* mapped_addr = snapuserd_->GetMappedAddr();
+    // Map the scratch space region into memory
+    metadata_buffer_ =
+            static_cast<void*>((char*)mapped_addr + snapuserd_->GetBufferMetadataOffset());
+    read_ahead_buffer_ = static_cast<void*>((char*)mapped_addr + snapuserd_->GetBufferDataOffset());
+}
+
+}  // namespace snapshot
+}  // namespace android
diff --git a/fs_mgr/libsnapshot/snapuserd_server.cpp b/fs_mgr/libsnapshot/snapuserd_server.cpp
index 64332d1..ff8a259 100644
--- a/fs_mgr/libsnapshot/snapuserd_server.cpp
+++ b/fs_mgr/libsnapshot/snapuserd_server.cpp
@@ -81,7 +81,7 @@
     : snapuserd_(snapuserd), misc_name_(snapuserd_->GetMiscName()) {}
 
 bool SnapuserdServer::Sendmsg(android::base::borrowed_fd fd, const std::string& msg) {
-    ssize_t ret = TEMP_FAILURE_RETRY(send(fd.get(), msg.data(), msg.size(), 0));
+    ssize_t ret = TEMP_FAILURE_RETRY(send(fd.get(), msg.data(), msg.size(), MSG_NOSIGNAL));
     if (ret < 0) {
         PLOG(ERROR) << "Snapuserd:server: send() failed";
         return false;
@@ -209,10 +209,11 @@
     }
 
     handler->snapuserd()->CloseFds();
+    handler->snapuserd()->CheckMergeCompletionStatus();
+    handler->snapuserd()->UnmapBufferRegion();
 
     auto misc_name = handler->misc_name();
     LOG(INFO) << "Handler thread about to exit: " << misc_name;
-    handler->snapuserd()->CheckMergeCompletionStatus();
 
     {
         std::lock_guard<std::mutex> lock(lock_);
diff --git a/fs_mgr/libsnapshot/snapuserd_worker.cpp b/fs_mgr/libsnapshot/snapuserd_worker.cpp
index 1002569..9f42ab8 100644
--- a/fs_mgr/libsnapshot/snapuserd_worker.cpp
+++ b/fs_mgr/libsnapshot/snapuserd_worker.cpp
@@ -135,14 +135,11 @@
     return true;
 }
 
-// Start the copy operation. This will read the backing
-// block device which is represented by cow_op->source.
-bool WorkerThread::ProcessCopyOp(const CowOperation* cow_op) {
+bool WorkerThread::ReadFromBaseDevice(const CowOperation* cow_op) {
     void* buffer = bufsink_.GetPayloadBuffer(BLOCK_SZ);
     CHECK(buffer != nullptr);
-
-    // Issue a single 4K IO. However, this can be optimized
-    // if the successive blocks are contiguous.
+    SNAP_LOG(DEBUG) << " ReadFromBaseDevice...: new-block: " << cow_op->new_block
+                    << " Source: " << cow_op->source;
     if (!android::base::ReadFullyAtOffset(backing_store_fd_, buffer, BLOCK_SZ,
                                           cow_op->source * BLOCK_SZ)) {
         SNAP_PLOG(ERROR) << "Copy-op failed. Read from backing store: " << backing_store_device_
@@ -153,6 +150,31 @@
     return true;
 }
 
+bool WorkerThread::GetReadAheadPopulatedBuffer(const CowOperation* cow_op) {
+    void* buffer = bufsink_.GetPayloadBuffer(BLOCK_SZ);
+    CHECK(buffer != nullptr);
+
+    if (!snapuserd_->GetReadAheadPopulatedBuffer(cow_op->new_block, buffer)) {
+        return false;
+    }
+
+    return true;
+}
+
+// Start the copy operation. This will read the backing
+// block device which is represented by cow_op->source.
+bool WorkerThread::ProcessCopyOp(const CowOperation* cow_op) {
+    if (!GetReadAheadPopulatedBuffer(cow_op)) {
+        SNAP_LOG(DEBUG) << " GetReadAheadPopulatedBuffer failed..."
+                        << " new_block: " << cow_op->new_block;
+        if (!ReadFromBaseDevice(cow_op)) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
 bool WorkerThread::ProcessZeroOp() {
     // Zero out the entire block
     void* buffer = bufsink_.GetPayloadBuffer(BLOCK_SZ);
@@ -386,8 +408,10 @@
 }
 
 int WorkerThread::GetNumberOfMergedOps(void* merged_buffer, void* unmerged_buffer, loff_t offset,
-                                       int unmerged_exceptions) {
+                                       int unmerged_exceptions, bool* copy_op, bool* commit) {
     int merged_ops_cur_iter = 0;
+    std::unordered_map<uint64_t, void*>& read_ahead_buffer_map = snapuserd_->GetReadAheadMap();
+    *copy_op = false;
     std::vector<std::pair<sector_t, const CowOperation*>>& chunk_vec = snapuserd_->GetChunkVec();
 
     // Find the operations which are merged in this cycle.
@@ -411,6 +435,23 @@
             const CowOperation* cow_op = it->second;
 
             CHECK(cow_op != nullptr);
+            if (snapuserd_->IsReadAheadFeaturePresent() && cow_op->type == kCowCopyOp) {
+                *copy_op = true;
+                // Every single copy operation has to come from read-ahead
+                // cache.
+                if (read_ahead_buffer_map.find(cow_op->new_block) == read_ahead_buffer_map.end()) {
+                    SNAP_LOG(ERROR)
+                            << " Block: " << cow_op->new_block << " not found in read-ahead cache"
+                            << " Source: " << cow_op->source;
+                    return -1;
+                }
+                // If this is a final block merged in the read-ahead buffer
+                // region, notify the read-ahead thread to make forward
+                // progress
+                if (cow_op->new_block == snapuserd_->GetFinalBlockMerged()) {
+                    *commit = true;
+                }
+            }
 
             CHECK(cow_op->new_block == cow_de->old_chunk);
             // zero out to indicate that operation is merged.
@@ -442,6 +483,8 @@
 bool WorkerThread::ProcessMergeComplete(chunk_t chunk, void* buffer) {
     uint32_t stride = exceptions_per_area_ + 1;
     const std::vector<std::unique_ptr<uint8_t[]>>& vec = snapuserd_->GetMetadataVec();
+    bool copy_op = false;
+    bool commit = false;
 
     // ChunkID to vector index
     lldiv_t divresult = lldiv(chunk, stride);
@@ -452,13 +495,24 @@
     int unmerged_exceptions = 0;
     loff_t offset = GetMergeStartOffset(buffer, vec[divresult.quot].get(), &unmerged_exceptions);
 
-    int merged_ops_cur_iter =
-            GetNumberOfMergedOps(buffer, vec[divresult.quot].get(), offset, unmerged_exceptions);
+    int merged_ops_cur_iter = GetNumberOfMergedOps(buffer, vec[divresult.quot].get(), offset,
+                                                   unmerged_exceptions, &copy_op, &commit);
 
     // There should be at least one operation merged in this cycle
     CHECK(merged_ops_cur_iter > 0);
-    if (!snapuserd_->CommitMerge(merged_ops_cur_iter)) {
-        return false;
+
+    if (copy_op) {
+        if (commit) {
+            // Push the flushing logic to read-ahead thread so that merge thread
+            // can make forward progress. Sync will happen in the background
+            snapuserd_->StartReadAhead();
+        }
+    } else {
+        // Non-copy ops and all ops in older COW format
+        if (!snapuserd_->CommitMerge(merged_ops_cur_iter)) {
+            SNAP_LOG(ERROR) << "CommitMerge failed...";
+            return false;
+        }
     }
 
     SNAP_LOG(DEBUG) << "Merge success: " << merged_ops_cur_iter << "chunk: " << chunk;
@@ -613,12 +667,21 @@
             }
         }
 
+        // Just return the header if it is an error
+        if (header->type == DM_USER_RESP_ERROR) {
+            ret = 0;
+        }
+
         // Daemon will not be terminated if there is any error. We will
         // just send the error back to dm-user.
         if (!WriteDmUserPayload(ret)) {
             return false;
         }
 
+        if (header->type == DM_USER_RESP_ERROR) {
+            break;
+        }
+
         remaining_size -= ret;
         offset += ret;
     } while (remaining_size > 0);
diff --git a/fs_mgr/libsnapshot/update_engine/update_metadata.proto b/fs_mgr/libsnapshot/update_engine/update_metadata.proto
index f31ee31..69d72e1 100644
--- a/fs_mgr/libsnapshot/update_engine/update_metadata.proto
+++ b/fs_mgr/libsnapshot/update_engine/update_metadata.proto
@@ -75,6 +75,7 @@
     repeated DynamicPartitionGroup groups = 1;
     optional bool vabc_enabled = 3;
     optional string vabc_compression_param = 4;
+    optional uint32 cow_version = 5;
 }
 
 message DeltaArchiveManifest {
diff --git a/fs_mgr/tests/fs_mgr_test.cpp b/fs_mgr/tests/fs_mgr_test.cpp
index 5887641..83174ef 100644
--- a/fs_mgr/tests/fs_mgr_test.cpp
+++ b/fs_mgr/tests/fs_mgr_test.cpp
@@ -184,6 +184,36 @@
         {"androidboot.space", "sha256 5248 androidboot.nospace = nope"},
 };
 
+bool CompareFlags(FstabEntry::FsMgrFlags& lhs, FstabEntry::FsMgrFlags& rhs) {
+    // clang-format off
+    return lhs.wait == rhs.wait &&
+           lhs.check == rhs.check &&
+           lhs.crypt == rhs.crypt &&
+           lhs.nonremovable == rhs.nonremovable &&
+           lhs.vold_managed == rhs.vold_managed &&
+           lhs.recovery_only == rhs.recovery_only &&
+           lhs.verify == rhs.verify &&
+           lhs.force_crypt == rhs.force_crypt &&
+           lhs.no_emulated_sd == rhs.no_emulated_sd &&
+           lhs.no_trim == rhs.no_trim &&
+           lhs.file_encryption == rhs.file_encryption &&
+           lhs.formattable == rhs.formattable &&
+           lhs.slot_select == rhs.slot_select &&
+           lhs.force_fde_or_fbe == rhs.force_fde_or_fbe &&
+           lhs.late_mount == rhs.late_mount &&
+           lhs.no_fail == rhs.no_fail &&
+           lhs.verify_at_boot == rhs.verify_at_boot &&
+           lhs.quota == rhs.quota &&
+           lhs.avb == rhs.avb &&
+           lhs.logical == rhs.logical &&
+           lhs.checkpoint_blk == rhs.checkpoint_blk &&
+           lhs.checkpoint_fs == rhs.checkpoint_fs &&
+           lhs.first_stage_mount == rhs.first_stage_mount &&
+           lhs.slot_select_other == rhs.slot_select_other &&
+           lhs.fs_verity == rhs.fs_verity;
+    // clang-format on
+}
+
 }  // namespace
 
 TEST(fs_mgr, fs_mgr_parse_cmdline) {
@@ -291,8 +321,7 @@
     EXPECT_EQ(i, fstab.size());
 }
 
-// TODO(124837435): enable it later when it can pass TreeHugger.
-TEST(fs_mgr, DISABLED_ReadFstabFromFile_MountOptions) {
+TEST(fs_mgr, ReadFstabFromFile_MountOptions) {
     TemporaryFile tf;
     ASSERT_TRUE(tf.fd != -1);
     std::string fstab_contents = R"fs(
@@ -316,88 +345,69 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(11U, fstab.size());
+    ASSERT_LE(11U, fstab.size());
 
-    EXPECT_EQ("/", fstab[0].mount_point);
-    EXPECT_EQ(static_cast<unsigned long>(MS_RDONLY), fstab[0].flags);
-    EXPECT_EQ("barrier=1", fstab[0].fs_options);
+    FstabEntry* entry = GetEntryForMountPoint(&fstab, "/");
+    ASSERT_NE(nullptr, entry);
+    EXPECT_EQ(static_cast<unsigned long>(MS_RDONLY), entry->flags);
+    EXPECT_EQ("barrier=1", entry->fs_options);
 
-    EXPECT_EQ("/metadata", fstab[1].mount_point);
-    EXPECT_EQ(static_cast<unsigned long>(MS_NOATIME | MS_NOSUID | MS_NODEV), fstab[1].flags);
-    EXPECT_EQ("discard", fstab[1].fs_options);
+    entry = GetEntryForMountPoint(&fstab, "/metadata");
+    ASSERT_NE(nullptr, entry);
+    EXPECT_EQ(static_cast<unsigned long>(MS_NOATIME | MS_NOSUID | MS_NODEV), entry->flags);
+    EXPECT_EQ("discard", entry->fs_options);
 
-    EXPECT_EQ("/data", fstab[2].mount_point);
-    EXPECT_EQ(static_cast<unsigned long>(MS_NOATIME | MS_NOSUID | MS_NODEV), fstab[2].flags);
-    EXPECT_EQ("discard,reserve_root=32768,resgid=1065,fsync_mode=nobarrier", fstab[2].fs_options);
+    entry = GetEntryForMountPoint(&fstab, "/data");
+    ASSERT_NE(nullptr, entry);
+    EXPECT_EQ(static_cast<unsigned long>(MS_NOATIME | MS_NOSUID | MS_NODEV), entry->flags);
+    EXPECT_EQ("discard,reserve_root=32768,resgid=1065,fsync_mode=nobarrier", entry->fs_options);
 
-    EXPECT_EQ("/misc", fstab[3].mount_point);
-    EXPECT_EQ(0U, fstab[3].flags);
-    EXPECT_EQ("", fstab[3].fs_options);
+    entry = GetEntryForMountPoint(&fstab, "/misc");
+    ASSERT_NE(nullptr, entry);
+    EXPECT_EQ(0U, entry->flags);
+    EXPECT_EQ("", entry->fs_options);
 
-    EXPECT_EQ("/vendor/firmware_mnt", fstab[4].mount_point);
-    EXPECT_EQ(static_cast<unsigned long>(MS_RDONLY), fstab[4].flags);
+    entry = GetEntryForMountPoint(&fstab, "/vendor/firmware_mnt");
+    ASSERT_NE(nullptr, entry);
+    EXPECT_EQ(static_cast<unsigned long>(MS_RDONLY), entry->flags);
     EXPECT_EQ(
             "shortname=lower,uid=1000,gid=1000,dmask=227,fmask=337,"
             "context=u:object_r:firmware_file:s0",
-            fstab[4].fs_options);
+            entry->fs_options);
 
-    EXPECT_EQ("auto", fstab[5].mount_point);
-    EXPECT_EQ(0U, fstab[5].flags);
-    EXPECT_EQ("", fstab[5].fs_options);
+    entry = GetEntryForMountPoint(&fstab, "auto");
+    ASSERT_NE(nullptr, entry);
+    EXPECT_EQ(0U, entry->flags);
+    EXPECT_EQ("", entry->fs_options);
 
-    EXPECT_EQ("none", fstab[6].mount_point);
-    EXPECT_EQ(0U, fstab[6].flags);
-    EXPECT_EQ("", fstab[6].fs_options);
+    entry = GetEntryForMountPoint(&fstab, "none");
+    ASSERT_NE(nullptr, entry);
+    EXPECT_EQ(0U, entry->flags);
+    EXPECT_EQ("", entry->fs_options);
 
-    EXPECT_EQ("none2", fstab[7].mount_point);
-    EXPECT_EQ(static_cast<unsigned long>(MS_NODIRATIME | MS_REMOUNT | MS_BIND), fstab[7].flags);
-    EXPECT_EQ("", fstab[7].fs_options);
+    entry = GetEntryForMountPoint(&fstab, "none2");
+    ASSERT_NE(nullptr, entry);
+    EXPECT_EQ(static_cast<unsigned long>(MS_NODIRATIME | MS_REMOUNT | MS_BIND), entry->flags);
+    EXPECT_EQ("", entry->fs_options);
 
-    EXPECT_EQ("none3", fstab[8].mount_point);
-    EXPECT_EQ(static_cast<unsigned long>(MS_UNBINDABLE | MS_PRIVATE | MS_SLAVE), fstab[8].flags);
-    EXPECT_EQ("", fstab[8].fs_options);
+    entry = GetEntryForMountPoint(&fstab, "none3");
+    ASSERT_NE(nullptr, entry);
+    EXPECT_EQ(static_cast<unsigned long>(MS_UNBINDABLE | MS_PRIVATE | MS_SLAVE), entry->flags);
+    EXPECT_EQ("", entry->fs_options);
 
-    EXPECT_EQ("none4", fstab[9].mount_point);
-    EXPECT_EQ(static_cast<unsigned long>(MS_NOEXEC | MS_SHARED | MS_REC), fstab[9].flags);
-    EXPECT_EQ("", fstab[9].fs_options);
+    entry = GetEntryForMountPoint(&fstab, "none4");
+    ASSERT_NE(nullptr, entry);
+    EXPECT_EQ(static_cast<unsigned long>(MS_NOEXEC | MS_SHARED | MS_REC), entry->flags);
+    EXPECT_EQ("", entry->fs_options);
 
-    EXPECT_EQ("none5", fstab[10].mount_point);
-    EXPECT_EQ(0U, fstab[10].flags);  // rw is the same as defaults
-    EXPECT_EQ("", fstab[10].fs_options);
+    entry = GetEntryForMountPoint(&fstab, "none5");
+    ASSERT_NE(nullptr, entry);
+    // rw is the default.
+    EXPECT_EQ(0U, entry->flags);
+    EXPECT_EQ("", entry->fs_options);
 }
 
-static bool CompareFlags(FstabEntry::FsMgrFlags& lhs, FstabEntry::FsMgrFlags& rhs) {
-    // clang-format off
-    return lhs.wait == rhs.wait &&
-           lhs.check == rhs.check &&
-           lhs.crypt == rhs.crypt &&
-           lhs.nonremovable == rhs.nonremovable &&
-           lhs.vold_managed == rhs.vold_managed &&
-           lhs.recovery_only == rhs.recovery_only &&
-           lhs.verify == rhs.verify &&
-           lhs.force_crypt == rhs.force_crypt &&
-           lhs.no_emulated_sd == rhs.no_emulated_sd &&
-           lhs.no_trim == rhs.no_trim &&
-           lhs.file_encryption == rhs.file_encryption &&
-           lhs.formattable == rhs.formattable &&
-           lhs.slot_select == rhs.slot_select &&
-           lhs.force_fde_or_fbe == rhs.force_fde_or_fbe &&
-           lhs.late_mount == rhs.late_mount &&
-           lhs.no_fail == rhs.no_fail &&
-           lhs.verify_at_boot == rhs.verify_at_boot &&
-           lhs.quota == rhs.quota &&
-           lhs.avb == rhs.avb &&
-           lhs.logical == rhs.logical &&
-           lhs.checkpoint_blk == rhs.checkpoint_blk &&
-           lhs.checkpoint_fs == rhs.checkpoint_fs &&
-           lhs.first_stage_mount == rhs.first_stage_mount &&
-           lhs.slot_select_other == rhs.slot_select_other &&
-           lhs.fs_verity == rhs.fs_verity;
-    // clang-format on
-}
-
-// TODO(124837435): enable it later when it can pass TreeHugger.
-TEST(fs_mgr, DISABLED_ReadFstabFromFile_FsMgrFlags) {
+TEST(fs_mgr, ReadFstabFromFile_FsMgrFlags) {
     TemporaryFile tf;
     ASSERT_TRUE(tf.fd != -1);
     std::string fstab_contents = R"fs(
@@ -412,10 +422,10 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(6U, fstab.size());
+    ASSERT_LE(6U, fstab.size());
 
-    auto entry = fstab.begin();
-    EXPECT_EQ("none0", entry->mount_point);
+    FstabEntry* entry = GetEntryForMountPoint(&fstab, "none0");
+    ASSERT_NE(nullptr, entry);
     {
         FstabEntry::FsMgrFlags flags = {};
         flags.wait = true;
@@ -426,9 +436,9 @@
         flags.verify = true;
         EXPECT_TRUE(CompareFlags(flags, entry->fs_mgr_flags));
     }
-    entry++;
 
-    EXPECT_EQ("none1", entry->mount_point);
+    entry = GetEntryForMountPoint(&fstab, "none1");
+    ASSERT_NE(nullptr, entry);
     {
         FstabEntry::FsMgrFlags flags = {};
         flags.avb = true;
@@ -439,9 +449,9 @@
         flags.no_fail = true;
         EXPECT_TRUE(CompareFlags(flags, entry->fs_mgr_flags));
     }
-    entry++;
 
-    EXPECT_EQ("none2", entry->mount_point);
+    entry = GetEntryForMountPoint(&fstab, "none2");
+    ASSERT_NE(nullptr, entry);
     {
         FstabEntry::FsMgrFlags flags = {};
         flags.first_stage_mount = true;
@@ -451,25 +461,25 @@
         flags.slot_select_other = true;
         EXPECT_TRUE(CompareFlags(flags, entry->fs_mgr_flags));
     }
-    entry++;
 
-    EXPECT_EQ("none3", entry->mount_point);
+    entry = GetEntryForMountPoint(&fstab, "none3");
+    ASSERT_NE(nullptr, entry);
     {
         FstabEntry::FsMgrFlags flags = {};
         flags.checkpoint_blk = true;
         EXPECT_TRUE(CompareFlags(flags, entry->fs_mgr_flags));
     }
-    entry++;
 
-    EXPECT_EQ("none4", entry->mount_point);
+    entry = GetEntryForMountPoint(&fstab, "none4");
+    ASSERT_NE(nullptr, entry);
     {
         FstabEntry::FsMgrFlags flags = {};
         flags.checkpoint_fs = true;
         EXPECT_TRUE(CompareFlags(flags, entry->fs_mgr_flags));
     }
-    entry++;
 
-    EXPECT_EQ("none5", entry->mount_point);
+    entry = GetEntryForMountPoint(&fstab, "none5");
+    ASSERT_NE(nullptr, entry);
     {
         FstabEntry::FsMgrFlags flags = {};
         EXPECT_TRUE(CompareFlags(flags, entry->fs_mgr_flags));
@@ -491,7 +501,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(3U, fstab.size());
+    ASSERT_LE(3U, fstab.size());
 
     auto entry = fstab.begin();
     EXPECT_EQ("none0", entry->mount_point);
@@ -561,7 +571,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(1U, fstab.size());
+    ASSERT_LE(1U, fstab.size());
 
     FstabEntry::FsMgrFlags flags = {};
     flags.crypt = true;
@@ -585,7 +595,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(4U, fstab.size());
+    ASSERT_LE(4U, fstab.size());
 
     FstabEntry::FsMgrFlags flags = {};
     flags.vold_managed = true;
@@ -626,7 +636,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(2U, fstab.size());
+    ASSERT_LE(2U, fstab.size());
 
     FstabEntry::FsMgrFlags flags = {};
 
@@ -652,7 +662,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(2U, fstab.size());
+    ASSERT_LE(2U, fstab.size());
 
     FstabEntry::FsMgrFlags flags = {};
 
@@ -682,7 +692,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(6U, fstab.size());
+    ASSERT_LE(6U, fstab.size());
 
     FstabEntry::FsMgrFlags flags = {};
 
@@ -728,7 +738,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(1U, fstab.size());
+    ASSERT_LE(1U, fstab.size());
 
     auto entry = fstab.begin();
     EXPECT_EQ("none0", entry->mount_point);
@@ -751,7 +761,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(1U, fstab.size());
+    ASSERT_LE(1U, fstab.size());
 
     auto entry = fstab.begin();
     EXPECT_EQ("none0", entry->mount_point);
@@ -775,7 +785,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(1U, fstab.size());
+    ASSERT_LE(1U, fstab.size());
 
     FstabEntry::FsMgrFlags flags = {};
     flags.file_encryption = true;
@@ -797,7 +807,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(2U, fstab.size());
+    ASSERT_LE(2U, fstab.size());
 
     FstabEntry::FsMgrFlags flags = {};
 
@@ -825,7 +835,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(4U, fstab.size());
+    ASSERT_LE(4U, fstab.size());
 
     FstabEntry::FsMgrFlags flags = {};
 
@@ -863,7 +873,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(4U, fstab.size());
+    ASSERT_LE(4U, fstab.size());
 
     FstabEntry::FsMgrFlags flags = {};
 
@@ -901,7 +911,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(4U, fstab.size());
+    ASSERT_LE(4U, fstab.size());
 
     FstabEntry::FsMgrFlags flags = {};
 
@@ -938,7 +948,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(2U, fstab.size());
+    ASSERT_LE(2U, fstab.size());
 
     auto entry = fstab.begin();
     EXPECT_EQ("none0", entry->mount_point);
@@ -967,7 +977,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(1U, fstab.size());
+    ASSERT_LE(1U, fstab.size());
 
     auto entry = fstab.begin();
     EXPECT_EQ("none0", entry->mount_point);
@@ -989,7 +999,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(1U, fstab.size());
+    ASSERT_LE(1U, fstab.size());
 
     auto entry = fstab.begin();
     EXPECT_EQ("adiantum", entry->metadata_encryption);
@@ -1006,7 +1016,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(1U, fstab.size());
+    ASSERT_LE(1U, fstab.size());
 
     auto entry = fstab.begin();
     EXPECT_EQ("aes-256-xts:wrappedkey_v0", entry->metadata_encryption);
@@ -1027,7 +1037,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(1U, fstab.size());
+    ASSERT_LE(1U, fstab.size());
 
     auto entry = fstab.begin();
     EXPECT_EQ("none0", entry->mount_point);
@@ -1053,7 +1063,7 @@
 
     Fstab fstab;
     EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
-    ASSERT_EQ(4U, fstab.size());
+    ASSERT_LE(4U, fstab.size());
 
     auto entry = fstab.begin();
 
@@ -1097,3 +1107,59 @@
     ASSERT_NE(nullptr, fs_mgr_get_mounted_entry_for_userdata(&fstab, block_device))
             << "/data wasn't mounted from default fstab";
 }
+
+TEST(fs_mgr, ReadFstabFromFile_FsMgrOptions_Readahead_Size_KB) {
+    TemporaryFile tf;
+    ASSERT_TRUE(tf.fd != -1);
+    std::string fstab_contents = R"fs(
+source none0       swap   defaults      readahead_size_kb=blah
+source none1       swap   defaults      readahead_size_kb=128
+source none2       swap   defaults      readahead_size_kb=5%
+source none3       swap   defaults      readahead_size_kb=5kb
+source none4       swap   defaults      readahead_size_kb=16385
+source none5       swap   defaults      readahead_size_kb=-128
+source none6       swap   defaults      readahead_size_kb=0
+)fs";
+    ASSERT_TRUE(android::base::WriteStringToFile(fstab_contents, tf.path));
+
+    Fstab fstab;
+    EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
+    ASSERT_LE(7U, fstab.size());
+
+    FstabEntry::FsMgrFlags flags = {};
+
+    auto entry = fstab.begin();
+    EXPECT_EQ("none0", entry->mount_point);
+    EXPECT_TRUE(CompareFlags(flags, entry->fs_mgr_flags));
+    EXPECT_EQ(-1, entry->readahead_size_kb);
+    entry++;
+
+    EXPECT_EQ("none1", entry->mount_point);
+    EXPECT_TRUE(CompareFlags(flags, entry->fs_mgr_flags));
+    EXPECT_EQ(128, entry->readahead_size_kb);
+    entry++;
+
+    EXPECT_EQ("none2", entry->mount_point);
+    EXPECT_TRUE(CompareFlags(flags, entry->fs_mgr_flags));
+    EXPECT_EQ(-1, entry->readahead_size_kb);
+    entry++;
+
+    EXPECT_EQ("none3", entry->mount_point);
+    EXPECT_TRUE(CompareFlags(flags, entry->fs_mgr_flags));
+    EXPECT_EQ(-1, entry->readahead_size_kb);
+    entry++;
+
+    EXPECT_EQ("none4", entry->mount_point);
+    EXPECT_TRUE(CompareFlags(flags, entry->fs_mgr_flags));
+    EXPECT_EQ(-1, entry->readahead_size_kb);
+    entry++;
+
+    EXPECT_EQ("none5", entry->mount_point);
+    EXPECT_TRUE(CompareFlags(flags, entry->fs_mgr_flags));
+    EXPECT_EQ(-1, entry->readahead_size_kb);
+    entry++;
+
+    EXPECT_EQ("none6", entry->mount_point);
+    EXPECT_TRUE(CompareFlags(flags, entry->fs_mgr_flags));
+    EXPECT_EQ(0, entry->readahead_size_kb);
+}
diff --git a/init/firmware_handler.cpp b/init/firmware_handler.cpp
index ba7e6bd..bdc2922 100644
--- a/init/firmware_handler.cpp
+++ b/init/firmware_handler.cpp
@@ -17,6 +17,7 @@
 #include "firmware_handler.h"
 
 #include <fcntl.h>
+#include <fnmatch.h>
 #include <glob.h>
 #include <pwd.h>
 #include <signal.h>
@@ -46,6 +47,20 @@
 namespace android {
 namespace init {
 
+namespace {
+bool PrefixMatch(const std::string& pattern, const std::string& path) {
+    return android::base::StartsWith(path, pattern);
+}
+
+bool FnMatch(const std::string& pattern, const std::string& path) {
+    return fnmatch(pattern.c_str(), path.c_str(), 0) == 0;
+}
+
+bool EqualMatch(const std::string& pattern, const std::string& path) {
+    return pattern == path;
+}
+}  // namespace
+
 static void LoadFirmware(const std::string& firmware, const std::string& root, int fw_fd,
                          size_t fw_size, int loading_fd, int data_fd) {
     // Start transfer.
@@ -66,6 +81,22 @@
     return access("/dev/.booting", F_OK) == 0;
 }
 
+ExternalFirmwareHandler::ExternalFirmwareHandler(std::string devpath, uid_t uid,
+                                                 std::string handler_path)
+    : devpath(std::move(devpath)), uid(uid), handler_path(std::move(handler_path)) {
+    auto wildcard_position = this->devpath.find('*');
+    if (wildcard_position != std::string::npos) {
+        if (wildcard_position == this->devpath.length() - 1) {
+            this->devpath.pop_back();
+            match = std::bind(PrefixMatch, this->devpath, std::placeholders::_1);
+        } else {
+            match = std::bind(FnMatch, this->devpath, std::placeholders::_1);
+        }
+    } else {
+        match = std::bind(EqualMatch, this->devpath, std::placeholders::_1);
+    }
+}
+
 FirmwareHandler::FirmwareHandler(std::vector<std::string> firmware_directories,
                                  std::vector<ExternalFirmwareHandler> external_firmware_handlers)
     : firmware_directories_(std::move(firmware_directories)),
@@ -160,7 +191,7 @@
 
 std::string FirmwareHandler::GetFirmwarePath(const Uevent& uevent) const {
     for (const auto& external_handler : external_firmware_handlers_) {
-        if (external_handler.devpath == uevent.path) {
+        if (external_handler.match(uevent.path)) {
             LOG(INFO) << "Launching external firmware handler '" << external_handler.handler_path
                       << "' for devpath: '" << uevent.path << "' firmware: '" << uevent.firmware
                       << "'";
diff --git a/init/firmware_handler.h b/init/firmware_handler.h
index 8b758ae..3c35b1f 100644
--- a/init/firmware_handler.h
+++ b/init/firmware_handler.h
@@ -30,11 +30,13 @@
 namespace init {
 
 struct ExternalFirmwareHandler {
-    ExternalFirmwareHandler(std::string devpath, uid_t uid, std::string handler_path)
-        : devpath(std::move(devpath)), uid(uid), handler_path(std::move(handler_path)) {}
+    ExternalFirmwareHandler(std::string devpath, uid_t uid, std::string handler_path);
+
     std::string devpath;
     uid_t uid;
     std::string handler_path;
+
+    std::function<bool(const std::string&)> match;
 };
 
 class FirmwareHandler : public UeventHandler {
diff --git a/init/first_stage_init.cpp b/init/first_stage_init.cpp
index 5cde167..84cda98 100644
--- a/init/first_stage_init.cpp
+++ b/init/first_stage_init.cpp
@@ -327,28 +327,22 @@
         LOG(INFO) << "Copied ramdisk prop to " << dest;
     }
 
-    if (ForceNormalBoot(cmdline, bootconfig)) {
-        mkdir("/first_stage_ramdisk", 0755);
-        // SwitchRoot() must be called with a mount point as the target, so we bind mount the
-        // target directory to itself here.
-        if (mount("/first_stage_ramdisk", "/first_stage_ramdisk", nullptr, MS_BIND, nullptr) != 0) {
-            LOG(FATAL) << "Could not bind mount /first_stage_ramdisk to itself";
-        }
-        SwitchRoot("/first_stage_ramdisk");
-    }
-
-    std::string force_debuggable("/force_debuggable");
+    // If "/force_debuggable" is present, the second-stage init will use a userdebug
+    // sepolicy and load adb_debug.prop to allow adb root, if the device is unlocked.
+    bool found_debuggable = false;
     std::string adb_debug_prop("/adb_debug.prop");
     std::string userdebug_sepolicy("/userdebug_plat_sepolicy.cil");
-    if (IsRecoveryMode()) {
-        // Update these file paths since we didn't switch root
-        force_debuggable.insert(0, "/first_stage_ramdisk");
+    if (access("/force_debuggable", F_OK) == 0) {
+        found_debuggable = true;
+    } else if (access("/first_stage_ramdisk/force_debuggable", F_OK) == 0) {
+        // Fallback to legacy debug resource paths.
+        // TODO(b/186485355): removes the fallback path once it is not needed.
+        found_debuggable = true;
         adb_debug_prop.insert(0, "/first_stage_ramdisk");
         userdebug_sepolicy.insert(0, "/first_stage_ramdisk");
     }
-    // If this file is present, the second-stage init will use a userdebug sepolicy
-    // and load adb_debug.prop to allow adb root, if the device is unlocked.
-    if (access(force_debuggable.c_str(), F_OK) == 0) {
+
+    if (found_debuggable) {
         std::error_code ec;  // to invoke the overloaded copy_file() that won't throw.
         if (!fs::copy_file(adb_debug_prop, kDebugRamdiskProp, ec) ||
             !fs::copy_file(userdebug_sepolicy, kDebugRamdiskSEPolicy, ec)) {
@@ -359,6 +353,16 @@
         }
     }
 
+    if (ForceNormalBoot(cmdline, bootconfig)) {
+        mkdir("/first_stage_ramdisk", 0755);
+        // SwitchRoot() must be called with a mount point as the target, so we bind mount the
+        // target directory to itself here.
+        if (mount("/first_stage_ramdisk", "/first_stage_ramdisk", nullptr, MS_BIND, nullptr) != 0) {
+            LOG(FATAL) << "Could not bind mount /first_stage_ramdisk to itself";
+        }
+        SwitchRoot("/first_stage_ramdisk");
+    }
+
     if (!DoFirstStageMount(!created_devices)) {
         LOG(FATAL) << "Failed to mount required partitions early ...";
     }
diff --git a/init/init.cpp b/init/init.cpp
index 7264b22..a7325ca 100644
--- a/init/init.cpp
+++ b/init/init.cpp
@@ -849,21 +849,6 @@
     auto is_installed = android::gsi::IsGsiInstalled() ? "1" : "0";
     SetProperty(gsi::kGsiInstalledProp, is_installed);
 
-    /*
-     * For debug builds of S launching devices, init mounts debugfs for
-     * enabling vendor debug data collection setup at boot time. Init will unmount it on
-     * boot-complete after vendor code has performed the required initializations
-     * during boot. Dumpstate will then mount debugfs in order to read data
-     * from the same using the dumpstate HAL during bugreport creation.
-     * Dumpstate will also unmount debugfs after bugreport creation.
-     * first_api_level comparison is done here instead
-     * of init.rc since init.rc parser does not support >/< operators.
-     */
-    auto api_level = android::base::GetIntProperty("ro.product.first_api_level", 0);
-    bool is_debuggable = android::base::GetBoolProperty("ro.debuggable", false);
-    auto mount_debugfs = (is_debuggable && (api_level >= 31)) ? "1" : "0";
-    SetProperty("init.mount_debugfs", mount_debugfs);
-
     am.QueueBuiltinAction(SetupCgroupsAction, "SetupCgroups");
     am.QueueBuiltinAction(SetKptrRestrictAction, "SetKptrRestrict");
     am.QueueBuiltinAction(TestPerfEventSelinuxAction, "TestPerfEventSelinux");
diff --git a/init/property_service.cpp b/init/property_service.cpp
index c2eb73c..fe3490d 100644
--- a/init/property_service.cpp
+++ b/init/property_service.cpp
@@ -1187,8 +1187,6 @@
         if (StartsWith(key, ANDROIDBOOT_PREFIX)) {
             InitPropertySet("ro.boot." + key.substr(ANDROIDBOOT_PREFIX.size()), value);
         } else if (StartsWith(key, qemu_prefix)) {
-            InitPropertySet("ro.kernel." + key, value);  // emulator specific, deprecated
-
             // emulator specific, should be retired once emulator migrates to
             // androidboot.
             const auto new_name =
@@ -1220,13 +1218,20 @@
     });
 }
 
+// bootconfig does not allow to populate `key=value` simultaneously with
+// `key.subkey=value` which does not work with the existing code for
+// `hardware` (e.g. we want both `ro.boot.hardware=value` and
+// `ro.boot.hardware.sku=value`) and for `qemu` (Android Stidio Emulator
+// specific).
+static bool IsAllowedBootconfigKey(const std::string_view key) {
+    return (key == "hardware"sv) || (key == "qemu"sv);
+}
+
 static void ProcessBootconfig() {
     ImportBootconfig([&](const std::string& key, const std::string& value) {
         if (StartsWith(key, ANDROIDBOOT_PREFIX)) {
             InitPropertySet("ro.boot." + key.substr(ANDROIDBOOT_PREFIX.size()), value);
-        } else if (key == "hardware") {
-            // "hardware" in bootconfig replaces "androidboot.hardware" kernel
-            // cmdline parameter
+        } else if (IsAllowedBootconfigKey(key)) {
             InitPropertySet("ro.boot." + key, value);
         }
     });
diff --git a/init/reboot.cpp b/init/reboot.cpp
index d9acee5..ab0e48e 100644
--- a/init/reboot.cpp
+++ b/init/reboot.cpp
@@ -450,10 +450,22 @@
 
 // zram is able to use backing device on top of a loopback device.
 // In order to unmount /data successfully, we have to kill the loopback device first
-#define ZRAM_DEVICE   "/dev/block/zram0"
-#define ZRAM_RESET    "/sys/block/zram0/reset"
-#define ZRAM_BACK_DEV "/sys/block/zram0/backing_dev"
+#define ZRAM_DEVICE       "/dev/block/zram0"
+#define ZRAM_RESET        "/sys/block/zram0/reset"
+#define ZRAM_BACK_DEV     "/sys/block/zram0/backing_dev"
+#define ZRAM_INITSTATE    "/sys/block/zram0/initstate"
 static Result<void> KillZramBackingDevice() {
+    std::string zram_initstate;
+    if (!android::base::ReadFileToString(ZRAM_INITSTATE, &zram_initstate)) {
+        return ErrnoError() << "Failed to read " << ZRAM_INITSTATE;
+    }
+
+    zram_initstate.erase(zram_initstate.length() - 1);
+    if (zram_initstate == "0") {
+        LOG(INFO) << "Zram has not been swapped on";
+        return {};
+    }
+
     if (access(ZRAM_BACK_DEV, F_OK) != 0 && errno == ENOENT) {
         LOG(INFO) << "No zram backing device configured";
         return {};
diff --git a/init/selinux.cpp b/init/selinux.cpp
index 2d3e06e..42d3023 100644
--- a/init/selinux.cpp
+++ b/init/selinux.cpp
@@ -240,25 +240,25 @@
     }
 
     // Use precompiled sepolicy only when all corresponding hashes are equal.
-    // plat_sepolicy is always checked, while system_ext and product are checked only when they
-    // exist.
     std::vector<std::pair<std::string, std::string>> sepolicy_hashes{
             {"/system/etc/selinux/plat_sepolicy_and_mapping.sha256",
              precompiled_sepolicy + ".plat_sepolicy_and_mapping.sha256"},
+            {"/system_ext/etc/selinux/system_ext_sepolicy_and_mapping.sha256",
+             precompiled_sepolicy + ".system_ext_sepolicy_and_mapping.sha256"},
+            {"/product/etc/selinux/product_sepolicy_and_mapping.sha256",
+             precompiled_sepolicy + ".product_sepolicy_and_mapping.sha256"},
     };
 
-    if (access("/system_ext/etc/selinux/system_ext_sepolicy.cil", F_OK) == 0) {
-        sepolicy_hashes.emplace_back(
-                "/system_ext/etc/selinux/system_ext_sepolicy_and_mapping.sha256",
-                precompiled_sepolicy + ".system_ext_sepolicy_and_mapping.sha256");
-    }
-
-    if (access("/product/etc/selinux/product_sepolicy.cil", F_OK) == 0) {
-        sepolicy_hashes.emplace_back("/product/etc/selinux/product_sepolicy_and_mapping.sha256",
-                                     precompiled_sepolicy + ".product_sepolicy_and_mapping.sha256");
-    }
-
     for (const auto& [actual_id_path, precompiled_id_path] : sepolicy_hashes) {
+        // Both of them should exist or both of them shouldn't exist.
+        if (access(actual_id_path.c_str(), R_OK) != 0) {
+            if (access(precompiled_id_path.c_str(), R_OK) == 0) {
+                return Error() << precompiled_id_path << " exists but " << actual_id_path
+                               << " doesn't";
+            }
+            continue;
+        }
+
         std::string actual_id;
         if (!ReadFirstLine(actual_id_path.c_str(), &actual_id)) {
             return ErrnoError() << "Failed to read " << actual_id_path;
@@ -372,6 +372,12 @@
         system_ext_mapping_file.clear();
     }
 
+    std::string system_ext_compat_cil_file("/system_ext/etc/selinux/mapping/" + vend_plat_vers +
+                                           ".compat.cil");
+    if (access(system_ext_compat_cil_file.c_str(), F_OK) == -1) {
+        system_ext_compat_cil_file.clear();
+    }
+
     std::string product_policy_cil_file("/product/etc/selinux/product_sepolicy.cil");
     if (access(product_policy_cil_file.c_str(), F_OK) == -1) {
         product_policy_cil_file.clear();
@@ -426,6 +432,9 @@
     if (!system_ext_mapping_file.empty()) {
         compile_args.push_back(system_ext_mapping_file.c_str());
     }
+    if (!system_ext_compat_cil_file.empty()) {
+        compile_args.push_back(system_ext_compat_cil_file.c_str());
+    }
     if (!product_policy_cil_file.empty()) {
         compile_args.push_back(product_policy_cil_file.c_str());
     }
diff --git a/init/service.cpp b/init/service.cpp
index 836dc47..c3069f5 100644
--- a/init/service.cpp
+++ b/init/service.cpp
@@ -460,7 +460,11 @@
         scon = *result;
     }
 
-    if (!IsDefaultMountNamespaceReady() && name_ != "apexd") {
+    // APEXd is always started in the "current" namespace because it is the process to set up
+    // the current namespace.
+    const bool is_apexd = args_[0] == "/system/bin/apexd";
+
+    if (!IsDefaultMountNamespaceReady() && !is_apexd) {
         // If this service is started before APEXes and corresponding linker configuration
         // get available, mark it as pre-apexd one. Note that this marking is
         // permanent. So for example, if the service is re-launched (e.g., due
diff --git a/init/ueventd_parser_test.cpp b/init/ueventd_parser_test.cpp
index 4e63ba5..c5aa9e3 100644
--- a/init/ueventd_parser_test.cpp
+++ b/init/ueventd_parser_test.cpp
@@ -154,6 +154,9 @@
 external_firmware_handler devpath root handler_path
 external_firmware_handler /devices/path/firmware/something001.bin system /vendor/bin/firmware_handler.sh
 external_firmware_handler /devices/path/firmware/something002.bin radio "/vendor/bin/firmware_handler.sh --has --arguments"
+external_firmware_handler /devices/path/firmware/* root "/vendor/bin/firmware_handler.sh"
+external_firmware_handler /devices/path/firmware/something* system "/vendor/bin/firmware_handler.sh"
+external_firmware_handler /devices/path/*/firmware/something*.bin radio "/vendor/bin/firmware_handler.sh"
 )";
 
     auto external_firmware_handlers = std::vector<ExternalFirmwareHandler>{
@@ -172,6 +175,21 @@
                     AID_RADIO,
                     "/vendor/bin/firmware_handler.sh --has --arguments",
             },
+            {
+                    "/devices/path/firmware/",
+                    AID_ROOT,
+                    "/vendor/bin/firmware_handler.sh",
+            },
+            {
+                    "/devices/path/firmware/something",
+                    AID_SYSTEM,
+                    "/vendor/bin/firmware_handler.sh",
+            },
+            {
+                    "/devices/path/*/firmware/something*.bin",
+                    AID_RADIO,
+                    "/vendor/bin/firmware_handler.sh",
+            },
     };
 
     TestUeventdFile(ueventd_file, {{}, {}, {}, {}, external_firmware_handlers});
diff --git a/libcutils/Android.bp b/libcutils/Android.bp
index 0f3763c..68b21c6 100644
--- a/libcutils/Android.bp
+++ b/libcutils/Android.bp
@@ -362,9 +362,10 @@
     source_stem: "bindings",
     local_include_dirs: ["include"],
     bindgen_flags: [
-        "--whitelist-function", "multiuser_get_app_id",
-        "--whitelist-function", "multiuser_get_user_id",
-        "--whitelist-function", "multiuser_get_uid",
-        "--whitelist-var", "AID_USER_OFFSET",
+        "--allowlist-function", "multiuser_get_app_id",
+        "--allowlist-function", "multiuser_get_uid",
+        "--allowlist-function", "multiuser_get_user_id",
+        "--allowlist-var", "AID_KEYSTORE",
+        "--allowlist-var", "AID_USER_OFFSET",
     ],
 }
diff --git a/libcutils/include/private/android_filesystem_config.h b/libcutils/include/private/android_filesystem_config.h
index 7489281..8f22d89 100644
--- a/libcutils/include/private/android_filesystem_config.h
+++ b/libcutils/include/private/android_filesystem_config.h
@@ -128,6 +128,8 @@
 #define AID_EXT_OBB_RW 1079       /* GID for OBB directories on external storage */
 #define AID_CONTEXT_HUB 1080      /* GID for access to the Context Hub */
 #define AID_VIRTMANAGER 1081      /* VirtManager daemon */
+#define AID_ARTD 1082             /* ART Service daemon */
+#define AID_UWB 1083              /* UWB subsystem */
 /* Changes to this file must be made in AOSP, *not* in internal branches. */
 
 #define AID_SHELL 2000 /* adb and debug shell user */
diff --git a/libprocessgroup/cgrouprc/Android.bp b/libprocessgroup/cgrouprc/Android.bp
index 0cbe0cc..7522cfe 100644
--- a/libprocessgroup/cgrouprc/Android.bp
+++ b/libprocessgroup/cgrouprc/Android.bp
@@ -28,7 +28,9 @@
     // defined below. The static library is built for tests.
     vendor_available: false,
     native_bridge_supported: true,
-    llndk_stubs: "libcgrouprc.llndk",
+    llndk: {
+        symbol_file: "libcgrouprc.map.txt",
+    },
     srcs: [
         "cgroup_controller.cpp",
         "cgroup_file.cpp",
@@ -59,12 +61,3 @@
         },
     },
 }
-
-llndk_library {
-    name: "libcgrouprc.llndk",
-    symbol_file: "libcgrouprc.map.txt",
-    native_bridge_supported: true,
-    export_include_dirs: [
-        "include",
-    ],
-}
diff --git a/libprocessgroup/profiles/task_profiles.json b/libprocessgroup/profiles/task_profiles.json
index 5b57bdd..bd94621 100644
--- a/libprocessgroup/profiles/task_profiles.json
+++ b/libprocessgroup/profiles/task_profiles.json
@@ -70,11 +70,11 @@
       "Name": "Frozen",
       "Actions": [
         {
-          "Name": "JoinCgroup",
+          "Name": "SetAttribute",
           "Params":
           {
-            "Controller": "freezer",
-            "Path": ""
+            "Name": "FreezerState",
+            "Value": "1"
           }
         }
       ]
@@ -83,11 +83,11 @@
       "Name": "Unfrozen",
       "Actions": [
         {
-          "Name": "JoinCgroup",
+          "Name": "SetAttribute",
           "Params":
           {
-            "Controller": "freezer",
-            "Path": "../"
+            "Name": "FreezerState",
+            "Value": "0"
           }
         }
       ]
@@ -558,32 +558,6 @@
         }
       ]
     },
-    {
-      "Name": "FreezerDisabled",
-      "Actions": [
-        {
-          "Name": "SetAttribute",
-          "Params":
-          {
-            "Name": "FreezerState",
-            "Value": "0"
-          }
-        }
-      ]
-    },
-    {
-      "Name": "FreezerEnabled",
-      "Actions": [
-        {
-          "Name": "SetAttribute",
-          "Params":
-          {
-            "Name": "FreezerState",
-            "Value": "1"
-          }
-        }
-      ]
-    }
   ],
 
   "AggregateProfiles": [
diff --git a/libprocessgroup/sched_policy.cpp b/libprocessgroup/sched_policy.cpp
index c51ee61..1a4196a 100644
--- a/libprocessgroup/sched_policy.cpp
+++ b/libprocessgroup/sched_policy.cpp
@@ -159,10 +159,9 @@
 
     if (!controller.IsUsable()) return -1;
 
-    if (!controller.GetTaskGroup(tid, &subgroup)) {
-        LOG(ERROR) << "Failed to find cgroup for tid " << tid;
+    if (!controller.GetTaskGroup(tid, &subgroup))
         return -1;
-    }
+
     return 0;
 }
 
@@ -174,11 +173,16 @@
     std::string group;
     if (schedboost_enabled()) {
         if ((getCGroupSubsys(tid, "schedtune", group) < 0) &&
-            (getCGroupSubsys(tid, "cpu", group) < 0))
-		return -1;
+            (getCGroupSubsys(tid, "cpu", group) < 0)) {
+                LOG(ERROR) << "Failed to find cpu cgroup for tid " << tid;
+                return -1;
+        }
     }
     if (group.empty() && cpusets_enabled()) {
-        if (getCGroupSubsys(tid, "cpuset", group) < 0) return -1;
+        if (getCGroupSubsys(tid, "cpuset", group) < 0) {
+            LOG(ERROR) << "Failed to find cpuset cgroup for tid " << tid;
+            return -1;
+        }
     }
 
     // TODO: replace hardcoded directories
diff --git a/libprocessgroup/task_profiles.cpp b/libprocessgroup/task_profiles.cpp
index f13a681..db00a49 100644
--- a/libprocessgroup/task_profiles.cpp
+++ b/libprocessgroup/task_profiles.cpp
@@ -518,10 +518,10 @@
                 std::string attr_filepath = params_val["FilePath"].asString();
                 std::string attr_value = params_val["Value"].asString();
                 if (!attr_filepath.empty() && !attr_value.empty()) {
-                    const Json::Value& logfailures = params_val["LogFailures"];
-                    bool attr_logfailures = logfailures.isNull() || logfailures.asBool();
+                    std::string attr_logfailures = params_val["LogFailures"].asString();
+                    bool logfailures = attr_logfailures.empty() || attr_logfailures == "true";
                     profile->Add(std::make_unique<WriteFileAction>(attr_filepath, attr_value,
-                                                                   attr_logfailures));
+                                                                   logfailures));
                 } else if (attr_filepath.empty()) {
                     LOG(WARNING) << "WriteFile: invalid parameter: "
                                  << "empty filepath";
diff --git a/libstats/pull_rust/Android.bp b/libstats/pull_rust/Android.bp
index 354c7b3..2a89e29 100644
--- a/libstats/pull_rust/Android.bp
+++ b/libstats/pull_rust/Android.bp
@@ -25,10 +25,10 @@
     source_stem: "bindings",
     bindgen_flags: [
         "--size_t-is-usize",
-        "--whitelist-function=AStatsEventList_addStatsEvent",
-        "--whitelist-function=AStatsEvent_.*",
-        "--whitelist-function=AStatsManager_.*",
-        "--whitelist-var=AStatsManager_.*",
+        "--allowlist-function=AStatsEventList_addStatsEvent",
+        "--allowlist-function=AStatsEvent_.*",
+        "--allowlist-function=AStatsManager_.*",
+        "--allowlist-var=AStatsManager_.*",
     ],
     target: {
         android: {
diff --git a/libstats/push_compat/Android.bp b/libstats/push_compat/Android.bp
index 4b2f40e..819066e 100644
--- a/libstats/push_compat/Android.bp
+++ b/libstats/push_compat/Android.bp
@@ -55,7 +55,7 @@
     export_header_lib_headers: [
         "libstatssocket_headers",
     ],
-    static_libs: ["libgtest_prod"],
+    header_libs: ["libgtest_prod_headers"],
     apex_available: ["com.android.resolv"],
     min_sdk_version: "29",
 }
diff --git a/libsync/Android.bp b/libsync/Android.bp
index 540a246..99c88cf 100644
--- a/libsync/Android.bp
+++ b/libsync/Android.bp
@@ -42,7 +42,9 @@
     recovery_available: true,
     native_bridge_supported: true,
     defaults: ["libsync_defaults"],
-    llndk_stubs: "libsync.llndk",
+    llndk: {
+        symbol_file: "libsync.map.txt",
+    },
     stubs: {
         symbol_file: "libsync.map.txt",
         versions: [
@@ -51,12 +53,6 @@
     },
 }
 
-llndk_library {
-    name: "libsync.llndk",
-    symbol_file: "libsync.map.txt",
-    export_include_dirs: ["include"],
-}
-
 cc_test {
     name: "sync-unit-tests",
     shared_libs: ["libsync"],
diff --git a/libutils/RefBase_test.cpp b/libutils/RefBase_test.cpp
index dcc469e..93f9654 100644
--- a/libutils/RefBase_test.cpp
+++ b/libutils/RefBase_test.cpp
@@ -242,12 +242,12 @@
 }
 
 TEST(RefBase, AssertWeakRefExistsSuccess) {
-    // uses some other refcounting method, or non at all
     bool isDeleted;
     sp<Foo> foo = sp<Foo>::make(&isDeleted);
     wp<Foo> weakFoo = foo;
 
     EXPECT_EQ(weakFoo, wp<Foo>::fromExisting(foo.get()));
+    EXPECT_EQ(weakFoo.unsafe_get(), wp<Foo>::fromExisting(foo.get()).unsafe_get());
 
     EXPECT_FALSE(isDeleted);
     foo = nullptr;
@@ -255,7 +255,7 @@
 }
 
 TEST(RefBase, AssertWeakRefExistsDeath) {
-    // uses some other refcounting method, or non at all
+    // uses some other refcounting method, or none at all
     bool isDeleted;
     Foo* foo = new Foo(&isDeleted);
 
diff --git a/libutils/SharedBuffer_test.cpp b/libutils/SharedBuffer_test.cpp
index 3f960d2..1d6317f 100644
--- a/libutils/SharedBuffer_test.cpp
+++ b/libutils/SharedBuffer_test.cpp
@@ -32,10 +32,25 @@
     EXPECT_DEATH(android::SharedBuffer::alloc(SIZE_MAX - sizeof(android::SharedBuffer)), "");
 }
 
-TEST(SharedBufferTest, alloc_null) {
-    // Big enough to fail, not big enough to abort.
+TEST(SharedBufferTest, alloc_max) {
     SKIP_WITH_HWASAN;  // hwasan has a 2GiB allocation limit.
-    ASSERT_EQ(nullptr, android::SharedBuffer::alloc(SIZE_MAX / 2));
+
+    android::SharedBuffer* buf =
+            android::SharedBuffer::alloc(SIZE_MAX - sizeof(android::SharedBuffer) - 1);
+    if (buf != nullptr) {
+        EXPECT_NE(nullptr, buf->data());
+        buf->release();
+    }
+}
+
+TEST(SharedBufferTest, alloc_big) {
+    SKIP_WITH_HWASAN;  // hwasan has a 2GiB allocation limit.
+
+    android::SharedBuffer* buf = android::SharedBuffer::alloc(SIZE_MAX / 2);
+    if (buf != nullptr) {
+        EXPECT_NE(nullptr, buf->data());
+        buf->release();
+    }
 }
 
 TEST(SharedBufferTest, alloc_zero_size) {
@@ -56,7 +71,13 @@
     // Big enough to fail, not big enough to abort.
     SKIP_WITH_HWASAN;  // hwasan has a 2GiB allocation limit.
     android::SharedBuffer* buf = android::SharedBuffer::alloc(10);
-    ASSERT_EQ(nullptr, buf->editResize(SIZE_MAX / 2));
+    android::SharedBuffer* buf2 = buf->editResize(SIZE_MAX / 2);
+    if (buf2 == nullptr) {
+        buf->release();
+    } else {
+        EXPECT_NE(nullptr, buf2->data());
+        buf2->release();
+    }
 }
 
 TEST(SharedBufferTest, editResize_zero_size) {
diff --git a/libutils/String16.cpp b/libutils/String16.cpp
index 70bf5a0..e3e5f11 100644
--- a/libutils/String16.cpp
+++ b/libutils/String16.cpp
@@ -390,28 +390,6 @@
     return static_cast<size_t>(*(p - 1));
 }
 
-status_t String16::makeLower()
-{
-    const size_t N = size();
-    const char16_t* str = string();
-    char16_t* edited = nullptr;
-    for (size_t i=0; i<N; i++) {
-        const char16_t v = str[i];
-        if (v >= 'A' && v <= 'Z') {
-            if (!edited) {
-                SharedBuffer* buf = static_cast<SharedBuffer*>(edit());
-                if (!buf) {
-                    return NO_MEMORY;
-                }
-                edited = (char16_t*)buf->data();
-                mString = str = edited;
-            }
-            edited[i] = tolower((char)v);
-        }
-    }
-    return OK;
-}
-
 status_t String16::replaceAll(char16_t replaceThis, char16_t withThis)
 {
     const size_t N = size();
diff --git a/libutils/String16_fuzz.cpp b/libutils/String16_fuzz.cpp
index 63c2800..defa0f5 100644
--- a/libutils/String16_fuzz.cpp
+++ b/libutils/String16_fuzz.cpp
@@ -34,11 +34,6 @@
                     str1.size();
                 }),
 
-                // Casing
-                ([](FuzzedDataProvider&, android::String16 str1, android::String16) -> void {
-                    str1.makeLower();
-                }),
-
                 // Comparison
                 ([](FuzzedDataProvider&, android::String16 str1, android::String16 str2) -> void {
                     str1.startsWith(str2);
diff --git a/libutils/String16_test.cpp b/libutils/String16_test.cpp
index 2505f44..c2e9b02 100644
--- a/libutils/String16_test.cpp
+++ b/libutils/String16_test.cpp
@@ -97,13 +97,6 @@
     EXPECT_STR16EQ(u" m", tmp);
 }
 
-TEST(String16Test, MakeLower) {
-    String16 tmp("Verify Me!");
-    tmp.makeLower();
-    EXPECT_EQ(10U, tmp.size());
-    EXPECT_STR16EQ(u"verify me!", tmp);
-}
-
 TEST(String16Test, ReplaceAll) {
     String16 tmp("Verify verify Verify");
     tmp.replaceAll(u'r', u'!');
@@ -176,14 +169,6 @@
     EXPECT_FALSE(tmp.isStaticString());
 }
 
-TEST(String16Test, StaticStringMakeLower) {
-    StaticString16 tmp(u"Verify me!");
-    tmp.makeLower();
-    EXPECT_EQ(10U, tmp.size());
-    EXPECT_STR16EQ(u"verify me!", tmp);
-    EXPECT_FALSE(tmp.isStaticString());
-}
-
 TEST(String16Test, StaticStringReplaceAll) {
     StaticString16 tmp(u"Verify verify Verify");
     tmp.replaceAll(u'r', u'!');
diff --git a/libutils/String8.cpp b/libutils/String8.cpp
index 3dc2026..195e122 100644
--- a/libutils/String8.cpp
+++ b/libutils/String8.cpp
@@ -25,6 +25,8 @@
 
 #include <ctype.h>
 
+#include <string>
+
 #include "SharedBuffer.h"
 
 /*
@@ -163,9 +165,7 @@
 }
 
 String8::String8(const char32_t* o)
-    : mString(allocFromUTF32(o, strlen32(o)))
-{
-}
+    : mString(allocFromUTF32(o, std::char_traits<char32_t>::length(o))) {}
 
 String8::String8(const char32_t* o, size_t len)
     : mString(allocFromUTF32(o, len))
@@ -415,50 +415,15 @@
 
 void String8::toLower()
 {
-    toLower(0, size());
-}
+    const size_t length = size();
+    if (length == 0) return;
 
-void String8::toLower(size_t start, size_t length)
-{
-    const size_t len = size();
-    if (start >= len) {
-        return;
-    }
-    if (start+length > len) {
-        length = len-start;
-    }
-    char* buf = lockBuffer(len);
-    buf += start;
-    while (length > 0) {
+    char* buf = lockBuffer(length);
+    for (size_t i = length; i > 0; --i) {
         *buf = static_cast<char>(tolower(*buf));
         buf++;
-        length--;
     }
-    unlockBuffer(len);
-}
-
-void String8::toUpper()
-{
-    toUpper(0, size());
-}
-
-void String8::toUpper(size_t start, size_t length)
-{
-    const size_t len = size();
-    if (start >= len) {
-        return;
-    }
-    if (start+length > len) {
-        length = len-start;
-    }
-    char* buf = lockBuffer(len);
-    buf += start;
-    while (length > 0) {
-        *buf = static_cast<char>(toupper(*buf));
-        buf++;
-        length--;
-    }
-    unlockBuffer(len);
+    unlockBuffer(length);
 }
 
 // ---------------------------------------------------------------------------
diff --git a/libutils/String8_fuzz.cpp b/libutils/String8_fuzz.cpp
index b02683c..a45d675 100644
--- a/libutils/String8_fuzz.cpp
+++ b/libutils/String8_fuzz.cpp
@@ -42,9 +42,6 @@
 
                 // Casing
                 [](FuzzedDataProvider*, android::String8* str1, android::String8*) -> void {
-                    str1->toUpper();
-                },
-                [](FuzzedDataProvider*, android::String8* str1, android::String8*) -> void {
                     str1->toLower();
                 },
                 [](FuzzedDataProvider*, android::String8* str1, android::String8* str2) -> void {
diff --git a/libutils/Unicode.cpp b/libutils/Unicode.cpp
index 843a81a..3ffcf7e 100644
--- a/libutils/Unicode.cpp
+++ b/libutils/Unicode.cpp
@@ -22,20 +22,6 @@
 
 #include <log/log.h>
 
-#if defined(_WIN32)
-# undef  nhtol
-# undef  htonl
-# undef  nhtos
-# undef  htons
-
-# define ntohl(x)    ( ((x) << 24) | (((x) >> 24) & 255) | (((x) << 8) & 0xff0000) | (((x) >> 8) & 0xff00) )
-# define htonl(x)    ntohl(x)
-# define ntohs(x)    ( (((x) << 8) & 0xff00) | (((x) >> 8) & 255) )
-# define htons(x)    ntohs(x)
-#else
-# include <netinet/in.h>
-#endif
-
 extern "C" {
 
 static const char32_t kByteMask = 0x000000BF;
@@ -115,24 +101,6 @@
     }
 }
 
-size_t strlen32(const char32_t *s)
-{
-  const char32_t *ss = s;
-  while ( *ss )
-    ss++;
-  return ss-s;
-}
-
-size_t strnlen32(const char32_t *s, size_t maxlen)
-{
-  const char32_t *ss = s;
-  while ((maxlen > 0) && *ss) {
-    ss++;
-    maxlen--;
-  }
-  return ss-s;
-}
-
 static inline int32_t utf32_at_internal(const char* cur, size_t *num_read)
 {
     const char first_char = *cur;
@@ -254,19 +222,6 @@
   return d;
 }
 
-char16_t *strcpy16(char16_t *dst, const char16_t *src)
-{
-  char16_t *q = dst;
-  const char16_t *p = src;
-  char16_t ch;
-
-  do {
-    *q++ = ch = *p++;
-  } while ( ch );
-
-  return dst;
-}
-
 size_t strlen16(const char16_t *s)
 {
   const char16_t *ss = s;
diff --git a/libutils/include/utils/RefBase.h b/libutils/include/utils/RefBase.h
index 5a5bd56..e07f574 100644
--- a/libutils/include/utils/RefBase.h
+++ b/libutils/include/utils/RefBase.h
@@ -416,13 +416,16 @@
     wp(std::nullptr_t) : wp() {}
 #else
     wp(T* other);  // NOLINT(implicit)
+    template <typename U>
+    wp(U* other);  // NOLINT(implicit)
+    wp& operator=(T* other);
+    template <typename U>
+    wp& operator=(U* other);
 #endif
+
     wp(const wp<T>& other);
     explicit wp(const sp<T>& other);
 
-#if !defined(ANDROID_UTILS_REF_BASE_DISABLE_IMPLICIT_CONSTRUCTION)
-    template<typename U> wp(U* other);  // NOLINT(implicit)
-#endif
     template<typename U> wp(const sp<U>& other);  // NOLINT(implicit)
     template<typename U> wp(const wp<U>& other);  // NOLINT(implicit)
 
@@ -430,15 +433,9 @@
 
     // Assignment
 
-#if !defined(ANDROID_UTILS_REF_BASE_DISABLE_IMPLICIT_CONSTRUCTION)
-    wp& operator = (T* other);
-#endif
     wp& operator = (const wp<T>& other);
     wp& operator = (const sp<T>& other);
 
-#if !defined(ANDROID_UTILS_REF_BASE_DISABLE_IMPLICIT_CONSTRUCTION)
-    template<typename U> wp& operator = (U* other);
-#endif
     template<typename U> wp& operator = (const wp<U>& other);
     template<typename U> wp& operator = (const sp<U>& other);
 
@@ -547,6 +544,7 @@
     refs->incWeakRequireWeak(other);
 
     wp<T> ret;
+    ret.m_ptr = other;
     ret.m_refs = refs;
     return ret;
 }
@@ -558,6 +556,31 @@
 {
     m_refs = other ? m_refs = other->createWeak(this) : nullptr;
 }
+
+template <typename T>
+template <typename U>
+wp<T>::wp(U* other) : m_ptr(other) {
+    m_refs = other ? other->createWeak(this) : nullptr;
+}
+
+template <typename T>
+wp<T>& wp<T>::operator=(T* other) {
+    weakref_type* newRefs = other ? other->createWeak(this) : nullptr;
+    if (m_ptr) m_refs->decWeak(this);
+    m_ptr = other;
+    m_refs = newRefs;
+    return *this;
+}
+
+template <typename T>
+template <typename U>
+wp<T>& wp<T>::operator=(U* other) {
+    weakref_type* newRefs = other ? other->createWeak(this) : 0;
+    if (m_ptr) m_refs->decWeak(this);
+    m_ptr = other;
+    m_refs = newRefs;
+    return *this;
+}
 #endif
 
 template<typename T>
@@ -574,15 +597,6 @@
     m_refs = m_ptr ? m_ptr->createWeak(this) : nullptr;
 }
 
-#if !defined(ANDROID_UTILS_REF_BASE_DISABLE_IMPLICIT_CONSTRUCTION)
-template<typename T> template<typename U>
-wp<T>::wp(U* other)
-    : m_ptr(other)
-{
-    m_refs = other ? other->createWeak(this) : nullptr;
-}
-#endif
-
 template<typename T> template<typename U>
 wp<T>::wp(const wp<U>& other)
     : m_ptr(other.m_ptr)
@@ -608,19 +622,6 @@
     if (m_ptr) m_refs->decWeak(this);
 }
 
-#if !defined(ANDROID_UTILS_REF_BASE_DISABLE_IMPLICIT_CONSTRUCTION)
-template<typename T>
-wp<T>& wp<T>::operator = (T* other)
-{
-    weakref_type* newRefs =
-        other ? other->createWeak(this) : nullptr;
-    if (m_ptr) m_refs->decWeak(this);
-    m_ptr = other;
-    m_refs = newRefs;
-    return *this;
-}
-#endif
-
 template<typename T>
 wp<T>& wp<T>::operator = (const wp<T>& other)
 {
@@ -645,19 +646,6 @@
     return *this;
 }
 
-#if !defined(ANDROID_UTILS_REF_BASE_DISABLE_IMPLICIT_CONSTRUCTION)
-template<typename T> template<typename U>
-wp<T>& wp<T>::operator = (U* other)
-{
-    weakref_type* newRefs =
-        other ? other->createWeak(this) : 0;
-    if (m_ptr) m_refs->decWeak(this);
-    m_ptr = other;
-    m_refs = newRefs;
-    return *this;
-}
-#endif
-
 template<typename T> template<typename U>
 wp<T>& wp<T>::operator = (const wp<U>& other)
 {
diff --git a/libutils/include/utils/String16.h b/libutils/include/utils/String16.h
index 1a4b47e..5ce48c6 100644
--- a/libutils/include/utils/String16.h
+++ b/libutils/include/utils/String16.h
@@ -85,8 +85,6 @@
 
             bool                contains(const char16_t* chrs) const;
 
-            status_t            makeLower();
-
             status_t            replaceAll(char16_t replaceThis,
                                            char16_t withThis);
 
diff --git a/libutils/include/utils/String8.h b/libutils/include/utils/String8.h
index 0bcb716..cee5dc6 100644
--- a/libutils/include/utils/String8.h
+++ b/libutils/include/utils/String8.h
@@ -130,9 +130,6 @@
             bool                removeAll(const char* other);
 
             void                toLower();
-            void                toLower(size_t start, size_t numChars);
-            void                toUpper();
-            void                toUpper(size_t start, size_t numChars);
 
 
     /*
diff --git a/libutils/include/utils/StrongPointer.h b/libutils/include/utils/StrongPointer.h
index 1f07052..bb1941b 100644
--- a/libutils/include/utils/StrongPointer.h
+++ b/libutils/include/utils/StrongPointer.h
@@ -62,31 +62,34 @@
     sp(std::nullptr_t) : sp() {}
 #else
     sp(T* other);  // NOLINT(implicit)
+    template <typename U>
+    sp(U* other);  // NOLINT(implicit)
+    sp& operator=(T* other);
+    template <typename U>
+    sp& operator=(U* other);
 #endif
+
     sp(const sp<T>& other);
     sp(sp<T>&& other) noexcept;
 
-#if !defined(ANDROID_UTILS_REF_BASE_DISABLE_IMPLICIT_CONSTRUCTION)
-    template<typename U> sp(U* other);  // NOLINT(implicit)
-#endif
     template<typename U> sp(const sp<U>& other);  // NOLINT(implicit)
     template<typename U> sp(sp<U>&& other);  // NOLINT(implicit)
 
+    // Cast a strong pointer directly from one type to another. Constructors
+    // allow changing types, but only if they are pointer-compatible. This does
+    // a static_cast internally.
+    template <typename U>
+    static inline sp<T> cast(const sp<U>& other);
+
     ~sp();
 
     // Assignment
 
-#if !defined(ANDROID_UTILS_REF_BASE_DISABLE_IMPLICIT_CONSTRUCTION)
-    sp& operator = (T* other);
-#endif
     sp& operator = (const sp<T>& other);
     sp& operator=(sp<T>&& other) noexcept;
 
     template<typename U> sp& operator = (const sp<U>& other);
     template<typename U> sp& operator = (sp<U>&& other);
-#if !defined(ANDROID_UTILS_REF_BASE_DISABLE_IMPLICIT_CONSTRUCTION)
-    template<typename U> sp& operator = (U* other);
-#endif
 
     //! Special optimization for use by ProcessState (and nobody else).
     void force_set(T* other);
@@ -241,6 +244,28 @@
         other->incStrong(this);
     }
 }
+
+template <typename T>
+template <typename U>
+sp<T>::sp(U* other) : m_ptr(other) {
+    if (other) {
+        check_not_on_stack(other);
+        (static_cast<T*>(other))->incStrong(this);
+    }
+}
+
+template <typename T>
+sp<T>& sp<T>::operator=(T* other) {
+    T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
+    if (other) {
+        check_not_on_stack(other);
+        other->incStrong(this);
+    }
+    if (oldPtr) oldPtr->decStrong(this);
+    if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
+    m_ptr = other;
+    return *this;
+}
 #endif
 
 template<typename T>
@@ -255,17 +280,6 @@
     other.m_ptr = nullptr;
 }
 
-#if !defined(ANDROID_UTILS_REF_BASE_DISABLE_IMPLICIT_CONSTRUCTION)
-template<typename T> template<typename U>
-sp<T>::sp(U* other)
-        : m_ptr(other) {
-    if (other) {
-        check_not_on_stack(other);
-        (static_cast<T*>(other))->incStrong(this);
-    }
-}
-#endif
-
 template<typename T> template<typename U>
 sp<T>::sp(const sp<U>& other)
         : m_ptr(other.m_ptr) {
@@ -279,6 +293,12 @@
     other.m_ptr = nullptr;
 }
 
+template <typename T>
+template <typename U>
+sp<T> sp<T>::cast(const sp<U>& other) {
+    return sp<T>::fromExisting(static_cast<T*>(other.get()));
+}
+
 template<typename T>
 sp<T>::~sp() {
     if (m_ptr)
@@ -307,21 +327,6 @@
     return *this;
 }
 
-#if !defined(ANDROID_UTILS_REF_BASE_DISABLE_IMPLICIT_CONSTRUCTION)
-template<typename T>
-sp<T>& sp<T>::operator =(T* other) {
-    T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
-    if (other) {
-        check_not_on_stack(other);
-        other->incStrong(this);
-    }
-    if (oldPtr) oldPtr->decStrong(this);
-    if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
-    m_ptr = other;
-    return *this;
-}
-#endif
-
 template<typename T> template<typename U>
 sp<T>& sp<T>::operator =(const sp<U>& other) {
     T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
diff --git a/libutils/include/utils/Unicode.h b/libutils/include/utils/Unicode.h
index 0087383..d60d5d6 100644
--- a/libutils/include/utils/Unicode.h
+++ b/libutils/include/utils/Unicode.h
@@ -27,7 +27,6 @@
 int strncmp16(const char16_t *s1, const char16_t *s2, size_t n);
 size_t strlen16(const char16_t *);
 size_t strnlen16(const char16_t *, size_t);
-char16_t *strcpy16(char16_t *, const char16_t *);
 char16_t *strstr16(const char16_t*, const char16_t*);
 
 // Version of comparison that supports embedded NULs.
@@ -39,10 +38,6 @@
 // equivalent result as strcmp16 (unlike strncmp16).
 int strzcmp16(const char16_t *s1, size_t n1, const char16_t *s2, size_t n2);
 
-// Standard string functions on char32_t strings.
-size_t strlen32(const char32_t *);
-size_t strnlen32(const char32_t *, size_t);
-
 /**
  * Measure the length of a UTF-32 string in UTF-8. If the string is invalid
  * such as containing a surrogate character, -1 will be returned.
diff --git a/libvndksupport/Android.bp b/libvndksupport/Android.bp
index 11c75f7..f800bf7 100644
--- a/libvndksupport/Android.bp
+++ b/libvndksupport/Android.bp
@@ -5,7 +5,9 @@
 cc_library {
     name: "libvndksupport",
     native_bridge_supported: true,
-    llndk_stubs: "libvndksupport.llndk",
+    llndk: {
+        symbol_file: "libvndksupport.map.txt",
+    },
     srcs: ["linker.cpp"],
     cflags: [
         "-Wall",
@@ -23,10 +25,3 @@
         versions: ["29"],
     },
 }
-
-llndk_library {
-    name: "libvndksupport.llndk",
-    native_bridge_supported: true,
-    symbol_file: "libvndksupport.map.txt",
-    export_include_dirs: ["include"],
-}
diff --git a/qemu_pipe/Android.bp b/qemu_pipe/Android.bp
deleted file mode 100644
index 42a69db..0000000
--- a/qemu_pipe/Android.bp
+++ /dev/null
@@ -1,24 +0,0 @@
-// Copyright 2011 The Android Open Source Project
-
-package {
-    default_applicable_licenses: ["Android-Apache-2.0"],
-}
-
-cc_library_static {
-    name: "libqemu_pipe",
-    vendor_available: true,
-    recovery_available: true,
-    apex_available: [
-        "com.android.adbd",
-        // TODO(b/151398197) remove the below
-        "//apex_available:platform",
-    ],
-    sanitize: {
-        misc_undefined: ["integer"],
-    },
-    srcs: ["qemu_pipe.cpp"],
-    local_include_dirs: ["include"],
-    static_libs: ["libbase"],
-    export_include_dirs: ["include"],
-    cflags: ["-Werror"],
-}
diff --git a/qemu_pipe/OWNERS b/qemu_pipe/OWNERS
deleted file mode 100644
index d67a329..0000000
--- a/qemu_pipe/OWNERS
+++ /dev/null
@@ -1,3 +0,0 @@
-bohu@google.com
-lfy@google.com
-rkir@google.com
diff --git a/qemu_pipe/include/qemu_pipe.h b/qemu_pipe/include/qemu_pipe.h
deleted file mode 100644
index 0987498..0000000
--- a/qemu_pipe/include/qemu_pipe.h
+++ /dev/null
@@ -1,64 +0,0 @@
-/*
- * Copyright (C) 2011 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-#ifndef ANDROID_CORE_INCLUDE_QEMU_PIPE_H
-#define ANDROID_CORE_INCLUDE_QEMU_PIPE_H
-
-#include <stddef.h>
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-// Try to open a new Qemu fast-pipe. This function returns a file descriptor
-// that can be used to communicate with a named service managed by the
-// emulator.
-//
-// This file descriptor can be used as a standard pipe/socket descriptor.
-//
-// 'pipeName' is the name of the emulator service you want to connect to,
-// and should begin with 'pipe:' (e.g. 'pipe:camera' or 'pipe:opengles').
-// For backward compatibility, the 'pipe:' prefix can be omitted, and in
-// that case, qemu_pipe_open will add it for you.
-
-// On success, return a valid file descriptor, or -1/errno on failure. E.g.:
-//
-// EINVAL  -> unknown/unsupported pipeName
-// ENOSYS  -> fast pipes not available in this system.
-//
-// ENOSYS should never happen, except if you're trying to run within a
-// misconfigured emulator.
-//
-// You should be able to open several pipes to the same pipe service,
-// except for a few special cases (e.g. GSM modem), where EBUSY will be
-// returned if more than one client tries to connect to it.
-int qemu_pipe_open(const char* pipeName);
-
-// Send a framed message |buff| of |len| bytes through the |fd| descriptor.
-// This really adds a 4-hexchar prefix describing the payload size.
-// Returns 0 on success, and -1 on error.
-int qemu_pipe_frame_send(int fd, const void* buff, size_t len);
-
-// Read a frame message from |fd|, and store it into |buff| of |len| bytes.
-// If the framed message is larger than |len|, then this returns -1 and the
-// content is lost. Otherwise, this returns the size of the message. NOTE:
-// empty messages are possible in a framed wire protocol and do not mean
-// end-of-stream.
-int qemu_pipe_frame_recv(int fd, void* buff, size_t len);
-
-#ifdef __cplusplus
-}
-#endif
-
-#endif /* ANDROID_CORE_INCLUDE_QEMU_PIPE_H */
diff --git a/qemu_pipe/qemu_pipe.cpp b/qemu_pipe/qemu_pipe.cpp
deleted file mode 100644
index 03afb21..0000000
--- a/qemu_pipe/qemu_pipe.cpp
+++ /dev/null
@@ -1,107 +0,0 @@
-/*
- * Copyright (C) 2011 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#include "qemu_pipe.h"
-
-#include <unistd.h>
-#include <fcntl.h>
-#include <string.h>
-#include <errno.h>
-#include <stdio.h>
-
-#include <android-base/file.h>
-
-using android::base::ReadFully;
-using android::base::WriteFully;
-
-// Define QEMU_PIPE_DEBUG if you want to print error messages when an error
-// occurs during pipe operations. The macro should simply take a printf-style
-// formatting string followed by optional arguments.
-#ifndef QEMU_PIPE_DEBUG
-#  define  QEMU_PIPE_DEBUG(...)   (void)0
-#endif
-
-int qemu_pipe_open(const char* pipeName) {
-    if (!pipeName) {
-        errno = EINVAL;
-        return -1;
-    }
-
-    int fd = TEMP_FAILURE_RETRY(open("/dev/qemu_pipe", O_RDWR));
-    if (fd < 0) {
-        QEMU_PIPE_DEBUG("%s: Could not open /dev/qemu_pipe: %s", __FUNCTION__,
-                        strerror(errno));
-        return -1;
-    }
-
-    // Write the pipe name, *including* the trailing zero which is necessary.
-    size_t pipeNameLen = strlen(pipeName);
-    if (WriteFully(fd, pipeName, pipeNameLen + 1U)) {
-        return fd;
-    }
-
-    // now, add 'pipe:' prefix and try again
-    // Note: host side will wait for the trailing '\0' to start
-    // service lookup.
-    const char pipe_prefix[] = "pipe:";
-    if (WriteFully(fd, pipe_prefix, strlen(pipe_prefix)) &&
-            WriteFully(fd, pipeName, pipeNameLen + 1U)) {
-        return fd;
-    }
-    QEMU_PIPE_DEBUG("%s: Could not write to %s pipe service: %s",
-            __FUNCTION__, pipeName, strerror(errno));
-    close(fd);
-    return -1;
-}
-
-int qemu_pipe_frame_send(int fd, const void* buff, size_t len) {
-    char header[5];
-    snprintf(header, sizeof(header), "%04zx", len);
-    if (!WriteFully(fd, header, 4)) {
-        QEMU_PIPE_DEBUG("Can't write qemud frame header: %s", strerror(errno));
-        return -1;
-    }
-    if (!WriteFully(fd, buff, len)) {
-        QEMU_PIPE_DEBUG("Can't write qemud frame payload: %s", strerror(errno));
-        return -1;
-    }
-    return 0;
-}
-
-int qemu_pipe_frame_recv(int fd, void* buff, size_t len) {
-    char header[5];
-    if (!ReadFully(fd, header, 4)) {
-        QEMU_PIPE_DEBUG("Can't read qemud frame header: %s", strerror(errno));
-        return -1;
-    }
-    header[4] = '\0';
-    size_t size;
-    if (sscanf(header, "%04zx", &size) != 1) {
-        QEMU_PIPE_DEBUG("Malformed qemud frame header: [%.*s]", 4, header);
-        return -1;
-    }
-    if (size > len) {
-        QEMU_PIPE_DEBUG("Oversized qemud frame (% bytes, expected <= %)", size,
-                        len);
-        return -1;
-    }
-    if (!ReadFully(fd, buff, size)) {
-        QEMU_PIPE_DEBUG("Could not read qemud frame payload: %s",
-                        strerror(errno));
-        return -1;
-    }
-    return size;
-}
diff --git a/rootdir/Android.bp b/rootdir/Android.bp
index 6a80808..ae21633 100644
--- a/rootdir/Android.bp
+++ b/rootdir/Android.bp
@@ -20,7 +20,10 @@
     name: "init.rc",
     src: "init.rc",
     sub_dir: "init/hw",
-    required: ["fsverity_init"],
+    required: [
+        "fsverity_init",
+        "platform-bootclasspath",
+    ],
 }
 
 prebuilt_etc {
@@ -35,3 +38,11 @@
     src: "etc/linker.config.json",
     installable: false,
 }
+
+// TODO(b/185211376) Scope the native APIs that microdroid will provide to the app payload
+prebuilt_etc {
+    name: "public.libraries.android.txt",
+    src: "etc/public.libraries.android.txt",
+    filename: "public.libraries.txt",
+    installable: false,
+}
\ No newline at end of file
diff --git a/rootdir/Android.mk b/rootdir/Android.mk
index 5503cc1..99d8f9a 100644
--- a/rootdir/Android.mk
+++ b/rootdir/Android.mk
@@ -56,7 +56,6 @@
 LOCAL_LICENSE_KINDS := SPDX-license-identifier-Apache-2.0
 LOCAL_LICENSE_CONDITIONS := notice
 LOCAL_MODULE_PATH := $(TARGET_ROOT_OUT)
-LOCAL_REQUIRED_MODULES := etc_classpath
 
 EXPORT_GLOBAL_ASAN_OPTIONS :=
 ifneq ($(filter address,$(SANITIZE_TARGET)),)
@@ -186,21 +185,6 @@
 endef
 
 #######################################
-# /etc/classpath
-include $(CLEAR_VARS)
-LOCAL_MODULE := etc_classpath
-LOCAL_MODULE_CLASS := ETC
-LOCAL_MODULE_PATH := $(TARGET_OUT_ETC)
-LOCAL_MODULE_STEM := classpath
-include $(BUILD_SYSTEM)/base_rules.mk
-$(LOCAL_BUILT_MODULE):
-	@echo "Generate: $@"
-	@mkdir -p $(dir $@)
-	$(hide) echo "export BOOTCLASSPATH $(PRODUCT_BOOTCLASSPATH)" > $@
-	$(hide) echo "export DEX2OATBOOTCLASSPATH $(PRODUCT_DEX2OAT_BOOTCLASSPATH)" >> $@
-	$(hide) echo "export SYSTEMSERVERCLASSPATH $(PRODUCT_SYSTEM_SERVER_CLASSPATH)" >> $@
-
-#######################################
 # sanitizer.libraries.txt
 include $(CLEAR_VARS)
 LOCAL_MODULE := sanitizer.libraries.txt
diff --git a/rootdir/etc/linker.config.json b/rootdir/etc/linker.config.json
index 83cb6ff..a22ef6f 100644
--- a/rootdir/etc/linker.config.json
+++ b/rootdir/etc/linker.config.json
@@ -1,8 +1,7 @@
 {
   "requireLibs": [
-    // Keep in sync with the "platform" namespace in art/build/apex/ld.config.txt.
-    "libdexfile_external.so",
-    "libdexfiled_external.so",
+    "libdexfile.so",
+    "libdexfiled.so",
     "libnativebridge.so",
     "libnativehelper.so",
     "libnativeloader.so",
@@ -19,6 +18,7 @@
     "libnetd_resolv.so",
     // nn
     "libneuralnetworks.so",
+    "libneuralnetworks_shim.so",
     // statsd
     "libstatspull.so",
     "libstatssocket.so",
diff --git a/rootdir/init-debug.rc b/rootdir/init-debug.rc
index 435d4cb..77a80cd 100644
--- a/rootdir/init-debug.rc
+++ b/rootdir/init-debug.rc
@@ -6,3 +6,11 @@
 
 on property:persist.mmc.cache_size=*
     write /sys/block/mmcblk0/cache_size ${persist.mmc.cache_size}
+
+on early-init && property:ro.product.debugfs_restrictions.enabled=true
+    mount debugfs debugfs /sys/kernel/debug
+    chmod 0755 /sys/kernel/debug
+
+on property:sys.boot_completed=1 && property:ro.product.debugfs_restrictions.enabled=true && \
+   property:persist.dbg.keep_debugfs_mounted=""
+   umount /sys/kernel/debug
diff --git a/rootdir/init.rc b/rootdir/init.rc
index 9a30ead..4ec5d33 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -471,9 +471,6 @@
     chmod 0664 /sys/module/lowmemorykiller/parameters/minfree
     start lmkd
 
-    # Set an initial boot level - start at 10 in case we need to add earlier ones.
-    setprop keystore.boot_level 10
-
     # Start essential services.
     start servicemanager
     start hwservicemanager
@@ -630,8 +627,6 @@
     write /sys/kernel/tracing/instances/bootreceiver/events/error_report/error_report_end/enable 1
 
 on post-fs-data
-    # Boot level 30 - at this point daemons like apexd and odsign run
-    setprop keystore.boot_level 30
 
     mark_post_data
 
@@ -652,6 +647,9 @@
     mkdir /data/bootchart 0755 shell shell encryption=Require
     bootchart start
 
+    # Avoid predictable entropy pool. Carry over entropy from previous boot.
+    copy /data/system/entropy.dat /dev/urandom
+
     mkdir /data/vendor 0771 root root encryption=Require
     mkdir /data/vendor_ce 0771 root root encryption=None
     mkdir /data/vendor_de 0771 root root encryption=None
@@ -667,7 +665,30 @@
     # Make sure that apexd is started in the default namespace
     enter_default_mount_ns
 
+    # set up keystore directory structure first so that we can end early boot
+    # and start apexd
+    mkdir /data/misc 01771 system misc encryption=Require
+    mkdir /data/misc/keystore 0700 keystore keystore
+    # work around b/183668221
+    restorecon /data/misc /data/misc/keystore
+
+    # Boot level 30
+    # odsign signing keys have MAX_BOOT_LEVEL=30
+    # This is currently the earliest boot level, but we start at 30
+    # to leave room for earlier levels.
+    setprop keystore.boot_level 30
+
+    # Now that /data is mounted and we have created /data/misc/keystore,
+    # we can tell keystore to stop allowing use of early-boot keys,
+    # and access its database for the first time to support creation and
+    # use of MAX_BOOT_LEVEL keys.
+    exec - system system -- /system/bin/vdc keymaster earlyBootEnded
+
     # /data/apex is now available. Start apexd to scan and activate APEXes.
+    #
+    # To handle userspace reboots as well as devices that use FDE, make sure
+    # that apexd is started cleanly here (set apexd.status="") and that it is
+    # restarted if it's already running.
     mkdir /data/apex 0755 root system encryption=None
     mkdir /data/apex/active 0755 root system
     mkdir /data/apex/backup 0700 root system
@@ -676,13 +697,10 @@
     mkdir /data/apex/sessions 0700 root system
     mkdir /data/app-staging 0751 system system encryption=DeleteIfNecessary
     mkdir /data/apex/ota_reserved 0700 root system encryption=Require
-    start apexd
+    setprop apexd.status ""
+    restart apexd
 
-    # Avoid predictable entropy pool. Carry over entropy from previous boot.
-    copy /data/system/entropy.dat /dev/urandom
-
-    # create basic filesystem structure
-    mkdir /data/misc 01771 system misc encryption=Require
+    # create rest of basic filesystem structure
     mkdir /data/misc/recovery 0770 system log
     copy /data/misc/recovery/ro.build.fingerprint /data/misc/recovery/ro.build.fingerprint.1
     chmod 0440 /data/misc/recovery/ro.build.fingerprint.1
@@ -706,7 +724,6 @@
     mkdir /data/misc/nfc 0770 nfc nfc
     mkdir /data/misc/nfc/logs 0770 nfc nfc
     mkdir /data/misc/credstore 0700 credstore credstore
-    mkdir /data/misc/keystore 0700 keystore keystore
     mkdir /data/misc/gatekeeper 0700 system system
     mkdir /data/misc/keychain 0771 system system
     mkdir /data/misc/net 0750 root shell
@@ -755,6 +772,8 @@
     mkdir /data/misc/snapshotctl_log 0755 root root
     # create location to store pre-reboot information
     mkdir /data/misc/prereboot 0700 system system
+    # directory used for on-device refresh metrics file.
+    mkdir /data/misc/odrefresh 0777 system system
     # directory used for on-device signing key blob
     mkdir /data/misc/odsign 0700 root root
 
@@ -903,7 +922,6 @@
     # Must start before 'odsign', as odsign depends on *CLASSPATH variables
     exec_start derive_classpath
     load_exports /data/system/environ/classpath
-    rm /data/system/environ/classpath
 
     # Start the on-device signing daemon, and wait for it to finish, to ensure
     # ART artifacts are generated if needed.
@@ -914,14 +932,13 @@
     # odsign to be done with the key
     wait_for_prop odsign.key.done 1
 
-    # After apexes are mounted, tell keymaster early boot has ended, so it will
-    # stop allowing use of early-boot keys
-    exec - system system -- /system/bin/vdc keymaster earlyBootEnded
-
     # Lock the fs-verity keyring, so no more keys can be added
     exec -- /system/bin/fsverity_init --lock
 
-    setprop keystore.boot_level 40
+    # Bump the boot level to 1000000000; this prevents further on-device signing.
+    # This is a special value that shuts down the thread which listens for
+    # further updates.
+    setprop keystore.boot_level 1000000000
 
     # Allow apexd to snapshot and restore device encrypted apex data in the case
     # of a rollback. This should be done immediately after DE_user data keys
@@ -985,9 +1002,6 @@
     write /proc/sys/vm/dirty_expire_centisecs 200
     write /proc/sys/vm/dirty_background_ratio  5
 
-on property:sys.boot_completed=1 && property:init.mount_debugfs=1
-   umount /sys/kernel/debug
-
 on boot
     # basic network init
     ifup lo
@@ -1231,7 +1245,6 @@
   setprop dev.bootcomplete ""
   setprop sys.init.updatable_crashing ""
   setprop sys.init.updatable_crashing_process_name ""
-  setprop apexd.status ""
   setprop sys.user.0.ce_available ""
   setprop sys.shutdown.requested ""
   setprop service.bootanim.exit ""
@@ -1263,10 +1276,6 @@
 on property:sys.boot_completed=1 && property:sys.init.userspace_reboot.in_progress=1
   setprop sys.init.userspace_reboot.in_progress ""
 
-on early-init && property:init.mount_debugfs=1
-    mount debugfs debugfs /sys/kernel/debug
-    chmod 0755 /sys/kernel/debug
-
 # Migrate tasks again in case kernel threads are created during boot
 on property:sys.boot_completed=1
   copy_per_line /dev/cpuctl/tasks /dev/cpuctl/system/tasks
diff --git a/rootdir/ueventd.rc b/rootdir/ueventd.rc
index 65e29c1..56e774b 100644
--- a/rootdir/ueventd.rc
+++ b/rootdir/ueventd.rc
@@ -67,6 +67,10 @@
 # CDMA radio interface MUX
 /dev/ppp                  0660   radio      vpn
 
+# Virtualisation is managed by Virt Manager
+/dev/kvm                  0600   virtmanager root
+/dev/vhost-vsock          0600   virtmanager root
+
 # sysfs properties
 /sys/devices/platform/trusty.*      trusty_version        0440  root   log
 /sys/devices/virtual/input/input*   enable      0660  root   input
diff --git a/trusty/fuzz/include/trusty/fuzz/utils.h b/trusty/fuzz/include/trusty/fuzz/utils.h
index bca84e9..c906412 100644
--- a/trusty/fuzz/include/trusty/fuzz/utils.h
+++ b/trusty/fuzz/include/trusty/fuzz/utils.h
@@ -34,6 +34,7 @@
     android::base::Result<void> Connect();
     android::base::Result<void> Read(void* buf, size_t len);
     android::base::Result<void> Write(const void* buf, size_t len);
+    void Disconnect();
 
     android::base::Result<int> GetRawFd();
 
diff --git a/trusty/fuzz/tipc_fuzzer.cpp b/trusty/fuzz/tipc_fuzzer.cpp
index 3258944..f265ced 100644
--- a/trusty/fuzz/tipc_fuzzer.cpp
+++ b/trusty/fuzz/tipc_fuzzer.cpp
@@ -41,6 +41,7 @@
 #error "Binary file name must be parameterized using -DTRUSTY_APP_FILENAME."
 #endif
 
+static TrustyApp kTrustyApp(TIPC_DEV, TRUSTY_APP_PORT);
 static std::unique_ptr<CoverageRecord> record;
 
 extern "C" int LLVMFuzzerInitialize(int* /* argc */, char*** /* argv */) {
@@ -52,8 +53,7 @@
     }
 
     /* Make sure lazy-loaded TAs have started and connected to coverage service. */
-    TrustyApp ta(TIPC_DEV, TRUSTY_APP_PORT);
-    auto ret = ta.Connect();
+    auto ret = kTrustyApp.Connect();
     if (!ret.ok()) {
         std::cerr << ret.error() << std::endl;
         exit(-1);
@@ -79,22 +79,18 @@
     ExtraCounters counters(record.get());
     counters.Reset();
 
-    TrustyApp ta(TIPC_DEV, TRUSTY_APP_PORT);
-    auto ret = ta.Connect();
+    auto ret = kTrustyApp.Write(data, size);
+    if (ret.ok()) {
+        ret = kTrustyApp.Read(&buf, sizeof(buf));
+    }
+
+    // Reconnect to ensure that the service is still up
+    kTrustyApp.Disconnect();
+    ret = kTrustyApp.Connect();
     if (!ret.ok()) {
         std::cerr << ret.error() << std::endl;
         android::trusty::fuzz::Abort();
     }
 
-    ret = ta.Write(data, size);
-    if (!ret.ok()) {
-        return -1;
-    }
-
-    ret = ta.Read(&buf, sizeof(buf));
-    if (!ret.ok()) {
-        return -1;
-    }
-
-    return 0;
+    return ret.ok() ? 0 : -1;
 }
diff --git a/trusty/fuzz/utils.cpp b/trusty/fuzz/utils.cpp
index 3526337..bb096be 100644
--- a/trusty/fuzz/utils.cpp
+++ b/trusty/fuzz/utils.cpp
@@ -127,6 +127,10 @@
     return ta_fd_;
 }
 
+void TrustyApp::Disconnect() {
+    ta_fd_.reset();
+}
+
 void Abort() {
     PrintTrustyLog();
     exit(-1);
diff --git a/trusty/metrics/Android.bp b/trusty/metrics/Android.bp
new file mode 100644
index 0000000..e0533bc
--- /dev/null
+++ b/trusty/metrics/Android.bp
@@ -0,0 +1,51 @@
+// Copyright (C) 2021 The Android Open-Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package {
+    default_applicable_licenses: ["Android-Apache-2.0"],
+}
+
+cc_library {
+    name: "libtrusty_metrics",
+    vendor: true,
+    srcs: [
+        "metrics.cpp",
+    ],
+    export_include_dirs: [
+        "include",
+    ],
+    shared_libs: [
+        "libbase",
+        "liblog",
+        "libtrusty",
+    ],
+}
+
+cc_test {
+    name: "libtrusty_metrics_test",
+    vendor: true,
+    srcs: [
+        "metrics_test.cpp",
+    ],
+    static_libs: [
+        "libtrusty_metrics",
+    ],
+    shared_libs: [
+        "libbase",
+        "libbinder",
+        "liblog",
+        "libtrusty",
+    ],
+    require_root: true,
+}
diff --git a/trusty/metrics/include/trusty/metrics/metrics.h b/trusty/metrics/include/trusty/metrics/metrics.h
new file mode 100644
index 0000000..6949e9b
--- /dev/null
+++ b/trusty/metrics/include/trusty/metrics/metrics.h
@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <functional>
+#include <memory>
+#include <string>
+
+#include <android-base/result.h>
+#include <android-base/unique_fd.h>
+
+namespace android {
+namespace trusty {
+namespace metrics {
+
+using android::base::Result;
+using android::base::unique_fd;
+
+class TrustyMetrics {
+  public:
+    /* Wait for next event with a given timeout. Negative timeout means infinite timeout. */
+    Result<void> WaitForEvent(int timeout_ms = -1);
+    /* Attempt to handle an event from Metrics TA in a non-blocking manner. */
+    Result<void> HandleEvent();
+    /* Expose TIPC channel so that client can integrate it into an event loop with other fds. */
+    int GetRawFd() { return metrics_fd_; };
+
+  protected:
+    TrustyMetrics(std::string tipc_dev) : tipc_dev_(std::move(tipc_dev)), metrics_fd_(-1) {}
+    virtual ~TrustyMetrics(){};
+
+    Result<void> Open();
+    virtual void HandleCrash(const std::string& app_id) = 0;
+    virtual void HandleEventDrop() = 0;
+
+  private:
+    std::string tipc_dev_;
+    unique_fd metrics_fd_;
+};
+
+}  // namespace metrics
+}  // namespace trusty
+}  // namespace android
diff --git a/trusty/metrics/include/trusty/metrics/tipc.h b/trusty/metrics/include/trusty/metrics/tipc.h
new file mode 100644
index 0000000..66d0876
--- /dev/null
+++ b/trusty/metrics/include/trusty/metrics/tipc.h
@@ -0,0 +1,103 @@
+/*
+ * Copyright 2021, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+/**
+ * DOC: Metrics
+ *
+ * Metrics interface provides a way for Android to get Trusty metrics data.
+ *
+ * Currently, only "push" model is supported. Clients are expected to connect to
+ * metrics service, listen for events, e.g. app crash events, and respond to
+ * every event with a &struct metrics_req.
+ *
+ * Communication is driven by metrics service, i.e. requests/responses are all
+ * sent from/to metrics service.
+ *
+ * Note that the type of the event is not known to the client ahead of time.
+ *
+ * In the future, if we need to have Android "pull" metrics data from Trusty,
+ * that can be done by introducing a separate port.
+ *
+ * This interface is shared between Android and Trusty. There is a copy in each
+ * repository. They must be kept in sync.
+ */
+
+#define METRICS_PORT "com.android.trusty.metrics"
+
+/**
+ * enum metrics_cmd - command identifiers for metrics interface
+ * @METRICS_CMD_RESP_BIT:          message is a response
+ * @METRICS_CMD_REQ_SHIFT:         number of bits used by @METRICS_CMD_RESP_BIT
+ * @METRICS_CMD_REPORT_EVENT_DROP: report gaps in the event stream
+ * @METRICS_CMD_REPORT_CRASH:      report an app crash event
+ */
+enum metrics_cmd {
+    METRICS_CMD_RESP_BIT = 1,
+    METRICS_CMD_REQ_SHIFT = 1,
+
+    METRICS_CMD_REPORT_EVENT_DROP = (1 << METRICS_CMD_REQ_SHIFT),
+    METRICS_CMD_REPORT_CRASH = (2 << METRICS_CMD_REQ_SHIFT),
+};
+
+/**
+ * enum metrics_error - metrics error codes
+ * @METRICS_NO_ERROR:        no error
+ * @METRICS_ERR_UNKNOWN_CMD: unknown or not implemented command
+ */
+enum metrics_error {
+    METRICS_NO_ERROR = 0,
+    METRICS_ERR_UNKNOWN_CMD = 1,
+};
+
+/**
+ * struct metrics_req - common structure for metrics requests
+ * @cmd:      command identifier - one of &enum metrics_cmd
+ * @reserved: must be 0
+ */
+struct metrics_req {
+    uint32_t cmd;
+    uint32_t reserved;
+} __attribute__((__packed__));
+
+/**
+ * struct metrics_resp - common structure for metrics responses
+ * @cmd: command identifier - %METRICS_CMD_RESP_BIT or'ed with a cmd in
+ *                            one of &enum metrics_cmd
+ * @status: response status, one of &enum metrics_error
+ */
+struct metrics_resp {
+    uint32_t cmd;
+    uint32_t status;
+} __attribute__((__packed__));
+
+/**
+ * struct metrics_report_crash_req - arguments of %METRICS_CMD_REPORT_CRASH
+ *                                   requests
+ * @app_id_len: length of app ID that follows this structure
+ */
+struct metrics_report_crash_req {
+    uint32_t app_id_len;
+} __attribute__((__packed__));
+
+#define METRICS_MAX_APP_ID_LEN 256
+
+#define METRICS_MAX_MSG_SIZE                                                \
+    (sizeof(struct metrics_req) + sizeof(struct metrics_report_crash_req) + \
+     METRICS_MAX_APP_ID_LEN)
diff --git a/trusty/metrics/metrics.cpp b/trusty/metrics/metrics.cpp
new file mode 100644
index 0000000..3ac128a
--- /dev/null
+++ b/trusty/metrics/metrics.cpp
@@ -0,0 +1,142 @@
+/*
+ * Copyright (C) 2021 The Android Open Sourete Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define LOG_TAG "metrics"
+
+#include <android-base/logging.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <trusty/metrics/metrics.h>
+#include <trusty/metrics/tipc.h>
+#include <trusty/tipc.h>
+#include <unistd.h>
+
+namespace android {
+namespace trusty {
+namespace metrics {
+
+using android::base::ErrnoError;
+using android::base::Error;
+
+Result<void> TrustyMetrics::Open() {
+    int fd = tipc_connect(tipc_dev_.c_str(), METRICS_PORT);
+    if (fd < 0) {
+        return ErrnoError() << "failed to connect to Trusty metrics TA";
+    }
+
+    int flags = fcntl(fd, F_GETFL, 0);
+    if (flags < 0) {
+        return ErrnoError() << "failed F_GETFL";
+    }
+
+    int rc = fcntl(fd, F_SETFL, flags | O_NONBLOCK);
+    if (rc < 0) {
+        return ErrnoError() << "failed F_SETFL";
+    }
+
+    metrics_fd_.reset(fd);
+    return {};
+}
+
+Result<void> TrustyMetrics::WaitForEvent(int timeout_ms) {
+    if (!metrics_fd_.ok()) {
+        return Error() << "connection to Metrics TA has not been initialized yet";
+    }
+
+    struct pollfd pfd = {
+            .fd = metrics_fd_,
+            .events = POLLIN,
+    };
+
+    int rc = poll(&pfd, 1, timeout_ms);
+    if (rc != 1) {
+        return ErrnoError() << "failed poll()";
+    }
+
+    if (!(pfd.revents & POLLIN)) {
+        return ErrnoError() << "channel not ready";
+    }
+
+    return {};
+}
+
+Result<void> TrustyMetrics::HandleEvent() {
+    if (!metrics_fd_.ok()) {
+        return Error() << "connection to Metrics TA has not been initialized yet";
+    }
+
+    uint8_t msg[METRICS_MAX_MSG_SIZE];
+
+    auto rc = read(metrics_fd_, msg, sizeof(msg));
+    if (rc < 0) {
+        return ErrnoError() << "failed to read metrics message";
+    }
+    size_t msg_len = rc;
+
+    if (msg_len < sizeof(metrics_req)) {
+        return Error() << "message too small: " << rc;
+    }
+    auto req = reinterpret_cast<metrics_req*>(msg);
+    size_t offset = sizeof(metrics_req);
+    uint32_t status = METRICS_NO_ERROR;
+
+    switch (req->cmd) {
+        case METRICS_CMD_REPORT_CRASH: {
+            if (msg_len < offset + sizeof(metrics_report_crash_req)) {
+                return Error() << "message too small: " << rc;
+            }
+            auto crash_args = reinterpret_cast<metrics_report_crash_req*>(msg + offset);
+            offset += sizeof(metrics_report_crash_req);
+
+            if (msg_len < offset + crash_args->app_id_len) {
+                return Error() << "message too small: " << rc;
+            }
+            auto app_id_ptr = reinterpret_cast<char*>(msg + offset);
+            std::string app_id(app_id_ptr, crash_args->app_id_len);
+
+            HandleCrash(app_id);
+            break;
+        }
+
+        case METRICS_CMD_REPORT_EVENT_DROP:
+            HandleEventDrop();
+            break;
+
+        default:
+            status = METRICS_ERR_UNKNOWN_CMD;
+            break;
+    }
+
+    metrics_resp resp = {
+            .cmd = req->cmd | METRICS_CMD_RESP_BIT,
+            .status = status,
+    };
+
+    rc = write(metrics_fd_, &resp, sizeof(resp));
+    if (rc < 0) {
+        return ErrnoError() << "failed to request next metrics event";
+    }
+
+    if (rc != (int)sizeof(resp)) {
+        return Error() << "unexpected number of bytes sent event: " << rc;
+    }
+
+    return {};
+}
+
+}  // namespace metrics
+}  // namespace trusty
+}  // namespace android
diff --git a/trusty/metrics/metrics_test.cpp b/trusty/metrics/metrics_test.cpp
new file mode 100644
index 0000000..407ddf2
--- /dev/null
+++ b/trusty/metrics/metrics_test.cpp
@@ -0,0 +1,139 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <android-base/unique_fd.h>
+#include <binder/IPCThreadState.h>
+#include <gtest/gtest.h>
+#include <poll.h>
+#include <trusty/metrics/metrics.h>
+#include <trusty/tipc.h>
+
+#define TIPC_DEV "/dev/trusty-ipc-dev0"
+#define CRASHER_PORT "com.android.trusty.metrics.test.crasher"
+
+namespace android {
+namespace trusty {
+namespace metrics {
+
+using android::base::unique_fd;
+
+static void TriggerCrash() {
+    size_t num_retries = 3;
+    int fd = -1;
+
+    for (size_t i = 0; i < num_retries; i++) {
+        /* It's possible to time out waiting for crasher TA to restart. */
+        fd = tipc_connect(TIPC_DEV, CRASHER_PORT);
+        if (fd >= 0) {
+            break;
+        }
+    }
+
+    unique_fd crasher(fd);
+    ASSERT_GE(crasher, 0);
+
+    int msg = 0;
+    int rc = write(crasher, &msg, sizeof(msg));
+    ASSERT_EQ(rc, sizeof(msg));
+}
+
+class TrustyMetricsTest : public TrustyMetrics, public ::testing::Test {
+  public:
+    TrustyMetricsTest() : TrustyMetrics(TIPC_DEV) {}
+
+    virtual void HandleCrash(const std::string& app_id) override { crashed_app_ = app_id; }
+
+    virtual void HandleEventDrop() override { event_drop_count_++; }
+
+    virtual void SetUp() override {
+        auto ret = Open();
+        ASSERT_TRUE(ret.ok()) << ret.error();
+    }
+
+    void WaitForAndHandleEvent() {
+        auto ret = WaitForEvent(30000 /* 30 second timeout */);
+        ASSERT_TRUE(ret.ok()) << ret.error();
+
+        ret = HandleEvent();
+        ASSERT_TRUE(ret.ok()) << ret.error();
+    }
+
+    std::string crashed_app_;
+    size_t event_drop_count_;
+};
+
+TEST_F(TrustyMetricsTest, Crash) {
+    TriggerCrash();
+    WaitForAndHandleEvent();
+
+    /* Check that correct TA crashed. */
+    ASSERT_EQ(crashed_app_, "36f5b435-5bd3-4526-8b76-200e3a7e79f3:crasher");
+}
+
+TEST_F(TrustyMetricsTest, PollSet) {
+    int binder_fd;
+    int rc = IPCThreadState::self()->setupPolling(&binder_fd);
+    ASSERT_EQ(rc, 0);
+    ASSERT_GE(binder_fd, 0);
+
+    TriggerCrash();
+
+    struct pollfd pfds[] = {
+            {
+                    .fd = binder_fd,
+                    .events = POLLIN,
+            },
+            {
+                    .fd = GetRawFd(),
+                    .events = POLLIN,
+            },
+    };
+
+    rc = poll(pfds, 2, 30000 /* 30 second timeout */);
+    /* We expect one event on the metrics fd. */
+    ASSERT_EQ(rc, 1);
+    ASSERT_TRUE(pfds[1].revents & POLLIN);
+
+    auto ret = HandleEvent();
+    ASSERT_TRUE(ret.ok()) << ret.error();
+
+    /* Check that correct TA crashed. */
+    ASSERT_EQ(crashed_app_, "36f5b435-5bd3-4526-8b76-200e3a7e79f3:crasher");
+}
+
+TEST_F(TrustyMetricsTest, EventDrop) {
+    /* We know the size of the internal event queue is less than this. */
+    size_t num_events = 3;
+
+    ASSERT_EQ(event_drop_count_, 0);
+
+    for (auto i = 0; i < num_events; i++) {
+        TriggerCrash();
+    }
+
+    for (auto i = 0; i < num_events; i++) {
+        WaitForAndHandleEvent();
+        if (event_drop_count_ > 0) {
+            break;
+        }
+    }
+
+    ASSERT_EQ(event_drop_count_, 1);
+}
+
+}  // namespace metrics
+}  // namespace trusty
+}  // namespace android