diff --git a/debuggerd/tombstoned/tombstoned.cpp b/debuggerd/tombstoned/tombstoned.cpp
index 0b87b7a..05d8050 100644
--- a/debuggerd/tombstoned/tombstoned.cpp
+++ b/debuggerd/tombstoned/tombstoned.cpp
@@ -165,8 +165,7 @@
 
     switch (dump_type) {
       case kDebuggerdNativeBacktrace:
-      case kDebuggerdJavaBacktrace:
-        // Don't generate tombstones for backtrace requests.
+        // Don't generate tombstones for native backtrace requests.
         return {};
 
       case kDebuggerdTombstoneProto:
@@ -178,6 +177,7 @@
         result.text = create_temporary_file();
         break;
 
+      case kDebuggerdJavaBacktrace:
       case kDebuggerdTombstone:
         result.text = create_temporary_file();
         break;
diff --git a/fs_mgr/fs_mgr_overlayfs.cpp b/fs_mgr/fs_mgr_overlayfs.cpp
index 9a94d79..9fb658e 100644
--- a/fs_mgr/fs_mgr_overlayfs.cpp
+++ b/fs_mgr/fs_mgr_overlayfs.cpp
@@ -92,7 +92,7 @@
     return false;
 }
 
-bool fs_mgr_overlayfs_mount_fstab_entry(const std::string&, const std::string&) {
+bool fs_mgr_overlayfs_mount_fstab_entry(const android::fs_mgr::FstabEntry&) {
     return false;
 }
 
@@ -1299,16 +1299,32 @@
     }
 }
 
-bool fs_mgr_overlayfs_mount_fstab_entry(const std::string& lowers,
-                                        const std::string& mount_point) {
+bool fs_mgr_overlayfs_mount_fstab_entry(const android::fs_mgr::FstabEntry& entry) {
     if (fs_mgr_overlayfs_invalid()) return false;
 
-    std::string aux = "lowerdir=" + lowers + ",override_creds=off";
-    auto rc = mount("overlay", mount_point.c_str(), "overlay", MS_RDONLY | MS_NOATIME, aux.c_str());
+    // Create the mount point in case it doesn't exist.
+    mkdir(entry.mount_point.c_str(), 0755);
 
-    if (rc == 0) return true;
+    auto options = kLowerdirOption + entry.lowerdir;
+    if (fs_mgr_overlayfs_valid() == OverlayfsValidResult::kOverrideCredsRequired) {
+        options += ",override_creds=off";
+    }
 
-    return false;
+    // Use "overlay-" + entry.blk_device as the mount() source, so that adb-remout-test don't
+    // confuse this with adb remount overlay, whose device name is "overlay".
+    // Overlayfs is a pseudo filesystem, so the source device is a symbolic value and isn't used to
+    // back the filesystem. However the device name would be shown in /proc/mounts.
+    auto source = "overlay-" + entry.blk_device;
+    auto report = "__mount(source=" + source + ",target=" + entry.mount_point + ",type=overlay," +
+                  options + ")=";
+    auto ret = mount(source.c_str(), entry.mount_point.c_str(), "overlay", MS_RDONLY | MS_NOATIME,
+                     options.c_str());
+    if (ret) {
+        PERROR << report << ret;
+        return false;
+    }
+    LINFO << report << ret;
+    return true;
 }
 
 bool fs_mgr_overlayfs_mount_all(Fstab* fstab) {
diff --git a/fs_mgr/fs_mgr_vendor_overlay.cpp b/fs_mgr/fs_mgr_vendor_overlay.cpp
index 830f0dd..1372511 100644
--- a/fs_mgr/fs_mgr_vendor_overlay.cpp
+++ b/fs_mgr/fs_mgr_vendor_overlay.cpp
@@ -92,7 +92,7 @@
     }
     auto report = "__mount(source=overlay,target="s + vendor_mount_point + ",type=overlay," +
                   options + ")=";
-    auto ret = mount("overlay", vendor_mount_point.c_str(), "overlay", MS_RDONLY | MS_RELATIME,
+    auto ret = mount("overlay", vendor_mount_point.c_str(), "overlay", MS_RDONLY | MS_NOATIME,
                      options.c_str());
     if (ret) {
         PERROR << report << ret;
diff --git a/fs_mgr/include/fs_mgr_overlayfs.h b/fs_mgr/include/fs_mgr_overlayfs.h
index ac95ef5..22d12e7 100644
--- a/fs_mgr/include/fs_mgr_overlayfs.h
+++ b/fs_mgr/include/fs_mgr_overlayfs.h
@@ -27,7 +27,7 @@
 android::fs_mgr::Fstab fs_mgr_overlayfs_candidate_list(const android::fs_mgr::Fstab& fstab);
 
 bool fs_mgr_overlayfs_mount_all(android::fs_mgr::Fstab* fstab);
-bool fs_mgr_overlayfs_mount_fstab_entry (const std::string& lowers, const std::string& mount_point);
+bool fs_mgr_overlayfs_mount_fstab_entry(const android::fs_mgr::FstabEntry& entry);
 std::vector<std::string> fs_mgr_overlayfs_required_devices(android::fs_mgr::Fstab* fstab);
 bool fs_mgr_overlayfs_setup(const char* backing = nullptr, const char* mount_point = nullptr,
                             bool* change = nullptr, bool force = true);
diff --git a/fs_mgr/libdm/dm.cpp b/fs_mgr/libdm/dm.cpp
index d5b8a61..c4874b8 100644
--- a/fs_mgr/libdm/dm.cpp
+++ b/fs_mgr/libdm/dm.cpp
@@ -35,6 +35,10 @@
 
 #include "utility.h"
 
+#ifndef DM_DEFERRED_REMOVE
+#define DM_DEFERRED_REMOVE (1 << 17)
+#endif
+
 namespace android {
 namespace dm {
 
@@ -133,6 +137,25 @@
     return DeleteDevice(name, 0ms);
 }
 
+bool DeviceMapper::DeleteDeviceDeferred(const std::string& name) {
+    struct dm_ioctl io;
+    InitIo(&io, name);
+
+    io.flags |= DM_DEFERRED_REMOVE;
+    if (ioctl(fd_, DM_DEV_REMOVE, &io)) {
+        PLOG(ERROR) << "DM_DEV_REMOVE with DM_DEFERRED_REMOVE failed for [" << name << "]";
+        return false;
+    }
+    return true;
+}
+
+bool DeviceMapper::DeleteDeviceIfExistsDeferred(const std::string& name) {
+    if (GetState(name) == DmDeviceState::INVALID) {
+        return true;
+    }
+    return DeleteDeviceDeferred(name);
+}
+
 static std::string GenerateUuid() {
     uuid_t uuid_bytes;
     uuid_generate(uuid_bytes);
diff --git a/fs_mgr/libdm/dm_test.cpp b/fs_mgr/libdm/dm_test.cpp
index 41d3145..8006db2 100644
--- a/fs_mgr/libdm/dm_test.cpp
+++ b/fs_mgr/libdm/dm_test.cpp
@@ -35,6 +35,7 @@
 #include <libdm/dm.h>
 #include <libdm/loop_control.h>
 #include "test_util.h"
+#include "utility.h"
 
 using namespace std;
 using namespace std::chrono_literals;
@@ -617,3 +618,64 @@
     auto sub_block_device = dm.GetParentBlockDeviceByPath(dev.path());
     ASSERT_EQ(loop.device(), *sub_block_device);
 }
+
+TEST(libdm, DeleteDeviceDeferredNoReferences) {
+    unique_fd tmp(CreateTempFile("file_1", 4096));
+    ASSERT_GE(tmp, 0);
+    LoopDevice loop(tmp, 10s);
+    ASSERT_TRUE(loop.valid());
+
+    DmTable table;
+    ASSERT_TRUE(table.Emplace<DmTargetLinear>(0, 1, loop.device(), 0));
+    ASSERT_TRUE(table.valid());
+    TempDevice dev("libdm-test-dm-linear", table);
+    ASSERT_TRUE(dev.valid());
+
+    DeviceMapper& dm = DeviceMapper::Instance();
+
+    std::string path;
+    ASSERT_TRUE(dm.GetDmDevicePathByName("libdm-test-dm-linear", &path));
+    ASSERT_EQ(0, access(path.c_str(), F_OK));
+
+    ASSERT_TRUE(dm.DeleteDeviceDeferred("libdm-test-dm-linear"));
+
+    ASSERT_TRUE(WaitForFileDeleted(path, 5s));
+    ASSERT_EQ(DmDeviceState::INVALID, dm.GetState("libdm-test-dm-linear"));
+    ASSERT_NE(0, access(path.c_str(), F_OK));
+    ASSERT_EQ(ENOENT, errno);
+}
+
+TEST(libdm, DeleteDeviceDeferredWaitsForLastReference) {
+    unique_fd tmp(CreateTempFile("file_1", 4096));
+    ASSERT_GE(tmp, 0);
+    LoopDevice loop(tmp, 10s);
+    ASSERT_TRUE(loop.valid());
+
+    DmTable table;
+    ASSERT_TRUE(table.Emplace<DmTargetLinear>(0, 1, loop.device(), 0));
+    ASSERT_TRUE(table.valid());
+    TempDevice dev("libdm-test-dm-linear", table);
+    ASSERT_TRUE(dev.valid());
+
+    DeviceMapper& dm = DeviceMapper::Instance();
+
+    std::string path;
+    ASSERT_TRUE(dm.GetDmDevicePathByName("libdm-test-dm-linear", &path));
+    ASSERT_EQ(0, access(path.c_str(), F_OK));
+
+    {
+        // Open a reference to block device.
+        unique_fd fd(TEMP_FAILURE_RETRY(open(dev.path().c_str(), O_RDONLY | O_CLOEXEC)));
+        ASSERT_GE(fd.get(), 0);
+
+        ASSERT_TRUE(dm.DeleteDeviceDeferred("libdm-test-dm-linear"));
+
+        ASSERT_EQ(0, access(path.c_str(), F_OK));
+    }
+
+    // After release device will be removed.
+    ASSERT_TRUE(WaitForFileDeleted(path, 5s));
+    ASSERT_EQ(DmDeviceState::INVALID, dm.GetState("libdm-test-dm-linear"));
+    ASSERT_NE(0, access(path.c_str(), F_OK));
+    ASSERT_EQ(ENOENT, errno);
+}
diff --git a/fs_mgr/libdm/include/libdm/dm.h b/fs_mgr/libdm/include/libdm/dm.h
index 5d6db46..70b14fa 100644
--- a/fs_mgr/libdm/include/libdm/dm.h
+++ b/fs_mgr/libdm/include/libdm/dm.h
@@ -95,6 +95,12 @@
     bool DeleteDevice(const std::string& name, const std::chrono::milliseconds& timeout_ms);
     bool DeleteDeviceIfExists(const std::string& name, const std::chrono::milliseconds& timeout_ms);
 
+    // Enqueues a deletion of device mapper device with the given name once last reference is
+    // closed.
+    // Returns 'true' on success, false otherwise.
+    bool DeleteDeviceDeferred(const std::string& name);
+    bool DeleteDeviceIfExistsDeferred(const std::string& name);
+
     // Fetches and returns the complete state of the underlying device mapper
     // device with given name.
     std::optional<Info> GetDetailedInfo(const std::string& name) const;
diff --git a/fs_mgr/libsnapshot/cow_snapuserd_test.cpp b/fs_mgr/libsnapshot/cow_snapuserd_test.cpp
index 3888eb1..767cd04 100644
--- a/fs_mgr/libsnapshot/cow_snapuserd_test.cpp
+++ b/fs_mgr/libsnapshot/cow_snapuserd_test.cpp
@@ -103,6 +103,7 @@
     void ReadSnapshotDeviceAndValidate();
     void Shutdown();
     void MergeInterrupt();
+    void ReadDmUserBlockWithoutDaemon();
 
     std::string snapshot_dev() const { return snapshot_dev_->path(); }
 
@@ -481,6 +482,36 @@
     ASSERT_TRUE(android::fs_mgr::WaitForFile(misc_device, 10s));
 }
 
+void CowSnapuserdTest::ReadDmUserBlockWithoutDaemon() {
+    DmTable dmuser_table;
+    std::string dm_user_name = "dm-test-device";
+    unique_fd fd;
+
+    // Create a dm-user block device
+    ASSERT_TRUE(dmuser_table.AddTarget(std::make_unique<DmTargetUser>(0, 123456, dm_user_name)));
+    ASSERT_TRUE(dmuser_table.valid());
+
+    dmuser_dev_ = std::make_unique<TempDevice>(dm_user_name, dmuser_table);
+    ASSERT_TRUE(dmuser_dev_->valid());
+    ASSERT_FALSE(dmuser_dev_->path().empty());
+
+    fd.reset(open(dmuser_dev_->path().c_str(), O_RDONLY));
+    ASSERT_GE(fd, 0);
+
+    std::unique_ptr<uint8_t[]> buffer = std::make_unique<uint8_t[]>(1_MiB);
+
+    loff_t offset = 0;
+    // Every IO should fail as there is no daemon to process the IO
+    for (size_t j = 0; j < 10; j++) {
+        ASSERT_EQ(ReadFullyAtOffset(fd, (char*)buffer.get() + offset, BLOCK_SZ, offset), false);
+
+        offset += BLOCK_SZ;
+    }
+
+    fd = {};
+    ASSERT_TRUE(dmuser_dev_->Destroy());
+}
+
 void CowSnapuserdTest::InitDaemon() {
     bool ok = client_->AttachDmUser(system_device_ctrl_name_);
     ASSERT_TRUE(ok);
@@ -909,6 +940,11 @@
     harness.Shutdown();
 }
 
+TEST(Snapuserd_Test, ReadDmUserBlockWithoutDaemon) {
+    CowSnapuserdTest harness;
+    harness.ReadDmUserBlockWithoutDaemon();
+}
+
 }  // namespace snapshot
 }  // namespace android
 
diff --git a/fs_mgr/libsnapshot/snapshotctl.cpp b/fs_mgr/libsnapshot/snapshotctl.cpp
index 5eb2003..67189d4 100644
--- a/fs_mgr/libsnapshot/snapshotctl.cpp
+++ b/fs_mgr/libsnapshot/snapshotctl.cpp
@@ -36,7 +36,9 @@
                  "  dump\n"
                  "    Print snapshot states.\n"
                  "  merge\n"
-                 "    Deprecated.\n";
+                 "    Deprecated.\n"
+                 "  map\n"
+                 "    Map all partitions at /dev/block/mapper\n";
     return EX_USAGE;
 }
 
diff --git a/fs_mgr/libsnapshot/snapuserd.h b/fs_mgr/libsnapshot/snapuserd.h
index 0a5ab50..212c78e 100644
--- a/fs_mgr/libsnapshot/snapuserd.h
+++ b/fs_mgr/libsnapshot/snapuserd.h
@@ -99,6 +99,7 @@
     struct dm_user_header* GetHeaderPtr();
     bool ReturnData(void*, size_t) override { return true; }
     void ResetBufferOffset() { buffer_offset_ = 0; }
+    void* GetPayloadBufPtr();
 
   private:
     std::unique_ptr<uint8_t[]> buffer_;
@@ -171,7 +172,7 @@
     bool DmuserReadRequest();
     bool DmuserWriteRequest();
     bool ReadDmUserPayload(void* buffer, size_t size);
-    bool WriteDmUserPayload(size_t size);
+    bool WriteDmUserPayload(size_t size, bool header_response);
 
     bool ReadDiskExceptions(chunk_t chunk, size_t size);
     bool ZerofillDiskExceptions(size_t read_size);
diff --git a/fs_mgr/libsnapshot/snapuserd_worker.cpp b/fs_mgr/libsnapshot/snapuserd_worker.cpp
index 7e0f493..682f9da 100644
--- a/fs_mgr/libsnapshot/snapuserd_worker.cpp
+++ b/fs_mgr/libsnapshot/snapuserd_worker.cpp
@@ -65,6 +65,12 @@
     return header;
 }
 
+void* BufferSink::GetPayloadBufPtr() {
+    char* buffer = reinterpret_cast<char*>(GetBufPtr());
+    struct dm_user_message* msg = reinterpret_cast<struct dm_user_message*>(&(buffer[0]));
+    return msg->payload.buf;
+}
+
 WorkerThread::WorkerThread(const std::string& cow_device, const std::string& backing_device,
                            const std::string& control_device, const std::string& misc_name,
                            std::shared_ptr<Snapuserd> snapuserd) {
@@ -241,6 +247,12 @@
         char* buffer = reinterpret_cast<char*>(bufsink_.GetBufPtr());
         struct dm_user_message* msg = (struct dm_user_message*)(&(buffer[0]));
 
+        if (skip_sector_size == BLOCK_SZ) {
+            SNAP_LOG(ERROR) << "Invalid un-aligned IO request at sector: " << sector
+                            << " Base-sector: " << it->first;
+            return -1;
+        }
+
         memmove(msg->payload.buf, (char*)msg->payload.buf + skip_sector_size,
                 (BLOCK_SZ - skip_sector_size));
     }
@@ -315,16 +327,30 @@
     }
 
     int num_ops = DIV_ROUND_UP(size, BLOCK_SZ);
+    sector_t read_sector = sector;
     while (num_ops) {
-        if (!ProcessCowOp(it->second)) {
+        // We have to make sure that the reads are
+        // sequential; there shouldn't be a data
+        // request merged with a metadata IO.
+        if (it->first != read_sector) {
+            SNAP_LOG(ERROR) << "Invalid IO request: read_sector: " << read_sector
+                            << " cow-op sector: " << it->first;
+            return -1;
+        } else if (!ProcessCowOp(it->second)) {
             return -1;
         }
         num_ops -= 1;
+        read_sector += (BLOCK_SZ >> SECTOR_SHIFT);
+
         it++;
+
+        if (it == chunk_vec.end() && num_ops) {
+            SNAP_LOG(ERROR) << "Invalid IO request at sector " << sector
+                            << " COW ops completed; pending read-request: " << num_ops;
+            return -1;
+        }
         // Update the buffer offset
         bufsink_.UpdateBufferOffset(BLOCK_SZ);
-
-        SNAP_LOG(DEBUG) << "ReadData at sector: " << sector << " size: " << size;
     }
 
     // Reset the buffer offset
@@ -589,6 +615,7 @@
         if (errno != ENOTBLK) {
             SNAP_PLOG(ERROR) << "Control-read failed";
         }
+
         return false;
     }
 
@@ -596,10 +623,16 @@
 }
 
 // Send the payload/data back to dm-user misc device.
-bool WorkerThread::WriteDmUserPayload(size_t size) {
-    if (!android::base::WriteFully(ctrl_fd_, bufsink_.GetBufPtr(),
-                                   sizeof(struct dm_user_header) + size)) {
-        SNAP_PLOG(ERROR) << "Write to dm-user failed size: " << size;
+bool WorkerThread::WriteDmUserPayload(size_t size, bool header_response) {
+    size_t payload_size = size;
+    void* buf = bufsink_.GetPayloadBufPtr();
+    if (header_response) {
+        payload_size += sizeof(struct dm_user_header);
+        buf = bufsink_.GetBufPtr();
+    }
+
+    if (!android::base::WriteFully(ctrl_fd_, buf, payload_size)) {
+        SNAP_PLOG(ERROR) << "Write to dm-user failed size: " << payload_size;
         return false;
     }
 
@@ -634,12 +667,13 @@
     // to flush per se; hence, just respond back with a success message.
     if (header->sector == 0) {
         if (!(header->len == 0)) {
+            SNAP_LOG(ERROR) << "Invalid header length received from sector 0: " << header->len;
             header->type = DM_USER_RESP_ERROR;
         } else {
             header->type = DM_USER_RESP_SUCCESS;
         }
 
-        if (!WriteDmUserPayload(0)) {
+        if (!WriteDmUserPayload(0, true)) {
             return false;
         }
         return true;
@@ -681,7 +715,7 @@
         header->type = DM_USER_RESP_ERROR;
     }
 
-    if (!WriteDmUserPayload(0)) {
+    if (!WriteDmUserPayload(0, true)) {
         return false;
     }
 
@@ -694,6 +728,7 @@
     loff_t offset = 0;
     sector_t sector = header->sector;
     std::vector<std::pair<sector_t, const CowOperation*>>& chunk_vec = snapuserd_->GetChunkVec();
+    bool header_response = true;
     do {
         size_t read_size = std::min(PAYLOAD_SIZE, remaining_size);
 
@@ -707,8 +742,13 @@
         // never see multiple IO requests. Additionally this IO
         // will always be a single 4k.
         if (header->sector == 0) {
-            ConstructKernelCowHeader();
-            SNAP_LOG(DEBUG) << "Kernel header constructed";
+            if (read_size == BLOCK_SZ) {
+                ConstructKernelCowHeader();
+                SNAP_LOG(DEBUG) << "Kernel header constructed";
+            } else {
+                SNAP_LOG(ERROR) << "Invalid read_size: " << read_size << " for sector 0";
+                header->type = DM_USER_RESP_ERROR;
+            }
         } else {
             auto it = std::lower_bound(chunk_vec.begin(), chunk_vec.end(),
                                        std::make_pair(header->sector, nullptr), Snapuserd::compare);
@@ -724,6 +764,7 @@
                 }
             } else {
                 chunk_t num_sectors_read = (offset >> SECTOR_SHIFT);
+
                 ret = ReadData(sector + num_sectors_read, read_size);
                 if (ret < 0) {
                     SNAP_LOG(ERROR) << "ReadData failed for chunk id: " << chunk
@@ -739,12 +780,19 @@
 
         // Just return the header if it is an error
         if (header->type == DM_USER_RESP_ERROR) {
+            SNAP_LOG(ERROR) << "IO read request failed...";
             ret = 0;
         }
 
+        if (!header_response) {
+            CHECK(header->type == DM_USER_RESP_SUCCESS)
+                    << " failed for sector: " << sector << " header->len: " << header->len
+                    << " remaining_size: " << remaining_size;
+        }
+
         // Daemon will not be terminated if there is any error. We will
         // just send the error back to dm-user.
-        if (!WriteDmUserPayload(ret)) {
+        if (!WriteDmUserPayload(ret, header_response)) {
             return false;
         }
 
@@ -754,6 +802,7 @@
 
         remaining_size -= ret;
         offset += ret;
+        header_response = false;
     } while (remaining_size > 0);
 
     return true;
@@ -799,11 +848,11 @@
         return false;
     }
 
-    SNAP_LOG(DEBUG) << "msg->seq: " << std::hex << header->seq;
-    SNAP_LOG(DEBUG) << "msg->type: " << std::hex << header->type;
-    SNAP_LOG(DEBUG) << "msg->flags: " << std::hex << header->flags;
-    SNAP_LOG(DEBUG) << "msg->sector: " << std::hex << header->sector;
-    SNAP_LOG(DEBUG) << "msg->len: " << std::hex << header->len;
+    SNAP_LOG(DEBUG) << "Daemon: msg->seq: " << std::dec << header->seq;
+    SNAP_LOG(DEBUG) << "Daemon: msg->len: " << std::dec << header->len;
+    SNAP_LOG(DEBUG) << "Daemon: msg->sector: " << std::dec << header->sector;
+    SNAP_LOG(DEBUG) << "Daemon: msg->type: " << std::dec << header->type;
+    SNAP_LOG(DEBUG) << "Daemon: msg->flags: " << std::dec << header->flags;
 
     switch (header->type) {
         case DM_USER_REQ_MAP_READ: {
diff --git a/fs_mgr/tests/adb-remount-test.sh b/fs_mgr/tests/adb-remount-test.sh
index 242fa93..0c5fe3d 100755
--- a/fs_mgr/tests/adb-remount-test.sh
+++ b/fs_mgr/tests/adb-remount-test.sh
@@ -735,23 +735,46 @@
   fi
 }
 
+[ "USAGE: join_with <delimiter> <strings>
+
+Joins strings with delimiter" ]
+join_with() {
+  if [ "${#}" -lt 2 ]; then
+    echo
+    return
+  fi
+  local delimiter="${1}"
+  local result="${2}"
+  shift 2
+  for element in "${@}"; do
+    result+="${delimiter}${element}"
+  done
+  echo "${result}"
+}
+
 [ "USAGE: skip_administrative_mounts [data] < /proc/mounts
 
 Filters out all administrative (eg: sysfs) mounts uninteresting to the test" ]
 skip_administrative_mounts() {
+  local exclude_filesystems=(
+    "overlay" "tmpfs" "none" "sysfs" "proc" "selinuxfs" "debugfs" "bpf"
+    "binfmt_misc" "cg2_bpf" "pstore" "tracefs" "adb" "mtp" "ptp" "devpts"
+    "ramdumpfs" "binder" "securityfs" "functionfs" "rootfs"
+  )
+  local exclude_devices=(
+    "[/]sys[/]kernel[/]debug" "[/]data[/]media" "[/]dev[/]block[/]loop[0-9]*"
+    "${exclude_filesystems[@]}"
+  )
+  local exclude_mount_points=(
+    "[/]cache" "[/]mnt[/]scratch" "[/]mnt[/]vendor[/]persist" "[/]persist"
+    "[/]metadata"
+  )
   if [ "data" = "${1}" ]; then
-    grep -v " /data "
-  else
-    cat -
-  fi |
-  grep -v \
-    -e "^\(overlay\|tmpfs\|none\|sysfs\|proc\|selinuxfs\|debugfs\|bpf\) " \
-    -e "^\(binfmt_misc\|cg2_bpf\|pstore\|tracefs\|adb\|mtp\|ptp\|devpts\) " \
-    -e "^\(ramdumpfs\|binder\|/sys/kernel/debug\|securityfs\) " \
-    -e " functionfs " \
-    -e "^\(/data/media\|/dev/block/loop[0-9]*\) " \
-    -e "^rootfs / rootfs rw," \
-    -e " /\(cache\|mnt/scratch\|mnt/vendor/persist\|persist\|metadata\) "
+    exclude_mount_points+=("[/]data")
+  fi
+  awk '$1 !~ /^('"$(join_with "|" "${exclude_devices[@]}")"')$/ &&
+      $2 !~ /^('"$(join_with "|" "${exclude_mount_points[@]}")"')$/ &&
+      $3 !~ /^('"$(join_with "|" "${exclude_filesystems[@]}")"')$/'
 }
 
 [ "USAGE: skip_unrelated_mounts < /proc/mounts
@@ -907,9 +930,11 @@
 
 # Acquire list of system partitions
 
+# KISS (assume system partition mount point is "/<partition name>")
 PARTITIONS=`adb_su cat /vendor/etc/fstab* </dev/null |
+              grep -v "^[#${SPACE}${TAB}]" |
               skip_administrative_mounts |
-              sed -n "s@^\([^ ${TAB}/][^ ${TAB}/]*\)[ ${TAB}].*[, ${TAB}]ro[, ${TAB}].*@\1@p" |
+              awk '$1 ~ /^[^/]+$/ && "/"$1 == $2 && $4 ~ /(^|,)ro(,|$)/ { print $1 }' |
               sort -u |
               tr '\n' ' '`
 PARTITIONS="${PARTITIONS:-system vendor}"
diff --git a/init/README.ueventd.md b/init/README.ueventd.md
index d22f68f..76f5193 100644
--- a/init/README.ueventd.md
+++ b/init/README.ueventd.md
@@ -123,7 +123,10 @@
 The exact firmware file to be served can be customized by running an external program by a
 `external_firmware_handler` line in a ueventd.rc file. This line takes the format of
 
-    external_firmware_handler <devpath> <user name to run as> <path to external program>
+    external_firmware_handler <devpath> <user [group]> <path to external program>
+
+The handler will be run as the given user, or if a group is provided, as the given user and group.
+
 For example
 
     external_firmware_handler /devices/leds/red/firmware/coeffs.bin system /vendor/bin/led_coeffs.bin
diff --git a/init/firmware_handler.cpp b/init/firmware_handler.cpp
index bdc2922..30e808d 100644
--- a/init/firmware_handler.cpp
+++ b/init/firmware_handler.cpp
@@ -19,6 +19,7 @@
 #include <fcntl.h>
 #include <fnmatch.h>
 #include <glob.h>
+#include <grp.h>
 #include <pwd.h>
 #include <signal.h>
 #include <stdlib.h>
@@ -81,9 +82,9 @@
     return access("/dev/.booting", F_OK) == 0;
 }
 
-ExternalFirmwareHandler::ExternalFirmwareHandler(std::string devpath, uid_t uid,
+ExternalFirmwareHandler::ExternalFirmwareHandler(std::string devpath, uid_t uid, gid_t gid,
                                                  std::string handler_path)
-    : devpath(std::move(devpath)), uid(uid), handler_path(std::move(handler_path)) {
+    : devpath(std::move(devpath)), uid(uid), gid(gid), 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) {
@@ -97,13 +98,17 @@
     }
 }
 
+ExternalFirmwareHandler::ExternalFirmwareHandler(std::string devpath, uid_t uid,
+                                                 std::string handler_path)
+    : ExternalFirmwareHandler(devpath, uid, 0, handler_path) {}
+
 FirmwareHandler::FirmwareHandler(std::vector<std::string> firmware_directories,
                                  std::vector<ExternalFirmwareHandler> external_firmware_handlers)
     : firmware_directories_(std::move(firmware_directories)),
       external_firmware_handlers_(std::move(external_firmware_handlers)) {}
 
 Result<std::string> FirmwareHandler::RunExternalHandler(const std::string& handler, uid_t uid,
-                                                        const Uevent& uevent) const {
+                                                        gid_t gid, const Uevent& uevent) const {
     unique_fd child_stdout;
     unique_fd parent_stdout;
     if (!Socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, &child_stdout, &parent_stdout)) {
@@ -140,6 +145,13 @@
         }
         c_args.emplace_back(nullptr);
 
+        if (gid != 0) {
+            if (setgid(gid) != 0) {
+                fprintf(stderr, "setgid() failed: %s", strerror(errno));
+                _exit(EXIT_FAILURE);
+            }
+        }
+
         if (setuid(uid) != 0) {
             fprintf(stderr, "setuid() failed: %s", strerror(errno));
             _exit(EXIT_FAILURE);
@@ -196,8 +208,8 @@
                       << "' for devpath: '" << uevent.path << "' firmware: '" << uevent.firmware
                       << "'";
 
-            auto result =
-                    RunExternalHandler(external_handler.handler_path, external_handler.uid, uevent);
+            auto result = RunExternalHandler(external_handler.handler_path, external_handler.uid,
+                                             external_handler.gid, uevent);
             if (!result.ok()) {
                 LOG(ERROR) << "Using default firmware; External firmware handler failed: "
                            << result.error();
diff --git a/init/firmware_handler.h b/init/firmware_handler.h
index 3c35b1f..d2f7347 100644
--- a/init/firmware_handler.h
+++ b/init/firmware_handler.h
@@ -16,6 +16,7 @@
 
 #pragma once
 
+#include <grp.h>
 #include <pwd.h>
 
 #include <functional>
@@ -31,9 +32,11 @@
 
 struct ExternalFirmwareHandler {
     ExternalFirmwareHandler(std::string devpath, uid_t uid, std::string handler_path);
+    ExternalFirmwareHandler(std::string devpath, uid_t uid, gid_t gid, std::string handler_path);
 
     std::string devpath;
     uid_t uid;
+    gid_t gid;
     std::string handler_path;
 
     std::function<bool(const std::string&)> match;
@@ -51,7 +54,7 @@
     friend void FirmwareTestWithExternalHandler(const std::string& test_name,
                                                 bool expect_new_firmware);
 
-    Result<std::string> RunExternalHandler(const std::string& handler, uid_t uid,
+    Result<std::string> RunExternalHandler(const std::string& handler, uid_t uid, gid_t gid,
                                            const Uevent& uevent) const;
     std::string GetFirmwarePath(const Uevent& uevent) const;
     void ProcessFirmwareEvent(const std::string& root, const std::string& firmware) const;
diff --git a/init/first_stage_mount.cpp b/init/first_stage_mount.cpp
index a733839..616d285 100644
--- a/init/first_stage_mount.cpp
+++ b/init/first_stage_mount.cpp
@@ -331,12 +331,6 @@
     if (devices.empty()) {
         return true;
     }
-    // excluding overlays
-    for (auto iter = devices.begin(); iter != devices.end(); ) {
-        if (*iter=="overlay")  iter = devices.erase(iter);
-        else iter++;
-    }
-
     return block_dev_init_.InitDevices(std::move(devices));
 }
 
@@ -548,6 +542,7 @@
             continue;
         }
 
+        // Handle overlayfs entries later.
         if (current->fs_type == "overlay") {
             ++current;
             continue;
@@ -577,6 +572,12 @@
         current = end;
     }
 
+    for (const auto& entry : fstab_) {
+        if (entry.fs_type == "overlay") {
+            fs_mgr_overlayfs_mount_fstab_entry(entry);
+        }
+    }
+
     // If we don't see /system or / in the fstab, then we need to create an root entry for
     // overlayfs.
     if (!GetEntryForMountPoint(&fstab_, "/system") && !GetEntryForMountPoint(&fstab_, "/")) {
@@ -602,13 +603,6 @@
     };
     MapScratchPartitionIfNeeded(&fstab_, init_devices);
 
-    for (auto current = fstab_.begin(); current != fstab_.end(); ) {
-        if (current->fs_type == "overlay") {
-            fs_mgr_overlayfs_mount_fstab_entry(current->lowerdir, current->mount_point);
-        }
-        ++current;
-    }
-
     fs_mgr_overlayfs_mount_all(&fstab_);
 
     return true;
@@ -695,6 +689,10 @@
     // Includes the partition names of fstab records.
     // Notes that fstab_rec->blk_device has A/B suffix updated by fs_mgr when A/B is used.
     for (const auto& fstab_entry : fstab_) {
+        // Skip pseudo filesystems.
+        if (fstab_entry.fs_type == "overlay") {
+            continue;
+        }
         if (!fstab_entry.fs_mgr_flags.logical) {
             devices->emplace(basename(fstab_entry.blk_device.c_str()));
         }
@@ -757,6 +755,10 @@
         if (fstab_entry.fs_mgr_flags.avb) {
             need_dm_verity_ = true;
         }
+        // Skip pseudo filesystems.
+        if (fstab_entry.fs_type == "overlay") {
+            continue;
+        }
         if (fstab_entry.fs_mgr_flags.logical) {
             // Don't try to find logical partitions via uevent regeneration.
             logical_partitions.emplace(basename(fstab_entry.blk_device.c_str()));
diff --git a/init/reboot.cpp b/init/reboot.cpp
index ab0e48e..0e788e4 100644
--- a/init/reboot.cpp
+++ b/init/reboot.cpp
@@ -478,6 +478,11 @@
     // cut the last "\n"
     backing_dev.erase(backing_dev.length() - 1);
 
+    if (android::base::StartsWith(backing_dev, "none")) {
+        LOG(INFO) << "No zram backing device configured";
+        return {};
+    }
+
     // shutdown zram handle
     Timer swap_timer;
     LOG(INFO) << "swapoff() start...";
diff --git a/init/ueventd_parser.cpp b/init/ueventd_parser.cpp
index 2221228..9a14406 100644
--- a/init/ueventd_parser.cpp
+++ b/init/ueventd_parser.cpp
@@ -101,8 +101,8 @@
 Result<void> ParseExternalFirmwareHandlerLine(
         std::vector<std::string>&& args,
         std::vector<ExternalFirmwareHandler>* external_firmware_handlers) {
-    if (args.size() != 4) {
-        return Error() << "external_firmware_handler lines must have exactly 3 parameters";
+    if (args.size() != 4 && args.size() != 5) {
+        return Error() << "external_firmware_handler lines must have 3 or 4 parameters";
     }
 
     if (std::find_if(external_firmware_handlers->begin(), external_firmware_handlers->end(),
@@ -117,7 +117,19 @@
         return ErrnoError() << "invalid handler uid'" << args[2] << "'";
     }
 
-    ExternalFirmwareHandler handler(std::move(args[1]), pwd->pw_uid, std::move(args[3]));
+    gid_t gid = 0;
+    int handler_index = 3;
+    if (args.size() == 5) {
+        struct group* grp = getgrnam(args[3].c_str());
+        if (!grp) {
+            return ErrnoError() << "invalid handler gid '" << args[3] << "'";
+        }
+        gid = grp->gr_gid;
+        handler_index = 4;
+    }
+
+    ExternalFirmwareHandler handler(std::move(args[1]), pwd->pw_uid, gid,
+                                    std::move(args[handler_index]));
     external_firmware_handlers->emplace_back(std::move(handler));
 
     return {};
diff --git a/init/ueventd_parser_test.cpp b/init/ueventd_parser_test.cpp
index c5aa9e3..d77cb03 100644
--- a/init/ueventd_parser_test.cpp
+++ b/init/ueventd_parser_test.cpp
@@ -49,6 +49,7 @@
                                  const ExternalFirmwareHandler& test) {
     EXPECT_EQ(expected.devpath, test.devpath) << expected.devpath;
     EXPECT_EQ(expected.uid, test.uid) << expected.uid;
+    EXPECT_EQ(expected.gid, test.gid) << expected.gid;
     EXPECT_EQ(expected.handler_path, test.handler_path) << expected.handler_path;
 }
 
@@ -157,39 +158,59 @@
 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"
+external_firmware_handler /devices/path/firmware/something003.bin system system /vendor/bin/firmware_handler.sh
+external_firmware_handler /devices/path/firmware/something004.bin radio radio "/vendor/bin/firmware_handler.sh --has --arguments"
 )";
 
     auto external_firmware_handlers = std::vector<ExternalFirmwareHandler>{
             {
                     "devpath",
                     AID_ROOT,
+                    AID_ROOT,
                     "handler_path",
             },
             {
                     "/devices/path/firmware/something001.bin",
                     AID_SYSTEM,
+                    AID_ROOT,
                     "/vendor/bin/firmware_handler.sh",
             },
             {
                     "/devices/path/firmware/something002.bin",
                     AID_RADIO,
+                    AID_ROOT,
                     "/vendor/bin/firmware_handler.sh --has --arguments",
             },
             {
                     "/devices/path/firmware/",
                     AID_ROOT,
+                    AID_ROOT,
                     "/vendor/bin/firmware_handler.sh",
             },
             {
                     "/devices/path/firmware/something",
                     AID_SYSTEM,
+                    AID_ROOT,
                     "/vendor/bin/firmware_handler.sh",
             },
             {
                     "/devices/path/*/firmware/something*.bin",
                     AID_RADIO,
+                    AID_ROOT,
                     "/vendor/bin/firmware_handler.sh",
             },
+            {
+                    "/devices/path/firmware/something003.bin",
+                    AID_SYSTEM,
+                    AID_SYSTEM,
+                    "/vendor/bin/firmware_handler.sh",
+            },
+            {
+                    "/devices/path/firmware/something004.bin",
+                    AID_RADIO,
+                    AID_RADIO,
+                    "/vendor/bin/firmware_handler.sh --has --arguments",
+            },
     };
 
     TestUeventdFile(ueventd_file, {{}, {}, {}, {}, external_firmware_handlers});
@@ -205,6 +226,7 @@
             {
                     "devpath",
                     AID_ROOT,
+                    AID_ROOT,
                     "handler_path",
             },
     };
@@ -305,7 +327,7 @@
     };
 
     auto external_firmware_handlers = std::vector<ExternalFirmwareHandler>{
-            {"/devices/path/firmware/firmware001.bin", AID_ROOT, "/vendor/bin/touch.sh"},
+            {"/devices/path/firmware/firmware001.bin", AID_ROOT, AID_ROOT, "/vendor/bin/touch.sh"},
     };
 
     size_t uevent_socket_rcvbuf_size = 6 * 1024 * 1024;
diff --git a/libutils/Timers.cpp b/libutils/Timers.cpp
index fd3f4a9..4cfac57 100644
--- a/libutils/Timers.cpp
+++ b/libutils/Timers.cpp
@@ -14,9 +14,6 @@
  * limitations under the License.
  */
 
-//
-// Timer functions.
-//
 #include <utils/Timers.h>
 
 #include <limits.h>
@@ -24,11 +21,12 @@
 #include <time.h>
 
 #include <android-base/macros.h>
+#include <utils/Log.h>
 
 static constexpr size_t clock_id_max = 5;
 
 static void checkClockId(int clock) {
-    if (clock < 0 || clock >= clock_id_max) abort();
+    LOG_ALWAYS_FATAL_IF(clock < 0 || clock >= clock_id_max, "invalid clock id");
 }
 
 #if defined(__linux__)
@@ -56,18 +54,10 @@
 }
 #endif
 
-int toMillisecondTimeoutDelay(nsecs_t referenceTime, nsecs_t timeoutTime)
-{
-    nsecs_t timeoutDelayMillis;
-    if (timeoutTime > referenceTime) {
-        uint64_t timeoutDelay = uint64_t(timeoutTime - referenceTime);
-        if (timeoutDelay > uint64_t((INT_MAX - 1) * 1000000LL)) {
-            timeoutDelayMillis = -1;
-        } else {
-            timeoutDelayMillis = (timeoutDelay + 999999LL) / 1000000LL;
-        }
-    } else {
-        timeoutDelayMillis = 0;
-    }
-    return (int)timeoutDelayMillis;
+int toMillisecondTimeoutDelay(nsecs_t referenceTime, nsecs_t timeoutTime) {
+    if (timeoutTime <= referenceTime) return 0;
+
+    uint64_t timeoutDelay = uint64_t(timeoutTime - referenceTime);
+    if (timeoutDelay > uint64_t((INT_MAX - 1) * 1000000LL)) return -1;
+    return (timeoutDelay + 999999LL) / 1000000LL;
 }
diff --git a/libutils/Timers_test.cpp b/libutils/Timers_test.cpp
index ec0051e..c0a6d49 100644
--- a/libutils/Timers_test.cpp
+++ b/libutils/Timers_test.cpp
@@ -27,3 +27,12 @@
     systemTime(SYSTEM_TIME_BOOTTIME);
     EXPECT_EXIT(systemTime(SYSTEM_TIME_BOOTTIME + 1), testing::KilledBySignal(SIGABRT), "");
 }
+
+TEST(Timers, toMillisecondTimeoutDelay) {
+    EXPECT_EQ(0, toMillisecondTimeoutDelay(100, 100));
+    EXPECT_EQ(0, toMillisecondTimeoutDelay(100, 10));
+
+    EXPECT_EQ(-1, toMillisecondTimeoutDelay(0, INT_MAX * 1000000LL));
+
+    EXPECT_EQ(123, toMillisecondTimeoutDelay(0, 123000000));
+}
diff --git a/libutils/include/utils/KeyedVector.h b/libutils/include/utils/KeyedVector.h
index 7bda99b..5cf7a11 100644
--- a/libutils/include/utils/KeyedVector.h
+++ b/libutils/include/utils/KeyedVector.h
@@ -47,7 +47,7 @@
 
     inline  void            clear()                     { mVector.clear(); }
 
-    /*! 
+    /*!
      * vector stats
      */
 
@@ -63,14 +63,14 @@
     // returns true if the arguments is known to be identical to this vector
     inline bool isIdenticalTo(const KeyedVector& rhs) const;
 
-    /*! 
+    /*!
      * accessors
      */
-            const VALUE&    valueFor(const KEY& key) const;
-            const VALUE&    valueAt(size_t index) const;
-            const KEY&      keyAt(size_t index) const;
-            ssize_t         indexOfKey(const KEY& key) const;
-            const VALUE&    operator[] (size_t index) const;
+    const VALUE& valueFor(const KEY& key) const;
+    const VALUE& valueAt(size_t index) const;
+    const KEY& keyAt(size_t index) const;
+    ssize_t indexOfKey(const KEY& key) const;
+    const VALUE& operator[](size_t index) const;
 
     /*!
      * modifying the array
@@ -79,10 +79,10 @@
             VALUE&          editValueFor(const KEY& key);
             VALUE&          editValueAt(size_t index);
 
-            /*! 
+            /*!
              * add/insert/replace items
              */
-             
+
             ssize_t         add(const KEY& key, const VALUE& item);
             ssize_t         replaceValueFor(const KEY& key, const VALUE& item);
             ssize_t         replaceValueAt(size_t index, const VALUE& item);
@@ -93,7 +93,7 @@
 
             ssize_t         removeItem(const KEY& key);
             ssize_t         removeItemsAt(size_t index, size_t count = 1);
-            
+
 private:
             SortedVector< key_value_pair_t<KEY, VALUE> >    mVector;
 };
@@ -208,7 +208,7 @@
 template<typename KEY, typename VALUE> inline
 const VALUE& DefaultKeyedVector<KEY,VALUE>::valueFor(const KEY& key) const {
     ssize_t i = this->indexOfKey(key);
-    return i >= 0 ? KeyedVector<KEY,VALUE>::valueAt(i) : mDefault;
+    return i >= 0 ? KeyedVector<KEY, VALUE>::valueAt(static_cast<size_t>(i)) : mDefault;
 }
 
 }  // namespace android