diff --git a/debuggerd/libdebuggerd/tombstone_proto.cpp b/debuggerd/libdebuggerd/tombstone_proto.cpp
index 74f9a8c..4cde986 100644
--- a/debuggerd/libdebuggerd/tombstone_proto.cpp
+++ b/debuggerd/libdebuggerd/tombstone_proto.cpp
@@ -203,7 +203,7 @@
 }
 
 static void dump_probable_cause(Tombstone* tombstone, unwindstack::AndroidUnwinder* unwinder,
-                                const ProcessInfo& process_info, const ThreadInfo& main_thread) {
+                                const ProcessInfo& process_info, const ThreadInfo& target_thread) {
 #if defined(USE_SCUDO)
   ScudoCrashData scudo_crash_data(unwinder->GetProcessMemory().get(), process_info);
   if (scudo_crash_data.CrashIsMine()) {
@@ -213,13 +213,13 @@
 #endif
 
   GwpAsanCrashData gwp_asan_crash_data(unwinder->GetProcessMemory().get(), process_info,
-                                       main_thread);
+                                       target_thread);
   if (gwp_asan_crash_data.CrashIsMine()) {
     gwp_asan_crash_data.AddCauseProtos(tombstone, unwinder);
     return;
   }
 
-  const siginfo *si = main_thread.siginfo;
+  const siginfo *si = target_thread.siginfo;
   auto fault_addr = reinterpret_cast<uint64_t>(si->si_addr);
   unwindstack::Maps* maps = unwinder->GetMaps();
 
@@ -238,14 +238,14 @@
     } else if (fault_addr == 0xffff0f60) {
       cause = "call to kuser_cmpxchg64";
     } else {
-      cause = get_stack_overflow_cause(fault_addr, main_thread.registers->sp(), maps);
+      cause = get_stack_overflow_cause(fault_addr, target_thread.registers->sp(), maps);
     }
   } else if (si->si_signo == SIGSEGV && si->si_code == SEGV_ACCERR) {
     auto map_info = maps->Find(fault_addr);
     if (map_info != nullptr && map_info->flags() == PROT_EXEC) {
       cause = "execute-only (no-read) memory access error; likely due to data in .text.";
     } else {
-      cause = get_stack_overflow_cause(fault_addr, main_thread.registers->sp(), maps);
+      cause = get_stack_overflow_cause(fault_addr, target_thread.registers->sp(), maps);
     }
   } else if (si->si_signo == SIGSYS && si->si_code == SYS_SECCOMP) {
     cause = StringPrintf("seccomp prevented call to disallowed %s system call %d", ABI_STRING,
@@ -685,7 +685,7 @@
 }
 
 void engrave_tombstone_proto(Tombstone* tombstone, unwindstack::AndroidUnwinder* unwinder,
-                             const std::map<pid_t, ThreadInfo>& threads, pid_t target_thread,
+                             const std::map<pid_t, ThreadInfo>& threads, pid_t target_tid,
                              const ProcessInfo& process_info, const OpenFilesList* open_files) {
   Tombstone result;
 
@@ -694,19 +694,19 @@
   result.set_revision(android::base::GetProperty("ro.revision", "unknown"));
   result.set_timestamp(get_timestamp());
 
-  const ThreadInfo& main_thread = threads.at(target_thread);
-  result.set_pid(main_thread.pid);
-  result.set_tid(main_thread.tid);
-  result.set_uid(main_thread.uid);
-  result.set_selinux_label(main_thread.selinux_label);
+  const ThreadInfo& target_thread = threads.at(target_tid);
+  result.set_pid(target_thread.pid);
+  result.set_tid(target_thread.tid);
+  result.set_uid(target_thread.uid);
+  result.set_selinux_label(target_thread.selinux_label);
   // The main thread must have a valid siginfo.
-  CHECK(main_thread.siginfo != nullptr);
+  CHECK(target_thread.siginfo != nullptr);
 
   struct sysinfo si;
   sysinfo(&si);
   android::procinfo::ProcessInfo proc_info;
   std::string error;
-  if (android::procinfo::GetProcessInfo(main_thread.pid, &proc_info, &error)) {
+  if (android::procinfo::GetProcessInfo(target_thread.pid, &proc_info, &error)) {
     uint64_t starttime = proc_info.starttime / sysconf(_SC_CLK_TCK);
     result.set_process_uptime(si.uptime - starttime);
   } else {
@@ -715,24 +715,24 @@
   }
 
   auto cmd_line = result.mutable_command_line();
-  for (const auto& arg : main_thread.command_line) {
+  for (const auto& arg : target_thread.command_line) {
     *cmd_line->Add() = arg;
   }
 
-  if (!main_thread.siginfo) {
+  if (!target_thread.siginfo) {
     async_safe_fatal("siginfo missing");
   }
 
   Signal sig;
-  sig.set_number(main_thread.signo);
-  sig.set_name(get_signame(main_thread.siginfo));
-  sig.set_code(main_thread.siginfo->si_code);
-  sig.set_code_name(get_sigcode(main_thread.siginfo));
+  sig.set_number(target_thread.signo);
+  sig.set_name(get_signame(target_thread.siginfo));
+  sig.set_code(target_thread.siginfo->si_code);
+  sig.set_code_name(get_sigcode(target_thread.siginfo));
 
-  if (signal_has_sender(main_thread.siginfo, main_thread.pid)) {
+  if (signal_has_sender(target_thread.siginfo, target_thread.pid)) {
     sig.set_has_sender(true);
-    sig.set_sender_uid(main_thread.siginfo->si_uid);
-    sig.set_sender_pid(main_thread.siginfo->si_pid);
+    sig.set_sender_uid(target_thread.siginfo->si_uid);
+    sig.set_sender_pid(target_thread.siginfo->si_pid);
   }
 
   if (process_info.has_fault_address) {
@@ -746,28 +746,28 @@
 
   dump_abort_message(&result, unwinder->GetProcessMemory(), process_info);
   dump_crash_details(&result, unwinder->GetProcessMemory(), process_info);
-  // Dump the main thread, but save the memory around the registers.
-  dump_thread(&result, unwinder, main_thread, /* memory_dump */ true);
+  // Dump the target thread, but save the memory around the registers.
+  dump_thread(&result, unwinder, target_thread, /* memory_dump */ true);
 
   for (const auto& [tid, thread_info] : threads) {
-    if (tid != target_thread) {
+    if (tid != target_tid) {
       dump_thread(&result, unwinder, thread_info);
     }
   }
 
-  dump_probable_cause(&result, unwinder, process_info, main_thread);
+  dump_probable_cause(&result, unwinder, process_info, target_thread);
 
   dump_mappings(&result, unwinder->GetMaps(), unwinder->GetProcessMemory());
 
   // Only dump logs on debuggable devices.
   if (android::base::GetBoolProperty("ro.debuggable", false)) {
     // Get the thread that corresponds to the main pid of the process.
-    const ThreadInfo& thread = threads.at(main_thread.pid);
+    const ThreadInfo& thread = threads.at(target_thread.pid);
 
     // Do not attempt to dump logs of the logd process because the gathering
     // of logs can hang until a timeout occurs.
     if (thread.thread_name != "logd") {
-      dump_logcat(&result, main_thread.pid);
+      dump_logcat(&result, target_thread.pid);
     }
   }
 
diff --git a/fs_mgr/libfstab/fstab.cpp b/fs_mgr/libfstab/fstab.cpp
index 6fa22fe..6273ee2 100644
--- a/fs_mgr/libfstab/fstab.cpp
+++ b/fs_mgr/libfstab/fstab.cpp
@@ -849,6 +849,14 @@
                             [&path](const FstabEntry& entry) { return entry.mount_point == path; });
 }
 
+FstabEntry* GetEntryForMountPoint(Fstab* fstab, const std::string_view path,
+                                  const std::string_view fstype) {
+    auto&& vec = GetEntriesByPred(fstab, [&path, fstype](const FstabEntry& entry) {
+        return entry.mount_point == path && entry.fs_type == fstype;
+    });
+    return vec.empty() ? nullptr : vec.front();
+}
+
 std::vector<const FstabEntry*> GetEntriesForMountPoint(const Fstab* fstab,
                                                        const std::string& path) {
     return GetEntriesByPred(fstab,
diff --git a/fs_mgr/libfstab/include/fstab/fstab.h b/fs_mgr/libfstab/include/fstab/fstab.h
index 5e4019c..dea7238 100644
--- a/fs_mgr/libfstab/include/fstab/fstab.h
+++ b/fs_mgr/libfstab/include/fstab/fstab.h
@@ -108,6 +108,9 @@
 FstabEntry* GetEntryForMountPoint(Fstab* fstab, const std::string& path);
 const FstabEntry* GetEntryForMountPoint(const Fstab* fstab, const std::string& path);
 
+FstabEntry* GetEntryForMountPoint(Fstab* fstab, const std::string_view path,
+                                  const std::string_view fstype);
+
 // This method builds DSU fstab entries and transfer the fstab.
 //
 // fstab points to the unmodified fstab.
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/cow_format.h b/fs_mgr/libsnapshot/include/libsnapshot/cow_format.h
index 6a7153d..991e17c 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/cow_format.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/cow_format.h
@@ -31,15 +31,9 @@
 static constexpr uint32_t kCowVersionMajor = 2;
 static constexpr uint32_t kCowVersionMinor = 0;
 
-static constexpr uint32_t kCowVersionManifest = 2;
-
 static constexpr uint32_t kMinCowVersion = 1;
 static constexpr uint32_t kMaxCowVersion = 3;
 
-// Normally, this should be kMaxCowVersion. When a new version is under testing
-// it may be the previous value of kMaxCowVersion.
-static constexpr uint32_t kDefaultCowVersion = 2;
-
 // 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:
 //
diff --git a/fs_mgr/libsnapshot/libsnapshot_cow/snapshot_reader_test.cpp b/fs_mgr/libsnapshot/libsnapshot_cow/snapshot_reader_test.cpp
index 10cb06d..f00f236 100644
--- a/fs_mgr/libsnapshot/libsnapshot_cow/snapshot_reader_test.cpp
+++ b/fs_mgr/libsnapshot/libsnapshot_cow/snapshot_reader_test.cpp
@@ -184,7 +184,7 @@
     unique_fd cow_fd(dup(cow_->fd));
     ASSERT_GE(cow_fd, 0);
 
-    auto writer = CreateCowWriter(kDefaultCowVersion, options, std::move(cow_fd));
+    auto writer = CreateCowWriter(2, options, std::move(cow_fd));
     ASSERT_NO_FATAL_FAILURE(WriteCow(writer.get()));
     ASSERT_NO_FATAL_FAILURE(TestReads(writer.get()));
 }
diff --git a/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_test.cpp b/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_test.cpp
index d05df82..56f7b59 100644
--- a/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_test.cpp
+++ b/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_test.cpp
@@ -135,7 +135,7 @@
     unique_fd fd(cow_system_->fd);
     cow_system_->fd = -1;
 
-    return CreateCowWriter(kDefaultCowVersion, options, std::move(fd));
+    return CreateCowWriter(2, options, std::move(fd));
 }
 
 std::unique_ptr<ICowWriter> SnapuserdTestBase::CreateV3Cow() {
diff --git a/init/Android.bp b/init/Android.bp
index 6d63e41..c4e74d0 100644
--- a/init/Android.bp
+++ b/init/Android.bp
@@ -96,6 +96,7 @@
     config_namespace: "ANDROID",
     bool_variables: [
         "PRODUCT_INSTALL_DEBUG_POLICY_TO_SYSTEM_EXT",
+        "release_write_appcompat_override_system_properties",
     ],
     properties: [
         "cflags",
@@ -159,6 +160,9 @@
                 "-DINSTALL_DEBUG_POLICY_TO_SYSTEM_EXT=1",
             ],
         },
+        release_write_appcompat_override_system_properties: {
+            cflags: ["-DWRITE_APPCOMPAT_OVERRIDE_SYSTEM_PROPERTIES"],
+        }
     },
     static_libs: [
         "libavb",
diff --git a/init/first_stage_mount.cpp b/init/first_stage_mount.cpp
index ae216c6..5d3a273 100644
--- a/init/first_stage_mount.cpp
+++ b/init/first_stage_mount.cpp
@@ -556,11 +556,11 @@
         return true;
     }
     // clang-format off
-    const std::array<const char*, 7> args = {
+    const std::array<const char*, 8> args = {
         "/system/bin/derive_microdroid_vendor_dice_node",
                 "--dice-driver", "/dev/open-dice0",
                 "--microdroid-vendor-disk-image", microdroid_vendor_block_dev->data(),
-                "--output", "/microdroid_resources/dice_chain.raw",
+                "--output", "/microdroid_resources/dice_chain.raw", nullptr,
     };
     // clang-format-on
     // ForkExecveAndWaitForCompletion calls waitpid to wait for the fork-ed process to finish.
diff --git a/init/property_service.cpp b/init/property_service.cpp
index 58a0a7f..5a1b63b 100644
--- a/init/property_service.cpp
+++ b/init/property_service.cpp
@@ -1308,12 +1308,14 @@
     }
     selinux_android_restorecon(PROP_TREE_FILE, 0);
 
+#ifdef WRITE_APPCOMPAT_OVERRIDE_SYSTEM_PROPERTIES
     mkdir(APPCOMPAT_OVERRIDE_PROP_FOLDERNAME, S_IRWXU | S_IXGRP | S_IXOTH);
     if (!WriteStringToFile(serialized_contexts, APPCOMPAT_OVERRIDE_PROP_TREE_FILE, 0444, 0, 0,
                            false)) {
         PLOG(ERROR) << "Unable to write appcompat override property infos to file";
     }
     selinux_android_restorecon(APPCOMPAT_OVERRIDE_PROP_TREE_FILE, 0);
+#endif
 }
 
 static void ExportKernelBootProps() {
diff --git a/libmodprobe/libmodprobe.cpp b/libmodprobe/libmodprobe.cpp
index 5023c79..1a40da1 100644
--- a/libmodprobe/libmodprobe.cpp
+++ b/libmodprobe/libmodprobe.cpp
@@ -484,7 +484,11 @@
                 return false;
             }
 
-            if (module_options_[cnd_last].find("load_sequential=1") != std::string::npos) {
+            std::string str = "load_sequential=1";
+            auto it = module_options_[cnd_last].find(str);
+            if (it != std::string::npos) {
+                module_options_[cnd_last].erase(it, it + str.size());
+
                 if (!LoadWithAliases(cnd_last, true)) {
                     return false;
                 }
diff --git a/libsysutils/include/sysutils/SocketListener.h b/libsysutils/include/sysutils/SocketListener.h
index 67a691a..a7fd09e 100644
--- a/libsysutils/include/sysutils/SocketListener.h
+++ b/libsysutils/include/sysutils/SocketListener.h
@@ -19,6 +19,7 @@
 #include <pthread.h>
 
 #include <unordered_map>
+#include <vector>
 
 #include <sysutils/SocketClient.h>
 #include "SocketClientCommand.h"
diff --git a/rootdir/Android.bp b/rootdir/Android.bp
index 9a64310..06227c3 100644
--- a/rootdir/Android.bp
+++ b/rootdir/Android.bp
@@ -107,3 +107,9 @@
     src: "etc/hosts",
     filename: "hosts",
 }
+
+prebuilt_etc {
+    name: "init-debug.rc",
+    src: "init-debug.rc",
+    sub_dir: "init",
+}
diff --git a/rootdir/Android.mk b/rootdir/Android.mk
index 593bb1e..fb91b58 100644
--- a/rootdir/Android.mk
+++ b/rootdir/Android.mk
@@ -3,19 +3,6 @@
 $(eval $(call declare-1p-copy-files,system/core/rootdir,))
 
 #######################################
-# init-debug.rc
-include $(CLEAR_VARS)
-
-LOCAL_MODULE := init-debug.rc
-LOCAL_LICENSE_KINDS := SPDX-license-identifier-Apache-2.0
-LOCAL_LICENSE_CONDITIONS := notice
-LOCAL_SRC_FILES := $(LOCAL_MODULE)
-LOCAL_MODULE_CLASS := ETC
-LOCAL_MODULE_PATH := $(TARGET_OUT_ETC)/init
-
-include $(BUILD_PREBUILT)
-
-#######################################
 # asan.options
 ifneq ($(filter address,$(SANITIZE_TARGET)),)
 
diff --git a/rootdir/init.rc b/rootdir/init.rc
index 1af46c1..e3896b1 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -425,16 +425,6 @@
     chown system system /proc/pressure/memory
     chmod 0664 /proc/pressure/memory
 
-    # qtaguid will limit access to specific data based on group memberships.
-    #   net_bw_acct grants impersonation of socket owners.
-    #   net_bw_stats grants access to other apps' detailed tagged-socket stats.
-    chown root net_bw_acct /proc/net/xt_qtaguid/ctrl
-    chown root net_bw_stats /proc/net/xt_qtaguid/stats
-
-    # Allow everybody to read the xt_qtaguid resource tracking misc dev.
-    # This is needed by any process that uses socket tagging.
-    chmod 0644 /dev/xt_qtaguid
-
     mount bpf bpf /sys/fs/bpf nodev noexec nosuid
 
     # pstore/ramoops previous console log
@@ -666,10 +656,6 @@
     exec -- /system/bin/fsverity_init --load-verified-keys
 
 # Only enable the bootreceiver tracing instance for kernels 5.10 and above.
-on late-fs && property:ro.kernel.version=4.9
-    setprop bootreceiver.enable 0
-on late-fs && property:ro.kernel.version=4.14
-    setprop bootreceiver.enable 0
 on late-fs && property:ro.kernel.version=4.19
     setprop bootreceiver.enable 0
 on late-fs && property:ro.kernel.version=5.4
diff --git a/toolbox/modprobe.cpp b/toolbox/modprobe.cpp
index 45dd9b8..b0e76ea 100644
--- a/toolbox/modprobe.cpp
+++ b/toolbox/modprobe.cpp
@@ -15,6 +15,7 @@
  */
 
 #include <ctype.h>
+#include <fcntl.h>
 #include <getopt.h>
 #include <stdlib.h>
 
@@ -27,6 +28,7 @@
 #include <modprobe/modprobe.h>
 
 #include <sys/utsname.h>
+#include <unistd.h>
 
 namespace {
 
@@ -105,6 +107,11 @@
     return 0;
 }
 
+std::string GetPageSizeSuffix() {
+    static const size_t page_size = sysconf(_SC_PAGE_SIZE);
+    return android::base::StringPrintf("_%zuk", page_size / 1024);
+}
+
 }  // anonymous namespace
 
 extern "C" int modprobe_main(int argc, char** argv) {
@@ -233,6 +240,19 @@
         // Allow modules to be directly inside /lib/modules
         mod_dirs.emplace_back(LIB_MODULES_PREFIX);
     }
+    if (getpagesize() != 4096) {
+        struct utsname uts {};
+        if (uname(&uts)) {
+            PLOG(FATAL) << "Failed to get kernel version";
+        }
+        const auto module_dir = android::base::StringPrintf("/lib/modules/%s%s", uts.release,
+                                                            GetPageSizeSuffix().c_str());
+        struct stat st {};
+        if (stat(module_dir.c_str(), &st) == 0 && S_ISDIR(st.st_mode)) {
+            mod_dirs.clear();
+            mod_dirs.emplace_back(module_dir);
+        }
+    }
 
     LOG(DEBUG) << "mode is " << mode;
     LOG(DEBUG) << "mod_dirs is: " << android::base::Join(mod_dirs, " ");
diff --git a/toolbox/setprop.cpp b/toolbox/setprop.cpp
index acf8c3e..91edf45 100644
--- a/toolbox/setprop.cpp
+++ b/toolbox/setprop.cpp
@@ -58,7 +58,7 @@
         }
     }
 
-    if (value.size() >= PROP_VALUE_MAX && !StartsWith(value, "ro.")) {
+    if (value.size() >= PROP_VALUE_MAX && !StartsWith(name, "ro.")) {
         std::cerr << "Value '" << value << "' is too long, " << value.size()
                   << " bytes vs a max of " << PROP_VALUE_MAX << std::endl;
         return EXIT_FAILURE;
diff --git a/trusty/storage/proxy/proxy.c b/trusty/storage/proxy/proxy.c
index 67e935e..6cb72d5 100644
--- a/trusty/storage/proxy/proxy.c
+++ b/trusty/storage/proxy/proxy.c
@@ -41,9 +41,13 @@
 static const char* trusty_devname;
 static const char* rpmb_devname;
 static const char* ss_srv_name = STORAGE_DISK_PROXY_PORT;
+static const char* max_file_size_from;
 
 static enum dev_type dev_type = MMC_RPMB;
 
+/* List head for storage mapping, elements added at init, and never removed */
+static struct storage_mapping_node* storage_mapping_head;
+
 static enum dev_type parse_dev_type(const char* dev_type_name) {
     if (!strcmp(dev_type_name, "mmc")) {
         return MMC_RPMB;
@@ -58,17 +62,61 @@
     }
 }
 
-static const char* _sopts = "hp:d:r:t:";
+static int parse_and_append_file_mapping(const char* file_mapping) {
+    if (file_mapping == NULL) {
+        ALOGE("Provided file mapping is null\n");
+        return -1;
+    }
+    char* file_mapping_dup = strdup(file_mapping);
+    if (file_mapping_dup == NULL) {
+        ALOGE("Couldn't duplicate string: %s\n", file_mapping);
+        return -1;
+    }
+    const char* file_name = strtok(file_mapping_dup, ":");
+    if (file_name == NULL) {
+        ALOGE("No file name found\n");
+        return -1;
+    }
+    const char* backing_storage = strtok(NULL, ":");
+    if (backing_storage == NULL) {
+        ALOGE("No backing storage found\n");
+        return -1;
+    }
+
+    struct storage_mapping_node* new_node = malloc(sizeof(struct storage_mapping_node));
+    if (new_node == NULL) {
+        ALOGE("Couldn't allocate additional storage_mapping_node\n");
+        return -1;
+    }
+    *new_node = (struct storage_mapping_node){.file_name = file_name,
+                                              .backing_storage = backing_storage,
+                                              .next = storage_mapping_head,
+                                              .fd = -1};
+    storage_mapping_head = new_node;
+    return 0;
+}
+
+static const char* _sopts = "hp:d:r:t:m:f:";
 static const struct option _lopts[] = {{"help", no_argument, NULL, 'h'},
                                        {"trusty_dev", required_argument, NULL, 'd'},
                                        {"data_path", required_argument, NULL, 'p'},
                                        {"rpmb_dev", required_argument, NULL, 'r'},
                                        {"dev_type", required_argument, NULL, 't'},
+                                       {"max_file_size_from", required_argument, NULL, 'm'},
+                                       {"file_storage_mapping", required_argument, NULL, 'f'},
                                        {0, 0, 0, 0}};
 
 static void show_usage_and_exit(int code) {
-    ALOGE("usage: storageproxyd -d <trusty_dev> -p <data_path> -r <rpmb_dev> -t <dev_type>\n");
+    ALOGE("usage: storageproxyd -d <trusty_dev> -p <data_path> -r <rpmb_dev> -t <dev_type>  [-m "
+          "<file>] [-f <file>:<mapping>]\n");
     ALOGE("Available dev types: mmc, virt\n");
+    ALOGE("-f = Maps secure storage files like `0` and `persist/0`\n"
+          "to block devices.  Storageproxyd will handle creating the\n"
+          "appropriate symlinks in the root datapath.\n");
+    ALOGE("-m = Specifies the max size constraint for file backed storages.\n"
+          "The constraint is chosen by giving a file, this allows for passing a\n"
+          "block device for which a max file size can be queried.  File based\n"
+          "storages will be constrained to that size as well.\n");
     exit(code);
 }
 
@@ -187,6 +235,7 @@
 static void parse_args(int argc, char* argv[]) {
     int opt;
     int oidx = 0;
+    int rc = 0;
 
     while ((opt = getopt_long(argc, argv, _sopts, _lopts, &oidx)) != -1) {
         switch (opt) {
@@ -210,6 +259,18 @@
                 }
                 break;
 
+            case 'f':
+                rc = parse_and_append_file_mapping(optarg);
+                if (rc < 0) {
+                    ALOGE("Failed to parse file mapping: %s\n", optarg);
+                    show_usage_and_exit(EXIT_FAILURE);
+                }
+                break;
+
+            case 'm':
+                max_file_size_from = strdup(optarg);
+                break;
+
             default:
                 ALOGE("unrecognized option (%c):\n", opt);
                 show_usage_and_exit(EXIT_FAILURE);
@@ -225,6 +286,12 @@
     ALOGI("storage data root: %s\n", ss_data_root);
     ALOGI("trusty dev: %s\n", trusty_devname);
     ALOGI("rpmb dev: %s\n", rpmb_devname);
+    ALOGI("File Mappings: \n");
+    const struct storage_mapping_node* curr = storage_mapping_head;
+    for (; curr != NULL; curr = curr->next) {
+        ALOGI("\t%s -> %s\n", curr->file_name, curr->backing_storage);
+    }
+    ALOGI("max file size from: %s\n", max_file_size_from ? max_file_size_from : "(unset)");
 }
 
 int main(int argc, char* argv[]) {
@@ -252,7 +319,7 @@
     ABinderProcess_startThreadPool();
 
     /* initialize secure storage directory */
-    rc = storage_init(ss_data_root);
+    rc = storage_init(ss_data_root, storage_mapping_head, max_file_size_from);
     if (rc < 0) return EXIT_FAILURE;
 
     /* open rpmb device */
diff --git a/trusty/storage/proxy/storage.c b/trusty/storage/proxy/storage.c
index 8c8edb7..6d0c616 100644
--- a/trusty/storage/proxy/storage.c
+++ b/trusty/storage/proxy/storage.c
@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+#include <assert.h>
 #include <cutils/properties.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -39,16 +40,20 @@
 #define ALTERNATE_DATA_DIR "alternate/"
 
 /* Maximum file size for filesystem backed storage (i.e. not block dev backed storage) */
-#define MAX_FILE_SIZE (0x10000000000)
+static uint64_t max_file_size = 0x10000000000;
 
 enum sync_state {
     SS_UNUSED = -1,
-    SS_CLEAN =  0,
-    SS_DIRTY =  1,
+    SS_CLEAN = 0,
+    SS_DIRTY = 1,
+    SS_CLEAN_NEED_SYMLINK = 2,
 };
 
 static const char *ssdir_name;
 
+/* List head for storage mapping, elements added at init, and never removed */
+static struct storage_mapping_node* storage_mapping_head;
+
 /*
  * Property set to 1 after we have opened a file under ssdir_name. The backing
  * files for both TD and TDP are currently located under /data/vendor/ss and can
@@ -75,24 +80,103 @@
    uint8_t data[MAX_READ_SIZE];
 }  read_rsp;
 
-static uint32_t insert_fd(int open_flags, int fd)
-{
+static uint32_t insert_fd(int open_flags, int fd, struct storage_mapping_node* node) {
     uint32_t handle = fd;
 
     if (handle < FD_TBL_SIZE) {
-            fd_state[fd] = SS_CLEAN; /* fd clean */
-            if (open_flags & O_TRUNC) {
-                fd_state[fd] = SS_DIRTY;  /* set fd dirty */
-            }
+        fd_state[fd] = SS_CLEAN; /* fd clean */
+        if (open_flags & O_TRUNC) {
+            assert(node == NULL);
+            fd_state[fd] = SS_DIRTY; /* set fd dirty */
+        }
+
+        if (node != NULL) {
+            fd_state[fd] = SS_CLEAN_NEED_SYMLINK;
+        }
     } else {
             ALOGW("%s: untracked fd %u\n", __func__, fd);
             if (open_flags & (O_TRUNC | O_CREAT)) {
                 fs_state = SS_DIRTY;
             }
     }
+
+    if (node != NULL) {
+        node->fd = fd;
+    }
+
     return handle;
 }
 
+static void clear_fd_symlink_status(uint32_t handle, struct storage_mapping_node* entry) {
+    /* Always clear FD, in case fd is not in FD_TBL */
+    entry->fd = -1;
+
+    if (handle >= FD_TBL_SIZE) {
+        ALOGE("%s: untracked fd=%u\n", __func__, handle);
+        return;
+    }
+
+    if (fd_state[handle] == SS_CLEAN_NEED_SYMLINK) {
+        fd_state[handle] = SS_CLEAN;
+    }
+}
+
+static struct storage_mapping_node* get_pending_symlink_mapping(uint32_t handle) {
+    /* Fast lookup failure, is it in FD TBL */
+    if (handle < FD_TBL_SIZE && fd_state[handle] != SS_CLEAN_NEED_SYMLINK) {
+        return NULL;
+    }
+
+    /* Go find our mapping */
+    struct storage_mapping_node* curr = storage_mapping_head;
+    for (; curr != NULL; curr = curr->next) {
+        if (curr->fd == handle) {
+            return curr;
+        }
+    }
+
+    /* Safety check: state inconsistent if we get here with handle inside table range */
+    assert(handle >= FD_TBL_SIZE);
+
+    return NULL;
+};
+
+static int possibly_symlink_and_clear_mapping(uint32_t handle) {
+    struct storage_mapping_node* entry = get_pending_symlink_mapping(handle);
+    if (entry == NULL) {
+        /* No mappings pending */
+        return 0;
+    }
+
+    /* Create full path */
+    char* path = NULL;
+    int rc = asprintf(&path, "%s/%s", ssdir_name, entry->file_name);
+    if (rc < 0) {
+        ALOGE("%s: asprintf failed\n", __func__);
+        return -1;
+    }
+
+    /* Try and setup the symlinking */
+    ALOGI("Creating symlink %s->%s\n", path, entry->backing_storage);
+    rc = symlink(entry->backing_storage, path);
+    if (rc < 0) {
+        ALOGE("%s: error symlinking %s->%s (%s)\n", __func__, path, entry->backing_storage,
+              strerror(errno));
+        free(path);
+        return rc;
+    }
+    free(path);
+
+    clear_fd_symlink_status(handle, entry);
+
+    return rc;
+}
+
+static bool is_pending_symlink(uint32_t handle) {
+    struct storage_mapping_node* entry = get_pending_symlink_mapping(handle);
+    return entry != NULL;
+}
+
 static int lookup_fd(uint32_t handle, bool dirty)
 {
     if (dirty) {
@@ -107,6 +191,12 @@
 
 static int remove_fd(uint32_t handle)
 {
+    /* Cleanup fd in symlink mapping if it exists */
+    struct storage_mapping_node* entry = get_pending_symlink_mapping(handle);
+    if (entry != NULL) {
+        entry->fd = -1;
+    }
+
     if (handle < FD_TBL_SIZE) {
         fd_state[handle] = SS_UNUSED; /* set to uninstalled */
     }
@@ -247,11 +337,73 @@
     watch_progress(watcher, "done syncing parent");
 }
 
+static struct storage_mapping_node* get_storage_mapping_entry(const char* source) {
+    struct storage_mapping_node* curr = storage_mapping_head;
+    for (; curr != NULL; curr = curr->next) {
+        if (!strcmp(source, curr->file_name)) {
+            ALOGI("Found backing file %s for %s\n", curr->backing_storage, source);
+            return curr;
+        }
+    }
+    return NULL;
+}
+
+static bool is_backing_storage_mapped(const char* source) {
+    const struct storage_mapping_node* curr = storage_mapping_head;
+    for (; curr != NULL; curr = curr->next) {
+        if (!strcmp(source, curr->backing_storage)) {
+            ALOGI("Backed storage mapping exists for %s\n", curr->backing_storage);
+            return true;
+        }
+    }
+    return false;
+}
+
+/* Attempts to open a backed file, if mapped, without creating the symlink. Symlink will be created
+ * later on the first write.  This allows us to continue reporting zero read sizes until the first
+ * write. */
+static int open_possibly_mapped_file(const char* short_path, const char* full_path, int open_flags,
+                                     struct storage_mapping_node** entry) {
+    /* See if mapping exists, report upstream if there is no mapping. */
+    struct storage_mapping_node* mapping_entry = get_storage_mapping_entry(short_path);
+    if (mapping_entry == NULL) {
+        return TEMP_FAILURE_RETRY(open(full_path, open_flags, S_IRUSR | S_IWUSR));
+    }
+
+    /* Check for existence of root path, we don't allow mappings during early boot */
+    struct stat buf = {0};
+    if (stat(ssdir_name, &buf) != 0) {
+        ALOGW("Root path not accessible yet, refuse to open mappings for now.\n");
+        return -1;
+    }
+
+    /* We don't support exclusive opening of mapped files */
+    if (open_flags & O_EXCL) {
+        ALOGE("Requesting exclusive open on backed storage isn't supported: %s\n", full_path);
+        return -1;
+    }
+
+    /* Try and open mapping file */
+    open_flags &= ~(O_CREAT | O_EXCL);
+    ALOGI("%s Attempting to open mapped file: %s\n", __func__, mapping_entry->backing_storage);
+    int fd =
+            TEMP_FAILURE_RETRY(open(mapping_entry->backing_storage, open_flags, S_IRUSR | S_IWUSR));
+    if (fd < 0) {
+        ALOGE("%s Failed to open mapping file: %s\n", __func__, mapping_entry->backing_storage);
+        return -1;
+    }
+
+    /* Let caller know which entry we used for opening */
+    *entry = mapping_entry;
+    return fd;
+}
+
 int storage_file_open(struct storage_msg* msg, const void* r, size_t req_len,
                       struct watcher* watcher) {
     char* path = NULL;
     const struct storage_file_open_req *req = r;
     struct storage_file_open_resp resp = {0};
+    struct storage_mapping_node* mapping_entry = NULL;
 
     if (req_len < sizeof(*req)) {
         ALOGE("%s: invalid request length (%zd < %zd)\n",
@@ -321,14 +473,18 @@
         if (req->flags & STORAGE_FILE_OPEN_CREATE_EXCLUSIVE) {
             /* create exclusive */
             open_flags |= O_CREAT | O_EXCL;
-            rc = TEMP_FAILURE_RETRY(open(path, open_flags, S_IRUSR | S_IWUSR));
+
+            /* Look for and attempt opening a mapping, else just do normal open. */
+            rc = open_possibly_mapped_file(req->name, path, open_flags, &mapping_entry);
         } else {
             /* try open first */
             rc = TEMP_FAILURE_RETRY(open(path, open_flags, S_IRUSR | S_IWUSR));
             if (rc == -1 && errno == ENOENT) {
                 /* then try open with O_CREATE */
                 open_flags |= O_CREAT;
-                rc = TEMP_FAILURE_RETRY(open(path, open_flags, S_IRUSR | S_IWUSR));
+
+                /* Look for and attempt opening a mapping, else just do normal open. */
+                rc = open_possibly_mapped_file(req->name, path, open_flags, &mapping_entry);
             }
 
         }
@@ -356,7 +512,7 @@
 
     /* at this point rc contains storage file fd */
     msg->result = STORAGE_NO_ERROR;
-    resp.handle = insert_fd(open_flags, rc);
+    resp.handle = insert_fd(open_flags, rc, mapping_entry);
     ALOGV("%s: \"%s\": fd = %u: handle = %d\n",
           __func__, path, rc, resp.handle);
 
@@ -433,6 +589,14 @@
         goto err_response;
     }
 
+    /* Handle any delayed symlinking for this handle if any */
+    rc = possibly_symlink_and_clear_mapping(req->handle);
+    if (rc < 0) {
+        ALOGE("Failed to symlink storage\n");
+        msg->result = STORAGE_ERR_GENERIC;
+        goto err_response;
+    }
+
     int fd = lookup_fd(req->handle, true);
     watch_progress(watcher, "writing");
     if (write_with_retry(fd, &req->data[0], req_len - sizeof(*req),
@@ -479,6 +643,14 @@
         goto err_response;
     }
 
+    /* If this handle has a delayed symlink we should report 0 size reads until first write occurs
+     */
+    if (is_pending_symlink(req->handle)) {
+        ALOGI("Pending symlink: Forcing read result 0.\n");
+        msg->result = STORAGE_NO_ERROR;
+        return ipc_respond(msg, &read_rsp, sizeof(read_rsp.hdr));
+    }
+
     int fd = lookup_fd(req->handle, false);
     watch_progress(watcher, "reading");
     ssize_t read_res = read_with_retry(fd, read_rsp.hdr.data, req->size,
@@ -592,7 +764,7 @@
             goto err_response;
         }
     } else {
-        max_size = MAX_FILE_SIZE;
+        max_size = max_file_size;
     }
 
     resp.max_size = max_size;
@@ -603,17 +775,79 @@
     return ipc_respond(msg, NULL, 0);
 }
 
-int storage_init(const char *dirname)
-{
+int determine_max_file_size(const char* max_file_size_from) {
+    /* Use default if none passed in */
+    if (max_file_size_from == NULL) {
+        ALOGI("No max file source given, continuing to use default: 0x%" PRIx64 "\n",
+              max_file_size);
+        return 0;
+    }
+
+    /* Check that max_file_size_from is part of our mapping list. */
+    if (!is_backing_storage_mapped(max_file_size_from)) {
+        ALOGE("%s: file doesn't match mapped storages (filename=%s)\n", __func__,
+              max_file_size_from);
+        return -1;
+    }
+
+    ALOGI("Using %s to determine max file size.\n", max_file_size_from);
+
+    /* Error if max file size source not found, possible misconfig. */
+    struct stat buf = {0};
+    int rc = stat(max_file_size_from, &buf);
+    if (rc < 0) {
+        ALOGE("%s: error stat'ing file (filename=%s): %s\n", __func__, max_file_size_from,
+              strerror(errno));
+        return -1;
+    }
+
+    /* Currently only support block device as max file size source */
+    if ((buf.st_mode & S_IFMT) != S_IFBLK) {
+        ALOGE("Unsupported max file size source type: %d\n", buf.st_mode);
+        return -1;
+    }
+
+    ALOGI("%s is a block device, determining block device size\n", max_file_size_from);
+    uint64_t max_size = 0;
+    int fd = TEMP_FAILURE_RETRY(open(max_file_size_from, O_RDONLY | O_NONBLOCK));
+    if (fd < 0) {
+        ALOGE("%s: failed to open backing file %s for ioctl: %s\n", __func__, max_file_size_from,
+              strerror(errno));
+        return -1;
+    }
+    rc = ioctl(fd, BLKGETSIZE64, &max_size);
+    if (rc < 0) {
+        ALOGE("%s: error calling ioctl on file (fd=%d): %s\n", __func__, fd, strerror(errno));
+        close(fd);
+        return -1;
+    }
+    close(fd);
+    max_file_size = max_size;
+
+    ALOGI("Using 0x%" PRIx64 " as max file size\n", max_file_size);
+    return 0;
+}
+
+int storage_init(const char* dirname, struct storage_mapping_node* mappings,
+                 const char* max_file_size_from) {
     /* If there is an active DSU image, use the alternate fs mode. */
     alternate_mode = is_gsi_running();
 
     fs_state = SS_CLEAN;
     for (uint i = 0; i < FD_TBL_SIZE; i++) {
-        fd_state[i] = SS_UNUSED;  /* uninstalled */
+        fd_state[i] = SS_UNUSED; /* uninstalled */
     }
 
     ssdir_name = dirname;
+
+    storage_mapping_head = mappings;
+
+    /* Set the max file size based on incoming configuration */
+    int rc = determine_max_file_size(max_file_size_from);
+    if (rc < 0) {
+        return rc;
+    }
+
     return 0;
 }
 
@@ -623,17 +857,17 @@
     watch_progress(watcher, "sync fd table");
     /* sync fd table and reset it to clean state first */
     for (uint fd = 0; fd < FD_TBL_SIZE; fd++) {
-         if (fd_state[fd] == SS_DIRTY) {
-             if (fs_state == SS_CLEAN) {
-                 /* need to sync individual fd */
-                 rc = fsync(fd);
-                 if (rc < 0) {
-                     ALOGE("fsync for fd=%d failed: %s\n", fd, strerror(errno));
-                     return rc;
-                 }
-             }
-             fd_state[fd] = SS_CLEAN; /* set to clean */
-         }
+        if (fd_state[fd] == SS_DIRTY) {
+            if (fs_state == SS_CLEAN) {
+                /* need to sync individual fd */
+                rc = fsync(fd);
+                if (rc < 0) {
+                    ALOGE("fsync for fd=%d failed: %s\n", fd, strerror(errno));
+                    return rc;
+                }
+            }
+            fd_state[fd] = SS_CLEAN; /* set to clean */
+        }
     }
 
     /* check if we need to sync all filesystems */
diff --git a/trusty/storage/proxy/storage.h b/trusty/storage/proxy/storage.h
index f29fdf2..6dbfe37 100644
--- a/trusty/storage/proxy/storage.h
+++ b/trusty/storage/proxy/storage.h
@@ -21,6 +21,14 @@
 /* Defined in watchdog.h */
 struct watcher;
 
+/* Is used for managing alternate backing storage, generally will be a block device. */
+struct storage_mapping_node {
+    struct storage_mapping_node* next;
+    const char* file_name;
+    const char* backing_storage;
+    int fd;
+};
+
 int storage_file_delete(struct storage_msg* msg, const void* req, size_t req_len,
                         struct watcher* watcher);
 
@@ -45,6 +53,7 @@
 int storage_file_get_max_size(struct storage_msg* msg, const void* req, size_t req_len,
                               struct watcher* watcher);
 
-int storage_init(const char* dirname);
+int storage_init(const char* dirname, struct storage_mapping_node* head,
+                 const char* max_file_size_from);
 
 int storage_sync_checkpoint(struct watcher* watcher);