diff --git a/fs_mgr/Android.bp b/fs_mgr/Android.bp
index bbd068b..15600fd 100644
--- a/fs_mgr/Android.bp
+++ b/fs_mgr/Android.bp
@@ -70,8 +70,9 @@
         "fs_mgr.cpp",
         "fs_mgr_format.cpp",
         "fs_mgr_dm_linear.cpp",
-        "fs_mgr_overlayfs.cpp",
         "fs_mgr_roots.cpp",
+        "fs_mgr_overlayfs_control.cpp",
+        "fs_mgr_overlayfs_mount.cpp",
         "fs_mgr_vendor_overlay.cpp",
         ":libfiemap_srcs",
     ],
diff --git a/fs_mgr/fs_mgr_overlayfs.cpp b/fs_mgr/fs_mgr_overlayfs_control.cpp
similarity index 61%
rename from fs_mgr/fs_mgr_overlayfs.cpp
rename to fs_mgr/fs_mgr_overlayfs_control.cpp
index 82a8b8b..69a2ac0 100644
--- a/fs_mgr/fs_mgr_overlayfs.cpp
+++ b/fs_mgr/fs_mgr_overlayfs_control.cpp
@@ -55,8 +55,9 @@
 #include <liblp/liblp.h>
 #include <storage_literals/storage_literals.h>
 
+#include "fs_mgr_overlayfs_control.h"
+#include "fs_mgr_overlayfs_mount.h"
 #include "fs_mgr_priv.h"
-#include "fs_mgr_priv_overlayfs.h"
 #include "libfiemap/utility.h"
 
 using namespace std::literals;
@@ -69,100 +70,18 @@
 namespace {
 
 constexpr char kDataScratchSizeMbProp[] = "fs_mgr.overlayfs.data_scratch_size_mb";
-constexpr char kPreferCacheBackingStorageProp[] = "fs_mgr.overlayfs.prefer_cache_backing_storage";
-
-bool fs_mgr_access(const std::string& path) {
-    return access(path.c_str(), F_OK) == 0;
-}
-
-const auto kLowerdirOption = "lowerdir=";
-const auto kUpperdirOption = "upperdir=";
-
-bool fs_mgr_in_recovery() {
-    // Check the existence of recovery binary instead of using the compile time
-    // __ANDROID_RECOVERY__ macro.
-    // If BOARD_USES_RECOVERY_AS_BOOT is true, both normal and recovery boot
-    // mode would use the same init binary, which would mean during normal boot
-    // the '/init' binary is actually a symlink pointing to
-    // init_second_stage.recovery, which would be compiled with
-    // __ANDROID_RECOVERY__ defined.
-    return fs_mgr_access("/system/bin/recovery");
-}
-
-bool fs_mgr_is_dsu_running() {
-    // Since android::gsi::CanBootIntoGsi() or android::gsi::MarkSystemAsGsi() is
-    // never called in recovery, the return value of android::gsi::IsGsiRunning()
-    // is not well-defined. In this case, just return false as being in recovery
-    // implies not running a DSU system.
-    if (fs_mgr_in_recovery()) return false;
-    return android::gsi::IsGsiRunning();
-}
-
-// list of acceptable overlayfs backing storage
-const auto kScratchMountPoint = "/mnt/scratch";
-const auto kCacheMountPoint = "/cache";
-
-bool IsABDevice() {
-    return !android::base::GetProperty("ro.boot.slot_suffix", "").empty();
-}
-
-std::vector<const std::string> OverlayMountPoints() {
-    // Never fallback to legacy cache mount point if within a DSU system,
-    // because running a DSU system implies the device supports dynamic
-    // partitions, which means legacy cache mustn't be used.
-    if (fs_mgr_is_dsu_running()) {
-        return {kScratchMountPoint};
-    }
-
-    // For non-A/B devices prefer cache backing storage if
-    // kPreferCacheBackingStorageProp property set.
-    if (!IsABDevice() && android::base::GetBoolProperty(kPreferCacheBackingStorageProp, false) &&
-        android::base::GetIntProperty("ro.vendor.api_level", -1) < __ANDROID_API_T__) {
-        return {kCacheMountPoint, kScratchMountPoint};
-    }
-
-    return {kScratchMountPoint, kCacheMountPoint};
-}
 
 // Return true if everything is mounted, but before adb is started.  Right
 // after 'trigger load_persist_props_action' is done.
-bool fs_mgr_boot_completed() {
+static bool fs_mgr_boot_completed() {
     return android::base::GetBoolProperty("ro.persistent_properties.ready", false);
 }
 
-bool fs_mgr_is_dir(const std::string& path) {
-    struct stat st;
-    return !stat(path.c_str(), &st) && S_ISDIR(st.st_mode);
-}
-
-bool fs_mgr_rw_access(const std::string& path) {
-    if (path.empty()) return false;
-    return access(path.c_str(), R_OK | W_OK) == 0;
-}
-
-// At less than 1% or 8MB of free space return value of false,
-// means we will try to wrap with overlayfs.
-bool fs_mgr_filesystem_has_space(const std::string& mount_point) {
-    // If we have access issues to find out space remaining, return true
-    // to prevent us trying to override with overlayfs.
-    struct statvfs vst;
-    if (statvfs(mount_point.c_str(), &vst)) {
-        PLOG(ERROR) << "statvfs " << mount_point;
-        return true;
-    }
-
-    static constexpr int kPercentThreshold = 1;                       // 1%
-    static constexpr unsigned long kSizeThreshold = 8 * 1024 * 1024;  // 8MB
-
-    return (vst.f_bfree >= (vst.f_blocks * kPercentThreshold / 100)) &&
-           (static_cast<uint64_t>(vst.f_bfree) * vst.f_frsize) >= kSizeThreshold;
-}
-
-const auto kPhysicalDevice = "/dev/block/by-name/";
+constexpr auto kPhysicalDevice = "/dev/block/by-name/";
 constexpr char kScratchImageMetadata[] = "/metadata/gsi/remount/lp_metadata";
 
 // Note: this is meant only for recovery/first-stage init.
-bool ScratchIsOnData() {
+static bool ScratchIsOnData() {
     // The scratch partition of DSU is managed by gsid.
     if (fs_mgr_is_dsu_running()) {
         return false;
@@ -170,97 +89,7 @@
     return fs_mgr_access(kScratchImageMetadata);
 }
 
-bool fs_mgr_update_blk_device(FstabEntry* entry) {
-    if (entry->fs_mgr_flags.logical) {
-        fs_mgr_update_logical_partition(entry);
-    }
-    if (fs_mgr_access(entry->blk_device)) {
-        return true;
-    }
-    if (entry->blk_device != "/dev/root") {
-        return false;
-    }
-
-    // special case for system-as-root (taimen and others)
-    auto blk_device = std::string(kPhysicalDevice) + "system";
-    if (!fs_mgr_access(blk_device)) {
-        blk_device += fs_mgr_get_slot_suffix();
-        if (!fs_mgr_access(blk_device)) {
-            return false;
-        }
-    }
-    entry->blk_device = blk_device;
-    return true;
-}
-
-bool fs_mgr_has_shared_blocks(const std::string& mount_point, const std::string& dev) {
-    struct statfs fs;
-    if ((statfs((mount_point + "/lost+found").c_str(), &fs) == -1) ||
-        (fs.f_type != EXT4_SUPER_MAGIC)) {
-        return false;
-    }
-
-    android::base::unique_fd fd(open(dev.c_str(), O_RDONLY | O_CLOEXEC));
-    if (fd < 0) return false;
-
-    struct ext4_super_block sb;
-    if ((TEMP_FAILURE_RETRY(lseek64(fd, 1024, SEEK_SET)) < 0) ||
-        (TEMP_FAILURE_RETRY(read(fd, &sb, sizeof(sb))) < 0)) {
-        return false;
-    }
-
-    struct fs_info info;
-    if (ext4_parse_sb(&sb, &info) < 0) return false;
-
-    return (info.feat_ro_compat & EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS) != 0;
-}
-
-#define F2FS_SUPER_OFFSET 1024
-#define F2FS_FEATURE_OFFSET 2180
-#define F2FS_FEATURE_RO 0x4000
-bool fs_mgr_is_read_only_f2fs(const std::string& dev) {
-    if (!fs_mgr_is_f2fs(dev)) return false;
-
-    android::base::unique_fd fd(open(dev.c_str(), O_RDONLY | O_CLOEXEC));
-    if (fd < 0) return false;
-
-    __le32 feat;
-    if ((TEMP_FAILURE_RETRY(lseek64(fd, F2FS_SUPER_OFFSET + F2FS_FEATURE_OFFSET, SEEK_SET)) < 0) ||
-        (TEMP_FAILURE_RETRY(read(fd, &feat, sizeof(feat))) < 0)) {
-        return false;
-    }
-
-    return (feat & cpu_to_le32(F2FS_FEATURE_RO)) != 0;
-}
-
-bool fs_mgr_overlayfs_enabled(FstabEntry* entry) {
-    // readonly filesystem, can not be mount -o remount,rw
-    // for squashfs, erofs or if free space is (near) zero making such a remount
-    // virtually useless, or if there are shared blocks that prevent remount,rw
-    if (!fs_mgr_filesystem_has_space(entry->mount_point)) {
-        return true;
-    }
-
-    // blk_device needs to be setup so we can check superblock.
-    // If we fail here, because during init first stage and have doubts.
-    if (!fs_mgr_update_blk_device(entry)) {
-        return true;
-    }
-
-    // f2fs read-only mode doesn't support remount,rw
-    if (fs_mgr_is_read_only_f2fs(entry->blk_device)) {
-        return true;
-    }
-
-    // check if ext4 de-dupe
-    auto has_shared_blocks = fs_mgr_has_shared_blocks(entry->mount_point, entry->blk_device);
-    if (!has_shared_blocks && (entry->mount_point == "/system")) {
-        has_shared_blocks = fs_mgr_has_shared_blocks("/", entry->blk_device);
-    }
-    return has_shared_blocks;
-}
-
-bool fs_mgr_rm_all(const std::string& path, bool* change = nullptr, int level = 0) {
+static bool fs_mgr_rm_all(const std::string& path, bool* change = nullptr, int level = 0) {
     std::unique_ptr<DIR, decltype(&closedir)> dir(opendir(path.c_str()), closedir);
     if (!dir) {
         if (errno == ENOENT) {
@@ -301,96 +130,6 @@
     return ret;
 }
 
-const auto kUpperName = "upper";
-const auto kWorkName = "work";
-const auto kOverlayTopDir = "/overlay";
-
-std::string fs_mgr_get_overlayfs_candidate(const std::string& mount_point) {
-    if (!fs_mgr_is_dir(mount_point)) return "";
-    const auto base = android::base::Basename(mount_point) + "/";
-    for (const auto& overlay_mount_point : OverlayMountPoints()) {
-        auto dir = overlay_mount_point + kOverlayTopDir + "/" + base;
-        auto upper = dir + kUpperName;
-        if (!fs_mgr_is_dir(upper)) continue;
-        auto work = dir + kWorkName;
-        if (!fs_mgr_is_dir(work)) continue;
-        if (!fs_mgr_rw_access(work)) continue;
-        return dir;
-    }
-    return "";
-}
-
-static inline bool KernelSupportsUserXattrs() {
-    struct utsname uts;
-    uname(&uts);
-
-    int major, minor;
-    if (sscanf(uts.release, "%d.%d", &major, &minor) != 2) {
-        return false;
-    }
-    return major > 5 || (major == 5 && minor >= 15);
-}
-
-const std::string fs_mgr_mount_point(const std::string& mount_point) {
-    if ("/"s != mount_point) return mount_point;
-    return "/system";
-}
-
-// default options for mount_point, returns empty string for none available.
-std::string fs_mgr_get_overlayfs_options(const FstabEntry& entry) {
-    const auto mount_point = fs_mgr_mount_point(entry.mount_point);
-    auto candidate = fs_mgr_get_overlayfs_candidate(mount_point);
-    if (candidate.empty()) return "";
-    auto ret = kLowerdirOption + mount_point + "," + kUpperdirOption + candidate + kUpperName +
-               ",workdir=" + candidate + kWorkName;
-    if (fs_mgr_overlayfs_valid() == OverlayfsValidResult::kOverrideCredsRequired) {
-        ret += ",override_creds=off";
-    }
-    if (KernelSupportsUserXattrs()) {
-        ret += ",userxattr";
-    }
-    for (const auto& flag : android::base::Split(entry.fs_options, ",")) {
-        if (android::base::StartsWith(flag, "context=")) {
-            ret += "," + flag;
-        }
-    }
-    return ret;
-}
-
-constexpr char kOverlayfsFileContext[] = "u:object_r:overlayfs_file:s0";
-
-class AutoSetFsCreateCon final {
-  public:
-    AutoSetFsCreateCon() {}
-    AutoSetFsCreateCon(const std::string& context) { Set(context); }
-    ~AutoSetFsCreateCon() { Restore(); }
-
-    bool Ok() const { return ok_; }
-    bool Set(const std::string& context) {
-        if (setfscreatecon(context.c_str())) {
-            PLOG(ERROR) << "setfscreatecon " << context;
-            return false;
-        }
-        ok_ = true;
-        return true;
-    }
-    bool Restore() {
-        if (restored_ || !ok_) {
-            return true;
-        }
-        if (setfscreatecon(nullptr)) {
-            PLOG(ERROR) << "setfscreatecon null";
-            return false;
-        }
-        restored_ = true;
-        return true;
-    }
-
-  private:
-    bool ok_ = false;
-    bool restored_ = false;
-};
-
 std::string fs_mgr_overlayfs_setup_dir(const std::string& dir) {
     auto top = dir + kOverlayTopDir;
 
@@ -452,15 +191,15 @@
     return true;
 }
 
-uint32_t fs_mgr_overlayfs_slot_number() {
+static uint32_t fs_mgr_overlayfs_slot_number() {
     return SlotNumberForSlotSuffix(fs_mgr_get_slot_suffix());
 }
 
-std::string fs_mgr_overlayfs_super_device(uint32_t slot_number) {
+static std::string fs_mgr_overlayfs_super_device(uint32_t slot_number) {
     return kPhysicalDevice + fs_mgr_get_super_partition_name(slot_number);
 }
 
-bool fs_mgr_overlayfs_has_logical(const Fstab& fstab) {
+static bool fs_mgr_overlayfs_has_logical(const Fstab& fstab) {
     for (const auto& entry : fstab) {
         if (entry.fs_mgr_flags.logical) {
             return true;
@@ -469,18 +208,6 @@
     return false;
 }
 
-// Returns true if immediate unmount succeeded and the scratch mount point was
-// removed.
-bool fs_mgr_overlayfs_umount_scratch() {
-    if (umount(kScratchMountPoint) != 0) {
-        return false;
-    }
-    if (rmdir(kScratchMountPoint) != 0 && errno != ENOENT) {
-        PLOG(ERROR) << "rmdir " << kScratchMountPoint;
-    }
-    return true;
-}
-
 OverlayfsTeardownResult TeardownDataScratch(IImageManager* images,
                                             const std::string& partition_name, bool was_mounted) {
     if (!images) {
@@ -619,214 +346,6 @@
     return ret;
 }
 
-bool fs_mgr_overlayfs_set_shared_mount(const std::string& mount_point, bool shared_flag) {
-    auto ret = mount(nullptr, mount_point.c_str(), nullptr, shared_flag ? MS_SHARED : MS_PRIVATE,
-                     nullptr);
-    if (ret) {
-        PERROR << "__mount(target=" << mount_point
-               << ",flag=" << (shared_flag ? "MS_SHARED" : "MS_PRIVATE") << ")=" << ret;
-        // If "/system" doesn't look like a mountpoint, retry with "/".
-        if (errno == EINVAL && mount_point == "/system") {
-            return fs_mgr_overlayfs_set_shared_mount("/", shared_flag);
-        }
-        return false;
-    }
-    return true;
-}
-
-bool fs_mgr_overlayfs_move_mount(const std::string& source, const std::string& target) {
-    auto ret = mount(source.c_str(), target.c_str(), nullptr, MS_MOVE, nullptr);
-    if (ret) {
-        PERROR << "__mount(source=" << source << ",target=" << target << ",flag=MS_MOVE)=" << ret;
-        return false;
-    }
-    return true;
-}
-
-struct mount_info {
-    std::string mount_point;
-    bool shared_flag;
-};
-
-std::vector<mount_info> ReadMountinfoFromFile(const std::string& path) {
-    std::vector<mount_info> info;
-
-    auto file = std::unique_ptr<FILE, decltype(&fclose)>{fopen(path.c_str(), "re"), fclose};
-    if (!file) {
-        PERROR << __FUNCTION__ << "(): cannot open file: '" << path << "'";
-        return info;
-    }
-
-    ssize_t len;
-    size_t alloc_len = 0;
-    char* line = nullptr;
-    while ((len = getline(&line, &alloc_len, file.get())) != -1) {
-        /* if the last character is a newline, shorten the string by 1 byte */
-        if (line[len - 1] == '\n') {
-            line[len - 1] = '\0';
-        }
-
-        static constexpr char delim[] = " \t";
-        char* save_ptr;
-        if (!strtok_r(line, delim, &save_ptr)) {
-            LERROR << "Error parsing mount ID";
-            break;
-        }
-        if (!strtok_r(nullptr, delim, &save_ptr)) {
-            LERROR << "Error parsing parent ID";
-            break;
-        }
-        if (!strtok_r(nullptr, delim, &save_ptr)) {
-            LERROR << "Error parsing mount source";
-            break;
-        }
-        if (!strtok_r(nullptr, delim, &save_ptr)) {
-            LERROR << "Error parsing root";
-            break;
-        }
-
-        char* p;
-        if (!(p = strtok_r(nullptr, delim, &save_ptr))) {
-            LERROR << "Error parsing mount_point";
-            break;
-        }
-        mount_info entry = {p, false};
-
-        if (!strtok_r(nullptr, delim, &save_ptr)) {
-            LERROR << "Error parsing mount_flags";
-            break;
-        }
-
-        while ((p = strtok_r(nullptr, delim, &save_ptr))) {
-            if ((p[0] == '-') && (p[1] == '\0')) break;
-            if (android::base::StartsWith(p, "shared:")) entry.shared_flag = true;
-        }
-        if (!p) {
-            LERROR << "Error parsing fields";
-            break;
-        }
-        info.emplace_back(std::move(entry));
-    }
-
-    free(line);
-    if (info.empty()) {
-        LERROR << __FUNCTION__ << "(): failed to load mountinfo from : '" << path << "'";
-    }
-    return info;
-}
-
-bool fs_mgr_overlayfs_mount(const FstabEntry& entry) {
-    const auto mount_point = fs_mgr_mount_point(entry.mount_point);
-    const auto options = fs_mgr_get_overlayfs_options(entry);
-    if (options.empty()) return false;
-
-    auto retval = true;
-
-    struct move_entry {
-        std::string mount_point;
-        std::string dir;
-        bool shared_flag;
-    };
-    std::vector<move_entry> move;
-    auto parent_private = false;
-    auto parent_made_private = false;
-    auto dev_private = false;
-    auto dev_made_private = false;
-    for (auto& entry : ReadMountinfoFromFile("/proc/self/mountinfo")) {
-        if ((entry.mount_point == mount_point) && !entry.shared_flag) {
-            parent_private = true;
-        }
-        if ((entry.mount_point == "/dev") && !entry.shared_flag) {
-            dev_private = true;
-        }
-
-        if (!android::base::StartsWith(entry.mount_point, mount_point + "/")) {
-            continue;
-        }
-        if (std::find_if(move.begin(), move.end(), [&entry](const auto& it) {
-                return android::base::StartsWith(entry.mount_point, it.mount_point + "/");
-            }) != move.end()) {
-            continue;
-        }
-
-        // use as the bound directory in /dev.
-        AutoSetFsCreateCon createcon;
-        auto new_context = fs_mgr_get_context(entry.mount_point);
-        if (new_context.empty() || !createcon.Set(new_context)) {
-            continue;
-        }
-        move_entry new_entry = {std::move(entry.mount_point), "/dev/TemporaryDir-XXXXXX",
-                                entry.shared_flag};
-        const auto target = mkdtemp(new_entry.dir.data());
-        if (!createcon.Restore()) {
-            return false;
-        }
-        if (!target) {
-            retval = false;
-            PERROR << "temporary directory for MS_BIND";
-            continue;
-        }
-
-        if (!parent_private && !parent_made_private) {
-            parent_made_private = fs_mgr_overlayfs_set_shared_mount(mount_point, false);
-        }
-        if (new_entry.shared_flag) {
-            new_entry.shared_flag = fs_mgr_overlayfs_set_shared_mount(new_entry.mount_point, false);
-        }
-        if (!fs_mgr_overlayfs_move_mount(new_entry.mount_point, new_entry.dir)) {
-            retval = false;
-            if (new_entry.shared_flag) {
-                fs_mgr_overlayfs_set_shared_mount(new_entry.mount_point, true);
-            }
-            continue;
-        }
-        move.emplace_back(std::move(new_entry));
-    }
-
-    // hijack __mount() report format to help triage
-    auto report = "__mount(source=overlay,target="s + mount_point + ",type=overlay";
-    const auto opt_list = android::base::Split(options, ",");
-    for (const auto& opt : opt_list) {
-        if (android::base::StartsWith(opt, kUpperdirOption)) {
-            report = report + "," + opt;
-            break;
-        }
-    }
-    report = report + ")=";
-
-    auto ret = mount("overlay", mount_point.c_str(), "overlay", MS_RDONLY | MS_NOATIME,
-                     options.c_str());
-    if (ret) {
-        retval = false;
-        PERROR << report << ret;
-    } else {
-        LINFO << report << ret;
-    }
-
-    // Move submounts back.
-    for (const auto& entry : move) {
-        if (!dev_private && !dev_made_private) {
-            dev_made_private = fs_mgr_overlayfs_set_shared_mount("/dev", false);
-        }
-
-        if (!fs_mgr_overlayfs_move_mount(entry.dir, entry.mount_point)) {
-            retval = false;
-        } else if (entry.shared_flag &&
-                   !fs_mgr_overlayfs_set_shared_mount(entry.mount_point, true)) {
-            retval = false;
-        }
-        rmdir(entry.dir.c_str());
-    }
-    if (dev_made_private) {
-        fs_mgr_overlayfs_set_shared_mount("/dev", true);
-    }
-    if (parent_made_private) {
-        fs_mgr_overlayfs_set_shared_mount(mount_point, true);
-    }
-
-    return retval;
-}
-
 // Mount kScratchMountPoint
 bool MountScratch(const std::string& device_path, bool readonly = false) {
     if (readonly) {
@@ -1010,21 +529,7 @@
         auto partition_size =
                 builder->AllocatableSpace() - builder->UsedSpace() + partition->size();
         if ((partition_size > kMinimumSize) || !partition->size()) {
-            // Leave some space for free space jitter of a few erase
-            // blocks, in case they are needed for any individual updates
-            // to any other partition that needs to be flashed while
-            // overlayfs is in force.  Of course if margin_size is not
-            // enough could normally get a flash failure, so
-            // ResizePartition() will delete the scratch partition in
-            // order to fulfill.  Deleting scratch will destroy all of
-            // the adb remount overrides :-( .
-            auto margin_size = uint64_t(3 * 256 * 1024);
-            BlockDeviceInfo info;
-            if (builder->GetBlockDeviceInfo(fs_mgr_get_super_partition_name(slot_number), &info)) {
-                margin_size = 3 * info.logical_block_size;
-            }
-            partition_size = std::max(std::min(kMinimumSize, partition_size - margin_size),
-                                      partition_size / 2);
+            partition_size = std::max(std::min(kMinimumSize, partition_size), partition_size / 2);
             if (partition_size > partition->size()) {
                 if (!builder->ResizePartition(partition, partition_size)) {
                     // Try to free up space by deallocating partitions in the other slot.
@@ -1032,8 +537,8 @@
 
                     partition_size =
                             builder->AllocatableSpace() - builder->UsedSpace() + partition->size();
-                    partition_size = std::max(std::min(kMinimumSize, partition_size - margin_size),
-                                              partition_size / 2);
+                    partition_size =
+                            std::max(std::min(kMinimumSize, partition_size), partition_size / 2);
                     if (!builder->ResizePartition(partition, partition_size)) {
                         LERROR << "resize " << partition_name;
                         return false;
@@ -1212,12 +717,6 @@
     return MountScratch(scratch_device);
 }
 
-#if ALLOW_ADBD_DISABLE_VERITY
-constexpr bool kAllowOverlayfs = true;
-#else
-constexpr bool kAllowOverlayfs = false;
-#endif
-
 // NOTE: OverlayfsSetupAllowed() must be "stricter" than OverlayfsTeardownAllowed().
 // Setup is allowed only if teardown is also allowed.
 bool OverlayfsSetupAllowed(bool verbose = false) {
@@ -1251,114 +750,6 @@
 
 }  // namespace
 
-bool fs_mgr_wants_overlayfs(FstabEntry* entry) {
-    // Don't check entries that are managed by vold.
-    if (entry->fs_mgr_flags.vold_managed || entry->fs_mgr_flags.recovery_only) return false;
-
-    // *_other doesn't want overlayfs.
-    if (entry->fs_mgr_flags.slot_select_other) return false;
-
-    // Only concerned with readonly partitions.
-    if (!(entry->flags & MS_RDONLY)) return false;
-
-    // If unbindable, do not allow overlayfs as this could expose us to
-    // security issues.  On Android, this could also be used to turn off
-    // the ability to overlay an otherwise acceptable filesystem since
-    // /system and /vendor are never bound(sic) to.
-    if (entry->flags & MS_UNBINDABLE) return false;
-
-    if (!fs_mgr_overlayfs_enabled(entry)) return false;
-
-    return true;
-}
-
-Fstab fs_mgr_overlayfs_candidate_list(const Fstab& fstab) {
-    android::fs_mgr::Fstab mounts;
-    if (!android::fs_mgr::ReadFstabFromFile("/proc/mounts", &mounts)) {
-        PLOG(ERROR) << "Failed to read /proc/mounts";
-        return {};
-    }
-
-    Fstab candidates;
-    for (const auto& entry : fstab) {
-        // Filter out partitions whose type doesn't match what's mounted.
-        // This avoids spammy behavior on devices which can mount different
-        // filesystems for each partition.
-        auto proc_mount_point = (entry.mount_point == "/system") ? "/" : entry.mount_point;
-        auto mounted = GetEntryForMountPoint(&mounts, proc_mount_point);
-        if (!mounted || mounted->fs_type != entry.fs_type) {
-            continue;
-        }
-
-        FstabEntry new_entry = entry;
-        if (!fs_mgr_overlayfs_already_mounted(entry.mount_point) &&
-            !fs_mgr_wants_overlayfs(&new_entry)) {
-            continue;
-        }
-        auto new_mount_point = fs_mgr_mount_point(entry.mount_point);
-        auto duplicate_or_more_specific = false;
-        for (auto it = candidates.begin(); it != candidates.end();) {
-            auto it_mount_point = fs_mgr_mount_point(it->mount_point);
-            if ((it_mount_point == new_mount_point) ||
-                (android::base::StartsWith(new_mount_point, it_mount_point + "/"))) {
-                duplicate_or_more_specific = true;
-                break;
-            }
-            if (android::base::StartsWith(it_mount_point, new_mount_point + "/")) {
-                it = candidates.erase(it);
-            } else {
-                ++it;
-            }
-        }
-        if (!duplicate_or_more_specific) candidates.emplace_back(std::move(new_entry));
-    }
-    return candidates;
-}
-
-static void TryMountScratch() {
-    // Note we get the boot scratch device here, which means if scratch was
-    // just created through ImageManager, this could fail. In practice this
-    // should not happen because "remount" detects this scenario (by checking
-    // if verity is still disabled, i.e. no reboot occurred), and skips calling
-    // fs_mgr_overlayfs_mount_all().
-    auto scratch_device = GetBootScratchDevice();
-    if (!fs_mgr_rw_access(scratch_device)) {
-        return;
-    }
-    if (!WaitForFile(scratch_device, 10s)) {
-        return;
-    }
-    if (!MountScratch(scratch_device, true /* readonly */)) {
-        return;
-    }
-    auto has_overlayfs_dir = fs_mgr_access(std::string(kScratchMountPoint) + kOverlayTopDir);
-    fs_mgr_overlayfs_umount_scratch();
-    if (has_overlayfs_dir) {
-        MountScratch(scratch_device);
-    }
-}
-
-bool fs_mgr_overlayfs_mount_all(Fstab* fstab) {
-    if (!OverlayfsSetupAllowed()) {
-        return false;
-    }
-    auto ret = true;
-    auto scratch_can_be_mounted = true;
-    for (const auto& entry : fs_mgr_overlayfs_candidate_list(*fstab)) {
-        if (fs_mgr_is_verity_enabled(entry)) continue;
-        auto mount_point = fs_mgr_mount_point(entry.mount_point);
-        if (fs_mgr_overlayfs_already_mounted(mount_point)) {
-            continue;
-        }
-        if (scratch_can_be_mounted) {
-            scratch_can_be_mounted = false;
-            TryMountScratch();
-        }
-        ret &= fs_mgr_overlayfs_mount(entry);
-    }
-    return ret;
-}
-
 bool fs_mgr_overlayfs_setup(const Fstab& fstab, const char* mount_point, bool* want_reboot,
                             bool just_disabled_verity) {
     if (!OverlayfsSetupAllowed(/*verbose=*/true)) {
@@ -1582,22 +973,6 @@
     return rv;
 }
 
-bool fs_mgr_overlayfs_is_setup() {
-    if (!OverlayfsSetupAllowed()) {
-        return false;
-    }
-    if (fs_mgr_overlayfs_already_mounted(kScratchMountPoint, false)) return true;
-    Fstab fstab;
-    if (!ReadDefaultFstab(&fstab)) {
-        return false;
-    }
-    for (const auto& entry : fs_mgr_overlayfs_candidate_list(fstab)) {
-        if (fs_mgr_is_verity_enabled(entry)) continue;
-        if (fs_mgr_overlayfs_already_mounted(fs_mgr_mount_point(entry.mount_point))) return true;
-    }
-    return false;
-}
-
 namespace android {
 namespace fs_mgr {
 
@@ -1714,23 +1089,3 @@
 
 }  // namespace fs_mgr
 }  // namespace android
-
-bool fs_mgr_overlayfs_already_mounted(const std::string& mount_point, bool overlay_only) {
-    Fstab fstab;
-    if (!ReadFstabFromFile("/proc/mounts", &fstab)) {
-        return false;
-    }
-    const auto lowerdir = kLowerdirOption + mount_point;
-    for (const auto& entry : fstab) {
-        if (overlay_only && "overlay" != entry.fs_type && "overlayfs" != entry.fs_type) continue;
-        if (mount_point != entry.mount_point) continue;
-        if (!overlay_only) return true;
-        const auto options = android::base::Split(entry.fs_options, ",");
-        for (const auto& opt : options) {
-            if (opt == lowerdir) {
-                return true;
-            }
-        }
-    }
-    return false;
-}
diff --git a/fs_mgr/fs_mgr_overlayfs_control.h b/fs_mgr/fs_mgr_overlayfs_control.h
new file mode 100644
index 0000000..50e83e8
--- /dev/null
+++ b/fs_mgr/fs_mgr_overlayfs_control.h
@@ -0,0 +1,44 @@
+// Copyright (C) 2023 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 <string>
+
+#include <fstab/fstab.h>
+
+// If "mount_point" is non-null, set up exactly one overlay.
+//
+// If "mount_point" is null, setup any overlays.
+//
+// If |want_reboot| is non-null, and a reboot is needed to apply overlays, then
+// it will be true on return. The caller is responsible for initializing it.
+bool fs_mgr_overlayfs_setup(const android::fs_mgr::Fstab& fstab, const char* mount_point = nullptr,
+                            bool* want_reboot = nullptr, bool just_disabled_verity = true);
+
+enum class OverlayfsTeardownResult {
+    Ok,
+    Busy,  // Indicates that overlays are still in use.
+    Error
+};
+OverlayfsTeardownResult fs_mgr_overlayfs_teardown(const char* mount_point = nullptr,
+                                                  bool* want_reboot = nullptr);
+
+namespace android {
+namespace fs_mgr {
+
+void CleanupOldScratchFiles();
+
+}  // namespace fs_mgr
+}  // namespace android
diff --git a/fs_mgr/fs_mgr_overlayfs_mount.cpp b/fs_mgr/fs_mgr_overlayfs_mount.cpp
new file mode 100644
index 0000000..c057c2b
--- /dev/null
+++ b/fs_mgr/fs_mgr_overlayfs_mount.cpp
@@ -0,0 +1,802 @@
+/*
+ * Copyright (C) 2018 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 <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/fs.h>
+#include <selinux/selinux.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/param.h>
+#include <sys/stat.h>
+#include <sys/statvfs.h>
+#include <sys/types.h>
+#include <sys/utsname.h>
+#include <sys/vfs.h>
+#include <unistd.h>
+
+#include <algorithm>
+#include <memory>
+#include <optional>
+#include <string>
+#include <vector>
+
+#include <android-base/file.h>
+#include <android-base/macros.h>
+#include <android-base/properties.h>
+#include <android-base/strings.h>
+#include <android-base/unique_fd.h>
+#include <ext4_utils/ext4_utils.h>
+#include <fs_mgr.h>
+#include <fs_mgr/file_wait.h>
+#include <fs_mgr_dm_linear.h>
+#include <fs_mgr_overlayfs.h>
+#include <fstab/fstab.h>
+#include <libdm/dm.h>
+#include <libgsi/libgsi.h>
+#include <storage_literals/storage_literals.h>
+
+#include "fs_mgr_overlayfs_mount.h"
+#include "fs_mgr_priv.h"
+
+using namespace std::literals;
+using namespace android::dm;
+using namespace android::fs_mgr;
+using namespace android::storage_literals;
+
+constexpr char kPreferCacheBackingStorageProp[] = "fs_mgr.overlayfs.prefer_cache_backing_storage";
+
+bool fs_mgr_access(const std::string& path) {
+    return access(path.c_str(), F_OK) == 0;
+}
+
+const auto kLowerdirOption = "lowerdir=";
+const auto kUpperdirOption = "upperdir=";
+
+bool fs_mgr_in_recovery() {
+    // Check the existence of recovery binary instead of using the compile time
+    // __ANDROID_RECOVERY__ macro.
+    // If BOARD_USES_RECOVERY_AS_BOOT is true, both normal and recovery boot
+    // mode would use the same init binary, which would mean during normal boot
+    // the '/init' binary is actually a symlink pointing to
+    // init_second_stage.recovery, which would be compiled with
+    // __ANDROID_RECOVERY__ defined.
+    return fs_mgr_access("/system/bin/recovery");
+}
+
+bool fs_mgr_is_dsu_running() {
+    // Since android::gsi::CanBootIntoGsi() or android::gsi::MarkSystemAsGsi() is
+    // never called in recovery, the return value of android::gsi::IsGsiRunning()
+    // is not well-defined. In this case, just return false as being in recovery
+    // implies not running a DSU system.
+    if (fs_mgr_in_recovery()) return false;
+    return android::gsi::IsGsiRunning();
+}
+
+const auto kCacheMountPoint = "/cache";
+
+static bool IsABDevice() {
+    return !android::base::GetProperty("ro.boot.slot_suffix", "").empty();
+}
+
+std::vector<const std::string> OverlayMountPoints() {
+    // Never fallback to legacy cache mount point if within a DSU system,
+    // because running a DSU system implies the device supports dynamic
+    // partitions, which means legacy cache mustn't be used.
+    if (fs_mgr_is_dsu_running()) {
+        return {kScratchMountPoint};
+    }
+
+    // For non-A/B devices prefer cache backing storage if
+    // kPreferCacheBackingStorageProp property set.
+    if (!IsABDevice() && android::base::GetBoolProperty(kPreferCacheBackingStorageProp, false) &&
+        android::base::GetIntProperty("ro.vendor.api_level", -1) < __ANDROID_API_T__) {
+        return {kCacheMountPoint, kScratchMountPoint};
+    }
+
+    return {kScratchMountPoint, kCacheMountPoint};
+}
+
+static bool fs_mgr_is_dir(const std::string& path) {
+    struct stat st;
+    return !stat(path.c_str(), &st) && S_ISDIR(st.st_mode);
+}
+
+bool fs_mgr_rw_access(const std::string& path) {
+    if (path.empty()) return false;
+    return access(path.c_str(), R_OK | W_OK) == 0;
+}
+
+// At less than 1% or 8MB of free space return value of false,
+// means we will try to wrap with overlayfs.
+bool fs_mgr_filesystem_has_space(const std::string& mount_point) {
+    // If we have access issues to find out space remaining, return true
+    // to prevent us trying to override with overlayfs.
+    struct statvfs vst;
+    if (statvfs(mount_point.c_str(), &vst)) {
+        PLOG(ERROR) << "statvfs " << mount_point;
+        return true;
+    }
+
+    static constexpr int kPercentThreshold = 1;                       // 1%
+    static constexpr unsigned long kSizeThreshold = 8 * 1024 * 1024;  // 8MB
+
+    return (vst.f_bfree >= (vst.f_blocks * kPercentThreshold / 100)) &&
+           (static_cast<uint64_t>(vst.f_bfree) * vst.f_frsize) >= kSizeThreshold;
+}
+
+const auto kPhysicalDevice = "/dev/block/by-name/";
+
+static bool fs_mgr_update_blk_device(FstabEntry* entry) {
+    if (entry->fs_mgr_flags.logical) {
+        fs_mgr_update_logical_partition(entry);
+    }
+    if (fs_mgr_access(entry->blk_device)) {
+        return true;
+    }
+    if (entry->blk_device != "/dev/root") {
+        return false;
+    }
+
+    // special case for system-as-root (taimen and others)
+    auto blk_device = std::string(kPhysicalDevice) + "system";
+    if (!fs_mgr_access(blk_device)) {
+        blk_device += fs_mgr_get_slot_suffix();
+        if (!fs_mgr_access(blk_device)) {
+            return false;
+        }
+    }
+    entry->blk_device = blk_device;
+    return true;
+}
+
+static bool fs_mgr_has_shared_blocks(const std::string& mount_point, const std::string& dev) {
+    struct statfs fs;
+    if ((statfs((mount_point + "/lost+found").c_str(), &fs) == -1) ||
+        (fs.f_type != EXT4_SUPER_MAGIC)) {
+        return false;
+    }
+
+    android::base::unique_fd fd(open(dev.c_str(), O_RDONLY | O_CLOEXEC));
+    if (fd < 0) return false;
+
+    struct ext4_super_block sb;
+    if ((TEMP_FAILURE_RETRY(lseek64(fd, 1024, SEEK_SET)) < 0) ||
+        (TEMP_FAILURE_RETRY(read(fd, &sb, sizeof(sb))) < 0)) {
+        return false;
+    }
+
+    struct fs_info info;
+    if (ext4_parse_sb(&sb, &info) < 0) return false;
+
+    return (info.feat_ro_compat & EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS) != 0;
+}
+
+#define F2FS_SUPER_OFFSET 1024
+#define F2FS_FEATURE_OFFSET 2180
+#define F2FS_FEATURE_RO 0x4000
+static bool fs_mgr_is_read_only_f2fs(const std::string& dev) {
+    if (!fs_mgr_is_f2fs(dev)) return false;
+
+    android::base::unique_fd fd(open(dev.c_str(), O_RDONLY | O_CLOEXEC));
+    if (fd < 0) return false;
+
+    __le32 feat;
+    if ((TEMP_FAILURE_RETRY(lseek64(fd, F2FS_SUPER_OFFSET + F2FS_FEATURE_OFFSET, SEEK_SET)) < 0) ||
+        (TEMP_FAILURE_RETRY(read(fd, &feat, sizeof(feat))) < 0)) {
+        return false;
+    }
+
+    return (feat & cpu_to_le32(F2FS_FEATURE_RO)) != 0;
+}
+
+static bool fs_mgr_overlayfs_enabled(FstabEntry* entry) {
+    // readonly filesystem, can not be mount -o remount,rw
+    // for squashfs, erofs or if free space is (near) zero making such a remount
+    // virtually useless, or if there are shared blocks that prevent remount,rw
+    if (!fs_mgr_filesystem_has_space(entry->mount_point)) {
+        return true;
+    }
+
+    // blk_device needs to be setup so we can check superblock.
+    // If we fail here, because during init first stage and have doubts.
+    if (!fs_mgr_update_blk_device(entry)) {
+        return true;
+    }
+
+    // f2fs read-only mode doesn't support remount,rw
+    if (fs_mgr_is_read_only_f2fs(entry->blk_device)) {
+        return true;
+    }
+
+    // check if ext4 de-dupe
+    auto has_shared_blocks = fs_mgr_has_shared_blocks(entry->mount_point, entry->blk_device);
+    if (!has_shared_blocks && (entry->mount_point == "/system")) {
+        has_shared_blocks = fs_mgr_has_shared_blocks("/", entry->blk_device);
+    }
+    return has_shared_blocks;
+}
+
+static std::string fs_mgr_get_overlayfs_candidate(const std::string& mount_point) {
+    if (!fs_mgr_is_dir(mount_point)) return "";
+    const auto base = android::base::Basename(mount_point) + "/";
+    for (const auto& overlay_mount_point : OverlayMountPoints()) {
+        auto dir = overlay_mount_point + kOverlayTopDir + "/" + base;
+        auto upper = dir + kUpperName;
+        if (!fs_mgr_is_dir(upper)) continue;
+        auto work = dir + kWorkName;
+        if (!fs_mgr_is_dir(work)) continue;
+        if (!fs_mgr_rw_access(work)) continue;
+        return dir;
+    }
+    return "";
+}
+
+static inline bool KernelSupportsUserXattrs() {
+    struct utsname uts;
+    uname(&uts);
+
+    int major, minor;
+    if (sscanf(uts.release, "%d.%d", &major, &minor) != 2) {
+        return false;
+    }
+    return major > 5 || (major == 5 && minor >= 15);
+}
+
+const std::string fs_mgr_mount_point(const std::string& mount_point) {
+    if ("/"s != mount_point) return mount_point;
+    return "/system";
+}
+
+// default options for mount_point, returns empty string for none available.
+static std::string fs_mgr_get_overlayfs_options(const FstabEntry& entry) {
+    const auto mount_point = fs_mgr_mount_point(entry.mount_point);
+    auto candidate = fs_mgr_get_overlayfs_candidate(mount_point);
+    if (candidate.empty()) return "";
+    auto ret = kLowerdirOption + mount_point + "," + kUpperdirOption + candidate + kUpperName +
+               ",workdir=" + candidate + kWorkName;
+    if (fs_mgr_overlayfs_valid() == OverlayfsValidResult::kOverrideCredsRequired) {
+        ret += ",override_creds=off";
+    }
+    if (KernelSupportsUserXattrs()) {
+        ret += ",userxattr";
+    }
+    for (const auto& flag : android::base::Split(entry.fs_options, ",")) {
+        if (android::base::StartsWith(flag, "context=")) {
+            ret += "," + flag;
+        }
+    }
+    return ret;
+}
+
+bool AutoSetFsCreateCon::Set(const std::string& context) {
+    if (setfscreatecon(context.c_str())) {
+        PLOG(ERROR) << "setfscreatecon " << context;
+        return false;
+    }
+    ok_ = true;
+    return true;
+}
+
+bool AutoSetFsCreateCon::Restore() {
+    if (restored_ || !ok_) {
+        return true;
+    }
+    if (setfscreatecon(nullptr)) {
+        PLOG(ERROR) << "setfscreatecon null";
+        return false;
+    }
+    restored_ = true;
+    return true;
+}
+
+// Returns true if immediate unmount succeeded and the scratch mount point was
+// removed.
+bool fs_mgr_overlayfs_umount_scratch() {
+    if (umount(kScratchMountPoint) != 0) {
+        return false;
+    }
+    if (rmdir(kScratchMountPoint) != 0 && errno != ENOENT) {
+        PLOG(ERROR) << "rmdir " << kScratchMountPoint;
+    }
+    return true;
+}
+
+static bool fs_mgr_overlayfs_set_shared_mount(const std::string& mount_point, bool shared_flag) {
+    auto ret = mount(nullptr, mount_point.c_str(), nullptr, shared_flag ? MS_SHARED : MS_PRIVATE,
+                     nullptr);
+    if (ret) {
+        PERROR << "__mount(target=" << mount_point
+               << ",flag=" << (shared_flag ? "MS_SHARED" : "MS_PRIVATE") << ")=" << ret;
+        // If "/system" doesn't look like a mountpoint, retry with "/".
+        if (errno == EINVAL && mount_point == "/system") {
+            return fs_mgr_overlayfs_set_shared_mount("/", shared_flag);
+        }
+        return false;
+    }
+    return true;
+}
+
+static bool fs_mgr_overlayfs_move_mount(const std::string& source, const std::string& target) {
+    auto ret = mount(source.c_str(), target.c_str(), nullptr, MS_MOVE, nullptr);
+    if (ret) {
+        PERROR << "__mount(source=" << source << ",target=" << target << ",flag=MS_MOVE)=" << ret;
+        return false;
+    }
+    return true;
+}
+
+struct mount_info {
+    std::string mount_point;
+    bool shared_flag;
+};
+
+static std::vector<mount_info> ReadMountinfoFromFile(const std::string& path) {
+    std::vector<mount_info> info;
+
+    auto file = std::unique_ptr<FILE, decltype(&fclose)>{fopen(path.c_str(), "re"), fclose};
+    if (!file) {
+        PERROR << __FUNCTION__ << "(): cannot open file: '" << path << "'";
+        return info;
+    }
+
+    ssize_t len;
+    size_t alloc_len = 0;
+    char* line = nullptr;
+    while ((len = getline(&line, &alloc_len, file.get())) != -1) {
+        /* if the last character is a newline, shorten the string by 1 byte */
+        if (line[len - 1] == '\n') {
+            line[len - 1] = '\0';
+        }
+
+        static constexpr char delim[] = " \t";
+        char* save_ptr;
+        if (!strtok_r(line, delim, &save_ptr)) {
+            LERROR << "Error parsing mount ID";
+            break;
+        }
+        if (!strtok_r(nullptr, delim, &save_ptr)) {
+            LERROR << "Error parsing parent ID";
+            break;
+        }
+        if (!strtok_r(nullptr, delim, &save_ptr)) {
+            LERROR << "Error parsing mount source";
+            break;
+        }
+        if (!strtok_r(nullptr, delim, &save_ptr)) {
+            LERROR << "Error parsing root";
+            break;
+        }
+
+        char* p;
+        if (!(p = strtok_r(nullptr, delim, &save_ptr))) {
+            LERROR << "Error parsing mount_point";
+            break;
+        }
+        mount_info entry = {p, false};
+
+        if (!strtok_r(nullptr, delim, &save_ptr)) {
+            LERROR << "Error parsing mount_flags";
+            break;
+        }
+
+        while ((p = strtok_r(nullptr, delim, &save_ptr))) {
+            if ((p[0] == '-') && (p[1] == '\0')) break;
+            if (android::base::StartsWith(p, "shared:")) entry.shared_flag = true;
+        }
+        if (!p) {
+            LERROR << "Error parsing fields";
+            break;
+        }
+        info.emplace_back(std::move(entry));
+    }
+
+    free(line);
+    if (info.empty()) {
+        LERROR << __FUNCTION__ << "(): failed to load mountinfo from : '" << path << "'";
+    }
+    return info;
+}
+
+static bool fs_mgr_overlayfs_mount(const FstabEntry& entry) {
+    const auto mount_point = fs_mgr_mount_point(entry.mount_point);
+    const auto options = fs_mgr_get_overlayfs_options(entry);
+    if (options.empty()) return false;
+
+    auto retval = true;
+
+    struct move_entry {
+        std::string mount_point;
+        std::string dir;
+        bool shared_flag;
+    };
+    std::vector<move_entry> move;
+    auto parent_private = false;
+    auto parent_made_private = false;
+    auto dev_private = false;
+    auto dev_made_private = false;
+    for (auto& entry : ReadMountinfoFromFile("/proc/self/mountinfo")) {
+        if ((entry.mount_point == mount_point) && !entry.shared_flag) {
+            parent_private = true;
+        }
+        if ((entry.mount_point == "/dev") && !entry.shared_flag) {
+            dev_private = true;
+        }
+
+        if (!android::base::StartsWith(entry.mount_point, mount_point + "/")) {
+            continue;
+        }
+        if (std::find_if(move.begin(), move.end(), [&entry](const auto& it) {
+                return android::base::StartsWith(entry.mount_point, it.mount_point + "/");
+            }) != move.end()) {
+            continue;
+        }
+
+        // use as the bound directory in /dev.
+        AutoSetFsCreateCon createcon;
+        auto new_context = fs_mgr_get_context(entry.mount_point);
+        if (new_context.empty() || !createcon.Set(new_context)) {
+            continue;
+        }
+        move_entry new_entry = {std::move(entry.mount_point), "/dev/TemporaryDir-XXXXXX",
+                                entry.shared_flag};
+        const auto target = mkdtemp(new_entry.dir.data());
+        if (!createcon.Restore()) {
+            return false;
+        }
+        if (!target) {
+            retval = false;
+            PERROR << "temporary directory for MS_BIND";
+            continue;
+        }
+
+        if (!parent_private && !parent_made_private) {
+            parent_made_private = fs_mgr_overlayfs_set_shared_mount(mount_point, false);
+        }
+        if (new_entry.shared_flag) {
+            new_entry.shared_flag = fs_mgr_overlayfs_set_shared_mount(new_entry.mount_point, false);
+        }
+        if (!fs_mgr_overlayfs_move_mount(new_entry.mount_point, new_entry.dir)) {
+            retval = false;
+            if (new_entry.shared_flag) {
+                fs_mgr_overlayfs_set_shared_mount(new_entry.mount_point, true);
+            }
+            continue;
+        }
+        move.emplace_back(std::move(new_entry));
+    }
+
+    // hijack __mount() report format to help triage
+    auto report = "__mount(source=overlay,target="s + mount_point + ",type=overlay";
+    const auto opt_list = android::base::Split(options, ",");
+    for (const auto& opt : opt_list) {
+        if (android::base::StartsWith(opt, kUpperdirOption)) {
+            report = report + "," + opt;
+            break;
+        }
+    }
+    report = report + ")=";
+
+    auto ret = mount("overlay", mount_point.c_str(), "overlay", MS_RDONLY | MS_NOATIME,
+                     options.c_str());
+    if (ret) {
+        retval = false;
+        PERROR << report << ret;
+    } else {
+        LINFO << report << ret;
+    }
+
+    // Move submounts back.
+    for (const auto& entry : move) {
+        if (!dev_private && !dev_made_private) {
+            dev_made_private = fs_mgr_overlayfs_set_shared_mount("/dev", false);
+        }
+
+        if (!fs_mgr_overlayfs_move_mount(entry.dir, entry.mount_point)) {
+            retval = false;
+        } else if (entry.shared_flag &&
+                   !fs_mgr_overlayfs_set_shared_mount(entry.mount_point, true)) {
+            retval = false;
+        }
+        rmdir(entry.dir.c_str());
+    }
+    if (dev_made_private) {
+        fs_mgr_overlayfs_set_shared_mount("/dev", true);
+    }
+    if (parent_made_private) {
+        fs_mgr_overlayfs_set_shared_mount(mount_point, true);
+    }
+
+    return retval;
+}
+
+// Mount kScratchMountPoint
+static bool MountScratch(const std::string& device_path, bool readonly = false) {
+    if (readonly) {
+        if (!fs_mgr_access(device_path)) {
+            LOG(ERROR) << "Path does not exist: " << device_path;
+            return false;
+        }
+    } else if (!fs_mgr_rw_access(device_path)) {
+        LOG(ERROR) << "Path does not exist or is not readwrite: " << device_path;
+        return false;
+    }
+
+    std::vector<const char*> filesystem_candidates;
+    if (fs_mgr_is_f2fs(device_path)) {
+        filesystem_candidates = {"f2fs", "ext4"};
+    } else if (fs_mgr_is_ext4(device_path)) {
+        filesystem_candidates = {"ext4", "f2fs"};
+    } else {
+        LOG(ERROR) << "Scratch partition is not f2fs or ext4";
+        return false;
+    }
+
+    AutoSetFsCreateCon createcon(kOverlayfsFileContext);
+    if (!createcon.Ok()) {
+        return false;
+    }
+    if (mkdir(kScratchMountPoint, 0755) && (errno != EEXIST)) {
+        PERROR << "create " << kScratchMountPoint;
+        return false;
+    }
+
+    FstabEntry entry;
+    entry.blk_device = device_path;
+    entry.mount_point = kScratchMountPoint;
+    entry.flags = MS_NOATIME | MS_RDONLY;
+    if (!readonly) {
+        entry.flags &= ~MS_RDONLY;
+        entry.flags |= MS_SYNCHRONOUS;
+        entry.fs_options = "nodiscard";
+        fs_mgr_set_blk_ro(device_path, false);
+    }
+    // check_fs requires apex runtime library
+    if (fs_mgr_overlayfs_already_mounted("/data", false)) {
+        entry.fs_mgr_flags.check = true;
+    }
+    bool mounted = false;
+    for (auto fs_type : filesystem_candidates) {
+        entry.fs_type = fs_type;
+        if (fs_mgr_do_mount_one(entry) == 0) {
+            mounted = true;
+            break;
+        }
+    }
+    if (!createcon.Restore()) {
+        return false;
+    }
+    if (!mounted) {
+        rmdir(kScratchMountPoint);
+        return false;
+    }
+    return true;
+}
+
+const std::string kMkF2fs("/system/bin/make_f2fs");
+const std::string kMkExt4("/system/bin/mke2fs");
+
+// Note: The scratch partition of DSU is managed by gsid, and should be initialized during
+// first-stage-mount. Just check if the DM device for DSU scratch partition is created or not.
+static std::string GetDsuScratchDevice() {
+    auto& dm = DeviceMapper::Instance();
+    std::string device;
+    if (dm.GetState(android::gsi::kDsuScratch) != DmDeviceState::INVALID &&
+        dm.GetDmDevicePathByName(android::gsi::kDsuScratch, &device)) {
+        return device;
+    }
+    return "";
+}
+
+// This returns the scratch device that was detected during early boot (first-
+// stage init). If the device was created later, for example during setup for
+// the adb remount command, it can return an empty string since it does not
+// query ImageManager. (Note that ImageManager in first-stage init will always
+// use device-mapper, since /data is not available to use loop devices.)
+static std::string GetBootScratchDevice() {
+    // Note: fs_mgr_is_dsu_running() always returns false in recovery or fastbootd.
+    if (fs_mgr_is_dsu_running()) {
+        return GetDsuScratchDevice();
+    }
+
+    auto& dm = DeviceMapper::Instance();
+
+    // If there is a scratch partition allocated in /data or on super, we
+    // automatically prioritize that over super_other or system_other.
+    // Some devices, for example, have a write-protected eMMC and the
+    // super partition cannot be used even if it exists.
+    std::string device;
+    auto partition_name = android::base::Basename(kScratchMountPoint);
+    if (dm.GetState(partition_name) != DmDeviceState::INVALID &&
+        dm.GetDmDevicePathByName(partition_name, &device)) {
+        return device;
+    }
+
+    return "";
+}
+
+// NOTE: OverlayfsSetupAllowed() must be "stricter" than OverlayfsTeardownAllowed().
+// Setup is allowed only if teardown is also allowed.
+bool OverlayfsSetupAllowed(bool verbose = false) {
+    if (!kAllowOverlayfs) {
+        if (verbose) {
+            LOG(ERROR) << "Overlayfs remounts can only be used in debuggable builds";
+        }
+        return false;
+    }
+    // Check mandatory kernel patches.
+    if (fs_mgr_overlayfs_valid() == OverlayfsValidResult::kNotSupported) {
+        if (verbose) {
+            LOG(ERROR) << "Kernel does not support overlayfs";
+        }
+        return false;
+    }
+    // in recovery or fastbootd, not allowed!
+    if (fs_mgr_in_recovery()) {
+        if (verbose) {
+            LOG(ERROR) << "Unsupported overlayfs setup from recovery";
+        }
+        return false;
+    }
+    return true;
+}
+
+bool fs_mgr_wants_overlayfs(FstabEntry* entry) {
+    // Don't check entries that are managed by vold.
+    if (entry->fs_mgr_flags.vold_managed || entry->fs_mgr_flags.recovery_only) return false;
+
+    // *_other doesn't want overlayfs.
+    if (entry->fs_mgr_flags.slot_select_other) return false;
+
+    // Only concerned with readonly partitions.
+    if (!(entry->flags & MS_RDONLY)) return false;
+
+    // If unbindable, do not allow overlayfs as this could expose us to
+    // security issues.  On Android, this could also be used to turn off
+    // the ability to overlay an otherwise acceptable filesystem since
+    // /system and /vendor are never bound(sic) to.
+    if (entry->flags & MS_UNBINDABLE) return false;
+
+    if (!fs_mgr_overlayfs_enabled(entry)) return false;
+
+    return true;
+}
+
+Fstab fs_mgr_overlayfs_candidate_list(const Fstab& fstab) {
+    android::fs_mgr::Fstab mounts;
+    if (!android::fs_mgr::ReadFstabFromFile("/proc/mounts", &mounts)) {
+        PLOG(ERROR) << "Failed to read /proc/mounts";
+        return {};
+    }
+
+    Fstab candidates;
+    for (const auto& entry : fstab) {
+        // Filter out partitions whose type doesn't match what's mounted.
+        // This avoids spammy behavior on devices which can mount different
+        // filesystems for each partition.
+        auto proc_mount_point = (entry.mount_point == "/system") ? "/" : entry.mount_point;
+        auto mounted = GetEntryForMountPoint(&mounts, proc_mount_point);
+        if (!mounted || mounted->fs_type != entry.fs_type) {
+            continue;
+        }
+
+        FstabEntry new_entry = entry;
+        if (!fs_mgr_overlayfs_already_mounted(entry.mount_point) &&
+            !fs_mgr_wants_overlayfs(&new_entry)) {
+            continue;
+        }
+        auto new_mount_point = fs_mgr_mount_point(entry.mount_point);
+        auto duplicate_or_more_specific = false;
+        for (auto it = candidates.begin(); it != candidates.end();) {
+            auto it_mount_point = fs_mgr_mount_point(it->mount_point);
+            if ((it_mount_point == new_mount_point) ||
+                (android::base::StartsWith(new_mount_point, it_mount_point + "/"))) {
+                duplicate_or_more_specific = true;
+                break;
+            }
+            if (android::base::StartsWith(it_mount_point, new_mount_point + "/")) {
+                it = candidates.erase(it);
+            } else {
+                ++it;
+            }
+        }
+        if (!duplicate_or_more_specific) candidates.emplace_back(std::move(new_entry));
+    }
+    return candidates;
+}
+
+static void TryMountScratch() {
+    // Note we get the boot scratch device here, which means if scratch was
+    // just created through ImageManager, this could fail. In practice this
+    // should not happen because "remount" detects this scenario (by checking
+    // if verity is still disabled, i.e. no reboot occurred), and skips calling
+    // fs_mgr_overlayfs_mount_all().
+    auto scratch_device = GetBootScratchDevice();
+    if (!fs_mgr_rw_access(scratch_device)) {
+        return;
+    }
+    if (!WaitForFile(scratch_device, 10s)) {
+        return;
+    }
+    if (!MountScratch(scratch_device, true /* readonly */)) {
+        return;
+    }
+    auto has_overlayfs_dir = fs_mgr_access(std::string(kScratchMountPoint) + kOverlayTopDir);
+    fs_mgr_overlayfs_umount_scratch();
+    if (has_overlayfs_dir) {
+        MountScratch(scratch_device);
+    }
+}
+
+bool fs_mgr_overlayfs_mount_all(Fstab* fstab) {
+    if (!OverlayfsSetupAllowed()) {
+        return false;
+    }
+    auto ret = true;
+    auto scratch_can_be_mounted = true;
+    for (const auto& entry : fs_mgr_overlayfs_candidate_list(*fstab)) {
+        if (fs_mgr_is_verity_enabled(entry)) continue;
+        auto mount_point = fs_mgr_mount_point(entry.mount_point);
+        if (fs_mgr_overlayfs_already_mounted(mount_point)) {
+            continue;
+        }
+        if (scratch_can_be_mounted) {
+            scratch_can_be_mounted = false;
+            TryMountScratch();
+        }
+        ret &= fs_mgr_overlayfs_mount(entry);
+    }
+    return ret;
+}
+
+bool fs_mgr_overlayfs_is_setup() {
+    if (!OverlayfsSetupAllowed()) {
+        return false;
+    }
+    if (fs_mgr_overlayfs_already_mounted(kScratchMountPoint, false)) return true;
+    Fstab fstab;
+    if (!ReadDefaultFstab(&fstab)) {
+        return false;
+    }
+    for (const auto& entry : fs_mgr_overlayfs_candidate_list(fstab)) {
+        if (fs_mgr_is_verity_enabled(entry)) continue;
+        if (fs_mgr_overlayfs_already_mounted(fs_mgr_mount_point(entry.mount_point))) return true;
+    }
+    return false;
+}
+
+bool fs_mgr_overlayfs_already_mounted(const std::string& mount_point, bool overlay_only) {
+    Fstab fstab;
+    if (!ReadFstabFromFile("/proc/mounts", &fstab)) {
+        return false;
+    }
+    const auto lowerdir = kLowerdirOption + mount_point;
+    for (const auto& entry : fstab) {
+        if (overlay_only && "overlay" != entry.fs_type && "overlayfs" != entry.fs_type) continue;
+        if (mount_point != entry.mount_point) continue;
+        if (!overlay_only) return true;
+        const auto options = android::base::Split(entry.fs_options, ",");
+        for (const auto& opt : options) {
+            if (opt == lowerdir) {
+                return true;
+            }
+        }
+    }
+    return false;
+}
diff --git a/fs_mgr/fs_mgr_overlayfs_mount.h b/fs_mgr/fs_mgr_overlayfs_mount.h
new file mode 100644
index 0000000..ae3ea84
--- /dev/null
+++ b/fs_mgr/fs_mgr_overlayfs_mount.h
@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2022 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 <string>
+
+#include <fstab/fstab.h>
+
+bool fs_mgr_overlayfs_already_mounted(const std::string& mount_point, bool overlay_only = true);
+bool fs_mgr_wants_overlayfs(android::fs_mgr::FstabEntry* entry);
+android::fs_mgr::Fstab fs_mgr_overlayfs_candidate_list(const android::fs_mgr::Fstab& fstab);
+
+#if ALLOW_ADBD_DISABLE_VERITY
+constexpr bool kAllowOverlayfs = true;
+#else
+constexpr bool kAllowOverlayfs = false;
+#endif
+
+class AutoSetFsCreateCon final {
+  public:
+    AutoSetFsCreateCon() {}
+    AutoSetFsCreateCon(const std::string& context) { Set(context); }
+    ~AutoSetFsCreateCon() { Restore(); }
+
+    bool Ok() const { return ok_; }
+    bool Set(const std::string& context);
+    bool Restore();
+
+  private:
+    bool ok_ = false;
+    bool restored_ = false;
+};
+
+constexpr auto kScratchMountPoint = "/mnt/scratch";
+constexpr char kOverlayfsFileContext[] = "u:object_r:overlayfs_file:s0";
+
+constexpr auto kUpperName = "upper";
+constexpr auto kWorkName = "work";
+constexpr auto kOverlayTopDir = "/overlay";
+
+bool fs_mgr_is_dsu_running();
+bool fs_mgr_in_recovery();
+bool fs_mgr_access(const std::string& path);
+bool fs_mgr_rw_access(const std::string& path);
+bool fs_mgr_filesystem_has_space(const std::string& mount_point);
+const std::string fs_mgr_mount_point(const std::string& mount_point);
+bool fs_mgr_overlayfs_umount_scratch();
+std::vector<const std::string> OverlayMountPoints();
diff --git a/fs_mgr/fs_mgr_priv_overlayfs.h b/fs_mgr/fs_mgr_priv_overlayfs.h
deleted file mode 100644
index 2033701..0000000
--- a/fs_mgr/fs_mgr_priv_overlayfs.h
+++ /dev/null
@@ -1,49 +0,0 @@
-/*
- * Copyright (C) 2022 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 <string>
-
-#include <fstab/fstab.h>
-
-bool fs_mgr_overlayfs_already_mounted(const std::string& mount_point, bool overlay_only = true);
-bool fs_mgr_wants_overlayfs(android::fs_mgr::FstabEntry* entry);
-android::fs_mgr::Fstab fs_mgr_overlayfs_candidate_list(const android::fs_mgr::Fstab& fstab);
-
-// If "mount_point" is non-null, set up exactly one overlay.
-// If "mount_point" is null, setup any overlays.
-//
-// If |want_reboot| is non-null, and a reboot is needed to apply overlays, then
-// it will be true on return. The caller is responsible for initializing it.
-bool fs_mgr_overlayfs_setup(const android::fs_mgr::Fstab& fstab, const char* mount_point = nullptr,
-                            bool* want_reboot = nullptr, bool just_disabled_verity = true);
-
-enum class OverlayfsTeardownResult {
-    Ok,
-    Busy,  // Indicates that overlays are still in use.
-    Error
-};
-OverlayfsTeardownResult fs_mgr_overlayfs_teardown(const char* mount_point = nullptr,
-                                                  bool* want_reboot = nullptr);
-
-namespace android {
-namespace fs_mgr {
-
-void CleanupOldScratchFiles();
-
-}  // namespace fs_mgr
-}  // namespace android
diff --git a/fs_mgr/fs_mgr_remount.cpp b/fs_mgr/fs_mgr_remount.cpp
index 5a9f391..4c45828 100644
--- a/fs_mgr/fs_mgr_remount.cpp
+++ b/fs_mgr/fs_mgr_remount.cpp
@@ -43,7 +43,8 @@
 #include <libavb_user/libavb_user.h>
 #include <libgsi/libgsid.h>
 
-#include "fs_mgr_priv_overlayfs.h"
+#include "fs_mgr_overlayfs_control.h"
+#include "fs_mgr_overlayfs_mount.h"
 
 using namespace std::literals;
 using android::fs_mgr::Fstab;