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Commit 31c14e15 authored by Mark Salyzyn's avatar Mark Salyzyn
Browse files

fs_mgr: overlayfs: dig harder for /dev/root equivalent 

Check for A/B /dev/block/by-name/system<slot> and also non-A/B
/dev/block/by-name/system to discover what /dev/root can be when
evaluating candidates for using overlayfs.

This is to handle a misconfigured (or legacy) system-as-root device.
It is recommended that the default fstab specifically mentions the
root mount's device node to prevent going down this path.

Test: adb-remount-test.sh
Bug: 138407617
Change-Id: I3853d203b9376d0f848cb490150ff00cc4ed3d5f
parent ef0bc630

fs_mgr/fs_mgr_overlayfs.cpp

+32 −9
Original line number Diff line number Diff line
@@ -150,6 +150,31 @@ bool fs_mgr_filesystem_has_space(const std::string& mount_point) { 
    return (vst.f_bfree >= (vst.f_blocks * kPercentThreshold / 100));

}



const auto kPhysicalDevice = "/dev/block/by-name/"s;



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 = 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_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
@@ -157,19 +182,19 @@ bool fs_mgr_overlayfs_enabled(FstabEntry* entry) { 
    if (!fs_mgr_filesystem_has_space(entry->mount_point)) {

        return true;

    }

    if (entry->fs_mgr_flags.logical) {

        fs_mgr_update_logical_partition(entry);



    // 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;

    }



    // check if ext4 de-dupe

    auto save_errno = errno;

    errno = 0;

    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);

    }

    // special case for first stage init for system as root (taimen)

    if (!has_shared_blocks && (errno == ENOENT) && (entry->blk_device == "/dev/root")) {

        has_shared_blocks = true;

    }

    errno = save_errno;

    return has_shared_blocks;

}
@@ -388,8 +413,6 @@ uint32_t fs_mgr_overlayfs_slot_number() { 
    return SlotNumberForSlotSuffix(fs_mgr_get_slot_suffix());

}



const auto kPhysicalDevice = "/dev/block/by-name/"s;



std::string fs_mgr_overlayfs_super_device(uint32_t slot_number) {

    return kPhysicalDevice + fs_mgr_get_super_partition_name(slot_number);

}