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
diff --git a/fs_mgr/fs_mgr_overlayfs.cpp b/fs_mgr/fs_mgr_overlayfs.cpp
index ac15ce4..4ee7db9 100644
--- a/fs_mgr/fs_mgr_overlayfs.cpp
+++ b/fs_mgr/fs_mgr_overlayfs.cpp
@@ -150,6 +150,31 @@
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 @@
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 @@
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);
}