On 2021/8/2 上午4:52, Matwey V. Kornilov wrote:
BTRFS volume consists of a number of subvolumes which can be mounted separately from each other. The top-level subvolume always exists even if no subvolumes were created manually. A subvolume can be denoted as the default subvolume i.e. the subvolume which is mounted by default.
The default "default subvolume" is the top-level one, but this is far from the common practices used in the wild. For instance, openSUSE provides an OS snapshot/rollback feature based on BTRFS. To achieve this, the actual OS root filesystem is located into a separate subvolume which is "default" but not "top-level". That means that the /boot/dtb/ directory is also located inside this default subvolume instead of top-level one.
However, the existing btrfs u-boot driver always uses the top-level subvolume as the filesystem root. This behaviour 1) is inconsistent with
mount /dev/sda1 /targetcommand, which mount the default subvolume 2) leads to the issues when /boot/dtb cannot be found properly (see the reference).
I also noticed the problem in the past, but forgot to fix it....
This patch uses the default subvolume as the filesystem root to overcome mentioned issues.
Reference: https://bugzilla.suse.com/show_bug.cgi?id=1185656 Signed-off-by: Matwey V. Kornilov matwey.kornilov@gmail.com
Reviewed-by: Qu Wenruo wqu@suse.com
Thanks, Qu
fs/btrfs/disk-io.c | 38 +++++++++++++++++++++++++++++++++++--- 1 file changed, 35 insertions(+), 3 deletions(-)
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index 349411c3cc..12f9579fcf 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -804,6 +804,30 @@ static int setup_root_or_create_block(struct btrfs_fs_info *fs_info, return 0; }
+static int get_default_subvolume(struct btrfs_fs_info *fs_info,
struct btrfs_key *key_ret)+{
- struct btrfs_root *root = fs_info->tree_root;
- struct btrfs_dir_item *dir_item;
- struct btrfs_path path;
- int ret = 0;
- btrfs_init_path(&path);
- dir_item = btrfs_lookup_dir_item(NULL, root, &path,
BTRFS_ROOT_TREE_DIR_OBJECTID,"default", 7, 0);- if (IS_ERR(dir_item)) {
ret = PTR_ERR(dir_item);goto out;- }
- btrfs_dir_item_key_to_cpu(path.nodes[0], dir_item, key_ret);
+out:
- btrfs_release_path(&path);
- return ret;
+}
- int btrfs_setup_all_roots(struct btrfs_fs_info *fs_info) { struct btrfs_super_block *sb = fs_info->super_copy;
@@ -833,9 +857,17 @@ int btrfs_setup_all_roots(struct btrfs_fs_info *fs_info)
fs_info->last_trans_committed = generation;
- key.objectid = BTRFS_FS_TREE_OBJECTID;
- key.type = BTRFS_ROOT_ITEM_KEY;
- key.offset = (u64)-1;
ret = get_default_subvolume(fs_info, &key);
if (ret) {
/** The default dir item isn't there. Linux kernel behaviour is* to silently use the top-level subvolume in this case.*/key.objectid = BTRFS_FS_TREE_OBJECTID;key.type = BTRFS_ROOT_ITEM_KEY;key.offset = (u64)-1;}
fs_info->fs_root = btrfs_read_fs_root(fs_info, &key);
if (IS_ERR(fs_info->fs_root))