diff options
| author | Anand Jain <asj@kernel.org> | 2026-04-27 18:18:04 +0800 |
|---|---|---|
| committer | David Sterba <dsterba@suse.com> | 2026-05-26 18:50:44 +0200 |
| commit | 64ba0eb3bb24abf8d5648134f7bb1860f2e66e43 (patch) | |
| tree | 227910ea4684cf3f2d7716eedad05356caef81a8 /fs | |
| parent | 2cd749334ae343446ef6d7e649698c5e40625401 (diff) | |
| download | linux-next-history-64ba0eb3bb24abf8d5648134f7bb1860f2e66e43.tar.gz | |
btrfs: derive f_fsid from on-disk fsid and dev_t
The f_fsid was originally derived from fs_devices->fsid and the
subvolume root ID. However, when temp_fsid is active, fs_devices->fsid
is randomized, making the standard derivation inconsistent.
Since metadata_uuid is optional, it is not a reliable alternative. This
patch instead retrieves the on-disk UUID from fs_info->super_copy->fsid.
To prevent f_fsid collisions between original and cloned filesystems,
this implementation hashes the dev_t for single-device btrfs filesystems
to ensure uniqueness. This is limited to single-device filesystems as
cloned mounts are currently only supported for that configuration. Note
that f_fsid will change if the device is replaced.
Additionally, since the kernel cannot distinguish between the original
and the cloned filesystem, this new f_fsid derivation is applied to
both.
Link: https://lore.kernel.org/linux-btrfs/cover.1772095546.git.asj@kernel.org/
Link: https://lore.kernel.org/linux-btrfs/cover.1774092915.git.asj@kernel.org/
Signed-off-by: Anand Jain <asj@kernel.org>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/btrfs/super.c | 41 |
1 files changed, 33 insertions, 8 deletions
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c index faa4777119ac2..1a5d1c126dfd5 100644 --- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -1732,12 +1732,13 @@ static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf) u64 total_free_data = 0; u64 total_free_meta = 0; u32 bits = fs_info->sectorsize_bits; - __be32 *fsid = (__be32 *)fs_info->fs_devices->fsid; + __be32 *fsid; unsigned factor = 1; struct btrfs_block_rsv *block_rsv = &fs_info->global_block_rsv; int ret; u64 thresh = 0; int mixed = 0; + __kernel_fsid_t f_fsid; list_for_each_entry(found, &fs_info->space_info, list) { if (found->flags & BTRFS_BLOCK_GROUP_DATA && @@ -1819,14 +1820,38 @@ static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf) buf->f_bsize = fs_info->sectorsize; buf->f_namelen = BTRFS_NAME_LEN; - /* We treat it as constant endianness (it doesn't matter _which_) - because we want the fsid to come out the same whether mounted - on a big-endian or little-endian host */ - buf->f_fsid.val[0] = be32_to_cpu(fsid[0]) ^ be32_to_cpu(fsid[2]); - buf->f_fsid.val[1] = be32_to_cpu(fsid[1]) ^ be32_to_cpu(fsid[3]); + /* + * fs_devices->fsid is dynamically generated when temp_fsid is active + * to support cloned filesystems. Use the original on-disk fsid instead, + * as it remains consistent across mount cycles. + */ + if (fs_info->fs_devices->temp_fsid) + fsid = (__be32 *)fs_info->super_copy->fsid; + else + fsid = (__be32 *)fs_info->fs_devices->fsid; + + /* + * We treat it as constant endianness (it doesn't matter _which_) + * because we want the fsid to come out the same whether mounted + * on a big-endian or little-endian host. + */ + f_fsid.val[0] = be32_to_cpu(fsid[0]) ^ be32_to_cpu(fsid[2]); + f_fsid.val[1] = be32_to_cpu(fsid[1]) ^ be32_to_cpu(fsid[3]); + /* Mask in the root object ID too, to disambiguate subvols */ - buf->f_fsid.val[0] ^= btrfs_root_id(BTRFS_I(d_inode(dentry))->root) >> 32; - buf->f_fsid.val[1] ^= btrfs_root_id(BTRFS_I(d_inode(dentry))->root); + f_fsid.val[0] ^= btrfs_root_id(BTRFS_I(d_inode(dentry))->root) >> 32; + f_fsid.val[1] ^= btrfs_root_id(BTRFS_I(d_inode(dentry))->root); + + /* Hash dev_t to avoid f_fsid collision with cloned filesystems. */ + if (fs_info->fs_devices->total_devices == 1) { + __kernel_fsid_t dev_fsid = + u64_to_fsid(huge_encode_dev(fs_info->fs_devices->latest_dev->bdev->bd_dev)); + + f_fsid.val[0] ^= dev_fsid.val[1]; + f_fsid.val[1] ^= dev_fsid.val[0]; + } + + memcpy(&buf->f_fsid, &f_fsid, sizeof(f_fsid)); return 0; } |