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btrfs: comment about fsid and metadata_uuid relationship

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Add a comment explaining the relationship between fsid and metadata_uuid
in the on-disk superblock and the in-memory struct btrfs_fs_devices.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Anand Jain 2023-09-07 00:16:41 +08:00 committed by David Sterba
parent 1246873114
commit cb6eb4757e
1 changed files with 9 additions and 0 deletions
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9
fs/btrfs/volumes.h
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@ -290,6 +290,15 @@ struct btrfs_fs_devices {
* - Following shall be true at all times:
* - metadata_uuid == btrfs_header::fsid
* - metadata_uuid == btrfs_dev_item::fsid
*
* - Relations between fsid and metadata_uuid in sb and fs_devices:
* - Normal:
* fs_devices->fsid == fs_devices->metadata_uuid == sb->fsid
* sb->metadata_uuid == 0
*
* - When the BTRFS_FEATURE_INCOMPAT_METADATA_UUID flag is set:
* fs_devices->fsid == sb->fsid
* fs_devices->metadata_uuid == sb->metadata_uuid
*/
u8 metadata_uuid[BTRFS_FSID_SIZE];