path: root/fs/btrfs/volumes.h
diff options
authorNikolay Borisov <nborisov@suse.com>2018-10-30 16:43:23 +0200
committerDavid Sterba <dsterba@suse.com>2018-12-17 14:51:37 +0100
commit7239ff4b2be8ec0c3160da7fdd1475785fdb4cb9 (patch)
tree9f78e24bf85c6d3ec165441ced9fd55d5086e104 /fs/btrfs/volumes.h
parentbtrfs: use EXPORT_FOR_TESTS for conditionally exported functions (diff)
btrfs: Introduce support for FSID change without metadata rewrite
This field is going to be used when the user wants to change the UUID of the filesystem without having to rewrite all metadata blocks. This field adds another level of indirection such that when the FSID is changed what really happens is the current UUID (the one with which the fs was created) is copied to the 'metadata_uuid' field in the superblock as well as a new incompat flag is set METADATA_UUID. When the kernel detects this flag is set it knows that the superblock in fact has 2 UUIDs: 1. Is the UUID which is user-visible, currently known as FSID. 2. Metadata UUID - this is the UUID which is stamped into all on-disk datastructures belonging to this file system. When the new incompat flag is present device scanning checks whether both fsid/metadata_uuid of the scanned device match any of the registered filesystems. When the flag is not set then both UUIDs are equal and only the FSID is retained on disk, metadata_uuid is set only in-memory during mount. Additionally a new metadata_uuid field is also added to the fs_info struct. It's initialised either with the FSID in case METADATA_UUID incompat flag is not set or with the metdata_uuid of the superblock otherwise. This commit introduces the new fields as well as the new incompat flag and switches all users of the fsid to the new logic. Signed-off-by: Nikolay Borisov <nborisov@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> [ minor updates in comments ] Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/volumes.h')
1 files changed, 1 insertions, 0 deletions
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 40820e0ec5a4..bdee4b60e0ba 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -210,6 +210,7 @@ BTRFS_DEVICE_GETSET_FUNCS(bytes_used);
struct btrfs_fs_devices {
u8 fsid[BTRFS_FSID_SIZE]; /* FS specific uuid */
+ u8 metadata_uuid[BTRFS_FSID_SIZE];
struct list_head fs_list;
u64 num_devices;