xfs: create new metadata UUID field and incompat flag

This adds a new superblock field, sb_meta_uuid.  If set, along with
a new incompat flag, the code will use that field on a V5 filesystem
to compare to metadata UUIDs, which allows us to change the user-
visible UUID at will.  Userspace handles the setting and clearing
of the incompat flag as appropriate, as the UUID gets changed; i.e.
setting the user-visible UUID back to the original UUID (as stored in
the new field) will remove the incompatible feature flag.

If the incompat flag is not set, this copies the user-visible UUID into
into the meta_uuid slot in memory when the superblock is read from disk;
the meta_uuid field is not written back to disk in this case.

The remainder of this patch simply switches verifiers, initializers,
etc to use the new sb_meta_uuid field.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
index df9851c46b5c..0f5e08fe64a2 100644
--- a/fs/xfs/libxfs/xfs_sb.c
+++ b/fs/xfs/libxfs/xfs_sb.c
@@ -398,6 +398,14 @@ __xfs_sb_from_disk(
 	to->sb_spino_align = be32_to_cpu(from->sb_spino_align);
 	to->sb_pquotino = be64_to_cpu(from->sb_pquotino);
 	to->sb_lsn = be64_to_cpu(from->sb_lsn);
+	/*
+	 * sb_meta_uuid is only on disk if it differs from sb_uuid and the
+	 * feature flag is set; if not set we keep it only in memory.
+	 */
+	if (xfs_sb_version_hasmetauuid(to))
+		uuid_copy(&to->sb_meta_uuid, &from->sb_meta_uuid);
+	else
+		uuid_copy(&to->sb_meta_uuid, &from->sb_uuid);
 	/* Convert on-disk flags to in-memory flags? */
 	if (convert_xquota)
 		xfs_sb_quota_from_disk(to);
@@ -539,6 +547,8 @@ xfs_sb_to_disk(
 				cpu_to_be32(from->sb_features_log_incompat);
 		to->sb_spino_align = cpu_to_be32(from->sb_spino_align);
 		to->sb_lsn = cpu_to_be64(from->sb_lsn);
+		if (xfs_sb_version_hasmetauuid(from))
+			uuid_copy(&to->sb_meta_uuid, &from->sb_meta_uuid);
 	}
 }