xfs_copy: Fix meta UUID handling on multiple copies

Zorro reported that when making multiple copies of a V5
filesystem with xfs_copy while generating new UUIDs, all
but the first copy were corrupt.

Upon inspection, the corruption was related to incorrect UUIDs;
the original UUID, as stamped into every metadata structure,
was not preserved in the sb_meta_uuid field of the superblock
on any but the first copy.

This happened because sb_update_uuid was using the UUID present in
the ag_hdr structure as the unchanging meta-uuid which is to match
existing structures, but it also /updates/ that UUID with the
new identifying UUID present in tcarg.  So the newly-generated
UUIDs moved transitively from tcarg->uuid to ag_hdr->xfs_sb->sb_uuid
to ag_hdr->xfs_sb->sb_meta_uuid each time the function got called.

Fix this by looking instead to the unchanging, original UUID
present in the xfs_sb_t we are given, which reflects the original
filesystem's metadata UUID, and copy /that/ UUID into each target
filesystem's meta_uuid field.

Most of this patch is changing comments and re-ordering tests
to match; the functional change is to simply use the *sb rather
than the *ag_hdr to identify the proper metadata UUID.

Reported-and-tested-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/copy/xfs_copy.c b/copy/xfs_copy.c
index 3c8998c7b366339dd205e50b4513915f9883dc52..22ded6b12b4b8b7b21fae2b465e0ba2d6691b111 100644 (file)
--- a/copy/xfs_copy.c
+++ b/copy/xfs_copy.c
@@ -494,27 +494,29 @@ write_wbuf(void)
 
 void
 sb_update_uuid(
-       xfs_sb_t        *sb,
-       ag_header_t     *ag_hdr,
-       thread_args     *tcarg)
+       xfs_sb_t        *sb,            /* Original fs superblock */
+       ag_header_t     *ag_hdr,        /* AG hdr to update for this copy */
+       thread_args     *tcarg)         /* Args for this thread, with UUID */
 {
        /*
         * If this filesystem has CRCs, the original UUID is stamped into
-        * all metadata.  If we are changing the UUID in the copy, we need
-        * to copy the original UUID into the meta_uuid slot and set the
-        * set the incompat flag if that hasn't already been done.
+        * all metadata.  If we don't have an existing meta_uuid field in the
+        * the original filesystem and we are changing the UUID in this copy,
+        * we must copy the original sb_uuid to the sb_meta_uuid slot and set
+        * the incompat flag for the feature on this copy.
         */
-       if (!uuid_equal(&tcarg->uuid, &ag_hdr->xfs_sb->sb_uuid) &&
-           xfs_sb_version_hascrc(sb) && !xfs_sb_version_hasmetauuid(sb)) {
+       if (xfs_sb_version_hascrc(sb) && !xfs_sb_version_hasmetauuid(sb) &&
+           !uuid_equal(&tcarg->uuid, &sb->sb_uuid)) {
                __be32 feat;
 
                feat = be32_to_cpu(ag_hdr->xfs_sb->sb_features_incompat);
                feat |= XFS_SB_FEAT_INCOMPAT_META_UUID;
                ag_hdr->xfs_sb->sb_features_incompat = cpu_to_be32(feat);
                platform_uuid_copy(&ag_hdr->xfs_sb->sb_meta_uuid,
-                                  &ag_hdr->xfs_sb->sb_uuid);
+                                  &sb->sb_uuid);
        }
 
+       /* Copy the (possibly new) fs-identifier UUID into sb_uuid */
        platform_uuid_copy(&ag_hdr->xfs_sb->sb_uuid, &tcarg->uuid);
 
        /* We may have changed the UUID, so update the superblock CRC */