Btrfs: use received_uuid of parent during send

Neil Horman pointed out a problem where if he did something like this

receive A
snap A B
change B
send -p A B

and then on another box do

recieve A
receive B

the receive B would fail because we use the UUID of A for the clone sources for
B.  This makes sense most of the time because normally you are sending from the
original sources, not a received source.  However when you use a recieved subvol
its UUID is going to be something completely different, so if you then try to
receive the diff on a different volume it won't find the UUID because the new A
will be something else.  The only constant is the received uuid.  So instead
check to see if we have received_uuid set on the root, and if so use that as the
clone source, as btrfs receive looks for matches either in received_uuid or
uuid.  Thanks,

Reported-by: Neil Horman <nhorman@redhat.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Reviewed-by: Hugo Mills <hugo@carfax.org.uk>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 21 insertions, 4 deletions

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 50ebc622a324..aa72bfd28f7d 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -2356,8 +2356,12 @@ static int send_subvol_begin(struct send_ctx *sctx)
         TLV_PUT_U64(sctx, BTRFS_SEND_A_CTRANSID,
                     le64_to_cpu(sctx->send_root->root_item.ctransid));
         if (parent_root) {
-                TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
-                                sctx->parent_root->root_item.uuid);
+                if (!btrfs_is_empty_uuid(parent_root->root_item.received_uuid))
+                        TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
+                                     parent_root->root_item.received_uuid);
+                else
+                        TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
+                                     parent_root->root_item.uuid);
                 TLV_PUT_U64(sctx, BTRFS_SEND_A_CLONE_CTRANSID,
                             le64_to_cpu(sctx->parent_root->root_item.ctransid));
         }
@@ -4586,8 +4590,21 @@ verbose_printk("btrfs: send_clone offset=%llu, len=%d, clone_root=%llu, "
         if (ret < 0)
                 goto out;
 
-        TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
-                        clone_root->root->root_item.uuid);
+        /*
+         * If the parent we're using has a received_uuid set then use that as
+         * our clone source as that is what we will look for when doing a
+         * receive.
+         *
+         * This covers the case that we create a snapshot off of a received
+         * subvolume and then use that as the parent and try to receive on a
+         * different host.
+         */
+        if (!btrfs_is_empty_uuid(clone_root->root->root_item.received_uuid))
+                TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
+                             clone_root->root->root_item.received_uuid);
+        else
+                TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
+                             clone_root->root->root_item.uuid);
         TLV_PUT_U64(sctx, BTRFS_SEND_A_CLONE_CTRANSID,
                     le64_to_cpu(clone_root->root->root_item.ctransid));
         TLV_PUT_PATH(sctx, BTRFS_SEND_A_CLONE_PATH, p);