commit b2c2832c6140cfe3ddc0de2d77eeb0b77dea8fd3
author Kevin Wolf <kwolf@redhat.com> Mon Feb 20 12:46:42 2017 +0100
committer Kevin Wolf <kwolf@redhat.com> Tue Feb 28 20:47:51 2017 +0100
tree a8887134fb47b8dbd8c23a0cd4da55bc979ecbbb
parent 12fa4af61fb2a08b156134c3b6717534c637c995

block: Add Error parameter to bdrv_append()

Aborting on error in bdrv_append() isn't correct. This patch fixes it
and lets the callers handle failures.

Test case 085 needs a reference output update. This is caused by the
reversed order of bdrv_set_backing_hd() and change_parent_backing_link()
in bdrv_append(): When the backing file of the new node is set, the
parent nodes are still pointing to the old top, so the backing blocker
is now initialised with the node name rather than the BlockBackend name.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

blockdev.c

diff --git a/blockdev.c b/blockdev.c
index ff781d9..8eb4e84 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1768,6 +1768,17 @@
 
     if (!state->new_bs->drv->supports_backing) {
         error_setg(errp, "The snapshot does not support backing images");
+        return;
+    }
+
+    /* This removes our old bs and adds the new bs. This is an operation that
+     * can fail, so we need to do it in .prepare; undoing it for abort is
+     * always possible. */
+    bdrv_ref(state->new_bs);
+    bdrv_append(state->new_bs, state->old_bs, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return;
     }
 }
 
@@ -1778,8 +1789,6 @@
 
     bdrv_set_aio_context(state->new_bs, state->aio_context);
 
-    /* This removes our old bs and adds the new bs */
-    bdrv_append(state->new_bs, state->old_bs);
     /* We don't need (or want) to use the transactional
      * bdrv_reopen_multiple() across all the entries at once, because we
      * don't want to abort all of them if one of them fails the reopen */
@@ -1794,7 +1803,9 @@
     ExternalSnapshotState *state =
                              DO_UPCAST(ExternalSnapshotState, common, common);
     if (state->new_bs) {
-        bdrv_unref(state->new_bs);
+        if (state->new_bs->backing) {
+            bdrv_replace_in_backing_chain(state->new_bs, state->old_bs);
+        }
     }
 }
 
@@ -1805,6 +1816,7 @@
     if (state->aio_context) {
         bdrv_drained_end(state->old_bs);
         aio_context_release(state->aio_context);
+        bdrv_unref(state->new_bs);
     }
 }