quorum: Add quorum_co_flush().

Makes a vote to select error if any.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/quorum.c

@@ -629,12 +629,40 @@ static void quorum_invalidate_cache(BlockDriverState *bs)
     }
 }
 
+static coroutine_fn int quorum_co_flush(BlockDriverState *bs)
+{
+    BDRVQuorumState *s = bs->opaque;
+    QuorumVoteVersion *winner = NULL;
+    QuorumVotes error_votes;
+    QuorumVoteValue result_value;
+    int i;
+    int result = 0;
+
+    QLIST_INIT(&error_votes.vote_list);
+    error_votes.compare = quorum_64bits_compare;
+
+    for (i = 0; i < s->num_children; i++) {
+        result = bdrv_co_flush(s->bs[i]);
+        result_value.l = result;
+        quorum_count_vote(&error_votes, &result_value, i);
+    }
+
+    winner = quorum_get_vote_winner(&error_votes);
+    result = winner->value.l;
+
+    quorum_free_vote_list(&error_votes);
+
+    return result;
+}
+
 static BlockDriver bdrv_quorum = {
     .format_name        = "quorum",
     .protocol_name      = "quorum",
 
     .instance_size      = sizeof(BDRVQuorumState),
 
+    .bdrv_co_flush_to_disk = quorum_co_flush,
+
     .bdrv_getlength     = quorum_getlength,
 
     .bdrv_aio_readv     = quorum_aio_readv,