block: Honour BDRV_REQ_NO_SERIALISING in copy range

This semantics is needed by drive-backup so implement it before using
this API there.
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NFam Zheng <famz@redhat.com>
Message-id: 20180703023758.14422-3-famz@redhat.com
Signed-off-by: NJeff Cody <jcody@redhat.com>

block/io.c

@@ -2930,8 +2930,10 @@ static int coroutine_fn bdrv_co_copy_range_internal(BdrvChild *src,
     tracked_request_begin(&dst_req, dst->bs, dst_offset,
                           bytes, BDRV_TRACKED_WRITE);
 
-    wait_serialising_requests(&src_req);
-    wait_serialising_requests(&dst_req);
+    if (!(flags & BDRV_REQ_NO_SERIALISING)) {
+        wait_serialising_requests(&src_req);
+        wait_serialising_requests(&dst_req);
+    }
     if (recurse_src) {
         ret = src->bs->drv->bdrv_co_copy_range_from(src->bs,
                                                     src, src_offset,

include/block/block.h

@@ -659,13 +659,14 @@ void bdrv_unregister_buf(BlockDriverState *bs, void *host);
  * @dst: Destination child to copy data to
  * @dst_offset: offset in @dst image to write data
  * @bytes: number of bytes to copy
- * @flags: request flags. Must be one of:
- *         0 - actually read data from src;
+ * @flags: request flags. Supported flags:
  *         BDRV_REQ_ZERO_WRITE - treat the @src range as zero data and do zero
  *                               write on @dst as if bdrv_co_pwrite_zeroes is
  *                               called. Used to simplify caller code, or
  *                               during BlockDriver.bdrv_co_copy_range_from()
  *                               recursion.
+ *         BDRV_REQ_NO_SERIALISING - do not serialize with other overlapping
+ *                                   requests currently in flight.
  *
  * Returns: 0 if succeeded; negative error code if failed.
  **/