qemu-io-cmds: Use bdrv_coroutine_enter

qemu_coroutine_create associates @co to qemu_aio_context but we poll
blk's context below. If the coroutine yields, it may never get resumed
again.

Use bdrv_coroutine_enter to make sure we are starting the I/O on the
right context.

Signed-off-by: Fam Zheng <famz@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>

qemu-io-cmds.c

@@ -521,7 +521,7 @@ static int do_co_pwrite_zeroes(BlockBackend *blk, int64_t offset,
     }
 
     co = qemu_coroutine_create(co_pwrite_zeroes_entry, &data);
-    qemu_coroutine_enter(co);
+    bdrv_coroutine_enter(blk_bs(blk), co);
     while (!data.done) {
         aio_poll(blk_get_aio_context(blk), true);
     }