[PATCH v3 17/25] block/block-copy: make progress_bytes_callback optional

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

We are going to stop use of this callback in the following commit.
Still the callback handling code will be dropped in a separate commit.
So, for now let's make it optional.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/block-copy.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/block/block-copy.c b/block/block-copy.c
index 82cf945693..61d82d9a1c 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -454,7 +454,9 @@ static coroutine_fn int block_copy_task_entry(AioTask *task)
         t->call_state->error_is_read = error_is_read;
     } else {
         progress_work_done(t->s->progress, t->bytes);
-        t->s->progress_bytes_callback(t->bytes, t->s->progress_opaque);
+        if (t->s->progress_bytes_callback) {
+            t->s->progress_bytes_callback(t->bytes, t->s->progress_opaque);
+        }
     }
     co_put_to_shres(t->s->mem, t->bytes);
     block_copy_task_end(t, ret);
-- 
2.21.3