On Thu, Apr 22, 2021 at 01:09:50AM +0300, Vladimir Sementsov-Ogievskiy wrote:
@@ -1981,8 +1985,15 @@ bdrv_co_write_req_prepare(BdrvChild *child, int64_t
offset, int64_t bytes,
} else {
assert(child->perm & BLK_PERM_WRITE);
}
- return notifier_with_return_list_notify(&bs->before_write_notifiers,
- req);
+ write_threshold = qatomic_read(&bs->write_threshold_offset);
+ if (write_threshold > 0 && offset + bytes > write_threshold) {
+ qapi_event_send_block_write_threshold(
+ bs->node_name,
+ offset + bytes - write_threshold,
+ write_threshold);
+ qatomic_set(&bs->write_threshold_offset, 0);
It's safer to reset the threshold before emitting the event. That way
there is no race with the QMP client setting a new threshold via
bdrv_write_threshold_is_set(). I guess the race is possible since
qatomic is used and there is no lock.
I like the idea of dropping write notifiers:
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>