blkdebug: Add "none" event

Together with @iotypes and @sector, this can be used to trap e.g. the
first read or write access to a certain sector without having to know
what happens internally in the block layer, i.e. which "real" events
happen right before such an access.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-id: 20190507203508.18026-5-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
diff --git a/block/blkdebug.c b/block/blkdebug.c
index 3f3ec11..1663ed2 100644
--- a/block/blkdebug.c
+++ b/block/blkdebug.c
@@ -491,6 +491,8 @@
         goto out;
     }
 
+    bdrv_debug_event(bs, BLKDBG_NONE);
+
     ret = 0;
 out:
     if (ret < 0) {