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>

block/blkdebug.c

@@ -491,6 +491,8 @@ static int blkdebug_open(BlockDriverState *bs, QDict *options, int flags,
         goto out;
     }
 
+    bdrv_debug_event(bs, BLKDBG_NONE);
+
     ret = 0;
 out:
     if (ret < 0) {

qapi/block-core.json

@@ -3244,6 +3244,8 @@
 #
 # @cluster_alloc_space: an allocation of file space for a cluster (since 4.1)
 #
+# @none: triggers once at creation of the blkdebug node (since 4.1)
+#
 # Since: 2.9
 ##
 { 'enum': 'BlkdebugEvent', 'prefix': 'BLKDBG',
@@ -3262,7 +3264,7 @@
             'pwritev_rmw_tail', 'pwritev_rmw_after_tail', 'pwritev',
             'pwritev_zero', 'pwritev_done', 'empty_image_prepare',
             'l1_shrink_write_table', 'l1_shrink_free_l2_clusters',
-            'cor_write', 'cluster_alloc_space'] }
+            'cor_write', 'cluster_alloc_space', 'none'] }
 
 ##
 # @BlkdebugIOType: