block: Use CAFs for debug breakpoints

When looking for a blkdebug node (which implements debug breakpoints),
use bdrv_primary_bs() to iterate through the graph, because that is
where a blkdebug node would be.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -5568,17 +5568,7 @@ void bdrv_debug_event(BlockDriverState *bs, BlkdebugEvent event)
 static BlockDriverState *bdrv_find_debug_node(BlockDriverState *bs)
 {
     while (bs && bs->drv && !bs->drv->bdrv_debug_breakpoint) {
-        if (bs->file) {
-            bs = bs->file->bs;
-            continue;
-        }
-
-        if (bs->drv->is_filter && bs->backing) {
-            bs = bs->backing->bs;
-            continue;
-        }
-
-        break;
+        bs = bdrv_primary_bs(bs);
     }
 
     if (bs && bs->drv && bs->drv->bdrv_debug_breakpoint) {
@@ -5613,7 +5603,7 @@ int bdrv_debug_remove_breakpoint(BlockDriverState *bs, const char *tag)
 int bdrv_debug_resume(BlockDriverState *bs, const char *tag)
 {
     while (bs && (!bs->drv || !bs->drv->bdrv_debug_resume)) {
-        bs = bs->file ? bs->file->bs : NULL;
+        bs = bdrv_primary_bs(bs);
     }
 
     if (bs && bs->drv && bs->drv->bdrv_debug_resume) {
@@ -5626,7 +5616,7 @@ int bdrv_debug_resume(BlockDriverState *bs, const char *tag)
 bool bdrv_debug_is_suspended(BlockDriverState *bs, const char *tag)
 {
     while (bs && bs->drv && !bs->drv->bdrv_debug_is_suspended) {
-        bs = bs->file ? bs->file->bs : NULL;
+        bs = bdrv_primary_bs(bs);
     }
 
     if (bs && bs->drv && bs->drv->bdrv_debug_is_suspended) {