Re: [PATCH v7 01/47] block: Add child access functions

[Vladimir Sementsov-Ogievskiy]

25.06.2020 18:21, Max Reitz wrote:
> There are BDS children that the general block layer code can access,
> namely bs->file and bs->backing.  Since the introduction of filters and
> external data files, their meaning is not quite clear.  bs->backing can
> be a COW source, or it can be a filtered child; bs->file can be a
> filtered child, it can be data and metadata storage, or it can be just
> metadata storage.
>
> This overloading really is not helpful.  This patch adds functions that
> retrieve the correct child for each exact purpose.  Later patches in
> this series will make use of them.  Doing so will allow us to handle
> filter nodes in a meaningful way.
>
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---

[..]

> +/*
> + * Return the primary child of this node: For filters, that is the
> + * filtered child.  For other nodes, that is usually the child storing
> + * metadata.
> + * (A generally more helpful description is that this is (usually) the
> + * child that has the same filename as @bs.)
> + *
> + * Drivers do not necessarily have a primary child; for example quorum
> + * does not.
> + */
> +BdrvChild *bdrv_primary_child(BlockDriverState *bs)
> +{
> +    BdrvChild *c;
> +
> +    QLIST_FOREACH(c, &bs->children, next) {
> +        if (c->role & BDRV_CHILD_PRIMARY) {
> +            return c;
> +        }
> +    }
> +
> +    return NULL;
> +}

Suggest squash-in to also assert that not more than one primary child:
--- a/block.c
+++ b/block.c
@@ -6998,13 +6998,14 @@ BdrvChild *bdrv_filter_or_cow_child(BlockDriverState 
*bs)
  */
 BdrvChild *bdrv_primary_child(BlockDriverState *bs)
 {
-    BdrvChild *c;
+    BdrvChild *c, *found = NULL;
 
     QLIST_FOREACH(c, &bs->children, next) {
         if (c->role & BDRV_CHILD_PRIMARY) {
-            return c;
+            assert(!found);
+            found = c;
         }
     }
 
-    return NULL;
+    return c;
 }


with or without:
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>


--
Best regards,
Vladimir