@@ -92,9 +92,17 @@ struct BlockDriver {
int instance_size;
/* set to true if the BlockDriver is a block filter. Block filters pass
- * certain callbacks that refer to data (see block.c) to their bs->file if
- * the driver doesn't implement them. Drivers that do not wish to forward
- * must implement them and return -ENOTSUP.
+ * certain callbacks that refer to data (see block.c) to their bs->file
+ * or bs->backing (whichever one exists) if the driver doesn't implement
+ * them. Drivers that do not wish to forward must implement them and return
+ * -ENOTSUP.
+ * Note that filters are not allowed to modify data.
+ *
+ * Filters generally cannot have more than a single filtered child,
+ * because the data they present must at all times be the same as
+ * that on their filtered child. That would be impossible to
+ * achieve for multiple filtered children.
+ * (And this filtered child must then be bs->file or bs->backing.)
*/
bool is_filter;
/*
@@ -1382,4 +1390,34 @@ BdrvDirtyBitmap *block_dirty_bitmap_remove(const char *node, const char *name,
BlockDriverState **bitmap_bs,
Error **errp);
+BdrvChild *bdrv_cow_child(BlockDriverState *bs);
+BdrvChild *bdrv_filter_child(BlockDriverState *bs);
+BdrvChild *bdrv_filter_or_cow_child(BlockDriverState *bs);
+BdrvChild *bdrv_primary_child(BlockDriverState *bs);
+
+static inline BlockDriverState *child_bs(BdrvChild *child)
+{
+ return child ? child->bs : NULL;
+}
+
+static inline BlockDriverState *bdrv_cow_bs(BlockDriverState *bs)
+{
+ return child_bs(bdrv_cow_child(bs));
+}
+
+static inline BlockDriverState *bdrv_filter_bs(BlockDriverState *bs)
+{
+ return child_bs(bdrv_filter_child(bs));
+}
+
+static inline BlockDriverState *bdrv_filter_or_cow_bs(BlockDriverState *bs)
+{
+ return child_bs(bdrv_filter_or_cow_child(bs));
+}
+
+static inline BlockDriverState *bdrv_primary_bs(BlockDriverState *bs)
+{
+ return child_bs(bdrv_primary_child(bs));
+}
+
#endif /* BLOCK_INT_H */
@@ -6943,3 +6943,94 @@ int bdrv_make_empty(BdrvChild *c, Error **errp)
return 0;
}
+
+/*
+ * Return the child that @bs acts as an overlay for, and from which data may be
+ * copied in COW or COR operations. Usually this is the backing file.
+ */
+BdrvChild *bdrv_cow_child(BlockDriverState *bs)
+{
+ if (!bs || !bs->drv) {
+ return NULL;
+ }
+
+ if (bs->drv->is_filter) {
+ return NULL;
+ }
+
+ if (!bs->backing) {
+ return NULL;
+ }
+
+ assert(bs->backing->role & BDRV_CHILD_COW);
+ return bs->backing;
+}
+
+/*
+ * If @bs acts as a filter for exactly one of its children, return
+ * that child.
+ */
+BdrvChild *bdrv_filter_child(BlockDriverState *bs)
+{
+ BdrvChild *c;
+
+ if (!bs || !bs->drv) {
+ return NULL;
+ }
+
+ if (!bs->drv->is_filter) {
+ return NULL;
+ }
+
+ /* Only one of @backing or @file may be used */
+ assert(!(bs->backing && bs->file));
+
+ c = bs->backing ?: bs->file;
+ if (!c) {
+ return NULL;
+ }
+
+ assert(c->role & BDRV_CHILD_FILTERED);
+ return c;
+}
+
+/*
+ * Return either the result of bdrv_cow_child() or bdrv_filter_child(),
+ * whichever is non-NULL.
+ *
+ * Return NULL if both are NULL.
+ */
+BdrvChild *bdrv_filter_or_cow_child(BlockDriverState *bs)
+{
+ BdrvChild *cow_child = bdrv_cow_child(bs);
+ BdrvChild *filter_child = bdrv_filter_child(bs);
+
+ /* Filter nodes cannot have COW backing files */
+ assert(!(cow_child && filter_child));
+
+ return cow_child ?: filter_child;
+}
+
+/*
+ * 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, *found = NULL;
+
+ QLIST_FOREACH(c, &bs->children, next) {
+ if (c->role & BDRV_CHILD_PRIMARY) {
+ assert(!found);
+ found = c;
+ }
+ }
+
+ return found;
+}