[PATCH v3 13/33] block: Add child_of_bds

[Max Reitz]

Any current user of child_file, child_format, and child_backing can and
should use this generic BdrvChildClass instead, as it can handle all of
these cases.  However, to be able to do so, the users must pass the
appropriate BdrvChildRole when the child is created/attached.  (The
following commits will take care of that.)

Signed-off-by: Max Reitz <address@hidden>
Reviewed-by: Eric Blake <address@hidden>
---
 block.c                   | 27 +++++++++++++++++++++++++++
 include/block/block_int.h |  1 +
 2 files changed, 28 insertions(+)

diff --git a/block.c b/block.c
index 0f24546863..1d33f58ff8 100644
--- a/block.c
+++ b/block.c
@@ -1094,6 +1094,33 @@ static void bdrv_inherited_options(BdrvChildRole role, 
bool parent_is_format,
     *child_flags = flags;
 }
 
+static int bdrv_backing_update_filename(BdrvChild *c, BlockDriverState *base,
+                                        const char *filename, Error **errp);
+
+static int bdrv_child_cb_update_filename(BdrvChild *c, BlockDriverState *base,
+                                         const char *filename, Error **errp)
+{
+    if (c->role & BDRV_CHILD_COW) {
+        return bdrv_backing_update_filename(c, base, filename, errp);
+    }
+    return 0;
+}
+
+const BdrvChildClass child_of_bds = {
+    .parent_is_bds   = true,
+    .get_parent_desc = bdrv_child_get_parent_desc,
+    .inherit_options = bdrv_inherited_options,
+    .drained_begin   = bdrv_child_cb_drained_begin,
+    .drained_poll    = bdrv_child_cb_drained_poll,
+    .drained_end     = bdrv_child_cb_drained_end,
+    .attach          = bdrv_child_cb_attach,
+    .detach          = bdrv_child_cb_detach,
+    .inactivate      = bdrv_child_cb_inactivate,
+    .can_set_aio_ctx = bdrv_child_cb_can_set_aio_ctx,
+    .set_aio_ctx     = bdrv_child_cb_set_aio_ctx,
+    .update_filename = bdrv_child_cb_update_filename,
+};
+
 /*
  * Returns the options and flags that bs->file should get if a protocol driver
  * is expected, based on the given options and flags for the parent BDS
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 1f8a818f76..dd7ccea35e 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -740,6 +740,7 @@ struct BdrvChildClass {
     void (*set_aio_ctx)(BdrvChild *child, AioContext *ctx, GSList **ignore);
 };
 
+extern const BdrvChildClass child_of_bds;
 extern const BdrvChildClass child_file;
 extern const BdrvChildClass child_format;
 extern const BdrvChildClass child_backing;
-- 
2.24.1