1 files changed, 29 insertions, 3 deletions

diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h
index 2982dd3..925a3e7 100644
--- a/include/block/block_int-common.h
+++ b/include/block/block_int-common.h
@@ -396,9 +396,23 @@ struct BlockDriver {
     int GRAPH_RDLOCK_PTR (*bdrv_probe_geometry)(
         BlockDriverState *bs, HDGeometry *geo);
 
+    /**
+     * Hot add a BDS's child. Used in combination with bdrv_del_child, so the
+     * user can take a child offline when it is broken and take a new child
+     * online.
+     *
+     * All block nodes must be drained.
+     */
     void GRAPH_WRLOCK_PTR (*bdrv_add_child)(
         BlockDriverState *parent, BlockDriverState *child, Error **errp);
 
+    /**
+     * Hot remove a BDS's child. Used in combination with bdrv_add_child, so the
+     * user can take a child offline when it is broken and take a new child
+     * online.
+     *
+     * All block nodes must be drained.
+     */
     void GRAPH_WRLOCK_PTR (*bdrv_del_child)(
         BlockDriverState *parent, BdrvChild *child, Error **errp);
 
@@ -983,9 +997,21 @@ struct BdrvChildClass {
                            bool backing_mask_protocol,
                            Error **errp);
 
-    bool (*change_aio_ctx)(BdrvChild *child, AioContext *ctx,
-                           GHashTable *visited, Transaction *tran,
-                           Error **errp);
+    /*
+     * Notifies the parent that the child is trying to change its AioContext.
+     * The parent may in turn change the AioContext of other nodes in the same
+     * transaction. Returns true if the change is possible and the transaction
+     * can be continued. Returns false and sets @errp if not and the transaction
+     * must be aborted.
+     *
+     * @visited will accumulate all visited BdrvChild objects. The caller is
+     * responsible for freeing the list afterwards.
+     *
+     * Must be called with the affected block nodes drained.
+     */
+    bool GRAPH_RDLOCK_PTR (*change_aio_ctx)(BdrvChild *child, AioContext *ctx,
+                                            GHashTable *visited,
+                                            Transaction *tran, Error **errp);
 
     /*
      * I/O API functions. These functions are thread-safe.