4 files changed, 44 insertions, 11 deletions
diff --git a/include/block/block-global-state.h b/include/block/block-global-state.h
index 9be34b3..84a2a4e 100644
--- a/include/block/block-global-state.h
+++ b/include/block/block-global-state.h
@@ -192,10 +192,10 @@ int bdrv_inactivate_all(void);
 
 int bdrv_flush_all(void);
 void bdrv_close_all(void);
-void bdrv_drain_all_begin(void);
+void GRAPH_UNLOCKED bdrv_drain_all_begin(void);
 void bdrv_drain_all_begin_nopoll(void);
 void bdrv_drain_all_end(void);
-void bdrv_drain_all(void);
+void GRAPH_UNLOCKED bdrv_drain_all(void);
 
 void bdrv_aio_cancel(BlockAIOCB *acb);
 
@@ -274,11 +274,16 @@ int bdrv_debug_remove_breakpoint(BlockDriverState *bs, const char *tag);
 int bdrv_debug_resume(BlockDriverState *bs, const char *tag);
 bool bdrv_debug_is_suspended(BlockDriverState *bs, const char *tag);
 
-bool bdrv_child_change_aio_context(BdrvChild *c, AioContext *ctx,
-                                   GHashTable *visited, Transaction *tran,
-                                   Error **errp);
-int bdrv_try_change_aio_context(BlockDriverState *bs, AioContext *ctx,
-                                BdrvChild *ignore_child, Error **errp);
+bool GRAPH_RDLOCK
+bdrv_child_change_aio_context(BdrvChild *c, AioContext *ctx,
+                              GHashTable *visited, Transaction *tran,
+                              Error **errp);
+int GRAPH_UNLOCKED
+bdrv_try_change_aio_context(BlockDriverState *bs, AioContext *ctx,
+                            BdrvChild *ignore_child, Error **errp);
+int GRAPH_RDLOCK
+bdrv_try_change_aio_context_locked(BlockDriverState *bs, AioContext *ctx,
+                                   BdrvChild *ignore_child, Error **errp);
 
 int GRAPH_RDLOCK bdrv_probe_blocksizes(BlockDriverState *bs, BlockSizes *bsz);
 int bdrv_probe_geometry(BlockDriverState *bs, HDGeometry *geo);
diff --git a/include/block/block-io.h b/include/block/block-io.h
index b99cc98..4cf83fb 100644
--- a/include/block/block-io.h
+++ b/include/block/block-io.h
@@ -431,7 +431,7 @@ bdrv_drain_poll(BlockDriverState *bs, BdrvChild *ignore_parent,
  *
  * This function can be recursive.
  */
-void bdrv_drained_begin(BlockDriverState *bs);
+void GRAPH_UNLOCKED bdrv_drained_begin(BlockDriverState *bs);
 
 /**
  * bdrv_do_drained_begin_quiesce:
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.
diff --git a/include/block/blockjob.h b/include/block/blockjob.h
index 7061ab7..990f3e1 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -137,6 +137,8 @@ BlockJob *block_job_get_locked(const char *id);
  * Add @bs to the list of BlockDriverState that are involved in
  * @job. This means that all operations will be blocked on @bs while
  * @job exists.
+ *
+ * All block nodes must be drained.
  */
 int GRAPH_WRLOCK
 block_job_add_bdrv(BlockJob *job, const char *name, BlockDriverState *bs,