block-coroutine-wrapper: Add no_co_wrapper_bdrv_rdlock functions

Add a new wrapper type for GRAPH_RDLOCK functions that should be called
from coroutine context.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230929145157.45443-3-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

include/block/block-common.h

@@ -66,13 +66,16 @@
  * function. The coroutine yields after scheduling the BH and is reentered when
  * the wrapped function returns.
  *
- * A no_co_wrapper_bdrv_wrlock function is a no_co_wrapper function that
- * automatically takes the graph wrlock when calling the wrapped function.
+ * A no_co_wrapper_bdrv_rdlock function is a no_co_wrapper function that
+ * automatically takes the graph rdlock when calling the wrapped function. In
+ * the same way, no_co_wrapper_bdrv_wrlock functions automatically take the
+ * graph wrlock.
  *
  * If the first parameter of the function is a BlockDriverState, BdrvChild or
  * BlockBackend pointer, the AioContext lock for it is taken in the wrapper.
  */
 #define no_co_wrapper
+#define no_co_wrapper_bdrv_rdlock
 #define no_co_wrapper_bdrv_wrlock
 
 #include "block/blockjob.h"

scripts/block-coroutine-wrapper.py

@@ -87,8 +87,9 @@ def __init__(self, wrapper_type: str, return_type: str, name: str,
                 raise ValueError(f"Invalid no_co function name: {self.name}")
             if not self.create_only_co:
                 raise ValueError(f"no_co function can't be mixed: {self.name}")
-            if self.graph_rdlock:
-                raise ValueError(f"no_co function can't be rdlock: {self.name}")
+            if self.graph_rdlock and self.graph_wrlock:
+                raise ValueError("function can't be both rdlock and wrlock: "
+                                 f"{self.name}")
             self.target_name = f'{subsystem}_{subname}'
 
         self.ctx = self.gen_ctx()
@@ -256,7 +257,10 @@ def gen_no_co_wrapper(func: FuncDecl) -> str:
 
     graph_lock=''
     graph_unlock=''
-    if func.graph_wrlock:
+    if func.graph_rdlock:
+        graph_lock='    bdrv_graph_rdlock_main_loop();'
+        graph_unlock='    bdrv_graph_rdunlock_main_loop();'
+    elif func.graph_wrlock:
         graph_lock='    bdrv_graph_wrlock(NULL);'
         graph_unlock='    bdrv_graph_wrunlock();'