[PATCH 07/20] graph-lock: implement WITH_GRAPH_RDLOCK_GUARD and GRAPH_RDLOCK_GUARD macros

[Emanuele Giuseppe Esposito <eesposit@redhat.com>]

Similar to the implementation in lockable.h, implement macros to
automatically take and release the rdlock.
Create the empty GraphLockable struct only to use it as a type for
G_DEFINE_AUTOPTR_CLEANUP_FUNC.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 include/block/graph-lock.h | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/include/block/graph-lock.h b/include/block/graph-lock.h
index 9430707dca..0d886a9ca3 100644
--- a/include/block/graph-lock.h
+++ b/include/block/graph-lock.h
@@ -141,5 +141,40 @@ void assert_bdrv_graph_readable(void);
  */
 void assert_bdrv_graph_writable(void);
 
+typedef struct GraphLockable { } GraphLockable;
+
+/*
+ * In C, compound literals have the lifetime of an automatic variable.
+ * In C++ it would be different, but then C++ wouldn't need QemuLockable
+ * either...
+ */
+#define GML_OBJ_() (&(GraphLockable) { })
+
+static inline GraphLockable *graph_lockable_auto_lock(GraphLockable *x)
+{
+    bdrv_graph_co_rdlock();
+    return x;
+}
+
+static inline void graph_lockable_auto_unlock(GraphLockable *x)
+{
+    bdrv_graph_co_rdunlock();
+}
+
+G_DEFINE_AUTOPTR_CLEANUP_FUNC(GraphLockable, graph_lockable_auto_unlock)
+
+#define WITH_GRAPH_RDLOCK_GUARD_(var)                                         \
+    for (g_autoptr(GraphLockable) var = graph_lockable_auto_lock(GML_OBJ_()); \
+         var;                                                                 \
+         graph_lockable_auto_unlock(var), var = NULL)
+
+#define WITH_GRAPH_RDLOCK_GUARD() \
+    WITH_GRAPH_RDLOCK_GUARD_(glue(graph_lockable_auto, __COUNTER__))
+
+#define GRAPH_RDLOCK_GUARD(x)                                       \
+    g_autoptr(GraphLockable)                                        \
+    glue(graph_lockable_auto, __COUNTER__) G_GNUC_UNUSED =          \
+            graph_lockable_auto_lock(GML_OBJ_())
+
 #endif /* GRAPH_LOCK_H */
 
-- 
2.31.1