[RFC PATCH 1/4] block/aio: Add automatically released aio_context variants

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Similarly to commit 5626f8c6d46 ("rcu: Add automatically
released rcu_read_lock variants"):

AIO_CONTEXT_ACQUIRE_GUARD() acquires the aio context and then uses
glib's g_auto infrastructure (and thus whatever the compiler's hooks
are) to release it on all exits of the block.

WITH_AIO_CONTEXT_ACQUIRE_GUARD() is similar but is used as a wrapper
for the lock, i.e.:

   WITH_AIO_CONTEXT_ACQUIRE_GUARD() {
       stuff with context acquired
   }

Inspired-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 include/block/aio.h | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/include/block/aio.h b/include/block/aio.h
index 47fbe9d81f2..4fa5a5c2720 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -294,6 +294,30 @@ void aio_context_acquire(AioContext *ctx);
 /* Relinquish ownership of the AioContext. */
 void aio_context_release(AioContext *ctx);
 
+static inline AioContext *aio_context_auto_acquire(AioContext *ctx)
+{
+    aio_context_acquire(ctx);
+    return ctx;
+}
+
+static inline void aio_context_auto_release(AioContext *ctx)
+{
+    aio_context_release(ctx);
+}
+
+G_DEFINE_AUTOPTR_CLEANUP_FUNC(AioContext, aio_context_auto_release)
+
+#define WITH_AIO_CONTEXT_ACQUIRE_GUARD(ctx) \
+    WITH_AIO_CONTEXT_ACQUIRE_GUARD_(glue(_aio_context_auto, __COUNTER__), ctx)
+
+#define WITH_AIO_CONTEXT_ACQUIRE_GUARD_(var, ctx) \
+    for (g_autoptr(AioContext) var = aio_context_auto_acquire(ctx); \
+        (var); aio_context_auto_release(var), (var) = NULL)
+
+#define AIO_CONTEXT_ACQUIRE_GUARD(ctx) \
+    g_autoptr(AioContext) _aio_context_auto __attribute__((unused)) \
+        = aio_context_auto_acquire(ctx)
+
 /**
  * aio_bh_schedule_oneshot_full: Allocate a new bottom half structure that will
  * run only once and as soon as possible.
-- 
2.31.1