[pve-devel] [PATCH qemu 2/4] util/async: Add aio_co_reschedule_self()

[Stefan Reiter]

From: Kevin Wolf <kwolf at redhat.com>

From: Kevin Wolf <kwolf at redhat.com>

Add a function that can be used to move the currently running coroutine
to a different AioContext (and therefore potentially a different
thread).

Signed-off-by: Kevin Wolf <kwolf at redhat.com>
---

Required for patch 3. See this discussion on the QEMU mailing list:
https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg07421.html

 include/block/aio.h | 10 ++++++++++
 util/async.c        | 30 ++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/include/block/aio.h b/include/block/aio.h
index 62ed954344..d5399c67d6 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -17,6 +17,7 @@
 #ifdef CONFIG_LINUX_IO_URING
 #include <liburing.h>
 #endif
+#include "qemu/coroutine.h"
 #include "qemu/queue.h"
 #include "qemu/event_notifier.h"
 #include "qemu/thread.h"
@@ -654,6 +655,15 @@ static inline bool aio_node_check(AioContext *ctx, bool is_external)
  */
 void aio_co_schedule(AioContext *ctx, struct Coroutine *co);
 
+/**
+ * aio_co_reschedule_self:
+ * @new_ctx: the new context
+ *
+ * Move the currently running coroutine to new_ctx. If the coroutine is already
+ * running in new_ctx, do nothing.
+ */
+void coroutine_fn aio_co_reschedule_self(AioContext *new_ctx);
+
 /**
  * aio_co_wake:
  * @co: the coroutine
diff --git a/util/async.c b/util/async.c
index 3165a28f2f..4eba1e6f1b 100644
--- a/util/async.c
+++ b/util/async.c
@@ -558,6 +558,36 @@ void aio_co_schedule(AioContext *ctx, Coroutine *co)
     aio_context_unref(ctx);
 }
 
+typedef struct AioCoRescheduleSelf {
+    Coroutine *co;
+    AioContext *new_ctx;
+} AioCoRescheduleSelf;
+
+static void aio_co_reschedule_self_bh(void *opaque)
+{
+    AioCoRescheduleSelf *data = opaque;
+    aio_co_schedule(data->new_ctx, data->co);
+}
+
+void coroutine_fn aio_co_reschedule_self(AioContext *new_ctx)
+{
+    AioContext *old_ctx = qemu_get_current_aio_context();
+
+    if (old_ctx != new_ctx) {
+        AioCoRescheduleSelf data = {
+            .co = qemu_coroutine_self(),
+            .new_ctx = new_ctx,
+        };
+        /*
+         * We can't directly schedule the coroutine in the target context
+         * because this would be racy: The other thread could try to enter the
+         * coroutine before it has yielded in this one.
+         */
+        aio_bh_schedule_oneshot(old_ctx, aio_co_reschedule_self_bh, &data);
+        qemu_coroutine_yield();
+    }
+}
+
 void aio_co_wake(struct Coroutine *co)
 {
     AioContext *ctx;
-- 
2.20.1