commit 0421b563ab4d947a388078331c057daa9b979f41
author Stefan Hajnoczi <stefanha@redhat.com> Thu Oct 13 14:58:56 2022 -0400
committer Stefan Hajnoczi <stefanha@redhat.com> Wed Oct 26 14:56:42 2022 -0400
tree 2806a9b2fec0cb8e8865016d269f9b4ec6071457
parent 79fc2fb685f35a5e71e23629760ef4025d6aba31

coroutine: add flag to re-queue at front of CoQueue

When a coroutine wakes up it may determine that it must re-queue.
Normally coroutines are pushed onto the back of the CoQueue, but for
fairness it may be necessary to push it onto the front of the CoQueue.

Add a flag to specify that the coroutine should be pushed onto the front
of the CoQueue. A later patch will use this to ensure fairness in the
bounce buffer CoQueue used by the blkio BlockDriver.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20221013185908.1297568-2-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

util/qemu-coroutine-lock.c

diff --git a/util/qemu-coroutine-lock.c b/util/qemu-coroutine-lock.c
index 15c82d9..45c6b57 100644
--- a/util/qemu-coroutine-lock.c
+++ b/util/qemu-coroutine-lock.c
@@ -39,10 +39,15 @@
     QSIMPLEQ_INIT(&queue->entries);
 }
 
-void coroutine_fn qemu_co_queue_wait_impl(CoQueue *queue, QemuLockable *lock)
+void coroutine_fn qemu_co_queue_wait_impl(CoQueue *queue, QemuLockable *lock,
+                                          CoQueueWaitFlags flags)
 {
     Coroutine *self = qemu_coroutine_self();
-    QSIMPLEQ_INSERT_TAIL(&queue->entries, self, co_queue_next);
+    if (flags & CO_QUEUE_WAIT_FRONT) {
+        QSIMPLEQ_INSERT_HEAD(&queue->entries, self, co_queue_next);
+    } else {
+        QSIMPLEQ_INSERT_TAIL(&queue->entries, self, co_queue_next);
+    }
 
     if (lock) {
         qemu_lockable_unlock(lock);