Re: [PATCH v5 03/10] vhost: Do not depend on !NULL VirtQueueElement on vhost_svq_flush

[Jason Wang]

在 2022/8/3 01:57, Eugenio Pérez 写道:

Since QEMU will be able to inject new elements on CVQ to restore the
state, we need not to depend on a VirtQueueElement to know if a new
element has been used by the device or not. Instead of check that, check
if there are new elements only using used idx on vhost_svq_flush.

Signed-off-by: Eugenio Pérez <epere...@redhat.com>
---
  hw/virtio/vhost-shadow-virtqueue.c | 18 +++++++++---------
  1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
b/hw/virtio/vhost-shadow-virtqueue.c
index e6eebd0e8d..fdb550c31b 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -491,7 +491,7 @@ static void vhost_svq_flush(VhostShadowVirtqueue *svq,
  /**
   * Poll the SVQ for one device used buffer.
   *
- * This function race with main event loop SVQ polling, so extra
+ * This function races with main event loop SVQ polling, so extra
   * synchronization is needed.
   *
   * Return the length written by the device.
@@ -499,20 +499,20 @@ static void vhost_svq_flush(VhostShadowVirtqueue *svq,
  size_t vhost_svq_poll(VhostShadowVirtqueue *svq)
  {
      int64_t start_us = g_get_monotonic_time();
-    do {
+    while (true) {
          uint32_t len;
-        VirtQueueElement *elem = vhost_svq_get_buf(svq, &len);
-        if (elem) {
-            return len;
-        }

if (unlikely(g_get_monotonic_time() - start_us > 10e6)) {

              return 0;
          }

- /* Make sure we read new used_idx */

-        smp_rmb();
-    } while (true);
+        if (!vhost_svq_more_used(svq)) {
+            continue;
+        }
+
+        vhost_svq_get_buf(svq, &len);

I wonder if this means we won't worry about the infinite wait?

Thanks

+        return len;
+    }
  }

/**