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vhost: add vhost_svq_poll

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It allows the Shadow Control VirtQueue to wait for the device to use the
available buffers.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
This commit is contained in:
Eugenio Pérez 2022-07-20 08:59:38 +02:00 • committed by Jason Wang
parent d0291f3f28
commit 3f44d13dda
2 changed files with 28 additions and 0 deletions
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27
hw/virtio/vhost-shadow-virtqueue.c
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@ -485,6 +485,33 @@ static void vhost_svq_flush(VhostShadowVirtqueue *svq,
} while (!vhost_svq_enable_notification(svq));
}
/**
* Poll the SVQ for one device used buffer.
*
* This function race with main event loop SVQ polling, so extra
* synchronization is needed.
*
* Return the length written by the device.
*/
size_t vhost_svq_poll(VhostShadowVirtqueue *svq)
{
int64_t start_us = g_get_monotonic_time();
do {
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);
}
/**
* Forward used buffers.
*