From 3f44d13dda83d390cc9563e56e7d337e4f6223f4 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Eugenio=20P=C3=A9rez?= Date: Wed, 20 Jul 2022 08:59:38 +0200 Subject: [PATCH] vhost: add vhost_svq_poll MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit It allows the Shadow Control VirtQueue to wait for the device to use the available buffers. Signed-off-by: Eugenio Pérez Reviewed-by: Michael S. Tsirkin Signed-off-by: Jason Wang --- hw/virtio/vhost-shadow-virtqueue.c | 27 +++++++++++++++++++++++++++ hw/virtio/vhost-shadow-virtqueue.h | 1 + 2 files changed, 28 insertions(+) diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c index c3a75ca89e..cc2ee4780d 100644 --- a/hw/virtio/vhost-shadow-virtqueue.c +++ b/hw/virtio/vhost-shadow-virtqueue.c @@ -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. * diff --git a/hw/virtio/vhost-shadow-virtqueue.h b/hw/virtio/vhost-shadow-virtqueue.h index dd78f4bec2..cf442f7dea 100644 --- a/hw/virtio/vhost-shadow-virtqueue.h +++ b/hw/virtio/vhost-shadow-virtqueue.h @@ -89,6 +89,7 @@ void vhost_svq_push_elem(VhostShadowVirtqueue *svq, int vhost_svq_add(VhostShadowVirtqueue *svq, const struct iovec *out_sg, size_t out_num, const struct iovec *in_sg, size_t in_num, VirtQueueElement *elem); +size_t vhost_svq_poll(VhostShadowVirtqueue *svq); void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd); void vhost_svq_set_svq_call_fd(VhostShadowVirtqueue *svq, int call_fd); -- 2.30.2