[Qemu-devel] [PULL v3 04/15] tests/vhost-user-bridge: workaround stale vring base

["Michael S. Tsirkin" <mst@redhat.com>]

From: Marc-André Lureau <marcandre.lureau@redhat.com>

This patch is a similar solution to what Yuanhan Liu/Huawei Xie have
suggested for DPDK. When vubr quits (killed or crashed), a restart of
vubr would get stale vring base from QEMU. That would break the kernel
virtio net completely, making it non-work any more, unless a driver
reset is done.

So, instead of getting the stale vring base from QEMU, Huawei suggested
we could get a proper one from used->idx. This works because the queues
packets are processed in order.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Tested-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: Victor Kaplansky <victork@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 tests/vhost-user-bridge.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tests/vhost-user-bridge.c b/tests/vhost-user-bridge.c
index e231ce9..36b3cd8 100644
--- a/tests/vhost-user-bridge.c
+++ b/tests/vhost-user-bridge.c
@@ -946,6 +946,13 @@ vubr_set_vring_addr_exec(VubrDev *dev, VhostUserMsg *vmsg)
     DPRINT("    vring_avail at %p\n", vq->avail);
 
     vq->last_used_index = vq->used->idx;
+
+    if (vq->last_avail_index != vq->used->idx) {
+        DPRINT("Last avail index != used index: %d != %d, resuming",
+               vq->last_avail_index, vq->used->idx);
+        vq->last_avail_index = vq->used->idx;
+    }
+
     return 0;
 }
 
-- 
MST