[Qemu-devel] [PATCH for-2.4] virtio-net: Flush incoming queues when DRIVER_OK is being set

[Fam Zheng <famz@redhat.com>]

This patch fixes network hang after "stop" then "cont", while network
packets keep arriving.

Tested both manually (tap, host pinging guest) and with Jason's qtest
series (plus his "[PATCH 2.4] socket: pass correct size in
net_socket_send()" fix).

As virtio_net_set_status is called when guest driver is setting status
byte and when vm state is changing, it is a good opportunity to flush
queued packets.

This is necessary because during vm stop the backend (e.g. tap) would
stop rx processing after .can_receive returns false, until the queue is
explicitly flushed or purged.

The other interesting condition in .can_receive, virtio_queue_ready(),
is handled by virtio_net_handle_rx() when guest kicks; the 3rd condition
is invalid queue index which doesn't need flushing.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 hw/net/virtio-net.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index d728233..7c178c6 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -162,8 +162,13 @@ static void virtio_net_set_status(struct VirtIODevice *vdev, uint8_t status)
     virtio_net_vhost_status(n, status);
 
     for (i = 0; i < n->max_queues; i++) {
+        NetClientState *ncs = qemu_get_subqueue(n->nic, i);
         q = &n->vqs[i];
 
+        if (status & VIRTIO_CONFIG_S_DRIVER_OK) {
+            qemu_flush_queued_packets(ncs);
+        }
+
         if ((!n->multiqueue && i != 0) || i >= n->curr_queues) {
             queue_status = 0;
         } else {
-- 
2.4.3