[Qemu-devel] [PATCHv3 1/2] net: notify peer about link status change

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

qemu makes it possible to disable link at tap
which is not communicated to the guest but
causes all packets to be dropped.

This works for virtio userspace, as qemu
stops giving it packets, but not for
virtio-net connected to vhost-net
as that does not get notified about this change.

Notify peer when this happens, which will then be used
by the follow-up patch to stop/start vhost-net.

Note: it might be a good idea to make peer link status match
tap in this case, so the guest gets an event
and updates the carrier state. For now
stay bug for bug compatible with what we used to have
in userspace.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reported-by: pradeep <psuriset@linux.vnet.ibm.com>
---
 net.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/net.c b/net.c
index 9ba5be2..ec4745d 100644
--- a/net.c
+++ b/net.c
@@ -1324,6 +1324,17 @@ done:
     if (vc->info->link_status_changed) {
         vc->info->link_status_changed(vc);
     }
+
+    /* Notify peer. Don't update peer link status: this makes it possible to
+     * disconnect from host network without notifying the guest.
+     * FIXME: is disconnected link status change operation useful?
+     *
+     * Current behaviour is compatible with qemu vlans where there could be
+     * multiple clients that can still communicate with each other in
+     * disconnected mode. For now maintain this compatibility. */
+    if (vc->peer && vc->peer->info->link_status_changed) {
+        vc->peer->info->link_status_changed(vc->peer);
+    }
     return 0;
 }
 
-- 
1.7.3.2.91.g446ac