virtio-net: bugfix: do not delete netdev before virtio net

For the vhost-user net-card, it is allow to delete its
network backend while the virtio-net device still exists.
However, when the status of the device changes in guest,
QEMU will check whether the network backend exists, otherwise
it will crash.
So do not allowed to delete the network backend directly
without delete virtio-net device.

Signed-off-by: Jinhua Cao <caojinhua1@huawei.com>

virtio-net-bugfix-do-not-delete-netdev-before-virtio.patch

@@ -0,0 +1,38 @@
+From 532566ba64b60f2dd2f8ff41d670712ccafe1e98 Mon Sep 17 00:00:00 2001
+From: Jinhua Cao <caojinhua1@huawei.com>
+Date: Thu, 10 Feb 2022 10:31:38 +0800
+Subject: [PATCH] virtio-net: bugfix: do not delete netdev before virtio net
+
+For the vhost-user net-card, it is allow to delete its
+network backend while the virtio-net device still exists.
+However, when the status of the device changes in guest,
+QEMU will check whether the network backend exists, otherwise
+it will crash.
+So do not allowed to delete the network backend directly
+without delete virtio-net device.
+
+Signed-off-by: Jinhua Cao <caojinhua1@huawei.com>
+---
+ net/net.c | 6 ++++++
+ 1 file changed, 6 insertions(+)
+
+diff --git a/net/net.c b/net/net.c
+index f0d14dbfc1..ed4b1c1740 100644
+--- a/net/net.c
++++ b/net/net.c
+@@ -1202,6 +1202,12 @@ void qmp_netdev_del(const char *id, Error **errp)
+         return;
+     }
+ 
++    if (nc->info->type == NET_CLIENT_DRIVER_VHOST_USER && nc->peer) {
++        error_setg(errp, "Device '%s' is a netdev for vhostuser,"
++                   "please delete the peer front-end device (virtio-net) first.", id);
++        return;
++    }
++
+     qemu_del_net_client(nc);
+ 
+     /*
+-- 
+2.27.0
+