[Qemu-devel] [PATCH] qdev: Catch attempt to attach more than one device to a netdev

[Markus Armbruster]

Guest device and host netdev are peers, i.e. it's a 1:1 relation.
However, we fail to enforce that:

    $ qemu -nodefaults --nographic -netdev user,id=net0 -device 
e1000,netdev=net0 -device virtio-net-pci,netdev=net0 -monitor stdio
    QEMU 0.12.50 monitor - type 'help' for more information
    (qemu) info network
    Devices not on any VLAN:
      net0: net=10.0.2.0, restricted=n peer=virtio-net-pci.0
      e1000.0: model=e1000,macaddr=52:54:00:12:34:56 peer=net0
      virtio-net-pci.0: model=virtio-net-pci,macaddr=52:54:00:12:34:57 peer=net0

It's all downhill from there.

Signed-off-by: Markus Armbruster <arm...@redhat.com>
---
 hw/qdev-properties.c |    3 +++
 net.c                |    1 +
 2 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/hw/qdev-properties.c b/hw/qdev-properties.c
index 277ff9e..89efd91 100644
--- a/hw/qdev-properties.c
+++ b/hw/qdev-properties.c
@@ -341,6 +341,9 @@ static int parse_netdev(DeviceState *dev, Property *prop, 
const char *str)
     *ptr = qemu_find_netdev(str);
     if (*ptr == NULL)
         return -1;
+    if ((*ptr)->peer) {
+        return -1;
+    }
     return 0;
 }
 
diff --git a/net.c b/net.c
index a1bf49f..e6c96d3 100644
--- a/net.c
+++ b/net.c
@@ -245,6 +245,7 @@ VLANClientState *qemu_new_net_client(NetClientInfo *info,
         QTAILQ_INSERT_TAIL(&vc->vlan->clients, vc, next);
     } else {
         if (peer) {
+            assert(!peer->peer);
             vc->peer = peer;
             peer->peer = vc;
         }
-- 
1.6.6