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Date: Thu, 25 Feb 2010 13:42:56 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20100225114256.GC9116@redhat.com>
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Subject: [Qemu-devel] Re: [PATCH] qdev: Catch attempt to attach more than
	one device to a netdev
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To: Markus Armbruster <armbru@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>, qemu-devel@nongnu.org, Gerd Hoffmann <kraxel@redhat.com>

On Thu, Feb 25, 2010 at 11:10:15AM +0100, Markus Armbruster wrote:
> 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 <armbru@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;
> +    }

Not even -EBUSY?
Can this produce a helpful diagnostic message?

>      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);

Do we ever get herE?

>              vc->peer = peer;
>              peer->peer = vc;
>          }
> -- 
> 1.6.6
> 
>