Anthony Liguori <anth...@codemonkey.ws> writes:
> On 07/15/2010 03:22 PM, Miguel Di Ciurcio Filho wrote:
>> Hello,
>>
>> This is a prototype suggestion. I mostly copied and pasted the code from
>> net/dump.c into net.c and made some adjustments. There is no command line
>> parsing involved yet, just the internals and small changes in net/tap.c and
>> net/slirp.c do make the thing work.
>>
>> In my tests, using tap as backend, e1000 as a guest device and running iperf
>> from
>> guest to host, the overhead of dumping the traffic caused a loss of around
>> 30%
>> of performance.
>>
>> I opened the dumped files in wireshark and they looked fine. When using slirp
>> all requests were dumped fine too.
>>
>
> A less invasive way to do this would be to chain netdev devices.
>
> Basically:
>
> -netdev tap,fd=X,id=foo
> -netdev dump,file=foo.pcap,netdev=foo,id=bar
> -net nic,model=virtio,netdev=bar
Is this really less invasive? It breaks the simple 1:1 relationship
between NIC and network backend. All the code dealing with
VLANClientState member peer needs to be touched. For instance, this is
the code to connect peers, in qemu_new_net_client():
if (peer) {
assert(!peer->peer);
vc->peer = peer;
peer->peer = vc;
}
Possibly worth it if we had a number of different things we want to
insert between the end points, but I don't see that right now.
> I think this has some clear advantages to this architecturally. From
> a user perspective, the only loss is that you have to add the dump
> device at startup (you can still enable/disable capture dynamically).
I don't like this restriction at all.
