Re: [Qemu-devel] [RFC PATCH] net: Enable vlans and dump for -netdev, too,

[Stefan Hajnoczi]

On Tue, May 26, 2015 at 3:36 PM, Daniel P. Berrange <address@hidden> wrote:
> On Tue, May 26, 2015 at 04:29:51PM +0200, Markus Armbruster wrote:
>> Stefan Hajnoczi <address@hidden> writes:
>>
>> > On Fri, May 22, 2015 at 09:22:19PM +0200, Thomas Huth wrote:
>> >> So far, it is not possible to use the network dump interface
>> >> with the "-netdev" option yet, it only works with the legacy
>> >> "-net" option. To be able to use it with "-netdev", too, this
>> >> patch now enables the "vlan" packet distribution for the
>> >> "-netdev" option, too, so that you can now dump network packets
>> >> like this:
>> >>
>> >> qemu... -device e1000,netdev=myhub -netdev hubport,hubid=1,id=myhub \
>> >>         -netdev user,id=n1,vlan=1,tftp=/tmp/tftp,bootfile=zImage \
>> >>         -netdev dump,id=n2,vlan=1,file=/tmp/dump.dat
>> >>
>> >> Signed-off-by: Thomas Huth <address@hidden>
>> >> ---
>> >>  net/net.c        | 3 +++
>> >>  qapi-schema.json | 1 +
>> >>  2 files changed, 4 insertions(+)
>> >>
>> >>  [Note: I'm quite new to this area of the code, please review carefully
>> >>   whether this approach makes sense or whether it should be done 
>> >> differently]
>> >
>> > We thought the QEMU "vlan" concept would be dropped completely in the
>> > future, so it was never added to -netdev.  No patches to do that have
>> > been posted over the years, so I think it was more of a conceptual goal
>> > than a concrete requirement.
>>
>> Well, patches to do that first need to replace the VLAN-only dump
>> feature.
>>
>> To fully deprecate -net, we also have to replace -net nic for
>> configuring onboard NICs.
>>
>> Prior discussion:
>> http://lists.nongnu.org/archive/html/qemu-devel/2013-02/msg03743.html
>>
>> We haven't really tried either.
>>
>> Thomas's patch declares defeat on VLANs: it ports them to -netdev,
>> perpetuating the concept.
>>
>> > I'm okay with merging this but will leave some time for discussion
>> > before merging the patch.
>> >
>> > "Speak now or forever hold your peace"
>>
>> Sure we're ready to give up without having tried?
>
> Seems to me that we'd be better off taking the -netdev arg and
> adding a new parameter 'dump=filename' that can be used with any
> netdev backend. eg with tap
>
>    -netdev tap,id=foo,fd=3,dump=/somefile,dumplen=1024
>
> The use of a dedicated 'dump' network backend always appear rather
> strange as a conceptual approach, and I don't think we should
> propagate its use into -netdev

I'm happy with this approach too.

Stefan