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

[Daniel P. Berrange]

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

Regards,
Daniel
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