Re: [Qemu-devel] using -net dump with tap networking

[Markus Armbruster]

Stefan Hajnoczi <address@hidden> writes:

> On Tue, Feb 19, 2013 at 09:53:07AM +0100, Markus Armbruster wrote:
>> Stefan Hajnoczi <address@hidden> writes:
>> 
>> > On Tue, Feb 19, 2013 at 12:37:28PM +1100, Alexey Kardashevskiy wrote:
>> >> On 14/02/13 21:26, Stefan Hajnoczi wrote:
>> >> 
>> >> >>>>Now I want to enable network dump. With the old "-net" syntax
>> >> >>>> I could do
>> >> >>>>that with "-net dump" but I cannot with the new syntax, tried many
>> >> >>>>variants, none works. What would the correct syntax be for
>> >> >>>> the case above?
>> >> 
>> >> The question was about new "-netdev" interface.
>> >> 
>> >> >I would do:
>> >> >
>> >> >qemu-system-ppc64 ...
>> >> >       -net tap,ifname=tap0,script=qemu-ifup.sh
>> >> >       -net nic,model=virtio
>> >> >       -net dump,file=./dump.lan.qemu.virtio
>> >> >
>> >> 
>> >> The answer is about old "-net" interface which I know how to use.
>> >> 
>> >> Does this mean that there is no way to use "dump" with "-netdev tap"?
>> >
>> > It is not possible using just -netdev/-device.  The closest you can get
>> > is:
>> >
>> >   $ qemu -netdev hubport,hubid=1,id=hubport0 \
>> >          -device virtio-net-pci,netdev=hubport0,... \
>> >     -net tap,vlan=1,... \
>> >     -net dump,vlan=1,...
>> 
>> Care to explain briefly how hubport works, and how it's connected to the
>> legacy "vlan" feature?
>
> -netdev hubport instantiates a new port on a hub with "vlan" number
> hubid=<number>.
>
> hubport is a -netdev, so it allows you to hook up a NIC to a hub using
> -netdev/-device syntax.
>
> This is just playing games with syntax, we still have a hub in between
> the virtio-net-pci, tap, and dump devices.  I didn't check if the
> offload features get plumbed through, but I wouldn't count on it.

Thanks.

Would you mind documenting net backend hubport in qemu-options.hx?  Was
forgotten in commit f6c874e3.

Your example uses -net to connect additional backends to the hubport.
If I understand you correctly, you can't use -netdev to do that.
Ignorant question: fundamental reason or just not implemented?