Re: [Qemu-devel] qemu -netdev tun/tap support can't handle macvtap type devices

[Jason Wang <jasowang@redhat.com>]

On 2016年12月07日 22:24, Daniel P. Berrange wrote:
> On Wed, Dec 07, 2016 at 02:21:24PM +0000, Peter Maydell wrote:
>> On 7 December 2016 at 14:07, Daniel P. Berrange <berrange@redhat.com> wrote:
>>> On Wed, Dec 07, 2016 at 12:30:31PM +0000, Peter Maydell wrote:
>>>> On 7 December 2016 at 12:04, Daniel P. Berrange <berrange@redhat.com> wrote:
>>>>> On Wed, Dec 07, 2016 at 12:01:14PM +0000, Peter Maydell wrote:
>>>>>> The usual suggested workaround is to use the -netdev fd option, like
>>>>>>    fd=3 3<>/dev/tap$(< /sys/class/net/tap0/ifindex)
>>>>>> (which gets the shell to open the right /dev/tap device).
>>>>>> Unfortunately this isn't compatible with multi-queue support
>>>>>> because netdev complains
>>>>>> "ifname=, script=, downscript=, vnet_hdr=, helper=, queues=, fds=,
>>>>>> and vhostfds= are invalid with fd="
>>>>>> so you can't pass options like "queues=4"...
>>>>> FWIW you should be able to instead do
>>>>>
>>>>>     fds=3 3<>/dev/tap$(< /sys/class/net/tap0/ifindex)
>>>>>
>>>>> note 'fds' plural, instead of 'fd'
>>>> What's the difference between that and the "usual suggested workaround"
>>>> I described above that doesn't work with queues=... ?
>>> It just seems the 'queues' param always wants you to use 'fds' instead
>>> of 'fd' - 'fds' takes a comma-separated list of FDs - one per queue
>>> and 'fd' only takes a single FD.
>> Oh, I see. That seems a bit obscure :-)
> And pointless, because QemuOpts would have allowed use of 'fd' multiple
> times instead of inventing a new arg.  fd=1,fd=3,fd=6 could have worked
> fine with multi-queue :-(
>
> Regards,
> Daniel

Yes, but not the time when multiqueue is introduced. I'm not sure how 
much value we can gain from this, consider libvirt has already use fds 
for years.

Thanks