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Date: Wed, 7 Dec 2016 14:24:49 +0000
From: "Daniel P. Berrange" <berrange@redhat.com>
Message-ID: <20161207142449.GC1476@redhat.com>
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Subject: Re: [Qemu-devel] qemu -netdev tun/tap support can't handle macvtap
 type devices
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>, Jason Wang <jasowang@redhat.com>

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
-- 
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