Re: [Qemu-devel] Help: Does Qemu support virtio-pci for net-device and disk device?

[Andrea Bolognani]

On Thu, 2016-08-18 at 08:38 +0200, Andrew Jones wrote:
> > > Finally, FWIW, with a guest kernel of 4.6.4-301.fc24.aarch64. The
> > > following qemu command line works for me.
> > > (notice the use of PCIe), and my network interface gets labeled enp0s1.
> > >  
> > > $QEMU -machine virt-2.6,accel=kvm -cpu host \
> > >   -m 1024 -smp 1 -nographic \
> > >   -bios /usr/share/AAVMF/AAVMF_CODE.fd \
> > >   -device ioh3420,bus=pcie.0,id=pcie.1,port=1,chassis=1 \
> > >   -device ioh3420,bus=pcie.0,id=pcie.2,port=2,chassis=2 \
> > >   -device 
> > >virtio-scsi-pci,disable-modern=off,disable-legacy=on,bus=pcie.1,addr=00.0,id=scsi0
> > > \
> > >   -drive 
> > >file=/home/drjones/.local/libvirt/images/fedora.qcow2,format=qcow2,if=none,id=drive-scsi0-0-0-0
> > > \
> > >   -device 
> > >scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0,bootindex=1
> > > \
> > >   -netdev user,id=hostnet0 \
> > >   -device 
> > >virtio-net-pci,disable-modern=off,disable-legacy=on,bus=pcie.2,addr=00.0,netdev=hostnet0,id=net0
> > >  
> > > I prefer always using virtio-scsi for the disk, but a similar command
> > > line can be used for a virtio-blk-pci disk.
> > 
> > Does the same command line work if you don't specify any of
> > the disable-* options?
> > 
> > I'm asking because I tried running a Fedora 24 guest through
> > libvirt, which doesn't support those options yet, and I get
> > 
> >   virtio_blk virtio2: virtio: device uses modern interface but
> >                               does not have VIRTIO_F_VERSION_1
> >   virtio_blk: probe of virtio2 failed with error -22
> 
> Doesn't work for me either. I can only boot with disable-modern=off,
> disable-legacy=on (at least when building my config the way I try to
> build it...) I presume that's a guest kernel issue.

I tried Fedora 24 and Debian testing, and for both of them
the result is the same: I can only boot the guest if I'm
setting up a legacy-free PCIe topology and use virt-2.7 to
obtain virtio-1.0 devices (see below); for every other
permutation of

  { PCI topology, PCIe topology } x { virt-2.6, virt-2.7 }

the guest doesn't boot at all.

On the other hand, a RHEL 7.3 guest was able to boot *every
single time*, even though the result was in some cases
quite questionable (eg. legacy PCI devices plugged into
ioh3420 ports).

> > Isn't the default for 2.6 disable-modern=off,
> > disable-legacy=off? Or was that 2.7? I tried both anyway ;)
> 
> Dunno. With the command line getting longer all the time, I just
> have a script that generates one that works for me, and haven't
> worried much about the defaults...

So I thought the default for 2.6 was supposed to be

  disable-modern=off,disable-legacy=off  [0.9+1.0]

but it turns out it's actually

  disable-modern=on,disable-legacy=off       [0.9]

whereas the default for 2.7 is

  disable-modern=off,disable-legacy=on       [1.0]

Is the idea that there would be a QEMU release with both
0.9 and 1.0 enabled by default something that I just
imagined? Or did the plan just change at some point?

-- 
Andrea Bolognani / Red Hat / Virtualization