Re: [Qemu-devel] [PATCH 0/4] add failover feature for assigned network devices

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, May 21, 2019 at 09:21:57AM +0200, Jens Freimann wrote:
> On Mon, May 20, 2019 at 04:56:57PM -0600, Alex Williamson wrote:
> > On Fri, 17 May 2019 14:58:16 +0200
> > Jens Freimann <jfreimann@redhat.com> wrote:
> > > Command line example:
> > > 
> > > qemu-system-x86_64 -enable-kvm -m 3072 -smp 3 \
> > >         -machine q35,kernel-irqchip=split -cpu host   \
> > >         -k fr   \
> > >         -serial stdio   \
> > >         -net none \
> > >         -qmp unix:/tmp/qmp.socket,server,nowait \
> > >         -monitor telnet:127.0.0.1:5555,server,nowait \
> > >         -device pcie-root-port,id=root0,multifunction=on,chassis=0,addr=0xa \
> > >         -device pcie-root-port,id=root1,bus=pcie.0,chassis=1 \
> > >         -device pcie-root-port,id=root2,bus=pcie.0,chassis=2 \
> > >         -netdev tap,script=/root/bin/bridge.sh,downscript=no,id=hostnet1,vhost=on \
> > >         -device virtio-net-pci,netdev=hostnet1,id=net1,mac=52:54:00:6f:55:cc,bus=root2,failover=on \
> > >         /root/rhel-guest-image-8.0-1781.x86_64.qcow2
> > > 
> > > Then the primary device can be hotplugged via
> > >  (qemu) device_add vfio-pci,host=5e:00.2,id=hostdev0,bus=root1,standby=net1
> > 
> > Is this standby= option only valid for Network/Ethernet class code
> > devices?  If so, perhaps vfio-pci code should reject the option on any
> > non-ethernet devices.  The option is also non-intuitive for users, only
> > through examples like above can we see it relates to the id of the
> > secondary device.  Could we instead name it something like
> > "standby_net_failover_pair_id="?
> 
> It is only for ethernet (VFs), I will add code to reject non-ethernet VF devices.
> I agree the name is not descriptive and the one you suggest seems good to
> me.
> > 
> > Also, this feature requires matching MAC addresses per the description,
> > where is that done?  Is it the user's responsibility to set the MAC on
> > the host device prior to the device_add?  If so, is this actually not
> > only specific to ethernet devices, but ethernet VFs?
> 
> Yes, it's the users responsibility and the MACs are then matched by
> the net_failover driver in the guest. It makes sense for ethernet VFs only,
> I'll add a check for that.

Actually is there a list of devices for which this has been tested
besides mlx5? I think someone said some old intel cards
don't support this well, we might need to blacklist these ...

> > 
> > Finally, please copy me on code touching vfio.  Thanks,
> 
> I'm sorry about that, will do.
> 
> Thanks for the review Alex!
> 
> regards,
> Jens