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

[si-wei liu]

On 5/21/2019 11:49 AM, Jens Freimann wrote:
On Tue, May 21, 2019 at 07:37:19AM -0400, Michael S. Tsirkin wrote:
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 <jfreim...@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 ...

So far I've tested mlx5 and XL710 which both worked, but I'm
working on testing with more devices. But of course help with testing
is greatly appreciated.
It won't work on Intel ixgbe and Broadcom bnxt_en, which requires 
toggling the state of tap backing the virtio-net in order to 
release/reprogram MAC filter. Actually, it's very few NICs that could 
work with this - even some works by chance the behavior is undefined. 
Instead of blacklisting it makes more sense to whitelist the NIC that 
supports it - with some new sysfs attribute claiming the support 
presumably.

-Siwei


regards,
Jens