Re: [Qemu-devel] [RFC 0/2] Attempt to implement the standby feature for assigned network devices

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

On Thu, Oct 25, 2018 at 05:06:29PM +0300, Sameeh Jubran wrote:
> From: Sameeh Jubran <sjubran@redhat.com>
> 
> Hi all,
> 
> Background:
> 
> There has been a few attempts to implement the standby feature for vfio
> assigned devices which aims to enable the migration of such devices. This
> is another attempt.
> 
> The series implements an infrastructure for hiding devices from the bus
> upon boot. What it does is the following:
> 
> * In the first patch the infrastructure for hiding the device is added
>   for the qbus and qdev APIs. A "hidden" boolean is added to the device
>   state and it is set based on a callback to the standby device which
>   registers itself for handling the assessment: "should the primary device
>   be hidden?" by cross validating the ids of the devices.
> 
> * In the second patch the virtio-net uses the API to hide the vfio
>   device and unhides it when the feature is acked.
> 
> Disclaimers:
> 
> * I have only scratch tested this and from qemu side, it seems to be
>   working.
> * This is an RFC so it lacks some proper error handling in few cases
>   and proper resource freeing. I wanted to get some feedback first
>   before it is finalized.
> 
> Command line example:
> 
> /home/sameeh/Builds/failover/qemu/x86_64-softmmu/qemu-system-x86_64 \
> -netdev tap,id=hostnet0,script=world_bridge_standalone.sh,downscript=no,ifname=cc1_71 \
> -netdev tap,vhost=on,id=hostnet1,script=world_bridge_standalone.sh,downscript=no,ifname=cc1_72,queues=4 \
> -device virtio-net,host_mtu=1500,netdev=hostnet1,id=cc1_72,vectors=10,mq=on,primary=cc1_71 \
> -device e1000,netdev=hostnet0,id=cc1_71,standby=cc1_72 \
> 
> Migration support:
> 
> Pre migration or during setup phase of the migration we should send an
> unplug request to the guest to unplug the primary device. I haven't had
> the chance to implement that part yet but should do soon. Do you know
> what's the best approach to do so? I wanted to have a callback to the
> virtio-net device which tries to send an unplug request to the guest and
> if succeeds then the migration continues. It needs to handle the case where
> the migration fails and then it has to replug the primary device back.
> 
> The following terms are used as interchangeable:
> standby - virtio-net
> primary - vfio-device - physical device - assigned device
> 
> Please share your thoughts and suggestions,
> Thanks!

Didn't have time to look at code yet. Could you test with a VF please?
That's the real test, isn't it?

> Sameeh Jubran (2):
>   qdev/qbus: Add hidden device support
>   virtio-net: Implement VIRTIO_NET_F_STANDBY feature
> 
>  hw/core/qdev.c                 | 48 +++++++++++++++++++++++++---
>  hw/net/virtio-net.c            | 25 +++++++++++++++
>  hw/pci/pci.c                   |  1 +
>  include/hw/pci/pci.h           |  2 ++
>  include/hw/qdev-core.h         | 11 ++++++-
>  include/hw/virtio/virtio-net.h |  5 +++
>  qdev-monitor.c                 | 58 ++++++++++++++++++++++++++++++++--
>  7 files changed, 142 insertions(+), 8 deletions(-)
> 
> -- 
> 2.17.0