Re: [PATCH v3 0/10] add failover feature for assigned network devices

[Jens Freimann]

On Tue, Oct 15, 2019 at 01:03:17PM -0600, Alex Williamson wrote:
> On Fri, 11 Oct 2019 13:20:05 +0200
> Jens Freimann <address@hidden> wrote:
>
> > This is implementing the host side of the net_failover concept
> > (https://www.kernel.org/doc/html/latest/networking/net_failover.html)
> >
> > Changes since v2:
> > * back out of creating failover pair when it is a non-networking
> >   vfio-pci device (Alex W)
> > * handle migration state change from within the migration thread. I do a
> >   timed wait on a semaphore and then check if all unplugs were
> >   succesful. Added a new function to each device that checks the device
> >   if the unplug for it has happened. When all devices report the succesful
> >   unplug *or* the time/retries is up, continue with the migration or
> >   cancel. When not all devices could be unplugged I am cancelling at the
> >   moment. It is likely that we can't plug it back at the destination which
> >   would result in degraded network performance.
> > * fix a few bugs regarding re-plug on migration source and target
> > * run full set of tests including migration tests
> > * add patch for libqos to tolerate new migration state
> > * squashed patch 1 and 2, added patch 8
> >
> > The general idea is that we have a pair of devices, a vfio-pci and a
> > virtio-net device. Before migration the vfio device is unplugged and data
> > flows to the virtio-net device, on the target side another vfio-pci device
> > is plugged in to take over the data-path. In the guest the net_failover
> > module will pair net devices with the same MAC address.
> >
> > * Patch 1 adds the infrastructure to hide the device for the qbus and qdev APIs
> >
> > * Patch 2 sets a new flag for PCIDevice 'partially_hotplugged' which we
> >   use to skip the unrealize code path when doing a unplug of the primary
> >   device
> >
> > * Patch 3 sets the pending_deleted_event before triggering the guest
> >   unplug request
>
> These only cover pcie hotplug, is this feature somehow dependent on
> pcie?  There's also ACPI-based PCI hotplug, SHPC hotplug, and it looks
> like s390 has it's own version (of course) of PCI hotplug.  IMO, we
> either need to make an attempt to support this universally or the
> option needs to fail if the hotplug controller doesn't support partial
> removal.  Thanks,

It is possible to make it work with non-pcie hotplug but as the first
step I want to enable it for pcie only. For that I would add a check
into pci_qdev_realize(), where I also check if the device is an
ethernet device, and fail if it is not a pcie device. Would that work
for you?

regards,
Jens