Re: [PATCH 02/11] pci: add option for net failover

[Jens Freimann]

On Mon, Oct 21, 2019 at 01:01:22PM -0600, Alex Williamson wrote:
> On Mon, 21 Oct 2019 20:45:46 +0200
> Jens Freimann <address@hidden> wrote:
>
> > On Mon, Oct 21, 2019 at 08:58:23AM -0600, Alex Williamson wrote:
> > >On Fri, 18 Oct 2019 22:20:31 +0200
> > >Jens Freimann <address@hidden> wrote:
> > >
> > >> This patch adds a net_failover_pair_id property to PCIDev which is
> > >> used to link the primary device in a failover pair (the PCI dev) to
> > >> a standby (a virtio-net-pci) device.
> > >>
> > >> It only supports ethernet devices. Also currently it only supports
> > >> PCIe devices. QEMU will exit with an error message otherwise.
> > >
> > >Doesn't the PCIe device also need to be hotpluggable?  We can have PCIe
> > >devices attached to the root bus where we don't currently support
> > >hotplug.  Thanks,
> >
> > How do I recognize such a device? hotpluggable in DeviceClass?
>
> I wouldn't expect it to be a device property, it's more of a function
> of whether the bus that it's attached to supports hotplug, so probably
> something related to the bus controller.  Thanks,

IIUC this is checked for in qdev_device_add() by this:

 if (qdev_hotplug && bus && !qbus_is_hotpluggable(bus)) {
       error_setg(errp, QERR_BUS_NO_HOTPLUG, bus->name);
       return NULL;
 }

So qemu will fail with 'Bus pcie.0 does not allow hotplug' when we try 
to hotplug the device. I tried a primary with bus=pcie.0 and it aborted.
Aborting qemu is not nice so I'll make it print a error message
QERR_BUS_NO_HOTPLUG instead but let it continue. This will be
a change in the virtio-net patch, not in this one. 

regards,
Jens