Re: [PATCH v3] failover: fix unplug pending detection

[Daniel P . Berrangé]

On Fri, Oct 01, 2021 at 12:45:14PM +0200, Gerd Hoffmann wrote:
> On Fri, Oct 01, 2021 at 10:25:02AM +0200, Laurent Vivier wrote:
> > Failover needs to detect the end of the PCI unplug to start migration
> > after the VFIO card has been unplugged.
> > 
> > To do that, a flag is set in pcie_cap_slot_unplug_request_cb() and reset in
> > pcie_unplug_device().
> 
> > +    /*
> > +     * pending_deleted_event is used by virtio-net failover to detect the
> > +     * end of the unplug operation, the flag is set to false in
> > +     * acpi_pcihp_eject_slot() when the operation is completed.
> > +     */
> > +    pdev->qdev.pending_deleted_event = true;
> 
> This has the side effect of blocking a second 'device_del' command.
> 
> So, in case the first time didn't work (for example due to the guest not
> listening because grub just doesn't do that), you can try a second time
> once the linux kernel is up'n'running.
> 
> I suspect this patch will break that (didn't actually test though).

That's important because OpenStack will definitely trigger
multiple device_del commands in a row if they don't get a
success from an initial one.

Regards,
Daniel
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