Re: [PATCH v4 02/11] PCI: liveupdate: Track outgoing preserved PCI devices

[David Matlack]

On Tue, Apr 28, 2026 at 1:20 PM Vipin Sharma <vipinsh@xxxxxxxxxx> wrote:
>
> On Thu, Apr 23, 2026 at 09:23:06PM +0000, David Matlack wrote:
> > +int pci_liveupdate_preserve(struct pci_dev *dev)
> > +{
> > +     struct pci_ser *ser;
> > +     int i, ret;
> > +
> > +     guard(mutex)(&pci_flb_outgoing_lock);
> > +
> > +     ret = liveupdate_flb_get_outgoing(&pci_liveupdate_flb, (void **)&ser);
> > +     if (ret)
> > +             return ret;
> > +
> > +     if (!ser)
> > +             return -ENOENT;
> > +
> > +     if (dev->is_virtfn)
> > +             return -EINVAL;
> > +
> > +     if (dev->liveupdate_outgoing)
> > +             return -EBUSY;
> > +
> > +     if (ser->nr_devices == ser->max_nr_devices)
> > +             return -ENOSPC;
> > +
> > +     for (i = 0; i < ser->max_nr_devices; i++) {
> > +             /*
> > +              * Start searching at index ser->nr_devices. This should result
> > +              * in a constant time search under expected conditions (devices
> > +              * are not getting unpreserved).
> > +              */
> > +             int index = (ser->nr_devices + i) % ser->max_nr_devices;
> > +             struct pci_dev_ser *dev_ser = &ser->devices[index];
> > +
> > +             if (dev_ser->refcount)
> > +                     continue;
> > +
> > +             pci_info(dev, "Device will be preserved across next Live Update\n");
> > +             ser->nr_devices++;
> > +
> > +             dev_ser->domain = pci_domain_nr(dev->bus);
> > +             dev_ser->bdf = pci_dev_id(dev);
> > +             dev_ser->refcount = 1;
> > +
> > +             dev->liveupdate_outgoing = dev_ser;
> > +             return 0;
> > +     }
> > +
> > +     return -ENOSPC;
>
> Since it is executing under a mutex, and we already failed
> 'if (ser->nr_devices == ser->max_nr_devices) check above, will we ever reach
> here and return -ENOSPC?

Yeah I wouldn't expect to ever reach here.

> > diff --git a/include/linux/kho/abi/pci.h b/include/linux/kho/abi/pci.h
> > index 5c0e92588c00..5b4c8d9e462c 100644
> > --- a/include/linux/kho/abi/pci.h
> > +++ b/include/linux/kho/abi/pci.h
> > @@ -23,19 +23,20 @@
> >   * incrementing the version number in the PCI_LUO_FLB_COMPATIBLE string.
> >   */
> >
> > -#define PCI_LUO_FLB_COMPATIBLE "pci-v1"
> > +#define PCI_LUO_FLB_COMPATIBLE "pci-v2"
>
> Just curious, why did we change the version here?

Because a field in struct pci_dev_ser changed.

> It's not like just
> previous patch is working enough to perform a live update. As the config
> is experimental, can't we just keep it PCI-v1 for the whole series?

What is the benefit of keeping "pci-v1"?

I think it makes sense to follow the rule we set which is to update
the compatibility string in any commit that changes the ABI.