Re: [PATCH 09/12] PCI: Add a PCI_ID_F_VFIO_DRIVER_OVERRIDE flag to struct pci_device_id

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Aug 12, 2021 at 10:57:07AM -0500, Bjorn Helgaas wrote:
> On Thu, Aug 12, 2021 at 10:27:28AM -0300, Jason Gunthorpe wrote:
> > On Wed, Aug 11, 2021 at 02:07:37PM -0500, Bjorn Helgaas wrote:
> > > On Thu, Aug 05, 2021 at 09:23:57PM -0300, Jason Gunthorpe wrote:
> 
> > > Do the other bus types have a flag analogous to
> > > PCI_ID_F_VFIO_DRIVER_OVERRIDE?  If we're doing something similar to
> > > other bus types, it'd be nice if the approach were similar.
> > 
> > They could, this series doesn't attempt it. I expect the approach to
> > be similar as driver_override was copied from PCI to other
> > busses. When this is completed I hope to take a look at it.
> 
> I think this would make more sense as two patches:
> 
>   - Add a "PCI_ID_DRIVER_OVERRIDE" flag.  This is not VFIO-specific,
>     since nothing in PCI depends on the VFIO-ness of drivers that use
>     the flag.  The only point here is that driver id_table entries
>     with this flag only match when driver_override matches the driver.

This would require using two flags, one to indicate the above to the
PCI code and another to indicate the vfio_pci string to
file2alias. This doesn't seem justified at this point, IMHO.

>   - Update file2alias.c to export the flags and the "vfio_pci:" alias.
>     This seems to be the only place where VFIO comes into play, and
>     putting it in a separate patch will make it much smaller and it
>     will be clear how it could be extended for other buses.

Well, I don't want to see a flag called PCI_ID_DRIVER_OVERRIDE mapped
to the string "vfio_pci", that is just really confusing.

Other busses need to copy pretty much the entire patch, there isn't
really any sharing here. I don't see splitting as good here..

What this logically wants is the match entry to have a

  const char *file2alias_prefix

Which would be set to "vfio_", but I'm not keen to bloat the match
entry further to do that..

> > The full sequence is more like:
> > 
> >      echo mlx5_vfio_pci > /sys/bus/pci/devices/0000:01:00.0/driver_override
> >      echo 0000:01:00.0 > /sys/bus/pci/devices/0000:01:00.0/driver/unbind
> >      echo 0000:01:00.0 > /sys/bus/pci/drivers_probe
> 
> Thanks a lot for this!  I didn't know about drivers_probe (see
> drivers_probe_store()), and it doesn't seem to be documented anywhere
> except sysfs-bus-usb, where it's only incidental to USB.

Okay, lets make the changes in the commit message, it does help

Jason