Re: [PATCH V4 10/13] PCI / VFIO: Add 'override_only' support for VFIO PCI sub system

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 25 Aug 2021 19:24:43 -0300
Jason Gunthorpe <jgg@nvidia.com> wrote:

> On Wed, Aug 25, 2021 at 04:05:46PM -0600, Alex Williamson wrote:
> > On Wed, 25 Aug 2021 16:51:36 +0300
> > Yishai Hadas <yishaih@nvidia.com> wrote:  
> > > diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
> > > index 7c97fa8e36bc..c3edbf73157e 100644
> > > +++ b/scripts/mod/file2alias.c
> > > @@ -426,7 +426,7 @@ static int do_ieee1394_entry(const char *filename,
> > >  	return 1;
> > >  }
> > >  
> > > -/* Looks like: pci:vNdNsvNsdNbcNscNiN. */
> > > +/* Looks like: pci:vNdNsvNsdNbcNscNiN or <prefix>_pci:vNdNsvNsdNbcNscNiN. */
> > >  static int do_pci_entry(const char *filename,
> > >  			void *symval, char *alias)
> > >  {
> > > @@ -440,8 +440,12 @@ static int do_pci_entry(const char *filename,
> > >  	DEF_FIELD(symval, pci_device_id, subdevice);
> > >  	DEF_FIELD(symval, pci_device_id, class);
> > >  	DEF_FIELD(symval, pci_device_id, class_mask);
> > > +	DEF_FIELD(symval, pci_device_id, override_only);
> > >  
> > > -	strcpy(alias, "pci:");
> > > +	if (override_only & PCI_ID_F_VFIO_DRIVER_OVERRIDE)
> > > +		strcpy(alias, "vfio_pci:");
> > > +	else
> > > +		strcpy(alias, "pci:");  
> > 
> > I'm a little concerned that we're allowing unknown, non-zero
> > override_only values to fall through to create "pci:" alias matches.
> > Should this be something like:
> > 
> > 	if (override_only & PCI_ID_F_VFIO_DRIVER_OVERRIDE) {  
> 
> Should probably be == not &, since in this new arrangement it is
> really more of an enum than a bit flags... A switch would be OK here
> too
> 
> > 		strcpy(alias, "vfio_pci:");
> > 	} else if (override_only) {
> > 		warn("Unknown PCI driver_override alias %08X\n",
> > 			driver_override);
> > 		return 0;
> > 	} else {
> > 		strcpy(alias, "pci:");
> > 	}  
> 
> It seems reasonable to me to throw a warn, it signals to a future
> developer that kbuild is not working right.
> 
> > And then if we can only have a single bit set in override_only (I
> > can't think of a use case for a single entry to have multiple
> > override options), should PCI_DEVICE_DRIVER_OVERRIDE() be defined to
> > take a "driver_override_shift" value where .driver_override is assigned
> > (1 << driver_override_shift)?  That would encode the semantics in the
> > prototypes a little better.    
> 
> I think it is just an enum of overrides, no reason to make it one hot
> encoded. Previously when it was flags the bit encode had a certain
> amount of logic, but no longer.

Yeah, a switch statement handling pci:/vfio_pci:/warn rather than
testing bits would clear things up for me.  Thanks,

Alex