Re: [PATCH v8 08/28] vfio: add region cache

[John Levon <levon@movementarian.org>]

On Thu, Apr 03, 2025 at 05:46:03PM +0200, Cédric Le Goater wrote:

> > +static void vfio_get_all_regions(VFIODevice *vbasedev)
> > +{
> > +    struct vfio_region_info *info;
> > +    int i;
> > +
> > +    for (i = 0; i < vbasedev->num_regions; i++) {
> > +        vfio_get_region_info(vbasedev, i, &info);
> > +    }
> > +}
> > +
> >   void vfio_prepare_device(VFIODevice *vbasedev, VFIOContainerBase *bcontainer,
> >                            VFIOGroup *group, struct vfio_device_info *info)
> >   {
> > @@ -1586,6 +1596,8 @@ void vfio_prepare_device(VFIODevice *vbasedev, VFIOContainerBase *bcontainer,
> >       }
> >       QLIST_INSERT_HEAD(&vfio_device_list, vbasedev, global_next);
> > +
> > +    vfio_get_all_regions(vbasedev);
> >   }

> > +    /* check cache */
> > +    if (vbasedev->regions[index] != NULL) {
> > +        *info = vbasedev->regions[index];
> > +        return 0;
> > +    }
> > +
> 
> why not populate vbasedev->regions[index] in vfio_get_all_regions() ?

Good question. I presume it's not possible for us to ever look up a region
that has somehow appeared *after* vfio_prepare_device() ?

We'd end up off the end of the array in that case anyway.

regards
john