Re: [PATCH v2 9/9] vfio/pci: Add mmap() attributes to DMABUF feature

[Matt Evans]

Hi Alex,

On 02/06/2026 20:14, Alex Williamson wrote:
> On Tue, 2 Jun 2026 17:50:04 +0100
> Matt Evans <mattev@xxxxxxxx> wrote:
> > On 29/05/2026 00:14, Alex Williamson wrote:
> > > On Wed, 27 May 2026 03:23:12 -0700
> > > Matt Evans <mattev@xxxxxxxx> wrote:
> > > > +		uint32_t old_attr = priv->memattr;
> > > > +
> > > > +		if (flags & VFIO_DEVICE_FEATURE_SET) {
> > > > +			switch(db_attr.memattr) {
> > > > +			case VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_NC:
> > > > +			case VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_WC:
> > > > +				priv->memattr = db_attr.memattr;
> > > > +				break;
> > > > +
> > > > +			default:
> > > > +				ret = -ENOTSUPP;
> > >
> > > -EINVAL
> >
> > I'd like to push back on this one; ENOTSUPP distinguishes trying to use
> > a wild attribute value from all manner of other screwups such as
> > trying to GET (with it no longer supported), passing an fd that isn't a
> > DMABUF, etc.
> >
> > I'm not wed to the value ENOTSUPP, just something distinctive versus the
> > other errors userspace might see, and that value seems appropriate.
>
> It needs to be a uAPI errno though, aiui ENOTSUPP is an internal NFS
> errno.  How about EOPNOTSUPP?  Thanks,

Ew, right!  TIL, and it's caught by checkpatch too (which I fastidiously 
run but still missed this somehow...) :(  "ENOTSUPP is not a standard 
error code and should be avoided in new patches.  EOPNOTSUPP should be 
used instead."

Fixed.

Thanks,


Matt