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

[Alex Williamson <alex@shazbot.org>]

On Tue, 2 Jun 2026 17:50:04 +0100
Matt Evans <mattev@meta.com> wrote:
> On 29/05/2026 00:14, Alex Williamson wrote:
> > On Wed, 27 May 2026 03:23:12 -0700
> > Matt Evans <mattev@meta.com> 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,

Alex