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 <mat...@meta.com> wrote:
On 29/05/2026 00:14, Alex Williamson wrote:
On Wed, 27 May 2026 03:23:12 -0700
Matt Evans <mat...@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,

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