Re: [RFC PATCH 2/3] vfio: mmap sparse regions backed by multiple FDs

[John Levon <john.levon@nutanix.com>]

On Fri, Aug 14, 2026 at 12:48:30PM -0700, Naman Gulati wrote:

> > Given that you've introduced a dependency on VFIORegion in the
> > include/hw/vfio/vfio-device.h for the other callback, I'm wondering why we don't
> > just store an array of VFIORegions in VFIODevice instead of reginfo+region_fds ?
> 
> I tried to maintain the idiom that the VFIORegion region is synonymous
> with one single BAR region. As before each VFIORegion has multiple
> mmap areas underneath, the fd for each is now held in the region_fds
> list.

Sure, I didn't mean to imply otherwise. i.e. each individual region - whatever
the type is - would have region info plus some number of fds.

> > I'm also not sure why we have a sparse mmaps callback - why can't that be
> > generic code that handles both capabilities? Are you concerned about the cap
> > number clashing in future vfio kernel versions perhaps?
> 
> Yes I wanted to encapsulate vfio-user specific handling within the
> vfio-user logic so that it doesn't conflict with the pure vfio device
> handling. It felt odd to me to introduce generic handling of a
> capability that's only exposed by one flavor of device and not the
> other. However, no strong opinions, I can refactor and generalize the
> cap handling if that's preferred, and the risks of cap number clashes
> are okay.

I can see the argument either way.

regards
john