Re: [PATCH v2 2/3] vfio-pci/zdev: Add VFIO FMB device feature

[Niklas Schnelle]

On Wed, 2026-06-03 at 08:35 -0400, Omar Elghoul wrote:
> On 6/2/26 6:24 PM, Alex Williamson wrote:
> 
> > On Tue, 19 May 2026 18:42:03 -0400
> > Omar Elghoul <oelghoul@xxxxxxxxxxxxx> wrote:
> > > 
--- snip ---
> > 
> > Since this is already provided via debugfs, why not make this a
> > userspace problem to interact with the existing interface?
>
> It might be possible but it would undoubtedly be really ugly and harder to
> maintain. I think what we'd dislike most about using debugfs is parsing
> text data into the FMB structure. If any of the text representations of the
> fields were to change, we would need to update them anywhere that uses them
> (e.g., in QEMU or any other user driver). The ABI would be super fragile.

I agree with Omar. The documentation for debugfs ([0] first paragraph)
even says that the files are not supposed to be treated as stable so
I'd really like to avoid treating the statistics as stable ourselves.

Thanks,
Niklas

[0] https://www.kernel.org/doc/Documentation/filesystems/debugfs.txt