Re: [LSF/MM/BPF TOPIC] Where is fuse going? API cleanup, restructuring and more

[John Groves <john@groves.net>]

On 26/02/05 09:52PM, Darrick J. Wong wrote:
> On Thu, Feb 05, 2026 at 10:27:52AM +0100, Amir Goldstein wrote:
> > On Thu, Feb 5, 2026 at 4:33 AM John Groves <john@jagalactic.com> wrote:
> > >
> > > On 26/02/04 11:06AM, Darrick J. Wong wrote:
> > >
> > > [ ... ]
> > >
> > > > >  - famfs: export distributed memory
> > > >
> > > > This has been, uh, hanging out for an extraordinarily long time.
> > >
> > > Um, *yeah*. Although a significant part of that time was on me, because
> > > getting it ported into fuse was kinda hard, my users and I are hoping we
> > > can get this upstreamed fairly soon now. I'm hoping that after the 6.19
> > > merge window dust settles we can negotiate any needed changes etc. and
> > > shoot for the 7.0 merge window.
> 
> I think we've all missed getting merged for 7.0 since 6.19 will be
> released in 3 days. :/
> 
> (Granted most of the maintainers I know are /much/ less conservative
> than I was about the schedule)

Doh - right you are...

> 
> > I think that the work on famfs is setting an example, and I very much
> > hope it will be a good example, of how improving existing infrastructure
> > (FUSE) is a better contribution than adding another fs to the pile.
> 
> Yeah.  Joanne and I spent a couple of days this week coprogramming a
> prototype of a way for famfs to create BPF programs to handle
> INTERLEAVED_EXTENT files.  We might be ready to show that off in a
> couple of weeks, and that might be a way to clear up the
> GET_FMAP/IOMAP_BEGIN logjam at last.

I'd love to learn more about this; happy to do a call if that's a
good way to get me briefed.

I [generally but not specifically] understand how this could avoid
GET_FMAP, but not GET_DAXDEV. 

But I'm not sure it could (or should) avoid dax_iomap_rw() and
dax_iomap_fault(). The thing is that those call my begin() function
to resolve an offset in a file to an offset on a daxdev, and then
dax completes the fault or memcpy. In that dance, famfs never knows
the kernel address of the memory at all (also true of xfs in fs-dax
mode, unless that's changed fairly recently). I think that's a pretty
decent interface all in all.

Also: dunno whether y'all have looked at the dax patches in the famfs
series, but the solution to working with Alistair's folio-ification 
and cleanup of the dax layer (which set me back months) was to create 
drivers/dax/fsdev.c, which, when bound to a daxdev in place of 
drivers/dax/device.c, configures folios & pages compatibly with 
fs-dax. So I kinda think I need the dax_iomap* interface.

As usual, if I'm overlooking something let me know...

Regards,
John