Re: [PATCH v13 10/12] famfs: Add runtime operation-permission (opts) framework

[Gregory Price]

On Sun, Aug 23, 2026 at 12:43:14PM -0400, Gregory Price wrote:
> On Sat, Aug 22, 2026 at 10:40:29AM -0700, Darrick J. Wong wrote:
> > 
> > A bigger question I just thought of is sharing cxlmem between files (aka
> > reflink).  Is that allowed?  I could see a theoretical usecase for
> > programs A and B wanting to share some cxlmem for communication or
> > heartbeats whilst having their own /a and /b files for their private
> > memory.  Probably you'd just create a /common file to do that and not
> > map the same cxlmem page into /a and /b, right?
> > 
> 
> Anyway, there's "allowed" and "useful".  You could technically do it
> (maybe not with FAMFS' current guard rails) - but it would be useless
> unless Process A and Process B were in the same coherence domain.
> 

One point of clarification - useless for both processes to write to the
same file concurrently, hence the need for a producer-consumer design as
John suggests.  And even then the software needs to handle coherence
and cacheline write ordering (which is also not guaranteed across
coherence domains by any current specification I know of).

~Gregory