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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id af79cd13be357-93749ea4cb8sm328642485a.41.2026.08.23.09.57.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 23 Aug 2026 09:57:20 -0700 (PDT) Date: Sun, 23 Aug 2026 12:57:17 -0400 From: Gregory Price To: "Darrick J. Wong" Cc: John Groves , John Groves , Miklos Szeredi , Dan Williams , Bernd Schubert , Alison Schofield , John Groves , Jonathan Corbet , Jake Edge , Shuah Khan , Vishal Verma , Dave Jiang , Matthew Wilcox , Jan Kara , Alexander Viro , David Hildenbrand , Christian Brauner , Randy Dunlap , Jeff Layton , Amir Goldstein , Jonathan Cameron , Stefan Hajnoczi , Joanne Koong , Josef Bacik , Bagas Sanjaya , Chen Linxuan , James Morse , Fuad Tabba , Sean Christopherson , Shivank Garg , Ackerley Tng , Andrew Morton , Namjae Jeon , Lorenzo Stoakes , Greg Kroah-Hartman , Ira Weiny , Pasha Tatashin , Haren Myneni , Pratyush Yadav , Giovanni Cabiddu , Jiri Slaby , Ethan Nelson-Moore , Gabriel Whigham , Aravind Ramesh , Ajay Joshi , "venkataravis@micron.com" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "nvdimm@lists.linux.dev" , "linux-cxl@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "fuse-devel@lists.linux.dev" Subject: Re: [PATCH v13 10/12] famfs: Add runtime operation-permission (opts) framework Message-ID: References: <0100019fed5850ec-2bdfb17a-3086-44ea-8fdd-777d3ce12a33-000000@email.amazonses.com> <20260810202539.96378-1-john@jagalactic.com> <0100019fed5a5210-a09f1bdb-c705-44fc-8108-a7e7995a7af0-000000@email.amazonses.com> <20260822000728.GB6047@frogsfrogsfrogs> <20260822174029.GC6110@frogsfrogsfrogs> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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