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Mon, 23 Mar 2026 10:14:19 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id A83lNnsSwWnBEQAAD6G6ig (envelope-from ); Mon, 23 Mar 2026 10:14:19 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id A22BFA0B2E; Mon, 23 Mar 2026 11:14:19 +0100 (CET) Date: Mon, 23 Mar 2026 11:14:19 +0100 From: Jan Kara To: Gao Xiang Cc: Jan Kara , Demi Marie Obenour , "Darrick J. Wong" , Miklos Szeredi , linux-fsdevel@vger.kernel.org, Joanne Koong , John Groves , Bernd Schubert , Amir Goldstein , Luis Henriques , Horst Birthelmer , Gao Xiang , lsf-pc@lists.linux-foundation.org Subject: Re: [Lsf-pc] [LSF/MM/BPF TOPIC] Where is fuse going? API cleanup, restructuring and more Message-ID: <4ubnjtpngijh7azvmqjavubnm3sj25uv2mjkpppzs35lwzjgax@nckcj2we3lru> References: <20260206053835.GD7693@frogsfrogsfrogs> <20260221004752.GE11076@frogsfrogsfrogs> <7de8630d-b6f5-406e-809a-bc2a2d945afb@linux.alibaba.com> <20260318215140.GL1742010@frogsfrogsfrogs> <361d312b-9706-45ca-8943-b655a75c765b@gmail.com> <4a1fd8dd-6c8a-43bd-877d-c37720ac1e21@linux.alibaba.com> <6ab85914-6328-4762-910a-2ad17d45a358@linux.alibaba.com> Precedence: bulk X-Mailing-List: linux-fsdevel@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: <6ab85914-6328-4762-910a-2ad17d45a358@linux.alibaba.com> X-Spamd-Result: default: False [-4.01 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_RHS_NOT_FQDN(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; MIME_TRACE(0.00)[0:+]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCPT_COUNT_TWELVE(0.00)[14]; ARC_NA(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; RCVD_COUNT_THREE(0.00)[3]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RCVD_TLS_LAST(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; FREEMAIL_CC(0.00)[suse.cz,gmail.com,kernel.org,szeredi.hu,vger.kernel.org,groves.net,bsbernd.com,igalia.com,birthelmer.de,lists.linux-foundation.org]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.cz:dkim]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:104:10:150:64:97:from,2a07:de40:b281:106:10:150:64:167:received]; RCVD_VIA_SMTP_AUTH(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; DKIM_TRACE(0.00)[suse.cz:+]; MISSING_XM_UA(0.00)[]; SUBJECT_HAS_QUESTION(0.00)[] X-Rspamd-Action: no action X-Spam-Flag: NO X-Spam-Score: -4.01 X-Spam-Level: X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Queue-Id: E98EB3E80D Hi Gao! On Mon 23-03-26 18:05:17, Gao Xiang wrote: > On 2026/3/23 17:43, Jan Kara wrote: > > And yes, when you have immutable filesystem, things are much simpler > > because the data structures and algorithms can be much simpler and as you > > wrote a lot of these inconsistencies don't matter (at least for the > > kernel). But once you add ability to modify the filesystem - here I don't > > think it matters whether through CoW or other means - things get > > complicated quickly and it gets much more complex to make your code > > resilient to all kinds of inconsistencies... > > I only consider the COW approach using OverlayFS for example, > it just copies up (meta)data into another filesystem (the > semantics is just like copy the file in the userspace) and > the immutable filesystem image won't change in any case. > > Overlayfs write goes through normal user write and the > writable filesystem is consistent, so I don't think it does > matter. Or am I missing something? (e.g could you point > out some case which OverlayFS cannot handle properly?) No, you are correct. For the usecases where immutable fs + overlayfs + empty initial writeable filesystem works, this is a safe design. Honza -- Jan Kara SUSE Labs, CR