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Wed, 13 Nov 2024 16:00:42 +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 tM8cBCrNNGdvKQAAD6G6ig (envelope-from ); Wed, 13 Nov 2024 16:00:42 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id BFC28A08D0; Wed, 13 Nov 2024 17:00:37 +0100 (CET) Date: Wed, 13 Nov 2024 17:00:37 +0100 From: Jan Kara To: Miklos Szeredi Cc: Jan Kara , Jeff Layton , Karel Zak , Christian Brauner , Ian Kent , Josef Bacik , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Alexander Viro , Lennart Poettering Subject: Re: [PATCH v4 0/3] fs: allow statmount to fetch the fs_subtype and sb_source Message-ID: <20241113160037.74vu5yqzsfbvk3ad@quack3> References: <20241111-statmount-v4-0-2eaf35d07a80@kernel.org> <20241112-antiseptisch-kinowelt-6634948a413e@brauner> <63f3aa4b3d69b33f1193f4740f655ce6dae06870.camel@kernel.org> <20241113151848.hta3zax57z7lprxg@quack3> Precedence: bulk X-Mailing-List: linux-kernel@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: X-Rspamd-Queue-Id: 1A8941F391 X-Spam-Score: -4.01 X-Rspamd-Action: no action 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)[]; R_DKIM_ALLOW(-0.20)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; ARC_NA(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; MIME_TRACE(0.00)[0:+]; RCVD_COUNT_THREE(0.00)[3]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; TO_DN_SOME(0.00)[]; RCPT_COUNT_SEVEN(0.00)[11]; FROM_EQ_ENVFROM(0.00)[]; RCVD_TLS_LAST(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; DKIM_TRACE(0.00)[suse.cz:+]; MISSING_XM_UA(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.com:email] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spam-Flag: NO X-Spam-Level: On Wed 13-11-24 16:49:52, Miklos Szeredi wrote: > On Wed, 13 Nov 2024 at 16:18, Jan Kara wrote: > > > > On Wed 13-11-24 08:45:06, Jeff Layton wrote: > > > On Wed, 2024-11-13 at 12:27 +0100, Karel Zak wrote: > > > > On Tue, Nov 12, 2024 at 02:39:21PM GMT, Christian Brauner wrote: > > > > Next on the wish list is a notification (a file descriptor that can be > > > > used in epoll) that returns a 64-bit ID when there is a change in the > > > > mount node. This will enable us to enhance systemd so that it does not > > > > have to read the entire mount table after every change. > > > > > > > > > > New fanotify events for mount table changes, perhaps? > > > > Now that I'm looking at it I'm not sure fanotify is a great fit for this > > usecase. A lot of fanotify functionality does not really work for virtual > > filesystems such as proc and hence we generally try to discourage use of > > fanotify for them. So just supporting one type of event (like FAN_MODIFY) > > on one file inside proc looks as rather inconsistent interface. But I > > vaguely remember we were discussing some kind of mount event, weren't we? > > Or was that for something else? > > Yeah, if memory serves right what we agreed on was that placing a > watch on a mount would result in events being generated for > mount/umount/move_mount directly under that mount. So this would not > be monitoring the entire namespace as poll on /proc/$$/mountinfo does. > IIRC Lennart said that this is okay and even desirable for systemd, > since it's only interested in a particular set of mounts. Oh, right. Thanks for reminding me. And yes, this would fit within what fanotify supports quite nicely. Honza -- Jan Kara SUSE Labs, CR