On Wed, 13 Nov 2024 at 16:18, Jan Kara <jack@xxxxxxx> 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. Thanks, Miklos
