On 25/03/04 05:41PM, Amir Goldstein wrote: > On Tue, Mar 4, 2025 at 5:05 PM Seyediman Seyedarab <imandevel@xxxxxxxxx> wrote: > > > > On 25/03/04 12:57PM, Amir Goldstein wrote: > > > On Tue, Mar 4, 2025 at 8:59 AM Seyediman Seyedarab <imandevel@xxxxxxxxx> wrote: > > I understand why it might seem like disallowing users from monitoring > > these filesystems could break userspace in some way. BUT, programs > > work incorrectly precisely because they do not receive any information > > from the kernel, so in other words they are already broken. There is no > > way for them to know if the fs is supported or not. I mean, even we are > > not sure at the moment, then how would they know. > > Programs not knowing is a problem that could be fixed with a new API > or new init flag to fanotify/inotify. > > Existing programs that would break due to this change is unacceptable. > Maybe something like IN_DISALLOW_REMOTE could work for now, at least until remote change notifications are properly implemented for those specific filesystems? Later, if needed, it could evolve into a new API, and the flag could become the default behavior when passed to that API. > > As an example, 'Waybar' is a userspace program affected by this patch. > > Since it relies on monitoring sysfs, it isn't working properly anyway. > > This is also due to the issue mentioned earlier... inotify_add_watch() > > returns without an error, so the developers haven't realized that > > inotify isn't actually supported on sysfs. There are over five > > discussions regarding this issue that you can find them here: > > https://github.com/Alexays/Waybar/pull/3474 > > > > You need to distinguish "inotify does not work" > from "inotify does not notify on 'remote' changes" > that is changes that happen on the network fs server or inside the > kernel (in sysfs case) vs. changes that happen via vfs syscalls > on the mounted fs, be it p9, cifs, sysfs. > > There are several discussions about supporting "remote change" > notifications for network filesystems - this is a more complex problem. > > In any case, I believe performing operations on the mounted fs > generated inotify events for all the fs that you listed and without > a claim that nobody is using this facility we cannot regress this > behavior without an opt-in from the application. Understood. So this is what I should work on (correct me if anything seems off): 1. Carefully list all filesystems where "remote" changes occur. 2. Introduce a flag like FS_DISALLOW_INOTIFY_REMOTE in fs_flags for these filesystems. 3. Provide an option for userspace, such as IN_DISALLOW_REMOTE, so applications can explicitly handle this behavior. 4. (Possibly later, if it makes sense) Introduce a new syscall where FS_DISALLOW_INOTIFY_REMOTE is the default behavior. Regards, Seyediman
