Re: [RFC][PATCH 1/2] fanotify: configurable limits via sysfs

[Amir Goldstein <amir73il@gmail.com>]

On Tue, Feb 16, 2021 at 6:27 PM Jan Kara <jack@suse.cz> wrote:
>
> Hi Amir!
>
>
> I'm sorry that I've got to this only now.
>
> On Sun 24-01-21 20:42:03, Amir Goldstein wrote:
> > fanotify has some hardcoded limits. The only APIs to escape those limits
> > are FAN_UNLIMITED_QUEUE and FAN_UNLIMITED_MARKS.
> >
> > Allow finer grained tuning of the system limits via sysfs tunables under
> > /proc/sys/fs/fanotify/, similar to tunables under /proc/sys/fs/inotify,
> > with some minor differences.
> >
> > - max_queued_events - global system tunable for group queue size limit.
> >   Like the inotify tunable with the same name, it defaults to 16384 and
> >   applies on initialization of a new group.
> >
> > - max_listener_marks - global system tunable of marks limit per group.
> >   Defaults to 8192. inotify has no per group marks limit.
> >
> > - max_user_marks - user ns tunable for marks limit per user.
> >   Like the inotify tunable named max_user_watches, it defaults to 1048576
> >   and is accounted for every containing user ns.
> >
> > - max_user_listeners - user ns tunable for number of listeners per user.
> >   Like the inotify tunable named max_user_instances, it defaults to 128
> >   and is accounted for every containing user ns.
>
> I think term 'group' is used in the manpages even more and in the code as
> well. 'listener' more generally tends to refer to the application listening
> to the events. So I'd rather call the limits 'max_group_marks' and
> 'max_user_groups'.
>
> > The slightly different tunable names are derived from the "listener" and
> > "mark" terminology used in the fanotify man pages.
> >
> > max_listener_marks was kept for compatibility with legacy fanotify
> > behavior. Given that inotify max_user_instances was increased from 8192
> > to 1048576 in kernel v5.10, we may want to consider changing also the
> > default for max_listener_marks or remove it completely, leaving only the
> > per user marks limit.
>
> Yes, probably I'd just drop 'max_group_marks' completely and leave just
> per-user marks limit. You can always tune it in init_user_ns if you wish.
> Can't you?
>

So I am fine with making this change but what about
FAN_UNLIMITED_MARKS?

What will it mean?
Should the group be able to escape ucount limits?

Thanks,
Amir.