Re: [RFC] [PATCH] sysctl for the latecomers

From: Horst H. von Brand
Date: Wed Aug 02 2006 - 10:54:54 EST

Chase Venters <chase.venters@xxxxxxxxxxxx> wrote:
> On Tue, 1 Aug 2006, Chase Venters wrote:
> > On Tue, 1 Aug 2006, Amit Gud wrote:
> >> /etc/sysctl.conf values are of no use to kernel modules that are inserted
> >> after init scripts call sysctl for the values in /etc/sysctl.conf
> >>
> >> For modules to use the values stored in the file /etc/sysctl.conf, sysctl
> >> kernel code can keep record of 'limited' values, for sysctl entries which
> >> haven't been registered yet. During registration, sysctl code can check
> >> against the stored values and call the appropriate strategy and
> >> proc_handler routines if a match is found.
> >>
> >> Attached patch does just that. This patch is NOT tested and is just to
> >> get opinions, if something like this is a right way of addressing this
> >> problem.

> > Do you anticipate any users that you could list? It seems like a
> > more appropriate approach would be to allow some kind of user-space
> > hook or event notification to run upon module insertion, which could
> > then apply the appropriate sysctl.

> Btw, wanted to add some comments on the specific approach:
> 1. A ring hard-coded to 32 elements is IMO unuseable. While it may not
> be a real limit for what use case you have in mind, if it's in the
> kernel sooner or later someone else is going to use it and get
> bitten. Imagine if they wrote in 33 entries, and the first one was
> some critical security setting that ended up getting silently
> ignored...


> 2. On the other hand, allowing it to grow unbounded is equally
> unacceptable without a mechanism to list and clear the current
> "pending" sysctl values. Unfortunately, at this point, you're starting
> to violate "KISS".


> Are the modules you refer to inserted during init at all? Because it
> seems like it would be a lot more appropriate to just move sysctl
> until after loading the modules, or perhaps running it again once they
> are loaded.

OK, lets step back a bit... sysctl(8) can be used to load other values, or
to change them, etc. Whatever is in sysctl.conf is just /default/ values,
/typically/ set on boot. You could let the initscripts set those, then
fiddle them by hand. If a module is now inserted, you can't just reset the
values to the ones in the file.

Perhaps module-specific values should be set in the configuration for the
module itself (i.e., arguments) or add to modprobe.conf something along
the lines:

sysctl mymod kernel.mystuff=42

and have modprobe(8) run sysctl(8) as needed after loading the module?
Sounds more KISSy to me...
Dr. Horst H. von Brand User #22616
Departamento de Informatica Fono: +56 32 654431
Universidad Tecnica Federico Santa Maria +56 32 654239
Casilla 110-V, Valparaiso, Chile Fax: +56 32 797513
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at