Re: [RFC] Migrating net/sched to new module interface

Rusty Russell (rusty@rustcorp.com.au)
Wed, 15 Jan 2003 19:16:24 +1100


In message <20030115043147.A1840@almesberger.net> you write:
> kuznet@ms2.inr.ac.ru wrote:
> > Somewhat overdone.
>
> I think it would be nice to introduce in 2.7 a shutdowncall
> (*) function class for modules that works like exitcall, but
> with the following differences:
>
> - does not return before the module has really de-registered
> itself everywhere, including synchronization with any
> callbacks, etc.
> - has a return code, and can fail if it would have to sleep
> for a possibly long time
>
> Before calling the shutdown function, all symbols exported by
> the module are hidden, and after the shutdown functions returns,
> the module can be unloaded.

This already happens. This is why all accesses to the module are
protected by try_module_get().

I've analyzed dozens of "here's my implementation idea" mails over the
last two years. Here's the executive summary:

1) It's simply not a good idea to force 1600 modules to change, no
matter what timescale. And changing it in a way that is *more*,
not *less* complex is even worse.

2) It's bad enough to force the interfaces to change: at least the
primitive they are to use is one many of them are already using,
and is very simple to understand.

Rusty.
PS. The *implementation* flaw in your scheme: someone starts using a
module as you try to deregister it. Either you re-register the
module (ie. you can never unload security modules), or you leave
it half unloaded (even worse).

--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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