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SubjectRe: [RFC] Raceless module interface
On Friday 13 September 2002 03:30, Rusty Russell wrote:
> In message <Pine.LNX.4.44.0209121520300.28515-100000@serv> you write:
> > The usecount is optional, the only important question a module must be
> > able to answer is: Are there any objects/references belonging to the
> > module? It's a simple yes/no question. If a module can't answer that, it
> > likely has more problem than just module unloading.
> Ah, we're assuming you insert synchronize_kernel() between the call
> to stop and the call to exit?
> In which case *why* do you check the use count *inside* exit_affs_fs?
> Why not get exit_module() to do "if (mod->usecount() != 0) return
> -EBUSY; else mod->exit();"?

Because mod->usecount may be a totally inadequate way of determining
if a module is busy. How does it work for LSM, for example?

> There's the other issue of symmetry. If you allocate memory, in
> start, do you clean it up in stop or exit?

Actually, I'm going to press you on why you think you even need a
two stage stop. I know you have your reasons, but I doubt any of
the effects you aim at cannot be achieved with a single stage
stop/exit. Could you please summarize the argument in favor of the
two stage stop?

> Similarly for other
> resources: you call mod->exit() every time start fails, so that is
> supposed to check that mod->start() succeeded?

He does? That's not right. ->start should clean up after itself if
it fails, like any other good Linux citizen.

> Of course, separating start into "init" and "start" allows you to
> solve the half-initialized problem as well as clarify the rules.

I doubt it gives any new capability at all. The same with the
entrenched separation at the user level between create and init
module: what does it give you that an error exit from a single
create/init would not? Sure, I know it's not going to change,
but I'd like to know what the thinking was, and especially, if
there's a non-bogus reason, I'd like to know it.

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