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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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