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    SubjectRe: [PATCH 1/7][QUOTA] Move sysctl management code under ifdef CONFIG_SYSCTL
    Andrew Morton <> writes:

    > On Tue, 04 Dec 2007 12:31:37 +0300 Pavel Emelyanov <> wrote:
    >> Andrew Morton wrote:
    >> > On Tue, 04 Dec 2007 11:58:30 +0300 Pavel Emelyanov <> wrote:
    >> >
    >> >>>> +#ifdef CONFIG_SYSCTL
    >> >>>> register_sysctl_table(sys_table);
    >> >>>> +#endif
    >> >>>>
    >> >>>> dquot_cachep = kmem_cache_create("dquot",
    >> >>>> sizeof(struct dquot), sizeof(unsigned long) * 4,
    >> >>> We should avoid the ifdefs around the register_sysctl_table() call.
    >> >>>
    >> >>> At present the !CONFIG_SYSCTL implementation of register_sysctl_table() is
    >> >>> a non-inlined NULL-returning stub. All we have to do is to inline that
    > stub
    >> >>> then these ifdefs can go away.
    >> >> What if some code checks for the return value to be not-NULL? In case
    >> >> CONFIG_SYSCTL=n this code will always think, that the registration failed.
    >> >
    >> > The stub function should return success?
    >> Well, I think yes. If some functionality is turned off, then the
    >> caller should think that everything is going fine (or he should
    >> explicitly removes the call to it with some other ifdef).
    >> At least this is true for stubs that return the error code, not
    >> the pointer. E.g. copy_semundo() always returns success if SYSVIPC
    >> is off, or namespaces cloning routines act in a similar way.
    >> Thus I though, that routines, that return pointers should better
    >> report that everything is OK (somehow) to reduce the number of
    >> "helpers" in the outer code. No?
    > Dunno. Returning NULL should be OK. If anyone is dereferenceing that
    > pointer with CONFIG_SYSCTL=n then they might need some attention?

    We do have some current code in the network stack that fails miserably
    when register_sysctl_table returns NULL, and there are explicit
    checks for that.


    I had forgotten about that.

    I expect the right answer is to simply have code ignore the fact
    that register_sysctl_xxxx returns NULL, and not error on it.

    The alternative is to get fancy and have everyone check the
    return code and make the return type an IS_ERR thing. That seems
    a lot more trouble then it is worth.

    We can probably define it as register_sysctl_xxxx always returns
    a token that must be passed to unregister_sysctl, and no errors
    will be reported except to dmesg. That at sounds simple sane
    and supportable from where we are now.


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