Messages in this thread | | | From | (Eric W. Biederman) | Subject | Re: [PATCH 1/7][QUOTA] Move sysctl management code under ifdef CONFIG_SYSCTL | Date | Tue, 04 Dec 2007 04:40:26 -0700 |
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Andrew Morton <akpm@linux-foundation.org> writes:
> On Tue, 04 Dec 2007 12:31:37 +0300 Pavel Emelyanov <xemul@openvz.org> wrote: > >> Andrew Morton wrote: >> > On Tue, 04 Dec 2007 11:58:30 +0300 Pavel Emelyanov <xemul@openvz.org> 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.
Grr.
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.
Eric
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