[Ksummit-2012-discuss] [ATTEND] Proposed discussion: Cleaning up the header file mess
davej at redhat.com
Thu Jun 21 19:49:32 UTC 2012
On Thu, Jun 21, 2012 at 07:43:51PM +0100, David Howells wrote:
> Firstly, Header file cleanups. I've been working on cleaning up the header
> files for a while, trying to eliminate circular dependencies. I have a number
> of steps I'd like to go through:
Kudos for even trying to do something about this hairball.
> (1) Split the Userspace API (UAPI) out of the kernel headers into its own
> header directories.
I'd really like to see this happen. I think it would fix a lot of problems
we've had historically with "oh, userspace shouldn't have been using that".
I wouldn't be surprised if there are still cases of that that will fall out of
such a reworking.
I suspect there's no coincidence you listed this as a first step.
Just untangling the kernel/user parts of some files seems like it would be
a pretty big (welcome) cleanup.
> (4) Split some headers into definitions containers and inline function
> containers to clean up recursion problems. The main culprit is very
> likely to be linux/sched.h, I think.
likely closely followed by mm.h / fs.h
> (6) Replace the traditional anti-reinclusion guards on header files with
> three-state anti-recursion guards that abort compilation if recursive
> inclusion is encountered.
interesting, have a pointer to documentation on these ?
> (7) Provide a script to go through and rejig the #includes of each source file
> to have just the ones that are actually required (a lot of cut'n'pasting
> goes on, and there are quite a few unnecessary #includes out there).
sounds like something that could eventually be folded into checkpatch too maybe.
(or perhaps called from it)
> (8) Provide a make target that tests all the KAPI and UAPI headers by simply
> passing them one at a time to the compiler and attempting to compile them.
I think someone did this before (Arnd maybe?) ISTR there being a lot of damage.
> (9) Use precompiled headers.
> What I'd like to find out is how best to go about getting what I have upstream
> to make it easier to deal with knottier problems (linux/sched.h being foremost).
The hardest part (after doing all the work of course!) I suspect is the timing
of the merge ? ie, how to get it in without screwing over everything pending ?
Maybe just get a pre-agreement from Linus to do a big merge post -rc1/rc2 ?
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