Re: [GIT PULL -tip v3] fix 39 'make headers_check' warnings

From: Harvey Harrison
Date: Mon Jan 19 2009 - 13:08:52 EST

On Mon, 2009-01-19 at 12:15 +0100, Ingo Molnar wrote:
> * Harvey Harrison <harvey.harrison@xxxxxxxxx> wrote:
> >
> > As part of doing the swab.h splitout it was very tempting to just stop
> > exporting _all_ of the asm/swab.h files now that there is a
> > linux/swab.h. But I ended up leaving things as they were on arches that
> > did expose their arch specific versions to userspace.
> i'd argue for a much narrower interface to user-space - we export so much
> stuff (more than 700 headers) and in such an unstructured way (75,000
> lines of code) that it's plain crazy.
> So if you think no x86 userspace actually needs swab.h, we can just wrap
> it all in __KERNEL__. I guess we cannot remove swab.h from
> include/linux/Kbuild, right?

Correct, include/linux/swab.h must stay as it provides the actual implementation
for the endian helpers cpu_to_le16, etc. But now that I've gotten all of this
split out of byteorder.h, we can hide all of the arch overrides by wrapping
the include of asm/swab.h in ifdef __KERNEL__ and unexporting it. That would
mean userpsace only gets the open-coded C versions and no inline asm from arch

So, there wouldn't be any breakage, just possibly pessimization of generated
code if the compiler won't generate the optimized byteswaps on that arch.


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