Re: [PATCH] lib/string: shrink lib/string.i via IWYU

[Al Viro <viro@zeniv.linux.org.uk>]

On Wed, Dec 06, 2023 at 12:01:56AM +0200, Andy Shevchenko wrote:
> On Tue, Dec 05, 2023 at 01:51:10PM -0800, Nick Desaulniers wrote:
> > On Tue, Dec 5, 2023 at 1:38 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
> > > On Tue, Dec 05, 2023 at 08:58:53PM +0000, tanzirh@google.com wrote:
> 
> ...
> 
> > > > IWYU is implemented using the IWYUScripts github repository which is a tool that is
> > > > currently undergoing development. These changes seek to improve build times.
> > > >
> > > > This change to lib/string.c resulted in a preprocessed size of
> > > > lib/string.i from 26371 lines to 5232 lines (-80%).
> > >
> > > It also breeds includes of asm/*.h, by the look of the output, which is
> > > not a good thing in general ;-/  E.g. #include <asm/uaccess.h> *anywhere*
> > > outside of linux/uaccess.h is a bad idea.
> > 
> > It's not clear to me when it's ok to #include <asm/*.h>.  Is there a
> > convention here that I'm missing?
> 
> The mandatory ones can be used, but not all of them.
> In some cases you even must include asm and not linux
> (unaligned.h, byteorder.h, maybe others...).
> 
> As I told, it comes with experience, we lack of the
> respective documentation (or file which is good for
> automation checks, like with IWYU).

It would certainly be nice to have such information in the tree;
"where should I pick $SYMBOL from?" is something one needs to
find out often enough.  To a large extent it's covered by "where
in include/*.h do we have it defined?", but that's not all there
is to it.  E.g. "get_user() => use linux/uaccess.h".

There's also stuff like "$SYMBOL should not be used outside of arch/*
and include/*, better use $OTHER_SYMBOL", etc.