Re: [PATCH 00/17] Add memberof(), split some headers, and slightly simplify code

Andy Shevchenko
2021-11-19T15:35:15Z

On Fri, Nov 19, 2021 at 04:06:27PM +0100, Alejandro Colomar (man-pages) wrote:
> Hi Arnd,
>
> On 11/19/21 15:47, Arnd Bergmann wrote:
> > On Fri, Nov 19, 2021 at 12:36 PM Alejandro Colomar
> > <alx.manpages@gmail.com> wrote:
> >>
> >> Alejandro Colomar (17):
> >> linux/container_of.h: Add memberof(T, m)
> >> Use memberof(T, m) instead of explicit NULL dereference
> >> Replace some uses of memberof() by its wrappers
> >> linux/memberof.h: Move memberof() to separate header
> >> linux/typeof_member.h: Move typeof_member() to a separate header
> >> Simplify sizeof(typeof_member()) to sizeof_field()
> >> linux/NULL.h: Move NULL to a separate header
> >> linux/offsetof.h: Move offsetof(T, m) to a separate header
> >> linux/offsetof.h: Implement offsetof() in terms of memberof()
> >> linux/container_of.h: Implement container_of_safe() in terms of
> >> container_of()
> >> linux/container_of.h: Cosmetic
> >> linux/container_of.h: Remove unnecessary cast to (void *)
> >
> > My feeling is that this takes the separation too far: by having this many header
> > files that end up being included from practically every single .c file
> > in the kernel,
> > I think you end up making compile speed worse overall.
> >
> > If your goal is to avoid having to recompile as much of the kernel
> > after touching
> > a header, I think a better approach is to help untangle the dependencies, e.g.
> > by splitting out type definitions from headers with inline functions (most
> > indirect header dependencies are on type definitions) and by focusing on
> > linux/fs.h, linux/sched.h, linux/mm.h and how they interact with the rest of the
> > headers. At the moment, these are included in most .c files and they in turn
> > include a ton of other headers.
>
> Yes, I would like to untangle the dependencies.
>
> The main reason I started doing this splitting
> is because I wouldn't be able to include
> <linux/stddef.h> in some headers,
> because it pulled too much stuff that broke unrelated things.
>
> So that's why I started from there.
>
> I for example would like to get NULL in memberof()
> without puling anything else,
> so <linux/NULL.h> makes sense for that.

I don't believe that the code that uses NULL won't include types.h.

--
With Best Regards,
Andy Shevchenko