Hi Arnd, On 11/19/21 15:47, Arnd Bergmann wrote: > On Fri, Nov 19, 2021 at 12:36 PM Alejandro Colomar > <alx.manpages@xxxxxxxxx> 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. It's clear that every .c wants NULL, but it's not so clear that every .c wants everything that <linux/stddef.h> pulls indirectly. But I'll note that linux/fs.h, linux/sched.h, linux/mm.h are interesting headers for further splitting. BTW, I also have a longstanding doubt about how header files are organized in the kernel, and which headers can and cannot be included from which other files. For example I see that files in samples or scripts or tools, that redefine many things such as offsetof() or ARRAY_SIZE(), and I don't know if there's a good reason for that, or if I should simply remove all that stuff and include <linux/offsetof.h> everywhere I see offsetof() being used. Thanks, Alex -- Alejandro Colomar Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es/
