Re: [RFC][PATCHES] untangling asm/param.h

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

On Mon, Dec 02, 2024 at 04:02:07AM +0000, Al Viro wrote:
> Currently the kernel-side include of asm/param.h is handled in four
> different ways, depending upon the architecture:
>     
> 1) alpha:
> asm/param.h resolves to arch/alpha/include/asm/param.h, which
> 	* pulls uapi/asm/param.h (resolves to arch/alpha/include/uapi/asm/param.h)
> 		* which defines HZ, EXEC_PAGESIZE, NOGROUP and MAXHOSTNAMELEN
> 	* undefines HZ
> 	* redefines HZ to CONFIG_HZ
> 	* defines USER_HZ to 1024, which is what uapi/asm/param.h had for HZ
> 	* defines CLOCKS_PER_SEC to USER_HZ
>     
> 2) arc, arm, csky, microblaze, nios2, parisc, powerpc, riscv, s390, sh, x86:
> asm/param.h resolves to (generated) arch/$ARCH/include/uapi/asm/param.h, which
> 	* pulls asm-generic/param.h, which resolves to include/asm-generic/param.h, which
> 		* pulls uapi/asm-generic/param.h (resolves to include/uapi/asm-generic/param.h)
> 			* which defines HZ, EXEC_PAGESIZE, NOGROUP and MAXHOSTNAMELEN
> 		* undefines HZ
> 		* redefines HZ to CONFIG_HZ
> 		* defines USER_HZ to 100, which is what uapi/asm-generic/param.h had for HZ
> 		* defines CLOCKS_PER_SEC to USER_HZ
>     
> 3) arm64, hexagon, m68k, mips, openrisc, sparc:
> asm/param.h resolves to arch/$ARCH/include/uapi/asm/param.h, which
> 	* defines EXEC_PAGESIZE
> 	* pulls asm-generic/param.h, which resolves to include/asm-generic/param.h, which
> 		* pulls uapi/asm-generic/param.h (resolves to include/uapi/asm-generic/param.h)
> 			* which defines HZ, NOGROUP and MAXHOSTNAMELEN
> 		* undefines HZ
> 		* redefines HZ to CONFIG_HZ
> 		* defines USER_HZ to 100, which is what uapi/asm-generic/param.h had for HZ
> 		* defines CLOCKS_PER_SEC to USER_HZ
> 
> 4) loongarch, um, xtensa:
> asm/param.h resolves to (generated) arch/$ARCH/include/asm/param.h, which
> 	* pulls asm-generic/param.h, which resolves to include/asm-generic/param.h, which
> 		* pulls uapi/asm-generic/param.h (resolves to include/uapi/asm-generic/param.h)
> 			* which defines HZ, EXEC_PAGESIZE, NOGROUP and MAXHOSTNAMELEN
> 		* undefines HZ
> 		* redefines HZ to CONFIG_HZ
> 		* defines USER_HZ to 100, which is what uapi/asm-generic/param.h had for HZ
> 		* defines CLOCKS_PER_SEC to USER_HZ
> 
> There is an additional complication for userland side of xtensa - it has
> a private copy of include/uapi/asm-generic/param.h, with extra definition
> (NGROUPS) stuck in it.
> 
> Once upon a time we used to have NGROUPS in all asm/param.h (all with the
> same value); in 2004 that got removed, along with the limit on number
> of supplementary groups.  Unfortunately, xtensa port got started out
> of tree before the purge and hadn't been merged into mainline until
> 2005, and several years down the road that was enough to escape the
> consolidation of asm/param.h.
> 
> The difference between alpha and the rest of architectures is that on
> alpha the userland HZ is not 100 but 1024.  That wouldn't be a big deal,
> but kernel-side we want the userland definition seen as USER_HZ, with
> HZ itself redefined as CONFIG_HZ.  Since nothing in the macro body gets
> expanded at #define time, there's no way to preserve the value HZ had
> been defined to - not after we redefine it.
> 
> This series massages the things to simpler and more uniform shape.
> By the end of it,
> 	* all arch/*/include/uapi/asm/param.h are either generated includes
> of <asm-generic/param.h> or a #define or two followed by such include.
> 	* no arch/*/include/asm/param.h anywhere, generated or not.
> 	* include <asm/param.h> resolves to arch/*/include/uapi/asm/param.h
> of the architecture in question (or that of host in case of uml).
> 	* include/asm-generic/param.h pulls uapi/asm-generic/param.h and
> deals with USER_HZ, CLOCKS_PER_SEC and with HZ redefinition after that.


Branch rebased to 6.16-rc1 and force-pushed to
git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git #headers.param

No changes in patches since the last time around; see
https://lore.kernel.org/all/20241202040207.GM3387508@ZenIV/ for the old
posting.

Folks, if nobody objects, I'm putting this stuff into -next this cycle.