netdev - Re: [PATCH v2 0/7] uapi: export all headers under uapi directories

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Date:   Mon, 09 Jan 2017 12:33:58 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     linuxppc-dev@...ts.ozlabs.org, linux-kbuild@...r.kernel.org
Cc:     Nicolas Dichtel <nicolas.dichtel@...nd.com>,
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Subject: Re: [PATCH v2 0/7] uapi: export all headers under uapi directories

On Friday, January 6, 2017 10:43:52 AM CET Nicolas Dichtel wrote:
> Here is the v2 of this series. The first 5 patches are just cleanup: some
> exported headers were still under a non-uapi directory.

Since this is meant as a cleanup, I commented on this to point out a cleaner
way to do the same.

> The patch 6 was spotted by code review: there is no in-tree user of this
> functionality.
> The last patch remove the use of header-y. Now all files under an uapi
> directory are exported.

Very nice!

> asm is a bit special, most of architectures export asm/<arch>/include/uapi/asm
> only, but there is two exceptions:
>  - cris which exports arch/cris/include/uapi/arch-v[10|32];

This is interesting, though not your problem. Maybe someone who understands
cris better can comment on this: How is the decision made about which of
the arch/user.h headers gets used? I couldn't find that in the sources,
but it appears to be based on kernel compile-time settings, which is
wrong for user space header files that should be independent of the kernel
config.

>  - tile which exports arch/tile/include/uapi/arch.
> Because I don't know if the output of 'make headers_install_all' can be changed,
> I introduce subdir-y in Kbuild file. The headers_install_all target copies all
> asm/<arch>/include/uapi/asm to usr/include/asm-<arch> but
> arch/cris/include/uapi/arch-v[10|32] and arch/tile/include/uapi/arch are not
> prefixed (they are put asis in usr/include/). If it's acceptable to modify the
> output of 'make headers_install_all' to export asm headers in
> usr/include/asm-<arch>/asm, then I could remove this new subdir-y and exports
> everything under arch/<arch>/include/uapi/.

I don't know if anyone still uses "make headers_install_all", I suspect
distros these days all use "make headers_install", so it probably
doesn't matter much.

In case of cris, it should be easy enough to move all the contents of the
uapi/arch-*/*.h headers into the respective uapi/asm/*.h headers, they
only seem to be referenced from there.

For tile, I suspect that would not work as the arch/*.h headers are
apparently defined as interfaces for both user space and kernel.

> Note also that exported files for asm are a mix of files listed by:
>  - include/uapi/asm-generic/Kbuild.asm;
>  - arch/x86/include/uapi/asm/Kbuild;
>  - arch/x86/include/asm/Kbuild.
> This complicates a lot the processing (arch/x86/include/asm/Kbuild is also
> used by scripts/Makefile.asm-generic).
> 
> This series has been tested with a 'make headers_install' on x86 and a
> 'make headers_install_all'. I've checked the result of both commands.
> 
> This patch is built against linus tree. I don't know if it should be
> made against antoher tree.

The series should probably get merged through the kbuild tree, but testing
it on mainline is fine here.

	Arnd