Re: [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations

From: Rich Felker <dalias@libc.org>
To: Dave Martin <Dave.Martin@arm.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
	linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
	Richard Henderson <rth@twiddle.net>,
	Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
	Matt Turner <mattst88@gmail.com>,
	Russell King <linux@armlinux.org.uk>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Tony Luck <tony.luck@intel.com>,
	Fenghua Yu <fenghua.yu@intel.com>,
	Michal Simek <monstr@monstr.eu>,
	Ralf Baechle <ralf@linux-mips.org>,
	James Hogan <jhogan@kernel.org>,
	Greentime Hu <green.hu@gmail.com>,
	Vincent Chen <deanbo422@gmail.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Palmer Dabbelt <palmer@sifive.com>, Albert Ou <albert@sifive.com>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	"David S. Miller" <davem@davemloft.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Chris Zankel <chris@zankel.net>,
	Max Filippov <jcmvbkbc@gmail.com>
Subject: Re: [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations
Date: Wed, 16 May 2018 11:29:13 -0400	[thread overview]
Message-ID: <20180516152913.GY1392@brightrain.aerifal.cx> (raw)
In-Reply-To: <1526480447-18185-1-git-send-email-Dave.Martin@arm.com>

On Wed, May 16, 2018 at 03:20:47PM +0100, Dave Martin wrote:
> There are constraints on defining AT_* auxvec tags that are not
> obvious to the casual maintainer of either the global
> <uapi/linux/auxvec.h> or the arch-specific headers.  This is likely
> to lead to mistakes.  (I certainly fell foul of it...)
> 
> For the benefit of future maintainers, this patch collects the
> relevant information in one place, documenting how the namespace
> needs to be managed, and noting all the values currently in use.
> 
> Maintaining a global list may result in some merge conflicts, but
> AT_* values are not added frequently.  I'm open to suggestions on
> the best approach.
> 
> I also assume that values 38 and 39 may have been used for
> historical purposes, such as an architecture that is no longer
> supported.  If they have definitely never been used for anything,
> they could be removed from the "reserved" list.

On the userspace side (elf.h) all the AT_* constants are in one file.
Why don't we just do the same here and eliminate the
arch/*/include/uapi/asm/auxvec.h files and likewise the need to
manually maintain consistency of the comments about reservations?

If there are reasons not to do that, I'm not opposed to this patch
as-is.

Rich