linux-kernel - Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting

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Date:	Wed, 26 Aug 2015 09:26:56 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>, adrian.hunter@...el.com,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Vince Weaver <vince@...ter.net>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting


* Ingo Molnar <mingo@...nel.org> wrote:

> ... but back then I didn't feel like complicating an error recovery ABI for the 
> needs of the 1%, robust error handling is all about simplicity: if it's not 
> simple, tools won't use it.

And note that it needs to be 'simple' in two places for usage to grow naturally: 

  - the usage site in the kernel
  - the tooling side that recovers the information.

That's why I think that such a form:

	return err_str(-EINVAL, "x86/perf: CPU does not support precise sampling");

is obviously simple on the kernel side as it returns -EINVAL, and is very simple 
on the tooling side as well, if we are allowed to extend prctl().

Thanks,

	Ingo
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