linux-kernel - Re: [RFD] perf syscall error handling

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Date:	Fri, 31 Oct 2014 12:28:24 +0000
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Vince Weaver <vince@...ter.net>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Stephane Eranian <eranian@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFD] perf syscall error handling

On Fri, 31 Oct, at 10:27:13AM, Ingo Molnar wrote:
> 
>  - user-space gets back the regular errno (-EOPNOTSUPP or -ENOSYS
>    or -EINVAL, etc.) and a string. Strings are really the most 
>    helpful information, because tools can just print that. They 
>    can also match on specific strings and programmatically react 
>    to them if they want to: we can promise to not arbitrarily 
>    change error strings once they are introduced. (but even if 
>    they change, user-space can still print them out.)

I guess we'd run into a problem if userspace doesn't want to just print
the kernel string but instead wants to parse it in some fashion.

That may or may not be a problem in practice, Vince can probably comment
on that. I'm just thinking along the lines of making the perf syscall
interface as useful as possible for tools other than tools/perf.

-- 
Matt Fleming, Intel Open Source Technology Center
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