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

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Message-ID: <CABPqkBS0gKWyTc=TFpGxRwOQkAe1o5zXtWaUyHezpO53LhCqrQ@mail.gmail.com>
Date:	Fri, 31 Oct 2014 22:22:19 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	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>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFD] perf syscall error handling

Hi,

On Fri, Oct 31, 2014 at 1:28 PM, Matt Fleming <matt@...sole-pimps.org> wrote:
> 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.
>
Maybe I missed something in the earlier thread, but I am trying to understand
why perf_event_open() would need such extended error retrieval system when
no other syscall does.

In any case, I would go with Ingo's proposal.
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