linux-kernel - Re: [PATCH] perf, ibs: Check syscall attribute flags

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Message-ID: <20120910130700.GS8285@erda.amd.com>
Date:	Mon, 10 Sep 2012 15:07:00 +0200
From:	Robert Richter <robert.richter@....com>
To:	David Ahern <dsahern@...il.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH] perf, ibs: Check syscall attribute flags

On 07.09.12 11:20:19, David Ahern wrote:
> I see now... intel returns ENOTSUP if exclude_guest is not set, amd 
> returns EINVAL if it is set.
> 
> For the AMD case the fallback_missing_features code kicks in for 
> perf-top and perf-record; I just need to fix up the pr_debug for that case.

It is EOPNOTSUP. I preferred returning EOPNOTSUP too. But then I saw
that fallback code is implemented to work mostly with EINVAL. It seems
to be the default answer to a syscall. ;)

There are several pieces of code in perf that implement fallback code,
it's hard to find it all and this already caused some bugs in the
past. I was looking at this to unify it, but it was too much effort.

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center

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