linux-kernel - Re: [patch 20/24] perfmon: system calls interface

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Message-ID: <20081127124116.GK6703@one.firstfloor.org>
Date:	Thu, 27 Nov 2008 13:41:16 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	eranian@...il.com
Cc:	Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	x86@...nel.org, andi@...stfloor.org, sfr@...b.auug.org.au,
	Roland McGrath <roland@...hat.com>
Subject: Re: [patch 20/24] perfmon: system calls interface

>  int pfm_create(int flags, pfarg_sinfo_t *sif, char *fmt_name, void
> *fmt_arg, size_t arg_sz);
> 
> The kernel would look at the last 3 arguments ONLY if it saw the
> PFM_FL_SMPL_FMT bit
>  set in flags. We follow the model used by open(2).

Normally it's a better model to enforce 0 (or whatever appropiate)
in unused argument. That can be done by checking and returning EINVAL.

> 
> I want to double-check that you are fine with this approach.

My recommendation would be to go with the full format 
from the beginning, because otherwise there is a versioning problem 
with glibc.


-Andi

-- 
ak@...ux.intel.com
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