linux-kernel - Re: [PATCH] perf_counter: extensible perf_counter

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Message-ID: <20090608215002.GB22049@elte.hu>
Date:	Mon, 8 Jun 2009 23:50:02 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf_counter: extensible perf_counter_attr


* Corey Ashford <cjashfor@...ux.vnet.ibm.com> wrote:

> Peter Zijlstra wrote:
>> On Mon, 2009-06-08 at 14:18 -0700, Corey Ashford wrote:
>>> pca.ext_attrs = &feature.head; /* secretly know that there's data 
>>> that lies past the attr struct header */
>>
>> Right, except its not so very secret since we have the type field
>> telling us.
>
> I see.  Thanks for the explanation.  Looks like a good plan to me!

i think we'd have a much simpler implementation by changing 
__reserved_1 to attr_size. When the kernel adds new attributes, the 
size will increase - old user-space will use the old size which the 
kernel detects and adopts to (by zeroing out that attribute space).

That way we'll always have a nice flat attributes structure, with no 
quirky chaining that has field-dependent data types ...

	Ingo
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