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

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Message-ID: <20090609065350.GB16707@elte.hu>
Date:	Tue, 9 Jun 2009 08:53:50 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf_counter: extensible perf_counter_attr


* Paul Mackerras <paulus@...ba.org> wrote:

> Peter Zijlstra writes:
> 
> > Allow extending the perf_counter_attr structure by linking extended
> > structures to it.
> 
> ...
> 
> > @@ -175,6 +175,13 @@ struct perf_counter_attr {
> >  	__u32			__reserved_3;
> >  
> >  	__u64			__reserved_4;
> > +
> > +	struct perf_counter_attr_ext *ext_attrs;
> > +};
> 
> Since this is a user-visible structure, you've just introduced an 
> ABI difference between 32-bit and 64-bit processes, which we've 
> managed to avoid so far. [...]

This is a good point too - handling pointers in ABIs is possible but 
should be avoided as much as possible: it creates the need to 
introduce a compat_sys_perf_counter_open() and doubles the syscall 
table complexity.

Lets do the s/__reserved_1/attr_size ABI i suggested (i outlined 
various properties of it in the previous mail). Agreed?

	Ingo
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