linux-kernel - Re: [PATCH 03/11] perf tool: Use PERF_EVENT_IOC

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Date:	Mon, 22 Oct 2012 10:40:16 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 03/11] perf tool: Use PERF_EVENT_IOC_ID perf ioctl to
 read event id

On Mon, Oct 22, 2012 at 04:57:24PM +0900, Namhyung Kim wrote:
> Hi,
> 
> Just a minor nitpicking..
> 
> 
> On Sat, 20 Oct 2012 16:33:11 +0200, Jiri Olsa wrote:
> > Changing the way we retrieve the event ID. Instead of parsing out
> > the ID out of the read data, using the PERF_EVENT_IOC_ID ioctl.
> >
> > Keeping the old way in place to support kernels without
> > PERF_EVENT_IOC_ID ioctl support.
> [snip]
> > +	} else if (errno)
> > +		return -1;
> 
> Is this check really needed?  I think that returning non-zero from the
> ioctl always sets the errno, no?  How about this:
> 
> 	ret = ioctl(fd, PERF_EVENT_IOC_ID, &id);
> 	if (!ret)
> 		goto add;
> 
> 	if (errno != ENOTTY)
> 		return -1;
> 
> 	...
> 
> I guess that it'll show you better diff stat. :)

yep, looks better.. v2 candidate ;)

thanks,
jirka
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