linux-kernel - Re: [PATCH] perf: make perf.data more self-descriptive (v8)

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Date:	Wed, 30 Nov 2011 16:08:29 +0100
From:	Robert Richter <robert.richter@....com>
To:	Stephane Eranian <eranian@...gle.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"acme@...hat.com" <acme@...hat.com>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"dsahern@...il.com" <dsahern@...il.com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"mingo@...e.hu" <mingo@...e.hu>
Subject: Re: [PATCH] perf: make perf.data more self-descriptive (v8)

On 29.11.11 10:35:24, Stephane Eranian wrote:
>         sec_start = header->data_offset + header->data_size;
>         lseek(fd, sec_start + sec_size, SEEK_SET);
> 
>         err = do_write_feat(fd, header, HEADER_TRACE_INFO, &p, evlist);
>         if (err)
>                 goto out_free;
> 
>         err = do_write_feat(fd, header, HEADER_BUILD_ID, &p, evlist);
>         if (err) {
>                 perf_header__clear_feat(header, HEADER_BUILD_ID);
>                 goto out_free;
>         }
> 
> The 'clear_feat' is missing for TRACE_INFO, that's all. The question is:
> is case do_write_feat(trace_info) fails, is there still a way to parse the file
> correctly? If not, then perf should bail out, if yes, then we need to add the
> clear_feat(TRACE_INFO) in case of error.

The question is, if do_write_feat() fails for HEADER_TRACE_INFO or
HEADER_BUILD_ID then perf_header__adds_write() fails. A failure of any
other feature simple disables it by calling clear_feat(). I noticed
this asymmetry and wonder why?

Also, is there a reason why HEADER_TRACE_INFO starts with bit 1 instead
of bit 0. Is bit 0 reserved for some reason?

Thanks,

-Robert

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

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