linux-kernel - Re: [PATCH] perf record: mmap output file

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Message-ID: <87ppr79cd5.fsf@sejong.aot.lge.com>
Date:	Tue, 15 Oct 2013 17:17:42 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	David Ahern <dsahern@...il.com>, acme@...stprotocols.net,
	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] perf record: mmap output file - v2

On Tue, 15 Oct 2013 09:25:40 +0200, Ingo Molnar wrote:
> * Namhyung Kim <namhyung@...nel.org> wrote:
>> No, st_size is bigger than rec->bytes_written due to the 
>> perf_file_header which is written without updating rec->bytes_written.
>
> Since all this is code that executes once during __cmd_record(), is this 
> all about the header writeout?
>
> That is what confused me about the stat() call and that's messy really: we 
> are the ones who write the file header, we have a very good idea about how 
> many bytes we wrote to the file! It should be entirely unnecessary to lose 
> that information and then execute a system call to recover that 
> information...

Right, I think session->header.data_offset has the info already.

Thanks,
Namhyung
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