linux-kernel - Re: [PATCH] perf: update perf.data file format documentation

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Message-ID: <20190217232246.GB26460@krava>
Date:   Mon, 18 Feb 2019 00:22:46 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Jonas Rabenstein <jonas.rabenstein@...dium.uni-erlangen.de>
Cc:     linux-perf-users@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        Stephane Eranian <eranian@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf: update perf.data file format documentation

On Fri, Feb 15, 2019 at 07:28:23PM +0100, Jonas Rabenstein wrote:
> I found that the documentation of the flags section is some how
> different from the actual format used and expected by the perf
> tools. In this patch the according section of the file format
> documentation is updated to conform to the expectations of the
> perf tool suite.
> 
> Signed-off-by: Jonas Rabenstein <jonas.rabenstein@...dium.uni-erlangen.de>
> ---
>  .../perf/Documentation/perf.data-file-format.txt  | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/tools/perf/Documentation/perf.data-file-format.txt b/tools/perf/Documentation/perf.data-file-format.txt
> index dfb218feaad9..6ea199f28330 100644
> --- a/tools/perf/Documentation/perf.data-file-format.txt
> +++ b/tools/perf/Documentation/perf.data-file-format.txt
> @@ -43,13 +43,10 @@ struct perf_file_section {
>  
>  Flags section:
>  
> -The header is followed by different optional headers, described by the bits set
> -in flags. Only headers for which the bit is set are included. Each header
> -consists of a perf_file_section located after the initial header.
> -The respective perf_file_section points to the data of the additional
> -header and defines its size.
> -
> -Some headers consist of strings, which are defined like this:
> +The Flags section is placed directly after the data section and consists of a
> +variable amount of information described by the flags-bitset in the perf_header.
> +A lot of the headers in the Flags section are simple strings and are represented
> +like this:

some how I find this more confusing.. please describe
what's actualy wrong with the current wording

>  
>  struct perf_header_string {
>         uint32_t len;
> @@ -82,7 +79,7 @@ assigned by the linker to an executable.
>  struct build_id_event {
>  	struct perf_event_header header;
>  	pid_t			 pid;
> -	uint8_t			 build_id[24];
> +	uint8_t			 build_id[PERF_ALIGN(24, sizeof(u64))];

isn't that always 24? I guess u meant:

  build_id[PERF_ALIGN(20, sizeof(u64))];


>  	char			 filename[header.size - offsetof(struct build_id_event, filename)];
>  };
>  
> @@ -131,7 +128,7 @@ An uint64_t with the total memory in bytes.
>  
>  	HEADER_CMDLINE = 11,
>  
> -A perf_header_string with the perf command line used to collect the data.
> +A perf_header_string_list with the perf arg-vector used to collect the data.

nice catch

thanks,
jirka

>  
>  	HEADER_EVENT_DESC = 12,
>  
> -- 
> 2.17.1
>