linux-kernel - Re: [PATCH] perf session: Try to read pipe data from file

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Date:   Fri, 1 May 2020 10:49:06 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Michael Petlan <mpetlan@...hat.com>
Subject: Re: [PATCH] perf session: Try to read pipe data from file

On Fri, May 1, 2020 at 4:35 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> From: Jiri Olsa <jolsa@...hat.com>
>
> Ian came with the idea of having support to read the pipe
> data also from file [1]. Currently pipe mode files fails
> like:
>
>   $ perf record -o - sleep 1 > /tmp/perf.pipe.data
>   $ perf report -i /tmp/perf.pipe.data
>   incompatible file format (rerun with -v to learn more)
>
> This patch adds the support to do that by trying the pipe
> header first, and if its successfully detected, switching

nit: s/its/it's/

> the perf data to pipe mode.
>
> [1] https://lore.kernel.org/lkml/20200409185744.255881-1-irogers@google.com/
> Original-patch-by: Ian Rogers <irogers@...gle.com>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>

Tested and works great, thanks!
Reviewed-by: Ian Rogers <irogers@...gle.com>

Thanks,
Ian

> ---
>  tools/perf/util/header.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index 0ce47283a8a1..8ca709f938b8 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -3574,7 +3574,7 @@ static int perf_header__read_pipe(struct perf_session *session)
>                 return -EINVAL;
>         }
>
> -       return 0;
> +       return f_header.size == sizeof(f_header) ? 0 : -1;
>  }
>
>  static int read_attr(int fd, struct perf_header *ph,
> @@ -3676,7 +3676,7 @@ int perf_session__read_header(struct perf_session *session)
>         struct perf_file_header f_header;
>         struct perf_file_attr   f_attr;
>         u64                     f_id;
> -       int nr_attrs, nr_ids, i, j;
> +       int nr_attrs, nr_ids, i, j, err;
>         int fd = perf_data__fd(data);
>
>         session->evlist = evlist__new();
> @@ -3685,8 +3685,16 @@ int perf_session__read_header(struct perf_session *session)
>
>         session->evlist->env = &header->env;
>         session->machines.host.env = &header->env;
> -       if (perf_data__is_pipe(data))
> -               return perf_header__read_pipe(session);
> +
> +       /*
> +        * We can read 'pipe' data event from regular file,
> +        * check for the pipe header regardless of source.
> +        */
> +       err = perf_header__read_pipe(session);
> +       if (!err || (err && perf_data__is_pipe(data))) {
> +               data->is_pipe = true;
> +               return err;
> +       }
>
>         if (perf_file_header__read(&f_header, header, fd) < 0)
>                 return -EINVAL;
> --
> 2.25.4
>