linux-kernel - Re: [PATCH] perf data: if a bad header size, retry in pipe mode

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Date:   Tue, 14 Apr 2020 07:01:19 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf data: if a bad header size, retry in pipe mode

On Tue, Apr 14, 2020 at 5:51 AM Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Thu, Apr 09, 2020 at 11:57:44AM -0700, Ian Rogers wrote:
> > Currently pipe mode files fail 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 change makes it so that if a perf.data file's header size is wrong
> > it is re-checked in pipe mode, where if wrong it fails as it currently
> > does.
> >
>
> hi,
> how about doing it the other way round like below,
> read header and find out if it's pipe..
>
> seems it's less changes
>
> jirka

Looks good to me. I think removing the function declaration from
util/header.h is still worthwhile, but needn't be in a patch with this
change.

Thanks!
Ian

> ---
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index acbd046bf95c..20c34cec9a46 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -3469,7 +3469,7 @@ 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,
> @@ -3571,7 +3571,7 @@ 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();
> @@ -3580,8 +3580,16 @@ 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 could still read 'pipe' data from regular file,
> +        * check for the pipe header first.
> +        */
> +       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;
>