linux-kernel - Re: [PATCHv2] perf tools: Detect when pipe is passed as perf data

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Date:   Wed, 6 Jan 2021 10:49:34 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Stephane Eranian <eranian@...gle.com>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Petlan <mpetlan@...hat.com>,
        Ian Rogers <irogers@...gle.com>,
        Alexei Budankov <abudankov@...wei.com>
Subject: Re: [PATCHv2] perf tools: Detect when pipe is passed as perf data

On Tue, Jan 05, 2021 at 05:33:38PM -0800, Stephane Eranian wrote:
> Hi,
> 
> On Wed, Dec 30, 2020 at 3:09 AM Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > Currently we allow pipe input/output only through '-' string
> > being passed to '-o' or '-i' options, like:
> >
> It seems to me it would be useful to auto-detect that the perf.data
> file is in pipe vs. file mode format.
> Your patch detects the type of the file which is something different
> from the format of its content.

hi,
it goes together with the format, once the output file
is pipe, the format is pipe as well

jirka

> Thanks.
> 
> >   # mkfifo perf.pipe
> >   # perf record --no-buffering -e 'sched:sched_switch' -o - > perf.pipe &
> >   [1] 354406
> >   # cat perf.pipe | ./perf --no-pager script -i - | head -3
> >             perf 354406 [000] 168190.164921: sched:sched_switch: perf:354406..
> >      migration/0    12 [000] 168190.164928: sched:sched_switch: migration/0:..
> >             perf 354406 [001] 168190.164981: sched:sched_switch: perf:354406..
> >   ...
> >
> > This patch detects if given path is pipe and set the perf data
> > object accordingly, so it's possible now to do above with:
> >
> >   # mkfifo perf.pipe
> >   # perf record --no-buffering -e 'sched:sched_switch' -o perf.pipe &
> >   [1] 360188
> >   # perf --no-pager script -i ./perf.pipe | head -3
> >             perf 354442 [000] 168275.464895: sched:sched_switch: perf:354442..
> >      migration/0    12 [000] 168275.464902: sched:sched_switch: migration/0:..
> >             perf 354442 [001] 168275.464953: sched:sched_switch: perf:354442..
> >
> > It's of course possible to combine any of above ways.
> >
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> > v2:
> >   - removed O_CREAT|O_TRUNC flags from pipe's write end
> >
> >  tools/perf/util/data.c | 27 +++++++++++++++++++++------
> >  1 file changed, 21 insertions(+), 6 deletions(-)
> >
> > diff --git a/tools/perf/util/data.c b/tools/perf/util/data.c
> > index f29af4fc3d09..4dfa9e0f2fec 100644
> > --- a/tools/perf/util/data.c
> > +++ b/tools/perf/util/data.c
> > @@ -159,7 +159,7 @@ int perf_data__update_dir(struct perf_data *data)
> >         return 0;
> >  }
> >
> > -static bool check_pipe(struct perf_data *data)
> > +static int check_pipe(struct perf_data *data)
> >  {
> >         struct stat st;
> >         bool is_pipe = false;
> > @@ -172,6 +172,15 @@ static bool check_pipe(struct perf_data *data)
> >         } else {
> >                 if (!strcmp(data->path, "-"))
> >                         is_pipe = true;
> > +               else if (!stat(data->path, &st) && S_ISFIFO(st.st_mode)) {
> > +                       int flags = perf_data__is_read(data) ?
> > +                                   O_RDONLY : O_WRONLY;
> > +
> > +                       fd = open(data->path, flags);
> > +                       if (fd < 0)
> > +                               return -EINVAL;
> > +                       is_pipe = true;
> > +               }
> >         }
> >
> >         if (is_pipe) {
> > @@ -190,7 +199,8 @@ static bool check_pipe(struct perf_data *data)
> >                 }
> >         }
> >
> > -       return data->is_pipe = is_pipe;
> > +       data->is_pipe = is_pipe;
> > +       return 0;
> >  }
> >
> >  static int check_backup(struct perf_data *data)
> > @@ -344,8 +354,11 @@ static int open_dir(struct perf_data *data)
> >
> >  int perf_data__open(struct perf_data *data)
> >  {
> > -       if (check_pipe(data))
> > -               return 0;
> > +       int err;
> > +
> > +       err = check_pipe(data);
> > +       if (err || data->is_pipe)
> > +               return err;
> >
> >         /* currently it allows stdio for pipe only */
> >         data->use_stdio = false;
> > @@ -410,8 +423,10 @@ int perf_data__switch(struct perf_data *data,
> >  {
> >         int ret;
> >
> > -       if (check_pipe(data))
> > -               return -EINVAL;
> > +       ret = check_pipe(data);
> > +       if (ret || data->is_pipe)
> > +               return ret;
> > +
> >         if (perf_data__is_read(data))
> >                 return -EINVAL;
> >
> > --
> > 2.26.2
> >
>