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Date:   Tue, 29 Dec 2020 10:45:24 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Namhyung Kim <namhyung@...nel.org>
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>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Petlan <mpetlan@...hat.com>,
        Ian Rogers <irogers@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        Alexei Budankov <abudankov@...wei.com>
Subject: Re: [PATCH] perf tools: Detect when pipe is passed as perf data

On Tue, Dec 29, 2020 at 02:53:36PM +0900, Namhyung Kim wrote:
> On Sat, Dec 26, 2020 at 7:21 AM Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > Currently we allow pipe input/output only through '-' string
> > being passed to '-o' or '-i' options, like:
> >
> >   # 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>
> > ---
> >  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..767b6c903cf5 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|O_CREAT|O_TRUNC;
> 
> I don't think we need O_CREAT here (maybe O_TRUNC as well).

I copied that from bash opening write end like:
  openat(AT_FDCWD, "perf.pipe", O_WRONLY|O_CREAT|O_TRUNC, 0666 <detached ...>

however I can't see any check on kernel side for that,
so it can removed.. I'll send new version

thanks,
jirka

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