linux-kernel - Re: [PATCH 4/5] perf tools: Propagate error info from tp

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Date:	Mon, 14 Sep 2015 23:35:57 -0300
From:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:	Raphaël Beamonte <raphael.beamonte@...il.com>
Cc:	Jiri Olsa <jolsa@...hat.com>, Jiri Olsa <jolsa@...nel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH 4/5] perf tools: Propagate error info from tp_format

Em Mon, Sep 14, 2015 at 06:05:38PM -0400, Raphaël Beamonte escreveu:
> 2015-09-14 17:36 GMT-04:00 Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>:
> > Em Mon, Sep 14, 2015 at 04:59:41PM -0400, Raphaël Beamonte escreveu:
> >> 2015-09-14 16:53 GMT-04:00 Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>:
> >> > +++ b/tools/perf/util/evsel.c
> >> > @@ -234,7 +234,9 @@ struct perf_evsel *perf_evsel__newtp_idx(const char *sys, const char *name, int
> >> >         struct perf_evsel *evsel = zalloc(perf_evsel__object.size);
> >> >         int err = -ENOMEM;
> >> >
> >> > -       if (evsel != NULL) {
> >> > +       if (evsel == NULL) {
> >> > +               goto out_err;
> >> > +       } else {
> >>
> >> Is the else really necessary after a goto?
> >
> > Not really, we can remove it and all would be equivalent (the code
> > with/without should be the same), its just that I wanted to avoid
> > touching the identation to reduce patch size and since we need o open a
> > brace to declare that attr variable...
> 
> Ok. Though, given the content of that function, we could probably
> declare attr in the first lines of the function and assign it its
> value after the if. But I understand the patch size argument! :o)

Yeah, in other times I would have cleaned it all up, having that else is
ugly, but review time is more expensive, I think, so we need to reduce
its cost.

Cleaning it up makes it easier to read, but we get the info about when
that particular code was written buried a bit below the reindentation
cset.

Would be nice to have a 'git blame' that would just unwind things like
that :-)

> On another subject, but on the same lines, shouldn't we use if
> (!evsel) instead of if (evsel == NULL)? (kernel code style if I'm not
> mistaken) Or is there something that prevents from using it here?

I'd say both are ok. (evsel) is shorter than (evsel != NULL), but the
later is more expressive, at a glance you know it is a pointer, etc.

- Arnaldo
 
> >> >                 struct perf_event_attr attr = {
> >> >                         .type          = PERF_TYPE_TRACEPOINT,
> >> >                         .sample_type   = (PERF_SAMPLE_RAW | PERF_SAMPLE_TIME |
> >> > @@ -261,6 +263,7 @@ struct perf_evsel *perf_evsel__newtp_idx(const char *sys, const char *name, int
> >> >  out_free:
> >> >         zfree(&evsel->name);
> >> >         free(evsel);
> >> > +out_err:
> >> >         return ERR_PTR(err);
> >> >  }
> >> >
> >> > diff --git a/tools/perf/util/trace-event.c b/tools/perf/util/trace-event.c
> >> > index 8e3a60e3e15f..802bb868d446 100644
> >> > --- a/tools/perf/util/trace-event.c
> >> > +++ b/tools/perf/util/trace-event.c
> >> > @@ -100,7 +100,7 @@ struct event_format*
> >> >  trace_event__tp_format(const char *sys, const char *name)
> >> >  {
> >> >         if (!tevent_initialized && trace_event__init2())
> >> > -               return NULL;
> >> > +               return ERR_PTR(-ENOMEM);
> >> >
> >> >         return tp_format(sys, name);
> >> >  }
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