linux-kernel - Re: [RFC PATCH v2 01/10] perf workqueue: threadpool creation and destruction

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Date:   Tue, 10 Aug 2021 17:24:00 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Riccardo Mancini <rickyman7@...il.com>,
        Ian Rogers <irogers@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Jiri Olsa <jolsa@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-perf-users <linux-perf-users@...r.kernel.org>,
        Alexey Bayduraev <alexey.v.bayduraev@...ux.intel.com>
Subject: Re: [RFC PATCH v2 01/10] perf workqueue: threadpool creation and
 destruction

Em Tue, Aug 10, 2021 at 11:54:19AM -0700, Namhyung Kim escreveu:
> On Mon, Aug 9, 2021 at 3:30 AM Riccardo Mancini <rickyman7@...il.com> wrote:
> > On Fri, 2021-08-06 at 19:24 -0700, Namhyung Kim wrote:
> > > > +/**
> > > > + * threadpool__strerror - print message regarding given @err in @pool
> > > > + *
> > > > + * Buffer size should be at least THREADPOOL_STRERR_BUFSIZE bytes.
> > > > + */
> > > > +int threadpool__strerror(struct threadpool *pool __maybe_unused, int err,
> > > > char *buf, size_t size)
> > > > +{
> > > > +       char sbuf[STRERR_BUFSIZE], *emsg;
> > > > +
> > > > +       emsg = str_error_r(err, sbuf, sizeof(sbuf));
> > > > +       return scnprintf(buf, size, "Error: %s.\n", emsg);
> > > > +}
> > > > +
> > > > +/**
> > > > + * threadpool__new_strerror - print message regarding @err_ptr
> > > > + *
> > > > + * Buffer size should be at least THREADPOOL_STRERR_BUFSIZE bytes.
> > > > + */
> > > > +int threadpool__new_strerror(struct threadpool *err_ptr, char *buf, size_t
> > > > size)
> > > > +{
> > > > +       return threadpool__strerror(err_ptr, PTR_ERR(err_ptr), buf, size);
> > > > +}

> > > Why two different functions?

> > Since when new fails you don't have a err number, just an err_ptr so it's not
> > very clear how to call threadpool__strerror. Therefore I made a wrapper to
> > remove any ambiguity.
> 
> What do you mean by "when new fails"?

I think 'new' is 'constructor', i.e. something__new() returns a newly
created object and this not an error number, so he uses ERR_PTR() and
then he needs to pass it to the 'strerror' specific to the
threadpool__new, which will use PTR_ERR() to get an integer, and then
map that to a proper error string, right?

- Arnaldo