linux-kernel - Re: [PATCH 01/12] perf tools: Separate generic code in dso__data_file

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Date:   Mon, 13 May 2019 22:00:15 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Stanislav Fomichev <sdf@...ichev.me>,
        Song Liu <songliubraving@...com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 01/12] perf tools: Separate generic code in
 dso__data_file_size

On Mon, May 13, 2019 at 04:47:54PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Wed, May 08, 2019 at 03:19:59PM +0200, Jiri Olsa escreveu:
> > Moving file specific code in dso__data_file_size function
> > into separate file_size function. I'll add bpf specific
> > code in following patches.
> 
> I'm applying this patch, as it just moves things around, no logic
> change, but can you please clarify a question I have after looking at
> this patch?
>  
> > Link: http://lkml.kernel.org/n/tip-rkcsft4a0f8sw33p67llxf0d@git.kernel.org
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  tools/perf/util/dso.c | 19 ++++++++++++-------
> >  1 file changed, 12 insertions(+), 7 deletions(-)
> > 
> > diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> > index e059976d9d93..cb6199c1390a 100644
> > --- a/tools/perf/util/dso.c
> > +++ b/tools/perf/util/dso.c
> > @@ -898,18 +898,12 @@ static ssize_t cached_read(struct dso *dso, struct machine *machine,
> >  	return r;
> >  }
> >  
> > -int dso__data_file_size(struct dso *dso, struct machine *machine)
> > +static int file_size(struct dso *dso, struct machine *machine)
> >  {
> >  	int ret = 0;
> >  	struct stat st;
> >  	char sbuf[STRERR_BUFSIZE];
> >  
> > -	if (dso->data.file_size)
> > -		return 0;
> > -
> > -	if (dso->data.status == DSO_DATA_STATUS_ERROR)
> > -		return -1;
> > -
> >  	pthread_mutex_lock(&dso__data_open_lock);
> >  
> >  	/*
> > @@ -938,6 +932,17 @@ int dso__data_file_size(struct dso *dso, struct machine *machine)
> >  	return ret;
> >  }
> >  
> > +int dso__data_file_size(struct dso *dso, struct machine *machine)
> > +{
> > +	if (dso->data.file_size)
> > +		return 0;
> > +
> > +	if (dso->data.status == DSO_DATA_STATUS_ERROR)
> > +		return -1;
> > +
> > +	return file_size(dso, machine);
> > +}
> 
> 
> So the name of the function suggests we want to know the
> "data_file_size" of a dso, then the logic in it returns _zero_ if a
> member named "dso->data.file_size" is _not_ zero, can you please
> clarify?
> 
> I was expecting something like:
> 
> 	if (dso->data.file_size)
> 		return dso->data.file_size;
> 
> I.e. if we had already read it, return the cached value, otherwise go
> and call some other function to get that info somehow.

we keep the data size in dso->data.file_size,
the function just updates it

the return code is the error code.. not sure,
why its like that, but it is ;-)

maybe we wanted separate size and error code,
because the size needs to be u64 and we use
int everywhere.. less casting

jirka