Re: [PATCH v9 1/8] perf evlist: Introduce aux evlist

[Wangnan (F)]

On 2016/6/22 21:40, Arnaldo Carvalho de Melo wrote:
> Em Wed, Jun 22, 2016 at 08:17:02AM -0500, Nilay Vaish escreveu:
> > On 22 June 2016 at 04:08, Wang Nan <wangnan0@xxxxxxxxxx> wrote:
> > > +struct perf_evlist *perf_evlist__new_aux(struct perf_evlist *parent)
> > > +{
> > > +       struct perf_evlist *evlist;
> > > +
> > > +       if (perf_evlist__is_aux(parent)) {
> > > +               pr_err("Internal error: create aux evlist from another aux evlist\n");
> > > +               return NULL;
> > > +       }
> > > +
> > > +       evlist = zalloc(sizeof(*evlist));
> > > +       if (!evlist)
> > > +               return NULL;
> > > +
> > > +       perf_evlist__init(evlist, parent->cpus, parent->threads);
> > > +       evlist->parent = parent->parent;
> > A very minor suggestion.  I think evlist->parent  should be set to
> > 'parent' and not 'parent->parent'.  I agree the two values are equal,
> > but setting to parent->parent just does not seem right.
> I felt like that, thought I was missing something, which is always a bad
> feeling when processing a patch... So, Wang, does that have some value
> we are not seeing?
>
> I thought about the possibility of adding an aux2 to an aux1 evlist and
> that making aux2 have the same parent as aux1, but that is checked on
> that pr_err() test...

The pr_err() test is added yesterday to emphasize we don't accept
grandchildren. Before we have this test, setting parent to parent->parent
is a defensive programming. And I think it is clever :)

Thank you.