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Subject: Re: [PATCH v9 1/8] perf evlist: Introduce aux evlist
To: Arnaldo Carvalho de Melo <acme@kernel.org>
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CC: Nilay Vaish <nilayvaish@gmail.com>,
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        Namhyung Kim <namhyung@kernel.org>, Zefan Li <lizefan@huawei.com>
From: "Wangnan (F)" <wangnan0@huawei.com>
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Date: Thu, 23 Jun 2016 09:29:57 +0800
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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@huawei.com> 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.