linux-kernel - Re: [PATCH v2] PM / wakeup: use seq

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Date:   Mon, 2 Apr 2018 08:46:58 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Ganesh Mahendran <opensource.ganesh@...il.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] PM / wakeup: use seq_open() to show wakeup stats

Hi Ganesh,

On Mon, Apr 2, 2018 at 3:33 AM, Ganesh Mahendran
<opensource.ganesh@...il.com> wrote:
> 2018-03-30 19:00 GMT+08:00 Geert Uytterhoeven <geert@...ux-m68k.org>:
>> On Fri, Mar 30, 2018 at 12:25 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>>> On Monday, March 5, 2018 9:47:46 AM CEST Ganesh Mahendran wrote:
>>>> single_open() interface requires that the whole output must
>>>> fit into a single buffer. This will lead to timeout when
>>>> system memory is not in a good situation.
>>>>
>>>> This patch use seq_open() to show wakeup stats. This method
>>>> need only one page, so timeout will not be observed.

>>>> --- a/drivers/base/power/wakeup.c
>>>> +++ b/drivers/base/power/wakeup.c
>>>> @@ -1029,32 +1029,77 @@ static int print_wakeup_source_stats(struct seq_file *m,
>>>>       return 0;
>>>>  }
>>>>
>>>> -/**
>>>> - * wakeup_sources_stats_show - Print wakeup sources statistics information.
>>>> - * @m: seq_file to print the statistics into.
>>>> - */
>>>> -static int wakeup_sources_stats_show(struct seq_file *m, void *unused)
>>>> +static void *wakeup_sources_stats_seq_start(struct seq_file *m,
>>>> +                                     loff_t *pos)
>>>>  {

>>>> +     list_for_each_entry_rcu(ws, &wakeup_sources, entry) {
>>>> +             if (n-- > 0)
>>>> +                     continue;
>>>> +             goto out;
>>>> +     }
>>>> +     ws = NULL;
>>>> +out:
>>>> +     return ws;
>>>> +}
>>>
>>> Please clean up the above at least.
>>>
>>> If I'm not mistaken, you don't need the label and the goto here.
>>
>> The continue is also not needed, if the test condition is inverted.
>
> Hi, Geert
>
> We need to locate to the last read item. What is your suggestion here?

I didn't mean to get rid of that logic, but to reorganize the code to make it
simpler:

        list_for_each_entry_rcu(ws, &wakeup_sources, entry) {
                if (n-- <= 0)
                        return ws;
        }

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds