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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Tue, 13 Mar 2018 18:39:47 +0200
Message-ID: <CAHp75VeNco97BovnVTcd=RH9zsK_gO=jmPALytP-sTFjK5Cq0Q@mail.gmail.com>
Subject: Re: [PATCH v2] PM / wakeup: use seq_open() to show wakeup stats
To:     Ganesh Mahendran <opensource.ganesh@gmail.com>
Cc:     "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Pavel Machek <pavel@ucw.cz>,
        "Brown, Len" <len.brown@intel.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Mon, Mar 5, 2018 at 10:47 AM, Ganesh Mahendran
<opensource.ganesh@gmail.com> 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.

> +       if (n == 0) {
> +               seq_puts(m, "name\t\tactive_count\tevent_count\twakeup_count\t"
> +                       "expire_count\tactive_since\ttotal_time\tmax_time\t"
> +                       "last_change\tprevent_suspend_time\n");
> +       }

Can't you do this once at ->open() stage, for example?

>  static int wakeup_sources_stats_open(struct inode *inode, struct file *file)
>  {
> -       return single_open(file, wakeup_sources_stats_show, NULL);
> +       return seq_open_private(file, &wakeup_sources_stats_seq_ops, sizeof(int));
>  }

-- 
With Best Regards,
Andy Shevchenko