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

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Date:   Fri, 30 Mar 2018 12:25:46 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Ganesh Mahendran <opensource.ganesh@...il.com>
Cc:     pavel@....cz, len.brown@...el.com, rafael@...nel.org,
        gregkh@...uxfoundation.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PM / wakeup: use seq_open() to show wakeup stats

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.
> 
> Signed-off-by: Ganesh Mahendran <opensource.ganesh@...il.com>
> ----
> v2: use srcu_read_lock instead of rcu_read_lock
> ---
>  drivers/base/power/wakeup.c | 77 +++++++++++++++++++++++++++++++++++----------
>  1 file changed, 61 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
> index ea01621..3bcab7d 100644
> --- 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)
>  {
>  	struct wakeup_source *ws;
> -	int srcuidx;
> +	loff_t n = *pos;
> +	int *srcuidx = m->private;
>  
> -	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");
> +	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");
> +	}
>  
> -	srcuidx = srcu_read_lock(&wakeup_srcu);
> -	list_for_each_entry_rcu(ws, &wakeup_sources, entry)
> -		print_wakeup_source_stats(m, ws);
> -	srcu_read_unlock(&wakeup_srcu, srcuidx);
> +	*srcuidx = srcu_read_lock(&wakeup_srcu);
> +	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.