linux-kernel - Re: [PATCH v3] PM / wakeup: use seq

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Date:   Sun, 13 May 2018 10:46:57 +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, geert@...ux-m68k.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] PM / wakeup: use seq_open() to show wakeup stats

On Wednesday, April 25, 2018 12:59:31 PM 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>
> ----
> v3: simplify wakeup_sources_stats_seq_start
> v2: use srcu_read_lock instead of rcu_read_lock
> ---
>  drivers/base/power/wakeup.c | 75 +++++++++++++++++++++++++++++++++++----------
>  1 file changed, 59 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
> index ea01621..5872705 100644
> --- a/drivers/base/power/wakeup.c
> +++ b/drivers/base/power/wakeup.c
> @@ -1029,32 +1029,75 @@ 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)
> +			return ws;
> +	}
> +
> +	return NULL;
> +}
> +
> +static void *wakeup_sources_stats_seq_next(struct seq_file *m,
> +					void *v, loff_t *pos)
> +{
> +	struct wakeup_source *ws = v;
> +	struct wakeup_source *next_ws = NULL;
> +
> +	++(*pos);
>  
> -	print_wakeup_source_stats(m, &deleted_ws);
> +	list_for_each_entry_continue_rcu(ws, &wakeup_sources, entry) {
> +		next_ws = ws;
> +		break;
> +	}
> +
> +	return next_ws;
> +}
> +
> +static void wakeup_sources_stats_seq_stop(struct seq_file *m, void *v)
> +{
> +	int *srcuidx = m->private;
> +
> +	srcu_read_unlock(&wakeup_srcu, *srcuidx);
> +}
> +
> +/**
> + * wakeup_sources_stats_seq_show - Print wakeup sources statistics information.
> + * @m: seq_file to print the statistics into.
> + * @v: wakeup_source of each iteration
> + */
> +static int wakeup_sources_stats_seq_show(struct seq_file *m, void *v)
> +{
> +	struct wakeup_source *ws = v;
> +
> +	print_wakeup_source_stats(m, ws);
>  
>  	return 0;
>  }
>  
> +static const struct seq_operations wakeup_sources_stats_seq_ops = {
> +	.start = wakeup_sources_stats_seq_start,
> +	.next  = wakeup_sources_stats_seq_next,
> +	.stop  = wakeup_sources_stats_seq_stop,
> +	.show  = wakeup_sources_stats_seq_show,
> +};
> +
>  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));
>  }
>  
>  static const struct file_operations wakeup_sources_stats_fops = {
> @@ -1062,7 +1105,7 @@ static int wakeup_sources_stats_open(struct inode *inode, struct file *file)
>  	.open = wakeup_sources_stats_open,
>  	.read = seq_read,
>  	.llseek = seq_lseek,
> -	.release = single_release,
> +	.release = seq_release_private,
>  };
>  
>  static int __init wakeup_sources_debugfs_init(void)
> 

Applied, thanks!