linux-kernel - Re: [PATCH 2/5] tracing_bprintk: don't increment @pos in t

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Date:	Fri, 19 Jun 2009 17:39:35 +0800
From:	Wang Liming <liming.wang@...driver.com>
To:	Li Zefan <lizf@...fujitsu.com>
CC:	Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/5] tracing_bprintk: don't increment @pos in t_start()

Hi,

Li Zefan wrote:
> It's wrong to increment @pos in t_start(), otherwise we'll lose
> some entries when reading printk_formats, if the output is large
> than PAGE_SIZE.
> 
> [ Impact: fix missing entries when reading printk_formats ]
> 
> Reported-by: Lai Jiangshan <laijs@...fujitsu.com>
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> ---
>  kernel/trace/trace_printk.c |   26 ++++++--------------------
>  1 files changed, 6 insertions(+), 20 deletions(-)
> 
> diff --git a/kernel/trace/trace_printk.c b/kernel/trace/trace_printk.c
> index 9bece96..7b62781 100644
> --- a/kernel/trace/trace_printk.c
> +++ b/kernel/trace/trace_printk.c
> @@ -155,25 +155,19 @@ int __ftrace_vprintk(unsigned long ip, const char *fmt, va_list ap)
>  EXPORT_SYMBOL_GPL(__ftrace_vprintk);
>  
>  static void *
> -t_next(struct seq_file *m, void *v, loff_t *pos)
> +t_start(struct seq_file *m, loff_t *pos)
>  {
> -	const char **fmt = m->private;
> -	const char **next = fmt;
> -
> -	(*pos)++;
> +	const char **fmt = __start___trace_bprintk_fmt + *pos;
>  
>  	if ((unsigned long)fmt >= (unsigned long)__stop___trace_bprintk_fmt)
>  		return NULL;
> -
> -	next = fmt;
> -	m->private = ++next;
> -
>  	return fmt;
>  }
>  
> -static void *t_start(struct seq_file *m, loff_t *pos)
> +static void *t_next(struct seq_file *m, void * v, loff_t *pos)
>  {
> -	return t_next(m, NULL, pos);
> +	(*pos)++;
> +	return t_start(m, pos);
>  }
>  
I prefer to .start to call .next, so I rewrite it to following:


@@ -157,17 +157,15 @@ EXPORT_SYMBOL_GPL(__ftrace_vprintk);
  static void *
  t_next(struct seq_file *m, void *v, loff_t *pos)
  {
-       const char **fmt = m->private;
-       const char **next = fmt;
+       const char **fmt;

-       (*pos)++;
+       if (v)
+               (*pos)++;
+       fmt = __start___trace_bprintk_fmt + *pos;

         if ((unsigned long)fmt >= (unsigned long)__stop___trace_bprintk_fmt)
                 return NULL;

-       next = fmt;
-       m->private = ++next;
-
         return fmt;
  }

but I have not tested it, if you have no objection, then:

Signed-off-by: walimis <walimisdev@...il.com>

Liming Wang

>  static int t_show(struct seq_file *m, void *v)
> @@ -224,15 +218,7 @@ static const struct seq_operations show_format_seq_ops = {
>  static int
>  ftrace_formats_open(struct inode *inode, struct file *file)
>  {
> -	int ret;
> -
> -	ret = seq_open(file, &show_format_seq_ops);
> -	if (!ret) {
> -		struct seq_file *m = file->private_data;
> -
> -		m->private = __start___trace_bprintk_fmt;
> -	}
> -	return ret;
> +	return seq_open(file, &show_format_seq_ops);
>  }
>  
>  static const struct file_operations ftrace_formats_fops = {

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