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

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Date:	Mon, 22 Jun 2009 08:38:57 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Wang Liming <liming.wang@...driver.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()

Wang Liming wrote:
> 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:
> 

Thanks for the comment, but I don't think .next calls .start is bad,
and I'm not the only one doing this. Grep c_start() to see some of
them.

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