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

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Date:	Mon, 22 Jun 2009 10:08:17 +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()

Li Zefan wrote:
> 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.
Yes, you are not the only one, but it's the only one in the tracing code. :)
I just think we should make the seq_* uniform so that we can understand them 
more clearly.

Liming Wang
> 
> 

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