linux-kernel - Re: [PATCH] tracing: fix trace_print

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Message-ID: <20090701140111.GB5097@nowhere>
Date:	Wed, 1 Jul 2009 16:01:12 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing: fix trace_print_seq()

On Wed, Jul 01, 2009 at 04:50:25PM +0800, Xiao Guangrong wrote:
> We will lose something if trace_seq->buffer[0] is 0, because the copy length
> is calculated by strlen() in seq_puts(), so using seq_write() instead of 
> seq_puts().
> 
> There have a example:
> after reboot:
> # echo kmemtrace > current_tracer
> # echo 0 > options/kmem_minimalistic
> # cat trace
> # tracer: kmemtrace
> #
> #
> Nothing is exported, because the first byte of trace_seq->buffer[ ]
> is KMEMTRACE_USER_ALLOC.
> ( the value of KMEMTRACE_USER_ALLOC is zero, seeing
>   kmemtrace_print_alloc_user() in kernel/trace/kmemtrace.c)
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
> ---
>  kernel/trace/trace_output.c |    3 +--
>  1 files changed, 1 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index 7938f3a..e0c2545 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -27,8 +27,7 @@ void trace_print_seq(struct seq_file *m, struct trace_seq *s)
>  {
>  	int len = s->len >= PAGE_SIZE ? PAGE_SIZE - 1 : s->len;
>  
> -	s->buffer[len] = 0;
> -	seq_puts(m, s->buffer);
> +	seq_write(m, s->buffer, len);
>  
>  	trace_seq_init(s);
>  }
> -- 
> 1.6.1.2
> 

Looks good, thanks.

Acked-by: Frederic Weisbecker <fweisbec@...il.com>

But having a '\0' in a non binary trace looks weird. Why do
we have such plain KMEMTRACE_USER_ALLOC whereas binary tracing
is not set, as your example shows it?

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