linux-kernel - Re: [PATCH 2/2] ftrace: Unify effect of writing to trace

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Date:	Thu, 06 Aug 2009 13:04:48 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Zhaolei <zhaolei@...fujitsu.com>
CC:	Steven Rostedt <srostedt@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] ftrace: Unify effect of writing to trace_options
 and option/*

Zhaolei wrote:
> "echo noglobal-clock > trace_options" can be used to change trace
> clock but "echo 0 > options/global-clock" can't.
> 
> We can fix it by using set_tracer_flags() in trace_options_core_write().
> 

Nice catch.

> Signed-off-by: Zhao Lei <zhaolei@...fujitsu.com>
> ---
>  kernel/trace/trace.c |    5 ++---
>  1 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 464b7bb..2fa2bac 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3893,12 +3893,11 @@ trace_options_core_write(struct file *filp, const char __user *ubuf, size_t cnt,
>  
>  	switch (val) {
>  	case 0:
> -		trace_flags &= ~(1 << index);
> +		set_tracer_flags(1 << index, 0);
>  		break;
>  	case 1:
> -		trace_flags |= 1 << index;
> +		set_tracer_flags(1 << index, 1);
>  		break;
> -
>  	default:
>  		return -EINVAL;
>  	}

The whole switch statement can be simplied:

	if (val != 0 || val != 1)
		return -EINVAL;
	set_tracer_flags(1 << index, val);


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