linux-kernel - Re: [PATCH 1/7] tracing: give easy way to clear trace buffer

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Date:	Thu, 19 Mar 2009 21:26:32 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 1/7] tracing: give easy way to clear trace buffer

On Thu, Mar 19, 2009 at 04:01:23PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@...hat.com>
> 
> There is currently no easy way to clear the trace buffer. Currently
> the only way is to change the current tracer.
> 
> This patch lets the user clear the trace buffer by simply writing
> into the trace files.
> 
>  echo > /debug/tracing/trace
> 
> or to clear a single cpu (i.e. for CPU 1):
> 
>  echo > /debug/tracing/per_cpu/cpu1/trace
> 
> Requested-by: Ingo Molnar <mingo@...e.hu>
> Signed-off-by: Steven Rostedt <srostedt@...hat.com>
> ---
>  kernel/trace/trace.c |   41 +++++++++++++++++++++++++++++++++--------
>  1 files changed, 33 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index a2d13e8..8d981ab 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -1941,9 +1941,14 @@ int tracing_open_generic(struct inode *inode, struct file *filp)
>  static int tracing_release(struct inode *inode, struct file *file)
>  {
>  	struct seq_file *m = (struct seq_file *)file->private_data;
> -	struct trace_iterator *iter = m->private;
> +	struct trace_iterator *iter;
>  	int cpu;
>  
> +	if (!(file->f_mode & FMODE_READ))
> +		return 0;
> +
> +	iter = m->private;
> +
>  	mutex_lock(&trace_types_lock);
>  	for_each_tracing_cpu(cpu) {
>  		if (iter->buffer_iter[cpu])
> @@ -1969,12 +1974,24 @@ static int tracing_open(struct inode *inode, struct file *file)
>  	struct trace_iterator *iter;
>  	int ret = 0;
>  
> -	iter = __tracing_open(inode, file);
> -	if (IS_ERR(iter))
> -		ret = PTR_ERR(iter);
> -	else if (trace_flags & TRACE_ITER_LATENCY_FMT)
> -		iter->iter_flags |= TRACE_FILE_LAT_FMT;
> +	/* If this file was open for write, then erase contents */
> +	if ((file->f_mode & FMODE_WRITE) &&
> +	    !(file->f_flags & O_APPEND)) {
> +		long cpu = (long) inode->i_private;
> +
> +		if (cpu == TRACE_PIPE_ALL_CPU)
> +			tracing_reset_online_cpus(&global_trace);
> +		else
> +			tracing_reset(&global_trace, cpu);
> +	}
>  
> +	if (file->f_mode & FMODE_READ) {
> +		iter = __tracing_open(inode, file);
> +		if (IS_ERR(iter))
> +			ret = PTR_ERR(iter);
> +		else if (trace_flags & TRACE_ITER_LATENCY_FMT)
> +			iter->iter_flags |= TRACE_FILE_LAT_FMT;
> +	}
>  	return ret;
>  }
>  
> @@ -2049,9 +2066,17 @@ static int show_traces_open(struct inode *inode, struct file *file)
>  	return ret;
>  }
>  
> +static ssize_t
> +tracing_write_stub(struct file *filp, const char __user *ubuf,
> +		   size_t count, loff_t *ppos)
> +{
> +	return count;
> +}


Is this one necessary?
I guess debugfs or vfs layers already provide a stub for write. No?

Anyway, that's a small detail for this good patch idea.

Frederic.


>  static const struct file_operations tracing_fops = {
>  	.open		= tracing_open,
>  	.read		= seq_read,
> +	.write		= tracing_write_stub,
>  	.llseek		= seq_lseek,
>  	.release	= tracing_release,
>  };
> @@ -3576,7 +3601,7 @@ static void tracing_init_debugfs_percpu(long cpu)
>  		pr_warning("Could not create debugfs 'trace_pipe' entry\n");
>  
>  	/* per cpu trace */
> -	entry = debugfs_create_file("trace", 0444, d_cpu,
> +	entry = debugfs_create_file("trace", 0644, d_cpu,
>  				(void *) cpu, &tracing_fops);
>  	if (!entry)
>  		pr_warning("Could not create debugfs 'trace' entry\n");
> @@ -3890,7 +3915,7 @@ static __init int tracer_init_debugfs(void)
>  	if (!entry)
>  		pr_warning("Could not create debugfs 'tracing_cpumask' entry\n");
>  
> -	entry = debugfs_create_file("trace", 0444, d_tracer,
> +	entry = debugfs_create_file("trace", 0644, d_tracer,
>  				 (void *) TRACE_PIPE_ALL_CPU, &tracing_fops);
>  	if (!entry)
>  		pr_warning("Could not create debugfs 'trace' entry\n");
> -- 
> 1.6.2
> 
> -- 
> --
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