linux-kernel - Re: [PATCH 5/5] tracing: add saved_cmdlines file to show cached task comms

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Date:	Thu, 16 Apr 2009 17:54:45 +0200
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>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Avadh Patel <avadh4all@...il.com>
Subject: Re: [PATCH 5/5] tracing: add saved_cmdlines file to show cached
	task comms

On Wed, Apr 15, 2009 at 10:18:35PM -0400, Steven Rostedt wrote:
> From: Avadh Patel <avadh4all@...il.com>
> 
> Export the cached task comms to userspace. This allows user apps to translate
> the pids from a trace into their respective task command lines.


Hi,

I don't understand why this is needed. The pid is already resolved
to its task comm into the trace.

Or is there another reason?

Frederic.



 
> [ added error checking and use of buf pointer to index file_buf
>     - Steven Rostedt ]
> 
> Signed-off-by: Avadh Patel <avadh4all@...il.com>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
>  kernel/trace/trace.c |   53 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 53 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 2d69b26..031c46f 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2422,6 +2422,56 @@ static const struct file_operations tracing_readme_fops = {
>  };
>  
>  static ssize_t
> +tracing_saved_cmdlines_read(struct file *file, char __user *ubuf,
> +				size_t cnt, loff_t *ppos)
> +{
> +	char *buf_comm;
> +	char *file_buf;
> +	char *buf;
> +	int len = 0;
> +	int pid;
> +	int i;
> +
> +	file_buf = kmalloc(SAVED_CMDLINES*(16+TASK_COMM_LEN), GFP_KERNEL);
> +	if (!file_buf)
> +		return -ENOMEM;
> +
> +	buf_comm = kmalloc(TASK_COMM_LEN, GFP_KERNEL);
> +	if (!buf_comm) {
> +		kfree(file_buf);
> +		return -ENOMEM;
> +	}
> +
> +	buf = file_buf;
> +
> +	for (i = 0; i < SAVED_CMDLINES; i++) {
> +		int r;
> +
> +		pid = map_cmdline_to_pid[i];
> +		if (pid == -1 || pid == NO_CMDLINE_MAP)
> +			continue;
> +
> +		trace_find_cmdline(pid, buf_comm);
> +		r = sprintf(buf, "%d %s\n", pid, buf_comm);
> +		buf += r;
> +		len += r;
> +	}
> +
> +	len = simple_read_from_buffer(ubuf, cnt, ppos,
> +				      file_buf, len);
> +
> +	kfree(file_buf);
> +	kfree(buf_comm);
> +
> +	return len;
> +}
> +
> +static const struct file_operations tracing_saved_cmdlines_fops = {
> +    .open       = tracing_open_generic,
> +    .read       = tracing_saved_cmdlines_read,
> +};
> +
> +static ssize_t
>  tracing_ctrl_read(struct file *filp, char __user *ubuf,
>  		  size_t cnt, loff_t *ppos)
>  {
> @@ -3973,6 +4023,9 @@ static __init int tracer_init_debugfs(void)
>  	trace_create_file("trace_marker", 0220, d_tracer,
>  			NULL, &tracing_mark_fops);
>  
> +	trace_create_file("saved_cmdlines", 0444, d_tracer,
> +			NULL, &tracing_saved_cmdlines_fops);
> +
>  #ifdef CONFIG_DYNAMIC_FTRACE
>  	trace_create_file("dyn_ftrace_total_info", 0444, d_tracer,
>  			&ftrace_update_tot_cnt, &tracing_dyn_info_fops);
> -- 
> 1.6.2.1
> 
> -- 

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