linux-kernel - Re: [RFC PATCH 2/4] tracing: Turn "id"->i

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Date:	Tue, 16 Jul 2013 15:49:06 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/4] tracing: Turn "id"->i_private into
 call->event.type

On Tue, 2013-07-16 at 20:57 +0200, Oleg Nesterov wrote:
> ftrace_event_id_fops and event_id_read() is overcomplicated.
> 
> 1. Change event_create_dir() to pass "data = call->event.type"
>    to debugfs_create_file().
> 
>    This means that ftrace_event_id_fops doesn't need .open()
>    and event_id_read() can simply print (int)i_private
> 
> 2. event_id_read() has no reason to kmalloc "struct trace_seq"
>    (more than PAGE_SIZE!), it can use a small buffer.

Make #2 a separate patch. You can add it before this one.

-- Steve

> 
> Note: "if (*ppos) return 0" looks strange and unneeded,
> simple_read_from_buffer(ppos) should handle this case corrrectly.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/trace/trace_events.c |   26 +++++++++-----------------
>  1 files changed, 9 insertions(+), 17 deletions(-)
> 
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index cbd1a57..cefbe85 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -962,24 +962,17 @@ static int trace_format_open(struct inode *inode, struct file *file)
>  static ssize_t
>  event_id_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
>  {
> -	struct ftrace_event_call *call = filp->private_data;
> -	struct trace_seq *s;
> -	int r;
> +	int id = (long)ACCESS_ONCE(file_inode(filp)->i_private);
> +	char buf[32];
> +	int len;
>  
> +	if (!id)
> +		return -ENODEV;
>  	if (*ppos)
>  		return 0;
>  
> -	s = kmalloc(sizeof(*s), GFP_KERNEL);
> -	if (!s)
> -		return -ENOMEM;
> -
> -	trace_seq_init(s);
> -	trace_seq_printf(s, "%d\n", call->event.type);
> -
> -	r = simple_read_from_buffer(ubuf, cnt, ppos,
> -				    s->buffer, s->len);
> -	kfree(s);
> -	return r;
> +	len = sprintf(buf, "%d\n", id);
> +	return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
>  }
>  
>  static ssize_t
> @@ -1264,7 +1257,6 @@ static const struct file_operations ftrace_event_format_fops = {
>  };
>  
>  static const struct file_operations ftrace_event_id_fops = {
> -	.open = tracing_open_generic,
>  	.read = event_id_read,
>  	.llseek = default_llseek,
>  };
> @@ -1496,8 +1488,8 @@ event_create_dir(struct dentry *parent,
>  
>  #ifdef CONFIG_PERF_EVENTS
>  	if (call->event.type && call->class->reg)
> -		trace_create_file("id", 0444, file->dir, call,
> -		 		  id);
> +		trace_create_file("id", 0444, file->dir,
> +				  (void*)(long)call->event.type, id);
>  #endif
>  
>  	/*


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