linux-kernel - Re: [PATCHv2] tracing - support multiple pids in set_pid

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Date:	Wed, 16 Sep 2009 10:15:56 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Li Zefan <lizf@...fujitsu.com>, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2] tracing - support multiple pids in set_pid_ftrace
	file

On Tue, Sep 15, 2009 at 09:33:33PM -0400, Steven Rostedt wrote:
> On Wed, 2009-09-16 at 09:00 +0800, Li Zefan wrote:
> > jolsa@...hat.com wrote:
> > > Adding the possibility to set more than 1 pid in the set_pid_ftrace file,
> > > thus allowing to trace more than 1 independent processes.
> > > 
> > > Usage:
> > > 
> > > sh-4.0# echo 284 > ./set_ftrace_pid 
> > > sh-4.0# cat ./set_ftrace_pid 
> > > 284
> > > sh-4.0# echo 1 >> ./set_ftrace_pid 
> > > sh-4.0# echo 0 >> ./set_ftrace_pid 
> > > sh-4.0# cat ./set_ftrace_pid 
> > > swapper tasks
> > > 1
> > > 284
> > > sh-4.0# echo 4 > ./set_ftrace_pid 
> > > sh-4.0# cat ./set_ftrace_pid 
> > > 4
> > > sh-4.0# echo > ./set_ftrace_pid 
> > > sh-4.0# cat ./set_ftrace_pid 
> > > no pid
> > > sh-4.0# 
> > > 
> > > 
> > > wbr,
> > > jirka
> > > 
> > > Signed-off-by: Jiri Olsa <jolsa@...hat.com>
> > 
> > Looks good.
> > 
> > Reviewed-by: Li Zefan <lizf@...fujitsu.com>
> 
> Thanks!
> 
> > 
> > a few nitpicks.
> > 
> > >  /* set when tracing only a pid */
> > 
> > This comment should be removed too.
> 
> Yeah, it goes with the deleted pointer below.
> 
> > 
> > > -struct pid *ftrace_pid_trace;
> > >  static struct pid * const ftrace_swapper_pid = &init_struct_pid;
> > >  
> > ...
> > > +static int ftrace_pid_add(int p)
> > > +{
> > > +	struct pid *pid;
> > > +	struct ftrace_pid *fpid;
> > > +	int ret = -EINVAL;
> > > +
> > > +	mutex_lock(&ftrace_lock);
> > > +
> > > +	if (!p)
> > > +		pid = ftrace_swapper_pid;
> > > +	else
> > > +		pid = find_get_pid(p);
> > > +
> > > +	if (!pid)
> > > +		goto out;
> > > +
> > > +	list_for_each_entry(fpid, &ftrace_pids, list)
> > > +		if (fpid->pid == pid)
> > > +			goto out_put;
> > 
> > rather than returning EINVAL, return EEXIST or just return 0?
> 
> I agree, return 0, if it already exists, there's no harm in it returning
> success.
> 
> -- Steve
thanks, I sent out v3

wbr,
jirka
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