linux-kernel - Re: [PATCH v3 25/33] tracing: Allow whitespace to surround hist trigger filter

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Date:   Wed, 18 Oct 2017 12:00:44 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Tom Zanussi <tom.zanussi@...ux.intel.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>, tglx@...utronix.de,
        mhiramat@...nel.org, vedang.patel@...el.com, bigeasy@...utronix.de,
        joel.opensrc@...il.com, joelaf@...gle.com,
        mathieu.desnoyers@...icios.com, baohong.liu@...el.com,
        rajvi.jingar@...el.com, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org, kernel-team@....com
Subject: Re: [PATCH v3 25/33] tracing: Allow whitespace to surround hist
 trigger filter

Hi Tom,

On Wed, Oct 04, 2017 at 02:05:17PM -0500, Tom Zanussi wrote:
> Hi Steve,
> 
> On Wed, 2017-10-04 at 14:11 -0400, Steven Rostedt wrote:
> > On Fri, 22 Sep 2017 15:00:05 -0500
> > Tom Zanussi <tom.zanussi@...ux.intel.com> wrote:
> > 
> > > The existing code only allows for one space before and after the 'if'
> > > specifying the filter for a hist trigger.  Add code to make that more
> > > permissive as far as whitespace goes.  Specifically, we want to allow
> > > spaces in the trigger itself now that we have additional syntax
> > > (onmatch/onmax) where spaces are more natural e.g. spaces after commas
> > > in param lists.
> > > 
> > > Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
> > > ---
> > >  kernel/trace/trace_events_hist.c | 24 +++++++++++++++++++-----
> > >  1 file changed, 19 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> > > index ba42fe2..431f2b2 100644
> > > --- a/kernel/trace/trace_events_hist.c
> > > +++ b/kernel/trace/trace_events_hist.c
> > > @@ -4857,7 +4857,7 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
> > >  	struct synth_event *se;
> > >  	const char *se_name;
> > >  	bool remove = false;
> > > -	char *trigger;
> > > +	char *trigger, *p;
> > >  	int ret = 0;
> > >  
> > >  	if (!param)
> > > @@ -4866,10 +4866,23 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
> > >  	if (glob[0] == '!')
> > >  		remove = true;
> > >  
> > > -	/* separate the trigger from the filter (k:v [if filter]) */
> > > -	trigger = strsep(&param, " \t");
> > > -	if (!trigger)
> > > -		return -EINVAL;
> > > +	/*
> > > +	 * separate the trigger from the filter (k:v [if filter])
> > > +	 * allowing for whitespace in the trigger
> > > +	 */
> > > +	trigger = param;
> > > +	p = strstr(param, " if");
> > > +	if (!p)
> > > +		p = strstr(param, "\tif");
> > > +	if (p) {
> > > +		if (p == trigger)
> > > +			return -EINVAL;
> > > +		param = p + 1;
> > > +		param = strstrip(param);
> > > +		*p = '\0';
> > > +		trigger = strstrip(trigger);
> > > +	} else
> > > +		param = NULL;
> > 
> > I think you forgot to update this:
> > 
> 
> I was going to but on closer inspection realized the simpler form
> wouldn't accomplish the same thing - the problem this is trying to solve
> is to allow bits of whitespace within the trigger (because we now have
> function-like syntax, which should allow whitespace after commas for
> instance) and separating the trigger from the filter ('if').  So we
> explicitly search for 'if' with preceding whitespace, which strsep won't
> accomplish.

What if a field name is started with 'if' (like "ifb")?  I think you
also need to check whitespace after the 'if'.

Thanks,
Namhyung