linux-kernel - Re: [PATCH] tracing/filters: allow event filters to be set only when not tracing

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Message-Id: <1238653371.6655.48.camel@bookworm>
Date:	Thu, 02 Apr 2009 01:22:51 -0500
From:	Tom Zanussi <tzanussi@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>, fweisbec@...il.com
Subject: Re: [PATCH] tracing/filters: allow event filters to be set only
 when not tracing

On Wed, 2009-04-01 at 14:24 +0200, Ingo Molnar wrote:
> * Tom Zanussi <tzanussi@...il.com> wrote:
> 
> > This patch adds code allowing the event filter to be set only if 
> > there's no active tracing going on.
> 
> > --- a/kernel/trace/trace_events.c
> > +++ b/kernel/trace/trace_events.c
> > @@ -498,6 +498,9 @@ event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt,
> >  	struct filter_pred *pred;
> >  	int err;
> >  
> > +	if (tracing_is_enabled() && (!tracer_is_nop() || call->enabled))
> > +		return -EBUSY;
> 
> hm, but it would be the normal use-case to set filters on the fly. 
> To experiment around with them and shape them until the output is 
> just right. Having to turn the tracer on/off during that seems quite 
> counterproductive to that use-case.
> 

I didn't see anything that could be used to temporarily disable tracing
(tracing_stop() and tracing_start() are 'quick' versions that mostly
just disable recording), so did it this way to avoid adding any overhead
to the filter-checking code.

But anyway, I'll post a new patch shortly that uses rcu and does allow
the filters to be set on the fly.

Tom

> 	Ingo

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