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

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Date:	Wed, 1 Apr 2009 14:24:08 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Tom Zanussi <tzanussi@...il.com>
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


* 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.

	Ingo
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