linux-kernel - Re: [PATCH 3/3] tracing/ksym_tracer: support quick clear for ksym_trace

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Message-ID: <20090722151759.GA11367@in.ibm.com>
Date:	Wed, 22 Jul 2009 20:47:59 +0530
From:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] tracing/ksym_tracer: support quick clear for
	ksym_trace_filter

On Wed, Jul 22, 2009 at 05:56:49PM +0800, Xiao Guangrong wrote:
> 
> 
> K.Prasad wrote:
> > On Wed, Jul 22, 2009 at 11:25:14AM +0800, Xiao Guangrong wrote:
> >> It's rather bored to clear symbol one by one in ksym_trace_filter
> >> file, so, this patch can let ksym_trace_filter file support quick
> >> clear, we can write "0" to this file, it can clear all symbols
> >>
> >> for example:
> >>  # cat ksym_trace_filter
> >>  ksym_filter_head:rw-
> >>  global_trace:rw-
> >>  # echo 0 > ksym_trace_filter
> >>  # cat ksym_trace_filter
> >>  #
> >>
> > 
> > It's nice to have this feature added and the other patches fix issues in
> > ksym tracer. Can you have this patch add the capability to clear all
> > breakpoints in one-shot through wild-cards?
> > 
> 
> It already can clear all breakpoints in one-shot by write "0" to
> ksym_trace_filter file, do you means that we need to support other
> way for it? like:
> 
> echo > ksym_trace_filter
> echo "*:---" > ksym_trace_filter
> 
> IMHO, one way to clear all breakpoints is enough, no need to add
> more code for the same function, for example, in trace events filter,
> only echo 0 > filter can properly clear all filters.
> 
> Are you sure other way is necessary? 
> 
> Thanks,
> Xiao
>

As I stated before, the ability to support
echo "*:---" > ksym_trace_filter was Ingo Molnar's suggestion, so if
he's not particular about having it now we may skip it.

However, given that it requires just a few lines of code in addition,
say

+	/* Clear all breakpoints if echo "*:---" > ksym_trace_filter */
+	if ((strncmp(ksymname, "*", strlen("*")) == 0) && (op == 0)) {
+		ksym_trace_reset(NULL);
+		kfree(input_string);
+		return count;
+	}

in ksym_trace_filter_write(), and that the patch is already present it
shouldn't be bothersome to add it.

Thanks,
K.Prasad

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