linux-kernel - Re: [Patch 2/3] ksym_tracer: Allow bulk removal using empty or wildcard string input

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Message-ID: <20090620133752.GA20214@in.ibm.com>
Date:	Sat, 20 Jun 2009 19:07:52 +0530
From:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Patch 2/3] ksym_tracer: Allow bulk removal using empty or
	wildcard string input

On Sat, Jun 20, 2009 at 01:16:41AM +0200, Frederic Weisbecker wrote:
> On Fri, Jun 19, 2009 at 10:55:12PM +0530, K.Prasad wrote:
> > Accept an empty string or wildcard input (of the form *:---) as input for
> > ksym_trace_filter to perform bulk removal of all monitored entries.
> >
> > Signed-off-by: K.Prasad <prasad@...ux.vnet.ibm.com>
> > ---
> >  kernel/trace/trace_ksym.c |   75 +++++++++++++++++++++++++---------------------
> >  1 file changed, 42 insertions(+), 33 deletions(-)
> > 
<snipped>
> >  /*
> >   * There can be several possible malformed requests and we attempt to capture
> >   * all of them. We enumerate some of the rules
> > @@ -163,7 +191,7 @@ static int parse_ksym_trace_str(char *in
> >  	/* Check for malformed request: (2), (1) and (5) */
> >  	if ((!input_string) ||
> >  		(strlen(input_string) != (KSYM_TRACER_OP_LEN + 1)) ||
> > -			(*addr == 0))
> > +			((*addr == 0) && strncmp(*ksymname, "*", strlen("*"))))
> 
> 
> I guess you can just use strcmp() here, no? As in other use
> of this same strncmp() in this patch.
> 

I see both functions being used in the kernel at random (what happened
to all the buffer-overflow scare?)! Isn't an strncmp() preferred over
the plain strcmp() (atleast it cannot be the other way round)?

> > @@ -251,9 +280,11 @@ static ssize_t ksym_trace_filter_write(s
> >  	unsigned long ksym_addr = 0;
> >  	int ret, op, changed = 0;
> >  
> > -	/* Ignore echo "" > ksym_trace_filter */
> > -	if (count == 0)
> > -		return 0;
> > +	/* Clear all breakpoint requests if echo "" > ksym_trace_filter */
> > +	if (count == 1) {
> > +		ksym_trace_reset(NULL);
> > +		return count;
> > +	}
> 
> 
> And then if I do:
> 
> echo -n 1 > ksym_trace_filter
> 
> That would also clean these breakpoints?
> 
> Frederic.
>

No, I did not think about this scenario and I am changing the patch to
handle such a case. Also, the value of 'count' cannot be '0' as such
inputs are ignored (e.g. echo -n "" > ksym_trace_filter is simply
ignored) and so I'm removing the check for the same.

Please find a new version of the patch sent here:
http://lkml.org/lkml/2009/6/20/73.

Thanks,
K.Prasad

 
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