linux-kernel - Re: [patch 11/11] ftrace plugin for kernel symbol tracing using HW Breakpoint interfaces

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Message-ID: <20090305121929.GB25213@in.ibm.com>
Date:	Thu, 5 Mar 2009 17:49:29 +0530
From:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	mingo@...e.hu, Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Roland McGrath <roland@...hat.com>
Subject: Re: [patch 11/11] ftrace plugin for kernel symbol tracing using HW
	Breakpoint interfaces

On Thu, Mar 05, 2009 at 05:03:59PM +0530, K.Prasad wrote:
> On Thu, Mar 05, 2009 at 07:37:04AM +0100, Frederic Weisbecker wrote:
> > On Thu, Mar 05, 2009 at 10:13:33AM +0530, prasad@...ux.vnet.ibm.com wrote:
> > > This patch adds an ftrace plugin to detect and profile memory access over
> > > kernel variables. It uses HW Breakpoint interfaces to 'watch memory
> > > addresses.
> > > 
> > > Signed-off-by: K.Prasad <prasad@...ux.vnet.ibm.com> 
> > > ---
> > 
> > 
> > > +
> > > +		ret = process_new_ksym_entry(entry, ksymname, op, ksym_addr);
> > 
> > 
> > You are passing an allocated entry as a parameter, but later on process_new_ksym_entry()
> > you allocate a new space for entry.
> > I'm confused.
> > 
> >
> 
> When changed = 1, entry points to the existing instance of 'struct
> trace_ksym' and will be used for changing the type of breakpoint. If the
> input is a new request to ksym_trace_filter file process_new_ksym_entry()
> takes a pointer to 'struct trace_ksym' i.e entry for
> allocation/initialisation rather than use it as a parameter in the true
> sense.
> 
> This is similar to the usage of parameters 'ksymname and addr' in
> parse_ksym_trace_str() where they are used to return multiple values.
> 
> I hope you find the usage acceptable.
>

aah....but entry isn't used anywhere anywhere in
ksym_trace_filter_write() after process_new_ksym_entry(). I was trying
to explain why I used entry as a parameter to let
process_new_ksym_entry() return multiple values, but it isn't used after
that. I will remove it, and thanks for pointing it.

-- K.Prasad

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