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

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Date:	Thu, 5 Mar 2009 13:30:28 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	"K.Prasad" <prasad@...ux.vnet.ibm.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 05:49:29PM +0530, K.Prasad wrote:
> 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
> 

Ah, I thought I misunderstood something :-)

Thanks.

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