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Date: Fri, 1 Jan 2010 00:18:04 +0530
From: "K.Prasad" <prasad@linux.vnet.ibm.com>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       "mingo@elte.hu" <mingo@elte.hu>, Peter Zijlstra <peterz@infradead.org>
Subject: Re: [Patch 1/1] Introduce register_user_hbp_by_pid() and
	unregister_user_hbp_by_pid()
Message-ID: <20091231184804.GA3676@in.ibm.com>
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On Wed, Dec 30, 2009 at 11:28:39PM +0100, Frederic Weisbecker wrote:
> On Tue, Dec 22, 2009 at 12:16:31AM +0530, K.Prasad wrote:
> > On Fri, Dec 18, 2009 at 09:47:48PM +0100, Frederic Weisbecker wrote:
> 
> > > And this function needs rcu too.
> > > 
> > > I don't see any in-kernel user for this new feature.
> > > That would be required to integrate it.
> > >
> > 
> > The proposed interfaces, as obvious, are mere wrappers over existing
> > (un)register_user_* interfaces, and don't do anything vastly different
> > in order to demonstrate them separately.
> > 
> > I can get a sample kernel module ready - that consumes pid and user-space
> > address to track write accesses, if you prefer it.
> 
> 
> Ok. The code looks good and useful.
> 
> But the usual philosophy in the kernel is to not add code
> that is left unused upstream. And samples don't substitute a user.
> I'm not sure this is a good idea to merge this.
>

Back to the old trick!...How about an ftrace plugin that accepts pid,
user-space address and memory access type and traces all the IP
addresses that caused access?

echo <pid>:<user_addr><access_type>  >  usym_trace_filter
echo 567:0x1234567:rw- > usym_trace_filter

Breakpoint	IP
------------	---------
567:0x1234567	0x0abcdef

I'm unsure if it sounds interesting at all, but I suspect it wouldn't be
as easy as above to gather the shown information through any existing
tools.

Thanks,
K.Prasad

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