Subject: Re: [PATCH][RFC] kprobes: Add user entry-handler in kretprobes
From: Jim Keniston <jkenisto@us.ibm.com>
To: Abhishek Sagar <sagar.abhishek@gmail.com>
Cc: Srinivasa Ds <srinivasa@in.ibm.com>, linux-kernel@vger.kernel.org,
       prasanna@in.ibm.com, davem@davemloft.net,
       anil.s.keshavamurthy@intel.com,
       Ananth N Mavinakayanahalli <ananth@in.ibm.com>
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Date: Thu, 15 Nov 2007 16:07:24 -0800
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On Thu, 2007-11-15 at 20:30 +0530, Abhishek Sagar wrote:
> On Nov 15, 2007 4:21 AM, Jim Keniston <jkenisto@us.ibm.com> wrote:
> > 2. Simplify the task of correlating data (e.g., timestamps) between
> > function entry and function return.
> 
> Would adding of data and len fields in ri help? Instead of "pouching"
> data in one go at registration time, this would let user handlers do
> the allocation

Yes and no.  Adding just a data field -- void*, or maybe unsigned long
long so it's big enought to accommodate big timestamps -- would be a big
improvement on your current proposal.  That would save the user the
drudgery of mapping the ri pointer to his/her per-instance data.
There's plenty of precedent for passing "private_data" values to
callbacks.

I don't think a len field would help much.  If such info were needed, it
could be stored in the data structure pointed to by the data field.

I still don't think "letting [i.e., requiring that] user handlers do the
allocation" is a win.  I'm still interested to see how this plays out in
real examples.

> and allow them to use different kinds of data
> structures per-instance.

I haven't been able to think of any scenarios where this would be
useful.  A "data pouch" could always contain a union, FWIW.

> 
> - Abhishek Sagar 

Jim


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