linux-kernel - Re: [PATCH 2/2] kernel: add support for live patching

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Date:	Fri, 7 Nov 2014 06:50:16 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Seth Jennings <sjenning@...hat.com>,
	Vojtech Pavlik <vojtech@...e.cz>,
	Steven Rostedt <rostedt@...dmis.org>,
	live-patching@...r.kernel.org, kpatch@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] kernel: add support for live patching

On Thu, Nov 06, 2014 at 11:20:48PM +0100, Jiri Kosina wrote:
> On Thu, 6 Nov 2014, Seth Jennings wrote:
> 
> > > Thanks a lot for having started the work on this!
> > > 
> > > We will be reviewing it carefully in the coming days and will getting back 
> > > to you (I was surprised to see that that diffstat indicates that it's 
> > > actually more code than our whole kgraft implementation including the 
> > > consistency model :) ).
> > 
> > The structure allocation and sysfs stuff is a lot of (mundane) code.
> > Lots of boring error path handling too.
> 
> Also, lpc_create_object(), lpc_create_func(), lpc_create_patch(), 
> lpc_create_objects(), lpc_create_funcs(), ... they all are pretty much 
> alike, and are asking for some kind of unification ... perhaps iterator 
> for generic structure initialization?

The allocation and initialization code is very simple and
straightforward.  I really don't see a problem there.

Can you give an example of what you mean by "iterator for generic
structure initialization"?

> I am not also really fully convinced that we need the patch->object->funcs 
> abstraction hierarchy (which also contributes to the structure allocation 
> being rather a spaghetti copy/paste code) ... wouldn't patch->funcs be 
> suffcient, with the "object" being made just a property of the function, 
> for example?
> 
> > Plus, I show that kernel/kgraft.c + kernel/kgraft_files.c is
> > 906+193=1099.  I'd say they are about the same size :)
> 
> Which is still seem to me to be a ratio worth thinking about improving :)

Yes, this code doesn't have a consistency model, but it does have some
other non-kGraft things like dynamic relocations, deferred module
patching, and a unified API.  There's really no point in comparing lines
of code.

-- 
Josh
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