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

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Message-ID: <alpine.LNX.2.00.1411071405170.29198@pobox.suse.cz>
Date:	Fri, 7 Nov 2014 14:13:37 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
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 Fri, 7 Nov 2014, Josh Poimboeuf wrote:

> > 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.

This really boils down to the question I had in previous mail, whether 
three-level hierarchy (patch->object->funcs), which is why there is a lot 
of very alike initialization code, is not a bit over-designed.

> > 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, 

BTW we need to put those into arch/x86/ as they are unfortunately not 
generic. But more on this later independently.

> deferred module patching,

FWIW kgraft supports that as well.

> and a unified API.  There's really no point in comparing lines of code.

Oh, sure, I didn't mean that this is any kind of metrics that should be 
taken too seriously at all. I was just expressing my surprise that 
unification of the API would bring so much code that it makes the result 
comparably sized to "the whole thing" :)

Thanks,

-- 
Jiri Kosina
SUSE Labs
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