linux-kernel - Re: [PULL] typesafe callbacks for kthread and stop

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Message-Id: <200808011039.30195.rusty@rustcorp.com.au>
Date:	Fri, 1 Aug 2008 10:39:29 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Bert Wesarg <bert.wesarg@...glemail.com>,
	Tejun Heo <htejun@...il.com>
Subject: Re: [PULL] typesafe callbacks for kthread and stop_machine

On Friday 01 August 2008 00:06:43 Andi Kleen wrote:
> On Thu, Jul 31, 2008 at 02:52:35PM +1000, Rusty Russell wrote:
> > Just the two places I look after.  And this time the conglomerate patch
> > is included below for more random commentry.
>
> I must say I personally don't like the wrapper macros that you require
> for each function that uses this. A wrapper macro has a large impact
> on code readability because everyone following a call chain has
> to do an additional grep/open file etc. step. I have my doubts not having
> casts outweights that disadvantage.

Yes, but the benefits of using them everywhere is that they do become part of 
the landscape.  "Oh, that's a typesafe callback, OK".

If this were just about neatness, I'd share your doubts.  But I want to be 
able to change the type of a var and have the compiler complain when I hand 
it to a function which expects the old type.  This bit me a few months back, 
leading to this experiment.

> I know that gcc has this funky transparent union extension that
> glibc socket() uses to allow different address types without casts.
> It has the advantage of not needing wrapper macros. Any chance of
> using that instead? Or has that one been considered already and
> discarded?

That's aimed at a slightly different case, where the function knows what types 
it can get.  But that doesn't work for truly generic callbacks: the type is 
completely controlled by the caller. ie. we want to allow whatever type 
matches the arg.

Hope that clarifies,
Rusty.
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