linux-kernel - Re: [RFC] timers, pointers to functions and type safety

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Date:	Sat, 02 Dec 2006 15:45:12 +0100
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Al Viro <viro@....linux.org.uk>
Cc:	Linus Torvalds <torvalds@...l.org>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] timers, pointers to functions and type safety

On Sat, 2006-12-02 at 14:05 +0000, Al Viro wrote:
> On Sat, Dec 02, 2006 at 01:59:30PM +0100, Thomas Gleixner wrote:
> > On Fri, 2006-12-01 at 17:21 +0000, Al Viro wrote:
> > > Now, there's another question: how do we get there?  Or, at least, from
> > > current void (*)(unsigned long) to void (*)(void *)...
> > 
> > I think the real solution should be 
> > 
> > 	void (*function)(struct timer_list *timer);
> > 
> > and hand the timer itself to the callback. Most of the timers are
> > embedded into data structures anyway and for the rest we can easily
> > build one.
> 
> Ewwwwwww....
> 
> Let's not.  It means more cruft in callbacks for no good reason.

What's the cruft ? 

struct bla = container_of(timer, struct bla, timer); ???

> And more cruft in code setting it up, while we are at it.

Err, you remove the timer->data = (unsigned long) hackery. Why is this
adding cruft ?

I looked deeper into it. We have following timer usage:

- timers which don't use data at all - no change except for the callback
argument of the function.

- timers which point to the data structure which embedds them - only the
callback has to get a container_of()

- static single instance timers, which use .data as local storage for
some value. That can be done with a simple static variable near the
timer and using that variable instead of .data

- some rather seldom multi instance timers, which need then to become a
data structure.

> > > "A fscking huge patch flipping everything at once" is obviously not an
> > > answer; too much PITA merging and impossible to review.
> > 
> > There are ~ 500 files affected and this is in the range of cleanups we
> > did recently at the end of the merge window already. I'd volunteer to
> > hack this up and keep the patch up to date until the final merge. I have
> > done that before and I'm not scared about it. The patches are a couple
> > of lines per file and I do not agree that this is impossible to review. 
> 
> I'd rather see that as patch series, TYVM.  And no, it won't be a couple
> of lines per file with your variant.

It will. Just some random files:

 arch/alpha/kernel/srmcons.c             |    7 +++--
 arch/arm/mach-pxa/lubbock.c             |    7 +++--
 arch/i386/kernel/tsc.c                  |    2 -
 arch/i386/mach-voyager/voyager_thread.c |    2 -
 arch/ia64/kernel/mca.c                  |    8 +++---
 arch/ia64/kernel/salinfo.c              |    2 -
 arch/ia64/sn/kernel/mca.c               |    2 -
 arch/ia64/sn/kernel/xpc_channel.c       |    3 --
 arch/ia64/sn/kernel/xpc_main.c          |    5 +++-
 arch/mips/lasat/picvue_proc.c           |    2 -
 arch/mips/sgi-ip22/ip22-reset.c         |   17 +++++++------
 include/asm-ia64/sn/xpc.h               |    2 -

> Anyway, I'm doing that series in my tree, will post when it's over...

Same here :)

	tglx


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