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

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Message-ID: <20061202224018.GO3078@ftp.linux.org.uk>
Date:	Sat, 2 Dec 2006 22:40:18 +0000
From:	Al Viro <viro@....linux.org.uk>
To:	Roman Zippel <zippel@...ux-m68k.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Matthew Wilcox <matthew@....cx>,
	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, Dec 02, 2006 at 11:13:21PM +0100, Roman Zippel wrote:
> Hi,
> 
> On Sat, 2 Dec 2006, Al Viro wrote:
> 
> > > You need some more magic macros to access/modify the data field.
> > 
> > Which is done bloody rarely.  grep and you'll see...  BTW, there are
> > other reasons why passing struct timer_list * is wrong:
> > 	* direct calls of the timer callback
> 
> Why should that be wrong?

Need to arrange a struct timer_list?

> > 	* callback being the same for two timers embedded into
> > different structs
> 
> That's done bloody rarely as well.
> 
> > 	* see a timer callback, decide it looks better as a tasklet.
> > What, need a different glue now?
> 
> What's wrong with changing the prototype? If you don't do it, the compiler 
> will complain about it anyway.

How about "not having to change it at all"?
 
> > Look, it's a delayed call.  The less glue we need, the better - the
> > rules are much simpler that way, so that alone means that we'll get
> > fewer fsckups.
> 
> You have the glue in a different place, so what?

Where?

> The other alternative has real _practical_ value in almost every case, 
> which I very much prefer. What's wrong with that?

Lack of any type safety whatsoever, magic boilerplates in callback instances,
rules more complex than "your callback should take a pointer, don't cast
anything, it's just a way to arrange for a delayed call, nothing magical
needed"?
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