linux-kernel - Re: [PATCH V2 0/3] Introduce and use DO

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Date:	Fri, 22 May 2009 09:44:49 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Joe Perches <joe@...ches.com>, linux-kernel@...r.kernel.org,
	cpufreq@...r.kernel.org, Dave Jones <davej@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	x86@...nel.org, Len Brown <len.brown@...el.com>,
	Mike Travis <travis@....com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH V2 0/3] Introduce and use DO_ONCE statement expression
	macro

* Al Viro <viro@...IV.linux.org.uk> wrote:

> On Thu, May 21, 2009 at 10:39:16PM -0700, Joe Perches wrote:
> > On Fri, 2009-05-22 at 06:26 +0100, Al Viro wrote:
> > > Your DO_ONCE(....) parses as "what the fuck is that?" followed by
> > > grepping for definition, and the cost is much higher.
> > 
> > So what do you suggest?
> > 
> > #define pr_info_once(fmt, args...)	printk_once(KERN_INFO pr_fmt(fmt), ##args)
> > #define pr_warning_once(fmt, args...)	printk_once(KERN_WARNING pr_fmt(fmt), ##args)
> > etc
> 
> That would be much saner.

Agreed.

The *_once() namespace meme is intuitive and easily understood, and 
we use it in a couple of places in the kernel and extend it on an 
as-needed basis for reoccuring (and boring and distracting) 
once-flag C code spam. We apply it to 'boring to begin with' 
constructs: printing a message or a warning, etc. So if a kernel 
coder sees a _once() or _ONCE() construct it can be assumed almost 
straight away that the code there is largely uninteresting from a 
code logic POV.

DO_ONCE() on the other hand is non-intuitive as it is a control 
structure that can be applied to _any_ code construct - interesting 
and uninteresting alike. For anything truly interesting that is not 
a kernel library/facility i dont want it to be hidden and abstracted 
away in 98% of the cases, i want to see the raw C form of it.

Otherwise we might as well write the kernel in C++.

	Ingo
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