linux-kernel - Re: [PATCH 02/27] drivers/net: fix sparse warnings: make do-while a compound statement

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Message-ID: <alpine.LFD.2.00.0812231008350.3535@localhost.localdomain>
Date:	Tue, 23 Dec 2008 10:08:50 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Krzysztof Halasa <khc@...waw.pl>
cc:	Harvey Harrison <harvey.harrison@...il.com>,
	Håkon Løvdal <hlovdal@...il.com>,
	Hannes Eder <hannes@...neseder.net>, netdev@...r.kernel.org,
	kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/27] drivers/net: fix sparse warnings: make do-while
 a compound statement

On Tue, 23 Dec 2008, Krzysztof Halasa wrote:

> Harvey Harrison <harvey.harrison@...il.com> writes:
> 
> >> There are many ways to make the code more merge friendly at a cost of
> >> readability. Hope we don't go this way.
> >
> > Linus himself added that particular warning to sparse...may want to check
> > with him the reason for it.
> 
> Once again, this is a personal thing, and a harmless one.

It's more than that. I added the check after some person who had been 
programming the kernel (and thus was supposedly fluent in C) literally 
could not parse a macro that had "do x while (y)" in it.

Why? Because it's so uncommon, and because "while (y)" on its own means 
something totally different.

So the syntactic sugar to _always_ have do-while loops have that brace is 
a way to avoid one of the rather few places where the C language has 
syntax that is very context-dependent.

Another example of this is "sizeof". The kernel universally (I hope) has 
parenthesis around the sizeof argument, even though it's clearly not 
required by the C language. 

It's a coding standard. 

And quite frankly, anybody who works on gcc has no place complaining about 
sparse coding standard warnings. They are a _hell_ of a lot better than 
some of the really crazy warnings gcc spews out with "-W". At least the 
sparse warnings you can make go away while making the code more 
understandable. Some of the -W warnings are unfixable without breaking the 
source code.

		Linus
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