Re: [PATCH] ARCH_HAS_IRQ_PER_CPU avoids dead code in __do_IRQ()

[Ingo Oeser <ioe-lkml@rameria.de>]

Hi Karsten,

On Sunday 07 August 2005 12:25, Karsten Wiese wrote:
> With my proposal the
> 	#if defined(ARCH_HAS_IRQ_PER_CPU)
> 	....
> 	#endif
> lets readers of __do_IRQ() immediately grasp:
>  "this block might not be compiled / depends an ARCH"
> And you'll get compile error's using IRQ_PER_CPU on ie i386,
> letting you immediately know,
> that you've got to change something to be able to use IRQ_PER_CPU.
> 
> That are advantages I think.

That's a valid argument. But an if is an if for the reader.
It is a conditional he has to be aware of and it usally has
no idention, if it is just inside "#if" instead of "if ()".

I have seen people seen missing "#if 0" [1] around code while 
reading it. Missing an normal if () is harder with proper idention.

A normal conditional has also the advantage, that the compiler
checks the code for syntactic and some semantic errors within it.

In an "#if 0" you can basically write any plain text[2] and any error
will go undetected, until it becomes an "#if 1".

Since your define is true for most compilations out there,
this argument is not very strong.

Last argument: Many kernel developers -- including Linus -- 
don't like "#if" in C files and prefer them in headers. 
Their reasons might be similiar to my own.


Regards

Ingo Oeser

[1] Let's just consider the values of the pre-processor symbols here, ok?
[2] Pavel Machek used this already to combine Makefile and C file :-)

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