Re: [PATCH 1/3] kernel.h: Add DO_ONCE statement expression macro

From: Rusty Russell
Date: Mon May 25 2009 - 06:28:43 EST

On Fri, 22 May 2009 08:30:22 am Joe Perches wrote:
> Add a DO_ONCE statement expression analogous to printk_once
> that executes any arbitrary statement exactly once.
> This will take the place of printk_once so that
> DO_ONCE(pr_<foo>) or any other statement performed
> a single time may be easily written.

If you're going to use a statement expression, was the intent to make
it usable for a test? If so, you want something vaguely like:

#define DO_ONCE(x...) ({ \
static bool __done = false; \
bool did = !__done; \
if (!__done) { \
x; \
__done = true; \
} \
did; \

Otherwise, why not just use a normal do {} while (0) ?

Anyway, statements in macros leave me uncomfortable. I prefer explicit
ONCE() macro which can be tested.

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