tlug: GCC compiler question

[Neil Booth <NeilB@example.com>]

I've been looking through some of the kernel source, and I keep seeing
things like the following:-

#define spin_lock_init(x)       do { (x)->lock = 0; } while(0)

What's the point of the do {} while(0) bit? Why not just

#define spin_lock_init(x)       { (x)->lock = 0; }

or even

#define spin_lock_init(x)       (x)->lock = 0;

The only point I can see is causing compile-time errors for misuse, such
as

   z += spin_lock_init(x);

which would compile under the 3rd alternative above. And who would
really write such code anyway? And why not the 2nd alternative?

Neil.
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