Re: Slab: Remove kmem_cache_t

[Linus Torvalds <torvalds@osdl.org>]

On Wed, 29 Nov 2006, Nick Piggin wrote:
> 
> Oh so it isn't a dependency problem, or one that prevents a cleaner
> slab bootstrapping process...

No, it really _can_ be a dependency issue.

A typedef really can only be done once. Which means that either you need 
to

 (a) avoid them (easy, clean, and simple - especially if the typedef 
     doesn't actually _buy_ you anything)

 (b) have more complicated header file structure and dependencies (for 
     example, you could have one special header that defines _just_ the 
     basic types, and have everybody include that)

 (c) declare it in multiple places, and use special markers that it's been 
     declared (see a lot of the standard header files in /usr/include for 
     thigns like this):

		#ifndef __HAVE_DECLARED_KMEM_CACHE_T
		#define __HAVE_DECLARED_KMEM_CACHE_T
		typedef struct kmem_cache kmem_cache_t
		#endif

and of the three choices, pick the simplest, cleanest, and least likely 
to cause confusion.

Hint: the winner is: "(a) don't use typedefs"

			Linus

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