Re: Slab: Remove kmem_cache_t

[Nick Piggin <nickpiggin@yahoo.com.au>]

Linus Torvalds wrote:
> 
> 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.

Ah true, but in this case it is not. In this case it is just being done
so some places that declare a struct kmem_cache * do not have to include
slab.h. Which doesn't seem like a good idea to me, but...

> 
> 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"

Or in this case "(d) include the correct header file when you use the type",
is pretty close as well.

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