Re: [Xen-devel] Suggested changes to xen/include from recent Linux

[Hollis Blanchard <hollisb@xxxxxxxxxx>]

On Sat, 2005-04-09 at 13:42 -0700, Magenheimer, Dan (HP Labs Fort
Collins) wrote:
> As I mentioned at the xummit (spelling intended :-), a
> Xen/ia64 contributor from SGI (Greg Edwards) is updating
> the Xen/ia64 Linux dependencies from 2.6.7 to 2.6.11.
> This is now working, but he identified a couple places
> where it would make sense to modify common (include/xen)
> files.  So, rather than just "fix" them in ia64-specific
> files, I thought I would publish them for comment and to
> see if they might/should go into include/xen:

I agree, there should be a minimum of "fixing" generic code in
arch-specific files.

> 1) In include/xen/spinlock.h:
> 
> Linux has started using the following define:
> 
> #define DEFINE_SPINLOCK(x) spinlock_t x = SPIN_LOCK_UNLOCKED
> 
> I see that the construct could be used throughout xen/arch/x86
> as well... indeed there are TWO C files where a similar macro
> is defined but called DECLARE_MUTEX.
> 
> I propose adding the macro.

In general I don't see the need to cling to Linux code, but I can see
how your copy-and-patch scheme makes you more sensitive to this.

I don't see the harm in this particular case.

> 2) In include/xen/types.h:
> 
> Starting in 2.6.9, there are some new type-checking attributes and
> the following lines have been added to include/linux/types.h.  There's
> some explanation of it here:
> 
> http://kerneltrap.org/node/3848  (search for __bitwise)
> 
> Since Jimi mentioned a need for bi-endian support in Xen/ppc, I thought
> these might be added eventually anyway, so they could be added now
> to include/xen/type.s.

Apparently this was actually a statement about x86-64. LE support on PPC
is a second-class citizen, and current rumors aside I think only WinNT
has used it.

> I propose adding the lines (possibly including the comment verbatim?)
> 
> /*
>  * Below are truly Linux-specific types that should never collide with
>  * any application/library that wants linux/types.h.
>  */
> 
> #ifdef __CHECKER__
> #define __bitwise __attribute__((bitwise))
> #else
> #define __bitwise
> #endif
> 
> typedef __u16 __bitwise __le16;
> typedef __u16 __bitwise __be16;
> typedef __u32 __bitwise __le32;
> typedef __u32 __bitwise __be32;
> #if defined(__GNUC__) && !defined(__STRICT_ANSI__)
> typedef __u64 __bitwise __le64;
> typedef __u64 __bitwise __be64;
> #endif

Maybe this could be added along with the first users of these types?

-- 
Hollis Blanchard
IBM Linux Technology Center


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