Xen devel - Apr 2005 - Suggested changes to xen/include from recent Linux

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:

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.

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.

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

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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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