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Date: Fri, 25 Apr 2008 09:48:23 +0200
From: Philippe Gerum <rpm@xenomai.org>
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Sender: Philippe Gerum <philippe.gerum@domain.hid>
Subject: Re: [Xenomai-core] [3/9] Define more atomic operations in user-space
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To: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
Cc: xenomai@xenomai.org

Gilles Chanteperdrix wrote:
> This patch implements the _read, _set, and _cmpxchg operations on atomic_long_t
> and atomic_ptr_t in user-space in include/asm-generic/atomic.h which should be
> included at the end of include/asm-*/atomic.h after the definition of the same
> operations for the atomic_t type and atomic64_t type on 64 bits platforms.
> 
> These operations are the basic operations used by user-space mutexes. Maybe we
> should add the xnarch_ prefix ?
>

Yes, but more generally, we should rework this to fit the existing atomic
support in include/asm-*/atomic.h, so that we don't end up with sideways to what
has been already designed to support set, get, xchg and the like, in both kernel
and userland context.

Also, unless you find a way to factor in common generic parts among per-arch
atomic ops, I don't see any upside to creating asm-generic/atomic.h, then rely
on arch-dep conditionals to fill them in.

NOTE: the current asm-*/atomic.h support in Xenomai is seldomly used (e.g.
userland only defines the xchg op IIRC), so we may change it globally to fit new
needs should not be that cumbersome.

> ---
>  Makefile.am |    2 -
>  atomic.h    |   68 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 69 insertions(+), 1 deletion(-)
> 
> Index: include/asm-generic/atomic.h
> ===================================================================
> --- include/asm-generic/atomic.h	(revision 0)
> +++ include/asm-generic/atomic.h	(revision 0)
> @@ -0,0 +1,68 @@
> +#ifndef ATOMIC_H
> +#define ATOMIC_H
> +
> +#ifndef __KERNEL__
> +#include <bits/wordsize.h>
> +#if __WORDSIZE == 64
> +typedef atomic64_t atomic_long_t;
> +
> +static inline long atomic_long_read(atomic_long_t *l)
> +{
> +        atomic64_t *v = (atomic64_t *)l;
> +
> +        return (long)atomic64_read(v);
> +}
> +
> +static inline void atomic_long_set(atomic_long_t *l, long i)
> +{
> +        atomic64_t *v = (atomic64_t *)l;
> +
> +        atomic64_set(v, i);
> +}
> +
> +#define atomic_long_cmpxchg(l, old, new) \
> +        (atomic64_cmpxchg((atomic64_t *)(l), (old), (new)))
> +
> +#else /* __WORDSIZE == 32 */
> +typedef atomic_t atomic_long_t;
> +
> +static inline long atomic_long_read(atomic_long_t *l)
> +{
> +        atomic_t *v = (atomic_t *)l;
> +
> +        return (long)atomic_read(v);
> +}
> +
> +static inline void atomic_long_set(atomic_long_t *l, long i)
> +{
> +        atomic_t *v = (atomic_t *)l;
> +
> +        atomic_set(v, i);
> +}
> +
> +#define atomic_long_cmpxchg(l, old, new) \
> +        (atomic_cmpxchg((atomic_t *)(l), (old), (new)))
> +#endif /* __WORDSIZE == 32 */
> +#endif /* __KERNEL__ */
> +
> +typedef atomic_long_t atomic_ptr_t;
> +
> +static inline void *atomic_ptr_read(atomic_ptr_t *l)
> +{
> +        atomic_long_t *v = (atomic_long_t *)l;
> +
> +        return (void *)atomic_long_read(v);
> +}
> +
> +static inline void atomic_ptr_set(atomic_ptr_t *l, void *i)
> +{
> +        atomic_long_t *v = (atomic_long_t *)l;
> +
> +        atomic_long_set(v, (long)i);
> +}
> +
> +#define atomic_ptr_cmpxchg(l, old, new) \
> +        (void *)(atomic_long_cmpxchg((atomic_long_t *)(l), \
> +                                     (long)(old), (long)(new)))
> +
> +#endif /* ATOMIC_H */
> Index: include/asm-generic/Makefile.am
> ===================================================================
> --- include/asm-generic/Makefile.am	(revision 3718)
> +++ include/asm-generic/Makefile.am	(working copy)
> @@ -1,5 +1,5 @@
>  includesubdir = $(includedir)/asm-generic
>  
> -includesub_HEADERS = arith.h features.h hal.h syscall.h system.h wrappers.h
> +includesub_HEADERS = arith.h features.h hal.h syscall.h system.h wrappers.h atomic.h
>  
>  SUBDIRS = bits
> 


-- 
Philippe.