On Fri, Apr 25, 2008 at 3:42 PM, Philippe Gerum <[EMAIL PROTECTED]> wrote:
>
> Gilles Chanteperdrix wrote:
>  > On Fri, Apr 25, 2008 at 9:48 AM, Philippe Gerum <[EMAIL PROTECTED]> wrote:
>  >> 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.
>  >
>  > That is not exactly sideways... Linux include/asm-generic/atomic.h
>  > defines operations for atomic_long_t. This file adds two things:
>  > - support for atomic_long_t in user-space (where we can not include
>  > linux include/asm-generic/atomic.h)
>  > - support for a new type atomic_ptr_t both to kernel-space and
>  > user-space, the aim is to avoid all the casts that would take place if
>  > we wanted to use atomic_long_t to store pointers.
>  >
>  > However for this file to work, it has to be included by asm-*/atomic.h
>  > after the definition of atomic_t (and atomic64_t on 64 bits
>  > platforms). So linux includes asm-generic/atomic.h at the end of
>  > asm/atomic.h, I simply reproduced this scheme with Xenomai
>  > include/asm-*/atomic.h.
>  >
>
>  Focusing on user-space: 1) xnarch_atomic_xchg is meant to work on long 
> types; 2)
>  set, get routines are not defined in that scope. If the purpose is to define
>  integer-type ops to handle pointer-type data atomically (i.e. intptr_t), 
> then I
>  would rather check whether we actually need non-long support at all in
>  user-space. In case we don't, I would simply reply on the existing
>  implementation of asm-*/atomic.h + the set / get extensions you provide.

I use both atomic_t and atomic_ptr_t for the implementation of
user-space mutexes. The problem is that I am constrained by the size
of pthread_mutex_t, so the "control block read-write locks"
implementation use atomic_t.

-- 
 Gilles

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