From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4811E8AE.1090000@domain.hid> Date: Fri, 25 Apr 2008 16:20:30 +0200 From: Philippe Gerum MIME-Version: 1.0 References: <18448.9649.956656.531081@domain.hid> <18448.9901.799115.445182@domain.hid> <18448.9967.355128.570111@domain.hid> <18448.10037.181558.14996@domain.hid> <48118CC7.4060408@domain.hid> <2ff1a98a0804250626h7104d6ddg282d35798af77cb9@domain.hid> <4811DFCB.8080107@domain.hid> <2ff1a98a0804250650s71a6448do67a55f27c6623af1@domain.hid> <4811E429.8020505@domain.hid> <2ff1a98a0804250713l5d0588a2m95f630f39426e3f3@domain.hid> In-Reply-To: <2ff1a98a0804250713l5d0588a2m95f630f39426e3f3@domain.hid> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: Philippe Gerum Subject: Re: [Xenomai-core] [3/9] Define more atomic operations in user-space Reply-To: rpm@xenomai.org List-Id: "Xenomai life and development \(bug reports, patches, discussions\)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: xenomai@xenomai.org Gilles Chanteperdrix wrote: > On Fri, Apr 25, 2008 at 4:01 PM, Philippe Gerum wrote: >> Gilles Chanteperdrix wrote: >> > On Fri, Apr 25, 2008 at 3:42 PM, Philippe Gerum wrote: >> >> Gilles Chanteperdrix wrote: >> >> > On Fri, Apr 25, 2008 at 9:48 AM, Philippe Gerum 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. >> > >> >> Ok, makes sense. Let's just fix the namespace then, so that we don't get the >> feeling of having duplicate sets of operations. > > That said, there is just enough room for replacing the atomic_t with > an atomic_long_t. So, we can make xnarch_atomic_t a long type. Have > you anything agains making an xnarch_atomic_ptr_t ? > No objection, just let us call it xnarch_atomic_intptr_t to ANSIfy this a bit more, and clearly state that we need this type to hold a pointer into an integer value, and operate atomically on it. -- Philippe.