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#ifndef _I386_SEMAPHORE_H #define _I386_SEMAPHORE_H #include <linux/linkage.h> #ifdef __KERNEL__ /* * SMP- and interrupt-safe semaphores.. * * (C) Copyright 1996 Linus Torvalds * * Modified 1996-12-23 by Dave Grothe <dave@gcom.com> to fix bugs in * the original code and to make semaphore waits * interruptible so that processes waiting on * semaphores can be killed. * Modified 1999-02-14 by Andrea Arcangeli, split the sched.c helper * functions in asm/sempahore-helper.h while fixing a * potential and subtle race discovered by Ulrich Schmid * in down_interruptible(). Since I started to play here I * also implemented the `trylock' semaphore operation. * 1999-07-02 Artur Skawina <skawina@geocities.com> * Optimized "0(ecx)" -> "(ecx)" (the assembler does not * do this). Changed calling sequences from push/jmp to * traditional call/ret. * Modified 2001-01-01 Andreas Franck <afranck@gmx.de> * Some hacks to ensure compatibility with recent * GCC snapshots, to avoid stack corruption when compiling * with -fomit-frame-pointer. It's not sure if this will * be fixed in GCC, as our previous implementation was a * bit dubious. * * If you would like to see an analysis of this implementation, please * ftp to gcom.com and download the file * /pub/linux/src/semaphore/semaphore-2.0.24.tar.gz. * */ #include <asm/system.h> #include <asm/atomic.h> #include <linux/wait.h> #include <linux/rwsem.h> struct semaphore { atomic_t count; int sleepers; wait_queue_head_t wait; }; #define __SEMAPHORE_INITIALIZER(name, n) \ { \ .count = ATOMIC_INIT(n), \ .sleepers = 0, \ .wait = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \ } #define __DECLARE_SEMAPHORE_GENERIC(name,count) \ struct semaphore name = __SEMAPHORE_INITIALIZER(name,count) #define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name,1) #define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name,0) static inline void sema_init (struct semaphore *sem, int val) { /* * *sem = (struct semaphore)__SEMAPHORE_INITIALIZER((*sem),val); * * i'd rather use the more flexible initialization above, but sadly * GCC 2.7.2.3 emits a bogus warning. EGCS doesn't. Oh well. */ atomic_set(&sem->count, val); sem->sleepers = 0; init_waitqueue_head(&sem->wait); } static inline void init_MUTEX (struct semaphore *sem) { sema_init(sem, 1); } static inline void init_MUTEX_LOCKED (struct semaphore *sem) { sema_init(sem, 0); } fastcall void __down_failed(void /* special register calling convention */); fastcall int __down_failed_interruptible(void /* params in registers */); fastcall int __down_failed_trylock(void /* params in registers */); fastcall void __up_wakeup(void /* special register calling convention */); /* * This is ugly, but we want the default case to fall through. * "__down_failed" is a special asm handler that calls the C * routine that actually waits. See arch/i386/kernel/semaphore.c */ static inline void down(struct semaphore * sem) { might_sleep(); __asm__ __volatile__( "# atomic down operation\n\t" LOCK "decl %0\n\t" /* --sem->count */ "js 2f\n" "1:\n" LOCK_SECTION_START("") "2:\tlea %0,%%eax\n\t" "call __down_failed\n\t" "jmp 1b\n" LOCK_SECTION_END :"=m" (sem->count) : :"memory","ax"); } /* * Interruptible try to acquire a semaphore. If we obtained * it, return zero. If we were interrupted, returns -EINTR */ static inline int down_interruptible(struct semaphore * sem) { int result; might_sleep(); __asm__ __volatile__( "# atomic interruptible down operation\n\t" LOCK "decl %1\n\t" /* --sem->count */ "js 2f\n\t" "xorl %0,%0\n" "1:\n" LOCK_SECTION_START("") "2:\tlea %1,%%eax\n\t" "call __down_failed_interruptible\n\t" "jmp 1b\n" LOCK_SECTION_END :"=a" (result), "=m" (sem->count) : :"memory"); return result; } /* * Non-blockingly attempt to down() a semaphore. * Returns zero if we acquired it */ static inline int down_trylock(struct semaphore * sem) { int result; __asm__ __volatile__( "# atomic interruptible down operation\n\t" LOCK "decl %1\n\t" /* --sem->count */ "js 2f\n\t" "xorl %0,%0\n" "1:\n" LOCK_SECTION_START("") "2:\tlea %1,%%eax\n\t" "call __down_failed_trylock\n\t" "jmp 1b\n" LOCK_SECTION_END :"=a" (result), "=m" (sem->count) : :"memory"); return result; } /* * Note! This is subtle. We jump to wake people up only if * the semaphore was negative (== somebody was waiting on it). * The default case (no contention) will result in NO * jumps for both down() and up(). */ static inline void up(struct semaphore * sem) { __asm__ __volatile__( "# atomic up operation\n\t" LOCK "incl %0\n\t" /* ++sem->count */ "jle 2f\n" "1:\n" LOCK_SECTION_START("") "2:\tlea %0,%%eax\n\t" "call __up_wakeup\n\t" "jmp 1b\n" LOCK_SECTION_END ".subsection 0\n" :"=m" (sem->count) : :"memory","ax"); } #endif #endif