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1#ifndef _I386_SEMAPHORE_H
2#define _I386_SEMAPHORE_H
3
4#include <linux/linkage.h>
5
6#ifdef __KERNEL__
7
8/*
9 * SMP- and interrupt-safe semaphores..
10 *
11 * (C) Copyright 1996 Linus Torvalds
12 *
13 * Modified 1996-12-23 by Dave Grothe <dave@gcom.com> to fix bugs in
14 * the original code and to make semaphore waits
15 * interruptible so that processes waiting on
16 * semaphores can be killed.
17 * Modified 1999-02-14 by Andrea Arcangeli, split the sched.c helper
18 * functions in asm/sempahore-helper.h while fixing a
19 * potential and subtle race discovered by Ulrich Schmid
20 * in down_interruptible(). Since I started to play here I
21 * also implemented the `trylock' semaphore operation.
22 * 1999-07-02 Artur Skawina <skawina@geocities.com>
23 * Optimized "0(ecx)" -> "(ecx)" (the assembler does not
24 * do this). Changed calling sequences from push/jmp to
25 * traditional call/ret.
26 * Modified 2001-01-01 Andreas Franck <afranck@gmx.de>
27 * Some hacks to ensure compatibility with recent
28 * GCC snapshots, to avoid stack corruption when compiling
29 * with -fomit-frame-pointer. It's not sure if this will
30 * be fixed in GCC, as our previous implementation was a
31 * bit dubious.
32 *
33 * If you would like to see an analysis of this implementation, please
34 * ftp to gcom.com and download the file
35 * /pub/linux/src/semaphore/semaphore-2.0.24.tar.gz.
36 *
37 */
38
39#include <asm/system.h>
40#include <asm/atomic.h>
41#include <linux/wait.h>
42#include <linux/rwsem.h>
43
44struct semaphore {
45 atomic_t count;
46 int sleepers;
47 wait_queue_head_t wait;
48};
49
50
51#define __SEMAPHORE_INITIALIZER(name, n) \
52{ \
53 .count = ATOMIC_INIT(n), \
54 .sleepers = 0, \
55 .wait = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
56}
57
58#define __DECLARE_SEMAPHORE_GENERIC(name,count) \
59 struct semaphore name = __SEMAPHORE_INITIALIZER(name,count)
60
61#define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name,1)
62
63static inline void sema_init (struct semaphore *sem, int val)
64{
65/*
66 * *sem = (struct semaphore)__SEMAPHORE_INITIALIZER((*sem),val);
67 *
68 * i'd rather use the more flexible initialization above, but sadly
69 * GCC 2.7.2.3 emits a bogus warning. EGCS doesn't. Oh well.
70 */
71 atomic_set(&sem->count, val);
72 sem->sleepers = 0;
73 init_waitqueue_head(&sem->wait);
74}
75
76static inline void init_MUTEX (struct semaphore *sem)
77{
78 sema_init(sem, 1);
79}
80
81static inline void init_MUTEX_LOCKED (struct semaphore *sem)
82{
83 sema_init(sem, 0);
84}
85
86extern asmregparm void __down_failed(atomic_t *count_ptr);
87extern asmregparm int __down_failed_interruptible(atomic_t *count_ptr);
88extern asmregparm int __down_failed_trylock(atomic_t *count_ptr);
89extern asmregparm void __up_wakeup(atomic_t *count_ptr);
90
91/*
92 * This is ugly, but we want the default case to fall through.
93 * "__down_failed" is a special asm handler that calls the C
94 * routine that actually waits. See arch/i386/kernel/semaphore.c
95 */
96static inline void down(struct semaphore * sem)
97{
98 might_sleep();
99 __asm__ __volatile__(
100 "# atomic down operation\n\t"
101 LOCK_PREFIX "decl %0\n\t" /* --sem->count */
102 "jns 2f\n"
103 "\tlea %0,%%eax\n\t"
104 "call __down_failed\n"
105 "2:"
106 :"+m" (sem->count)
107 :
108 :"memory","ax");
109}
110
111/*
112 * Interruptible try to acquire a semaphore. If we obtained
113 * it, return zero. If we were interrupted, returns -EINTR
114 */
115static inline int down_interruptible(struct semaphore * sem)
116{
117 int result;
118
119 might_sleep();
120 __asm__ __volatile__(
121 "# atomic interruptible down operation\n\t"
122 "xorl %0,%0\n\t"
123 LOCK_PREFIX "decl %1\n\t" /* --sem->count */
124 "jns 2f\n\t"
125 "lea %1,%%eax\n\t"
126 "call __down_failed_interruptible\n"
127 "2:"
128 :"=&a" (result), "+m" (sem->count)
129 :
130 :"memory");
131 return result;
132}
133
134/*
135 * Non-blockingly attempt to down() a semaphore.
136 * Returns zero if we acquired it
137 */
138static inline int down_trylock(struct semaphore * sem)
139{
140 int result;
141
142 __asm__ __volatile__(
143 "# atomic interruptible down operation\n\t"
144 "xorl %0,%0\n\t"
145 LOCK_PREFIX "decl %1\n\t" /* --sem->count */
146 "jns 2f\n\t"
147 "lea %1,%%eax\n\t"
148 "call __down_failed_trylock\n\t"
149 "2:\n"
150 :"=&a" (result), "+m" (sem->count)
151 :
152 :"memory");
153 return result;
154}
155
156/*
157 * Note! This is subtle. We jump to wake people up only if
158 * the semaphore was negative (== somebody was waiting on it).
159 */
160static inline void up(struct semaphore * sem)
161{
162 __asm__ __volatile__(
163 "# atomic up operation\n\t"
164 LOCK_PREFIX "incl %0\n\t" /* ++sem->count */
165 "jg 1f\n\t"
166 "lea %0,%%eax\n\t"
167 "call __up_wakeup\n"
168 "1:"
169 :"+m" (sem->count)
170 :
171 :"memory","ax");
172}
173
174#endif
175#endif