linux/include/linux/rwsem.h
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   1/* rwsem.h: R/W semaphores, public interface
   2 *
   3 * Written by David Howells (dhowells@redhat.com).
   4 * Derived from asm-i386/semaphore.h
   5 */
   6
   7#ifndef _LINUX_RWSEM_H
   8#define _LINUX_RWSEM_H
   9
  10#include <linux/linkage.h>
  11
  12#include <linux/types.h>
  13#include <linux/kernel.h>
  14#include <linux/list.h>
  15#include <linux/spinlock.h>
  16
  17#include <linux/atomic.h>
  18
  19struct rw_semaphore;
  20
  21#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
  22#include <linux/rwsem-spinlock.h> /* use a generic implementation */
  23#else
  24/* All arch specific implementations share the same struct */
  25struct rw_semaphore {
  26        long                    count;
  27        raw_spinlock_t          wait_lock;
  28        struct list_head        wait_list;
  29#ifdef CONFIG_DEBUG_LOCK_ALLOC
  30        struct lockdep_map      dep_map;
  31#endif
  32};
  33
  34extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  35extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  36extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
  37extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  38
  39/* Include the arch specific part */
  40#include <asm/rwsem.h>
  41
  42/* In all implementations count != 0 means locked */
  43static inline int rwsem_is_locked(struct rw_semaphore *sem)
  44{
  45        return sem->count != 0;
  46}
  47
  48#endif
  49
  50/* Common initializer macros and functions */
  51
  52#ifdef CONFIG_DEBUG_LOCK_ALLOC
  53# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
  54#else
  55# define __RWSEM_DEP_MAP_INIT(lockname)
  56#endif
  57
  58#define __RWSEM_INITIALIZER(name)                       \
  59        { RWSEM_UNLOCKED_VALUE,                         \
  60          __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),     \
  61          LIST_HEAD_INIT((name).wait_list)              \
  62          __RWSEM_DEP_MAP_INIT(name) }
  63
  64#define DECLARE_RWSEM(name) \
  65        struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  66
  67extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
  68                         struct lock_class_key *key);
  69
  70#define init_rwsem(sem)                                         \
  71do {                                                            \
  72        static struct lock_class_key __key;                     \
  73                                                                \
  74        __init_rwsem((sem), #sem, &__key);                      \
  75} while (0)
  76
  77/*
  78 * lock for reading
  79 */
  80extern void down_read(struct rw_semaphore *sem);
  81
  82/*
  83 * trylock for reading -- returns 1 if successful, 0 if contention
  84 */
  85extern int down_read_trylock(struct rw_semaphore *sem);
  86
  87/*
  88 * lock for writing
  89 */
  90extern void down_write(struct rw_semaphore *sem);
  91
  92/*
  93 * trylock for writing -- returns 1 if successful, 0 if contention
  94 */
  95extern int down_write_trylock(struct rw_semaphore *sem);
  96
  97/*
  98 * release a read lock
  99 */
 100extern void up_read(struct rw_semaphore *sem);
 101
 102/*
 103 * release a write lock
 104 */
 105extern void up_write(struct rw_semaphore *sem);
 106
 107/*
 108 * downgrade write lock to read lock
 109 */
 110extern void downgrade_write(struct rw_semaphore *sem);
 111
 112#ifdef CONFIG_DEBUG_LOCK_ALLOC
 113/*
 114 * nested locking. NOTE: rwsems are not allowed to recurse
 115 * (which occurs if the same task tries to acquire the same
 116 * lock instance multiple times), but multiple locks of the
 117 * same lock class might be taken, if the order of the locks
 118 * is always the same. This ordering rule can be expressed
 119 * to lockdep via the _nested() APIs, but enumerating the
 120 * subclasses that are used. (If the nesting relationship is
 121 * static then another method for expressing nested locking is
 122 * the explicit definition of lock class keys and the use of
 123 * lockdep_set_class() at lock initialization time.
 124 * See Documentation/lockdep-design.txt for more details.)
 125 */
 126extern void down_read_nested(struct rw_semaphore *sem, int subclass);
 127extern void down_write_nested(struct rw_semaphore *sem, int subclass);
 128extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
 129
 130# define down_write_nest_lock(sem, nest_lock)                   \
 131do {                                                            \
 132        typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
 133        _down_write_nest_lock(sem, &(nest_lock)->dep_map);      \
 134} while (0);
 135
 136#else
 137# define down_read_nested(sem, subclass)                down_read(sem)
 138# define down_write_nest_lock(sem, nest_lock)   down_write(sem)
 139# define down_write_nested(sem, subclass)       down_write(sem)
 140#endif
 141
 142#endif /* _LINUX_RWSEM_H */
 143
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