LXR linux/include/linux/rwsem.h

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