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 <asm/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        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, __SPIN_LOCK_UNLOCKED(name.wait_lock),   \
  61          LIST_HEAD_INIT((name).wait_list) __RWSEM_DEP_MAP_INIT(name) }
  62
  63#define DECLARE_RWSEM(name) \
  64        struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  65
  66extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
  67                         struct lock_class_key *key);
  68
  69#define init_rwsem(sem)                                         \
  70do {                                                            \
  71        static struct lock_class_key __key;                     \
  72                                                                \
  73        __init_rwsem((sem), #sem, &__key);                      \
  74} while (0)
  75
  76/*
  77 * lock for reading
  78 */
  79extern void down_read(struct rw_semaphore *sem);
  80
  81/*
  82 * trylock for reading -- returns 1 if successful, 0 if contention
  83 */
  84extern int down_read_trylock(struct rw_semaphore *sem);
  85
  86/*
  87 * lock for writing
  88 */
  89extern void down_write(struct rw_semaphore *sem);
  90
  91/*
  92 * trylock for writing -- returns 1 if successful, 0 if contention
  93 */
  94extern int down_write_trylock(struct rw_semaphore *sem);
  95
  96/*
  97 * release a read lock
  98 */
  99extern void up_read(struct rw_semaphore *sem);
 100
 101/*
 102 * release a write lock
 103 */
 104extern void up_write(struct rw_semaphore *sem);
 105
 106/*
 107 * downgrade write lock to read lock
 108 */
 109extern void downgrade_write(struct rw_semaphore *sem);
 110
 111#ifdef CONFIG_DEBUG_LOCK_ALLOC
 112/*
 113 * nested locking. NOTE: rwsems are not allowed to recurse
 114 * (which occurs if the same task tries to acquire the same
 115 * lock instance multiple times), but multiple locks of the
 116 * same lock class might be taken, if the order of the locks
 117 * is always the same. This ordering rule can be expressed
 118 * to lockdep via the _nested() APIs, but enumerating the
 119 * subclasses that are used. (If the nesting relationship is
 120 * static then another method for expressing nested locking is
 121 * the explicit definition of lock class keys and the use of
 122 * lockdep_set_class() at lock initialization time.
 123 * See Documentation/lockdep-design.txt for more details.)
 124 */
 125extern void down_read_nested(struct rw_semaphore *sem, int subclass);
 126extern void down_write_nested(struct rw_semaphore *sem, int subclass);
 127/*
 128 * Take/release a lock when not the owner will release it.
 129 *
 130 * [ This API should be avoided as much as possible - the
 131 *   proper abstraction for this case is completions. ]
 132 */
 133extern void down_read_non_owner(struct rw_semaphore *sem);
 134extern void up_read_non_owner(struct rw_semaphore *sem);
 135#else
 136# define down_read_nested(sem, subclass)                down_read(sem)
 137# define down_write_nested(sem, subclass)       down_write(sem)
 138# define down_read_non_owner(sem)               down_read(sem)
 139# define up_read_non_owner(sem)                 up_read(sem)
 140#endif
 141
 142#endif /* _LINUX_RWSEM_H */
 143