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
  20 struct 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 */
  26 struct 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
  35 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  36 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  37 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
  38 extern 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 */
  44 static 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
  68 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
  69                          struct lock_class_key *key);
  70
  71 #define init_rwsem(sem)                                         \
  72 do {                                                            \
  73         static struct lock_class_key __key;                     \
  74                                                                 \
  75         __init_rwsem((sem), #sem, &__key);                      \
  76 } while (0)
  77
  78 /*
  79  * lock for reading
  80  */
  81 extern void down_read(struct rw_semaphore *sem);
  82
  83 /*
  84  * trylock for reading -- returns 1 if successful, 0 if contention
  85  */
  86 extern int down_read_trylock(struct rw_semaphore *sem);
  87
  88 /*
  89  * lock for writing
  90  */
  91 extern void down_write(struct rw_semaphore *sem);
  92
  93 /*
  94  * trylock for writing -- returns 1 if successful, 0 if contention
  95  */
  96 extern int down_write_trylock(struct rw_semaphore *sem);
  97
  98 /*
  99  * release a read lock
 100  */
 101 extern void up_read(struct rw_semaphore *sem);
 102
 103 /*
 104  * release a write lock
 105  */
 106 extern void up_write(struct rw_semaphore *sem);
 107
 108 /*
 109  * downgrade write lock to read lock
 110  */
 111 extern 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  */
 127 extern void down_read_nested(struct rw_semaphore *sem, int subclass);
 128 extern 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 */