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         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, __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
  66 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
  67                          struct lock_class_key *key);
  68
  69 #define init_rwsem(sem)                                         \
  70 do {                                                            \
  71         static struct lock_class_key __key;                     \
  72                                                                 \
  73         __init_rwsem((sem), #sem, &__key);                      \
  74 } while (0)
  75
  76 /*
  77  * lock for reading
  78  */
  79 extern void down_read(struct rw_semaphore *sem);
  80
  81 /*
  82  * trylock for reading -- returns 1 if successful, 0 if contention
  83  */
  84 extern int down_read_trylock(struct rw_semaphore *sem);
  85
  86 /*
  87  * lock for writing
  88  */
  89 extern void down_write(struct rw_semaphore *sem);
  90
  91 /*
  92  * trylock for writing -- returns 1 if successful, 0 if contention
  93  */
  94 extern int down_write_trylock(struct rw_semaphore *sem);
  95
  96 /*
  97  * release a read lock
  98  */
  99 extern void up_read(struct rw_semaphore *sem);
 100
 101 /*
 102  * release a write lock
 103  */
 104 extern void up_write(struct rw_semaphore *sem);
 105
 106 /*
 107  * downgrade write lock to read lock
 108  */
 109 extern 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  */
 125 extern void down_read_nested(struct rw_semaphore *sem, int subclass);
 126 extern void down_write_nested(struct rw_semaphore *sem, int subclass);
 127 #else
 128 # define down_read_nested(sem, subclass)                down_read(sem)
 129 # define down_write_nested(sem, subclass)       down_write(sem)
 130 #endif
 131
 132 #endif /* _LINUX_RWSEM_H */