include/linux/rwsem-spinlock.h

   1 /* rwsem-spinlock.h: fallback C implementation
   2  *
   3  * Copyright (c) 2001   David Howells (dhowells@redhat.com).
   4  * - Derived partially from ideas by Andrea Arcangeli <andrea@suse.de>
   5  * - Derived also from comments by Linus
   6  */
   7
   8 #ifndef _LINUX_RWSEM_SPINLOCK_H
   9 #define _LINUX_RWSEM_SPINLOCK_H
  10
  11 #ifndef _LINUX_RWSEM_H
  12 #error "please don't include linux/rwsem-spinlock.h directly, use linux/rwsem.h instead"
  13 #endif
  14
  15 #include <linux/spinlock.h>
  16 #include <linux/list.h>
  17
  18 #ifdef __KERNEL__
  19
  20 #include <linux/types.h>
  21
  22 struct rwsem_waiter;
  23
  24 /*
  25  * the rw-semaphore definition
  26  * - if activity is 0 then there are no active readers or writers
  27  * - if activity is +ve then that is the number of active readers
  28  * - if activity is -1 then there is one active writer
  29  * - if wait_list is not empty, then there are processes waiting for the semaphore
  30  */
  31 struct rw_semaphore {
  32         __s32                   activity;
  33         spinlock_t              wait_lock;
  34         struct list_head        wait_list;
  35 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  36         struct lockdep_map dep_map;
  37 #endif
  38 };
  39
  40 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  41 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
  42 #else
  43 # define __RWSEM_DEP_MAP_INIT(lockname)
  44 #endif
  45
  46 #define __RWSEM_INITIALIZER(name) \
  47 { 0, __SPIN_LOCK_UNLOCKED(name.wait_lock), LIST_HEAD_INIT((name).wait_list) \
  48   __RWSEM_DEP_MAP_INIT(name) }
  49
  50 #define DECLARE_RWSEM(name) \
  51         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  52
  53 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
  54                          struct lock_class_key *key);
  55
  56 #define init_rwsem(sem)                                         \
  57 do {                                                            \
  58         static struct lock_class_key __key;                     \
  59                                                                 \
  60         __init_rwsem((sem), #sem, &__key);                      \
  61 } while (0)
  62
  63 extern void __down_read(struct rw_semaphore *sem);
  64 extern int __down_read_trylock(struct rw_semaphore *sem);
  65 extern void __down_write(struct rw_semaphore *sem);
  66 extern void __down_write_nested(struct rw_semaphore *sem, int subclass);
  67 extern int __down_write_trylock(struct rw_semaphore *sem);
  68 extern void __up_read(struct rw_semaphore *sem);
  69 extern void __up_write(struct rw_semaphore *sem);
  70 extern void __downgrade_write(struct rw_semaphore *sem);
  71
  72 static inline int rwsem_is_locked(struct rw_semaphore *sem)
  73 {
  74         return (sem->activity != 0);
  75 }
  76
  77 #endif /* __KERNEL__ */
  78 #endif /* _LINUX_RWSEM_SPINLOCK_H */