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 <asm/system.h>
  15 #include <asm/atomic.h>
  16
  17 struct rw_semaphore;
  18
  19 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
  20 #include <linux/rwsem-spinlock.h> /* use a generic implementation */
  21 #else
  22 #include <asm/rwsem.h> /* use an arch-specific implementation */
  23 #endif
  24
  25 /*
  26  * lock for reading
  27  */
  28 extern void down_read(struct rw_semaphore *sem);
  29
  30 /*
  31  * trylock for reading -- returns 1 if successful, 0 if contention
  32  */
  33 extern int down_read_trylock(struct rw_semaphore *sem);
  34
  35 /*
  36  * lock for writing
  37  */
  38 extern void down_write(struct rw_semaphore *sem);
  39
  40 /*
  41  * trylock for writing -- returns 1 if successful, 0 if contention
  42  */
  43 extern int down_write_trylock(struct rw_semaphore *sem);
  44
  45 /*
  46  * release a read lock
  47  */
  48 extern void up_read(struct rw_semaphore *sem);
  49
  50 /*
  51  * release a write lock
  52  */
  53 extern void up_write(struct rw_semaphore *sem);
  54
  55 /*
  56  * downgrade write lock to read lock
  57  */
  58 extern void downgrade_write(struct rw_semaphore *sem);
  59
  60 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  61 /*
  62  * nested locking. NOTE: rwsems are not allowed to recurse
  63  * (which occurs if the same task tries to acquire the same
  64  * lock instance multiple times), but multiple locks of the
  65  * same lock class might be taken, if the order of the locks
  66  * is always the same. This ordering rule can be expressed
  67  * to lockdep via the _nested() APIs, but enumerating the
  68  * subclasses that are used. (If the nesting relationship is
  69  * static then another method for expressing nested locking is
  70  * the explicit definition of lock class keys and the use of
  71  * lockdep_set_class() at lock initialization time.
  72  * See Documentation/lockdep-design.txt for more details.)
  73  */
  74 extern void down_read_nested(struct rw_semaphore *sem, int subclass);
  75 extern void down_write_nested(struct rw_semaphore *sem, int subclass);
  76 /*
  77  * Take/release a lock when not the owner will release it.
  78  *
  79  * [ This API should be avoided as much as possible - the
  80  *   proper abstraction for this case is completions. ]
  81  */
  82 extern void down_read_non_owner(struct rw_semaphore *sem);
  83 extern void up_read_non_owner(struct rw_semaphore *sem);
  84 #else
  85 # define down_read_nested(sem, subclass)                down_read(sem)
  86 # define down_write_nested(sem, subclass)       down_write(sem)
  87 # define down_read_non_owner(sem)               down_read(sem)
  88 # define up_read_non_owner(sem)                 up_read(sem)
  89 #endif
  90
  91 #endif /* _LINUX_RWSEM_H */