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#ifdef __KERNEL__
  13
  14#include <linux/types.h>
  15#include <linux/kernel.h>
  16#include <asm/system.h>
  17#include <asm/atomic.h>
  18
  19struct rw_semaphore;
  20
  21#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
  22#include <linux/rwsem-spinlock.h> /* use a generic implementation */
  23#else
  24#include <asm/rwsem.h> /* use an arch-specific implementation */
  25#endif
  26
  27/*
  28 * lock for reading
  29 */
  30extern void down_read(struct rw_semaphore *sem);
  31
  32/*
  33 * trylock for reading -- returns 1 if successful, 0 if contention
  34 */
  35extern int down_read_trylock(struct rw_semaphore *sem);
  36
  37/*
  38 * lock for writing
  39 */
  40extern void down_write(struct rw_semaphore *sem);
  41
  42/*
  43 * trylock for writing -- returns 1 if successful, 0 if contention
  44 */
  45extern int down_write_trylock(struct rw_semaphore *sem);
  46
  47/*
  48 * release a read lock
  49 */
  50extern void up_read(struct rw_semaphore *sem);
  51
  52/*
  53 * release a write lock
  54 */
  55extern void up_write(struct rw_semaphore *sem);
  56
  57/*
  58 * downgrade write lock to read lock
  59 */
  60extern void downgrade_write(struct rw_semaphore *sem);
  61
  62#ifdef CONFIG_DEBUG_LOCK_ALLOC
  63/*
  64 * nested locking. NOTE: rwsems are not allowed to recurse
  65 * (which occurs if the same task tries to acquire the same
  66 * lock instance multiple times), but multiple locks of the
  67 * same lock class might be taken, if the order of the locks
  68 * is always the same. This ordering rule can be expressed
  69 * to lockdep via the _nested() APIs, but enumerating the
  70 * subclasses that are used. (If the nesting relationship is
  71 * static then another method for expressing nested locking is
  72 * the explicit definition of lock class keys and the use of
  73 * lockdep_set_class() at lock initialization time.
  74 * See Documentation/lockdep-design.txt for more details.)
  75 */
  76extern void down_read_nested(struct rw_semaphore *sem, int subclass);
  77extern void down_write_nested(struct rw_semaphore *sem, int subclass);
  78/*
  79 * Take/release a lock when not the owner will release it.
  80 *
  81 * [ This API should be avoided as much as possible - the
  82 *   proper abstraction for this case is completions. ]
  83 */
  84extern void down_read_non_owner(struct rw_semaphore *sem);
  85extern void up_read_non_owner(struct rw_semaphore *sem);
  86#else
  87# define down_read_nested(sem, subclass)                down_read(sem)
  88# define down_write_nested(sem, subclass)       down_write(sem)
  89# define down_read_non_owner(sem)               down_read(sem)
  90# define up_read_non_owner(sem)                 up_read(sem)
  91#endif
  92
  93#endif /* __KERNEL__ */
  94#endif /* _LINUX_RWSEM_H */
  95