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
  19 struct 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  */
  30 extern void down_read(struct rw_semaphore *sem);
  31
  32 /*
  33  * trylock for reading -- returns 1 if successful, 0 if contention
  34  */
  35 extern int down_read_trylock(struct rw_semaphore *sem);
  36
  37 /*
  38  * lock for writing
  39  */
  40 extern void down_write(struct rw_semaphore *sem);
  41
  42 /*
  43  * trylock for writing -- returns 1 if successful, 0 if contention
  44  */
  45 extern int down_write_trylock(struct rw_semaphore *sem);
  46
  47 /*
  48  * release a read lock
  49  */
  50 extern void up_read(struct rw_semaphore *sem);
  51
  52 /*
  53  * release a write lock
  54  */
  55 extern void up_write(struct rw_semaphore *sem);
  56
  57 /*
  58  * downgrade write lock to read lock
  59  */
  60 extern 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  */
  76 extern void down_read_nested(struct rw_semaphore *sem, int subclass);
  77 extern 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  */
  84 extern void down_read_non_owner(struct rw_semaphore *sem);
  85 extern 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 */