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   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 #define RWSEM_DEBUG 0
  13
  14 #ifdef __KERNEL__
  15
  16 #include <linux/types.h>
  17 #include <linux/kernel.h>
  18 #include <asm/system.h>
  19 #include <asm/atomic.h>
  20
  21 struct rw_semaphore;
  22
  23 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
  24 #include <linux/rwsem-spinlock.h> /* use a generic implementation */
  25 #else
  26 #include <asm/rwsem.h> /* use an arch-specific implementation */
  27 #endif
  28
  29 #ifndef rwsemtrace
  30 #if RWSEM_DEBUG
  31 extern void FASTCALL(rwsemtrace(struct rw_semaphore *sem, const char *str));
  32 #else
  33 #define rwsemtrace(SEM,FMT)
  34 #endif
  35 #endif
  36
  37 /*
  38  * lock for reading
  39  */
  40 static inline void down_read(struct rw_semaphore *sem)
  41 {
  42         might_sleep();
  43         rwsemtrace(sem,"Entering down_read");
  44         __down_read(sem);
  45         rwsemtrace(sem,"Leaving down_read");
  46 }
  47
  48 /*
  49  * trylock for reading -- returns 1 if successful, 0 if contention
  50  */
  51 static inline int down_read_trylock(struct rw_semaphore *sem)
  52 {
  53         int ret;
  54         rwsemtrace(sem,"Entering down_read_trylock");
  55         ret = __down_read_trylock(sem);
  56         rwsemtrace(sem,"Leaving down_read_trylock");
  57         return ret;
  58 }
  59
  60 /*
  61  * lock for writing
  62  */
  63 static inline void down_write(struct rw_semaphore *sem)
  64 {
  65         might_sleep();
  66         rwsemtrace(sem,"Entering down_write");
  67         __down_write(sem);
  68         rwsemtrace(sem,"Leaving down_write");
  69 }
  70
  71 /*
  72  * trylock for writing -- returns 1 if successful, 0 if contention
  73  */
  74 static inline int down_write_trylock(struct rw_semaphore *sem)
  75 {
  76         int ret;
  77         rwsemtrace(sem,"Entering down_write_trylock");
  78         ret = __down_write_trylock(sem);
  79         rwsemtrace(sem,"Leaving down_write_trylock");
  80         return ret;
  81 }
  82
  83 /*
  84  * release a read lock
  85  */
  86 static inline void up_read(struct rw_semaphore *sem)
  87 {
  88         rwsemtrace(sem,"Entering up_read");
  89         __up_read(sem);
  90         rwsemtrace(sem,"Leaving up_read");
  91 }
  92
  93 /*
  94  * release a write lock
  95  */
  96 static inline void up_write(struct rw_semaphore *sem)
  97 {
  98         rwsemtrace(sem,"Entering up_write");
  99         __up_write(sem);
 100         rwsemtrace(sem,"Leaving up_write");
 101 }
 102
 103 /*
 104  * downgrade write lock to read lock
 105  */
 106 static inline void downgrade_write(struct rw_semaphore *sem)
 107 {
 108         rwsemtrace(sem,"Entering downgrade_write");
 109         __downgrade_write(sem);
 110         rwsemtrace(sem,"Leaving downgrade_write");
 111 }
 112
 113 #endif /* __KERNEL__ */
 114 #endif /* _LINUX_RWSEM_H */