kolibrios/drivers/include/asm/rwsem.h
Sergey Semyonov (Serge) cf125b5b49 ddk: update
git-svn-id: svn://kolibrios.org@6102 a494cfbc-eb01-0410-851d-a64ba20cac60
2016-01-27 05:30:28 +00:00

113 lines
3.5 KiB
C

/* rwsem.h: R/W semaphores implemented using XADD/CMPXCHG for i486+
*
* Written by David Howells (dhowells@redhat.com).
*
* Derived from asm-x86/semaphore.h
*
*
* The MSW of the count is the negated number of active writers and waiting
* lockers, and the LSW is the total number of active locks
*
* The lock count is initialized to 0 (no active and no waiting lockers).
*
* When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case of an
* uncontended lock. This can be determined because XADD returns the old value.
* Readers increment by 1 and see a positive value when uncontended, negative
* if there are writers (and maybe) readers waiting (in which case it goes to
* sleep).
*
* The value of WAITING_BIAS supports up to 32766 waiting processes. This can
* be extended to 65534 by manually checking the whole MSW rather than relying
* on the S flag.
*
* The value of ACTIVE_BIAS supports up to 65535 active processes.
*
* This should be totally fair - if anything is waiting, a process that wants a
* lock will go to the back of the queue. When the currently active lock is
* released, if there's a writer at the front of the queue, then that and only
* that will be woken up; if there's a bunch of consequtive readers at the
* front, then they'll all be woken up, but no other readers will be.
*/
#ifndef _ASM_X86_RWSEM_H
#define _ASM_X86_RWSEM_H
#ifndef _LINUX_RWSEM_H
#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
#endif
#ifdef __KERNEL__
#include <asm/asm.h>
#define FASTCALL __attribute__ ((fastcall)) __attribute__ ((dllimport))
void FASTCALL InitRwsem(struct rw_semaphore *sem)__asm__("InitRwsem");
void FASTCALL DownRead(struct rw_semaphore *sem)__asm__("DownRead");
void FASTCALL DownWrite(struct rw_semaphore *sem)__asm__("DownWrite");
void FASTCALL UpRead(struct rw_semaphore *sem)__asm__("UpRead");
void FASTCALL UpWrite(struct rw_semaphore *sem)__asm__("UpWrite");
static inline void __init_rwsem(struct rw_semaphore *sem, const char *name,
struct lock_class_key *key)
{
InitRwsem(sem);
}
/*
* lock for reading
*/
static inline void down_read(struct rw_semaphore *sem)
{
DownRead(sem);
}
static inline void down_write(struct rw_semaphore *sem)
{
DownWrite(sem);
}
/*
* unlock after reading
*/
static inline void up_read(struct rw_semaphore *sem)
{
UpRead(sem);
}
/*
* unlock after writing
*/
static inline void up_write(struct rw_semaphore *sem)
{
UpWrite(sem);
}
#define RWSEM_UNLOCKED_VALUE 0x00000000L
#define RWSEM_ACTIVE_BIAS 0x00000001L
#define RWSEM_WAITING_BIAS (-RWSEM_ACTIVE_MASK-1)
#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
static inline int down_read_trylock(struct rw_semaphore *sem)
{
long result, tmp;
asm volatile("# beginning __down_read_trylock\n\t"
" mov %0,%1\n\t"
"1:\n\t"
" mov %1,%2\n\t"
" add %3,%2\n\t"
" jle 2f\n\t"
LOCK_PREFIX " cmpxchg %2,%0\n\t"
" jnz 1b\n\t"
"2:\n\t"
"# ending __down_read_trylock\n\t"
: "+m" (sem->count), "=&a" (result), "=&r" (tmp)
: "i" (RWSEM_ACTIVE_READ_BIAS)
: "memory", "cc");
return result >= 0 ? 1 : 0;
}
#endif /* __KERNEL__ */
#endif /* _ASM_X86_RWSEM_H */