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/*

 *  Generic semaphore code. Buyer beware. Do your own

 * specific changes in <asm/semaphore-helper.h>

 */

#include <linux/config.h>

#include <linux/sched.h>

#include <asm/semaphore-helper.h>

#ifndef CONFIG_RMW_INSNS

spinlock_t semaphore_wake_lock;

#endif

/*

 * Semaphores are implemented using a two-way counter:

 * The "count" variable is decremented for each process

 * that tries to sleep, while the "waking" variable is

 * incremented when the "up()" code goes to wake up waiting

 * processes.

 *

 * Notably, the inline "up()" and "down()" functions can

 * efficiently test if they need to do any extra work (up

 * needs to do something only if count was negative before

 * the increment operation.

 *

 * waking_non_zero() (from asm/semaphore.h) must execute

 * atomically.

 *

 * When __up() is called, the count was negative before

 * incrementing it, and we need to wake up somebody.

 *

 * This routine adds one to the count of processes that need to

 * wake up and exit.  ALL waiting processes actually wake up but

 * only the one that gets to the "waking" field first will gate

 * through and acquire the semaphore.  The others will go back

 * to sleep.

 *

 * Note that these functions are only called when there is

 * contention on the lock, and as such all this is the

 * "non-critical" part of the whole semaphore business. The

 * critical part is the inline stuff in <asm/semaphore.h>

 * where we want to avoid any extra jumps and calls.

 */

void __up(struct semaphore *sem)

{

        wake_one_more(sem);

        wake_up(&sem->wait);

}

/*

 * Perform the "down" function.  Return zero for semaphore acquired,

 * return negative for signalled out of the function.

 *

 * If called from __down, the return is ignored and the wait loop is

 * not interruptible.  This means that a task waiting on a semaphore

 * using "down()" cannot be killed until someone does an "up()" on

 * the semaphore.

 *

 * If called from __down_interruptible, the return value gets checked

 * upon return.  If the return value is negative then the task continues

 * with the negative value in the return register (it can be tested by

 * the caller).

 *

 * Either form may be used in conjunction with "up()".

 *

 */

#define DOWN_HEAD(task_state)                                           \

                                                                        \

                                                                        \

        current->state = (task_state);                                  \

        add_wait_queue(&sem->wait, &wait);                              \

                                                                        \

        /*                                                              \

         * Ok, we're set up.  sem->count is known to be less than zero  \

         * so we must wait.                                             \

         *                                                              \

         * We can let go the lock for purposes of waiting.              \

         * We re-acquire it after awaking so as to protect              \

         * all semaphore operations.                                    \

         *                                                              \

         * If "up()" is called before we call waking_non_zero() then    \

         * we will catch it right away.  If it is called later then     \

         * we will have to go through a wakeup cycle to catch it.       \

         *                                                              \

         * Multiple waiters contend for the semaphore lock to see       \

         * who gets to gate through and who has to wait some more.      \

         */                                                             \

        for (;;) {

#define DOWN_TAIL(task_state)                   \

                current->state = (task_state);  \

        }                                       \

        current->state = TASK_RUNNING;          \

        remove_wait_queue(&sem->wait, &wait);

void __down(struct semaphore * sem)

{

        DECLARE_WAITQUEUE(wait, current);

        DOWN_HEAD(TASK_UNINTERRUPTIBLE)

        if (waking_non_zero(sem))

                break;

        schedule();

        DOWN_TAIL(TASK_UNINTERRUPTIBLE)

}

int __down_interruptible(struct semaphore * sem)

{

        DECLARE_WAITQUEUE(wait, current);

        int ret = 0;

        DOWN_HEAD(TASK_INTERRUPTIBLE)

        ret = waking_non_zero_interruptible(sem, current);

        if (ret)

        {

                if (ret == 1)

                        /* ret != 0 only if we get interrupted -arca */

                        ret = 0;

                break;

        }

        schedule();

        DOWN_TAIL(TASK_INTERRUPTIBLE)

        return ret;

}

int __down_trylock(struct semaphore * sem)

{

        return waking_non_zero_trylock(sem);

}