linux 内核－信号－队列

linux 内核－信号－队列

分类： linux2011-01-27
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static ssize_t mxc_v4l_read(struct file *file, char *buf, size_t count,

loff_t *ppos)

{

int err = 0;

u8 *v_address[2];

struct video_device *dev = video_devdata(file);

cam_data *cam = video_get_drvdata(dev);

if (down_interruptible(&cam->busy_lock))

return -EINTR;

/* Stop the viewfinder */

if (cam->overlay_on == true)

stop_preview(cam);

v_address[0] = dma_alloc_coherent(0,

PAGE_ALIGN(cam->v2f.fmt.pix.sizeimage),

&cam->still_buf[0],

GFP_DMA | GFP_KERNEL);

v_address[1] = dma_alloc_coherent(0,

PAGE_ALIGN(cam->v2f.fmt.pix.sizeimage),

&cam->still_buf[1],

GFP_DMA | GFP_KERNEL);

if (!v_address[0] || !v_address[1]) {

err = -ENOBUFS;

goto exit0;

}

err = prp_still_select(cam);

if (err != 0) {

err = -EIO;

goto exit0;

}

cam->still_counter = 0;

err = cam->csi_start(cam);

if (err != 0) {

err = -EIO;

goto exit1;

}

if (!wait_event_interruptible_timeout(cam->still_queue,

cam->still_counter != 0,

10 * HZ)) {

pr_err("ERROR: v4l2 capture: mxc_v4l_read timeout counter %x/n",

cam->still_counter);

err = -ETIME;

goto exit1;

}

err = copy_to_user(buf, v_address[1], cam->v2f.fmt.pix.sizeimage);

exit1:

prp_still_deselect(cam);

exit0:

if (v_address[0] != 0)

dma_free_coherent(0, cam->v2f.fmt.pix.sizeimage, v_address[0],

cam->still_buf[0]);

if (v_address[1] != 0)

dma_free_coherent(0, cam->v2f.fmt.pix.sizeimage, v_address[1],

cam->still_buf[1]);

cam->still_buf[0] = cam->still_buf[1] = 0;

if (cam->overlay_on == true) {

start_preview(cam);

}

up(&cam->busy_lock);

if (err < 0)

return err;

return (cam->v2f.fmt.pix.sizeimage - err);

}





kernel/include/semaphore.h



#define init_MUTEX(sem) sema_init(sem, 1)

#define init_MUTEX_LOCKED(sem) sema_init(sem, 0)



kernel/semaphore.c

int down_interruptible(struct semaphore *sem)



/**

* down_interruptible - acquire the semaphore unless interrupted

* @sem: the semaphore to be acquired

*

* Attempts to acquire the semaphore. If no more tasks are allowed to

* acquire the semaphore, calling this function will put the task to sleep.

* If the sleep is interrupted by a signal, this function will return -EINTR.

* If the semaphore is successfully acquired, this function returns 0.

*/





调用down_interruptible()的进程在调用down_interruptible()之后，如果sem<0，那么就进入到可中断的睡眠状态并调度其它进程运行， 但是一旦该进程获得信号，那么就会从down_interruptible函数中返回。如果是被别的信号中断则返回错误号-EINTR。







/**

* up - release the semaphore

* @sem: the semaphore to release

*

* Release the semaphore. Unlike mutexes, up() may be called from any

* context and even by tasks which have never called down().

*/

void up(struct semaphore *sem)



＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊队列

wait_event_interruptible_timeout和schedule_timeout的 一、适用情况 wait_event_interruptible_timeout和schedule_timeout的区别 当在某个硬件驱动程序中使用wait_event_interruptible_timeout时，执行的继续可以通过以下两种方式获得： 1.其他人在等待队列上调用了wake_up（并且condition满足） 2.超时到期。 而调用schedule_timeout的进程始终会在超时到期时被唤醒。 二、函数原型 wait_event_interruptible_timeout(queue, condition, timeout) 返回值： 大于零：剩余时间(以jiffy计) 零:给定的时间到期。 signed long schedule_timeout(signed long timeout); 返回值： 零：正常返回值 大于零：函数提前返回（比如响应某个信号），返回值为剩余时间 三、使用实例 1.wait_event_interrruptible_timeout (1)初始化等待队列 int flags = 0; wait_queue_head_t select_wait; init_waitqueue_head(&select_wait); (2)等待事件的发生（条件满足） { ... wait_event_interruptible_timeout(select_wait, flags != 0, HZ/10); ... } (3)唤醒等待队列 { ... if(waitqueue_active(&select_wait)) { flags = 1; wake_up_interruptible( &nd->select_in_wait ); } ... }

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