在Linux驱动程序设计中，可以使用等待队列来实现进程的阻塞，等待队列可以看做保存进程的容器，在阻塞进程时，将进程放入等待队列，当唤醒进程时，从等待队列中取出进程。
Linux2.6内核提供了如下关于等待队列的操作
1、 定义等待队列
wait_queue_head_t my_queue
2、 初始化等待队列
init_waitqueue_head(&my_queue)
3、 定义并初始化等待队列
DECLARE_WAIT_QUEUE_HEAD(my_queue)
4、 有条件睡眠
wait_event(queue,condition)
当condition为真时，立即返回；否则让进程进入TASK_UNINTERRUPTIBLE模式的睡眠
wait_event_interruptible(queue,condition)
当condition为真时，立即返回；否则让进程进入TASK_INTERRUPTIBLE模式的睡眠
int wait_event_killable(wait_queue_t queue, condition)
当condition为真时，立即返回；否则让进程进入TASK_KILLABLE模式的睡眠
5、 无条件睡眠
sleep_on(wait_queue_head_t *q)
让进程进入不可中断的睡眠
interruptible_sleep_on(wait_queue_head_t*q)
让进程进入可中断的睡眠
6、 从等待队列中唤醒进程
wake_up(wait_queue_t *q)
可以唤醒所有模式的等待队列
wake_up_interruptible(wait_queue_t*q)
唤醒TASK_INTERRUPTIBLE模式的进程
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <asm/io.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include "memdev.h"
static mem_major = MEMDEV_MAJOR;
bool have_data = false; /*表明设备有足够数据可供读*/
module_param(mem_major, int, S_IRUGO);
struct mem_dev *mem_devp; /*设备结构体指针*/
struct cdev cdev;
/*文件打开函数*/
int mem_open(struct inode *inode, structfile *filp)
{
struct mem_dev *dev;
/*获取次设备号*/
int num = MINOR(inode->i_rdev);
if (num >= MEMDEV_NR_DEVS)
return -ENODEV;
dev = &mem_devp[num];
/*将设备描述结构指针赋值给文件私有数据指针*/
filp->private_data = dev;
return 0;
}
/*文件释放函数*/
int mem_release(struct inode *inode, structfile *filp)
{
return 0;
}
/*读函数*/
static ssize_t mem_read(struct file *filp,char __user *buf, size_t size, loff_t *ppos)
{
unsigned long p = *ppos;
unsigned int count = size;
intret = 0;
struct mem_dev *dev = filp->private_data; /*获得设备结构体指针*/
/*判断读位置是否有效*/
if(p >= MEMDEV_SIZE)
return 0;
if(count > MEMDEV_SIZE - p)
count = MEMDEV_SIZE - p;
while (!have_data) /* 没有数据可读，考虑为什么不用if，而用while,中断信号唤醒 */
{
if (filp->f_flags & O_NONBLOCK)
return -EAGAIN;
wait_event_interruptible(dev->inq,have_data);
}
/*读数据到用户空间*/
if(copy_to_user(buf, (void*)(dev->data + p), count))
{
ret = - EFAULT;
}
else
{
*ppos += count;
ret = count;
printk(KERN_INFO "read %d bytes(s) from %d\n", count, p);
}
have_data = false; /* 表明不再有数据可读 */
return ret;
}
/*写函数*/
static ssize_t mem_write(struct file *filp,const char __user *buf, size_t size, loff_t *ppos)
{
unsigned long p = *ppos;
unsigned int count = size;
intret = 0;
struct mem_dev *dev = filp->private_data; /*获得设备结构体指针*/
/*分析和获取有效的写长度*/
if(p >= MEMDEV_SIZE)
return 0;
if(count > MEMDEV_SIZE - p)
count = MEMDEV_SIZE - p;
/*从用户空间写入数据*/
if(copy_from_user(dev->data + p, buf, count))
ret = - EFAULT;
else
{
*ppos += count;
ret = count;
printk(KERN_INFO "written %d bytes(s) from %d\n", count, p);
}
have_data = true; /* 有新的数据可读 */
/* 唤醒读进程 */
wake_up(&(dev->inq));
return ret;
}
/* seek文件定位函数 */
static loff_t mem_llseek(struct file *filp,loff_t offset, int whence)
{
loff_t newpos;
switch(whence) {
case 0: /* SEEK_SET */
newpos = offset;
break;
case 1: /* SEEK_CUR */
newpos = filp->f_pos + offset;
break;
case 2: /* SEEK_END */
newpos = MEMDEV_SIZE -1 + offset;
break;
default: /* can't happen */
return -EINVAL;
}
if ((newpos<0) || (newpos>MEMDEV_SIZE))
return -EINVAL;
filp->f_pos = newpos;
return newpos;
}
/*文件操作结构体*/
static const struct file_operationsmem_fops =
{
.owner = THIS_MODULE,
.llseek = mem_llseek,
.read = mem_read,
.write = mem_write,
.open = mem_open,
.release = mem_release,
};
/*设备驱动模块加载函数*/
static int memdev_init(void)
{
intresult;
inti;
dev_t devno = MKDEV(mem_major, 0);
/* 静态申请设备号*/
if(mem_major)
result = register_chrdev_region(devno, 2, "memdev");
else /* 动态分配设备号 */
{
result = alloc_chrdev_region(&devno, 0, 2, "memdev");
mem_major = MAJOR(devno);
}
if(result < 0)
return result;
/*初始化cdev结构*/
cdev_init(&cdev, &mem_fops);
cdev.owner = THIS_MODULE;
cdev.ops = &mem_fops;
/* 注册字符设备 */
cdev_add(&cdev, MKDEV(mem_major, 0), MEMDEV_NR_DEVS);
/* 为设备描述结构分配内存*/
mem_devp = kmalloc(MEMDEV_NR_DEVS * sizeof(struct mem_dev), GFP_KERNEL);
if(!mem_devp) /*申请失败*/
{
result = - ENOMEM;
goto fail_malloc;
}
memset(mem_devp, 0, sizeof(struct mem_dev));
/*为设备分配内存*/
for(i=0; i < MEMDEV_NR_DEVS; i++)
{
mem_devp[i].size = MEMDEV_SIZE;
mem_devp[i].data = kmalloc(MEMDEV_SIZE, GFP_KERNEL);
memset(mem_devp[i].data, 0, MEMDEV_SIZE);
/*初始化等待队列*/
init_waitqueue_head(&(mem_devp[i].inq));
}
return 0;
fail_malloc:
unregister_chrdev_region(devno, 1);
return result;
}
/*模块卸载函数*/
static void memdev_exit(void)
{
cdev_del(&cdev); /*注销设备*/
kfree(mem_devp); /*释放设备结构体内存*/
unregister_chrdev_region(MKDEV(mem_major, 0), 2); /*释放设备号*/
}
MODULE_AUTHOR("David Xie");
MODULE_LICENSE("GPL");
module_init(memdev_init);
module_exit(memdev_exit);
