在Linux驱动程序中，可以使用等待队列（wait queue）来实现阻塞进程的唤醒。等待队列可以用来同步对系统资源的访问。
1.定义和初始化队列头
wait_queue_head_t wqh;
init_waitqueue_head(wait_queue_head_t *wqh);
2.定义和初始化等待队列
DECLARE_WAITQUEUE(name, tsk);
3.添加、移除等待队列
add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait);
remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait);将等待队列wait添加到等待队列头q执行的等待队列链表中，或者从中删除。
4.等待事件
wait_event(queue, condition);当condition为真时，立即返回；否则进程进入TASK_UNINTERRUPTIBLE类型的睡眠状态，并挂在queue指定的等待队列头上。
add_wait_queue(queue, conditon);当condition为真时，立即返回；否则进程进入TASK_INTERRUPTIBLE类型的睡眠状态，并挂在queue指定的等待队列头上。
5.唤醒队列
wake_up(wait_queue_head_t *queue);
wake_up_interruptible(wait_queue_head_t *queue);唤醒由queue指向的等待队列头链表中所有等待队列对应的进程。
6.在等待队列中睡眠
sleep_on(wait_queue_head_t *q);让进程进入不可中断的睡眠，并将它放入等待队列
interruptible_sleep_on(wait_queue_head_t *q);让进程进入不可中断的睡眠，并将它进入等待队列。
内核等待队列一般使用方法：
a.定义和初始化等待队列，将进程状态改变，并将等待队列添加到等待队列数据链中
b.改变进程状态的方法：调用set_current_state(state_value)函数、调用set_task_state(task, state_value)函数、直接采用current->state = TASK_INTERRUPTIBLE,类似于赋值语句。
c.通过schedule()调用放弃cpu，调度其他进程执行
d.进程被其它地方唤醒，将等待队列移出等待队列头指向的数据链
/**
*Copyright (c) 2013.TianYuan
*All rights reserved.
*
*文件名称: char_device_driver13.c
*文件标识: 等待队列
*
*当前版本：1.0
*作者：wuyq
*
*取代版本：xxx
*原作者：xxx
*完成日期：2013-11-29
*/
#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/slab.h>
#include <asm/uaccess.h>
#include <asm/gpio.h>
#include <plat/gpio-cfg.h>
#include <linux/spinlock_types.h>
#include <linux/sched.h>
MODULE_LICENSE("GPL");
#define CDD_MAJOR 200//cat /proc/devices找一个尚未使用的
#define CDD_MINOR 0
#define CDD_COUNT 2
dev_t dev = 0;
u32 cdd_major = 0;
u32 cdd_minor = 0;
struct class *dev_class = NULL;
#define BUF_SIZE 100
struct cdd_cdev{
struct cdev cdev;
struct device *dev_device;
u8 led;
char kbuf[BUF_SIZE];
u32 data_len;//记录缓冲区中已经写入数据的长度
//定义等待队列头
wait_queue_head_t wqh;
};
struct cdd_cdev *cdd_cdevp = NULL;
unsigned long led_gpio_table[2] = {
S5PV210_GPC1(3),//数字
S5PV210_GPC1(4),
};
int cdd_open(struct inode* inode, struct file *filp)
{
struct cdd_cdev *pcdevp = NULL;
printk("enter cdd_open!\n");
pcdevp = container_of(inode->i_cdev, struct cdd_cdev, cdev);
printk("led = %d\n", pcdevp->led);
/*获取信号量*/
//down获取信号量不成功，会导致进程睡眠（第3个进程的时候）
//down(&pcdevp->sem_open);
if(down_interruptible(&pcdevp->sem_open)<0){
return -1;
}
filp->private_data = pcdevp;
//申请gpio管脚
gpio_request(led_gpio_table[0], "GPC1_3");
gpio_request(led_gpio_table[1], "GPC1_4");
return 0;
}
int cdd_read(struct file *filp, char __user *buf, size_t count, loff_t *offset)
{
int ret = 0;
u32 pos = *offset;
u32 cnt = count;
struct cdd_cdev *cdevp = filp->private_data;
#if 0
//定义并初始化一个等待队列
DECLARE_WAITQUEUE(wq, current);
//将等待队列添加到wqh指向的链表
add_wait_queue(&pcdevp->wqh, &wq);
//判断设备有没有数据供用户空间读,假设led不为0，表示有数据供用户空间读取
if(pcdevp->led == 0){
printk("no data for reading! sleep...\n");
//设置当前线程为睡眠状态
set_current_state(TASK_INTERRUPTIBLE);
schedule();//内核调度cpu的算法
printk("have data for reading!\n");
}
//从指定的链表中删除等待队列
remove_wait_queue(&pcdevp->wqh, &wq);
#endif
wait_event_interruptible(&pcdevp->wqh, pcdevp->led != 0);
//printk("enter cdd_read!\n");
if(cnt > (cdevp->data_len-pos) ){
cnt = cdevp->data_len - pos;
}
ret = copy_to_user(buf, cdevp->kbuf+pos, cnt);
//printk("kernel kbuf content:%s\n", cdevp->kbuf);
*offset += cnt;
pcdevp->led = 0;
return ret;
}
int cdd_write(struct file *filp, const char __user *buf, size_t count, loff_t *offset)
{
int ret = 0;
struct cdd_cdev *cdevp = filp->private_data;
u32 pos = *offset;
u32 cnt = count;
//printk("enter cdd_write!\n");
if(cnt > (BUF_SIZE - pos) ){
cnt = BUF_SIZE - pos;
}
ret = copy_from_user(cdevp->kbuf+pos, buf, cnt);
*offset += cnt;
if(*offset > cdevp->data_len){
cdevp->data_len = *offset;
}
pcdevp->led = 1;
//唤醒等待队列头中的一个等待队列
wake_up_interruptible(&pcdevp->wqh);
return ret;
}
int cdd_ioctl(struct inode *inode, struct file *filp, unsigned int cmd, unsigned long data)
{
//printk("enter cdd_ioctl!\n");
switch(cmd){
case 1://点亮灯
//设置管脚为输出功能
//参数：1.要设置的管脚编号2.默认的输出值 0低电平1高电平
gpio_direction_output(led_gpio_table[data], 0);
//禁止内部上拉
s3c_gpio_setpull(led_gpio_table[data], SEC_GPIO_PULL_NONE);
//设置输出值
gpio_set_value(led_gpio_table[data], 1);
break;
case 0://熄灭灯
//设置管脚为输出功能
//参数：1.要设置的管脚编号2.默认的输出值 0低电平1高电平
gpio_direction_output(led_gpio_table[data], 0);
//禁止内部上拉
s3c_gpio_setpull(led_gpio_table[data], SEC_GPIO_PULL_NONE);
//设置输出值
gpio_set_value(led_gpio_table[data], 0);
break;
default:
return -EINVAL;
}
return 0;
}
int cdd_release(struct inode *inode, struct file *filp)
{
struct cdd_cdev *pcdevp = filp->private_data;
printk("enter cdd_release!\n");
gpio_free(led_gpio_table[0]);
gpio_free(led_gpio_table[1]);
up(&pcdevp->sem_open);
return 0;
}
loff_t cdd_llseek(struct file *filp, loff_t offset, int whence)
{
struct cdd_cdev *pcdevp = filp->private_data;
loff_t newpos = 0;
switch(whence){
case SEEK_SET:
newpos = offset;
break;
case SEEK_CUR:
newpos = filp->f_pos + offset;
break;
case SEEK_END:
newpos = pcdevp->data_len + offset;
break;
default:
return -EINVAL;//无效的参数
}
if( newpos<0 || newpos>= BUF_SIZE ){
return -EINVAL;
}
filp->f_pos = newpos;
return newpos;
}
struct file_operations cdd_fops = {
.owner = THIS_MODULE,
.open = cdd_open,
.read = cdd_read,
.write = cdd_write,
.ioctl = cdd_ioctl,
.release = cdd_release,
.llseek = cdd_llseek,
};
int __init cdd_init(void)
{
int ret = 0;
int i = 0;
if(cdd_major){
dev = MKDEV(CDD_MAJOR, CDD_MINOR);//生成设备号
//注册设备号;1、要注册的起始设备号2、连续注册的设备号个数3、名字
ret = register_chrdev_region(dev, CDD_COUNT, "cdd_demo");
}else{
// 动态分配设备号
ret = alloc_chrdev_region(&dev, cdd_minor, CDD_COUNT, "cdd_demo02");
}
if(ret < 0){
printk("register_chrdev_region failed!\n");
goto failure_register_chrdev;
}
//获取主设备号
cdd_major = MAJOR(dev);
printk("cdd_major = %d\n", cdd_major);
cdd_cdevp = kzalloc(sizeof(struct cdd_cdev)*CDD_COUNT, GFP_KERNEL);
if(IS_ERR(cdd_cdevp)){
printk("kzalloc failed!\n");
goto failure_kzalloc;
}
/*创建设备类*/
dev_class = class_create(THIS_MODULE, "cdd_class");
if(IS_ERR(dev_class)){
printk("class_create failed!\n");
goto failure_dev_class;
}
for(i=0; i<CDD_COUNT; i++){
/*初始化cdev*/
cdev_init(&(cdd_cdevp[i].cdev), &cdd_fops);
/*添加cdev到内核*/
cdev_add(&(cdd_cdevp[i].cdev), dev+i, 1);
/* “/dev/xxx” */
device_create(dev_class, NULL, dev+i, NULL, "cdd%d", i);
cdd_cdevp[i].led = i;
//初始化等待队列头
init_waitqueue_head(&cdd_cdevp[i].wqh);
}
return 0;
failure_dev_class:
kfree(cdd_cdevp);
failure_kzalloc:
unregister_chrdev_region(dev, CDD_COUNT);
failure_register_chrdev:
return ret;
}
void __exit cdd_exit(void)
{
/*逆序消除*/
int i = 0;
for(; i < CDD_COUNT; i++){
device_destroy(dev_class, dev+i);
cdev_del(&(cdd_cdevp[i].cdev));
//cdev_del(&((cdd_cdevp+i)->cdev));
}
class_destroy(dev_class);
kfree(cdd_cdevp);
unregister_chrdev_region(dev, CDD_COUNT);
}
module_init(cdd_init);
module_exit(cdd_exit);
/**
*Copyright (c) 2013.TianYuan
*All rights reserved.
*
*文件名称: char_device_driver13_test0.c
*文件标识: 此程序运行r，此时发生阻塞，进入等待
*
*当前版本：1.0
*作者：wuyq
*
*取代版本：xxx
*原作者：xxx
*完成日期：2013-11-29
*/
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
/*手工创建设备节点文件
mknod /dev/cdd c 248 0
*/
int fd = 0;
char rbuf[100];
char wbuf[100] = "nihao!\n";
int main()
{
char ch;
fd = open("/dev/cdd0", O_RDWR);
if(fd < 0){
printf("open failed!\n");
return -1;
}
printf("open successed fd = %d\n", fd);
while(1)
{
printf("starting to test /dev/cdd...\n");
ch = getchar();
getchar();//取走回车
if(ch == 'q'){
break;
}
switch(ch){
case 'r':
memset(rbuf, 0, 100);//清空
read(fd, rbuf, 3);
printf("user space from kernel: %s\n", rbuf);
break;
case 'w':
write(fd, wbuf, strlen(wbuf) );
break;
case 'o':
ioctl(fd, 0, 0);
break;
case 'O':
ioctl(fd, 1, 0);
break;
case 'p':
ioctl(fd, 0, 1);
break;
case 'P':
ioctl(fd, 1, 1);
break;
case 'l':
lseek(fd, 0, SEEK_SET);//移动的文件的开头
break;
default:
break;
}
sleep(1);
}
close(fd);
return 0;
}
/**
*Copyright (c) 2013.TianYuan
*All rights reserved.
*
*文件名称: char_device_driver13_test1.c
*文件标识: test0 和 test1两个测试：此程序执行w，观察阻塞的r进程被唤醒，完成操作。
*
*当前版本：1.0
*作者：wuyq
*
*取代版本：xxx
*原作者：xxx
*完成日期：2013-11-29
*/
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
/*手工创建设备节点文件
mknod /dev/cdd c 248 0
*/
int fd = 0;
char rbuf[100];
char wbuf[100] = "nihao!\n";
int main()
{
char ch;
fd = open("/dev/cdd1", O_RDWR);
if(fd < 0){
printf("open failed!\n");
return -1;
}
printf("open successed fd = %d\n", fd);
while(1)
{
printf("starting to test /dev/cdd...\n");
ch = getchar();
getchar();//取走回车
if(ch == 'q'){
break;
}
switch(ch){
case 'r':
memset(rbuf, 0, 100);//清空
read(fd, rbuf, 3);
printf("user space from kernel: %s\n", rbuf);
break;
case 'w':
write(fd, wbuf, strlen(wbuf) );
break;
case 'o':
ioctl(fd, 0, 0);
break;
case 'O':
ioctl(fd, 1, 0);
break;
case 'p':
ioctl(fd, 0, 1);
break;
case 'P':
ioctl(fd, 1, 1);
break;
case 'l':
lseek(fd, 0, SEEK_SET);//移动的文件的开头
break;
default:
break;
}
sleep(1);
}
close(fd);
return 0;
}
