#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 <linux/poll.h>
#define GLOBALFIFO_SIZE 0x1000 /*全局fifo最大4K字节*/
#define FIFO_CLEAR 0x1 /*清0全局内存的长度*/
#define GLOBALFIFO_MAJOR 253 /*预设的globalfifo的主设备号*/
static int globalfifo_major = GLOBALFIFO_MAJOR;
/*globalfifo设备结构体*/
struct globalfifo_dev
{
struct cdev cdev; /*cdev结构体*/
unsigned int current_len; /*fifo有效数据长度*/
unsigned char mem[GLOBALFIFO_SIZE]; /*全局内存*/
struct semaphore sem; /*并发控制用的信号量*/
// 所谓阻塞，就是如果不能获得资源时，则挂起进程，进入休眠。唤醒它常发生在中断里，因为硬件资源的获得。
//对于驱动程序来说，设备资源不可获取时，需在读写操作中将进程阻塞直到资源可以获取。
//所谓非阻塞，并不挂起，它或放弃，或不停的查询（这回浪费CPU，不好），直到可以操作为止。
//对于驱动程序来说，当设备资源不可获取时，读写操作应该立即返回。
wait_queue_head_t r_wait; /*阻塞读用的等待队列头*/
wait_queue_head_t w_wait; /*阻塞写用的等待队列头*/
};
struct globalfifo_dev *globalfifo_devp; /*设备结构体指针*/
/*文件打开函数*/
int globalfifo_open(struct inode *inode, struct file *filp)
{
/*将设备结构体指针赋值给文件私有数据指针*/
filp->private_data = globalfifo_devp;
return 0;
}
/*文件释放函数*/
int globalfifo_release(struct inode *inode, struct file *filp)
{
return 0;
}
/* ioctl设备控制函数 */
static int globalfifo_ioctl(struct inode *inodep, struct file *filp, unsigned
int cmd, unsigned long arg)
{
struct globalfifo_dev *dev = filp->private_data;/*获得设备结构体指针*/
switch (cmd)
{
case FIFO_CLEAR:
down(&dev->sem); //获得信号量
dev->current_len = 0;
memset(dev->mem,0,GLOBALFIFO_SIZE);
up(&dev->sem); //释放信号量
printk(KERN_INFO "globalfifo is set to zero\n");
break;
default:
return - EINVAL;
}
return 0;
}
static unsigned int globalfifo_poll(struct file *filp, poll_table *wait)
{
unsigned int mask = 0;
struct globalfifo_dev *dev = filp->private_data; /*获得设备结构体指针*/
down(&dev->sem);
poll_wait(filp, &dev->r_wait, wait);//1 对可能引起的设备状态改变的等待队列调用poll_wait，
//所做的工作是把当前进程添加到poll_table参数指定的等待列表中,不阻塞
poll_wait(filp, &dev->w_wait, wait);
/*fifo非空*/
if (dev->current_len != 0)
{
mask |= POLLIN | POLLRDNORM; /*标示数据可获得*/
}
/*fifo非满*/
if (dev->current_len != GLOBALFIFO_SIZE)
{
mask |= POLLOUT | POLLWRNORM; /*标示数据可写入*/
}
up(&dev->sem);
return mask; //返回是否能对设备进行无阻塞读，写访问的掩码
}
/*globalfifo读函数*/
static ssize_t globalfifo_read(struct file *filp, char __user *buf, size_t count,
loff_t *ppos)
{
int ret;
struct globalfifo_dev *dev = filp->private_data; //获得设备结构体指针
DECLARE_WAITQUEUE(wait, current); //定义等待队列
down(&dev->sem); //获得信号量
add_wait_queue(&dev->r_wait, &wait); //进入读等待队列头
/* 等待FIFO非空 */
while (dev->current_len == 0)//数据空间为空的时候不读。
{
if (filp->f_flags &O_NONBLOCK)
{
ret = - EAGAIN;
goto out;
}
__set_current_state(TASK_INTERRUPTIBLE); //改变进程状态为睡眠
up(&dev->sem);
schedule(); //调度其他进程执行
if (signal_pending(current))
//如果是因为信号唤醒
{
ret = - ERESTARTSYS;
goto out2;
}
down(&dev->sem);
}
/* 拷贝到用户空间 */
if (count > dev->current_len)
count = dev->current_len;
if (copy_to_user(buf, dev->mem, count))
{
ret = - EFAULT;
goto out;
}
else
{
memcpy(dev->mem, dev->mem + count, dev->current_len - count); //fifo数据前移
dev->current_len -= count; //有效数据长度减少
printk(KERN_INFO "read %d bytes(s),current_len:%d\n", count, dev->current_len);
wake_up_interruptible(&dev->w_wait); //唤醒写等待队列
ret = count;
}
out: up(&dev->sem); //释放信号量
out2:remove_wait_queue(&dev->w_wait, &wait); //从附属的等待队列头移除
set_current_state(TASK_RUNNING);
return ret;
}
/*globalfifo写操作*/
static ssize_t globalfifo_write(struct file *filp, const char __user *buf,
size_t count, loff_t *ppos)
{
struct globalfifo_dev *dev = filp->private_data; //获得设备结构体指针
int ret;
DECLARE_WAITQUEUE(wait, current); //定义并初始化等待队列
down(&dev->sem); //获取信号量
add_wait_queue(&dev->w_wait, &wait); //进入写等待队列头，用于将等待队列wait添加到等待队列头dev->w_wait。
/* 等待FIFO非满 */ 下面代码跟wait_event_interruptible效果差不多，但是区别在于up(&dev->sem); 这一句。所以不能用wait_event_interruptible代替
while (dev->current_len == GLOBALFIFO_SIZE)//满了就不写。
{
if (filp->f_flags &O_NONBLOCK)
//如果是非阻塞访问,即返回
{
ret = - EAGAIN;
goto out;
}
__set_current_state(TASK_INTERRUPTIBLE); //改变进程状态为睡眠，并不调用sleep_on()或interrupttible_sleep_on()等改变当前进程状态为TASK_INTERRUPTIBLE
//这里up意义重大，非如此，则会发生死锁
up(&dev->sem);
schedule(); //调度其他进程执行
if (signal_pending(current))
//如果是因为信号唤醒
{
ret = - ERESTARTSYS;
goto out2;
}
down(&dev->sem); //获得信号量
}
/*从用户空间拷贝到内核空间*/
if (count > GLOBALFIFO_SIZE - dev->current_len)
count = GLOBALFIFO_SIZE - dev->current_len;
if (copy_from_user(dev->mem + dev->current_len, buf, count))
{
ret = - EFAULT;
goto out;
}
else
{
dev->current_len += count;
printk(KERN_INFO "written %d bytes(s),current_len:%d\n", count, dev
->current_len);
wake_up_interruptible(&dev->r_wait); //写设备完了之后唤醒读等待队列，与wait_event_interruptible成对。
ret = count;
}
out: up(&dev->sem); //释放信号量
out2:remove_wait_queue(&dev->w_wait, &wait); //从附属的等待队列头移除wait
set_current_state(TASK_RUNNING);//改变状态
return ret;
}
/*文件操作结构体*/
static const struct file_operations globalfifo_fops =
{
.owner = THIS_MODULE,
.read = globalfifo_read,
.write = globalfifo_write,
.ioctl = globalfifo_ioctl,
.poll = globalfifo_poll,
.open = globalfifo_open,
.release = globalfifo_release,
};
/*初始化并注册cdev*/
static void globalfifo_setup_cdev(struct globalfifo_dev *dev, int index)
{
int err, devno = MKDEV(globalfifo_major, index);
cdev_init(&dev->cdev, &globalfifo_fops);
dev->cdev.owner = THIS_MODULE;
dev->cdev.ops = &globalfifo_fops;
err = cdev_add(&dev->cdev, devno, 1);
if (err)
printk(KERN_NOTICE "Error %d adding LED%d", err, index);
}
/*设备驱动模块加载函数*/
int globalfifo_init(void)
{
int ret;
dev_t devno = MKDEV(globalfifo_major, 0);
/* 申请设备号*/
if (globalfifo_major)
ret = register_chrdev_region(devno, 1, "globalfifo");
else /* 动态申请设备号 */
{
ret = alloc_chrdev_region(&devno, 0, 1, "globalfifo");
globalfifo_major = MAJOR(devno);
}
if (ret < 0)
return ret;
/* 动态申请设备结构体的内存*/
globalfifo_devp = kmalloc(sizeof(struct globalfifo_dev), GFP_KERNEL);
if (!globalfifo_devp) /*申请失败*/
{
ret = - ENOMEM;
goto fail_malloc;
}
memset(globalfifo_devp, 0, sizeof(struct globalfifo_dev));
globalfifo_setup_cdev(globalfifo_devp, 0);
init_MUTEX(&globalfifo_devp->sem); /*初始化信号量*/
init_waitqueue_head(&globalfifo_devp->r_wait); /*初始化读等待队列头*/ 也可使用DECLARE_WAIT_QUEUE_HEAD(name)宏定义并初始化等待队列
init_waitqueue_head(&globalfifo_devp->w_wait); /*初始化写等待队列头*/
return 0;
fail_malloc: unregister_chrdev_region(devno, 1);
return ret;
}
/*模块卸载函数*/
void globalfifo_exit(void)
{
cdev_del(&globalfifo_devp->cdev); /*注销cdev*/
kfree(globalfifo_devp); /*释放设备结构体内存*/
unregister_chrdev_region(MKDEV(globalfifo_major, 0), 1); /*释放设备号*/
}
MODULE_AUTHOR("Song Baohua");
MODULE_LICENSE("Dual BSD/GPL");
module_param(globalfifo_major, int, S_IRUGO);
module_init(globalfifo_init);
module_exit(globalfifo_exit);
#define wait_event_interruptible(wq, condition) \
({ \
int __ret = 0; \
if (!(condition)) \
__wait_event_interruptible(wq, condition, __ret); \
__ret; \
})
#define __wait_event_interruptible(wq, condition, ret) \
do { \
DEFINE_WAIT(__wait); \
\
for (;;) { \
prepare_to_wait(&wq, &__wait, TASK_INTERRUPTIBLE); \
if (condition) \
break; \
if (!signal_pending(current)) { \
schedule(); \
continue; \
} \
ret = -ERESTARTSYS; \
break; \
} \
finish_wait(&wq, &__wait); \
} while (0)
在用户空间可以这样来测试效果：
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/time.h>
#define FIFO_CLEAR 0x1
#define BUFFER_LEN 20
main()
{
int fd, num;
char rd_ch[BUFFER_LEN];
fd_set rfds,wfds;
/*以非阻塞方式打开/dev/globalmem设备文件*/
fd = open("/dev/globalfifo", O_RDONLY | O_NONBLOCK);
if (fd != - 1)
{
/*FIFO清0*/
if (ioctl(fd, FIFO_CLEAR, 0) < 0)
{
printf("ioctl command failed\n");
}
while (1)
{
FD_ZERO(&rfds);
FD_ZERO(&wfds);
FD_SET(fd, &rfds);
FD_SET(fd, &wfds);
select(fd + 1, &rfds, &wfds, NULL, NULL);
/*数据可获得*/
if (FD_ISSET(fd, &rfds))
{
printf("Poll monitor:can be read\n");
}
/*数据可写入*/
if (FD_ISSET(fd, &wfds))
{
printf("Poll monitor:can be written\n");
}
}
}
else
{
printf("Device open failure\n");
}
}