信号量和队列：semaphore and wait_queue_head_t

这一次是在globalmem的字符设备驱动的基础上，增加了并发控制（也就是多进程多共享资源的访问的控制），还增加了阻塞I/O 和poll轮询操作，因为我还是菜鸟，有很多东西还不懂，希望与大侠能指点学习Linux设备驱动的要点和关键点。还是看代码吧

#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 /* 清零全局内存的长度 */#define GLOBALFIFO_MAJOR 250 /* 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 */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/* 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;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; //获取设备结构体指针down(&dev->sem);poll_wait(filp, &dev->r_wait, wait);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;}/* 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;DECLARE_WAITQUEUE(wait, current); //定义等待队列down(&dev->sem); //获取信号量add_wait_queue(&dev->r_wait,&wait); //进入读等待队列头//等待FIFO非空if(dev->current_len == 0){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; // 获取设备结构体指针int ret ;DECLARE_WAITQUEUE(wait, current); // 定义等待队列down(&dev->sem); //获取信号量add_wait_queue(&dev->w_wait, &wait); //进入写等待队列头/* 等待FIFO非满 */if(dev->current_len == GLOBALFIFO_SIZE){if(filp->f_flags & O_NONBLOCK){//如果是非阻塞访问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); //获取信号量}/* 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, current_len:%d\n", count, dev->current_len);wake_up_interruptible(&dev->r_wait); //唤醒读等待队列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;}/* 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_INFO "Error %d adding LED%d", err, index);}/* 设备驱动模块加载 */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){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cdevkfree(globalfifo_devp); //释放设备结构内存unregister_chrdev_region(MKDEV(globalfifo_major, 0), 1); // 释放设备号}MODULE_LICENSE("Dual BSD/GPL");module_param(globalfifo_major, int, S_IRUGO);module_init(globalfifo_init);module_exit(globalfifo_exit);