9--2支持异步通知的globalfifo驱动

在设备驱动和应用程序的异步通知交互中，仅仅在应用程序端捕获信号时不够的，因为信号 没有的源头在设备驱动端。因此，应该在合适的时机让设备驱动释放信号 ，在设备驱动程序中增加信号释放的相关代码。

设备驱动中异步通知编程比较简单，组要用到一项数据结构和两个函数。数据结构式fasync_struct结构体，两个函数分别如下：

 

处理FASYNC标志变更的函数。

int fasync_helper(int fd,struct file *flip,int mode,struct fasync strcuct **fa)

 

释放信号用的函数

void kill_fasync(struct fasync_struct **fa,int sig,in band);

和其他的设备驱动一样，将fasync_struct 结构体指针放在设备结构体重 仍然是 最佳选择，

 

*********************代码说明*********************************

在设备资源可以获得时，应该调用kill_fasync()释放SIGIO信号，可读时第三个参数设置为POLL_IN,可写时

第三个参数设置为POLL—OUT

************************************************************

/*====================================================================== A globalfifo driver as an example of char device drivers This example is to introduce asynchronous notifier The initial developer of the original code is Baohua Song <author@linuxdriver.cn>. All Rights Reserved. ======================================================================*/ #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*/ 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 fasync_struct *async_queue; /* 异步结构体指针，用于读 */ }; 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) { /* 将文件从异步通知列表中删除 */ globalfifo_fasync( - 1, filp, 0); 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); 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 fasync函数*/ static int globalfifo_fasync(int fd, struct file *filp, int mode) { struct globalfifo_dev *dev = filp->private_data; return fasync_helper(fd, filp, mode, &dev->async_queue); } /*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 */ 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; //获得设备结构体指针 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); //唤醒读等待队列 /* 产生异步读信号 */ if (dev->async_queue) kill_fasync(&dev->async_queue, SIGIO, POLL_IN); 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, .fasync = globalfifo_fasync, }; /*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*/ 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);