一：异步通知
异步通知的核心是信号，它不同于阻塞与非阻塞方式，阻塞方式访问会使应用程序处于休眠态，等待驱动设备可以使用，非阻塞方式则会通过应用程序的poll函数来不断的轮询，查看驱动设备文件是否可以使用。这两种方式都需要应用程序主动去查询设备的使用情况。而异步通知则是驱动主动去通知应用程序自己可以被访问，应用程序获取到信号后就可以对驱动设备进行读写操作，类似于硬件上使用的“中断”处理方式。
Linux所支持的信号：这些信号相当于中断号，不同的中断号代表了不同的中断，不同的中断所做的处理不同，因此，驱动程序可以通过向应用程序发送不同的信号来实现不同的功能。
#define SIGHUP 1 /* 终端挂起或控制进程终止 */
#define SIGINT 2 /* 终端中断(Ctrl+C 组合键) */
#define SIGQUIT 3 /* 终端退出(Ctrl+\组合键) */
#define SIGILL 4 /* 非法指令 */
#define SIGTRAP 5 /* debug 使用，有断点指令产生 */
#define SIGABRT 6 /* 由 abort(3)发出的退出指令 */
#define SIGIOT 6 /* IOT 指令 */
#define SIGBUS 7 /* 总线错误 */
#define SIGFPE 8 /* 浮点运算错误 */
#define SIGKILL 9 /* 杀死、终止进程 */
#define SIGUSR1 10 /* 用户自定义信号 1 */
#define SIGSEGV 11 /* 段违例(无效的内存段) */
#define SIGUSR2 12 /* 用户自定义信号 2 */
#define SIGPIPE 13 /* 向非读管道写入数据 */
#define SIGALRM 14 /* 闹钟 */
#define SIGTERM 15 /* 软件终止 */
#define SIGSTKFLT 16 /* 栈异常 */
#define SIGCHLD 17 /* 子进程结束 */
#define SIGCONT 18 /* 进程继续 */
#define SIGSTOP 19 /* 停止进程的执行，只是暂停 */
#define SIGTSTP 20 /* 停止进程的运行(Ctrl+Z 组合键) */
#define SIGTTIN 21 /* 后台进程需要从终端读取数据 */
#define SIGTTOU 22 /* 后台进程需要向终端写数据 */
#define SIGURG 23 /* 有"紧急"数据 */
#define SIGXCPU 24 /* 超过 CPU 资源限制 */
#define SIGXFSZ 25 /* 文件大小超额 */
#define SIGVTALRM 26 /* 虚拟时钟信号 */
#define SIGPROF 27 /* 时钟信号描述 */
#define SIGWINCH 28 /* 窗口大小改变 */
#define SIGIO 29 /* 可以进行输入/输出操作 */
#define SIGPOLL SIGIO
/* #define SIGLOS 29 */
#define SIGPWR 30 /* 断点重启 */
#define SIGSYS 31 /* 非法的系统调用 */
#define SIGUNUSED 31 /* 未使用信号 */如果在应用程序中使用信号，那么就必须设置信号所使用的信号处理函数，在应用程序中使用signal函数来设置指定信号的处理函数：
signum：要设置处理函数的信号
handler：信号的处理函数
返回值：设置成功的话返回信号的前一个处理函数，设置失败返回SIG_ERR。
sighandler_t signal(int signum, sighandler_t handler)信号处理函数：
typedef void (*sighandler_t)(int)二：驱动中的信号处理
1、fasync_struct结构体
struct fasync_struct {spinlock_t fa_lock;int magic;int fa_fd;struct fasync_struct *fa_next; /* singly linked list */struct file *fa_file;struct rcu_head fa_rcu;
};2、fasync函数
如果要使用异步通知，需要实现file_operations中的fasync函数：
int (*fasync) (int fd, struct file *filp, int on)
fasync函数中一般通过调用fasync_helper函数来初始化前面定义的fasync_strcut结构体指针：
int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fapp)当应用程序通过函数“fcntl”改变fasync标记的时候，驱动程序file_operations中的fasync函数就会被执行：
（1）应用程序：
重点最后三行代码
fcntl(fd, F_SETOWN, getpid()); //告诉内核
oflags = fcntl(fd, F_GETFL); // 获取当前进程状态
fcntl(fd, F_SETFL, oflags | FASYNC);//改变fasync，会调用驱动中的fasync函数指针对应的函数。
void signal_fun(int signum)
{unsigned char key_val;read(fd, &key_val, 1);printf("key_val: 0x%x\n", key_val);
}int main(int argc, char **argv)
{unsigned char key_val;int ret;int oflags;signal(SIGIO, signal_fun);fd = open("/dev/signal", O_RDWR);if (fd < 0){printf("can't open!\n");}fcntl(fd, F_SETOWN, getpid()); //告诉内核oflags = fcntl(fd, F_GETFL); // 获取当前进程状态fcntl(fd, F_SETFL, oflags | FASYNC);//改变fasync，会调用驱动中的fasync函数指针对应的函数。}（2）驱动程序：
static int signal_drv_fasync(int fd, struct file *filp, int on)
{printk("driver: signal_drv_fasync\n");return fasync_helper (fd, filp, on, &signal_fasync);
}static int signal_drv_release(struct inode *inode, struct file *filp)
{return signal_drv_fasync(-1, filp, 0); /* 删除异步通知 */
}static struct file_operations signal_drv_fops =
{.fasync = signal_drv_fasync,.release = signal_drv_release,
};
3、kill_fasync函数
当设备可以访问的时候，驱动程序需要向应用程序发出信号，相当于产生“中断”，kill_fasync函数负责发送指定信号：
fp：要操作的fasync_struct
sig：要发送的信号
band：可读时设置为POLL_IN，可写时设置为POLL_OUT
void kill_fasync(struct fasync_struct **fp, int sig, int band)static irqreturn_t xxx_irq(int irq, void *dev_id)
{struct pin_desc *pindesc = (struct pin_desc *)dev_id;unsigned int pinval;pinval = xxx_gpio_getpin(pindesc->pin);kill_fasync(&signal_fasync, SIGIO, POLL_IN);return IRQ_RETVAL(IRQ_HANDLED);
}三：示例
1、应用程序
#include "sys/stat.h"
#include "sys/types.h"
#include "unistd.h"
#include "fcntl.h"
#include "stdlib.h"
#include "string.h"
#include "stdio.h"
#include "poll.h"
#include "sys/time.h"
#include "linux/ioctl.h"
#include "signal.h"#define LED_ON 1
#define LED_OFF 0int fd1, fd2;
char keyval, ledval;
char val = 0;static void key_fasync(int signum)
{read(fd1, &keyval, sizeof(keyval));if(keyval == LED_ON){val = !val;}if(val == LED_ON){ledval = LED_ON;write(fd2, &ledval, sizeof(ledval));}else if(val == LED_OFF){ledval = LED_OFF;write(fd2, &ledval, sizeof(ledval));}
}int main(int argc, char const *argv[])
{int flags = 0;if(argc != 3){printf("Error Usage : ./app /dev/key /dev/led\n");}fd1 = open(argv[1], O_RDWR | O_NONBLOCK);if(fd1 < 0){printf("%s can't open!\n", argv[1]);return -1;}fd2 = open(argv[2], O_RDWR);if(fd2 < 0){printf("%s can't open!\n", argv[2]);return -1;}signal(SIGIO, key_fasync);fcntl(fd1, F_SETOWN, getpid());flags = fcntl(fd1, F_GETFD);fcntl(fd1, F_SETFL, flags | FASYNC);while (1){sleep(2);}close(fd2);close(fd1);return 0;
}
2、按键驱动，（LED驱动与第七章内容相同）
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/ide.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/gpio.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_gpio.h>
#include <linux/semaphore.h>
#include <linux/timer.h>
#include <linux/of_irq.h>
#include <linux/irq.h>
#include <asm/mach/map.h>
#include <asm/uaccess.h>
#include <asm/io.h>
#include <linux/poll.h>
#include <linux/fcntl.h>#define KEY_NUM 1struct st_keyirq
{int gpio;int irqnum;unsigned char value;char name[10];irqreturn_t (*handler)(int, void *);
};struct st_keydev {dev_t devid;struct cdev cdev;struct class *class;struct device *device;int major;int minor;struct device_node *nd;struct mutex lock;atomic_t keyvalue;atomic_t releasekey;struct timer_list timer;struct st_keyirq irqkeydesc[KEY_NUM];unsigned char curkeynum;struct fasync_struct *key_fasync;
};
struct st_keydev keydev;
static DECLARE_WAIT_QUEUE_HEAD(key_waitq);static int key_open(struct inode *inode, struct file *file)
{file->private_data = &keydev;if(mutex_trylock(&keydev.lock) == 0){return -EBUSY;}return 0;
}static ssize_t key_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{struct st_keydev *dev = (struct st_keydev *)file->private_data;unsigned char releasekey = 0;char val = 0;int retvalue = 0;releasekey = atomic_read(&dev->releasekey);if(releasekey){val = 1;retvalue = copy_to_user(buf, &val, sizeof(val));atomic_set(&dev->releasekey, 0);}else{val = 0;retvalue = copy_to_user(buf, &val, sizeof(val));}return 0;
}static int key_fasync(int fd, struct file *filp, int on)
{struct st_keydev *dev = (struct st_keydev *)filp->private_data;return fasync_helper(fd, filp, on, &dev->key_fasync);
}static int key_release(struct inode *inode, struct file *file)
{struct st_keydev *dev = (struct st_keydev *)file->private_data;mutex_unlock(&dev->lock);return key_fasync(-1, file, 0);
};struct file_operations key_fops = {.owner = THIS_MODULE,.open = key_open,.read = key_read,.fasync = key_fasync,.release = key_release,
};static irqreturn_t key1_handler(int irq, void *keydev)
{struct st_keydev *dev = (struct st_keydev *)keydev;dev->curkeynum = 0;dev->timer.data = (volatile long)keydev;mod_timer(&dev->timer, jiffies + msecs_to_jiffies(5));return IRQ_RETVAL(IRQ_HANDLED);
}void timer_function(unsigned long data)
{unsigned char value;unsigned char num;struct st_keyirq *keydesc;struct st_keydev *dev = (struct st_keydev *)data;num = dev->curkeynum;keydesc = &dev->irqkeydesc[num];value = gpio_get_value(keydesc->gpio);if(value == 0){atomic_set(&dev->releasekey, 0);}else{atomic_set(&dev->releasekey, 1);if(dev->key_fasync){kill_fasync(&dev->key_fasync, SIGIO, POLL_IN);}}
}static int key1_init(void)
{int retval = 0;unsigned char i = 0;mutex_init(&keydev.lock);keydev.nd = of_find_node_by_path("/key");if(keydev.nd == NULL){printk("Key node not find!\n");return -EINVAL;}else{printk("key node find!\n");}for (i = 0; i < KEY_NUM; i++){keydev.irqkeydesc[i].gpio = of_get_named_gpio(keydev.nd, "key-gpio", i);if(keydev.irqkeydesc[i].gpio < 0){printk("Can't get key%d!\n", i);return -EINVAL;}}for (i = 0; i < KEY_NUM; i++){memset(keydev.irqkeydesc[i].name, 0, sizeof(keydev.irqkeydesc[i].name));sprintf(keydev.irqkeydesc[i].name, "KEY%d", i);retval = gpio_request(keydev.irqkeydesc[i].gpio, keydev.irqkeydesc[i].name);if(retval < 0){printk("request failed!\n");return -EINVAL;}retval = gpio_direction_input(keydev.irqkeydesc[i].gpio);if(retval < 0){printk("set input failed!\n");return -EINVAL;}keydev.irqkeydesc[i].irqnum = irq_of_parse_and_map(keydev.nd, i);printk("key%d:gpio=%d, irqnum=%d\n", i, keydev.irqkeydesc[i].gpio, keydev.irqkeydesc[i].irqnum);}keydev.irqkeydesc[0].handler = key1_handler;for (i = 0; i < KEY_NUM; i++){/* code */retval = request_irq(keydev.irqkeydesc[i].irqnum, keydev.irqkeydesc[i].handler,IRQF_TRIGGER_FALLING | IRQF_TRIGGER_RISING, keydev.irqkeydesc[i].name, &keydev);if(retval < 0){printk("irq %d request failed!\n", keydev.irqkeydesc[i].irqnum);return -EFAULT;}}if(keydev.major){keydev.devid = MKDEV(keydev.major, 0);register_chrdev_region(keydev.devid, 1, "key");}else{alloc_chrdev_region(&keydev.devid, 0, 1, "key");keydev.major = MAJOR(keydev.devid);keydev.minor = MINOR(keydev.devid);}printk("keydev major : %d minor : %d\n", keydev.major, keydev.minor);keydev.cdev.owner = THIS_MODULE;cdev_init(&keydev.cdev, &key_fops);cdev_add(&keydev.cdev, keydev.devid, 1);keydev.class = class_create(THIS_MODULE, "key");keydev.device = device_create(keydev.class, NULL, keydev.devid, NULL, "key");init_timer(&keydev.timer);keydev.timer.function = timer_function;return 0;
}static void key1_exit(void)
{unsigned char i = 0;del_timer_sync(&keydev.timer);for (i = 0; i < KEY_NUM; i++){/* code */free_irq(keydev.irqkeydesc[i].irqnum, &keydev);}device_destroy(keydev.class, keydev.devid);class_destroy(keydev.class);cdev_del(&keydev.cdev);unregister_chrdev_region(keydev.devid, 1);
}module_init(key1_init);
module_exit(key1_exit);
MODULE_LICENSE("GPL");