转载：Linux异步通知---fasync_helper()、kill_fasync()函数介绍与使用_面朝大海0902的博客-CSDN博客
一、fasync_helper()与kill_fasync()函数
应用程序通过fcntl置FASYNC标志位，触发对应驱动文件的fasync()函数执行（上节有解释原因Linux异步通知—signal()、fcntl()函数介绍与使用）,该函数需要使用fasync_helper()函数进行fasync_struct结构体初始化，函数原型：
/* * fasync_helper() is used by almost all character device drivers * to set up the fasync queue, and for regular files by the file * lease code. It returns negative on error, 0 if it did no changes * and positive if it added/deleted the entry. */ int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fapp) { if (!on) return fasync_remove_entry(filp, fapp); return fasync_add_entry(fd, filp, fapp); }
之后如果需要往应用层发信号，我们可以使用kill_fasync()函数，我理解该函数最终会往进程pid为fp->fa_file->f_owner->pid的所有线程发送信号。
void kill_fasync(struct fasync_struct **fp, int sig, int band) { if (*fp) { rcu_read_lock(); kill_fasync_rcu(rcu_dereference(*fp), sig, band); rcu_read_unlock(); } }
调用关系如下：
kill_fasync
kill_fasync_rcu
send_sigio
send_sigio_to_task
看下完整的驱动代码如下：
#include <linux/module.h> #include <linux/poll.h> #include <linux/fs.h> #include <linux/errno.h> #include <linux/miscdevice.h> #include <linux/kernel.h> #include <linux/major.h> #include <linux/mutex.h> #include <linux/proc_fs.h> #include <linux/seq_file.h> #include <linux/stat.h> #include <linux/init.h> #include <linux/device.h> #include <linux/tty.h> #include <linux/kmod.h> #include <linux/gfp.h> #include <linux/gpio/consumer.h> #include <linux/platform_device.h> #include <linux/of_gpio.h> #include <linux/of_irq.h> #include <linux/interrupt.h> #include <linux/irq.h> #include <linux/slab.h> #include <linux/fcntl.h> /* by 面朝大海0902 */ struct gpio_key{ int gpio; struct gpio_desc *gpiod; int flag; int irq; }; static struct gpio_key *ptr_gpio_key; static int major =0; static struct class *key_class; static int g_key_value = 0; struct fasync_struct *key_fasync; /* 环形缓冲区 */ #define BUF_LEN 128 static int g_keys[BUF_LEN]; static int r, w; #define NEXT_POS(x) ((x+1) % BUF_LEN) static int is_key_buf_empty(void) { return (r == w); } static int is_key_buf_full(void) { return (r == NEXT_POS(w)); } static void put_key(int key) { if (!is_key_buf_full()) { g_keys[w] = key; w = NEXT_POS(w); } } static int get_key(void) { int key = 0; if (!is_key_buf_empty()) { key = g_keys[r]; r = NEXT_POS(r); } return key; } static DECLARE_WAIT_QUEUE_HEAD(key_wait); static int key_drv_read(struct file *file, char __user *buf, size_t size, loff_t *offset) { printk(KERN_INFO "%s %s line is %d \r\n", __FILE__, __FUNCTION__, __LINE__); wait_event_interruptible(key_wait, !is_key_buf_empty()); g_key_value = get_key(); copy_to_user(buf, &g_key_value, 4); return 4; } /* by 面朝大海0902 */ static unsigned int key_drv_poll(struct file *fp, poll_table * wait) { printk(KERN_INFO "%s %s line is %d \r\n", __FILE__, __FUNCTION__, __LINE__); poll_wait(fp, &key_wait, wait);//非阻塞函数 return is_key_buf_empty() ? 0 : POLLIN | POLLRDNORM; } static int key_drv_fasync(int fd, struct file *file, int on) { printk(KERN_INFO "%s %s line is %d \r\n", __FILE__, __FUNCTION__, __LINE__); if(fasync_helper(fd, file, on, &key_fasync) >= 0) return 0; else return -EIO; } static struct file_operations key_drv = { .owner = THIS_MODULE, .read = key_drv_read, .poll = key_drv_poll, .fasync = key_drv_fasync, }; /* by 面朝大海0902 */ static irqreturn_t gpio_key_isr(int irq, void *dev_id) { int value; struct gpio_key *ptr_gpio_key_temp = dev_id; value = gpiod_get_value(ptr_gpio_key_temp->gpiod); g_key_value = (ptr_gpio_key_temp->gpio << 8) | value; printk(KERN_INFO "g_key_value is %d \r\n", g_key_value); put_key(g_key_value); wake_up_interruptible(&key_wait); kill_fasync(&key_fasync, SIGIO, POLLIN); return IRQ_HANDLED; } static int key_probe(struct platform_device *pdev) { int count = 0; int i=0; enum of_gpio_flags flag; struct device_node *node = pdev->dev.of_node; printk(KERN_INFO "%s %s line is %d \r\n", __FILE__, __FUNCTION__, __LINE__); count = of_gpio_count(node); ptr_gpio_key = kzalloc(sizeof(struct gpio_key)*count, GFP_KERNEL); for(i=0;i<count;i++) { ptr_gpio_key[i].gpio = of_get_gpio_flags(node, i, &flag); if(ptr_gpio_key[i].gpio < 0) { printk(KERN_ERR "of_get_gpio_flags is err\r\n"); } ptr_gpio_key[i].gpiod = gpio_to_desc(ptr_gpio_key[i].gpio); ptr_gpio_key[i].flag = flag & OF_GPIO_ACTIVE_LOW; ptr_gpio_key[i].irq = gpio_to_irq(ptr_gpio_key[i].gpio); request_irq(ptr_gpio_key[i].irq, gpio_key_isr, IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, "gpio_key", &ptr_gpio_key[i]); } major = register_chrdev(0, "my_keydrv", &key_drv); key_class = class_create(THIS_MODULE, "my_key_class"); if(IS_ERR(key_class)) { printk(KERN_ERR "class_create is err\r\n"); } device_create(key_class, NULL, MKDEV(major, 0), NULL, "my_key%d", 0); return 0; } static int key_remove(struct platform_device *pdev) { int count = 0; int i = 0; struct device_node *node = pdev->dev.of_node; printk(KERN_INFO "%s %s line is %d \r\n", __FILE__, __FUNCTION__, __LINE__); count = of_gpio_count(node); device_destroy(key_class, MKDEV(major, 0)); class_destroy(key_class); unregister_chrdev(major, "my_keydrv"); for(i=0;i<count;i++) { free_irq(ptr_gpio_key[i].irq, &ptr_gpio_key[i]); } kfree(ptr_gpio_key); return 0; } /* by 面朝大海0902 */ static const struct of_device_id my_key[] = { {.compatible = "my,key_driver"}, {}, }; /* by 面朝大海0902 */ static struct platform_driver key_driver = { .probe = key_probe, .remove = key_remove, .driver = { .name = "key_gpio", .of_match_table = my_key, }, }; static int __init my_key_init(void) { int result; printk(KERN_INFO "%s %s line is %d \r\n", __FILE__, __FUNCTION__, __LINE__); result = platform_driver_register(&key_driver); return result; } /* by 面朝大海0902 */ static void __exit my_key_exit(void) { printk(KERN_INFO "%s %s line is %d \r\n", __FILE__, __FUNCTION__, __LINE__); platform_driver_unregister(&key_driver); } module_init(my_key_init); module_exit(my_key_exit); MODULE_LICENSE("GPL");
将驱动程序编译加载，并跑上面的应用程序，测试按键，通过打印可以看到应用程序刚运行起来设置文件FASYNC标志时触发驱动key_drv_fasync()函数调用；
不按键超时打印“by mianchaodahai 0902”，按键后首先中断处理函数gpio_key_isr()被调用并通过kill_fasync()函数向应用发送信号，应用注册的信号处理函数sig_func()被回调到读取key值并触发内核read函数执行，实验结果打印如下：
./key-fasync-test /dev/my_key0 [ 311.353315] /home/book/code/test/key-fasync.c key_drv_fasync line is 100 by mianchaodahai 0902 by mianchaodahai 0902 [ 318.209253] g_key_value is 33024 [ 318.213132] /home/book/code/test/key-fasync.c key_drv_read line is 82 get button : 0x8100 by mianchaodahai 0902 [ 318.391082] g_key_value is 33025 [ 318.394867] /home/book/code/test/key-fasync.c key_drv_read line is 82 get button : 0x8101 by mianchaodahai 0902