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
标签：__,struct,helper,int,---,fasync,key,include From： https://www.cnblogs.com/zhiminyu/p/17614969.html