[Linux内核驱动]异步通知

异步通知

概念

异步通知：一旦设备就绪，则主动通知应用程序，这样应用程序就不需要查询设备状态，类似于“中断”。Linux中通过信号来通知应用程序。

信号的接收

在应用程序中，可以通过signal()函数来设置对应信号的处理函数。

void (*signal)(int signum,void(*handler)(int))(int);

-

第一个参数指定信号的值，即信号类型

-

第二个参数指定信号的处理函数

• 若是 SIG_IGN 表示忽略该信号
• 若是 SIG_DFL 表示使用默认处理函数

-

如果signal()调用成功返回处理函数handler的值，失败返回SIG_ERR

信号的释放

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是不够的，因为信号的源头在设备驱动端，所以应该在合适的时机让设备驱动释放信号。

为了让设备驱动支持异步通知机制，驱动程序中涉及3项工作

• 支持 F_SETOWN 命令，能在这个控制命令处理中设置filp->f_owner为对应进程ID（这项工作由内核完成，设备驱动无须处理）。
• 支持 F_SETFL 命令的处理，每当 FASYNC 标志改变时，驱动程序中的 fasyna()函数将执行。所以驱动程序需要实现fasyna()函数。
• 在设备资源可获得时，调用kill_fasync()函数激发相应的信号。

驱动中的上面3项工作和应用程序中的是一一对应的

用户空间驱动空间fcntl(fd, F_SETOWN, getpid())内核设置filp->f_ownerfcntl(fd,F_GETFL)设备驱动fasync()函数signal()函数绑定信号和处理函数资源可获得时，调用kill_fasync()函数释放信号

设备驱动中的异步通知编写

• 处理FASYNC标志变更的函数

int fasync_helper(int fd, struct file *filp, int mode, struct fasync_struct **fa);

• 释放信号用的函数

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

• 模板

struct xxx_dev{
 struct cdev cdev;
 ...
 struct fasync_struct *fasync_queue; // 异步结构体指针
};

static int xxx_fasync(int fd,struct file *filp,int mode)
{
 struct xxx_dev *dev = filp->private_data;
	return fasync_helper(fd, filp, mode, &dev->async_queue);
}

static ssize_t xxx_write(struct file *filp, const char __user *buff, size_t count, loff_t *f_pos)
{
 struct xxx_dev *dev = filp->private_data;
 ...
 // 激发信号
 if(dev->fasync_queue)
 kill_fasync(dev->fasync_queue, SIGIO, POLL_IN);
 ...
}

static int xxx_release(struct inode *inode,struct file *filp)
{
 // 将文件从异步通知列表中删除
 xxx_fasync(-1,filp,0);
 ...
 return 0;
}

测试

dmesg -C

make
gcc test_fasync.c -o test_fasync

insmod fasync.ko
./test_fasync &

echo "hello world" > /dev/fasync0
cat /dev/fasync0

dmesg

rmmod fasync.ko

代码

/*
 * @Date: 2024-05-13 09:57:33
 * @author: lidonghang-02 [email protected]
 * @LastEditTime: 2024-06-03 11:41:27
 */
#include <linux/init.h>
#include <linux/module.h>
#include <linux/cdev.h>
#include <linux/uaccess.h>
#include <linux/slab.h>
#include <linux/device.h>
#include <linux/types.h>
#include <linux/sched.h>
#include <linux/poll.h>

#include "fasync.h"

#define FASYNC_SIZE 0x10
#define FASYNC_MAJOR 0
#define FASYNC_MINOR 0
#define FASYNC_NR_DEVS 1

static int fasync_major = FASYNC_MAJOR;
static int fasync_minor = FASYNC_MINOR;
static int fasync_nr_devs = FASYNC_NR_DEVS;

static struct class *fasync_cls;
struct fasync_dev
{
 struct cdev cdev;
 struct device *class_dev;
 unsigned int len;
 unsigned char mem[FASYNC_SIZE];
 struct mutex mutex;
 wait_queue_head_t r_wq;
 wait_queue_head_t w_wq;

 struct fasync_struct *fasync_queue;
};

static struct fasync_dev *fasync_devp;

static int fasync_fasync_func(int fd, struct file *filp, int mode)
{
 struct fasync_dev *dev = filp->private_data;
 return fasync_helper(fd, filp, mode, &dev->fasync_queue);
}

static int fasync_open_func(struct inode *inode, struct file *filp)
{
 struct fasync_dev *dev = container_of(inode->i_cdev, struct fasync_dev, cdev);
 filp->private_data = dev;
 printk(KERN_INFO "fasync_open\n");
 return 0;
}

static int fasync_release_func(struct inode *inode, struct file *filp)
{
 fasync_fasync_func(-1, filp, 0);
 printk(KERN_INFO "fasync_release\n");
 return 0;
}

static ssize_t fasync_read_func(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
{
 struct fasync_dev *dev = filp->private_data;
 int ret = 0;
 DECLARE_WAITQUEUE(wait, current);
 mutex_lock(&dev->mutex);
 add_wait_queue(&dev->r_wq, &wait);

 while (dev->len == 0)
 {
 if (filp->f_flags & O_NONBLOCK)
 {
 ret = -EAGAIN;
 goto out_1;
 }
 __set_current_state(TASK_INTERRUPTIBLE);
 mutex_unlock(&dev->mutex);

 schedule();
 if (signal_pending(current))
 {
 ret = -ERESTARTSYS;
 goto out_2;
 }
 mutex_lock(&dev->mutex);
 }

 if (count > dev->len)
 count = dev->len;

 if (copy_to_user(buf, dev->mem, count) != 0)
 ret = -EFAULT;
 else
 {
 dev->len = dev->len - count;
 memcpy(dev->mem, dev->mem + count, dev->len);
 ret = count;
 wake_up_interruptible(&dev->w_wq);
 }

out_1:
 mutex_unlock(&dev->mutex);
out_2:
 remove_wait_queue(&dev->r_wq, &wait);
 set_current_state(TASK_RUNNING);
 return ret;
}

static ssize_t fasync_write_func(struct file *filp, const char __user *buf, size_t count, loff_t *f_pos)
{
 int ret = -ENOMEM;
 struct fasync_dev *dev = filp->private_data;
 DECLARE_WAITQUEUE(wait, current);

 mutex_lock(&dev->mutex);
 add_wait_queue(&dev->w_wq, &wait);

 while (dev->len == FASYNC_SIZE)
 {
 if (filp->f_flags & O_NONBLOCK)
 {
 ret = -EAGAIN;
 goto out_1;
 }

 __set_current_state(TASK_INTERRUPTIBLE);

 mutex_unlock(&dev->mutex);

 schedule();
 if (signal_pending(current))
 {
 ret = -ERESTARTSYS;
 goto out_2;
 }
 mutex_lock(&dev->mutex);
 }
 if (count > FASYNC_SIZE - dev->len)
 count = FASYNC_SIZE - dev->len;

 if (copy_from_user(dev->mem + dev->len, buf, count))
 ret = -EFAULT;
 else
 {
 dev->len += count;
 wake_up_interruptible(&dev->r_wq);
 ret = count;

 // 产生异步读信号
 if (dev->fasync_queue)
 {
 kill_fasync(&dev->fasync_queue, SIGIO, POLL_IN);
 printk(KERN_DEBUG "%s kill SIGIO\n", __func__);
 }
 }
out_1:
 mutex_unlock(&dev->mutex);
out_2:
 remove_wait_queue(&dev->w_wq, &wait);
 set_current_state(TASK_RUNNING);
 return ret;
}

static long fasync_ioctl_func(struct file *filp, unsigned int cmd, unsigned long arg)
{
 struct fasync_dev *dev = filp->private_data;
 int ret = 0;

 // 检查幻数(返回值POSIX标准规定，也用-EINVAL)
 if (_IOC_TYPE(cmd) != FASYNC_CHR_MAGIC)
 return -ENOTTY;
 // 检查命令编号
 if (_IOC_NR(cmd) > FASYNC_MAXNR)
 return -ENOTTY;
 // 检查命令方向，并验证用户空间指针的访问权限。
 if (_IOC_DIR(cmd) & _IOC_READ)
 ret = !access_ok(VERIFY_WRITE, (void __user *)arg, _IOC_SIZE(cmd));
 else if (_IOC_DIR(cmd) & _IOC_WRITE)
 ret = !access_ok(VERIFY_READ, (void __user *)arg, _IOC_SIZE(cmd));

 if (ret)
 return -EFAULT;

 switch (cmd)
 {
 case FASYNC_CLEAR:
 mutex_lock(&dev->mutex);
 dev->len = 0;
 memset(dev->mem, 0, FASYNC_SIZE);
 mutex_unlock(&dev->mutex);
 break;
 default:
 return -EINVAL;
 }
 return 0;
}

static unsigned int fasync_poll_func(struct file *filp, poll_table *wait)
{
 unsigned int mask = 0;
 struct fasync_dev *dev = filp->private_data;

 mutex_lock(&dev->mutex);
 poll_wait(filp, &dev->r_wq, wait);
 poll_wait(filp, &dev->w_wq, wait);

 if (dev->len != 0)
 mask |= POLLIN | POLLRDNORM;
 if (dev->len != FASYNC_SIZE)
 mask |= POLLOUT | POLLWRNORM;

 mutex_unlock(&dev->mutex);
 return mask;
}

static const struct file_operations fasync_fops =
 {
 .owner = THIS_MODULE,
 .read = fasync_read_func,
 .write = fasync_write_func,
 .unlocked_ioctl = fasync_ioctl_func,
 .poll = fasync_poll_func,
 .open = fasync_open_func,
 .release = fasync_release_func,
 .fasync = fasync_fasync_func,
};

static int __init fasync_init_module(void)
{
 int ret = 0, i;
 dev_t devno = MKDEV(fasync_major, fasync_minor);

 if (fasync_major)
 ret = register_chrdev_region(devno, fasync_nr_devs, "fasync");
 else
 {
 ret = alloc_chrdev_region(&devno, fasync_minor, fasync_nr_devs, "fasync");
 fasync_major = MAJOR(devno);
 }

 if (ret < 0)
 return ret;

 fasync_devp = kzalloc(sizeof(struct fasync_dev) * fasync_nr_devs, GFP_KERNEL);
 if (!fasync_devp)
 {
 printk(KERN_WARNING "alloc mem failed");
 ret = -ENOMEM;
 goto out_1;
 }

 fasync_cls = class_create(THIS_MODULE, "fasync");
 if (IS_ERR(fasync_cls))
 {
 printk(KERN_WARNING "Error creating class for ioctl");
 goto out_2;
 }

 for (i = 0; i < fasync_nr_devs; i++)
 {
 cdev_init(&fasync_devp[i].cdev, &fasync_fops);
 fasync_devp[i].cdev.owner = THIS_MODULE;
 ret = cdev_add(&fasync_devp[i].cdev, MKDEV(fasync_major, fasync_minor + i), 1);
 if (ret)
 printk(KERN_WARNING "Error adding cdev for device %d", i);
 else
 {
 fasync_devp[i].class_dev = device_create(fasync_cls, NULL, MKDEV(fasync_major, fasync_minor + i), NULL, "fasync%d", i);
 if (IS_ERR(fasync_devp[i].class_dev))
 printk(KERN_WARNING "Error creating device for device %d", i);
 }
 mutex_init(&fasync_devp[i].mutex);
 init_waitqueue_head(&fasync_devp[i].r_wq);
 init_waitqueue_head(&fasync_devp[i].w_wq);
 }
 return 0;
out_2:
 kfree(fasync_devp);
out_1:
 unregister_chrdev_region(devno, fasync_nr_devs);
 return ret;
}

static void __exit fasync_exit_module(void)
{
 int i;
 for (i = 0; i < fasync_nr_devs; i++)
 {
 device_destroy(fasync_cls, MKDEV(fasync_major, fasync_minor + i));
 cdev_del(&fasync_devp[i].cdev);
 }
 class_destroy(fasync_cls);
 kfree(fasync_devp);
 unregister_chrdev_region(MKDEV(fasync_major, fasync_minor), fasync_nr_devs);
 printk(KERN_INFO "fasync exit\n");
}

module_param(fasync_major, int, S_IRUGO);
module_param(fasync_minor, int, S_IRUGO);
module_param(fasync_nr_devs, int, S_IRUGO);

module_init(fasync_init_module);
module_exit(fasync_exit_module);

MODULE_AUTHOR("lidonghang-02");
MODULE_LICENSE("GPL");

#ifndef _FASYNC_H_
#define _FASYNC_H_

#define FASYNC_CHR_MAGIC 'c'

#define FASYNC_CLEAR _IO(FASYNC_CHR_MAGIC, 0)

#define FASYNC_MAXNR 1

#endif /* _FASYNC_H_ */

测试代码

/*
 * @Date: 2024-05-13 11:15:20
 * @author: lidonghang-02 [email protected]
 * @LastEditTime: 2024-06-15 10:36:16
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <signal.h>
#include <sys/stat.h>

static void signalio_handler(int signum)
{
 printf("receive a signal from globalfifo,signalnum:%d\n", signum);
}

void main(void)
{
 int fd, oflags;
 fd = open("/dev/fasync0", O_RDWR, S_IRUSR | S_IWUSR);
 if (fd != -1)
 {
 signal(SIGIO, signalio_handler);
 fcntl(fd, F_SETOWN, getpid());
 oflags = fcntl(fd, F_GETFL);
 fcntl(fd, F_SETFL, oflags | FASYNC);
 while (1)
 {
 sleep(100);
 }
 }
 else
 {
 printf("device open failure\n");
 }
}