源码

  1. /*mydemodrv_misc.c*/
  2. #include <linux/module.h>
  3. #include <linux/fs.h>
  4. #include <linux/uaccess.h>
  5. #include <linux/init.h>
  6. #include <linux/miscdevice.h>
  8. #define DEMO_NAME "my_demo_dev"
  9. static struct device *mydemodrv_device;
  11. static int demodrv_open(struct inode *inode, struct file *file)
  12. {
  13.     int major = MAJOR(inode->i_rdev);
  14.     int minor = MINOR(inode->i_rdev);
  16.     printk("%s: major=%d, minor=%d\n", __func__, major, minor);
  18.     return 0;
  19. }
  21. static int demodrv_release(struct inode *inode, struct file *file)
  22. {
  23.     return 0;
  24. }
  26. static ssize_t
  27. demodrv_read(struct file *file, char __user *buf, size_t lbuf, loff_t *ppos)
  28. {
  29.     printk("%s enter\n", __func__);
  30.     return 0;
  31. }
  33. static ssize_t
  34. demodrv_write(struct file *file, const char __user *buf, size_t count, loff_t *f_pos)
  35. {
  36.     printk("%s enter\n", __func__);
  37.     return 0;
  39. }
  41. static const struct file_operations demodrv_fops = {
  42.     .owner = THIS_MODULE,
  43.     .open = demodrv_open,
  44.     .release = demodrv_release,
  45.     .read = demodrv_read,
  46.     .write = demodrv_write
  47. };
  49. static struct miscdevice mydemodrv_misc_device = {
  50.     .minor = MISC_DYNAMIC_MINOR,
  51.     .name = DEMO_NAME,
  52.     .fops = &demodrv_fops,
  53. };
  55. static int __init simple_char_init(void)
  56. {
  57.     int ret;
  59.     ret = misc_register(&mydemodrv_misc_device);
  60.     if (ret) {
  61.         printk("failed register misc device\n");
  62.         return ret;
  63.     }
  65.     mydemodrv_device = mydemodrv_misc_device.this_device;
  67.     printk("succeeded register char device: %s\n", DEMO_NAME);
  69.     return 0;
  70. }
  72. static void __exit simple_char_exit(void)
  73. {
  74.     printk("removing device\n");
  76.     misc_deregister(&mydemodrv_misc_device);
  77. }
  79. module_init(simple_char_init);
  80. module_exit(simple_char_exit);
  82. MODULE_LICENSE("GPL");
  83. MODULE_AUTHOR("zhouchengzhu <1073355312@qq.com>");
  84. MODULE_DESCRIPTION("A simple hello world driver");
  85. MODULE_VERSION("2:1.0");

测试用例

  1. #include <stdio.h>
  2. #include <fcntl.h>
  3. #include <unistd.h>
  5. #define DEMO_DEV_NAME "/dev/my_demo_dev"
  7. int main()
  8. {
  9.     char buffer[64];
  10.     int fd;
  12.     fd = open(DEMO_DEV_NAME, O_RDONLY);
  13.     if (fd < 0) {
  14.         printf("open device %s failded\n", DEMO_DEV_NAME);
  15.         return -1;
  16.     }
  18.     read(fd, buffer, 64);
  19.     close(fd);
  21.     return 0;
  22. }

使用

  1. [root@imx6ull:~/NFS]# insmod mydemodrv_misc.ko 
  2. succeeded register char device: my_demo_dev
  3. [root@imx6ull:~/NFS]# ./test.run 
  4. demodrv_open: major=10, minor=56
  5. demodrv_read enter

设备分析

misc字符设备，又称为杂项设备，内核首先把不符合预先确定得字符设备划分为杂项设备。这一类设备得主设备号就是 10。使用得结构体

misc设备

  1. struct miscdevice  {
  2.     int minor;
  3.     const char *name;
  4.     const struct file_operations *fops;
  5.     struct list_head list;
  6.     struct device *parent;
  7.     struct device *this_device;
  8.     const struct attribute_group **groups;
  9.     const char *nodename;
  10.     umode_t mode;
  11. };

对应得API

这两个函数用作创建misc字符设备。

  1. extern int misc_register(struct miscdevice *misc);
  2. extern void misc_deregister(struct miscdevice *misc);

参考资料

各种杂项设备文档
linux MISC 驱动模型分析