代码

  1. #include <linux/module.h>
  2. #include <linux/fs.h>
  3. #include <linux/uaccess.h>
  4. #include <linux/init.h>
  5. #include <linux/cdev.h>
  7. #define DEMO_NAME "my_demo_dev"
  8. static dev_t dev;
  9. static struct cdev *demo_cdev;
  10. static signed count = 1;
  12. static int demodrv_open(struct inode *inode, struct file *file)
  13. {
  14.     int major = MAJOR(inode->i_rdev);
  15.     int minor = MINOR(inode->i_rdev);
  17.     printk("%s: major=%d, minor=%d\n", __func__, major, minor);
  19.     return 0;
  20. }
  22. static int demodrv_release(struct inode *inode, struct file *file)
  23. {
  24.     return 0;
  25. }
  27. static ssize_t
  28. demodrv_read(struct file *file, char __user *buf, size_t lbuf, loff_t *ppos)
  29. {
  30.     printk("%s enter\n", __func__);
  31.     return 0;
  32. }
  34. static ssize_t
  35. demodrv_write(struct file *file, const char __user *buf, size_t count, loff_t *f_pos)
  36. {
  37.     printk("%s enter\n", __func__);
  38.     return 0;
  40. }
  42. static const struct file_operations demodrv_fops = {
  43.     .owner = THIS_MODULE,
  44.     .open = demodrv_open,
  45.     .release = demodrv_release,
  46.     .read = demodrv_read,
  47.     .write = demodrv_write
  48. };
  51. static int __init simple_char_init(void)
  52. {
  53.     int ret;
  55.     ret = alloc_chrdev_region(&dev, 0, count, DEMO_NAME);
  56.     if (ret) {
  57.         printk("failed to allocate char device region");
  58.         return ret;
  59.     }
  61.     demo_cdev = cdev_alloc();
  62.     if (!demo_cdev) {
  63.         printk("cdev_alloc failed\n");
  64.         goto unregister_chrdev;
  65.     }
  67.     cdev_init(demo_cdev, &demodrv_fops);
  69.     ret = cdev_add(demo_cdev, dev, count);
  70.     if (ret) {
  71.         printk("cdev_add failed\n");
  72.         goto cdev_fail;
  73.     }
  75.     printk("succeeded register char device: %s\n", DEMO_NAME);
  76.     printk("Major number = %d, minor number = %d\n",
  77.             MAJOR(dev), MINOR(dev));
  79.     return 0;
  81. cdev_fail:
  82.     cdev_del(demo_cdev);
  83. unregister_chrdev:
  84.     unregister_chrdev_region(dev, count);
  86.     return ret;
  87. }
  89. static void __exit simple_char_exit(void)
  90. {
  91.     printk("removing device\n");
  93.     if (demo_cdev)
  94.         cdev_del(demo_cdev);
  96.     unregister_chrdev_region(dev, count);
  97. }
  99. module_init(simple_char_init);
  100. module_exit(simple_char_exit);
  102. MODULE_LICENSE("GPL");
  103. MODULE_AUTHOR("zhouchengzhu <1073355312@qq.com>");
  104. MODULE_DESCRIPTION("A simple hello world driver");
  105. MODULE_VERSION("2:1.0");

使用

  1. [root@imx6ull:~/NFS]# insmod simple_char.ko
  2. Major number = 245, minor number = 0
  3. [root@imx6ull:~/NFS]# cat /proc/devices  | grep my_demo_dev 
  4. 245 my_demo_dev
  5. # 然后我们查看/dev/下是否存在 主设备号 245 的设备
  6. [root@imx6ull:~/NFS]# ls -al  /dev | grep 245
  7. # 发现并没对应主设备号的设备
  8. # 那么我们自动手动创建两个
  9. # 设备名称为 demo_drv  字符设备  主设备号 245 次设备号 0
  10. [root@imx6ull:~/NFS]# mknod /dev/demo_drv c 245 0 
  11. [root@imx6ull:~/NFS]# mknod /dev/demo_drv1 c 245 1

上面我们创建了设备，现在可以使用设备了。使用下面的测试用例测试

  1. # 输出了主次设备号
  2. [root@imx6ull:~/NFS]# ./test
  3. demodrv_open: major=245, minor=0

测试用例

  1. #include <stdio.h>
  2. #include <fcntl.h>
  3. #include <unistd.h>
  5. # 前面我们创建的设备名称
  6. #define DEMO_DEV_NAME "/dev/demo_drv"
  8. int main()
  9. {
  10.     char buffer[64];
  11.     int fd;
  13.     fd = open(DEMO_DEV_NAME, O_RDONLY);
  14.     if (fd < 0) {
  15.         printf("open device %s failded\n", DEMO_DEV_NAME);
  16.         return -1;
  17.     }
  19.     read(fd, buffer, 64);
  20.     close(fd);
  22.     return 0;
  23. }

使用函数简介

  1. fs/char_dev.c:214
  2. int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
  3.             const char *name)
  4. void unregister_chrdev_region(dev_t from, unsigned count)
  5. struct cdev *cdev_alloc(void)
  6. void cdev_init(struct cdev *cdev, const struct file_operations *fops)
  7. int cdev_add(struct cdev *p, dev_t dev, unsigned count)
  8. void cdev_del(struct cdev *p)

下一篇文章我们将会来分析一下使用到的这些函数。