字符设备注册步骤：
1.分配cdev结构体
2.分配设备号，register_chrdev_region()/alloc_chrdev_region();
3.添加设备到系统，cdev_add();
字符设备注销步骤：
1. 从系统中删除设备，cdev_del();
2. 释放设备号，unregister_chrdev_region();
除了以上按步骤注册/注销字符设备外，系统也提供了函数直接完成设备的注册与注销。
1 /** 2 * __register_chrdev() - create and register a cdev occupying a range of minors 3 * @major: major device number or 0 for dynamic allocation 4 * @baseminor: first of the requested range of minor numbers 5 * @count: the number of minor numbers required 6 * @name: name of this range of devices 7 * @fops: file operations associated with this devices 8 * 9 * If @major == 0 this functions will dynamically allocate a major and return 10 * its number. 11 * 12 * If @major > 0 this function will attempt to reserve a device with the given 13 * major number and will return zero on success. 14 * 15 * Returns a -ve errno on failure. 16 * 17 * The name of this device has nothing to do with the name of the device in 18 * /dev. It only helps to keep track of the different owners of devices. If 19 * your module name has only one type of devices it's ok to use e.g. the name 20 * of the module here. 21 */ 22 int __register_chrdev(unsigned int major, unsigned int baseminor, 23 unsigned int count, const char *name, 24 const struct file_operations *fops) 25 { 26 struct char_device_struct *cd; 27 struct cdev *cdev; 28 int err = -ENOMEM; 29 30 cd = __register_chrdev_region(major, baseminor, count, name); 31 if (IS_ERR(cd)) 32 return PTR_ERR(cd); 33 34 cdev = cdev_alloc(); 35 if (!cdev) 36 goto out2; 37 38 cdev->owner = fops->owner; 39 cdev->ops = fops; 40 kobject_set_name(&cdev->kobj, "%s", name); 41 42 err = cdev_add(cdev, MKDEV(cd->major, baseminor), count); 43 if (err) 44 goto out; 45 46 cd->cdev = cdev; 47 48 return major ? 0 : cd->major; 49 out: 50 kobject_put(&cdev->kobj); 51 out2: 52 kfree(__unregister_chrdev_region(cd->major, baseminor, count)); 53 return err; 54 } 55 static inline int register_chrdev(unsigned int major, const char *name, 56 const struct file_operations *fops) 57 { 58 return __register_chrdev(major, 0, 256, name, fops); 59 }
1 /** 2 * __unregister_chrdev - unregister and destroy a cdev 3 * @major: major device number 4 * @baseminor: first of the range of minor numbers 5 * @count: the number of minor numbers this cdev is occupying 6 * @name: name of this range of devices 7 * 8 * Unregister and destroy the cdev occupying the region described by 9 * @major, @baseminor and @count. This function undoes what 10 * __register_chrdev() did. 11 */ 12 void __unregister_chrdev(unsigned int major, unsigned int baseminor, 13 unsigned int count, const char *name) 14 { 15 struct char_device_struct *cd; 16 17 cd = __unregister_chrdev_region(major, baseminor, count); 18 if (cd && cd->cdev) 19 cdev_del(cd->cdev); 20 kfree(cd); 21 } 22 static inline void unregister_chrdev(unsigned int major, const char *name) 23 { 24 __unregister_chrdev(major, 0, 256, name); 25 }