在linux内核中，字符设备是由dev结构体来描述的，它位于/include/linux/cdev.h中
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_CDEV_H
#define _LINUX_CDEV_H#include <linux/kobject.h>
#include <linux/kdev_t.h>
#include <linux/list.h>
#include <linux/device.h>struct file_operations;
struct inode;
struct module;struct cdev {struct kobject kobj;struct module *owner;const struct file_operations *ops;struct list_head list; //list字段来将所有的字符设备组织成一个链表。每个设备由主设备号与次设备号确定，dev_t dev; //dev就是字符设备的设备号，包括主设备号和次设备号unsigned int count; //count字段是同一个主设备号中次设备号的个数
} __randomize_layout;void cdev_init(struct cdev *, const struct file_operations *);struct cdev *cdev_alloc(void);void cdev_put(struct cdev *p);int cdev_add(struct cdev *, dev_t, unsigned);void cdev_set_parent(struct cdev *p, struct kobject *kobj);
int cdev_device_add(struct cdev *cdev, struct device *dev);
void cdev_device_del(struct cdev *cdev, struct device *dev);void cdev_del(struct cd