#include <linux/cdev.h> //for struct cdev
#include <linux/fs.h>  //for struct file
#include <asm-generic/uaccess.h>  //for copy_to_user
#include <linux/errno.h>      //for error number


/* 準備操作方法集 */
/* 
struct file_operations {
  struct module *owner;  //THIS_MODULE
  
  //讀設備
  ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
  //寫設備
  ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);

  //映射內(nèi)核空間到用戶空間
  int (*mmap) (struct file *, struct vm_area_struct *);

  //讀寫設備參數(shù)、讀設備狀態(tài)、控制設備
  long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);

  //打開設備
  int (*open) (struct inode *, struct file *);
  //關(guān)閉設備
  int (*release) (struct inode *, struct file *);

  //刷新設備
  int (*flush) (struct file *, fl_owner_t id);

  //文件定位
  loff_t (*llseek) (struct file *, loff_t, int);

  //異步通知
  int (*fasync) (int, struct file *, int);
  //POLL機制
  unsigned int (*poll) (struct file *, struct poll_table_struct *);
  。。。
};
*/

ssize_t myread(struct file *filep, char __user * user_buf, size_t size, loff_t* offset)
{
  return 0;
}

struct file fops = {
  .owner = THIS_MODULE,
  .read = myread，
  ...
};


/* 字符設備對象類型 */
struct cdev {
  //public  
  struct module *owner;        //模塊所有者（THIS_MODULE），用于模塊計數(shù)
  const struct file_operations *ops; //操作方法集（分工:打開、關(guān)閉、讀/寫、...）
  dev_t dev;             //設備號（第一個）
  unsigned int count;         //設備數(shù)量
  //private
  ...
};

static int __init chrdev_init(void)
{
  ...
  /* 構(gòu)造cdev設備對象 */
  struct cdev *cdev_alloc(void);

  /* 初始化cdev設備對象 */
  void cdev_init(struct cdev*, const struct file_opeartions*);

  /* 為字符設備靜態(tài)申請設備號 */
  int register_chedev_region(dev_t from, unsigned count, const char* name);

  /* 為字符設備動態(tài)申請主設備號 */
  int alloc_chedev_region(dev_t* dev, unsigned baseminor, unsigned count, const char* name);

  MKDEV(ma,mi)  //將主設備號和次設備號組合成設備號
  MAJOR(dev)   //從dev_t數(shù)據(jù)中得到主設備號
  MINOR(dev)   //從dev_t數(shù)據(jù)中得到次設備號

  /* 注冊字符設備對象cdev到內(nèi)核 */
  int cdev_add(struct cdev* , dev_t, unsigned);
  ...
}

static void __exit chrdev_exit(void)
{
  ...
  /* 從內(nèi)核注銷cdev設備對象 */
  void cdev_del(struct cdev* );

  /* 從內(nèi)核注銷cdev設備對象 */
  void cdev_put(stuct cdev *);

  /* 回收設備號 */
  void unregister_chrdev_region(dev_t from, unsigned count);
  ...
}

long copy_from_user(void *to, const void __user * from, unsigned long n)

long copy_to_user(void __user *to, const void *from, unsigned long n)

ssize_t myread(struct file *filep, char __user * user_buf, size_t size, loff_t* offset)
{
  long ret = 0;
  size = size > MAX_KBUF?MAX_KBUF:size;
  if(copy_to_user(user_buf, kbuf,size)
    return -EAGAIN;
  }
  return 0;
}

//mycmd.h
...
#include <asm/ioctl.h>
#define CMDT 'A'
#define KARG_SIZE 36
struct karg{
  int kval;
  char kbuf[KARG_SIZE];
};
#define CMD_OFF _IO(CMDT,0)
#define CMD_ON _IO(CMDT,1)
#define CMD_R  _IOR(CMDT,2,struct karg)
#define CMD_W  _IOW(CMDT,3,struct karg)
...

//chrdev.c
static long demo_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
  static struct karg karg = {
    .kval = 0,
    .kbuf = {0},
  };
  struct karg *usr_arg;

  switch(cmd){
  case CMD_ON:
    /* 開燈 */
    break;
  case CMD_OFF:
    /* 關(guān)燈 */
    break;
  case CMD_R:
    if(_IOC_SIZE(cmd) != sizeof(karg)){
      return -EINVAL;
    }
    usr_arg = (struct karg *)arg;
    if(copy_to_user(usr_arg, &karg, sizeof(karg))){
      return -EAGAIN;
    }
    break;
  case CMD_W:   
    if(_IOC_SIZE(cmd) != sizeof(karg)){
      return -EINVAL;
    }
    usr_arg = (struct karg *)arg;
    if(copy_from_user(&karg, usr_arg, sizeof(karg))){
      return -EAGAIN;
    }
    break;
  default:
    ;
  };
  return 0;
}

Device Drivers --->
    Generic Driver Options --->
      [*]Maintain a devtmpfs filesystem to mount at /dev
      [*] Automount devtmpfs at /dev,after the kernel mounted the rootfs
OR

mount -t sysfs none sysfs /sys
mdev -s //udev也行

class_create(owner,name);
struct device *device_create_vargs(struct class *cls, struct device *parent,dev_t devt, void *drvdata,const char *fmt, va_list vargs);

void class_destroy(struct class *cls);  
void device_destroy(struct class *cls, dev_t devt);

 /* 在/sys中導出設備類信息 */
  cls = class_create(THIS_MODULE,DEV_NAME);

  /* 在cls指向的類中創(chuàng)建一組(個)設備文件 */
  for(i= minor;i<(minor+cnt);i++){
    devp = device_create(cls,NULL,MKDEV(major,i),NULL,"%s%d",DEV_NAME,i);
  } 

/* 在cls指向的類中刪除一組(個)設備文件 */
  for(i= minor;i<(minor+cnt);i++){
    device_destroy(cls,MKDEV(major,i));
  }

  /* 在/sys中刪除設備類信息 */
  class_destroy(cls);       //一定要先卸載device再卸載class