1.註冊裝置

insmod driverName.ko

//主要是呼叫xxx_init()函式向chrdev中註冊裝置號（代表一類裝置），和將要使用的裝置數量

// xxx_init()中利用函式結構體，file_operations初始化cdev,然後把cdev和註冊的裝置號關聯。

// 利用 cat /proc/devices 可以看到主裝置號，和裝置號。

2.建立裝置檔案

mknod /dev/xxxdevice c 260 1
mknod /dev/xxxdevice c 260 2

3.TODO:

// 區分裝置

4. code 例項（一）

static mem_major = MEMDEV_MAJOR;

module_param(mem_major, int, S_IRUGO);

struct mem_dev *mem_devp; /*裝置結構體指標*/

struct cdev cdev; 

/*檔案開啟函式*/
int mem_open(struct inode *inode, struct file *filp)
{
    struct mem_dev *dev;
    
    /*獲取次裝置號*/
    int num = MINOR(inode->i_rdev);

    if (num >= MEMDEV_NR_DEVS) 
            return -ENODEV;
    dev = &mem_devp[num];
    
    /*將裝置描述結構指標賦值給檔案私有資料指標*/
    filp->private_data = dev;
    
    return 0; 
}

/*檔案釋放函式*/
int mem_release(struct inode *inode, struct file *filp)
{
  return 0;
}

/*讀函式*/
static ssize_t mem_read(struct file *filp, char __user *buf, size_t size, loff_t *ppos)
{
  unsigned long p =  *ppos;        /*記錄檔案指標偏移位置*/  
  unsigned int count = size;    /*記錄需要讀取的位元組數*/ 
  int ret = 0;    /*返回值*/  
  struct mem_dev *dev = filp->private_data; /*獲得裝置結構體指標*/

  /*判斷讀位置是否有效*/
  if (p >= MEMDEV_SIZE)    /*要讀取的偏移大於裝置的記憶體空間*/  
    return 0;
  if (count > MEMDEV_SIZE - p)     /*要讀取的位元組大於裝置的記憶體空間*/ 
    count = MEMDEV_SIZE - p;

  /*讀資料到使用者空間:核心空間->使用者空間交換資料*/  
  if (copy_to_user(buf, (void*)(dev->data + p), count))
  {
    ret =  - EFAULT;
  }
  else
  {
    *ppos += count;
    ret = count;
    
    printk(KERN_INFO "read %d bytes(s) from %d\n", count, p);
  }

  return ret;
}

/*寫函式*/
static ssize_t mem_write(struct file *filp, const char __user *buf, size_t size, loff_t *ppos)
{
  unsigned long p =  *ppos;
  unsigned int count = size;
  int ret = 0;
  struct mem_dev *dev = filp->private_data; /*獲得裝置結構體指標*/
  
  /*分析和獲取有效的寫長度*/
  if (p >= MEMDEV_SIZE)
    return 0;
  if (count > MEMDEV_SIZE - p)    /*要寫入的位元組大於裝置的記憶體空間*/
    count = MEMDEV_SIZE - p;
    
  /*從使用者空間寫入資料*/
  if (copy_from_user(dev->data + p, buf, count))
    ret =  - EFAULT;
  else
  {
    *ppos += count;      /*增加偏移位置*/  
    ret = count;      /*返回實際的寫入位元組數*/ 
    
    printk(KERN_INFO "written %d bytes(s) from %d\n", count, p);
  }

  return ret;
}

/* seek檔案定位函式 */
static loff_t mem_llseek(struct file *filp, loff_t offset, int whence)
{ 
    loff_t newpos;      

    switch(whence) {
      case 0: /* SEEK_SET */       /*相對檔案開始位置偏移*/ 
        newpos = offset;           /*更新檔案指標位置*/
        break;

      case 1: /* SEEK_CUR */
        newpos = filp->f_pos + offset;    
        break;

      case 2: /* SEEK_END */
        newpos = MEMDEV_SIZE -1 + offset;
        break;

      default: /* can't happen */
        return -EINVAL;
    }
    if ((newpos<0) || (newpos>MEMDEV_SIZE))
        return -EINVAL;
        
    filp->f_pos = newpos;
    return newpos;

}

/*檔案操作結構體*/
static const struct file_operations mem_fops =
{
  .owner = THIS_MODULE,
  .llseek = mem_llseek,
  .read = mem_read,
  .write = mem_write,
  .open = mem_open,
  .release = mem_release,
};

/*裝置驅動模組載入函式*/
static int memdev_init(void)
{
  int result;
  int i;

  dev_t devno = MKDEV(mem_major, 0);

   /* 申請裝置號，當xxx_major不為0時，表示靜態指定；當為0時，表示動態申請*/ 
  /* 靜態申請裝置號*/
  if (mem_major)
    result = register_chrdev_region(devno, 2, "memdev");
  else  /* 動態分配裝置號 */
  {
    result = alloc_chrdev_region(&devno, 0, 2, "memdev");
    mem_major = MAJOR(devno);    /*獲得申請的主裝置號*/
  }  
  
  if (result < 0)
    return result;

 /*初始化cdev結構，並傳遞file_operations結構指標*/ 
  cdev_init(&cdev, &mem_fops);    
  cdev.owner = THIS_MODULE;    /*指定所屬模組*/
  cdev.ops = &mem_fops;
  
  /* 註冊字元裝置 */
  cdev_add(&cdev, MKDEV(mem_major, 0), MEMDEV_NR_DEVS);
   
  /* 為裝置描述結構分配記憶體，此處是重點（1）*/
  mem_devp = kmalloc(MEMDEV_NR_DEVS * sizeof(struct mem_dev), GFP_KERNEL);
  if (!mem_devp)    /*申請失敗*/
  {
    result =  - ENOMEM;
    goto fail_malloc;
  }
  memset(mem_devp, 0, sizeof(struct mem_dev));
  
  /*為裝置分配記憶體*/
  for (i=0; i < MEMDEV_NR_DEVS; i++) 
  {
        mem_devp[i].size = MEMDEV_SIZE;
        mem_devp[i].data = kmalloc(MEMDEV_SIZE, GFP_KERNEL);
        memset(mem_devp[i].data, 0, MEMDEV_SIZE);
  }
    
  return 0;

  fail_malloc: 
  unregister_chrdev_region(devno, 1);
  
  return result;
}

/*模組解除安裝函式*/
static void memdev_exit(void)
{
  cdev_del(&cdev);   /*登出裝置*/
  kfree(mem_devp);     /*釋放裝置結構體記憶體*/
  unregister_chrdev_region(MKDEV(mem_major, 0), 2); /*釋放裝置號*/
}

MODULE_AUTHOR("David Xie");
MODULE_LICENSE("GPL");

module_init(memdev_init);
module_exit(memdev_exit);
 

#include <stdio.h>

int main()
{
    FILE *fp0 = NULL;
    char Buf[4096];
    
    /*初始化Buf*/
    strcpy(Buf,"Mem is char dev!");
    printf("BUF: %s\n",Buf);
    
    /*開啟裝置檔案*/
    fp0 = fopen("/dev/memdev0","r+");
    if (fp0 == NULL)
    {
        printf("Open Memdev0 Error!\n");
        return -1;
    }
    
    /*寫入裝置*/
    fwrite(Buf, sizeof(Buf), 1, fp0);
    
    /*重新定位檔案位置（思考沒有該指令，會有何後果)*/
    fseek(fp0,0,SEEK_SET);
    
    /*清除Buf*/
    strcpy(Buf,"Buf is NULL!");
    printf("BUF: %s\n",Buf);
    
    
    /*讀出裝置*/
    fread(Buf, sizeof(Buf), 1, fp0);
    
    /*檢測結果*/
    printf("BUF: %s\n",Buf);
    
    return 0;    

}