电子技术论坛_中国专业的电子工程师学习交流社区-中电网技术论坛

标题: linux设备驱动程序之简单字符设备驱动（2） [打印本页]

作者: yuyang911220 时间: 2017-1-25 21:27 标题: linux设备驱动程序之简单字符设备驱动（2）

五：字符设备驱动程序分析：
（1）memdev.h
View Code

(2)memdev.c
复制代码
static mem_major = MEMDEV_MAJOR;
module_param(mem_major, int, S_IRUGO);
struct mem_dev *mem_devp; /*设备结构体指针*/
struct cdev cdev;
/*文件打开函数*/
int mem_open(struct inode *inode, struct file *filp)
{
struct mem_dev *dev;

/*获取次设备号*/
int num = MINOR(inode->i_rdev);
if (num >= MEMDEV_NR_DEVS)
         return -ENODEV;
dev = &mem_devp[num];

/*将设备描述结构指针赋值给文件私有数据指针*/
filp->private_data = dev;

return 0;
}
/*文件释放函数*/
int mem_release(struct inode *inode, struct file *filp)
{
  return 0;
}
/*读函数*/
static ssize_t mem_read(struct file *filp, char __user *buf, size_t size, loff_t *ppos)
{
  unsigned long p =  *ppos;       /*记录文件指针偏移位置*/
  unsigned int count = size; /*记录需要读取的字节数*/
  int ret = 0; /*返回值*/
  struct mem_dev *dev = filp->private_data; /*获得设备结构体指针*/
  /*判断读位置是否有效*/
  if (p >= MEMDEV_SIZE) /*要读取的偏移大于设备的内存空间*/
return 0;
  if (count > MEMDEV_SIZE - p)    /*要读取的字节大于设备的内存空间*/
count = MEMDEV_SIZE - p;
  /*读数据到用户空间:内核空间->用户空间交换数据*/
  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;
}
/*写函数*/
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; /*获得设备结构体指针*/

  /*分析和获取有效的写长度*/
  if (p >= MEMDEV_SIZE)
return 0;
  if (count > MEMDEV_SIZE - p) /*要写入的字节大于设备的内存空间*/
count = MEMDEV_SIZE - p;

  /*从用户空间写入数据*/
  if (copy_from_user(dev->data + p, buf, count))
ret =  - EFAULT;
  else
  {
*ppos += count;    /*增加偏移位置*/
ret = count;    /*返回实际的写入字节数*/

printk(KERN_INFO "written %d bytes(s) from %d\n", count, p);
  }
  return ret;
}
/* seek文件定位函数 */
static loff_t mem_llseek(struct file *filp, loff_t offset, int whence)
{
loff_t newpos;
switch(whence) {
   case 0: /* SEEK_SET */    /*相对文件开始位置偏移*/
      newpos = offset;          /*更新文件指针位置*/
      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;
}
/*文件操作结构体*/
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,
};
/*设备驱动模块加载函数*/
static int memdev_init(void)
{
  int result;
  int i;
  dev_t devno = MKDEV(mem_major, 0);
/* 申请设备号，当xxx_major不为0时，表示静态指定；当为0时，表示动态申请*/
  /* 静态申请设备号*/
  if (mem_major)
result = register_chrdev_region(devno, 2, "memdev");
  else  /* 动态分配设备号 */
  {
result = alloc_chrdev_region(&devno, 0, 2, "memdev");
mem_major = MAJOR(devno); /*获得申请的主设备号*/
  }

  if (result < 0)
return result;
/*初始化cdev结构，并传递file_operations结构指针*/
  cdev_init(&cdev, &mem_fops);
  cdev.owner = THIS_MODULE; /*指定所属模块*/
  cdev.ops = &mem_fops;

  /* 注册字符设备 */
  cdev_add(&cdev, MKDEV(mem_major, 0), MEMDEV_NR_DEVS);

  /* 为设备描述结构分配内存*/
  mem_devp = kmalloc(MEMDEV_NR_DEVS * sizeof(struct mem_dev), GFP_KERNEL);
  if (!mem_devp) /*申请失败*/
  {
result =  - ENOMEM;
goto fail_malloc;
  }
  memset(mem_devp, 0, sizeof(struct mem_dev));

  /*为设备分配内存*/
  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;
}
/*模块卸载函数*/
static void memdev_exit(void)
{
  cdev_del(&cdev); /*注销设备*/
  kfree(mem_devp);    /*释放设备结构体内存*/
  unregister_chrdev_region(MKDEV(mem_major, 0), 2); /*释放设备号*/
}
MODULE_AUTHOR("David Xie");
MODULE_LICENSE("GPL");
module_init(memdev_init);
module_exit(memdev_exit);

欢迎光临电子技术论坛_中国专业的电子工程师学习交流社区-中电网技术论坛 (http://bbs.eccn.com/)