LINUX字符设备驱动程序实例(scull)

lionhg

　　【1.系统环境】
　　该驱动程序在UBUNTU10.04LTS编译通过，系统内核为linux-2.6.32-24(可使用uname -r 命令来查看当前内核的版本号)
　　由于安装UBUNTU10.04LTS时，没有安装LINUX内核源码，因此需要在www.kernel.org下载LINUX源码，下载linux-2.6.32.22.tar.bz2(与系统运行的LINUX内核版本尽量保持一致)，使用如下命令安装内核：
1.解压内核

cd /us/src tar jxvf linux-2.6.32.22.tar.bz2

　　2.为系统的include创建链接文件

cd /usr/include rm -rf asm linux scsi ln -s /usr/src/linux-2.6.32.22/include/asm-generic asm ln -s /usr/src/linux-2.6.32.22/include/linux linux ln -s /usr/src/linux-2.6.32.22/include/scsi scsi

LINUX内核源码安装完毕 　　【2.驱动程序代码】
[table=95%,#f1f1f1][tr][td]
/******************************************************************************
*Name: memdev.c
*Desc: 字符设备驱动程序的框架结构，该字符设备并不是一个真实的物理设备，
* 而是使用内存来模拟一个字符设备
*Parameter:
*Return:
*Author: yoyoba(stuyou@126.com)
*Date: 2010-9-26
*Modify: 2010-9-26
********************************************************************************/
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include

#include "memdev.h"

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;
  unsigned int count = size;
  int ret = 0;
  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)
    return 0;
  if (count > MEMDEV_SIZE - p)
    count = MEMDEV_SIZE - p;

  /*读数据到用户空间*/
  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)
    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;
    ret = count;
   
    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 */
        newpos = offset;
        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 ((newposMEMDEV_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);

  /* 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);
  }
  
  if (result