虚拟内存设备驱动memdev及实例代码

驱动：

#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <asm/io.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <linux/slab.h>
#include <linux/device.h>

#ifndef MEMDEV_MAJOR
#define MEMDEV_MAJOR 0   /*预设的mem的主设备号*/
#endif

#ifndef MEMDEV_NR_DEVS
#define MEMDEV_NR_DEVS 2    /*设备数*/
#endif

#ifndef MEMDEV_SIZE
#define MEMDEV_SIZE 4096
#endif

#define DEVICE_NAME "memdev"

/*udev自动添加设备节点*/
struct class *mem_class;

static int mem_major = MEMDEV_MAJOR;

module_param(mem_major, int, S_IRUGO);

struct mem_dev
{
  struct cdev cdev; /*cdev结构体*/
  unsigned char mem[MEMDEV_SIZE]; /*全局内存*/
};

struct mem_dev *mem_devp; /*设备结构体指针*/

/*文件打开函数*/
int mem_open(struct inode *inode, struct file *filp)
{
    struct mem_dev *dev;

    dev=container_of(inode->i_cdev,struct mem_dev,cdev);//通过结构体成员的指针找到对应结构体的指针

    /*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 ;
}

/*文件释放函数*/
int mem_release(struct inode *inode, struct file *filp)
{
  return ;
}

/*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 = ;
  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 ;
  if (count > MEMDEV_SIZE - p)
    count = MEMDEV_SIZE - p;

  /*读数据到用户空间*/
  if (copy_to_user(buf, (void*)(dev->mem+ p), count))
  {
    ret =  - EFAULT;
  }
  else
  {
    *ppos += count;
    ret = count;

    printk(KERN_INFO "read %d bytes(s) from postion  %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 = ;
  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 ;
  if (count > MEMDEV_SIZE - p)
    count = MEMDEV_SIZE - p;

  /*从用户空间写入数据*/
  if (copy_from_user(dev->mem + p, buf, count))
    ret =  - EFAULT;
  else
  {
    *ppos += count;
    ret = count;

    printk(KERN_INFO "written %d bytes(s) to postion %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 : /* SEEK_SET */
        newpos = offset;
        break;

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

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

      default: /* can't happen */
        return -EINVAL;
    }
    if ((newpos<) || (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,
};

/*初始化并注册cdev*/
static void mem_setup_cdev(struct mem_dev *dev, int index)
{
  int err, devno = MKDEV(mem_major, index);

  cdev_init(&dev->cdev, &mem_fops);
  dev->cdev.owner = THIS_MODULE;
  dev->cdev.ops = &mem_fops;
  err = cdev_add(&dev->cdev, devno, );
  if (err)
    printk(KERN_NOTICE "Error %d adding LED%d", err, index);
}

/*设备驱动模块加载函数*/
static int memdev_init(void)
{
  int result;

  dev_t devno = MKDEV(mem_major, );

  /* 静态申请设备号*/
  if (mem_major)
    result = register_chrdev_region(devno, MEMDEV_NR_DEVS, DEVICE_NAME);
  else  /* 动态分配设备号 */
  {
    result = alloc_chrdev_region(&devno, , MEMDEV_NR_DEVS, DEVICE_NAME);
    mem_major = MAJOR(devno);
  }  

  if (result < )
    return result;

  /* 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, , *sizeof(struct mem_dev));

  /*为设备分配内存*/
  mem_setup_cdev(&mem_devp[], );
  mem_setup_cdev(&mem_devp[], );

  /*udev机制可以自动添加设备节点，只需要添加xxx_class这个类，以及device_create()*/
  mem_class = class_create(THIS_MODULE, "mem_class");/*在sys目录下创建xx_class这个类,/sys/class/~*/
  device_create(mem_class, NULL, mem_devp[].cdev.dev,      NULL, "memdev0");/*自动创建设备/dev/$DEVICE_NAME*/
  device_create(mem_class, NULL, mem_devp[].cdev.dev,   NULL, "memdev1");/*自动创建设备/dev/$DEVICE_NAME*/

  printk("memdev driver installed, with major %d\n", mem_major);
  printk("the device name is %s\n",DEVICE_NAME);
  return ;

  fail_malloc:
  unregister_chrdev_region(devno, );

  return result;
}

/*模块卸载函数*/
static void memdev_exit(void)
{

  device_destroy(mem_class, mem_devp[].cdev.dev);
  device_destroy(mem_class, mem_devp[].cdev.dev);
  class_destroy(mem_class);
  cdev_del(&(mem_devp[].cdev));   /*注销设备*/
  cdev_del(&(mem_devp[].cdev)); 

  kfree(mem_devp);     /*释放设备结构体内存*/
  unregister_chrdev_region(MKDEV(mem_major, ), ); /*释放设备号*/
  printk("memdev driver uninstalled\n");
}

MODULE_AUTHOR("mhb@SEU");
MODULE_LICENSE("GPL");

module_init(memdev_init);
module_exit(memdev_exit);

测试代码：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>

#include <string.h>

int main()
{
    FILE *fp0 = NULL;
    char Buf[];
    int result;

    /*初始化Buf*/
    strcpy(Buf,"Mem is char dev!");
    printf("BUF: %s\n",Buf);

    /*打开设备文件*/
    fp0 = fopen("/dev/memdev0","r+");
    if (fp0 == NULL)
    {
        perror("Open Memdev0 Error!\n");
        return -;
    }

    /*写入设备*/
    result = fwrite(Buf, sizeof(Buf), , fp0);
    if (result  == -)
    {
        perror("fwrite Error!\n");
        return -;
    }

    /*重新定位文件位置（思考没有该指令，会有何后果)*/
    fseek(fp0,,SEEK_SET);

    /*清除Buf*/
    strcpy(Buf,"Buf is NULL!");
    printf("BUF: %s\n",Buf);

    sleep();
    /*读出设备*/
    result = fread(Buf, sizeof(Buf), , fp0);
    if (result  == -)
    {
        perror("fread Error!\n");
        return -;
    }

    /*检测结果*/
    printf("BUF: %s\n",Buf);

    return ;    

}