Linux字元裝置驅動程式

實驗內容：
使用記憶體模擬字元裝置，編寫一個簡單字元型別裝置驅動程式（要求該驅動程式支援字元的讀寫操作和字元裝置的開啟與釋放），然後採用make命令對該程式進行編譯生成模組，並將該模組動態插入到Linux核心。在此基礎上再編寫一個測試程式來測試所編寫的字元裝置驅動程式
實驗過程：
（1）字元裝置驅動程式原始碼

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/slab.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 <linux/version.h>
#if LINUX_VERSION_CODE > KERNEL_VERSION(3,3,0)
#include <asm/switch_to.h>
#else
#include <asm/system.h>
#endif
#include <asm/uaccess.h>
#include "memdev.h"


static mem_major = MEMDEV_MAJOR;
module_param(mem_major, int, S_IRUGO);
struct mem_dev *mem_devp; 
struct cdev cdev;
int mem_open(struct inode *inode, struct file *filp)
{
    struct mem_dev *dev;
    int num = MINOR(inode->i_rdev);

    if (num >= MEMDEV_NR_DEVS)
            return -ENODEV;
    dev = &mem_devp[num];


    filp->private_data = dev;
    return 0;
}

int mem_release(struct inode *inode, struct file *filp)
{
  return 0;
}
 
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; 

  if (p >= MEMDEV_SIZE)
    return 0;
  if (count > MEMDEV_SIZE - p)
    count = MEMDEV_SIZE - p;

  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;
}

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; 
  if (p >= MEMDEV_SIZE)
    return 0;
  if (count > MEMDEV_SIZE - p)
    count = MEMDEV_SIZE - p;
  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;
}
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 ((newpos<0) || (newpos>MEMDEV_SIZE))
     return -EINVAL;
    filp->f_pos = newpos;
    return newpos;

}

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,
};


static int memdev_init(void)
{
  int result;
  int i;
  dev_t devno = MKDEV(mem_major, 0);
  if (mem_major)
    result = register_chrdev_region(devno, 2, "memdev");
  else 
  {
    result = alloc_chrdev_region(&devno, 0, 2, "memdev");
    mem_major = MAJOR(devno);
  }
  if (result < 0)
    return result;
  cdev_init(&cdev, &mem_fops);
  cdev.owner = THIS_MODULE;
  cdev.ops = &mem_fops;
  cdev_add(&cdev, MKDEV(mem_major, 0), MEMDEV_NR_DEVS); 
  mem_devp = kmalloc(MEMDEV_NR_DEVS * sizeof(struct mem_dev), GFP_KERNEL);
  if (!mem_devp) 
  {
    result = - ENOMEM;
    goto fail_malloc;
  }
  memset(mem_devp, 0, sizeof(struct mem_dev));
  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;
}

static void memdev_exit(void)
{
  cdev_del(&cdev); 
  kfree(mem_devp); 
  unregister_chrdev_region(MKDEV(mem_major, 0), 2);
}
MODULE_LICENSE("GPL");
module_init(memdev_init);
module_exit(memdev_exit);
 

（2）makefile檔案內容

ifneq ($(KERNELRELEASE),)
obj-m:=memdev.o
else
KERNELDIR:=/lib/modules/$(shell uname -r)/build
PWD:=$(shell pwd)
default:
 $(MAKE) -C $(KERNELDIR) M=$(PWD) modules
clean:
 rm -rf *.o *.mod.c *.mod.o *.ko
endif

（3）編譯生成字元裝置驅動程式模組及模組安裝
uname -r 命令來檢視當前核心的版本號
sudo make -C /lib/modules/3.5.0-17-generic/build M=/home/lenovo/zhang modules
cat /proc/devices
sudo insmod ./memdev.ko
（4）測試程式
原始碼：

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <linux/i2c.h>
#include <linux/fcntl.h>

int main()
{
 int fd;
 char buf[]="this is a example for character devices driver!";
 char buf_read[4096]; 
 if((fd=open("/dev/memdev",O_RDWR))==-1) 
  printf("open memdev WRONG \n");
 else
  printf("open memdev SUCCESS!\n");
 printf("buf is %s\n",buf);
 write(fd,buf,sizeof(buf));  
 lseek(fd,0,SEEK_SET); 
 read(fd,buf_read,sizeof(buf)); 
 printf("buf_read is %s\n",buf_read);
 return 0;
}
 

ubuntu中內容
在/dev/目錄下建立與該驅動程式相對應的檔案節點
sudo mknod /dev/memdev c 260 0
改變檔案節點的許可權
sudo chmod 777 /dev/memdev
測試驅動程式
編譯memdevtest.c，然後測試執行
解除安裝程式
sudo rmmod ./memdev.ko
刪除檔案結點
sudo rm /dev/memdev
再檢視
cat /proc/devices
實驗截圖：