基於宋寶華老師的字元裝置驅動

作為linux驅動小白，在這裡謝謝song的指導，在這裡記載一下核心模組的編譯與載入(若發現錯誤，請給我留言)

以下是宋寶華老師的字元裝置驅動程式

#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>

#define GLOBALMEM_SIZE 0x1000
#define MEM_CLEAR 0X1
#define GLOBALMEM_MAJOR 111

static int globalmem_major = GLOBALMEM_MAJOR;

struct globalmem_dev{
 struct cdev cdev;
 unsigned char mem[GLOBALMEM_SIZE];
};

struct globalmem_dev *globalmem_devp;

int globalmem_open(struct inode *inode, struct file *filp)
{
 filp->private_data = globalmem_devp;
 return 0;
}

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

static int globalmem_ioctl(struct inode *inodep, struct file *filp, unsigned int cmd, unsigned long arg )
{
 struct globalmem_dev *dev = filp->private_data;
 
 switch (cmd) {
 case MEM_CLEAR:
  memset(dev->mem, 0, GLOBALMEM_SIZE);
  printk(KERN_INFO "globalmem is set to zero \n");
  break;
 default:
  return - EINVAL;
 }
 return 0;
}

static ssize_t globalmem_read(struct file *filp, char __user *buf, size_t size,loff_t *ppos)
{
 unsigned int p = *ppos;
 unsigned int count = size;
 int ret = 0;
 struct globalmem_dev *dev = filp->private_data;
 if(p >= GLOBALMEM_SIZE)
  return 0;
 if(count > GLOBALMEM_SIZE - p)
  count = GLOBALMEM_SIZE - p;
 
 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 %d\n", count, p);
 }
 
 return ret;
}

static ssize_t globalmem_write(struct file *filp, const char __user *buf, size_t size,loff_t *ppos)
{
 unsigned int p = *ppos;
 unsigned int count = size;
 int ret = 0;
 struct globalmem_dev *dev = filp->private_data;
 if(p >= GLOBALMEM_SIZE)
  return 0;
 if(count > GLOBALMEM_SIZE - p)
  count = GLOBALMEM_SIZE - p;
 
 if(copy_from_user(dev->mem + p, buf, count))
  ret = - EFAULT;
 else {
  *ppos +=  count;
  ret = count;
  printk(KERN_INFO "write %d bytes(s) from %d\n", count, p);
 }
 return ret;
}

static loff_t globalmem_llseek(struct file *filp, loff_t offset, int orig)
{
 loff_t ret = 0;
 switch(orig){
 case 0:
  if(offset < 0){
   ret = -EINVAL;
   break;
  }
  if((unsigned int)offset > GLOBALMEM_SIZE ){
   ret = -EINVAL;
   break;
  }
  filp->f_pos = (unsigned int)offset;
  ret = filp->f_pos;
  break;
 case 1:
  if((filp->f_pos + offset) > GLOBALMEM_SIZE){
   return -EINVAL;
   break;
  }
  if((filp->f_pos + offset) <0){
   return -EINVAL;
   break;
  }
  filp->f_pos += offset;
  ret = filp->f_pos;
  break;
 default:
  ret = -EINVAL;
  break;
 }
 return ret;
}

static const struct file_operations globalmem_fops = {
 .owner = THIS_MODULE,
 .llseek = globalmem_llseek,
 .read = globalmem_read,
 .write = globalmem_write,
 .ioctl = globalmem_ioctl,
 .open = globalmem_open,
 .release = globalmem_release,
};

static void globalmem_setup_cdev(struct globalmem_dev *dev,int index)
{
 int err, devno = MKDEV(globalmem_major,index);
 
 cdev_init(&dev->cdev, &globalmem_fops);
 dev->cdev.owner = THIS_MODULE;
 dev->cdev.ops = &globalmem_fops;
 err = cdev_add(&dev->cdev,devno,1);
 if(err)
  printk(KERN_NOTICE "Error %d adding globalmem %d",err,index);
 
}
 
int globalmem_init(void)
{
 int result;
 dev_t devno = MKDEV(globalmem_major,0);
 
 if (globalmem_major)
  result = register_chrdev_region(devno,1,"globalmem");
 else {
  result = alloc_chrdev_region(&devno,0,1,"globalmem");
  globalmem_major = MAJOR(devno);
 }
 if (result < 0)
  return result;
 
 globalmem_devp = kmalloc(sizeof(struct globalmem_dev),GFP_KERNEL);
 if (!globalmem_devp){
  result = - ENOMEM;
  goto fail_malloc;
 }
 
 memset(globalmem_devp,0,sizeof(struct globalmem_dev));
 
 globalmem_setup_cdev(globalmem_devp,0);
 return 0;
 
fail_malloc:
 unregister_chrdev_region(devno,1);
 return result;
 
}

void globalmem_exit(void)
{
 cdev_del(&globalmem_devp->cdev);
 kfree(globalmem_devp);
 unregister_chrdev_region(MKDEV(globalmem_major,0),1);
}

MODULE_AUTHOR("lirui's first driver");
MODULE_LICENSE("Dual BSD/GPL");

module_param(globalmem_major,int,S_IRUGO);

module_init(globalmem_init);
module_exit(globalmem_exit);

到這裡程式就結束了，下面就是核心模組的編譯與載入了

第一步編寫Makefile

以下是基於不同平臺的Makefile

 第一種

ifneq ($(KERNELRELEASE),)

obj-m := memdev.o

else
 
KDIR := /opt/linux-2.6.30.4
all:
 make -C $(KDIR) M=$(PWD) modules ARCH=arm CROSS_COMPILE=arm-linux-
clean:
 rm -f *.ko *.o *.mod.o *.mod.c *.symvers

endif

 第二種

ifneq ($(KERNELRELEASE),)

obj-m := memdev.o

else
 
KDIR := /lib/modules/$(shell uname -r)/build
all:
 make -C $(KDIR) M=$(PWD) modules
clean:
 rm -f *.ko *.o *.mod.o *.mod.c *.symvers

endif

一，二種的區別主要在於KDIR不同，根據執行平臺不同選擇好路徑

第一種編譯出的模組執行於ARM平臺（KDIR所指的路徑為已配置好的基於arm平臺的核心）。第二種執行於LINUX下。

 

第二步編譯 make

在這注意，驅動程式放置在任何目錄下都可以，但是必須與Makefile放置在一個目錄下

 

第三步 載入模組 insmod  xxx.ko

在這注意，若編寫Makefile是指定的目錄是已裁剪好的基於ARM平臺的核心的目錄，卻在linux下insmod，則會出現錯誤insmod: error inserting 'memdev.ko': -1 Invalid module format

 

第四步 建立節點 mknod  /dev/globalmem  c 111 0

可以通過命令 cat  /proc/devices 檢視

 

第五步就是測試一下了

echo "hello word" > /etc/globalmem

cat /etc/globalmem

 

最後一步就是解除安裝了 rmmod memdev