第六章 字符设备驱动

一个间的字符设备驱动是比较简单，并没有考虑太多的问题。。。。

套框架很容易去编写的。。。。。。

#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 0x100//全局内存大小4KB；
#define MEM_CLEAR 0x1//清零全局内存
#define GLOBALMEM_MAJOR 254 //预设的globalmem的主设备号
static int globalmem_major=GLOBALMEM_MAJOR;
struct globalmem_dev
{
 struct cdev cdev;//cdev结构体
 unsigned char mem[GLOBALMEM_SIZE]; //全局内存
};
struct globalmem_dev *globalmem_devp;//设备结构体实例
int globalmem_open(struct inode *inode,struct file *filp)
{
 //将设备结构体指针赋值给文件私有数据指针
 filp->private_data=globalmem_devp;
 return 0;
}
int globalmem_release(struct inode *inode,struct file *filp)
{
 return 0;
}
static ssize_t globalmem_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 globalmem_dev *dev=filp->private_data;
 //分析和获取有效的读长度
 if(p>=GLOBALMEM_SIZE)
  return count? -ENXIO:0;
 if(count>GLOBALMEM_SIZE-p)
  count=GLOBALMEM_SIZE-p;
 //内核空间到用户空间
 if (copy_to_user(buf,(void*)(dev->mem+p),count))
 {
  ret=-EFAULT;
 }
 else
 {
  *ppos+=count;
  ret=count;
  printk(KERN_INFO "read %d bytes from %d \n",count,p);
 }
 return ret;
}
static ssize_t globalmem_write(struct file *filp,char __user *buf,size_t size,loff_t *ppos)
{
 unsigned long p=*ppos;
 unsigned int count=size;
 int ret=0;
 struct globalmem_dev *dev=filp->private_data;//获得设备结构体指针
 //分析和获取有效的读长度
 if(p>=GLOBALMEM_SIZE)
  return count? -ENXIO:0;
 if(count>GLOBALMEM_SIZE-p)
  count=GLOBALMEM_SIZE-p;
 //用户空间到内核空间
 if (copy_from_user(dev->mem+p,buf,count))
 {
  ret=-EFAULT;
 }
 else
 {
  *ppos+=count;
  ret=count;

  printk(KERN_INFO "read %d bytes from %d \n",count,p);
 }
 return ret;

}
static loff_t globalmem_llseek(struct file *filp,loff_t offset,int orig)
{
 loff_t ret;
 switch(orig)
 {
 case 0://从开头开始偏移
  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)
   {
    ret=-EINVAL;
    break;
   }
   if ((filp->f_pos+offset)<0)
   {
    ret=-EINVAL;
    break;
   }
   filp->f_pos+=offset;
   ret=filp->f_pos;
   break;
 default:
  ret=-EINVAL;
 }
 return ret;
}
static int globalmem_ioctl(struct inode *inodep,struct file *filp,unsigned int cmd,unsigned long arg)
{
 struct globalmem_dev *dev=filp->private_data;//获得设备结构体指针
 switch (cmd)
 {
 case MEM_CLEAR:
  memset(dev->mem,0,GLOBALMEM_SIZE);
  printk(KERN_INFO "globalmem is set to zero\n");
  break;
 default:
  return -EINVAL;//其他的命令不支持
 }
 return 0;
}

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,
};
/* 初始化并添加cdev结构体*/
static void globalmem_setup_cdev(struct globalmem_dev *dev,int index)
{
 int err,devno=MKDEV(globalmem_major,0);

 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",err);
 }
}
int globalmem_init(void)
{
 int result;
 dev_t devno=MKDEV(globalmem_major,0);//生产设备号
 // 申请字符设备驱动区域
 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;
 }
 //动态申请设备结构体内存
 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);//删除cdev结构
 kfree(globalmem_devp);
 unregister_chrdev_region(MKDEV(globalmem_major,0),1);//注销设备区域
}
MODULE_LICENSE("GPL");
module_param(globalmem_major,int,S_IRUGO);
module_init(globalmem_init);
module_exit(globalmem_exit);