globalmem虚拟字符设备驱动--字符驱动讲解（2）

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

#define GLOBALMEM_SIZE 0X1000 /*全局内存最大4KB*/
#define MEM_CLEAR 0x1 /*清零全局内存*/
#define GLOBALMEM_MAJOR 254

static globalmem_major = GLOBALMEM_MAJOR;/*预设的globalmem的主设备号*/

/*globalmem的设备结构体：包含了对应于globalmem字符设备的cdev 和 使用内存mem[GLOBALMEM_SIZE]*/
struct globalmem_dev
{
struct cdev cdev;  //cdev结构体
unsigned char mem[GLOBALMEM_SIZE);  //全局内存
};

struct globalmem_dev *globalmem_devp;  //设备结构体指针

/*文件打开函数*/
int globalmem_open(struct inode *inode,struct file *filp)
{
filp->private_data = globalmem_devp; //将设备结构体指针赋值给文件私有数据指针
return 0
}

/*文件释放函数*/
int globalmem_release(struct inode *inode,struct file *filp)
{
return 0;
}

/*设备控制函数：ioctl()函数接受的MEM_CLEAR命令，这个命令将全局内存的有效数据长度清零，对于设备不支持的命令，ioctl()函数应该返回-EINVAL*/
static int globalmen_ioctl(struct inode *inodep,struct file *filp,unsigned int cmd,unsigned long arg)
{
struct globalmen_dev *dev = filp->private_data; //获得设备结构体指针
switch(cmd)
{
case  MEE_CLEAR:
memset(dev->mem,0,GLOBALMEM_SIZE);
printk(KERN_INFO"globalmem is set to zero\n);
break;
default:
return -EINVAL;
}
return 0;
}

/*读函数：读写函数主要是让设备结构体的mem[]数组与用户空间交互数据，并随着访问字节数变更返回用户的文件读写偏移位置*/
static ssizez_t globalmem_read(struct file *filp,char __user *buf,size_t size,loff_t *opps)
{
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

if(p >= GLOBALMEM_SIZE)  //分析和获取有效的写长度
{
return count ? -ENXIO:0;
}
if(count > GLOBAL_SIZE - P)
{
count = GLOBALMEN_SIZE - P;
}

if(copy_to_user(buf,(void *)(dev->mem+p),count))  //内核空间->用户空间
{
ret = -ENAU;T;
}
else
{
*oppos += count;
ret = count;
printk(KERN_INFO"read %d bytes(s) from %d\n",count,p);
}
return ret;
}

/*写函数*/
static ssize_t globalmem_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 globalmem_dev *dev = filp->private_data;

if(p >= CLOBALMEM_SIZE)  //分析和获取有效的写长度
{
return count? -ENXIO:0;
}

if(count > GLOBALMEN_SIZE - P)
{
count = CLOBALMEN_SIZE - P;
}

if(copy_from_user(dev->mem + p,buf,count)) // 用户空间->内核空间
{
ret = -ENAULT;
}
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：seek()函数对文件定位的起始地址可以是文件开头(SEEK_SET,0)、当前位置(SEEK_CUR,1)、文件尾(SEEK_END,2)*/
static loff_t globalmem_llseek(struct file *filp,loff_t offset,int orig)
{
loff_t ret = 0;
switch(orig)
{
case 0:   //相对文件开始位置偏移
if(offset <0 )
{
ret = -EINVAL;
break;
}

if((unsigned int )offset > GLOBALMEM_SIZE)
{
ret = - EINVAL;
break;
}
filp->f_ops = (unsigned int)offset;
ret = filp->f_pos;
break;

case 1:   //相对文件当前位置偏移
if((filp->f_ops + offset) > GLOBALMEMSIZE)
{
ret = -EINVAL;
break;
}
if((filp->f_ops + offset)<0)
{
ret = -ENVAL;
break;
}
filp->f_ops +=offset;
ret = filp->f_ops;
break;
default:
ret = -EINVAL;
break;
}
return ret;
}

/*文件操作结构体*/
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;
};

/*初始化并注册cdev*/
static void globalmem_setup_cdev(struct globalmem_dev *dev,int index)
{
int err,devno = MKDEV(globalmen_major,index);
cdev_init(&dev->cdev,&globalmem_fops);
dev->cdev.owner = THIS_MOUDEL;
dev->cdev.ops = &golbalmem_fops;
err = cdev_add(&dev->cdev,devno,1);
if(err)
{
printk(KERN_NOTICE"Error %d adding LED%d",err,index);
}

}

/*设备驱动模块加载函数*/
static int __init globalmem_init(void)
{
int result;
dev_t devno = MKDEV(globalmem_major,0);

if(globalmem_major) //申请设备号
{
result = register_chrdev-region(devno,1,"globalmem");
}
else  //动态申请设备号
{
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); //申请设备结构体的内存
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;
}

/*模块卸载函数*/
void __eixt globalmem_exit(void)
{
cdev_del(&globalmem_devp->cdev); //注销cdev
kfree(globalmem_devp);          //释放设备结构体内存
unregister_chrdev_region(MKDEV(globalmem_major,0),1); //释放设备号
}

MODULE_AUTHOR("NOODLE");
MODULE_LICENSE("GPL");

mdule_param(globalmem_major,int,S_IRUGO);

module_init(globalmem_init);
module_exit(globalmem_exit);