简单的一个字符设备驱动

#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>/*包含内存管理两个核心函数*/

#include "memdev.h"

static int mem_major=MEM_MAJOR;

struct mem_dev *mem_devp; /*指向设备结构体的指针*/

/*文件打开函数*/

int mem_open(struct inode *inode,struct file *filp)

{

filp->private_data=mem_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 mem_release(struct inode *inode,struct file *filp)

{

return 0;

}

/*ioctl设备控制函数*/

static int mem_ioctl(struct inode *inodep,struct file *filp,unsigned int cmd,unsigned long arg)

{

struct mem_dev *dev=filp->private_data;/*获得设备结构体指针*/

switch(cmd){

case MEM_CLEAR:

memset(dev->mem,0,MEM_SIZE);

printk(KERN_INFO "mem is set to zero!\n");

break;

default:

return -EINVAL;

}

return 0;

}

/*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=0;

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>=MEM_SIZE)

return 0;

if(count>MEM_SIZE-p)

count=MEM_SIZE-p;

/*内核空间--用户空间*/

if(copy_to_user(buf,(void*)(dev->mem+p),count))/*完全复制成功返回0*/

{

ret=-EFAULT;

}

else

{

*ppos+=count;

ret=count;

printk(KERN_INFO "read %u bytes(s) from %lu\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=0;

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>=MEM_SIZE)

return 0;

if(count>MEM_SIZE-p)

count=MEM_SIZE-p;

/*用户空间--内核空间*/

if(copy_from_user(dev->mem+p,buf,count))

ret=-EFAULT;

else{

*ppos+=count;

ret=count;

printk(KERN_INFO "written %u bytes from %lu\n",count,p);

}

return ret;

}

/*seek文件定位函数*/

static loff_t mem_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>MEM_SIZE)

{

ret=-EINVAL;

break;

}

case 1:/*相对文件当前位置偏移*/

if((filp->f_pos+offset)>MEM_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;

break;

}

return ret;

}

/*文件操作结构体,对应的系统调用，实现赋值给函数指针*/

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);/*建立cdev和file_operations之间的连接*/

dev->cdev.owner=THIS_MODULE;

err=cdev_add(&dev->cdev,devno,1);/*向系统添加一个cdev结构体*/

if(err)

printk(KERN_NOTICE"erro %d adding mem %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,0);

/*申请设备号*/

if(mem_major)

result=register_chrdev_region(devno,1,"mem");

else{/*动态申请设备号*/

result=alloc_chrdev_region(&devno,0,1,"mem");

mem_major=MAJOR(devno);

}

if(result<0)

return result;

/*分配cdev为设备结构体分配内存*/

mem_devp=kmalloc(sizeof(struct mem_dev),GFP_KERNEL);

{

if(!mem_devp){/*申请失败*/

result= -ENOMEM;

goto fail_malloc;

}

}

memset(mem_devp,0,sizeof(struct mem_dev));

/*初始化并注册cdev*/

mem_setup_cdev(mem_devp,0);

return 0;

fail_malloc:

unregister_chrdev_region(devno,1);

return result;

}

/*设备模块卸载函数*/

static memdev_exit(void)

{

cdev_del(&mem_devp->cdev);/*注销cdev*/

kfree(mem_devp);/*释放设备结构体内存*/

unregister_chrdev_region(MKDEV(mem_major,0),1);/*释放设备号*/

}

MODULE_AUTHOR("wanghy");

MODULE_LICENSE("GPL");

module_param(mem_major,int ,S_IRUGO);

module_init(memdev_init);

module_exit(memdev_exit);

#define MEM_SIZE 0x1000 /*全局内存最大4KB*/

#define MEM_CLEAR 0x1 /*清零全局内存*/

#define MEM_MAJOR 250 /*预设的主设备号*/

/*mem设备结构体*/

struct mem_dev{

struct cdev cdev; /*cdev结构体*/

unsigned char mem[MEM_SIZE]; /*全局内存*/

};

makefile编写

ifneq ($(KERNELRELEASE),)

obj-m := memdev.o

else

KDIR := /home/whyzl/linux-2.6.37.4

all:

make -C $(KDIR) M=$(PWD) modules ARCH=arm CROSS_COMPILE=arm-linux-

clean:

rm -f *.ko *.o *.mod.o *.mod.c *.symvers modul*

endif