1、驱动头文件memdev.h
#ifndef _MEMDEV_H_
#define _MEMDEV_H_
#ifndef MEMDEV_MAJOR
#define MEMDEV_MAJOR 0 /*预设的mem的主设备号*/
#endif
#ifndef MEMDEV_NR_DEVS
#define MEMDEV_NR_DEVS 2 /*设备数*/
#endif
#ifndef MEMDEV_SIZE
#define MEMDEV_SIZE 4096
#endif
/*mem设备描述结构体*/
struct mem_dev {
char *data;
unsigned long size;
struct semaphore sem; /* 定义信号量 */
};
#endif /* _MEMDEV_H_ */
2、驱动源代码文件
#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/errno.h>
#include <linux/cdev.h>
#include <asm/uaccess.h>
#include "memdev.h"
static int mem_major = MEMDEV_MAJOR;
module_param(mem_major, int, S_IRUGO);
struct mem_dev *mem_devp; /*设备结构体指针*/
struct cdev cdev;
/*文件打开函数*/
static int mem_open(struct inode *inode, struct file *filp)
{
struct mem_dev *dev;
/*获取次设备号*/
int num = MINOR(inode->i_rdev);
if (num >= MEMDEV_NR_DEVS)
return -ENODEV;
dev = &mem_devp[num];
/*将设备描述结构指针赋值给文件私有数据指针*/
filp->private_data = dev;
return 0;
}
/*文件释放函数*/
static int mem_release(struct inode *inode, struct file *filp)
{
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*/
/* 获取信号量 */
if (down_interruptible(&dev->sem))// 可以被信号或中断唤醒
return -ERESTARTSYS;
/*判断读位置是否有效*/
if (p >= MEMDEV_SIZE)
return 0;
if (count > MEMDEV_SIZE - p)
count = MEMDEV_SIZE - p;
/*读数据到用户空间*/
if (copy_to_user(buf, (void*)(dev->data + p), count)){
ret = - EFAULT;
goto out;
} else {
*ppos += count;
ret = count;
printk(KERN_INFO "read %d bytes(s) from %d\n", count, p);
}
out:
/* 释放信号量 */
up(&dev->sem);
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*/
/* 获取信号量 */
if (down_interruptible(&dev->sem)) // 可以被信号或中断唤醒
return -ERESTARTSYS;
/*分析和获取有效的写长度*/
if (p >= MEMDEV_SIZE)
return 0;
if (count > MEMDEV_SIZE - p)
count = MEMDEV_SIZE - p;
/*从用户空间写入数据*/
if (copy_from_user(dev->data + p, buf, count))
ret = - EFAULT;
goto out;
else {
*ppos += count;
ret = count;
printk(KERN_INFO "written %d bytes(s) from %d\n", count, p);
}
out:
/* 释放信号量 */
up(&dev->sem);
return ret;
}
/* seek文件定位函数 */
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;
}
/*文件操作结构体*/
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,
};
/*设备驱动模块加载函数*/
static __init int memdev_init(void)
{
int result;
int i;
dev_t devno = MKDEV(mem_major, 0);
/* 静态申请设备号*/
if (mem_major)
result = register_chrdev_region(devno, 2, "memdev");
else { /* 动态分配设备号 */
result = alloc_chrdev_region(&devno, 0, 2, "memdev");
mem_major = MAJOR(devno);
}
if (result < 0)
return result;
/*初始化cdev结构*/
cdev_init(&cdev, &mem_fops);
cdev.owner = THIS_MODULE;
cdev.ops = &mem_fops;
/* 注册字符设备 */
cdev_add(&cdev, MKDEV(mem_major, 0), MEMDEV_NR_DEVS);
/* 为设备描述结构分配内存*/
mem_devp = kmalloc(MEMDEV_NR_DEVS * 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));
/*为设备分配内存*/
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);
/* 初始化信号量 */
sema_init(&mem_devp[i].sem, 1);
}
return 0;
fail_malloc:
unregister_chrdev_region(devno, 1);
return result;
}
/*模块卸载函数*/
static __exit void memdev_exit(void)
{
cdev_del(&cdev); /*注销设备*/
kfree(mem_devp); /*释放设备结构体内存*/
unregister_chrdev_region(MKDEV(mem_major, 0), 2); /*释放设备号*/
}
MODULE_LICENSE("GPL");
MODULE_VERSION("v1.0");
MODULE_AUTHOR("[email protected]");
MODULE_DESCRIPTION("Char Driver Module");
MODULE_ALIAS("char driver module");
module_init(memdev_init);
module_exit(memdev_exit);
3、Makefile
ifeq ($(KERNELRELEASE),)
KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
all:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
clean:
$(MAKE) -C $(KERNELDIR) M=$(PWD) clean
else
obj-m := mem_dev.o
endif
4、应用程序
#include <stdio.h>
#include <string.h>
int main(void)
{
FILE *fp0 = NULL;
char Buf[4096];
/*初始化Buf*/
strcpy(Buf,"Mem is char dev!");
printf("BUF: %s\n",Buf);
/*打开设备文件*/
fp0 = fopen("/dev/memdev0","r+");
if (fp0 == NULL){
printf("Open Memdev0 Error!\n");
return -1;
}
/*写入设备*/
fwrite(Buf, sizeof(Buf), 1, fp0);
/*重新定位文件位置（思考没有该指令，会有何后果)*/
fseek(fp0,0,SEEK_SET);
/*清除Buf*/
strcpy(Buf,"Buf is NULL!");
printf("BUF: %s\n",Buf);
/*读出设备*/
fread(Buf, sizeof(Buf), 1, fp0);
/*检测结果*/
printf("BUF: %s\n",Buf);
fclose(fp0);
fp0 = NULL;
return 0;
}
5、验证
1、sudo insmod mem_dev.ko
2、
sudo mknod /dev/memdev0 c 238 0
sudo mknod /dev/memdev1 c 238 1
sudo chmod 0666 /dev/memdev*
3、
gcc app_mem.c -o test
4、
./test
5、观察结果
写入什么数据，读出什么数据。