linux驱动入门---test驱动模块加载

编写一简单的字符驱动程序，这里的设备也就是一段内存，实现简单的都写功能， 并列出常用格式的Makefile以及驱动加载和卸载脚本。

/* test_drv.c */
#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/cdev.h>
#include <asm/uaccess.h>

#define TEST_DEVICE_NAME "test_dev"
#define BUFF_SZ           1024

//全局变量
static struct cdev test_dev;
unsigned int major = 0;
static char *data = NULL;

//读函数
static ssize_t test_read(struct file *file ,
                         char *buf, 
                         size_t count,
                         loff_t *f_pos)
{
    int len;
    if (count < 0)
    {
        return -EINVAL;
    }
    len = strlen(data);
    count = (len > count) ? count : len;
    if (copy_to_user(buf, data, count))//将内核缓冲数据拷贝到用户空间
    {
         return -EFAULT;
    }
    return count;
}

//写函数
static ssize_t test_write(struct file *file, const char *buffer,
                          size_t count, loff_t *f_pos)
{
    if (count < 0)
    {
         return -EINVAL;
    }
    memset(data, 0, BUFF_SZ);
    count = (BUFF_SZ > count) ? count : BUFF_SZ;
    if (copy_from_user(data, buffer, count))//将用户缓冲的数据复制到内核空间
    {
         return -EFAULT;
    }
    return count;
}

//打开函数
static int test_open(struct inode *inode, struct file *file)
{
    printk("This is open operation\n");
    //分配并初始化缓冲区
    data = (char*)kmalloc(sizeof(char) * BUFF_SZ, GFP_KERNEL);
    if (!data)
    {
        return -ENOMEM;
    }
    memset(data, 0, BUFF_SZ);
    return 0;
}

//关闭函数
static int test_release(struct inode *inode, struct file *file)
{
    printk("This is release opertion\n");
    if (data)
    {
         kfree(data);//释放缓冲区
         data = NULL; //防止出现野指针
    }
    return 0;
}

//创建，初始化字符设备，并且注册到系统
static void test_setup_cdev(struct cdev *dev, int minor, 
                            struct file_operations *fops)
{
     int err, devno = MKDEV(major, minor);
     cdev_init(dev, fops);
     dev->owner = THIS_MODULE;
     dev->ops = fops;
     err = cdev_add(dev, devno, 1);
     if (err)
     {
         printk(KERN_NOTICE "Error %d adding test %d", err, minor);
     }
}

//虚拟设备的file_operations结构
static struct file_operations test_fops =
{
    .owner   = THIS_MODULE,
    .read    = test_read,
    .write   = test_write,
    .open    = test_open,
    .release = test_release,
};

//模块注册入口
int init_module(void)
{
     int result;
     dev_t dev = MKDEV(major, 0);
     
     if (major)
     {
     //静态注册一个设备，设备号先前指定好，
     //并设定设备名，用cat /proc/devices来察看
         result = register_chrdev_region(dev, 1, TEST_DEVICE_NAME);
     }
     else
     {
         result = alloc_chrdev_region(&dev, 0, 1, TEST_DEVICE_NAME);
     }

     if (result < 0)
     {
         printk(KERN_WARNING "Test device: unable to get major %d\n", major);
         return result;
     }
     test_setup_cdev(&test_dev, 0, &test_fops);
     printk("The major of the test device is %d\n", major);
     return 0;
}

//卸载模块
void cleanup_module(void)
{
     cdev_del(&test_dev);
     unregister_chrdev_region(MKDEV(major, 0), 1);
     printk("Test device uninstalled\n");

}

 Makefile文件：

ifeq ($(KERNELRELEASE),)
#内核编译路径
#KERNELDIR ?= /lib/modules/$(shell uname -r) /build  
#KERNELDIR ?= /root/src/linux-2.6.27.62 
KERNELDIR ?= /lib/modules/2.6.32-41-generic/build 
PWD := $(shell pwd)
modules:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
modules_install:
$(MAKE) -C $(KERNELDIR) M=$(PWD) medules_install
clean:
rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions .PHONY: modules modules_install clean
else
obj-m := test_drv.o 
endif

加载和卸载脚本:

#!/bin/sh
# 驱动模块名称
modulel="test_drv"
#设备名称，在/proc/devices中出现
device="test_dev"
#设备文件的属性
mode="664"
group="adm"

#特此说明，这里的加载脚本有问题，能加载驱动模块，但是不能创建文件节点，
#如果有高手能指点一二，就非常感谢了。
#删除已存在的设备节点
rm -f /dev/${device}
#加载驱动模块
/sbin/insmod -f ./$modulel.ko $* || exit 1
#查到创建设备的主设备号
#major='cat /proc/devices | awk "\$2=="test_dev" {print \$1}"'

major = $(awk "\$2=="test_dev"{print \$1}" /proc/devices)
#major=$(cat /proc/devices | grep test_dev |cut -c -3)
echo $major
#创建设备文件节点
mknod /dev/${device} c $major 0
#echo $(mknod /dev/${device} c $major 0)
#设置设备文件属性
chgrp $group /dev/${device}
chmod $mode /dev/${device}

卸载驱动脚本：

#!/bin/sh
module="test_drv"
device="test_dev"

#卸载驱动模块
/sbin/rmmod $module $* || exit 1
#删除设备文件
rm -f /dev/${device}
exit 0

 用户层测试程序：

/* test.c   2012-07-24 19:00  */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>

#define TEST_DEVICE_FILENAME   "/dev/test_dev"  //设备文件名
#define BUFF_SZ                 1024            //缓存大小

int main()
{
    int fd, nwrite, nread;
    char buff[BUFF_SZ];    //缓冲区
    //打开设备文件
    fd = open(TEST_DEVICE_FILENAME, O_RDWR);
    if (fd == -1)
    {
        perror("open");
        exit(1);
    }

    do 
    {
        printf("Input some words to kernel(enter 'quit' to exit):");
        memset(buff, 0, BUFF_SZ);
        if (fgets(buff, BUFF_SZ, stdin) == NULL)
        {
            perror("fgets");
            break; 
        }
        buff[strlen(buff) - 1] = '\0';
        if (write(fd, buff, strlen(buff)) < 0) //向设备写入数据
        {
            perror("write");
            break;
        }
        if (read(fd, buff, BUFF_SZ) < 0)      //从设备读取数据
        {
            perror("read");
            break;
        }
        else
        {
            printf("The read string is from kernel:%s\n", buff);
        }
    } while(strncmp(buff, "quit", 4));
    close(fd);
    exit(0);
}