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已经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);//静态注册     }     else     {         result = alloc_chrdev_region(&dev, 0, 1, TEST_DEVICE_NAME);//动态注册     }     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");}MODULE_LICENSE("Dual BSD/GPL"); Makefile文件：

ifeq ($(KERNELRELEASE),)
#内核编译路径
KERNELDIR ?= /lib/modules/$(shell uname -r) /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:(当然这个可以不用，可以用insmod加载和rmmod卸载，这里列出来主要是方便创建文件节点，也就是设备文件，用到的命令：mknod)

#!/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"

#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 = $(awk "\$2=="test_dev"{print \$1}" /proc/devices) 

#这里要说明的是，如果不是用动态加载设备号的话，完全可以用静态指定的设备号来创建

#如果要察看对应设备的主设备号用命令：cat /proc/devices | grep device_name

#major=$(cat /proc/devices | grep test_dev |cut -c -3)
echo $major #打印设备号
#创建设备文件节点
mknod /dev/${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);}