linux驅動入門---test驅動模塊加載

         編寫一簡單的字符驅動程序，這裏的設備也就是一段內存，實現簡單的都寫功能， 並列出經常使用格式的Makefile已經驅動加載和卸載腳本。

/* 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

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

//讀函數
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))//將內核緩衝數據拷貝到用戶空間
    {
         return -EFAULT;
    }
    return count;
}

//寫函數
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))//將用戶緩衝的數據複製到內核空間
    {
         return -EFAULT;
    }
    return count;
}

//打開函數
static int test_open(struct inode *inode, struct file *file)
{
    printk("This is open operation\n");
    //分配並初始化緩衝區
    data = (char*)kmalloc(sizeof(char) * BUFF_SZ, GFP_KERNEL);
    if (!data)
    {
        return -ENOMEM;
    }
    memset(data, 0, BUFF_SZ);
    return 0;
}

//關閉函數
static int test_release(struct inode *inode, struct file *file)
{
    printk("This is release opertion\n");
    if (data)
    {
         kfree(data);//釋放緩衝區
         data = NULL; //防止出現野指針
    }
    return 0;
}

//建立，初始化字符設備，而且註冊到系統
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);
     }
}

//虛擬設備的file_operations結構
static struct file_operations test_fops =
{
    .owner   = THIS_MODULE,
    .read    = test_read,
    .write   = test_write,
    .open    = test_open,
    .release = test_release,
};

//模塊註冊入口
int init_module(void)
{
     int result;
     dev_t dev = MKDEV(major, 0);
     
     if (major)
     {
     //靜態註冊一個設備，設備號先前指定好，
     //並設定設備名，用cat /proc/devices來察看
         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;
}

//卸載模塊
void cleanup_module(void)
{
     cdev_del(&test_dev);
     unregister_chrdev_region(MKDEV(major, 0), 1);
     printk("Test device uninstalled\n");

}

     Makefile文件：

ifeq ($(KERNELRELEASE),)
#內核編譯路徑
#KERNELDIR ?= /lib/modules/$(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

加載和卸載腳本:

#!/bin/sh
# 驅動模塊名稱
modulel="test_drv"
#設備名稱，在/proc/devices中出現
device="test_dev"
#設備文件的屬性
mode="664"
group="adm"

#特此說明，這裏的加載腳本有問題，能加載驅動模塊，可是不能建立文件節點，
#若是有高手能指點一二，就很是感謝了。
#刪除已存在的設備節點
rm -f /dev/${device}
#加載驅動模塊
/sbin/insmod -f ./$modulel.ko $* || exit 1
#查到建立設備的主設備號
#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 $major
#建立設備文件節點
mknod /dev/${device} c $major 0
#echo $(mknod /dev/${device} c $major 0)
#設置設備文件屬性
chgrp $group /dev/${device}
chmod $mode /dev/${device}

卸載驅動腳本：

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

#卸載驅動模塊
/sbin/rmmod $module $* || exit 1
#刪除設備文件
rm -f /dev/${device}
exit 0

 用戶層測試程序：

/* 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"  //設備文件名
#define BUFF_SZ                 1024            //緩存大小

int main()
{
    int fd, nwrite, nread;
    char buff[BUFF_SZ];    //緩衝區
    //打開設備文件
    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) //向設備寫入數據
        {
            perror("write");
            break;
        }
        if (read(fd, buff, BUFF_SZ) < 0)      //從設備讀取數據
        {
            perror("read");
            break;
        }
        else
        {
            printf("The read string is from kernel:%s\n", buff);
        }
    } while(strncmp(buff, "quit", 4));
    close(fd);
    exit(0);
}