hello.c

支持Linux 内核2.4版本的字符设备模块示例

#ifndef MODULE
#define MODULE
#endif //MODULE

#ifndef __KERNEL__
#define __KERNEL__
#endif //__KERNEL__

#ifndef LINUX
#define LINUX
#endif //LINUX

#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <error.h>
#include <asm/uaccess.h>

MODULE_LICENSE("GPL");

#define DATA_BUFFER_SIZE 4096
#define DRIVER_NAME "my_device"
static int g_iMajor = 0;
static char *g_pData = 0;

//wrapper "read" function
static int my_read(struct file *filp, char *charp, size_t iLen, loff_t *pPos)
{
    printk("my driver read.\n");
    if((charp == 0) 
        || (iLen < 0))
    {
        return -EINVAL;
    }
    if(g_pData == 0)
    {
        return -ENOMEM;
    }

    int iRealBytes = iLen>strlen(g_pData)?strlen(g_pData):iLen;
    int iRet = copy_to_user(charp, g_pData, iRealBytes);
    return iRet==0?iRealBytes:iRealBytes-iRet;
}

//wrapper "write" function
static int my_write(struct file *filp, const char *charp, size_t iLen, loff_t *pPos)
{
    printk("my driver write.\n");
    if((iLen < 0) 
        || (charp == 0))
    {
        return -EINVAL;
    }
    if(g_pData == 0)
    {
        return -ENOMEM;
    }

    int iRealBytes = iLen>DATA_BUFFER_SIZE?DATA_BUFFER_SIZE:iLen;
    int iRet = copy_from_user(g_pData, charp, iRealBytes);
    return iRet==0?iRealBytes:iRealBytes-iRet;
}

//wrapper "open" function
static int my_open(struct inode *pinode, struct file *filp)
{
    MOD_INC_USE_COUNT;
    printk("my driver open.\n");
    g_pData = (char*)kmalloc(DATA_BUFFER_SIZE, GFP_KERNEL);
    return 0;
}

//wrapper "release" function
static int my_release(struct inode *pinode, struct file *filp)
{
    MOD_DEC_USE_COUNT;
    printk("my driver close\n");
    kfree(g_pData);
    g_pData = 0;
    return 0;
}

//register callback function
static struct file_operations my_fops = 
{
    open        : my_open,
    release     : my_release,
    read        : my_read,
    write       : my_write,
};

//driver initial function
static int __init my_init(void)
{
    printk("Hello! My friend! this is my first driver in linux.\n");
//    printk("kernel version:%d.%d.%d\n", (LINUX_VERSION_CODE>>16)&0xff, (LINUX_VERSION_CODE>>8)&0xff, LINUX_VERSION_CODE&0xff);
    printk("kernel version:%s\n", UTS_RELEASE);
    
    g_iMajor = register_chrdev(0, DRIVER_NAME, &my_fops);
    if(g_iMajor < 0)
    {
        return 1;
    }
    return 0;
}

//driver uninitital function
static void __exit my_cleanup(void)
{
    printk("Goodbye my friend! my first driver exit.\n");
    unregister_chrdev(g_iMajor, DRIVER_NAME);
}

//register driver initial function
module_init(my_init);
//register driver uninitital function
module_exit(my_cleanup);