linux字符设备驱动学习笔记（一）：简单的字符设备驱动
最近在鼓捣lnux字符设备驱动，在网上搜集的各种关于linux设备驱动的代码和注释，要么是针对2.4的，要么是错误百出，根本就不能运行成功，真希望大家在发博客的时候能认真核对下代码的正确性，特别是要把代码的运行环境和依赖条件列举出来，否则会对读者造成很大的误解。
以下代码的运行环境为：
操作系统:debian 6
内核版本:2.6.32(amd 64)
gcc版本：4.4.5
源代码如下所示(源代码确保编译可通过，运行无bug)：
#include<linux/module.h>
#include<linux/kernel.h>
#include<linux/fs.h>
#include<linux/types.h>
#include<linux/cdev.h>
#include<asm/uaccess.h>
#include <linux/init.h>
MODULE_LICENSE("GPL");
static int yang_open(struct inode*, struct file*);
static int yang_release(struct inode*, struct file*);
static ssize_t yang_read(struct file*, char *,size_t, loff_t*);
static ssize_t yang_write(struct file*,const char*, size_t,loff_t*);
loff_t yang_llseek(struct file *filp, loff_t off, int whence);
static int major;
static int device_open = 0;
static char *device_name = "myvar";
static dev_t devid;
static struct mydev *my_cdev;
struct mydev{
char *data;
struct cdev cdev;
unsigned long size;
};
static struct file_operations fops =
{
.owner = THIS_MODULE,
.read = yang_read,
.write = yang_write,
.open = yang_open,
.release = yang_release,
.llseek = yang_llseek
};
int init_yang_module(void)
{
struct mydev *dev = (struct mydev *)kmalloc(sizeof(struct mydev),GFP_KERNEL);
my_cdev = dev;//注册为全局变量，便于模块卸载
memset(dev, 0, sizeof(struct mydev));
dev->size = 10;
int err;
alloc_chrdev_region(&devid, 0, 1, "myvar");
major = MAJOR(devid);
cdev_init(&dev->cdev, &fops);
err = cdev_add(&dev->cdev, devid, 1);
if(err)
{
printk(KERN_INFO"I was major number %d.\n",major);
return -1;
}
printk("major number is %d\n",MAJOR(devid));
dev->data = (char*)kmalloc(dev->size * sizeof(char),GFP_KERNEL);
memset(dev->data,0,dev->size * sizeof(char));
return 0;
}
void cleanup_yang_module(void)
{
cdev_del(&my_cdev->cdev);
unregister_chrdev_region(devid, 1);
printk("cleanup done\n");
}
loff_t yang_llseek(struct file *filp, loff_t off, int whence)
{
struct mydev *dev = filp->private_data;
loff_t newpos;
switch(whence)
{
case SEEK_SET:
newpos = off;
case SEEK_CUR:
newpos = filp->f_pos + off;
case SEEK_END:
newpos = dev->size + off;
break;
default:
return -EINVAL;
}
if(newpos < 0) return -EINVAL;
filp->f_pos = newpos;
return newpos;
}
static int yang_open(struct inode* inode, struct file* file)
{
struct mydev *dev;
dev = container_of(inode->i_cdev, struct mydev, cdev);
file->private_data = dev;
return 0;
}
static int yang_release(struct inode* inode, struct file* file)
{
return 0;
}
static ssize_t yang_read(struct file* filp, char *buffer,size_t length, loff_t* off)
{
struct mydev *dev = filp->private_data;
if(*off >= dev->size)
{
return 0;
}
if(*off + length > dev->size)
length = dev->size - *off;
if(copy_to_user(buffer,dev->data + *off,length * sizeof(char)))
{
return -EFAULT;
}
*off += length;
return length;
}
static ssize_t yang_write(struct file* filp,const char* buffer, size_t length,loff_t* off)
{
struct mydev *dev = filp->private_data;
if(length > dev->size)
{
return -EFAULT;
}
if(copy_from_user(dev->data,buffer,dev->size * sizeof(char)))
{
return -EFAULT;
}
*off += length;
return dev->size;
}
module_init(init_yang_module);
module_exit(cleanup_yang_module);
以后有时间我再把注释加上，如果有兄弟刚刚学习linux设备驱动，这份源代码是最好的礼物。