字符设备（3）lseek

/*
改进：读写时，新添加了利用llseek()函数,修改偏移量属性
*/
/*
对设备属性进行了封装，读写时重要的改变
*/
#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/cdev.h>
#include <linux/fs.h>
#include <asm/uaccess.h>
#include <linux/errno.h>
#include <linux/slab.h>

#define P_DEBUG(fmt, args...) printk("<kernel>[%s]:"fmt, __FUNCTION__, ##args)
#define DEVSIZE 512
//将设备属性封装成一个结构体，表示一个字符设备
struct test_dev_t {
char kbuf[DEVSIZE];
int curr_size;
int major;
int minor;
dev_t devno;
struct cdev test_cdev;
}*dev;
/*
static dev_t devno;
static int major = 0;
static int minor = 0;
struct cdev test_cdev;
*/
//设备驱动的操作方法
static int test_open(struct inode *,struct file *);
static int test_close(struct inode *,struct file *);
static ssize_t test_read(struct file *, char __user *, size_t , loff_t *);
static ssize_t test_write(struct file *, const char __user *, size_t, loff_t *);
static off_t test_llseek(struct file *, off_t, int);

struct file_operations test_fops = {
.open = test_open,
.release = test_close,
.read = test_read,
.write = test_write,
.llseek = test_llseek,
};
//打开设备
static int test_open(struct inode *inode,struct file *filp)
{
P_DEBUG("dev open!\n");
//***重要改变，打开设备时将设备属性结构体赋值给打开设备文件的似有数据
struct test_dev_t *dev;//驱动程序获取设备的通用方法
dev = container_of(inode->i_cdev,struct test_dev_t,test_cdev);
filp->private_data = dev;//利用设备文件的私有数据结构，保存设备相关的数据结构

return 0;
}
//释放设备
static int test_close(struct inode *inode,struct file *filp)
{
P_DEBUG("dev close!\n");
return 0;
}
//从设备读取
static ssize_t test_read(struct file *filp, char __user *buf, size_t count, loff_t *offset)
{
int ret;
//***重要改变，现在从设备读取
struct test_dev_t *dev = filp->private_data;

//比较上一版本有修改（对偏移量进行判断）
if (*offset > DEVSIZE) {//如果偏移量已经超过了设备大小
return count ? -ENXIO : 0;
} //count不为0则分会错误号，地址越界

if (*offset + count > DEVSIZE) {   //如果读取字节数超过了最大偏移量
count = DEVSIZE - *offset;
}

if (copy_to_user(buf, dev->kbuf + *offset, count)) {//安全性检查
return -EFAULT;
}
else {
P_DEBUG("offset is [%d]\n", *offset);
ret = count;
//修改设备文件当前大小
//dev->curr_size -= count;
*offset += count;//偏移量增加
P_DEBUG("buf is [%s]\n", buf);
}
return ret;
}

//写入设备
static ssize_t test_write(struct file *filp, const char __user *buf, size_t count, loff_t *offset)
{
int ret;
//***重要改变，现在写到设备
struct test_dev_t *dev = filp->private_data;
P_DEBUG("dev->curr_size[%d]\n",dev->curr_size);

//比较上一版本有修改
if (*offset > DEVSIZE) {//如果偏移量已经超过了设备大小
return count ? -ENXIO : 0;
} //count不为0则分会错误号，地址越界

if (*offset + count > DEVSIZE) {   //如果写入字节数超过了最大偏移量
count = DEVSIZE - *offset;
}

if (copy_from_user(dev->kbuf,buf,count)) {//有问题，总是写在kbuf开始字节
return -EFAULT;
}
else {
ret = count;
//修改设备文件当前偏移量
dev->curr_size += count;
*offset += count;//偏移量增加
P_DEBUG("dev->curr_size[%d]\n",dev->curr_size);
P_DEBUG("kbuf is [%s]\n", dev->kbuf);
}
return ret;
}

//修改设备文件偏移量
static off_t test_llseek(struct file *filp, off_t offset, int whence)
{
off_t new_pos;
off_t old_pos = filp->f_pos;

switch (whence) {
case SEEK_SET :
new_pos = offset;
break;
case SEEK_CUR :
new_pos = old_pos + offset;
break;
case SEEK_END :
new_pos = old_pos + DEVSIZE;
break;
default:
P_DEBUG("unknown whence!\n");
return -EINVAL;
}

if (new_pos < 0 || new_pos > DEVSIZE) {
P_DEBUG("f_ops over failed!\n");
return -EINVAL;
}

filp->f_pos = new_pos;
return new_pos;//返回新的偏移量
}
//初始化设备属性
static struct test_dev_t* dev_init(struct test_dev_t *dev)
{
dev = kmalloc(sizeof(struct test_dev_t),GFP_KERNEL);
memset(dev->kbuf,0,DEVSIZE);
dev->curr_size = 0;
dev->major = 0;
dev->minor = 0;

return dev;
}

static int __init test_init(void)
{
int ret;
//很重要的部分，定义并初始化一个设备
dev = dev_init(dev);
//申请字符设备号
if (dev->major) {
dev->devno = MKDEV(dev->major,dev->minor);
ret = register_chrdev_region(dev->devno,1,"test_dev");
}
else {//动态分配
ret = alloc_chrdev_region(&dev->devno,dev->minor,1,"test_dev");
dev->major = MAJOR(dev->devno);
dev->minor = MINOR(dev->devno);
}

if (ret < 0) {
P_DEBUG("register chrdev devno err!\n");
goto err_regDevno;
}

printk("major[%d] minor[%d]\n",dev->major,dev->minor);

//注册设备
cdev_init(&dev->test_cdev,&test_fops);//初始化cdev结构体
dev->test_cdev.owner = THIS_MODULE;
ret = cdev_add(&dev->test_cdev,dev->devno,1);//将设备加到字符设备数据库

if (ret < 0) {
P_DEBUG("add cdev error!\n");
goto err_addCdev;
}

return 0;
err_addCdev:
unregister_chrdev_region(dev->devno,1);
err_regDevno:
return ret;
}

static int __exit test_exit(void)
{
cdev_del(&dev->test_cdev);//从字符设备数据库删除cdev
unregister_chrdev_region(dev->devno,1);//释放设备号

return 0;
}

module_init(test_init);
module_exit(test_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("LL");
MODULE_VERSION("1.4");