linux驱动开发--字符设备：添加文件指针偏移的功能

设备移位操作llseek
对应lseek系统调用的设备移位操作为llseek
默认情况为允许设备移位操作
大部分字符设备提供的都是数据流而不是一个数据区，比如串口，对于这些设备而言移位操作毫无意义
设备可选择是否支持移位操作

支持设备移位操作
loff_t (*llseek)(struct file *filp, loff_t off, int whence);
filp:待操作的设备文件file结构体指针
off:待操作的定位偏移值(可正可负)
whence:待操作的定位起始位置
返回：返回移位后的新文件读、写位置，并且新位置总为正值
定位起始位置
  SEEK_SET:0，表示文件开头
  SEEK_CUR:1，表示当前位置

  SEEK_END:2，表示文件尾

  应该根据当前文件位置检查当前读、写操作合法性

  返回新位置

  返回实际可读、写字节数变量值

/**
*Copyright (c) 2013.TianYuan
*All rights reserved.
*
*文件名称: char_device_driver09.c
*文件标识: copy_to_user 、copy_from_user函数的使用。添加偏移的功能
*
*当前版本：1.0
*作者：wuyq
*
*取代版本：xxx
*原作者：xxx
*完成日期：2013-11-29
*/
#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/slab.h>
#include <asm/uaccess.h>
MODULE_LICENSE("GPL");
#define CDD_MAJOR	200//cat /proc/devices找一个尚未使用的
#define CDD_MINOR	0
#define CDD_COUNT	10
dev_t dev = 0;
u32 cdd_major = 0;
u32 cdd_minor = 0;
struct class *dev_class = NULL;
#define BUF_SIZE	100
struct cdd_cdev{
struct cdev cdev;
struct device *dev_device;
u8 led;
char kbuf[BUF_SIZE];
u32 data_len;//记录缓冲区中已经写入数据的长度
};
struct cdd_cdev *cdd_cdevp = NULL;
int cdd_open(struct inode* inode, struct file *filp)
{
struct cdd_cdev *pcdevp = NULL;
printk("enter cdd_open!n");
pcdevp = container_of(inode->i_cdev, struct cdd_cdev, cdev);
printk("led = %dn", pcdevp->led);
filp->private_data = pcdevp;
return 0;
}
int cdd_read(struct file *filp, char __user *buf, size_t count, loff_t *offset)
{
int ret = 0;
u32 pos = *offset;
u32 cnt = count;
struct cdd_cdev *cdevp = filp->private_data;
//printk("enter cdd_read!n");
if(cnt > (cdevp->data_len-pos) ){
cnt = cdevp->data_len - pos;
}
ret = copy_to_user(buf, cdevp->kbuf+pos, cnt);
//printk("kernel kbuf content:%sn", cdevp->kbuf);
*offset += cnt;
return ret;
}
int cdd_write(struct file *filp, const char __user *buf, size_t count, loff_t *offset)
{
int ret = 0;
struct cdd_cdev *cdevp = filp->private_data;
u32 pos = *offset;
u32 cnt = count;
//printk("enter cdd_write!n");
if(cnt > (BUF_SIZE - pos) ){
cnt = BUF_SIZE - pos;
}
ret = copy_from_user(cdevp->kbuf+pos, buf, cnt);
*offset += cnt;
if(*offset > cdevp->data_len){
cdevp->data_len = *offset;
}
return ret;
}
int cdd_ioctl(struct inode *inode, struct file *filp, unsigned int cmd, unsigned long data)
{
printk("enter cdd_ioctl!n");
return 0;
}
int cdd_release(struct inode *inode, struct file *filp)
{
printk("enter cdd_release!n");
return 0;
}
loff_t cdd_llseek(struct file *filp, loff_t offset, int whence)
{
struct cdd_cdev *pcdevp = filp->private_data;
loff_t newpos = 0;
switch(whence){
case SEEK_SET:
newpos = offset;
break;
case SEEK_CUR:
newpos = filp->f_pos + offset;
break;
case SEEK_END:
newpos = pcdevp->data_len + offset;
break;
default:
return -EINVAL;//无效的参数
}
if( newpos<0 || newpos>= BUF_SIZE ){
return -EINVAL;
}
filp->f_pos = newpos;
return newpos;
}
struct file_operations cdd_fops = {
.owner = THIS_MODULE,
.open = cdd_open,
.read = cdd_read,
.write = cdd_write,
.ioctl = cdd_ioctl,
.release = cdd_release,
.llseek = cdd_llseek,
};
int __init cdd_init(void)
{
int ret = 0;
int i = 0;
if(cdd_major){
dev = MKDEV(CDD_MAJOR, CDD_MINOR);//生成设备号
//注册设备号;1、要注册的起始设备号2、连续注册的设备号个数3、名字
ret = register_chrdev_region(dev, CDD_COUNT, "cdd_demo");
}else{
// 动态分配设备号
ret = alloc_chrdev_region(&dev, cdd_minor, CDD_COUNT, "cdd_demo02");
}
if(ret < 0){
printk("register_chrdev_region failed!n");
goto failure_register_chrdev;
}
//获取主设备号
cdd_major = MAJOR(dev);
printk("cdd_major = %dn", cdd_major);
cdd_cdevp = kzalloc(sizeof(struct cdd_cdev)*CDD_COUNT, GFP_KERNEL);
if(IS_ERR(cdd_cdevp)){
printk("kzalloc failed!n");
goto failure_kzalloc;
}
/*创建设备类*/
dev_class = class_create(THIS_MODULE, "cdd_class");
if(IS_ERR(dev_class)){
printk("class_create failed!n");
goto failure_dev_class;
}
for(i=0; i<CDD_COUNT; i++){
/*初始化cdev*/
cdev_init(&(cdd_cdevp[i].cdev), &cdd_fops);
/*添加cdev到内核*/
cdev_add(&(cdd_cdevp[i].cdev), dev+i, 1);
/* “/dev/xxx” */
device_create(dev_class, NULL, dev+i, NULL, "cdd%d", i);
cdd_cdevp[i].led = i;
}
return 0;
failure_dev_class:
kfree(cdd_cdevp);
failure_kzalloc:
unregister_chrdev_region(dev, CDD_COUNT);
failure_register_chrdev:
return ret;
}
void __exit cdd_exit(void)
{
/*逆序消除*/
int i = 0;
for(; i < CDD_COUNT; i++){
device_destroy(dev_class, dev+i);
cdev_del(&(cdd_cdevp[i].cdev));
//cdev_del(&((cdd_cdevp+i)->cdev));
}
class_destroy(dev_class);
kfree(cdd_cdevp);
unregister_chrdev_region(dev, CDD_COUNT);
}
module_init(cdd_init);
module_exit(cdd_exit);

/**
*Copyright (c) 2013.TianYuan
*All rights reserved.
*
*文件名称: char_device_driver09_test.c
*文件标识: 测试程序：测试内核空间的copy_to_user、copy_frome_user。添加偏移的功能
*	执行：先./char_device_driver08_test	r、w、l、r、
*当前版本：1.0
*作者：wuyq
*
*取代版本：xxx
*原作者：xxx
*完成日期：2013-11-29
*/
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
/*手工创建设备节点文件
mknod /dev/cdd c 248 0
*/
int fd = 0;
char rbuf[100];
char wbuf[100] = "nihao!n";
int main()
{
char ch;
fd = open("/dev/cdd5", O_RDWR);
if(fd < 0){
printf("open failed!n");
return -1;
}
printf("open successed fd = %dn", fd);
while(1)
{
printf("starting to test /dev/cdd...n");
ch = getchar();
getchar();//取走回车
if(ch == 'q'){
break;
}
switch(ch){
case 'r':
memset(rbuf, 0, 100);//清空
read(fd, rbuf, 3);
printf("user space from kernel: %sn", rbuf);
break;
case 'w':
write(fd, wbuf, strlen(wbuf) );
break;
case 'o':
ioctl(fd, 0, 0);
break;
case 'l':
lseek(fd, 0, SEEK_SET);//移动的文件的开头
break;
default:
break;
}
sleep(1);
}
close(fd);
return 0;
}

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