理論知識參考Linux Device Driver, 3rd Edition。實驗中使用主動分配主設備號，按照LDD3中說的最好是自動分配設備號，這裡只是為了理解。
實驗步驟如下：
（1）使用cat/proc/device查看字符設備主設備號，這裡假設50主設備號沒有使用而在本設備中使用。
創建字符設備文件節點：mknod/dev/mycdev c 50 0
修改設備文件權限：chmod 777/dev/mycdev
其中的mycdev為步驟（2）中要安裝的模塊名。
（2）編寫驅動程序：注意代碼中 #define MYCDEV_MAJOR (50)
/* =====================================================================
* Filename: mycdev.c
*
* Description:
*
* Version: 1.0 (02/26/2013)
* Created: xhzuoxin([email protected])
* Compiler: gcc
*======================================================================
*/
#include<linux/init.h>
#include<linux/module.h>
#include<linux/types.h>
#include<linux/fs.h>
#include<linux/mm.h>
#include<linux/sched.h>
#include<linux/cdev.h>
#include<asm/system.h>
#include<asm/io.h>
#include<asm/uaccess.h>
#include<linux/kernel.h>
#include<linux/errno.h>
#include<linux/slab.h>
MODULE_LICENSE("GPL");
#defineMYCDEV_MAJOR (50)
#defineMYCDEV_SIZE 0x1000
staticdev_t mycdev_major = MYCDEV_MAJOR;
structmycdev {
struct cdev cdev;
unsigned charmem[255];
};
//struct mycdev dev;
structmycdev *devp;
static int mycdev_open(structinode *inode,struct file *fp)
{
fp->private_data= devp;
return 0;
}
static int mycdev_release(structinode *inode,struct file *fp)
{
return 0;
}
staticssize_t mycdev_read(struct file *fp,char __user *buf, size_t size, loff_t *pos)
{
unsigned long p =*pos;
unsigned int count =size;
struct mycdev *tmp_dev = fp->private_data;
if (p >= MYCDEV_SIZE) {
return -1;
}
if (count > MYCDEV_SIZE - p) {
count =MYCDEV_SIZE - p;
}
if (copy_to_user(buf, (void*)(tmp_dev->mem + p), count) != 0) {
printk("read error!\n");
return -1;
} else {
*pos +=count;
printk(KERN_INFO"read %d bytes from %ld\n", count, p);
}
return count;
}
staticssize_t mycdev_write(struct file *fp,const char __user*buf, size_t size, loff_t *pos)
{
unsigned long p =*pos;
unsigned int count =size;
struct mycdev *tmp_dev = fp->private_data;
if (p > MYCDEV_SIZE) {
return -1;
}
if (p > MYCDEV_SIZE - count) {
count =MYCDEV_SIZE - p;
}
if (copy_from_user((void*)(tmp_dev->mem + p), buf, count) != 0) {
return -1;
} else {
*pos +=count;
printk(KERN_INFO"write %d bytes from %ld\n", count, p);
}
return count;
}
staticloff_t mycdev_llseek(struct file *fp, loff_toff,int whence)
{
// structmycdev *dev = fp->private_data;
loff_tnew_pos = 0;
switch(whence) {
case SEEK_SET:
new_pos= off;
break;
case SEEK_CUR:
new_pos= fp->f_pos + off;
break;
case SEEK_END:
new_pos= MYCDEV_SIZE + off;
}
if (new_pos < 0) {
return -EINVAL;
} else {
fp->f_pos= new_pos;
return new_pos;
}
}
/* paddingg struct file operation */
static const structfile_operations mycdev_fops = {
.owner =THIS_MODULE,
.read =mycdev_read,
.write =mycdev_write,
.open =mycdev_open,
.release =mycdev_release,
.llseek =mycdev_llseek,
};
static void setup_mycdev(structmycdev *dev,int index)
{
int ret;
int devno = MKDEV(mycdev_major, index);
cdev_init(&dev->cdev,&mycdev_fops);
dev->cdev.owner= THIS_MODULE;
dev->cdev.ops= &mycdev_fops;
ret =cdev_add(&dev->cdev, devno, 1);
if (ret) {
printk("adding mycdev error!\n");
}
}
static int __init mycdev_init(void)
{
int ret;
dev_tdevno = 0;
if (mycdev_major) { /* 靜態分配*/
devno =MKDEV(mycdev_major, 0);
ret =register_chrdev_region(devno, 1, "mycdev");
} else { /* 動態分配 */
ret =alloc_chrdev_region(&devno, 0, 1, "mycdev");
mycdev_major= MAJOR(devno);
}
devp =kmalloc(sizeof(structmycdev), GFP_KERNEL);
if (!devp) {
ret =-ENOMEM;
unregister_chrdev_region(devno,1);
return ret;
}
memset(devp,0, sizeof(structmycdev));
setup_mycdev(devp,0);
return 0;
}
static void __exit mycdev_exit(void)
{
printk("mycdev module is leaving...\n");
cdev_del(&devp->cdev);
kfree(devp);
unregister_chrdev_region(MKDEV(mycdev_major,0), 1);
}
module_init(mycdev_init);
module_exit(mycdev_exit);