驱动程序：
- /*chardev.c*/
- #include linux/kernel.h>
- #include linux/fs.h> /*for file-f_op*/
- #include linux/module.h>
- #include asm/uaccess.h> /*for copy_to_user()*/
- #include linux/cdev.h> /*for cdev ,cdev_init,cdev_add....*/
- MODULE_LICENSE("GPL");
- MODULE_AUTHOR("Helight");
- #define DP_MAJOR 250 /*the major number of the chardev*/
- #define DP_MINOR 0 /*the minor number of the chardev*/
- static int char_read(struct file *filp,char __user *buffer,size_t,loff_t *); /*the read operation of the chardev----read the data from kernel*/
- static int char_open(struct inode *,struct file *); /*open the chardev*/
- static int char_write(struct file *filp,const char __user *buffer,size_t ,loff_t*); /*write data to kernel*/
- static int char_release(struct inode *,struct file *); /*release the chardev*/
- static int chropen; /*the chardev open or not*/
- struct cdev *chardev; /*define a char device*/
- static int len;
- static const struct file_operations char_ops = {
- .read = char_read,
- .write = char_write,
- .open = char_open,
- .release = char_release,
- };
- static int __init char_init(void)
- {
- dev_t dev;
- printk(KERN_ALERT"Initing......\n");
- dev=MKDEV(DP_MAJOR,DP_MINOR);
- chardev = cdev_alloc( );
- if(chardev==NULL){
- return -1;
- }
- if(register_chrdev_region(dev,10,"chardev")){
- printk(KERN_ALERT"Register char dev error\n");
- return -1;
- }
- chropen=0;
- len=0;
- cdev_init(chardev,&char_ops);
- if(cdev_add(chardev,dev,1))
- {
- printk(KERN_ALERT"Add char dev error\n");
- }
- return 0;
- }
- static int char_open(struct inode *inode,struct file *file)
- {
- if(chropen==0)
- chropen++;
- else{
- printk(KERN_ALERT"Another process open the char device\n");
- return -1;
- }
- try_module_get(THIS_MODULE);
- return 0;
- }
- static int char_release(struct inode *inode,struct file *file)
- {
- chropen--;
- module_put(THIS_MODULE);
- return 0;
- }
- static int char_read(struct file *filp,char __user *buffer,size_t length,loff_t *offset)
- {
- if(length12)
- if(!copy_to_user(buffer,"hello world!",length))
- {
- return 0;
- }
- }else
- {
- if(!copy_to_user(buffer,"hello world!",strlen("hello world!")))
- {
- return 0;
- }
- }
- return -1;
- }
- static int char_write(struct file *filp,const char __user *buffer,size_t length,loff_t *offset)
- {
- return 0;
- }
- static void __exit module_close(void)
- {
- len=0;
- printk(KERN_ALERT"Unloading..........\n");
- unregister_chrdev_region(MKDEV(DP_MAJOR,DP_MINOR),10);
- cdev_del(chardev);
- }
- module_init(char_init);
- module_exit(module_close);
用户测试程序：
- /*main.c*/
- #include stdio.h>
- #include stdlib.h>
- #include sys/types.h>
- #include sys/stat.h>
- #include unistd.h>
- #include fcntl.h>
- #include string.h>
- int main(void)
- {
- int testdev;
- int i,rf=0;
- char buf[15];
- memset(buf, 0, sizeof(buf));
- testdev = open("/dev/chardev0",O_RDWR);
- if ( testdev == -1 )
- {
- perror("open\n");
- exit(0);
- }
- rf=read(testdev,buf,12);
- if(rf0)
- perror("read error\n");
- printf("R:%s\n",buf);
- close(testdev);
- return 0;
- }
编译加载和使用：
程序chardev.c是字符驱动程序，是以内核模块的形式插入内核的，所以编译方法和内核模块的编译方法一致。
模块的加载和卸载也和上面所述的内核模块的加载和卸载方法一致。
设备节点的创建，mknod /dev/chardev0 c 250 0
命令解释：
mknod是建立设备节点的命令；
/dev/chardev0：在/dev/目录下建立chardev0这样一个节点。
c:这个节点是指向一个字符设备的节点
250：这个设备的主设备号
0：次设备号
编译用户程序gcc -o chardev_test main.c
运行chmod 666 /dev/chardev0 使其它用户也可以对这个设备进行读写操作，否则只有root用户可以对它进行读写。
运行chardev_test，如果没有什么问题的话应该要输出这几个字符。
R：hello world!
