2.6驱动程序-字符驱动

驱动程序:

/*chardev.c*/
#include #include /*for file-f_op*/
#include #include /*for copy_to_user()*/
#include /*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(length<12) 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
#include
#include
#include
#include
#include
#include

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(rf<0) perror("read error\n"); printf("R:%s\n",buf); close(testdev); return 0; }
编译加载和使用:
<1>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。
<2>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。
<3>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
<3>编译用户程序gcc -o chardev_test main.c
<4>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。
<5>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!.

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