[嵌入式]嵌入式学习记录3----自动创建设备节点，实现读写接口

1、自动创建设备节点

涉及的函数：

struct class *class_create(struct module *owner, const char *name)；

----在/sys/class/目录下会创建对应的类

void class_destroy(struct class *cls)

struct device *device_create(struct class *class, struct device *parent,
?? ??? ??? ? ? ? dev_t devt, const char *fmt, ...)；

----在/dev/目录下会创建结点

void device_destroy(struct class *class, dev_t devt)；

注意：某一步失败，要说释放掉前边申请的资源。

#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <linux/cdev.h>

static unsigned int major = 250;
static unsigned int minor = 0;

struct class *cls;
dev_t devno = 0;

int hello_open(struct inode *inode, struct file *file)
{
	printk("hello_open\n");
	return 0;
}
int hello_release(struct inode *inode, struct file *file)
{
	printk("hello_release\n");
	return 0;
}
struct file_operations fops = 
{
	.open = hello_open,
	.release = hello_release,
};


static int hello_init(void)
{
	int ret = 0;;
	struct device *class_dev;
	printk("hello_init\n");
	ret = register_chrdev(major, "zlyinit", &fops);
	if(ret < 0)
	{
		printk("register_chrdev fail\n");
		return ret;
	}
	cls = class_create(THIS_MODULE, "hellozlycls");// /sys/class/
	if (IS_ERR(cls)) {
		printk("class_create fail\n");
	    ret = PTR_ERR(cls);
		goto out_err_1;
	}
	devno = MKDEV(major, minor);
	class_dev = device_create(cls, NULL, devno, "hellozlydev");// /dev/hellozlydev
	if (IS_ERR(class_dev)) {
		ret = PTR_ERR(class_dev);
		printk("device_create fail\n");
		goto out_err_2;
	}
	printk("device_create succ\n");
	return ret;
out_err_2:
	class_destroy(cls);
out_err_1:
	unregister_chrdev(major, "zlyinit");
	printk("ret=[%u]\n", ret);
	return ret;
}

static void hello_exit(void)
{
	printk("hello_exit\n");
	device_destroy(cls, devno);
	class_destroy(cls);
	unregister_chrdev(major, "zlyinit");
	return;
}
module_init(hello_init);
module_exit(hello_exit);
MODULE_LICENSE("GPL");

2、实现read和write接口

#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <linux/cdev.h>
#include <linux/uaccess.h>

static unsigned int major = 250;
static unsigned int minor = 0;

struct class *cls;
dev_t devno = 0;
#define KMAX_LEN 32
char kbuf[KMAX_LEN] = "kernel";


int hello_open(struct inode *inode, struct file *file)
{
	printk("hello_open\n");
	return 0;
}
int hello_release(struct inode *inode, struct file *file)
{
	printk("hello_release\n");
	return 0;
}
//read(fd,buff,len);
ssize_t hello_read(struct file *filep, char __user *buf, size_t size, loff_t *pos)
{
    int error;
	printk("hello_read\n");
	if(size > KMAX_LEN)
	{
		size = KMAX_LEN;
	}
	if(copy_to_user(buf, kbuf, size))
	{
		error=-EFAULT;
		return error;
	}
	return size;
}
//write(fd,buff,len)
ssize_t hello_write(struct file *filep, const char __user *buf, size_t size, loff_t *pos)
{
	int error;
	printk("hello_write\n");
	if(size > KMAX_LEN)
    {
		size = KMAX_LEN;
	}
	memset(kbuf, 0, KMAX_LEN);
	if(copy_from_user(kbuf, buf, size))
	{
		error = -EFAULT;
		return error;
	}
	printk("hello_write:%s\n", kbuf);
	return size;
}

struct file_operations fops = 
{
	.open = hello_open,
	.release = hello_release,
	.read = hello_read,
	.write = hello_write,
};


static int hello_init(void)
{
	int ret = 0;;
	struct device *class_dev;
	printk("hello_init\n");
	ret = register_chrdev(major, "zlyinit", &fops);
	if(ret < 0)
	{
		printk("register_chrdev fail\n");
		return ret;
	}
	cls = class_create(THIS_MODULE, "hellozlycls");// /sys/class/
	if (IS_ERR(cls)) {
		printk("class_create fail\n");
	    ret = PTR_ERR(cls);
		goto out_err_1;
	}
	devno = MKDEV(major, minor);
	class_dev = device_create(cls, NULL, devno, "hellozlydev");// /dev/hellozlydev
	if (IS_ERR(class_dev)) {
		ret = PTR_ERR(class_dev);
		printk("device_create fail\n");
		goto out_err_2;
	}
	printk("device_create succ\n");
	return ret;
out_err_2:
	class_destroy(cls);
out_err_1:
	unregister_chrdev(major, "zlyinit");
	printk("ret=[%u]\n", ret);
	return ret;
}

static void hello_exit(void)
{
	printk("hello_exit\n");
	device_destroy(cls, devno);
	class_destroy(cls);
	unregister_chrdev(major, "zlyinit");
	return;
}
module_init(hello_init);
module_exit(hello_exit);
MODULE_LICENSE("GPL");