static ssize_t write_handlerFile4(struct kobject *kobj, struct bin_attribute *battr, char *buf, loff_t off, size_t len)
{
        int i;
        int leng;
        leng = len;
        kfree(buffer);
        buffer = kmalloc(leng,GFP_KERNEL)
        
        for (i = 0; i < leng ; i ++) {
                buffer[i] = buf[i];
        }
        if (off >= len)
                return 0;
        else
                return len;
}

static ssize_t read_handler(struct kobject *kobj,struct bin_attribute *battr, char *buf, loff_t off, size_t len) 
{
        strcpy(buf,buffer);
        len = strlen(buffer);
        if (off >= len)
                return 0;
        else
              return len;  
}

for (i = 0; i < len ; i ++) {
    buffer[i] = buf[i];
}
buffer[len] = 0;

static ssize_t read_handler(struct kobject *kobj,struct bin_attribute *battr, char *buf, loff_t off, size_t len) 
{
        memcpy(buf,buffer, count);

        if (off > 0)
	        return 0;
        else
                return count;
}

static ssize_t write_handler(struct kobject *kobj, struct bin_attribute *battr, char *buf, loff_t off, size_t len)
{
        memcpy(buffer,buf,len);
        count = len  ;

        return len;
}

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/sysfs.h>

struct kset *test_subsys;  
struct kobject *koObjDir1;

#define MAX 100
char *buffer;
int count;

int flag = 0;

static ssize_t read_handlerFile4(struct kobject *kobj,struct bin_attribute *battr, char *buf, loff_t off, size_t len) ;
static ssize_t write_handlerFile4(struct kobject *kobj, struct bin_attribute *battr, char *buf, loff_t off, size_t len);

static struct bin_attribute file4 = { // file 4
          .attr = {
            .owner = THIS_MODULE,
            .mode  = 0666,
            .name  = "file4",
          },
          .read = read_handlerFile4,
          .write = write_handlerFile4,
};


static int hello_start (void) 
{
    int err;
	buffer = kmalloc(MAX,GFP_KERNEL);
	if (!buffer) {
	        printk("can't malloc");
	        return 0;
	}
	
	memset(buffer,'A',MAX);
	count = MAX;

    test_subsys = kset_create_and_add("test",NULL,NULL); // create subder test
    if (!test_subsys) {
            return -ENOMEM;
    }
    flag++;
    koObjDir1   = kobject_create_and_add("dir1",&test_subsys->kobj); // create dir dir1
    if (!koObjDir1) {
            kset_unregister(test_subsys); // del subdir test
            return -ENOMEM;
    }
    flag++;
    err = sysfs_create_bin_file(koObjDir1, &file4); // create file4
    if (err) {
            kobject_del(koObjDir1);
            kset_unregister(test_subsys);
            return err;
    }
    flag++;
	return 1;
}

static void hello_end (void)
{
        if (flag == 3) {
                sysfs_remove_bin_file(koObjDir1, &file4); 
                kobject_del(koObjDir1);
                kset_unregister(test_subsys);
        }
        kfree(buffer);
	printk("This modules is close ^^!\n");
}

static ssize_t read_handlerFile4(struct kobject *kobj,struct bin_attribute *battr, char *buf, loff_t off, size_t len) 
{
        memcpy(buf,buffer, count);

        if (off > 0)
	        return 0;
        else
                return count;
}

static ssize_t write_handlerFile4(struct kobject *kobj, struct bin_attribute *battr, char *buf, loff_t off, size_t len)
{
        memcpy(buffer,buf,len);
        count = len  ;

        return len;
}

module_init(hello_start);
module_exit(hello_end);
MODULE_LICENSE("GPL");