#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <asm/uaccess.h>

MODULE_LICENSE("GPL");
#define HELLOFS_MAGIC 0x20060313

static int hellofs_open(struct inode *inode, struct file *filp) { return 0; }

static ssize_t hellofs_read_file(struct file *filp, char *buf,
				 size_t count, loff_t *offset)
{
  const char *s = "Hello World!\n";
  if (*offset != 0)
    return 0;
  if (copy_to_user(buf, s, strlen(s)+1))
    return -EFAULT;
  *offset += count;
  return count;
}

static struct file_operations hellofs_file_ops = {
  .open   = hellofs_open,
  .read   = hellofs_read_file,
};

struct tree_descr hellofiles[] = {
  { NULL, NULL, 0 },
  { "hello.txt", &hellofs_file_ops, S_IWUSR|S_IRUGO },
  { "", NULL, 0},
};

static int hellofs_fill_super (struct super_block *sb, void *data, int silent)
{
  return simple_fill_super(sb, HELLOFS_MAGIC, hellofiles);
}

static struct super_block *hellofs_get_super(struct file_system_type *fst,
					     int flags, const char *devname, void *data)
{
  return mount_bdev(fst, flags, devname, data, hellofs_fill_super);
}

static struct file_system_type hellofs_type = {
  .owner          = THIS_MODULE,
  .name           = "hellofs",
  .mount          = hellofs_get_super,
  .kill_sb        = kill_litter_super,
};

static int __init hellofs_init(void)
{
  return register_filesystem(&hellofs_type);
}

static void __exit hellofs_exit(void)
{
  unregister_filesystem(&hellofs_type);
}

module_init(hellofs_init);
module_exit(hellofs_exit);