/*
   *	fs/libfs.c
   *	Library for filesystems writers.
   */
  
  #include <linux/module.h>
  #include <linux/pagemap.h>

  #include <linux/slab.h>

  #include <linux/mount.h>
  #include <linux/vfs.h>

  #include <linux/quotaops.h>

  #include <linux/mutex.h>

  #include <linux/exportfs.h>

  #include <linux/writeback.h>

  #include <linux/buffer_head.h> /* sync_mapping_buffers */

  #include <asm/uaccess.h>

  #include "internal.h"

  static inline int simple_positive(struct dentry *dentry)
  {
  	return dentry->d_inode && !d_unhashed(dentry);
  }

  int simple_getattr(struct vfsmount *mnt, struct dentry *dentry,
  		   struct kstat *stat)
  {
  	struct inode *inode = dentry->d_inode;
  	generic_fillattr(inode, stat);
  	stat->blocks = inode->i_mapping->nrpages << (PAGE_CACHE_SHIFT - 9);
  	return 0;
  }

  int simple_statfs(struct dentry *dentry, struct kstatfs *buf)

  {

  	buf->f_type = dentry->d_sb->s_magic;

  	buf->f_bsize = PAGE_CACHE_SIZE;
  	buf->f_namelen = NAME_MAX;
  	return 0;
  }
  
  /*
   * Retaining negative dentries for an in-memory filesystem just wastes
   * memory and lookup time: arrange for them to be deleted immediately.
   */

  static int simple_delete_dentry(const struct dentry *dentry)

  {
  	return 1;
  }
  
  /*
   * Lookup the data. This is trivial - if the dentry didn't already
   * exist, we know it is negative.  Set d_op to delete negative dentries.
   */
  struct dentry *simple_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
  {

  	static const struct dentry_operations simple_dentry_operations = {

  		.d_delete = simple_delete_dentry,
  	};
  
  	if (dentry->d_name.len > NAME_MAX)
  		return ERR_PTR(-ENAMETOOLONG);

  	d_set_d_op(dentry, &simple_dentry_operations);

  	d_add(dentry, NULL);
  	return NULL;
  }

  int dcache_dir_open(struct inode *inode, struct file *file)
  {
  	static struct qstr cursor_name = {.len = 1, .name = "."};

  	file->private_data = d_alloc(file->f_path.dentry, &cursor_name);

  
  	return file->private_data ? 0 : -ENOMEM;
  }
  
  int dcache_dir_close(struct inode *inode, struct file *file)
  {
  	dput(file->private_data);
  	return 0;
  }
  
  loff_t dcache_dir_lseek(struct file *file, loff_t offset, int origin)
  {

  	struct dentry *dentry = file->f_path.dentry;
  	mutex_lock(&dentry->d_inode->i_mutex);

  	switch (origin) {
  		case 1:
  			offset += file->f_pos;
  		case 0:
  			if (offset >= 0)
  				break;
  		default:

  			mutex_unlock(&dentry->d_inode->i_mutex);

  			return -EINVAL;
  	}
  	if (offset != file->f_pos) {
  		file->f_pos = offset;
  		if (file->f_pos >= 2) {
  			struct list_head *p;
  			struct dentry *cursor = file->private_data;
  			loff_t n = file->f_pos - 2;

  			spin_lock(&dentry->d_lock);
  			/* d_lock not required for cursor */

  			list_del(&cursor->d_u.d_child);

  			p = dentry->d_subdirs.next;
  			while (n && p != &dentry->d_subdirs) {

  				struct dentry *next;

  				next = list_entry(p, struct dentry, d_u.d_child);

  				spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);

  				if (simple_positive(next))

  					n--;

  				spin_unlock(&next->d_lock);

  				p = p->next;
  			}

  			list_add_tail(&cursor->d_u.d_child, p);

  			spin_unlock(&dentry->d_lock);

  		}
  	}

  	mutex_unlock(&dentry->d_inode->i_mutex);

  	return offset;
  }
  
  /* Relationship between i_mode and the DT_xxx types */
  static inline unsigned char dt_type(struct inode *inode)
  {
  	return (inode->i_mode >> 12) & 15;
  }
  
  /*
   * Directory is locked and all positive dentries in it are safe, since
   * for ramfs-type trees they can't go away without unlink() or rmdir(),
   * both impossible due to the lock on directory.
   */
  
  int dcache_readdir(struct file * filp, void * dirent, filldir_t filldir)
  {

  	struct dentry *dentry = filp->f_path.dentry;

  	struct dentry *cursor = filp->private_data;

  	struct list_head *p, *q = &cursor->d_u.d_child;

  	ino_t ino;
  	int i = filp->f_pos;
  
  	switch (i) {
  		case 0:
  			ino = dentry->d_inode->i_ino;
  			if (filldir(dirent, ".", 1, i, ino, DT_DIR) < 0)
  				break;
  			filp->f_pos++;
  			i++;
  			/* fallthrough */
  		case 1:
  			ino = parent_ino(dentry);
  			if (filldir(dirent, "..", 2, i, ino, DT_DIR) < 0)
  				break;
  			filp->f_pos++;
  			i++;
  			/* fallthrough */
  		default:

  			spin_lock(&dentry->d_lock);

  			if (filp->f_pos == 2)
  				list_move(q, &dentry->d_subdirs);

  			for (p=q->next; p != &dentry->d_subdirs; p=p->next) {
  				struct dentry *next;

  				next = list_entry(p, struct dentry, d_u.d_child);

  				spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);
  				if (!simple_positive(next)) {
  					spin_unlock(&next->d_lock);

  					continue;

  				}

  				spin_unlock(&next->d_lock);

  				spin_unlock(&dentry->d_lock);

  				if (filldir(dirent, next->d_name.name, 
  					    next->d_name.len, filp->f_pos, 
  					    next->d_inode->i_ino, 
  					    dt_type(next->d_inode)) < 0)

  					return 0;

  				spin_lock(&dentry->d_lock);
  				spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);

  				/* next is still alive */

  				list_move(q, p);

  				spin_unlock(&next->d_lock);

  				p = q;
  				filp->f_pos++;
  			}

  			spin_unlock(&dentry->d_lock);

  	}
  	return 0;
  }
  
  ssize_t generic_read_dir(struct file *filp, char __user *buf, size_t siz, loff_t *ppos)
  {
  	return -EISDIR;
  }

  const struct file_operations simple_dir_operations = {

  	.open		= dcache_dir_open,
  	.release	= dcache_dir_close,
  	.llseek		= dcache_dir_lseek,
  	.read		= generic_read_dir,
  	.readdir	= dcache_readdir,

  	.fsync		= noop_fsync,

  };

  const struct inode_operations simple_dir_inode_operations = {

  	.lookup		= simple_lookup,
  };

  static const struct super_operations simple_super_operations = {
  	.statfs		= simple_statfs,
  };

  /*
   * Common helper for pseudo-filesystems (sockfs, pipefs, bdev - stuff that
   * will never be mountable)
   */

  struct dentry *mount_pseudo(struct file_system_type *fs_type, char *name,

  	const struct super_operations *ops,
  	const struct dentry_operations *dops, unsigned long magic)

  {
  	struct super_block *s = sget(fs_type, NULL, set_anon_super, NULL);

  	struct dentry *dentry;
  	struct inode *root;
  	struct qstr d_name = {.name = name, .len = strlen(name)};
  
  	if (IS_ERR(s))

  		return ERR_CAST(s);

  
  	s->s_flags = MS_NOUSER;

  	s->s_maxbytes = MAX_LFS_FILESIZE;

  	s->s_blocksize = PAGE_SIZE;
  	s->s_blocksize_bits = PAGE_SHIFT;

  	s->s_magic = magic;

  	s->s_op = ops ? ops : &simple_super_operations;

  	s->s_time_gran = 1;
  	root = new_inode(s);
  	if (!root)
  		goto Enomem;

  	/*
  	 * since this is the first inode, make it number 1. New inodes created
  	 * after this must take care not to collide with it (by passing
  	 * max_reserved of 1 to iunique).
  	 */
  	root->i_ino = 1;

  	root->i_mode = S_IFDIR | S_IRUSR | S_IWUSR;

  	root->i_atime = root->i_mtime = root->i_ctime = CURRENT_TIME;

  	dentry = __d_alloc(s, &d_name);

  	if (!dentry) {
  		iput(root);
  		goto Enomem;
  	}

  	d_instantiate(dentry, root);
  	s->s_root = dentry;

  	s->s_d_op = dops;

  	s->s_flags |= MS_ACTIVE;

  	return dget(s->s_root);

  
  Enomem:

  	deactivate_locked_super(s);

  	return ERR_PTR(-ENOMEM);

  }
  
  int simple_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
  {
  	struct inode *inode = old_dentry->d_inode;
  
  	inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;

  	inc_nlink(inode);

  	ihold(inode);

  	dget(dentry);
  	d_instantiate(dentry, inode);
  	return 0;
  }

  int simple_empty(struct dentry *dentry)
  {
  	struct dentry *child;
  	int ret = 0;

  	spin_lock(&dentry->d_lock);

  	list_for_each_entry(child, &dentry->d_subdirs, d_u.d_child) {
  		spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
  		if (simple_positive(child)) {
  			spin_unlock(&child->d_lock);

  			goto out;

  		}
  		spin_unlock(&child->d_lock);
  	}

  	ret = 1;
  out:

  	spin_unlock(&dentry->d_lock);

  	return ret;
  }
  
  int simple_unlink(struct inode *dir, struct dentry *dentry)
  {
  	struct inode *inode = dentry->d_inode;
  
  	inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;

  	drop_nlink(inode);

  	dput(dentry);
  	return 0;
  }
  
  int simple_rmdir(struct inode *dir, struct dentry *dentry)
  {
  	if (!simple_empty(dentry))
  		return -ENOTEMPTY;

  	drop_nlink(dentry->d_inode);

  	simple_unlink(dir, dentry);

  	drop_nlink(dir);

  	return 0;
  }
  
  int simple_rename(struct inode *old_dir, struct dentry *old_dentry,
  		struct inode *new_dir, struct dentry *new_dentry)
  {
  	struct inode *inode = old_dentry->d_inode;
  	int they_are_dirs = S_ISDIR(old_dentry->d_inode->i_mode);
  
  	if (!simple_empty(new_dentry))
  		return -ENOTEMPTY;
  
  	if (new_dentry->d_inode) {
  		simple_unlink(new_dir, new_dentry);

  		if (they_are_dirs) {
  			drop_nlink(new_dentry->d_inode);

  			drop_nlink(old_dir);

  		}

  	} else if (they_are_dirs) {

  		drop_nlink(old_dir);

  		inc_nlink(new_dir);

  	}
  
  	old_dir->i_ctime = old_dir->i_mtime = new_dir->i_ctime =
  		new_dir->i_mtime = inode->i_ctime = CURRENT_TIME;
  
  	return 0;
  }

  /**

   * simple_setattr - setattr for simple filesystem

   * @dentry: dentry
   * @iattr: iattr structure
   *
   * Returns 0 on success, -error on failure.
   *

   * simple_setattr is a simple ->setattr implementation without a proper
   * implementation of size changes.
   *
   * It can either be used for in-memory filesystems or special files
   * on simple regular filesystems.  Anything that needs to change on-disk
   * or wire state on size changes needs its own setattr method.

   */
  int simple_setattr(struct dentry *dentry, struct iattr *iattr)
  {
  	struct inode *inode = dentry->d_inode;
  	int error;

  	WARN_ON_ONCE(inode->i_op->truncate);

  	error = inode_change_ok(inode, iattr);
  	if (error)
  		return error;

  	if (iattr->ia_valid & ATTR_SIZE)
  		truncate_setsize(inode, iattr->ia_size);

  	setattr_copy(inode, iattr);

  	mark_inode_dirty(inode);
  	return 0;

  }
  EXPORT_SYMBOL(simple_setattr);

  int simple_readpage(struct file *file, struct page *page)
  {

  	clear_highpage(page);

  	flush_dcache_page(page);
  	SetPageUptodate(page);

  	unlock_page(page);
  	return 0;
  }

  int simple_write_begin(struct file *file, struct address_space *mapping,
  			loff_t pos, unsigned len, unsigned flags,
  			struct page **pagep, void **fsdata)
  {
  	struct page *page;
  	pgoff_t index;

  
  	index = pos >> PAGE_CACHE_SHIFT;

  	page = grab_cache_page_write_begin(mapping, index, flags);

  	if (!page)
  		return -ENOMEM;
  
  	*pagep = page;

  	if (!PageUptodate(page) && (len != PAGE_CACHE_SIZE)) {
  		unsigned from = pos & (PAGE_CACHE_SIZE - 1);
  
  		zero_user_segments(page, 0, from, from + len, PAGE_CACHE_SIZE);
  	}
  	return 0;

  }

  /**
   * simple_write_end - .write_end helper for non-block-device FSes
   * @available: See .write_end of address_space_operations
   * @file: 		"
   * @mapping: 		"
   * @pos: 		"
   * @len: 		"
   * @copied: 		"
   * @page: 		"
   * @fsdata: 		"
   *
   * simple_write_end does the minimum needed for updating a page after writing is
   * done. It has the same API signature as the .write_end of
   * address_space_operations vector. So it can just be set onto .write_end for
   * FSes that don't need any other processing. i_mutex is assumed to be held.
   * Block based filesystems should use generic_write_end().
   * NOTE: Even though i_size might get updated by this function, mark_inode_dirty
   * is not called, so a filesystem that actually does store data in .write_inode
   * should extend on what's done here with a call to mark_inode_dirty() in the
   * case that i_size has changed.
   */

  int simple_write_end(struct file *file, struct address_space *mapping,
  			loff_t pos, unsigned len, unsigned copied,
  			struct page *page, void *fsdata)
  {

  	struct inode *inode = page->mapping->host;
  	loff_t last_pos = pos + copied;

  
  	/* zero the stale part of the page if we did a short copy */
  	if (copied < len) {

  		unsigned from = pos & (PAGE_CACHE_SIZE - 1);
  
  		zero_user(page, from + copied, len - copied);

  	}

  	if (!PageUptodate(page))
  		SetPageUptodate(page);
  	/*
  	 * No need to use i_size_read() here, the i_size
  	 * cannot change under us because we hold the i_mutex.
  	 */
  	if (last_pos > inode->i_size)
  		i_size_write(inode, last_pos);

  	set_page_dirty(page);

  	unlock_page(page);
  	page_cache_release(page);
  
  	return copied;
  }

  /*
   * the inodes created here are not hashed. If you use iunique to generate
   * unique inode values later for this filesystem, then you must take care
   * to pass it an appropriate max_reserved value to avoid collisions.
   */

  int simple_fill_super(struct super_block *s, unsigned long magic,
  		      struct tree_descr *files)

  {

  	struct inode *inode;
  	struct dentry *root;
  	struct dentry *dentry;
  	int i;
  
  	s->s_blocksize = PAGE_CACHE_SIZE;
  	s->s_blocksize_bits = PAGE_CACHE_SHIFT;
  	s->s_magic = magic;

  	s->s_op = &simple_super_operations;

  	s->s_time_gran = 1;
  
  	inode = new_inode(s);
  	if (!inode)
  		return -ENOMEM;

  	/*
  	 * because the root inode is 1, the files array must not contain an
  	 * entry at index 1
  	 */
  	inode->i_ino = 1;

  	inode->i_mode = S_IFDIR | 0755;

  	inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
  	inode->i_op = &simple_dir_inode_operations;
  	inode->i_fop = &simple_dir_operations;

  	set_nlink(inode, 2);

  	root = d_alloc_root(inode);
  	if (!root) {
  		iput(inode);
  		return -ENOMEM;
  	}
  	for (i = 0; !files->name || files->name[0]; i++, files++) {
  		if (!files->name)
  			continue;

  
  		/* warn if it tries to conflict with the root inode */
  		if (unlikely(i == 1))
  			printk(KERN_WARNING "%s: %s passed in a files array"
  				"with an index of 1!
  ", __func__,
  				s->s_type->name);

  		dentry = d_alloc_name(root, files->name);
  		if (!dentry)
  			goto out;
  		inode = new_inode(s);

  		if (!inode) {
  			dput(dentry);

  			goto out;

  		}

  		inode->i_mode = S_IFREG | files->mode;

  		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
  		inode->i_fop = files->ops;
  		inode->i_ino = i;
  		d_add(dentry, inode);
  	}
  	s->s_root = root;
  	return 0;
  out:
  	d_genocide(root);
  	dput(root);
  	return -ENOMEM;
  }
  
  static DEFINE_SPINLOCK(pin_fs_lock);

  int simple_pin_fs(struct file_system_type *type, struct vfsmount **mount, int *count)

  {
  	struct vfsmount *mnt = NULL;
  	spin_lock(&pin_fs_lock);
  	if (unlikely(!*mount)) {
  		spin_unlock(&pin_fs_lock);

  		mnt = vfs_kern_mount(type, 0, type->name, NULL);

  		if (IS_ERR(mnt))
  			return PTR_ERR(mnt);
  		spin_lock(&pin_fs_lock);
  		if (!*mount)
  			*mount = mnt;
  	}
  	mntget(*mount);
  	++*count;
  	spin_unlock(&pin_fs_lock);
  	mntput(mnt);
  	return 0;
  }
  
  void simple_release_fs(struct vfsmount **mount, int *count)
  {
  	struct vfsmount *mnt;
  	spin_lock(&pin_fs_lock);
  	mnt = *mount;
  	if (!--*count)
  		*mount = NULL;
  	spin_unlock(&pin_fs_lock);
  	mntput(mnt);
  }

  /**
   * simple_read_from_buffer - copy data from the buffer to user space
   * @to: the user space buffer to read to
   * @count: the maximum number of bytes to read
   * @ppos: the current position in the buffer
   * @from: the buffer to read from
   * @available: the size of the buffer
   *
   * The simple_read_from_buffer() function reads up to @count bytes from the
   * buffer @from at offset @ppos into the user space address starting at @to.
   *
   * On success, the number of bytes read is returned and the offset @ppos is
   * advanced by this number, or negative value is returned on error.
   **/

  ssize_t simple_read_from_buffer(void __user *to, size_t count, loff_t *ppos,
  				const void *from, size_t available)
  {
  	loff_t pos = *ppos;

  	size_t ret;

  	if (pos < 0)
  		return -EINVAL;

  	if (pos >= available || !count)

  		return 0;
  	if (count > available - pos)
  		count = available - pos;

  	ret = copy_to_user(to, from + pos, count);
  	if (ret == count)

  		return -EFAULT;

  	count -= ret;

  	*ppos = pos + count;
  	return count;
  }

  /**

   * simple_write_to_buffer - copy data from user space to the buffer
   * @to: the buffer to write to
   * @available: the size of the buffer
   * @ppos: the current position in the buffer
   * @from: the user space buffer to read from
   * @count: the maximum number of bytes to read
   *
   * The simple_write_to_buffer() function reads up to @count bytes from the user
   * space address starting at @from into the buffer @to at offset @ppos.
   *
   * On success, the number of bytes written is returned and the offset @ppos is
   * advanced by this number, or negative value is returned on error.
   **/
  ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos,
  		const void __user *from, size_t count)
  {
  	loff_t pos = *ppos;
  	size_t res;
  
  	if (pos < 0)
  		return -EINVAL;
  	if (pos >= available || !count)
  		return 0;
  	if (count > available - pos)
  		count = available - pos;
  	res = copy_from_user(to + pos, from, count);
  	if (res == count)
  		return -EFAULT;
  	count -= res;
  	*ppos = pos + count;
  	return count;
  }
  
  /**

   * memory_read_from_buffer - copy data from the buffer
   * @to: the kernel space buffer to read to
   * @count: the maximum number of bytes to read
   * @ppos: the current position in the buffer
   * @from: the buffer to read from
   * @available: the size of the buffer
   *
   * The memory_read_from_buffer() function reads up to @count bytes from the
   * buffer @from at offset @ppos into the kernel space address starting at @to.
   *
   * On success, the number of bytes read is returned and the offset @ppos is
   * advanced by this number, or negative value is returned on error.
   **/

  ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
  				const void *from, size_t available)
  {
  	loff_t pos = *ppos;
  
  	if (pos < 0)
  		return -EINVAL;
  	if (pos >= available)
  		return 0;
  	if (count > available - pos)
  		count = available - pos;
  	memcpy(to, from + pos, count);
  	*ppos = pos + count;
  
  	return count;
  }

  /*
   * Transaction based IO.
   * The file expects a single write which triggers the transaction, and then
   * possibly a read which collects the result - which is stored in a
   * file-local buffer.
   */

  
  void simple_transaction_set(struct file *file, size_t n)
  {
  	struct simple_transaction_argresp *ar = file->private_data;
  
  	BUG_ON(n > SIMPLE_TRANSACTION_LIMIT);
  
  	/*
  	 * The barrier ensures that ar->size will really remain zero until
  	 * ar->data is ready for reading.
  	 */
  	smp_mb();
  	ar->size = n;
  }

  char *simple_transaction_get(struct file *file, const char __user *buf, size_t size)
  {
  	struct simple_transaction_argresp *ar;
  	static DEFINE_SPINLOCK(simple_transaction_lock);
  
  	if (size > SIMPLE_TRANSACTION_LIMIT - 1)
  		return ERR_PTR(-EFBIG);
  
  	ar = (struct simple_transaction_argresp *)get_zeroed_page(GFP_KERNEL);
  	if (!ar)
  		return ERR_PTR(-ENOMEM);
  
  	spin_lock(&simple_transaction_lock);
  
  	/* only one write allowed per open */
  	if (file->private_data) {
  		spin_unlock(&simple_transaction_lock);
  		free_page((unsigned long)ar);
  		return ERR_PTR(-EBUSY);
  	}
  
  	file->private_data = ar;
  
  	spin_unlock(&simple_transaction_lock);
  
  	if (copy_from_user(ar->data, buf, size))
  		return ERR_PTR(-EFAULT);
  
  	return ar->data;
  }
  
  ssize_t simple_transaction_read(struct file *file, char __user *buf, size_t size, loff_t *pos)
  {
  	struct simple_transaction_argresp *ar = file->private_data;
  
  	if (!ar)
  		return 0;
  	return simple_read_from_buffer(buf, size, pos, ar->data, ar->size);
  }
  
  int simple_transaction_release(struct inode *inode, struct file *file)
  {
  	free_page((unsigned long)file->private_data);
  	return 0;
  }

  /* Simple attribute files */
  
  struct simple_attr {

  	int (*get)(void *, u64 *);
  	int (*set)(void *, u64);

  	char get_buf[24];	/* enough to store a u64 and "
  \0" */
  	char set_buf[24];
  	void *data;
  	const char *fmt;	/* format for read operation */

  	struct mutex mutex;	/* protects access to these buffers */

  };
  
  /* simple_attr_open is called by an actual attribute open file operation
   * to set the attribute specific access operations. */
  int simple_attr_open(struct inode *inode, struct file *file,

  		     int (*get)(void *, u64 *), int (*set)(void *, u64),

  		     const char *fmt)
  {
  	struct simple_attr *attr;
  
  	attr = kmalloc(sizeof(*attr), GFP_KERNEL);
  	if (!attr)
  		return -ENOMEM;
  
  	attr->get = get;
  	attr->set = set;

  	attr->data = inode->i_private;

  	attr->fmt = fmt;

  	mutex_init(&attr->mutex);

  
  	file->private_data = attr;
  
  	return nonseekable_open(inode, file);
  }

  int simple_attr_release(struct inode *inode, struct file *file)

  {
  	kfree(file->private_data);
  	return 0;
  }
  
  /* read from the buffer that is filled with the get function */
  ssize_t simple_attr_read(struct file *file, char __user *buf,
  			 size_t len, loff_t *ppos)
  {
  	struct simple_attr *attr;
  	size_t size;
  	ssize_t ret;
  
  	attr = file->private_data;
  
  	if (!attr->get)
  		return -EACCES;

  	ret = mutex_lock_interruptible(&attr->mutex);
  	if (ret)
  		return ret;

  	if (*ppos) {		/* continued read */

  		size = strlen(attr->get_buf);

  	} else {		/* first read */
  		u64 val;
  		ret = attr->get(attr->data, &val);
  		if (ret)
  			goto out;

  		size = scnprintf(attr->get_buf, sizeof(attr->get_buf),

  				 attr->fmt, (unsigned long long)val);
  	}

  
  	ret = simple_read_from_buffer(buf, len, ppos, attr->get_buf, size);

  out:

  	mutex_unlock(&attr->mutex);

  	return ret;
  }
  
  /* interpret the buffer as a number to call the set function with */
  ssize_t simple_attr_write(struct file *file, const char __user *buf,
  			  size_t len, loff_t *ppos)
  {
  	struct simple_attr *attr;
  	u64 val;
  	size_t size;
  	ssize_t ret;
  
  	attr = file->private_data;

  	if (!attr->set)
  		return -EACCES;

  	ret = mutex_lock_interruptible(&attr->mutex);
  	if (ret)
  		return ret;

  	ret = -EFAULT;
  	size = min(sizeof(attr->set_buf) - 1, len);
  	if (copy_from_user(attr->set_buf, buf, size))
  		goto out;

  	attr->set_buf[size] = '\0';

  	val = simple_strtoll(attr->set_buf, NULL, 0);

  	ret = attr->set(attr->data, val);
  	if (ret == 0)
  		ret = len; /* on success, claim we got the whole input */

  out:

  	mutex_unlock(&attr->mutex);

  	return ret;
  }

  /**
   * generic_fh_to_dentry - generic helper for the fh_to_dentry export operation
   * @sb:		filesystem to do the file handle conversion on
   * @fid:	file handle to convert
   * @fh_len:	length of the file handle in bytes
   * @fh_type:	type of file handle
   * @get_inode:	filesystem callback to retrieve inode
   *
   * This function decodes @fid as long as it has one of the well-known
   * Linux filehandle types and calls @get_inode on it to retrieve the
   * inode for the object specified in the file handle.
   */
  struct dentry *generic_fh_to_dentry(struct super_block *sb, struct fid *fid,
  		int fh_len, int fh_type, struct inode *(*get_inode)
  			(struct super_block *sb, u64 ino, u32 gen))
  {
  	struct inode *inode = NULL;
  
  	if (fh_len < 2)
  		return NULL;
  
  	switch (fh_type) {
  	case FILEID_INO32_GEN:
  	case FILEID_INO32_GEN_PARENT:
  		inode = get_inode(sb, fid->i32.ino, fid->i32.gen);
  		break;
  	}

  	return d_obtain_alias(inode);

  }
  EXPORT_SYMBOL_GPL(generic_fh_to_dentry);
  
  /**
   * generic_fh_to_dentry - generic helper for the fh_to_parent export operation
   * @sb:		filesystem to do the file handle conversion on
   * @fid:	file handle to convert
   * @fh_len:	length of the file handle in bytes
   * @fh_type:	type of file handle
   * @get_inode:	filesystem callback to retrieve inode
   *
   * This function decodes @fid as long as it has one of the well-known
   * Linux filehandle types and calls @get_inode on it to retrieve the
   * inode for the _parent_ object specified in the file handle if it
   * is specified in the file handle, or NULL otherwise.
   */
  struct dentry *generic_fh_to_parent(struct super_block *sb, struct fid *fid,
  		int fh_len, int fh_type, struct inode *(*get_inode)
  			(struct super_block *sb, u64 ino, u32 gen))
  {
  	struct inode *inode = NULL;
  
  	if (fh_len <= 2)
  		return NULL;
  
  	switch (fh_type) {
  	case FILEID_INO32_GEN_PARENT:
  		inode = get_inode(sb, fid->i32.parent_ino,
  				  (fh_len > 3 ? fid->i32.parent_gen : 0));
  		break;
  	}

  	return d_obtain_alias(inode);

  }
  EXPORT_SYMBOL_GPL(generic_fh_to_parent);

  /**
   * generic_file_fsync - generic fsync implementation for simple filesystems
   * @file:	file to synchronize
   * @datasync:	only synchronize essential metadata if true
   *
   * This is a generic implementation of the fsync method for simple
   * filesystems which track all non-inode metadata in the buffers list
   * hanging off the address_space structure.
   */

  int generic_file_fsync(struct file *file, loff_t start, loff_t end,
  		       int datasync)

  {

  	struct inode *inode = file->f_mapping->host;

  	int err;
  	int ret;

  	err = filemap_write_and_wait_range(inode->i_mapping, start, end);
  	if (err)
  		return err;
  
  	mutex_lock(&inode->i_mutex);

  	ret = sync_mapping_buffers(inode->i_mapping);
  	if (!(inode->i_state & I_DIRTY))

  		goto out;

  	if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))

  		goto out;

  	err = sync_inode_metadata(inode, 1);

  	if (ret == 0)
  		ret = err;

  out:
  	mutex_unlock(&inode->i_mutex);

  	return ret;
  }

  EXPORT_SYMBOL(generic_file_fsync);

  /**
   * generic_check_addressable - Check addressability of file system
   * @blocksize_bits:	log of file system block size
   * @num_blocks:		number of blocks in file system
   *
   * Determine whether a file system with @num_blocks blocks (and a
   * block size of 2**@blocksize_bits) is addressable by the sector_t
   * and page cache of the system.  Return 0 if so and -EFBIG otherwise.
   */
  int generic_check_addressable(unsigned blocksize_bits, u64 num_blocks)
  {
  	u64 last_fs_block = num_blocks - 1;

  	u64 last_fs_page =
  		last_fs_block >> (PAGE_CACHE_SHIFT - blocksize_bits);

  
  	if (unlikely(num_blocks == 0))
  		return 0;
  
  	if ((blocksize_bits < 9) || (blocksize_bits > PAGE_CACHE_SHIFT))
  		return -EINVAL;

  	if ((last_fs_block > (sector_t)(~0ULL) >> (blocksize_bits - 9)) ||
  	    (last_fs_page > (pgoff_t)(~0ULL))) {

  		return -EFBIG;
  	}
  	return 0;
  }
  EXPORT_SYMBOL(generic_check_addressable);

  /*
   * No-op implementation of ->fsync for in-memory filesystems.
   */

  int noop_fsync(struct file *file, loff_t start, loff_t end, int datasync)

  {
  	return 0;
  }

  EXPORT_SYMBOL(dcache_dir_close);
  EXPORT_SYMBOL(dcache_dir_lseek);
  EXPORT_SYMBOL(dcache_dir_open);
  EXPORT_SYMBOL(dcache_readdir);
  EXPORT_SYMBOL(generic_read_dir);

  EXPORT_SYMBOL(mount_pseudo);

  EXPORT_SYMBOL(simple_write_begin);
  EXPORT_SYMBOL(simple_write_end);

  EXPORT_SYMBOL(simple_dir_inode_operations);
  EXPORT_SYMBOL(simple_dir_operations);
  EXPORT_SYMBOL(simple_empty);

  EXPORT_SYMBOL(simple_fill_super);
  EXPORT_SYMBOL(simple_getattr);
  EXPORT_SYMBOL(simple_link);
  EXPORT_SYMBOL(simple_lookup);
  EXPORT_SYMBOL(simple_pin_fs);

  EXPORT_SYMBOL(simple_readpage);
  EXPORT_SYMBOL(simple_release_fs);
  EXPORT_SYMBOL(simple_rename);
  EXPORT_SYMBOL(simple_rmdir);
  EXPORT_SYMBOL(simple_statfs);

  EXPORT_SYMBOL(noop_fsync);

  EXPORT_SYMBOL(simple_unlink);
  EXPORT_SYMBOL(simple_read_from_buffer);

  EXPORT_SYMBOL(simple_write_to_buffer);

  EXPORT_SYMBOL(memory_read_from_buffer);

  EXPORT_SYMBOL(simple_transaction_set);

  EXPORT_SYMBOL(simple_transaction_get);
  EXPORT_SYMBOL(simple_transaction_read);
  EXPORT_SYMBOL(simple_transaction_release);

  EXPORT_SYMBOL_GPL(simple_attr_open);

  EXPORT_SYMBOL_GPL(simple_attr_release);

  EXPORT_SYMBOL_GPL(simple_attr_read);
  EXPORT_SYMBOL_GPL(simple_attr_write);