/*

   * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)

   * Licensed under the GPL
   *
   * Ported the filesystem routines to 2.5.
   * 2003-02-10 Petr Baudis <pasky@ucw.cz>
   */

  #include <linux/fs.h>

  #include <linux/magic.h>

  #include <linux/module.h>

  #include <linux/mm.h>

  #include <linux/pagemap.h>

  #include <linux/statfs.h>

  #include <linux/slab.h>

  #include <linux/seq_file.h>

  #include <linux/mount.h>

  #include <linux/namei.h>

  #include "hostfs.h"

  #include <init.h>
  #include <kern.h>

  
  struct hostfs_inode_info {

  	int fd;

  	fmode_t mode;

  	struct inode vfs_inode;

  	struct mutex open_mutex;

  };
  
  static inline struct hostfs_inode_info *HOSTFS_I(struct inode *inode)
  {

  	return list_entry(inode, struct hostfs_inode_info, vfs_inode);

  }

  #define FILE_HOSTFS_I(file) HOSTFS_I(file_inode(file))

  /* Changed in hostfs_args before the kernel starts running */

  static char *root_ino = "";

  static int append = 0;

  static const struct inode_operations hostfs_iops;
  static const struct inode_operations hostfs_dir_iops;

  static const struct inode_operations hostfs_link_iops;

  
  #ifndef MODULE
  static int __init hostfs_args(char *options, int *add)
  {
  	char *ptr;
  
  	ptr = strchr(options, ',');

  	if (ptr != NULL)

  		*ptr++ = '\0';

  	if (*options != '\0')

  		root_ino = options;
  
  	options = ptr;

  	while (options) {

  		ptr = strchr(options, ',');

  		if (ptr != NULL)

  			*ptr++ = '\0';

  		if (*options != '\0') {
  			if (!strcmp(options, "append"))

  				append = 1;
  			else printf("hostfs_args - unsupported option - %s
  ",
  				    options);
  		}
  		options = ptr;
  	}

  	return 0;

  }
  
  __uml_setup("hostfs=", hostfs_args,
  "hostfs=<root dir>,<flags>,...
  "
  "    This is used to set hostfs parameters.  The root directory argument
  "
  "    is used to confine all hostfs mounts to within the specified directory
  "
  "    tree on the host.  If this isn't specified, then a user inside UML can
  "
  "    mount anything on the host that's accessible to the user that's running
  "
  "    it.
  "
  "    The only flag currently supported is 'append', which specifies that all
  "
  "    files opened by hostfs will be opened in append mode.
  
  "
  );
  #endif

  static char *__dentry_name(struct dentry *dentry, char *name)

  {

  	char *p = dentry_path_raw(dentry, name, PATH_MAX);

  	char *root;
  	size_t len;

  	root = dentry->d_sb->s_fs_info;
  	len = strlen(root);
  	if (IS_ERR(p)) {
  		__putname(name);

  		return NULL;

  	}

  
  	/*
  	 * This function relies on the fact that dentry_path_raw() will place
  	 * the path name at the end of the provided buffer.
  	 */
  	BUG_ON(p + strlen(p) + 1 != name + PATH_MAX);

  	strlcpy(name, root, PATH_MAX);

  	if (len > p - name) {
  		__putname(name);
  		return NULL;
  	}

  
  	if (p > name + len)
  		strcpy(name + len, p);

  	return name;

  }

  static char *dentry_name(struct dentry *dentry)
  {
  	char *name = __getname();
  	if (!name)
  		return NULL;

  	return __dentry_name(dentry, name);

  }

  static char *inode_name(struct inode *ino)

  {
  	struct dentry *dentry;

  	char *name;

  	dentry = d_find_alias(ino);
  	if (!dentry)

  		return NULL;

  
  	name = dentry_name(dentry);
  
  	dput(dentry);
  
  	return name;

  }

  static char *follow_link(char *link)
  {
  	int len, n;
  	char *name, *resolved, *end;

  	name = __getname();
  	if (!name) {

  		n = -ENOMEM;

  		goto out_free;

  	}

  
  	n = hostfs_do_readlink(link, name, PATH_MAX);

  	if (n < 0)

  		goto out_free;

  	else if (n == PATH_MAX) {
  		n = -E2BIG;
  		goto out_free;
  	}

  	if (*name == '/')

  		return name;

  
  	end = strrchr(link, '/');

  	if (end == NULL)

  		return name;

  
  	*(end + 1) = '\0';
  	len = strlen(link) + strlen(name) + 1;
  
  	resolved = kmalloc(len, GFP_KERNEL);

  	if (resolved == NULL) {

  		n = -ENOMEM;
  		goto out_free;
  	}
  
  	sprintf(resolved, "%s%s", link, name);

  	__putname(name);

  	kfree(link);

  	return resolved;

  
   out_free:

  	__putname(name);

  	return ERR_PTR(n);

  }

  static struct inode *hostfs_iget(struct super_block *sb)
  {

  	struct inode *inode = new_inode(sb);

  	if (!inode)
  		return ERR_PTR(-ENOMEM);

  	return inode;
  }

  static int hostfs_statfs(struct dentry *dentry, struct kstatfs *sf)

  {

  	/*
  	 * do_statfs uses struct statfs64 internally, but the linux kernel

  	 * struct statfs still has 32-bit versions for most of these fields,
  	 * so we convert them here
  	 */
  	int err;
  	long long f_blocks;
  	long long f_bfree;
  	long long f_bavail;
  	long long f_files;
  	long long f_ffree;

  	err = do_statfs(dentry->d_sb->s_fs_info,

  			&sf->f_bsize, &f_blocks, &f_bfree, &f_bavail, &f_files,
  			&f_ffree, &sf->f_fsid, sizeof(sf->f_fsid),

  			&sf->f_namelen);

  	if (err)

  		return err;

  	sf->f_blocks = f_blocks;
  	sf->f_bfree = f_bfree;
  	sf->f_bavail = f_bavail;
  	sf->f_files = f_files;
  	sf->f_ffree = f_ffree;
  	sf->f_type = HOSTFS_SUPER_MAGIC;

  	return 0;

  }
  
  static struct inode *hostfs_alloc_inode(struct super_block *sb)
  {
  	struct hostfs_inode_info *hi;

  	hi = kmalloc(sizeof(*hi), GFP_KERNEL);

  	if (hi == NULL)

  		return NULL;

  	hi->fd = -1;

  	hi->mode = 0;

  	inode_init_once(&hi->vfs_inode);

  	mutex_init(&hi->open_mutex);

  	return &hi->vfs_inode;

  }

  static void hostfs_evict_inode(struct inode *inode)

  {

  	truncate_inode_pages_final(&inode->i_data);

  	clear_inode(inode);

  	if (HOSTFS_I(inode)->fd != -1) {

  		close_file(&HOSTFS_I(inode)->fd);
  		HOSTFS_I(inode)->fd = -1;
  	}

  }

  static void hostfs_i_callback(struct rcu_head *head)

  {

  	struct inode *inode = container_of(head, struct inode, i_rcu);

  	kfree(HOSTFS_I(inode));
  }

  
  static void hostfs_destroy_inode(struct inode *inode)
  {
  	call_rcu(&inode->i_rcu, hostfs_i_callback);
  }

  static int hostfs_show_options(struct seq_file *seq, struct dentry *root)

  {

  	const char *root_path = root->d_sb->s_fs_info;

  	size_t offset = strlen(root_ino) + 1;
  
  	if (strlen(root_path) > offset)
  		seq_printf(seq, ",%s", root_path + offset);

  	if (append)
  		seq_puts(seq, ",append");

  	return 0;
  }

  static const struct super_operations hostfs_sbops = {

  	.alloc_inode	= hostfs_alloc_inode,

  	.destroy_inode	= hostfs_destroy_inode,

  	.evict_inode	= hostfs_evict_inode,

  	.statfs		= hostfs_statfs,

  	.show_options	= hostfs_show_options,

  };

  static int hostfs_readdir(struct file *file, struct dir_context *ctx)

  {
  	void *dir;
  	char *name;
  	unsigned long long next, ino;
  	int error, len;

  	unsigned int type;

  	name = dentry_name(file->f_path.dentry);

  	if (name == NULL)

  		return -ENOMEM;

  	dir = open_dir(name, &error);

  	__putname(name);

  	if (dir == NULL)

  		return -error;

  	next = ctx->pos;

  	seek_dir(dir, next);

  	while ((name = read_dir(dir, &next, &ino, &len, &type)) != NULL) {

  		if (!dir_emit(ctx, name, len, ino, type))
  			break;
  		ctx->pos = next;

  	}
  	close_dir(dir);

  	return 0;

  }

  static int hostfs_open(struct inode *ino, struct file *file)

  {
  	char *name;

  	fmode_t mode;

  	int err;

  	int r, w, fd;

  
  	mode = file->f_mode & (FMODE_READ | FMODE_WRITE);

  	if ((mode & HOSTFS_I(ino)->mode) == mode)

  		return 0;

  	mode |= HOSTFS_I(ino)->mode;

  retry:

  	r = w = 0;

  	if (mode & FMODE_READ)

  		r = 1;

  	if (mode & FMODE_WRITE)

  		r = w = 1;

  	name = dentry_name(file->f_path.dentry);

  	if (name == NULL)

  		return -ENOMEM;

  
  	fd = open_file(name, r, w, append);

  	__putname(name);

  	if (fd < 0)

  		return fd;

  	mutex_lock(&HOSTFS_I(ino)->open_mutex);

  	/* somebody else had handled it first? */
  	if ((mode & HOSTFS_I(ino)->mode) == mode) {

  		mutex_unlock(&HOSTFS_I(ino)->open_mutex);

  		close_file(&fd);

  		return 0;
  	}
  	if ((mode | HOSTFS_I(ino)->mode) != mode) {
  		mode |= HOSTFS_I(ino)->mode;

  		mutex_unlock(&HOSTFS_I(ino)->open_mutex);

  		close_file(&fd);
  		goto retry;
  	}
  	if (HOSTFS_I(ino)->fd == -1) {
  		HOSTFS_I(ino)->fd = fd;
  	} else {
  		err = replace_file(fd, HOSTFS_I(ino)->fd);
  		close_file(&fd);
  		if (err < 0) {

  			mutex_unlock(&HOSTFS_I(ino)->open_mutex);

  			return err;
  		}
  	}
  	HOSTFS_I(ino)->mode = mode;

  	mutex_unlock(&HOSTFS_I(ino)->open_mutex);

  	return 0;

  }

  static int hostfs_file_release(struct inode *inode, struct file *file)
  {
  	filemap_write_and_wait(inode->i_mapping);
  
  	return 0;
  }

  static int hostfs_fsync(struct file *file, loff_t start, loff_t end,
  			int datasync)

  {

  	struct inode *inode = file->f_mapping->host;
  	int ret;
  
  	ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
  	if (ret)
  		return ret;
  
  	mutex_lock(&inode->i_mutex);
  	ret = fsync_file(HOSTFS_I(inode)->fd, datasync);
  	mutex_unlock(&inode->i_mutex);
  
  	return ret;

  }

  static const struct file_operations hostfs_file_fops = {

  	.llseek		= generic_file_llseek,

  	.splice_read	= generic_file_splice_read,

  	.read_iter	= generic_file_read_iter,

  	.write_iter	= generic_file_write_iter,

  	.mmap		= generic_file_mmap,

  	.open		= hostfs_open,

  	.release	= hostfs_file_release,

  	.fsync		= hostfs_fsync,
  };

  static const struct file_operations hostfs_dir_fops = {

  	.llseek		= generic_file_llseek,

  	.iterate	= hostfs_readdir,

  	.read		= generic_read_dir,

  	.open		= hostfs_open,
  	.fsync		= hostfs_fsync,

  };

  static int hostfs_writepage(struct page *page, struct writeback_control *wbc)

  {
  	struct address_space *mapping = page->mapping;
  	struct inode *inode = mapping->host;
  	char *buffer;

  	loff_t base = page_offset(page);

  	int count = PAGE_CACHE_SIZE;
  	int end_index = inode->i_size >> PAGE_CACHE_SHIFT;
  	int err;
  
  	if (page->index >= end_index)
  		count = inode->i_size & (PAGE_CACHE_SIZE-1);
  
  	buffer = kmap(page);

  
  	err = write_file(HOSTFS_I(inode)->fd, &base, buffer, count);

  	if (err != count) {

  		ClearPageUptodate(page);
  		goto out;
  	}
  
  	if (base > inode->i_size)
  		inode->i_size = base;
  
  	if (PageError(page))
  		ClearPageError(page);
  	err = 0;
  
   out:
  	kunmap(page);
  
  	unlock_page(page);
  	return err;
  }

  static int hostfs_readpage(struct file *file, struct page *page)

  {
  	char *buffer;

  	loff_t start = page_offset(page);

  	int bytes_read, ret = 0;

  	buffer = kmap(page);

  	bytes_read = read_file(FILE_HOSTFS_I(file)->fd, &start, buffer,

  			PAGE_CACHE_SIZE);

  	if (bytes_read < 0) {

  		ClearPageUptodate(page);
  		SetPageError(page);

  		ret = bytes_read;

  		goto out;

  	}

  	memset(buffer + bytes_read, 0, PAGE_CACHE_SIZE - bytes_read);

  	ClearPageError(page);

  	SetPageUptodate(page);

   out:

  	flush_dcache_page(page);

  	kunmap(page);
  	unlock_page(page);

  	return ret;

  }

  static int hostfs_write_begin(struct file *file, struct address_space *mapping,
  			      loff_t pos, unsigned len, unsigned flags,
  			      struct page **pagep, void **fsdata)

  {

  	pgoff_t index = pos >> PAGE_CACHE_SHIFT;

  	*pagep = grab_cache_page_write_begin(mapping, index, flags);

  	if (!*pagep)
  		return -ENOMEM;
  	return 0;

  }

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

  {

  	struct inode *inode = mapping->host;

  	void *buffer;
  	unsigned from = pos & (PAGE_CACHE_SIZE - 1);
  	int err;

  	buffer = kmap(page);

  	err = write_file(FILE_HOSTFS_I(file)->fd, &pos, buffer + from, copied);
  	kunmap(page);

  	if (!PageUptodate(page) && err == PAGE_CACHE_SIZE)
  		SetPageUptodate(page);

  	/*
  	 * If err > 0, write_file has added err to pos, so we are comparing

  	 * i_size against the last byte written.
  	 */
  	if (err > 0 && (pos > inode->i_size))
  		inode->i_size = pos;
  	unlock_page(page);
  	page_cache_release(page);

  	return err;

  }

  static const struct address_space_operations hostfs_aops = {

  	.writepage 	= hostfs_writepage,
  	.readpage	= hostfs_readpage,

  	.set_page_dirty = __set_page_dirty_nobuffers,

  	.write_begin	= hostfs_write_begin,
  	.write_end	= hostfs_write_end,

  };

  static int read_name(struct inode *ino, char *name)

  {

  	dev_t rdev;
  	struct hostfs_stat st;
  	int err = stat_file(name, &st, -1);
  	if (err)
  		return err;

  	/* Reencode maj and min with the kernel encoding.*/

  	rdev = MKDEV(st.maj, st.min);

  	switch (st.mode & S_IFMT) {
  	case S_IFLNK:

  		ino->i_op = &hostfs_link_iops;

  		break;

  	case S_IFDIR:
  		ino->i_op = &hostfs_dir_iops;
  		ino->i_fop = &hostfs_dir_fops;

  		break;

  	case S_IFCHR:
  	case S_IFBLK:
  	case S_IFIFO:
  	case S_IFSOCK:
  		init_special_inode(ino, st.mode & S_IFMT, rdev);
  		ino->i_op = &hostfs_iops;

  		break;

  	case S_IFREG:

  		ino->i_op = &hostfs_iops;
  		ino->i_fop = &hostfs_file_fops;
  		ino->i_mapping->a_ops = &hostfs_aops;

  		break;
  	default:
  		return -EIO;

  	}

  
  	ino->i_ino = st.ino;
  	ino->i_mode = st.mode;

  	set_nlink(ino, st.nlink);

  	i_uid_write(ino, st.uid);
  	i_gid_write(ino, st.gid);

  	ino->i_atime = st.atime;
  	ino->i_mtime = st.mtime;
  	ino->i_ctime = st.ctime;
  	ino->i_size = st.size;
  	ino->i_blocks = st.blocks;
  	return 0;

  }

  static int hostfs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
  			 bool excl)

  {
  	struct inode *inode;
  	char *name;
  	int error, fd;

  	inode = hostfs_iget(dir->i_sb);
  	if (IS_ERR(inode)) {
  		error = PTR_ERR(inode);

  		goto out;

  	}

  	error = -ENOMEM;

  	name = dentry_name(dentry);

  	if (name == NULL)

  		goto out_put;

  	fd = file_create(name, mode & S_IFMT);

  	if (fd < 0)

  		error = fd;

  	else

  		error = read_name(inode, name);

  	__putname(name);

  	if (error)

  		goto out_put;
  
  	HOSTFS_I(inode)->fd = fd;
  	HOSTFS_I(inode)->mode = FMODE_READ | FMODE_WRITE;
  	d_instantiate(dentry, inode);

  	return 0;

  
   out_put:
  	iput(inode);
   out:

  	return error;

  }

  static struct dentry *hostfs_lookup(struct inode *ino, struct dentry *dentry,
  				    unsigned int flags)

  {
  	struct inode *inode;
  	char *name;
  	int err;

  	inode = hostfs_iget(ino->i_sb);
  	if (IS_ERR(inode)) {
  		err = PTR_ERR(inode);

  		goto out;

  	}

  	err = -ENOMEM;

  	name = dentry_name(dentry);

  	if (name == NULL)

  		goto out_put;
  
  	err = read_name(inode, name);

  	__putname(name);

  	if (err == -ENOENT) {

  		iput(inode);
  		inode = NULL;
  	}

  	else if (err)

  		goto out_put;
  
  	d_add(dentry, inode);

  	return NULL;

  
   out_put:
  	iput(inode);
   out:

  	return ERR_PTR(err);

  }

  static int hostfs_link(struct dentry *to, struct inode *ino,
  		       struct dentry *from)

  {

  	char *from_name, *to_name;
  	int err;

  	if ((from_name = dentry_name(from)) == NULL)

  		return -ENOMEM;

  	to_name = dentry_name(to);

  	if (to_name == NULL) {

  		__putname(from_name);

  		return -ENOMEM;

  	}

  	err = link_file(to_name, from_name);

  	__putname(from_name);
  	__putname(to_name);

  	return err;

  }

  static int hostfs_unlink(struct inode *ino, struct dentry *dentry)

  {
  	char *file;
  	int err;

  	if (append)

  		return -EPERM;

  	if ((file = dentry_name(dentry)) == NULL)
  		return -ENOMEM;

  	err = unlink_file(file);

  	__putname(file);

  	return err;

  }

  static int hostfs_symlink(struct inode *ino, struct dentry *dentry,
  			  const char *to)

  {
  	char *file;
  	int err;

  	if ((file = dentry_name(dentry)) == NULL)

  		return -ENOMEM;

  	err = make_symlink(file, to);

  	__putname(file);

  	return err;

  }

  static int hostfs_mkdir(struct inode *ino, struct dentry *dentry, umode_t mode)

  {
  	char *file;
  	int err;

  	if ((file = dentry_name(dentry)) == NULL)

  		return -ENOMEM;

  	err = do_mkdir(file, mode);

  	__putname(file);

  	return err;

  }

  static int hostfs_rmdir(struct inode *ino, struct dentry *dentry)

  {
  	char *file;
  	int err;

  	if ((file = dentry_name(dentry)) == NULL)

  		return -ENOMEM;

  	err = do_rmdir(file);

  	__putname(file);

  	return err;

  }

  static int hostfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)

  {
  	struct inode *inode;
  	char *name;

  	int err;

  	inode = hostfs_iget(dir->i_sb);
  	if (IS_ERR(inode)) {
  		err = PTR_ERR(inode);

  		goto out;

  	}

  	err = -ENOMEM;

  	name = dentry_name(dentry);

  	if (name == NULL)

  		goto out_put;
  
  	init_special_inode(inode, mode, dev);

  	err = do_mknod(name, mode, MAJOR(dev), MINOR(dev));

  	if (!err)

  		goto out_free;
  
  	err = read_name(inode, name);

  	__putname(name);

  	if (err)
  		goto out_put;

  	if (err)

  		goto out_put;
  
  	d_instantiate(dentry, inode);

  	return 0;

  
   out_free:

  	__putname(name);

   out_put:
  	iput(inode);
   out:

  	return err;

  }

  static int hostfs_rename2(struct inode *old_dir, struct dentry *old_dentry,
  			  struct inode *new_dir, struct dentry *new_dentry,
  			  unsigned int flags)

  {

  	char *old_name, *new_name;

  	int err;

  	if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
  		return -EINVAL;
  
  	old_name = dentry_name(old_dentry);
  	if (old_name == NULL)

  		return -ENOMEM;

  	new_name = dentry_name(new_dentry);
  	if (new_name == NULL) {
  		__putname(old_name);

  		return -ENOMEM;

  	}

  	if (!flags)
  		err = rename_file(old_name, new_name);
  	else
  		err = rename2_file(old_name, new_name, flags);
  
  	__putname(old_name);
  	__putname(new_name);

  	return err;

  }

  static int hostfs_permission(struct inode *ino, int desired)

  {
  	char *name;
  	int r = 0, w = 0, x = 0, err;

  	if (desired & MAY_NOT_BLOCK)

  		return -ECHILD;

  	if (desired & MAY_READ) r = 1;
  	if (desired & MAY_WRITE) w = 1;
  	if (desired & MAY_EXEC) x = 1;

  	name = inode_name(ino);

  	if (name == NULL)
  		return -ENOMEM;

  
  	if (S_ISCHR(ino->i_mode) || S_ISBLK(ino->i_mode) ||

  	    S_ISFIFO(ino->i_mode) || S_ISSOCK(ino->i_mode))

  		err = 0;
  	else
  		err = access_file(name, r, w, x);

  	__putname(name);

  	if (!err)

  		err = generic_permission(ino, desired);

  	return err;
  }

  static int hostfs_setattr(struct dentry *dentry, struct iattr *attr)

  {

  	struct inode *inode = d_inode(dentry);

  	struct hostfs_iattr attrs;
  	char *name;
  	int err;

  	int fd = HOSTFS_I(inode)->fd;

  	err = inode_change_ok(inode, attr);

  	if (err)
  		return err;

  	if (append)

  		attr->ia_valid &= ~ATTR_SIZE;
  
  	attrs.ia_valid = 0;

  	if (attr->ia_valid & ATTR_MODE) {

  		attrs.ia_valid |= HOSTFS_ATTR_MODE;
  		attrs.ia_mode = attr->ia_mode;
  	}

  	if (attr->ia_valid & ATTR_UID) {

  		attrs.ia_valid |= HOSTFS_ATTR_UID;

  		attrs.ia_uid = from_kuid(&init_user_ns, attr->ia_uid);

  	}

  	if (attr->ia_valid & ATTR_GID) {

  		attrs.ia_valid |= HOSTFS_ATTR_GID;

  		attrs.ia_gid = from_kgid(&init_user_ns, attr->ia_gid);

  	}

  	if (attr->ia_valid & ATTR_SIZE) {

  		attrs.ia_valid |= HOSTFS_ATTR_SIZE;
  		attrs.ia_size = attr->ia_size;
  	}

  	if (attr->ia_valid & ATTR_ATIME) {

  		attrs.ia_valid |= HOSTFS_ATTR_ATIME;
  		attrs.ia_atime = attr->ia_atime;
  	}

  	if (attr->ia_valid & ATTR_MTIME) {

  		attrs.ia_valid |= HOSTFS_ATTR_MTIME;
  		attrs.ia_mtime = attr->ia_mtime;
  	}

  	if (attr->ia_valid & ATTR_CTIME) {

  		attrs.ia_valid |= HOSTFS_ATTR_CTIME;
  		attrs.ia_ctime = attr->ia_ctime;
  	}

  	if (attr->ia_valid & ATTR_ATIME_SET) {

  		attrs.ia_valid |= HOSTFS_ATTR_ATIME_SET;
  	}

  	if (attr->ia_valid & ATTR_MTIME_SET) {

  		attrs.ia_valid |= HOSTFS_ATTR_MTIME_SET;
  	}

  	name = dentry_name(dentry);

  	if (name == NULL)

  		return -ENOMEM;

  	err = set_attr(name, &attrs, fd);

  	__putname(name);

  	if (err)

  		return err;

  	if ((attr->ia_valid & ATTR_SIZE) &&

  	    attr->ia_size != i_size_read(inode))

  		truncate_setsize(inode, attr->ia_size);

  
  	setattr_copy(inode, attr);
  	mark_inode_dirty(inode);
  	return 0;

  }

  static const struct inode_operations hostfs_iops = {

  	.permission	= hostfs_permission,
  	.setattr	= hostfs_setattr,

  };

  static const struct inode_operations hostfs_dir_iops = {

  	.create		= hostfs_create,
  	.lookup		= hostfs_lookup,
  	.link		= hostfs_link,
  	.unlink		= hostfs_unlink,
  	.symlink	= hostfs_symlink,
  	.mkdir		= hostfs_mkdir,
  	.rmdir		= hostfs_rmdir,
  	.mknod		= hostfs_mknod,

  	.rename2	= hostfs_rename2,

  	.permission	= hostfs_permission,
  	.setattr	= hostfs_setattr,

  };

  static void *hostfs_follow_link(struct dentry *dentry, struct nameidata *nd)
  {
  	char *link = __getname();
  	if (link) {
  		char *path = dentry_name(dentry);
  		int err = -ENOMEM;
  		if (path) {

  			err = hostfs_do_readlink(path, link, PATH_MAX);

  			if (err == PATH_MAX)
  				err = -E2BIG;

  			__putname(path);

  		}
  		if (err < 0) {
  			__putname(link);
  			link = ERR_PTR(err);
  		}
  	} else {
  		link = ERR_PTR(-ENOMEM);

  	}

  
  	nd_set_link(nd, link);
  	return NULL;
  }
  
  static void hostfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
  {
  	char *s = nd_get_link(nd);
  	if (!IS_ERR(s))
  		__putname(s);

  }

  static const struct inode_operations hostfs_link_iops = {
  	.readlink	= generic_readlink,
  	.follow_link	= hostfs_follow_link,
  	.put_link	= hostfs_put_link,

  };
  
  static int hostfs_fill_sb_common(struct super_block *sb, void *d, int silent)
  {
  	struct inode *root_inode;

  	char *host_root_path, *req_root = d;

  	int err;
  
  	sb->s_blocksize = 1024;
  	sb->s_blocksize_bits = 10;
  	sb->s_magic = HOSTFS_SUPER_MAGIC;
  	sb->s_op = &hostfs_sbops;

  	sb->s_d_op = &simple_dentry_operations;

  	sb->s_maxbytes = MAX_LFS_FILESIZE;

  	/* NULL is printed as <NULL> by sprintf: avoid that. */

  	if (req_root == NULL)
  		req_root = "";

  
  	err = -ENOMEM;

  	sb->s_fs_info = host_root_path =
  		kmalloc(strlen(root_ino) + strlen(req_root) + 2, GFP_KERNEL);

  	if (host_root_path == NULL)

  		goto out;

  	sprintf(host_root_path, "%s/%s", root_ino, req_root);

  	root_inode = new_inode(sb);
  	if (!root_inode)

  		goto out;

  	err = read_name(root_inode, host_root_path);
  	if (err)
  		goto out_put;

  	if (S_ISLNK(root_inode->i_mode)) {

  		char *name = follow_link(host_root_path);
  		if (IS_ERR(name))
  			err = PTR_ERR(name);
  		else
  			err = read_name(root_inode, name);
  		kfree(name);

  		if (err)
  			goto out_put;

  	}

  	err = -ENOMEM;

  	sb->s_root = d_make_root(root_inode);

  	if (sb->s_root == NULL)

  		goto out;

  	return 0;

  out_put:
  	iput(root_inode);

  out:
  	return err;

  }

  static struct dentry *hostfs_read_sb(struct file_system_type *type,

  			  int flags, const char *dev_name,

  			  void *data)

  {

  	return mount_nodev(type, flags, data, hostfs_fill_sb_common);

  }

  static void hostfs_kill_sb(struct super_block *s)
  {
  	kill_anon_super(s);
  	kfree(s->s_fs_info);
  }

  static struct file_system_type hostfs_type = {
  	.owner 		= THIS_MODULE,
  	.name 		= "hostfs",

  	.mount	 	= hostfs_read_sb,

  	.kill_sb	= hostfs_kill_sb,

  	.fs_flags 	= 0,
  };

  MODULE_ALIAS_FS("hostfs");

  
  static int __init init_hostfs(void)
  {

  	return register_filesystem(&hostfs_type);

  }
  
  static void __exit exit_hostfs(void)
  {
  	unregister_filesystem(&hostfs_type);
  }
  
  module_init(init_hostfs)
  module_exit(exit_hostfs)
  MODULE_LICENSE("GPL");