/*

   * 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/module.h>

  #include <linux/mm.h>

  #include <linux/pagemap.h>

  #include <linux/statfs.h>

  #include <linux/seq_file.h>

  #include <linux/mount.h>

  #include "hostfs.h"

  #include "init.h"

  #include "kern.h"

  
  struct hostfs_inode_info {
  	char *host_filename;
  	int fd;

  	fmode_t mode;

  	struct inode vfs_inode;
  };
  
  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)->f_path.dentry->d_inode)

  static int hostfs_d_delete(struct dentry *dentry)

  {

  	return 1;

  }

  static const struct dentry_operations hostfs_dentry_ops = {

  	.d_delete		= hostfs_d_delete,
  };
  
  /* Changed in hostfs_args before the kernel starts running */

  static char *root_ino = "";

  static int append = 0;
  
  #define HOSTFS_SUPER_MAGIC 0x00c0ffee

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

  static const struct address_space_operations hostfs_link_aops;

  
  #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, int extra)
  {
  	struct dentry *parent;
  	char *root, *name;
  	int len;
  
  	len = 0;
  	parent = dentry;

  	while (parent->d_parent != parent) {

  		len += parent->d_name.len + 1;
  		parent = parent->d_parent;
  	}
  
  	root = HOSTFS_I(parent->d_inode)->host_filename;
  	len += strlen(root);
  	name = kmalloc(len + extra + 1, GFP_KERNEL);

  	if (name == NULL)

  		return NULL;

  
  	name[len] = '\0';
  	parent = dentry;

  	while (parent->d_parent != parent) {

  		len -= parent->d_name.len + 1;
  		name[len] = '/';
  		strncpy(&name[len + 1], parent->d_name.name,
  			parent->d_name.len);
  		parent = parent->d_parent;
  	}
  	strncpy(name, root, strlen(root));

  	return name;

  }
  
  static char *inode_name(struct inode *ino, int extra)
  {
  	struct dentry *dentry;
  
  	dentry = list_entry(ino->i_dentry.next, struct dentry, d_alias);

  	return dentry_name(dentry, extra);

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

  	/*
  	 * The non-int inode fields are copied into ints by stat_file and

  	 * then copied into the inode because passing the actual pointers
  	 * in and having them treated as int * breaks on big-endian machines
  	 */
  	int err;
  	int i_mode, i_nlink, i_blksize;
  	unsigned long long i_size;
  	unsigned long long i_ino;
  	unsigned long long i_blocks;
  
  	err = stat_file(name, &i_ino, &i_mode, &i_nlink, &ino->i_uid,
  			&ino->i_gid, &i_size, &ino->i_atime, &ino->i_mtime,

  			&ino->i_ctime, &i_blksize, &i_blocks, -1);

  	if (err)

  		return err;

  
  	ino->i_ino = i_ino;
  	ino->i_mode = i_mode;
  	ino->i_nlink = i_nlink;
  	ino->i_size = i_size;

  	ino->i_blocks = i_blocks;

  	return 0;

  }
  
  static char *follow_link(char *link)
  {
  	int len, n;
  	char *name, *resolved, *end;
  
  	len = 64;

  	while (1) {

  		n = -ENOMEM;
  		name = kmalloc(len, GFP_KERNEL);

  		if (name == NULL)

  			goto out;

  		n = hostfs_do_readlink(link, name, len);

  		if (n < len)

  			break;
  		len *= 2;
  		kfree(name);
  	}

  	if (n < 0)

  		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);
  	kfree(name);
  	kfree(link);

  	return resolved;

  
   out_free:
  	kfree(name);
   out:

  	return ERR_PTR(n);

  }

  static int hostfs_read_inode(struct inode *ino)

  {
  	char *name;
  	int err = 0;

  	/*
  	 * Unfortunately, we are called from iget() when we don't have a dentry

  	 * allocated yet.
  	 */

  	if (list_empty(&ino->i_dentry))

  		goto out;
  
  	err = -ENOMEM;
  	name = inode_name(ino, 0);

  	if (name == NULL)

  		goto out;

  	if (file_type(name, NULL, NULL) == OS_TYPE_SYMLINK) {

  		name = follow_link(name);

  		if (IS_ERR(name)) {

  			err = PTR_ERR(name);
  			goto out;
  		}
  	}
  
  	err = read_name(ino, name);
  	kfree(name);
   out:

  	return err;

  }

  static struct inode *hostfs_iget(struct super_block *sb)
  {
  	struct inode *inode;
  	long ret;
  
  	inode = iget_locked(sb, 0);
  	if (!inode)
  		return ERR_PTR(-ENOMEM);
  	if (inode->i_state & I_NEW) {
  		ret = hostfs_read_inode(inode);
  		if (ret < 0) {
  			iget_failed(inode);
  			return ERR_PTR(ret);
  		}
  		unlock_new_inode(inode);
  	}
  	return inode;
  }

  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(HOSTFS_I(dentry->d_sb->s_root->d_inode)->host_filename,

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

  	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 = ((struct hostfs_inode_info) { .host_filename	= NULL,
  					    .fd			= -1,
  					    .mode		= 0 });
  	inode_init_once(&hi->vfs_inode);

  	return &hi->vfs_inode;

  }
  
  static void hostfs_delete_inode(struct inode *inode)
  {

  	truncate_inode_pages(&inode->i_data, 0);

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

  		close_file(&HOSTFS_I(inode)->fd);
  		HOSTFS_I(inode)->fd = -1;
  	}
  	clear_inode(inode);
  }
  
  static void hostfs_destroy_inode(struct inode *inode)
  {

  	kfree(HOSTFS_I(inode)->host_filename);

  	/*
  	 * XXX: This should not happen, probably. The check is here for
  	 * additional safety.
  	 */
  	if (HOSTFS_I(inode)->fd != -1) {

  		close_file(&HOSTFS_I(inode)->fd);
  		printk(KERN_DEBUG "Closing host fd in .destroy_inode
  ");
  	}
  
  	kfree(HOSTFS_I(inode));
  }

  static int hostfs_show_options(struct seq_file *seq, struct vfsmount *vfs)
  {
  	struct inode *root = vfs->mnt_sb->s_root->d_inode;
  	const char *root_path = HOSTFS_I(root)->host_filename;
  	size_t offset = strlen(root_ino) + 1;
  
  	if (strlen(root_path) > offset)
  		seq_printf(seq, ",%s", root_path + offset);
  
  	return 0;
  }

  static const struct super_operations hostfs_sbops = {

  	.alloc_inode	= hostfs_alloc_inode,
  	.drop_inode	= generic_delete_inode,
  	.delete_inode   = hostfs_delete_inode,
  	.destroy_inode	= hostfs_destroy_inode,

  	.statfs		= hostfs_statfs,

  	.show_options	= hostfs_show_options,

  };
  
  int hostfs_readdir(struct file *file, void *ent, filldir_t filldir)
  {
  	void *dir;
  	char *name;
  	unsigned long long next, ino;
  	int error, len;

  	name = dentry_name(file->f_path.dentry, 0);

  	if (name == NULL)

  		return -ENOMEM;

  	dir = open_dir(name, &error);
  	kfree(name);

  	if (dir == NULL)

  		return -error;

  	next = file->f_pos;

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

  		error = (*filldir)(ent, name, len, file->f_pos,
  				   ino, DT_UNKNOWN);

  		if (error) break;

  		file->f_pos = next;
  	}
  	close_dir(dir);

  	return 0;

  }
  
  int hostfs_file_open(struct inode *ino, struct file *file)
  {
  	char *name;

  	fmode_t mode = 0;
  	int r = 0, w = 0, fd;

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

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

  		return 0;

  	/*
  	 * The file may already have been opened, but with the wrong access,

  	 * so this resets things and reopens the file with the new access.
  	 */

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

  		close_file(&HOSTFS_I(ino)->fd);
  		HOSTFS_I(ino)->fd = -1;
  	}
  
  	HOSTFS_I(ino)->mode |= mode;

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

  		r = 1;

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

  		w = 1;

  	if (w)

  		r = 1;

  	name = dentry_name(file->f_path.dentry, 0);

  	if (name == NULL)

  		return -ENOMEM;

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

  	if (fd < 0)

  		return fd;

  	FILE_HOSTFS_I(file)->fd = fd;

  	return 0;

  }
  
  int hostfs_fsync(struct file *file, struct dentry *dentry, int datasync)
  {

  	return fsync_file(HOSTFS_I(dentry->d_inode)->fd, datasync);

  }

  static const struct file_operations hostfs_file_fops = {

  	.llseek		= generic_file_llseek,

  	.read		= do_sync_read,

  	.splice_read	= generic_file_splice_read,

  	.aio_read	= generic_file_aio_read,
  	.aio_write	= generic_file_aio_write,

  	.write		= do_sync_write,

  	.mmap		= generic_file_mmap,
  	.open		= hostfs_file_open,
  	.release	= NULL,
  	.fsync		= hostfs_fsync,
  };

  static const struct file_operations hostfs_dir_fops = {

  	.llseek		= generic_file_llseek,
  	.readdir	= hostfs_readdir,
  	.read		= generic_read_dir,
  };
  
  int hostfs_writepage(struct page *page, struct writeback_control *wbc)
  {
  	struct address_space *mapping = page->mapping;
  	struct inode *inode = mapping->host;
  	char *buffer;
  	unsigned long long base;
  	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);
  	base = ((unsigned long long) page->index) << PAGE_CACHE_SHIFT;
  
  	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;
  }
  
  int hostfs_readpage(struct file *file, struct page *page)
  {
  	char *buffer;
  	long long start;
  	int err = 0;
  
  	start = (long long) page->index << PAGE_CACHE_SHIFT;
  	buffer = kmap(page);
  	err = read_file(FILE_HOSTFS_I(file)->fd, &start, buffer,
  			PAGE_CACHE_SIZE);

  	if (err < 0)
  		goto out;

  
  	memset(&buffer[err], 0, PAGE_CACHE_SIZE - err);
  
  	flush_dcache_page(page);
  	SetPageUptodate(page);
  	if (PageError(page)) ClearPageError(page);
  	err = 0;
   out:
  	kunmap(page);
  	unlock_page(page);

  	return err;

  }

  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;

  }

  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 init_inode(struct inode *inode, struct dentry *dentry)
  {
  	char *name;
  	int type, err = -ENOMEM;
  	int maj, min;
  	dev_t rdev = 0;

  	if (dentry) {

  		name = dentry_name(dentry, 0);

  		if (name == NULL)

  			goto out;
  		type = file_type(name, &maj, &min);

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

  		rdev = MKDEV(maj, min);
  		kfree(name);
  	}
  	else type = OS_TYPE_DIR;
  
  	err = 0;

  	if (type == OS_TYPE_SYMLINK)

  		inode->i_op = &page_symlink_inode_operations;

  	else if (type == OS_TYPE_DIR)

  		inode->i_op = &hostfs_dir_iops;
  	else inode->i_op = &hostfs_iops;

  	if (type == OS_TYPE_DIR) inode->i_fop = &hostfs_dir_fops;

  	else inode->i_fop = &hostfs_file_fops;

  	if (type == OS_TYPE_SYMLINK)

  		inode->i_mapping->a_ops = &hostfs_link_aops;
  	else inode->i_mapping->a_ops = &hostfs_aops;
  
  	switch (type) {
  	case OS_TYPE_CHARDEV:
  		init_special_inode(inode, S_IFCHR, rdev);
  		break;
  	case OS_TYPE_BLOCKDEV:
  		init_special_inode(inode, S_IFBLK, rdev);
  		break;
  	case OS_TYPE_FIFO:
  		init_special_inode(inode, S_IFIFO, 0);
  		break;
  	case OS_TYPE_SOCK:
  		init_special_inode(inode, S_IFSOCK, 0);
  		break;
  	}
   out:

  	return err;

  }
  
  int hostfs_create(struct inode *dir, struct dentry *dentry, int mode,

  		  struct nameidata *nd)

  {
  	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 = init_inode(inode, dentry);

  	if (error)

  		goto out_put;
  
  	error = -ENOMEM;
  	name = dentry_name(dentry, 0);

  	if (name == NULL)

  		goto out_put;
  
  	fd = file_create(name,
  			 mode & S_IRUSR, mode & S_IWUSR, mode & S_IXUSR,
  			 mode & S_IRGRP, mode & S_IWGRP, mode & S_IXGRP,
  			 mode & S_IROTH, mode & S_IWOTH, mode & S_IXOTH);

  	if (fd < 0)

  		error = fd;
  	else error = read_name(inode, name);
  
  	kfree(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;

  }
  
  struct dentry *hostfs_lookup(struct inode *ino, struct dentry *dentry,

  			     struct nameidata *nd)

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

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

  		goto out;

  	}

  
  	err = init_inode(inode, dentry);

  	if (err)

  		goto out_put;
  
  	err = -ENOMEM;
  	name = dentry_name(dentry, 0);

  	if (name == NULL)

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

  	if (err == -ENOENT) {

  		iput(inode);
  		inode = NULL;
  	}

  	else if (err)

  		goto out_put;
  
  	d_add(dentry, inode);
  	dentry->d_op = &hostfs_dentry_ops;

  	return NULL;

  
   out_put:
  	iput(inode);
   out:

  	return ERR_PTR(err);

  }
  
  static char *inode_dentry_name(struct inode *ino, struct dentry *dentry)
  {

  	char *file;

  	int len;
  
  	file = inode_name(ino, dentry->d_name.len + 1);

  	if (file == NULL)

  		return NULL;
  	strcat(file, "/");

  	len = strlen(file);

  	strncat(file, dentry->d_name.name, dentry->d_name.len);

  	file[len + dentry->d_name.len] = '\0';

  	return file;

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

  	char *from_name, *to_name;
  	int err;

  	if ((from_name = inode_dentry_name(ino, from)) == NULL)

  		return -ENOMEM;
  	to_name = dentry_name(to, 0);

  	if (to_name == NULL) {

  		kfree(from_name);

  		return -ENOMEM;

  	}

  	err = link_file(to_name, from_name);
  	kfree(from_name);
  	kfree(to_name);
  	return err;

  }
  
  int hostfs_unlink(struct inode *ino, struct dentry *dentry)
  {
  	char *file;
  	int err;

  	if ((file = inode_dentry_name(ino, dentry)) == NULL)

  		return -ENOMEM;

  	if (append)

  		return -EPERM;

  
  	err = unlink_file(file);
  	kfree(file);

  	return err;

  }
  
  int hostfs_symlink(struct inode *ino, struct dentry *dentry, const char *to)
  {
  	char *file;
  	int err;

  	if ((file = inode_dentry_name(ino, dentry)) == NULL)

  		return -ENOMEM;

  	err = make_symlink(file, to);
  	kfree(file);

  	return err;

  }
  
  int hostfs_mkdir(struct inode *ino, struct dentry *dentry, int mode)
  {
  	char *file;
  	int err;

  	if ((file = inode_dentry_name(ino, dentry)) == NULL)

  		return -ENOMEM;

  	err = do_mkdir(file, mode);
  	kfree(file);

  	return err;

  }
  
  int hostfs_rmdir(struct inode *ino, struct dentry *dentry)
  {
  	char *file;
  	int err;

  	if ((file = inode_dentry_name(ino, dentry)) == NULL)

  		return -ENOMEM;

  	err = do_rmdir(file);
  	kfree(file);

  	return err;

  }
  
  int hostfs_mknod(struct inode *dir, struct dentry *dentry, int 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 = init_inode(inode, dentry);

  	if (err)

  		goto out_put;
  
  	err = -ENOMEM;
  	name = dentry_name(dentry, 0);

  	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);
  	kfree(name);

  	if (err)

  		goto out_put;
  
  	d_instantiate(dentry, inode);

  	return 0;

  
   out_free:
  	kfree(name);
   out_put:
  	iput(inode);
   out:

  	return err;

  }
  
  int hostfs_rename(struct inode *from_ino, struct dentry *from,
  		  struct inode *to_ino, struct dentry *to)
  {
  	char *from_name, *to_name;
  	int err;

  	if ((from_name = inode_dentry_name(from_ino, from)) == NULL)

  		return -ENOMEM;

  	if ((to_name = inode_dentry_name(to_ino, to)) == NULL) {

  		kfree(from_name);

  		return -ENOMEM;

  	}
  	err = rename_file(from_name, to_name);
  	kfree(from_name);
  	kfree(to_name);

  	return err;

  }

  int hostfs_permission(struct inode *ino, int desired)

  {
  	char *name;
  	int r = 0, w = 0, x = 0, err;
  
  	if (desired & MAY_READ) r = 1;
  	if (desired & MAY_WRITE) w = 1;
  	if (desired & MAY_EXEC) x = 1;
  	name = inode_name(ino, 0);

  	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);
  	kfree(name);

  	if (!err)

  		err = generic_permission(ino, desired, NULL);
  	return err;
  }
  
  int hostfs_setattr(struct dentry *dentry, struct iattr *attr)
  {
  	struct hostfs_iattr attrs;
  	char *name;
  	int err;

  	int fd = HOSTFS_I(dentry->d_inode)->fd;

  	err = inode_change_ok(dentry->d_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 = attr->ia_uid;
  	}

  	if (attr->ia_valid & ATTR_GID) {

  		attrs.ia_valid |= HOSTFS_ATTR_GID;
  		attrs.ia_gid = 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, 0);

  	if (name == NULL)

  		return -ENOMEM;

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

  	kfree(name);

  	if (err)

  		return err;

  	return inode_setattr(dentry->d_inode, attr);

  }

  static const struct inode_operations hostfs_iops = {

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

  	.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,
  	.rename		= hostfs_rename,

  	.permission	= hostfs_permission,
  	.setattr	= hostfs_setattr,

  };
  
  int hostfs_link_readpage(struct file *file, struct page *page)
  {
  	char *buffer, *name;

  	int err;

  	buffer = kmap(page);
  	name = inode_name(page->mapping->host, 0);

  	if (name == NULL)

  		return -ENOMEM;

  	err = hostfs_do_readlink(name, buffer, PAGE_CACHE_SIZE);

  	kfree(name);

  	if (err == PAGE_CACHE_SIZE)

  		err = -E2BIG;

  	else if (err > 0) {

  		flush_dcache_page(page);
  		SetPageUptodate(page);
  		if (PageError(page)) ClearPageError(page);
  		err = 0;
  	}
  	kunmap(page);
  	unlock_page(page);

  	return err;

  }

  static const struct address_space_operations hostfs_link_aops = {

  	.readpage	= hostfs_link_readpage,
  };
  
  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_maxbytes = MAX_LFS_FILESIZE;

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

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

  
  	err = -ENOMEM;

  	host_root_path = kmalloc(strlen(root_ino) + 1
  				 + strlen(req_root) + 1, GFP_KERNEL);

  	if (host_root_path == NULL)

  		goto out;

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

  	root_inode = hostfs_iget(sb);
  	if (IS_ERR(root_inode)) {
  		err = PTR_ERR(root_inode);

  		goto out_free;

  	}

  
  	err = init_inode(root_inode, NULL);

  	if (err)

  		goto out_put;

  	HOSTFS_I(root_inode)->host_filename = host_root_path;

  	/*
  	 * Avoid that in the error path, iput(root_inode) frees again
  	 * host_root_path through hostfs_destroy_inode!
  	 */

  	host_root_path = NULL;

  
  	err = -ENOMEM;
  	sb->s_root = d_alloc_root(root_inode);

  	if (sb->s_root == NULL)

  		goto out_put;

  	err = hostfs_read_inode(root_inode);

  	if (err) {

  		/* No iput in this case because the dput does that for us */
  		dput(sb->s_root);
  		sb->s_root = NULL;

  		goto out;

  	}

  	return 0;

  out_put:
  	iput(root_inode);
  out_free:

  	kfree(host_root_path);

  out:
  	return err;

  }

  static int hostfs_read_sb(struct file_system_type *type,
  			  int flags, const char *dev_name,
  			  void *data, struct vfsmount *mnt)

  {

  	return get_sb_nodev(type, flags, data, hostfs_fill_sb_common, mnt);

  }
  
  static struct file_system_type hostfs_type = {
  	.owner 		= THIS_MODULE,
  	.name 		= "hostfs",
  	.get_sb 	= hostfs_read_sb,
  	.kill_sb	= kill_anon_super,
  	.fs_flags 	= 0,
  };
  
  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");