/*
   * Copyright (C) Neil Brown 2002
   * Copyright (C) Christoph Hellwig 2007
   *
   * This file contains the code mapping from inodes to NFS file handles,
   * and for mapping back from file handles to dentries.
   *
   * For details on why we do all the strange and hairy things in here

   * take a look at Documentation/filesystems/nfs/Exporting.

   */

  #include <linux/exportfs.h>

  #include <linux/fs.h>
  #include <linux/file.h>
  #include <linux/module.h>

  #include <linux/mount.h>

  #include <linux/namei.h>

  #include <linux/sched.h>

  #define dprintk(fmt, args...) do{}while(0)

  static int get_name(struct vfsmount *mnt, struct dentry *dentry, char *name,

  		struct dentry *child);

  static int exportfs_get_name(struct vfsmount *mnt, struct dentry *dir,
  		char *name, struct dentry *child)

  {

  	const struct export_operations *nop = dir->d_sb->s_export_op;

  
  	if (nop->get_name)
  		return nop->get_name(dir, name, child);
  	else

  		return get_name(mnt, dir, name, child);

  }

  /*
   * Check if the dentry or any of it's aliases is acceptable.
   */

  static struct dentry *
  find_acceptable_alias(struct dentry *result,
  		int (*acceptable)(void *context, struct dentry *dentry),
  		void *context)
  {
  	struct dentry *dentry, *toput = NULL;

  	struct inode *inode;

  	if (acceptable(context, result))
  		return result;

  	inode = result->d_inode;
  	spin_lock(&inode->i_lock);
  	list_for_each_entry(dentry, &inode->i_dentry, d_alias) {

  		dget(dentry);

  		spin_unlock(&inode->i_lock);

  		if (toput)
  			dput(toput);
  		if (dentry != result && acceptable(context, dentry)) {
  			dput(result);
  			return dentry;
  		}

  		spin_lock(&inode->i_lock);

  		toput = dentry;
  	}

  	spin_unlock(&inode->i_lock);

  
  	if (toput)
  		dput(toput);
  	return NULL;
  }

  /*
   * Find root of a disconnected subtree and return a reference to it.
   */
  static struct dentry *
  find_disconnected_root(struct dentry *dentry)
  {
  	dget(dentry);

  	while (!IS_ROOT(dentry)) {
  		struct dentry *parent = dget_parent(dentry);
  
  		if (!(parent->d_flags & DCACHE_DISCONNECTED)) {
  			dput(parent);
  			break;
  		}

  		dput(dentry);
  		dentry = parent;

  	}

  	return dentry;
  }

  /*
   * Make sure target_dir is fully connected to the dentry tree.

   *

   * It may already be, as the flag isn't always updated when connection happens.

   */

  static int

  reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)

  {

  	int noprogress = 0;
  	int err = -ESTALE;

  
  	/*

  	 * It is possible that a confused file system might not let us complete

  	 * the path to the root.  For example, if get_parent returns a directory
  	 * in which we cannot find a name for the child.  While this implies a
  	 * very sick filesystem we don't want it to cause knfsd to spin.  Hence
  	 * the noprogress counter.  If we go through the loop 10 times (2 is
  	 * probably enough) without getting anywhere, we just give up
  	 */

  	while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {

  		struct dentry *pd = find_disconnected_root(target_dir);

  
  		if (!IS_ROOT(pd)) {
  			/* must have found a connected parent - great */
  			spin_lock(&pd->d_lock);
  			pd->d_flags &= ~DCACHE_DISCONNECTED;
  			spin_unlock(&pd->d_lock);
  			noprogress = 0;

  		} else if (pd == mnt->mnt_sb->s_root) {

  			printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible
  ");
  			spin_lock(&pd->d_lock);
  			pd->d_flags &= ~DCACHE_DISCONNECTED;
  			spin_unlock(&pd->d_lock);
  			noprogress = 0;
  		} else {

  			/*
  			 * We have hit the top of a disconnected path, try to
  			 * find parent and connect.
  			 *
  			 * Racing with some other process renaming a directory
  			 * isn't much of a problem here.  If someone renames
  			 * the directory, it will end up properly connected,
  			 * which is what we want
  			 *
  			 * Getting the parent can't be supported generically,
  			 * the locking is too icky.
  			 *
  			 * Instead we just return EACCES.  If server reboots
  			 * or inodes get flushed, you lose

  			 */

  			struct dentry *ppd = ERR_PTR(-EACCES);

  			struct dentry *npd;

  			mutex_lock(&pd->d_inode->i_mutex);

  			if (mnt->mnt_sb->s_export_op->get_parent)
  				ppd = mnt->mnt_sb->s_export_op->get_parent(pd);

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

  
  			if (IS_ERR(ppd)) {
  				err = PTR_ERR(ppd);

  				dprintk("%s: get_parent of %ld failed, err %d
  ",

  					__func__, pd->d_inode->i_ino, err);

  				dput(pd);
  				break;
  			}

  			dprintk("%s: find name of %lu in %lu
  ", __func__,

  				pd->d_inode->i_ino, ppd->d_inode->i_ino);

  			err = exportfs_get_name(mnt, ppd, nbuf, pd);

  			if (err) {
  				dput(ppd);
  				dput(pd);
  				if (err == -ENOENT)
  					/* some race between get_parent and
  					 * get_name?  just try again
  					 */
  					continue;
  				break;
  			}

  			dprintk("%s: found name: %s
  ", __func__, nbuf);

  			mutex_lock(&ppd->d_inode->i_mutex);

  			npd = lookup_one_len(nbuf, ppd, strlen(nbuf));

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

  			if (IS_ERR(npd)) {
  				err = PTR_ERR(npd);

  				dprintk("%s: lookup failed: %d
  ",

  					__func__, err);

  				dput(ppd);
  				dput(pd);
  				break;
  			}
  			/* we didn't really want npd, we really wanted
  			 * a side-effect of the lookup.
  			 * hopefully, npd == pd, though it isn't really
  			 * a problem if it isn't
  			 */
  			if (npd == pd)
  				noprogress = 0;
  			else

  				printk("%s: npd != pd
  ", __func__);

  			dput(npd);
  			dput(ppd);
  			if (IS_ROOT(pd)) {
  				/* something went wrong, we have to give up */
  				dput(pd);
  				break;
  			}
  		}
  		dput(pd);
  	}
  
  	if (target_dir->d_flags & DCACHE_DISCONNECTED) {
  		/* something went wrong - oh-well */
  		if (!err)
  			err = -ESTALE;

  		return err;

  	}

  
  	return 0;
  }

  struct getdents_callback {
  	char *name;		/* name that was found. It already points to a
  				   buffer NAME_MAX+1 is size */
  	unsigned long ino;	/* the inum we are looking for */
  	int found;		/* inode matched? */
  	int sequence;		/* sequence counter */
  };
  
  /*
   * A rather strange filldir function to capture
   * the name matching the specified inode number.
   */
  static int filldir_one(void * __buf, const char * name, int len,

  			loff_t pos, u64 ino, unsigned int d_type)

  {
  	struct getdents_callback *buf = __buf;
  	int result = 0;
  
  	buf->sequence++;
  	if (buf->ino == ino) {
  		memcpy(buf->name, name, len);
  		buf->name[len] = '\0';
  		buf->found = 1;
  		result = -1;
  	}
  	return result;
  }
  
  /**
   * get_name - default export_operations->get_name function
   * @dentry: the directory in which to find a name
   * @name:   a pointer to a %NAME_MAX+1 char buffer to store the name
   * @child:  the dentry for the child directory.
   *
   * calls readdir on the parent until it finds an entry with
   * the same inode number as the child, and returns that.
   */

  static int get_name(struct vfsmount *mnt, struct dentry *dentry,
  		char *name, struct dentry *child)

  {

  	const struct cred *cred = current_cred();

  	struct inode *dir = dentry->d_inode;
  	int error;
  	struct file *file;
  	struct getdents_callback buffer;
  
  	error = -ENOTDIR;
  	if (!dir || !S_ISDIR(dir->i_mode))
  		goto out;
  	error = -EINVAL;
  	if (!dir->i_fop)
  		goto out;
  	/*
  	 * Open the directory ...
  	 */

  	file = dentry_open(dget(dentry), mntget(mnt), O_RDONLY, cred);

  	error = PTR_ERR(file);
  	if (IS_ERR(file))
  		goto out;
  
  	error = -EINVAL;
  	if (!file->f_op->readdir)
  		goto out_close;
  
  	buffer.name = name;
  	buffer.ino = child->d_inode->i_ino;
  	buffer.found = 0;
  	buffer.sequence = 0;
  	while (1) {
  		int old_seq = buffer.sequence;
  
  		error = vfs_readdir(file, filldir_one, &buffer);

  		if (buffer.found) {
  			error = 0;
  			break;
  		}

  
  		if (error < 0)
  			break;

  		error = -ENOENT;
  		if (old_seq == buffer.sequence)
  			break;
  	}
  
  out_close:
  	fput(file);
  out:
  	return error;
  }

  /**
   * export_encode_fh - default export_operations->encode_fh function
   * @dentry:  the dentry to encode
   * @fh:      where to store the file handle fragment
   * @max_len: maximum length to store there
   * @connectable: whether to store parent information
   *
   * This default encode_fh function assumes that the 32 inode number
   * is suitable for locating an inode, and that the generation number
   * can be used to check that it is still valid.  It places them in the
   * filehandle fragment where export_decode_fh expects to find them.
   */

  static int export_encode_fh(struct dentry *dentry, struct fid *fid,
  		int *max_len, int connectable)

  {
  	struct inode * inode = dentry->d_inode;
  	int len = *max_len;

  	int type = FILEID_INO32_GEN;

  
  	if (connectable && (len < 4)) {
  		*max_len = 4;
  		return 255;
  	} else if (len < 2) {
  		*max_len = 2;

  		return 255;

  	}

  
  	len = 2;

  	fid->i32.ino = inode->i_ino;
  	fid->i32.gen = inode->i_generation;

  	if (connectable && !S_ISDIR(inode->i_mode)) {
  		struct inode *parent;
  
  		spin_lock(&dentry->d_lock);
  		parent = dentry->d_parent->d_inode;

  		fid->i32.parent_ino = parent->i_ino;
  		fid->i32.parent_gen = parent->i_generation;

  		spin_unlock(&dentry->d_lock);
  		len = 4;

  		type = FILEID_INO32_GEN_PARENT;

  	}
  	*max_len = len;
  	return type;
  }

  int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,

  		int connectable)
  {

  	const struct export_operations *nop = dentry->d_sb->s_export_op;

  	int error;

  	if (nop->encode_fh)

  		error = nop->encode_fh(dentry, fid->raw, max_len, connectable);

  	else

  		error = export_encode_fh(dentry, fid, max_len, connectable);

  
  	return error;

  }
  EXPORT_SYMBOL_GPL(exportfs_encode_fh);

  struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
  		int fh_len, int fileid_type,
  		int (*acceptable)(void *, struct dentry *), void *context)

  {

  	const struct export_operations *nop = mnt->mnt_sb->s_export_op;

  	struct dentry *result, *alias;

  	char nbuf[NAME_MAX+1];

  	int err;

  	/*

  	 * Try to get any dentry for the given file handle from the filesystem.
  	 */

  	if (!nop || !nop->fh_to_dentry)
  		return ERR_PTR(-ESTALE);

  	result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type);

  	if (!result)
  		result = ERR_PTR(-ESTALE);

  	if (IS_ERR(result))
  		return result;
  
  	if (S_ISDIR(result->d_inode->i_mode)) {
  		/*
  		 * This request is for a directory.
  		 *
  		 * On the positive side there is only one dentry for each
  		 * directory inode.  On the negative side this implies that we
  		 * to ensure our dentry is connected all the way up to the
  		 * filesystem root.
  		 */
  		if (result->d_flags & DCACHE_DISCONNECTED) {

  			err = reconnect_path(mnt, result, nbuf);

  			if (err)
  				goto err_result;
  		}
  
  		if (!acceptable(context, result)) {
  			err = -EACCES;
  			goto err_result;
  		}
  
  		return result;

  	} else {

  		/*
  		 * It's not a directory.  Life is a little more complicated.
  		 */
  		struct dentry *target_dir, *nresult;

  
  		/*
  		 * See if either the dentry we just got from the filesystem
  		 * or any alias for it is acceptable.  This is always true
  		 * if this filesystem is exported without the subtreecheck
  		 * option.  If the filesystem is exported with the subtree
  		 * check option there's a fair chance we need to look at
  		 * the parent directory in the file handle and make sure
  		 * it's connected to the filesystem root.
  		 */
  		alias = find_acceptable_alias(result, acceptable, context);
  		if (alias)
  			return alias;
  
  		/*
  		 * Try to extract a dentry for the parent directory from the
  		 * file handle.  If this fails we'll have to give up.
  		 */
  		err = -ESTALE;
  		if (!nop->fh_to_parent)
  			goto err_result;
  
  		target_dir = nop->fh_to_parent(mnt->mnt_sb, fid,
  				fh_len, fileid_type);

  		if (!target_dir)
  			goto err_result;

  		err = PTR_ERR(target_dir);
  		if (IS_ERR(target_dir))
  			goto err_result;
  
  		/*
  		 * And as usual we need to make sure the parent directory is
  		 * connected to the filesystem root.  The VFS really doesn't
  		 * like disconnected directories..
  		 */

  		err = reconnect_path(mnt, target_dir, nbuf);

  		if (err) {
  			dput(target_dir);
  			goto err_result;
  		}
  
  		/*
  		 * Now that we've got both a well-connected parent and a
  		 * dentry for the inode we're after, make sure that our
  		 * inode is actually connected to the parent.
  		 */

  		err = exportfs_get_name(mnt, target_dir, nbuf, result);

  		if (!err) {
  			mutex_lock(&target_dir->d_inode->i_mutex);
  			nresult = lookup_one_len(nbuf, target_dir,
  						 strlen(nbuf));
  			mutex_unlock(&target_dir->d_inode->i_mutex);
  			if (!IS_ERR(nresult)) {
  				if (nresult->d_inode) {
  					dput(result);
  					result = nresult;
  				} else
  					dput(nresult);
  			}
  		}
  
  		/*
  		 * At this point we are done with the parent, but it's pinned
  		 * by the child dentry anyway.
  		 */
  		dput(target_dir);
  
  		/*
  		 * And finally make sure the dentry is actually acceptable
  		 * to NFSD.
  		 */
  		alias = find_acceptable_alias(result, acceptable, context);
  		if (!alias) {
  			err = -EACCES;
  			goto err_result;
  		}
  
  		return alias;

  	}

   err_result:
  	dput(result);
  	return ERR_PTR(err);

  }
  EXPORT_SYMBOL_GPL(exportfs_decode_fh);

  MODULE_LICENSE("GPL");