fs/exportfs/expfs.c - kernel/msm-4.9 - Gitiles

 /*
  * 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(const struct path *path, 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;
 	struct path path = {.mnt = mnt, .dentry = dir};

 	if (nop->get_name)
 		return nop->get_name(dir, name, child);
 	else
 		return get_name(&path, 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);
 	hlist_for_each_entry(dentry, &inode->i_dentry, d_u.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;
 }

 static bool dentry_connected(struct dentry *dentry)
 {
 	dget(dentry);
 	while (dentry->d_flags & DCACHE_DISCONNECTED) {
 		struct dentry *parent = dget_parent(dentry);

 		dput(dentry);
 		if (dentry == parent) {
 			dput(parent);
 			return false;
 		}
 		dentry = parent;
 	}
 	dput(dentry);
 	return true;
 }

 static void clear_disconnected(struct dentry *dentry)
 {
 	dget(dentry);
 	while (dentry->d_flags & DCACHE_DISCONNECTED) {
 		struct dentry *parent = dget_parent(dentry);

 		WARN_ON_ONCE(IS_ROOT(dentry));

 		spin_lock(&dentry->d_lock);
 		dentry->d_flags &= ~DCACHE_DISCONNECTED;
 		spin_unlock(&dentry->d_lock);

 		dput(dentry);
 		dentry = parent;
 	}
 	dput(dentry);
 }

 /*
  * Reconnect a directory dentry with its parent.
  *
  * This can return a dentry, or NULL, or an error.
  *
  * In the first case the returned dentry is the parent of the given
  * dentry, and may itself need to be reconnected to its parent.
  *
  * In the NULL case, a concurrent VFS operation has either renamed or
  * removed this directory.  The concurrent operation has reconnected our
  * dentry, so we no longer need to.
  */
 static struct dentry *reconnect_one(struct vfsmount *mnt,
 		struct dentry *dentry, char *nbuf)
 {
 	struct dentry *parent;
 	struct dentry *tmp;
 	int err;

 	parent = ERR_PTR(-EACCES);
 	inode_lock(dentry->d_inode);
 	if (mnt->mnt_sb->s_export_op->get_parent)
 		parent = mnt->mnt_sb->s_export_op->get_parent(dentry);
 	inode_unlock(dentry->d_inode);

 	if (IS_ERR(parent)) {
 		dprintk("%s: get_parent of %ld failed, err %d\n",
 			__func__, dentry->d_inode->i_ino, PTR_ERR(parent));
 		return parent;
 	}

 	dprintk("%s: find name of %lu in %lu\n", __func__,
 		dentry->d_inode->i_ino, parent->d_inode->i_ino);
 	err = exportfs_get_name(mnt, parent, nbuf, dentry);
 	if (err == -ENOENT)
 		goto out_reconnected;
 	if (err)
 		goto out_err;
 	dprintk("%s: found name: %s\n", __func__, nbuf);
 	tmp = lookup_one_len_unlocked(nbuf, parent, strlen(nbuf));
 	if (IS_ERR(tmp)) {
 		dprintk("%s: lookup failed: %d\n", __func__, PTR_ERR(tmp));
 		goto out_err;
 	}
 	if (tmp != dentry) {
 		/*
 		 * Somebody has renamed it since exportfs_get_name();
 		 * great, since it could've only been renamed if it
 		 * got looked up and thus connected, and it would
 		 * remain connected afterwards.  We are done.
 		 */
 		dput(tmp);
 		goto out_reconnected;
 	}
 	dput(tmp);
 	if (IS_ROOT(dentry)) {
 		err = -ESTALE;
 		goto out_err;
 	}
 	return parent;

 out_err:
 	dput(parent);
 	return ERR_PTR(err);
 out_reconnected:
 	dput(parent);
 	/*
 	 * Someone must have renamed our entry into another parent, in
 	 * which case it has been reconnected by the rename.
 	 *
 	 * Or someone removed it entirely, in which case filehandle
 	 * lookup will succeed but the directory is now IS_DEAD and
 	 * subsequent operations on it will fail.
 	 *
 	 * Alternatively, maybe there was no race at all, and the
 	 * filesystem is just corrupt and gave us a parent that doesn't
 	 * actually contain any entry pointing to this inode.  So,
 	 * double check that this worked and return -ESTALE if not:
 	 */
 	if (!dentry_connected(dentry))
 		return ERR_PTR(-ESTALE);
 	return NULL;
 }

 /*
  * Make sure target_dir is fully connected to the dentry tree.
  *
  * On successful return, DCACHE_DISCONNECTED will be cleared on
  * target_dir, and target_dir->d_parent->...->d_parent will reach the
  * root of the filesystem.
  *
  * Whenever DCACHE_DISCONNECTED is unset, target_dir is fully connected.
  * But the converse is not true: target_dir may have DCACHE_DISCONNECTED
  * set but already be connected.  In that case we'll verify the
  * connection to root and then clear the flag.
  *
  * Note that target_dir could be removed by a concurrent operation.  In
  * that case reconnect_path may still succeed with target_dir fully
  * connected, but further operations using the filehandle will fail when
  * necessary (due to S_DEAD being set on the directory).
  */
 static int
 reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
 {
 	struct dentry *dentry, *parent;

 	dentry = dget(target_dir);

 	while (dentry->d_flags & DCACHE_DISCONNECTED) {
 		BUG_ON(dentry == mnt->mnt_sb->s_root);

 		if (IS_ROOT(dentry))
 			parent = reconnect_one(mnt, dentry, nbuf);
 		else
 			parent = dget_parent(dentry);

 		if (!parent)
 			break;
 		dput(dentry);
 		if (IS_ERR(parent))
 			return PTR_ERR(parent);
 		dentry = parent;
 	}
 	dput(dentry);
 	clear_disconnected(target_dir);
 	return 0;
 }

 struct getdents_callback {
 	struct dir_context ctx;
 	char *name;		/* name that was found. It already points to a
 				   buffer NAME_MAX+1 is size */
 	u64 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(struct dir_context *ctx, const char *name, int len,
 			loff_t pos, u64 ino, unsigned int d_type)
 {
 	struct getdents_callback *buf =
 		container_of(ctx, struct getdents_callback, ctx);
 	int result = 0;

 	buf->sequence++;
 	if (buf->ino == ino && len <= NAME_MAX) {
 		memcpy(buf->name, name, len);
 		buf->name[len] = '\0';
 		buf->found = 1;
 		result = -1;
 	}
 	return result;
 }

 /**
  * get_name - default export_operations->get_name function
  * @path:   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(const struct path *path, char *name, struct dentry *child)
 {
 	const struct cred *cred = current_cred();
 	struct inode *dir = path->dentry->d_inode;
 	int error;
 	struct file *file;
 	struct kstat stat;
 	struct path child_path = {
 		.mnt = path->mnt,
 		.dentry = child,
 	};
 	struct getdents_callback buffer = {
 		.ctx.actor = filldir_one,
 		.name = name,
 	};

 	error = -ENOTDIR;
 	if (!dir || !S_ISDIR(dir->i_mode))
 		goto out;
 	error = -EINVAL;
 	if (!dir->i_fop)
 		goto out;
 	/*
 	 * inode->i_ino is unsigned long, kstat->ino is u64, so the
 	 * former would be insufficient on 32-bit hosts when the
 	 * filesystem supports 64-bit inode numbers.  So we need to
 	 * actually call ->getattr, not just read i_ino:
 	 */
 	error = vfs_getattr_nosec(&child_path, &stat);
 	if (error)
 		return error;
 	buffer.ino = stat.ino;
 	/*
 	 * Open the directory ...
 	 */
 	file = dentry_open(path, O_RDONLY, cred);
 	error = PTR_ERR(file);
 	if (IS_ERR(file))
 		goto out;

 	error = -EINVAL;
 	if (!file->f_op->iterate && !file->f_op->iterate_shared)
 		goto out_close;

 	buffer.sequence = 0;
 	while (1) {
 		int old_seq = buffer.sequence;

 		error = iterate_dir(file, &buffer.ctx);
 		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
  * @inode:   the object to encode
  * @fid:     where to store the file handle fragment
  * @max_len: maximum length to store there
  * @parent:  parent directory inode, if wanted
  *
  * 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 inode *inode, struct fid *fid,
 		int *max_len, struct inode *parent)
 {
 	int len = *max_len;
 	int type = FILEID_INO32_GEN;

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

 	len = 2;
 	fid->i32.ino = inode->i_ino;
 	fid->i32.gen = inode->i_generation;
 	if (parent) {
 		fid->i32.parent_ino = parent->i_ino;
 		fid->i32.parent_gen = parent->i_generation;
 		len = 4;
 		type = FILEID_INO32_GEN_PARENT;
 	}
 	*max_len = len;
 	return type;
 }

 int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
 			     int *max_len, struct inode *parent)
 {
 	const struct export_operations *nop = inode->i_sb->s_export_op;

 	if (nop && nop->encode_fh)
 		return nop->encode_fh(inode, fid->raw, max_len, parent);

 	return export_encode_fh(inode, fid, max_len, parent);
 }
 EXPORT_SYMBOL_GPL(exportfs_encode_inode_fh);

 int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
 		int connectable)
 {
 	int error;
 	struct dentry *p = NULL;
 	struct inode *inode = dentry->d_inode, *parent = NULL;

 	if (connectable && !S_ISDIR(inode->i_mode)) {
 		p = dget_parent(dentry);
 		/*
 		 * note that while p might've ceased to be our parent already,
 		 * it's still pinned by and still positive.
 		 */
 		parent = p->d_inode;
 	}

 	error = exportfs_encode_inode_fh(inode, fid, max_len, parent);
 	dput(p);

 	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 (PTR_ERR(result) == -ENOMEM)
 		return ERR_CAST(result);
 	if (IS_ERR_OR_NULL(result))
 		return ERR_PTR(-ESTALE);

 	if (d_is_dir(result)) {
 		/*
 		 * 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) {
 			inode_lock(target_dir->d_inode);
 			nresult = lookup_one_len(nbuf, target_dir,
 						 strlen(nbuf));
 			inode_unlock(target_dir->d_inode);
 			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);
 	if (err != -ENOMEM)
 		err = -ESTALE;
 	return ERR_PTR(err);
 }
 EXPORT_SYMBOL_GPL(exportfs_decode_fh);

 MODULE_LICENSE("GPL");
	/*
	* 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(const struct path path, 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;
	struct path path = {.mnt = mnt, .dentry = dir};

	if (nop->get_name)
	return nop->get_name(dir, name, child);
	else
	return get_name(&path, 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);
	hlist_for_each_entry(dentry, &inode->i_dentry, d_u.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;
	}

	static bool dentry_connected(struct dentry *dentry)
	{
	dget(dentry);
	while (dentry->d_flags & DCACHE_DISCONNECTED) {
	struct dentry *parent = dget_parent(dentry);

	dput(dentry);
	if (dentry == parent) {
	dput(parent);
	return false;
	}
	dentry = parent;
	}
	dput(dentry);
	return true;
	}

	static void clear_disconnected(struct dentry *dentry)
	{
	dget(dentry);
	while (dentry->d_flags & DCACHE_DISCONNECTED) {
	struct dentry *parent = dget_parent(dentry);

	WARN_ON_ONCE(IS_ROOT(dentry));

	spin_lock(&dentry->d_lock);
	dentry->d_flags &= ~DCACHE_DISCONNECTED;
	spin_unlock(&dentry->d_lock);

	dput(dentry);
	dentry = parent;
	}
	dput(dentry);
	}

	/*
	* Reconnect a directory dentry with its parent.
	*
	* This can return a dentry, or NULL, or an error.
	*
	* In the first case the returned dentry is the parent of the given
	* dentry, and may itself need to be reconnected to its parent.
	*
	* In the NULL case, a concurrent VFS operation has either renamed or
	* removed this directory. The concurrent operation has reconnected our
	* dentry, so we no longer need to.
	*/
	static struct dentry reconnect_one(struct vfsmount mnt,
	struct dentry dentry, char nbuf)
	{
	struct dentry *parent;
	struct dentry *tmp;
	int err;

	parent = ERR_PTR(-EACCES);
	inode_lock(dentry->d_inode);
	if (mnt->mnt_sb->s_export_op->get_parent)
	parent = mnt->mnt_sb->s_export_op->get_parent(dentry);
	inode_unlock(dentry->d_inode);

	if (IS_ERR(parent)) {
	dprintk("%s: get_parent of %ld failed, err %d\n",
	__func__, dentry->d_inode->i_ino, PTR_ERR(parent));
	return parent;
	}

	dprintk("%s: find name of %lu in %lu\n", __func__,
	dentry->d_inode->i_ino, parent->d_inode->i_ino);
	err = exportfs_get_name(mnt, parent, nbuf, dentry);
	if (err == -ENOENT)
	goto out_reconnected;
	if (err)
	goto out_err;
	dprintk("%s: found name: %s\n", __func__, nbuf);
	tmp = lookup_one_len_unlocked(nbuf, parent, strlen(nbuf));
	if (IS_ERR(tmp)) {
	dprintk("%s: lookup failed: %d\n", __func__, PTR_ERR(tmp));
	goto out_err;
	}
	if (tmp != dentry) {
	/*
	* Somebody has renamed it since exportfs_get_name();
	* great, since it could've only been renamed if it
	* got looked up and thus connected, and it would
	* remain connected afterwards. We are done.
	*/
	dput(tmp);
	goto out_reconnected;
	}
	dput(tmp);
	if (IS_ROOT(dentry)) {
	err = -ESTALE;
	goto out_err;
	}
	return parent;

	out_err:
	dput(parent);
	return ERR_PTR(err);
	out_reconnected:
	dput(parent);
	/*
	* Someone must have renamed our entry into another parent, in
	* which case it has been reconnected by the rename.
	*
	* Or someone removed it entirely, in which case filehandle
	* lookup will succeed but the directory is now IS_DEAD and
	* subsequent operations on it will fail.
	*
	* Alternatively, maybe there was no race at all, and the
	* filesystem is just corrupt and gave us a parent that doesn't
	* actually contain any entry pointing to this inode. So,
	* double check that this worked and return -ESTALE if not:
	*/
	if (!dentry_connected(dentry))
	return ERR_PTR(-ESTALE);
	return NULL;
	}

	/*
	* Make sure target_dir is fully connected to the dentry tree.
	*
	* On successful return, DCACHE_DISCONNECTED will be cleared on
	* target_dir, and target_dir->d_parent->...->d_parent will reach the
	* root of the filesystem.
	*
	* Whenever DCACHE_DISCONNECTED is unset, target_dir is fully connected.
	* But the converse is not true: target_dir may have DCACHE_DISCONNECTED
	* set but already be connected. In that case we'll verify the
	* connection to root and then clear the flag.
	*
	* Note that target_dir could be removed by a concurrent operation. In
	* that case reconnect_path may still succeed with target_dir fully
	* connected, but further operations using the filehandle will fail when
	* necessary (due to S_DEAD being set on the directory).
	*/
	static int
	reconnect_path(struct vfsmount mnt, struct dentry target_dir, char *nbuf)
	{
	struct dentry dentry, parent;

	dentry = dget(target_dir);

	while (dentry->d_flags & DCACHE_DISCONNECTED) {
	BUG_ON(dentry == mnt->mnt_sb->s_root);

	if (IS_ROOT(dentry))
	parent = reconnect_one(mnt, dentry, nbuf);
	else
	parent = dget_parent(dentry);

	if (!parent)
	break;
	dput(dentry);
	if (IS_ERR(parent))
	return PTR_ERR(parent);
	dentry = parent;
	}
	dput(dentry);
	clear_disconnected(target_dir);
	return 0;
	}

	struct getdents_callback {
	struct dir_context ctx;
	char name; / name that was found. It already points to a
	buffer NAME_MAX+1 is size */
	u64 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(struct dir_context ctx, const char name, int len,
	loff_t pos, u64 ino, unsigned int d_type)
	{
	struct getdents_callback *buf =
	container_of(ctx, struct getdents_callback, ctx);
	int result = 0;

	buf->sequence++;
	if (buf->ino == ino && len <= NAME_MAX) {
	memcpy(buf->name, name, len);
	buf->name[len] = '\0';
	buf->found = 1;
	result = -1;
	}
	return result;
	}

	/**
	* get_name - default export_operations->get_name function
	* @path: 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(const struct path path, char name, struct dentry *child)
	{
	const struct cred *cred = current_cred();
	struct inode *dir = path->dentry->d_inode;
	int error;
	struct file *file;
	struct kstat stat;
	struct path child_path = {
	.mnt = path->mnt,
	.dentry = child,
	};
	struct getdents_callback buffer = {
	.ctx.actor = filldir_one,
	.name = name,
	};

	error = -ENOTDIR;
	if (!dir \|\| !S_ISDIR(dir->i_mode))
	goto out;
	error = -EINVAL;
	if (!dir->i_fop)
	goto out;
	/*
	* inode->i_ino is unsigned long, kstat->ino is u64, so the
	* former would be insufficient on 32-bit hosts when the
	* filesystem supports 64-bit inode numbers. So we need to
	* actually call ->getattr, not just read i_ino:
	*/
	error = vfs_getattr_nosec(&child_path, &stat);
	if (error)
	return error;
	buffer.ino = stat.ino;
	/*
	* Open the directory ...
	*/
	file = dentry_open(path, O_RDONLY, cred);
	error = PTR_ERR(file);
	if (IS_ERR(file))
	goto out;

	error = -EINVAL;
	if (!file->f_op->iterate && !file->f_op->iterate_shared)
	goto out_close;

	buffer.sequence = 0;
	while (1) {
	int old_seq = buffer.sequence;

	error = iterate_dir(file, &buffer.ctx);
	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
	* @inode: the object to encode
	* @fid: where to store the file handle fragment
	* @max_len: maximum length to store there
	* @parent: parent directory inode, if wanted
	*
	* 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 inode inode, struct fid fid,
	int max_len, struct inode parent)
	{
	int len = *max_len;
	int type = FILEID_INO32_GEN;

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

	len = 2;
	fid->i32.ino = inode->i_ino;
	fid->i32.gen = inode->i_generation;
	if (parent) {
	fid->i32.parent_ino = parent->i_ino;
	fid->i32.parent_gen = parent->i_generation;
	len = 4;
	type = FILEID_INO32_GEN_PARENT;
	}
	*max_len = len;
	return type;
	}

	int exportfs_encode_inode_fh(struct inode inode, struct fid fid,
	int max_len, struct inode parent)
	{
	const struct export_operations *nop = inode->i_sb->s_export_op;

	if (nop && nop->encode_fh)
	return nop->encode_fh(inode, fid->raw, max_len, parent);

	return export_encode_fh(inode, fid, max_len, parent);
	}
	EXPORT_SYMBOL_GPL(exportfs_encode_inode_fh);

	int exportfs_encode_fh(struct dentry dentry, struct fid fid, int *max_len,
	int connectable)
	{
	int error;
	struct dentry *p = NULL;
	struct inode inode = dentry->d_inode, parent = NULL;

	if (connectable && !S_ISDIR(inode->i_mode)) {
	p = dget_parent(dentry);
	/*
	* note that while p might've ceased to be our parent already,
	* it's still pinned by and still positive.
	*/
	parent = p->d_inode;
	}

	error = exportfs_encode_inode_fh(inode, fid, max_len, parent);
	dput(p);

	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 (PTR_ERR(result) == -ENOMEM)
	return ERR_CAST(result);
	if (IS_ERR_OR_NULL(result))
	return ERR_PTR(-ESTALE);

	if (d_is_dir(result)) {
	/*
	* 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) {
	inode_lock(target_dir->d_inode);
	nresult = lookup_one_len(nbuf, target_dir,
	strlen(nbuf));
	inode_unlock(target_dir->d_inode);
	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);
	if (err != -ENOMEM)
	err = -ESTALE;
	return ERR_PTR(err);
	}
	EXPORT_SYMBOL_GPL(exportfs_decode_fh);

	MODULE_LICENSE("GPL");