[PATCH take 3 15/29] UBIFS: add TNC implementation

[Artem Bityutskiy]

TNC - tree node cache - the central UBIFS entity. It is basically
in-RAM cache of the on-flash indexing B-tree. But TNC also indexes
the journal, so that they are not always equivalent.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@xxxxxxxxx>
Signed-off-by: Adrian Hunter <ext-adrian.hunter@xxxxxxxxx>
---
 fs/ubifs/tnc.c | 3330 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 3330 insertions(+), 0 deletions(-)

diff --git a/fs/ubifs/tnc.c b/fs/ubifs/tnc.c
new file mode 100644
index 0000000..5fd1480
--- /dev/null
+++ b/fs/ubifs/tnc.c
@@ -0,0 +1,3330 @@
+/*
+ * This file is part of UBIFS.
+ *
+ * Copyright (C) 2006-2008 Nokia Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * Authors: Adrian Hunter
+ *          Artem Bityutskiy (Битюцкий Артём)
+ */
+
+/*
+ * This file implements TNC (Tree Node Cache) which caches indexing nodes of
+ * the UBIFS B-tree.
+ *
+ * At the moment the locking rules of the TNC tree are quite simple and
+ * straightforward. We just have a mutex and lock it when we traverse the
+ * tree. If a znode is not in memory, we read it from flash while still having
+ * the mutex locked.
+ */
+
+#include <linux/crc32.h>
+#include "ubifs.h"
+
+/*
+ * Returned codes of 'matches_name()' and 'fallible_matches_name()' functions.
+ * @NAME_LESS: name corresponding to the first argument is less than second
+ * @NAME_MATCHES: names match
+ * @NAME_GREATER: name corresponding to the second argument is greater than
+ *                first
+ * @NOT_ON_MEDIA: node referred by zbranch does not exist on the media
+ *
+ * These constants were introduce to improve readability.
+ */
+enum {
+	NAME_LESS    = 0,
+	NAME_MATCHES = 1,
+	NAME_GREATER = 2,
+	NOT_ON_MEDIA = 3,
+};
+
+/**
+ * insert_old_idx - record an index node obsoleted since the last commit start.
+ * @c: UBIFS file-system description object
+ * @lnum: LEB number of obsoleted index node
+ * @offs: offset of obsoleted index node
+ *
+ * Returns %0 on success, and a negative error code on failure.
+ *
+ * For recovery, there must always be a complete intact version of the index on
+ * flash at all times. That is called the "old index". It is the index as at the
+ * time of the last successful commit. Many of the index nodes in the old index
+ * may be dirty, but they must not be erased until the next successful commit
+ * (at which point that index becomes the old index).
+ *
+ * That means that the garbage collection and the in-the-gaps method of
+ * committing must be able to determine if an index node is in the old index.
+ * Most of the old index nodes can be found by looking up the TNC using the
+ * 'lookup_znode()' function. However, some of the old index nodes may have
+ * been deleted from the current index or may have been changed so much that
+ * they cannot be easily found. In those cases, an entry is added to an RB-tree.
+ * That is what this function does. The RB-tree is ordered by LEB number and
+ * offset because they uniquely identify the old index node.
+ */
+static int insert_old_idx(struct ubifs_info *c, int lnum, int offs)
+{
+	struct ubifs_old_idx *old_idx, *o;
+	struct rb_node **p, *parent = NULL;
+
+	old_idx = kmalloc(sizeof(struct ubifs_old_idx), GFP_NOFS);
+	if (unlikely(!old_idx))
+		return -ENOMEM;
+	old_idx->lnum = lnum;
+	old_idx->offs = offs;
+
+	p = &c->old_idx.rb_node;
+	while (*p) {
+		parent = *p;
+		o = rb_entry(parent, struct ubifs_old_idx, rb);
+		if (lnum < o->lnum)
+			p = &(*p)->rb_left;
+		else if (lnum > o->lnum)
+			p = &(*p)->rb_right;
+		else if (offs < o->offs)
+			p = &(*p)->rb_left;
+		else if (offs > o->offs)
+			p = &(*p)->rb_right;
+		else {
+			ubifs_err("old idx added twice!");
+			kfree(old_idx);
+			return 0;
+		}
+	}
+	rb_link_node(&old_idx->rb, parent, p);
+	rb_insert_color(&old_idx->rb, &c->old_idx);
+	return 0;
+}
+
+/**
+ * insert_old_idx_znode - record a znode obsoleted since last commit start.
+ * @c: UBIFS file-system description object
+ * @znode: znode of obsoleted index node
+ *
+ * Returns %0 on success, and a negative error code on failure.
+ */
+int insert_old_idx_znode(struct ubifs_info *c, struct ubifs_znode *znode)
+{
+	if (znode->parent) {
+		struct ubifs_zbranch *zbr;
+
+		zbr = &znode->parent->zbranch[znode->iip];
+		if (zbr->len)
+			return insert_old_idx(c, zbr->lnum, zbr->offs);
+	} else
+		if (c->zroot.len)
+			return insert_old_idx(c, c->zroot.lnum,
+					      c->zroot.offs);
+	return 0;
+}
+
+/**
+ * ins_clr_old_idx_znode - record a znode obsoleted since last commit start.
+ * @c: UBIFS file-system description object
+ * @znode: znode of obsoleted index node
+ *
+ * Returns %0 on success, and a negative error code on failure.
+ */
+static int ins_clr_old_idx_znode(struct ubifs_info *c,
+				 struct ubifs_znode *znode)
+{
+	int err;
+
+	if (znode->parent) {
+		struct ubifs_zbranch *zbr;
+
+		zbr = &znode->parent->zbranch[znode->iip];
+		if (zbr->len) {
+			err = insert_old_idx(c, zbr->lnum, zbr->offs);
+			if (err)
+				return err;
+			zbr->lnum = 0;
+			zbr->offs = 0;
+			zbr->len = 0;
+		}
+	} else
+		if (c->zroot.len) {
+			err = insert_old_idx(c, c->zroot.lnum, c->zroot.offs);
+			if (err)
+				return err;
+			c->zroot.lnum = 0;
+			c->zroot.offs = 0;
+			c->zroot.len = 0;
+		}
+	return 0;
+}
+
+/**
+ * destroy_old_idx - destroy the old_idx RB-tree.
+ * @c: UBIFS file-system description object
+ *
+ * During start commit, the old_idx RB-tree is used to avoid overwriting index
+ * nodes that were in the index last commit but have since been deleted.  This
+ * is necessary for recovery i.e. the old index must be kept intact until the
+ * new index is successfully written.  The old-idx RB-tree is used for the
+ * in-the-gaps method of writing index nodes and is destroyed every commit.
+ */
+void destroy_old_idx(struct ubifs_info *c)
+{
+	struct rb_node *this = c->old_idx.rb_node;
+	struct ubifs_old_idx *old_idx;
+
+	while (this) {
+		if (this->rb_left) {
+			this = this->rb_left;
+			continue;
+		} else if (this->rb_right) {
+			this = this->rb_right;
+			continue;
+		}
+		old_idx = rb_entry(this, struct ubifs_old_idx, rb);
+		this = rb_parent(this);
+		if (this) {
+			if (this->rb_left == &old_idx->rb)
+				this->rb_left = NULL;
+			else
+				this->rb_right = NULL;
+		}
+		kfree(old_idx);
+	}
+	c->old_idx = RB_ROOT;
+}
+
+/**
+ * read_znode - read an indexing node from flash and fill znode.
+ * @c: UBIFS file-system description object
+ * @lnum: LEB of the indexing node to read
+ * @offs: node offset
+ * @len: node length
+ * @znode: znode to read to
+ *
+ * This function reads an indexing node from the flash media and fills znode
+ * with the read data. Returns zero in case of success and a negative error
+ * code in case of failure. The read indexing node is validated and if anything
+ * is wrong with it, this function prints complaint messages and returns
+ * %-EINVAL.
+ */
+static int read_znode(struct ubifs_info *c, int lnum, int offs, int len,
+		      struct ubifs_znode *znode)
+{
+	int i, err, type, cmp;
+	struct ubifs_idx_node *idx;
+
+	idx = kmalloc(c->max_idx_node_sz, GFP_NOFS);
+	if (!idx)
+		return -ENOMEM;
+
+	err = ubifs_read_node(c, idx, UBIFS_IDX_NODE, len, lnum, offs);
+	if (err < 0)
+		goto out;
+
+	znode->child_cnt = le16_to_cpu(idx->child_cnt);
+	znode->level = le16_to_cpu(idx->level);
+
+	dbg_tnc("LEB %d:%d, level %d, %d branch",
+		lnum, offs, znode->level, znode->child_cnt);
+
+	if (znode->child_cnt > c->fanout || znode->level > UBIFS_MAX_LEVELS) {
+		dbg_err("current fanout %d, branch count %d",
+			c->fanout, znode->child_cnt);
+		dbg_err("max levels %d, znode level %d",
+			UBIFS_MAX_LEVELS, znode->level);
+		goto out_dump;
+	}
+
+	for (i = 0; i < znode->child_cnt; i++) {
+		const struct ubifs_branch *br = ubifs_idx_branch(c, idx, i);
+		struct ubifs_zbranch *zbr = &znode->zbranch[i];
+
+		key_read(c, &br->key, &zbr->key);
+		zbr->lnum = le32_to_cpu(br->lnum);
+		zbr->offs = le32_to_cpu(br->offs);
+		zbr->len  = le32_to_cpu(br->len);
+		zbr->znode = NULL;
+
+		/* Validate branch */
+
+		if (zbr->lnum < c->main_first ||
+		    zbr->lnum >= c->leb_cnt || zbr->offs < 0 ||
+		    zbr->offs + zbr->len > c->leb_size || zbr->offs & 7) {
+			dbg_err("bad branch %d", i);
+			goto out_dump;
+		}
+
+		switch (key_type(c, &zbr->key)) {
+		case UBIFS_INO_KEY:
+		case UBIFS_DATA_KEY:
+		case UBIFS_DENT_KEY:
+		case UBIFS_XENT_KEY:
+			break;
+		default:
+			dbg_msg("bad key type at slot %d: %s", i,
+				DBGKEY(&zbr->key));
+			goto out_dump;
+		}
+
+		if (znode->level)
+			continue;
+
+		type = key_type(c, &zbr->key);
+		if (c->ranges[type].max_len == 0) {
+			if (zbr->len != c->ranges[type].len) {
+				dbg_err("bad target node (type %d) length (%d)",
+					type, zbr->len);
+				dbg_err("have to be %d", c->ranges[type].len);
+				goto out_dump;
+			}
+		} else if (zbr->len < c->ranges[type].min_len ||
+			   zbr->len > c->ranges[type].max_len) {
+			dbg_err("bad target node (type %d) length (%d)",
+				type, zbr->len);
+			dbg_err("have to be in range of %d-%d",
+				c->ranges[type].min_len,
+				c->ranges[type].max_len);
+			goto out_dump;
+		}
+	}
+
+	/*
+	 * Ensure that the next key is greater or equivalent to the
+	 * previous one.
+	 */
+	for (i = 0; i < znode->child_cnt - 1; i++) {
+		const union ubifs_key *key1, *key2;
+
+		key1 = &znode->zbranch[i].key;
+		key2 = &znode->zbranch[i + 1].key;
+
+		cmp = keys_cmp(c, key1, key2);
+		if (cmp > 0) {
+			dbg_err("bad key order (keys %d and %d)", i, i + 1);
+			goto out_dump;
+		} else if (cmp == 0 && !is_hash_key(c, key1)) {
+			/* These can only be keys with colliding hash */
+			dbg_err("keys %d and %d are not hashed but equivalent",
+				i, i + 1);
+			goto out_dump;
+		}
+	}
+
+	kfree(idx);
+	return 0;
+
+out:
+	kfree(idx);
+	return err;
+
+out_dump:
+	ubifs_err("bad indexing node at LEB %d:%d", lnum, offs);
+	dbg_dump_node(c, idx);
+	kfree(idx);
+	return -EINVAL;
+}
+
+/**
+ * load_znode - load znode to TNC cache.
+ * @c: UBIFS file-system description object
+ * @zbr: znode branch
+ * @parent: znode's parent
+ * @iip: index in parent
+ *
+ * This function loads znode pointed to by @zbr into the TNC cache and
+ * returns pointer to it in case of success and a negative error code in case
+ * of failure.
+ */
+static struct ubifs_znode *load_znode(struct ubifs_info *c,
+				      struct ubifs_zbranch *zbr,
+				      struct ubifs_znode *parent, int iip)
+{
+	int err;
+	struct ubifs_znode *znode;
+
+	ubifs_assert(!zbr->znode);
+	/*
+	 * A slab cache is not presently used for znodes because the znode size
+	 * depends on the fanout which is stored in the superblock.
+	 */
+	znode = kzalloc(c->max_znode_sz, GFP_NOFS);
+	if (!znode)
+		return ERR_PTR(-ENOMEM);
+
+	err = read_znode(c, zbr->lnum, zbr->offs, zbr->len, znode);
+	if (err)
+		goto out;
+
+	atomic_long_inc(&c->clean_zn_cnt);
+
+	/*
+	 * Increment the global clean znode counter as well. It is OK that
+	 * global and per-FS clean znode counters may be inconsistent for some
+	 * short time (because we might be preempted at this point), the global
+	 * one is only used in shrinker.
+	 */
+	atomic_long_inc(&ubifs_clean_zn_cnt);
+
+	zbr->znode = znode;
+	znode->parent = parent;
+	znode->time = get_seconds();
+	znode->iip = iip;
+
+	return znode;
+
+out:
+	kfree(znode);
+	return ERR_PTR(err);
+}
+
+/**
+ * copy_znode - copy a dirty znode.
+ * @c: UBIFS file-system description object
+ * @znode: znode to copy
+ *
+ * A dirty znode being committed may not be changed, so it is copied.
+ */
+static struct ubifs_znode *copy_znode(struct ubifs_info *c,
+				      struct ubifs_znode *znode)
+{
+	struct ubifs_znode *zn;
+
+	zn = kmalloc(c->max_znode_sz, GFP_NOFS);
+	if (unlikely(!zn))
+		return ERR_PTR(-ENOMEM);
+
+	memcpy(zn, znode, c->max_znode_sz);
+	zn->cnext = NULL;
+	__set_bit(DIRTY_ZNODE, &zn->flags);
+	__clear_bit(COW_ZNODE, &zn->flags);
+
+	ubifs_assert(!test_bit(OBSOLETE_ZNODE, &znode->flags));
+	__set_bit(OBSOLETE_ZNODE, &znode->flags);
+
+	if (znode->level != 0) {
+		int i;
+		const int n = zn->child_cnt;
+
+		/* The children now have new parent */
+		for (i = 0; i < n; i++) {
+			struct ubifs_zbranch *zbr = &zn->zbranch[i];
+
+			if (zbr->znode)
+				zbr->znode->parent = zn;
+		}
+	}
+
+	atomic_long_inc(&c->dirty_zn_cnt);
+	return zn;
+}
+
+/**
+ * add_idx_dirt - add dirt due to a dirty znode.
+ * @c: UBIFS file-system description object
+ * @lnum: LEB number of index node
+ * @dirt: size of index node
+ *
+ * This function updates lprops dirty space and the new size of the index.
+ */
+static int add_idx_dirt(struct ubifs_info *c, int lnum, int dirt)
+{
+	c->calc_idx_sz -= ALIGN(dirt, 8);
+	return ubifs_add_dirt(c, lnum, dirt);
+}
+
+/**
+ * dirty_cow_znode - ensure a znode is not being committed.
+ * @c: UBIFS file-system description object
+ * @zbr: branch of znode to check
+ *
+ * Returns dirtied znode on success or negative error code on failure.
+ */
+static struct ubifs_znode *dirty_cow_znode(struct ubifs_info *c,
+					   struct ubifs_zbranch *zbr)
+{
+	struct ubifs_znode *znode = zbr->znode;
+	struct ubifs_znode *zn;
+	int err;
+
+	if (!test_bit(COW_ZNODE, &znode->flags)) {
+		/* znode is not being committed */
+		if (!test_and_set_bit(DIRTY_ZNODE, &znode->flags)) {
+			atomic_long_inc(&c->dirty_zn_cnt);
+			atomic_long_dec(&c->clean_zn_cnt);
+			atomic_long_dec(&ubifs_clean_zn_cnt);
+			err = add_idx_dirt(c, zbr->lnum, zbr->len);
+			if (unlikely(err))
+				return ERR_PTR(err);
+		}
+		return znode;
+	}
+
+	zn = copy_znode(c, znode);
+	if (unlikely(IS_ERR(zn)))
+		return zn;
+
+	if (zbr->len) {
+		err = insert_old_idx(c, zbr->lnum, zbr->offs);
+		if (unlikely(err))
+			return ERR_PTR(err);
+		err = add_idx_dirt(c, zbr->lnum, zbr->len);
+	} else
+		err = 0;
+
+	zbr->znode = zn;
+	zbr->lnum = 0;
+	zbr->offs = 0;
+	zbr->len = 0;
+
+	if (unlikely(err))
+		return ERR_PTR(err);
+	return zn;
+}
+
+/**
+ * ubifs_validate_entry - validate directory or extended attribute entry node.
+ * @c: UBIFS file-system description object
+ * @dent: the node to validate
+ *
+ * This function validates directory or extended attribute entry node @dent.
+ * Returns zero if the node is all right and a %-EINVAL if not.
+ */
+int ubifs_validate_entry(struct ubifs_info *c,
+			 const struct ubifs_dent_node *dent)
+{
+	int key_type = key_type_flash(c, dent->key);
+	int nlen = le16_to_cpu(dent->nlen);
+
+	if (le32_to_cpu(dent->ch.len) != nlen + UBIFS_DENT_NODE_SZ + 1 ||
+	    dent->type >= UBIFS_ITYPES_CNT ||
+	    nlen > UBIFS_MAX_NLEN || dent->name[nlen] != 0 ||
+	    strnlen(dent->name, nlen) != nlen ||
+	    le64_to_cpu(dent->inum) > MAX_INUM) {
+		ubifs_err("bad %s node", key_type == UBIFS_DENT_KEY ?
+			  "directory entry" : "extended attribute entry");
+		return -EINVAL;
+	}
+
+	if (key_type != UBIFS_DENT_KEY && key_type != UBIFS_XENT_KEY) {
+		ubifs_err("bad key type %d", key_type);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/**
+ * lnc_add - add a leaf node to the leaf node cache.
+ * @c: UBIFS file-system description object
+ * @zbr: zbranch of leaf node
+ * @node: leaf node
+ *
+ * Leaf nodes are non-index nodes directory entry nodes or data nodes. The
+ * purpose of the leaf node cache is to save re-reading the same leaf node over
+ * and over again. Most things are cached by VFS, however the file system must
+ * cache directory entries for readdir and for resolving hash collisions. The
+ * present implementation of the leaf node cache is extremely simple, and
+ * allows for error returns that are not used but that may be needed if a more
+ * complex implementation is created.
+ *
+ * Note, this function does not add the @node object to LNC directly, but
+ * allocates a copy of the object and adds the copy to LNC. The reason for this
+ * is that @node has been allocated outside of the TNC subsystem and will be
+ * used with @c->tnc_mutex unlock upon return from the TNC subsystem. But LNC
+ * may be changed at any time, e.g. freed by the shrinker.
+ */
+static int lnc_add(struct ubifs_info *c, struct ubifs_zbranch *zbr,
+		   const void *node)
+{
+	int err;
+	void *lnc_node;
+	const struct ubifs_dent_node *dent = node;
+
+	ubifs_assert(!zbr->leaf);
+	ubifs_assert(zbr->len != 0);
+	ubifs_assert(is_hash_key(c, &zbr->key));
+
+	err = ubifs_validate_entry(c, dent);
+	if (err) {
+		dbg_dump_node(c, dent);
+		return err;
+	}
+
+	lnc_node = kmalloc(zbr->len, GFP_NOFS);
+	if (!lnc_node)
+		/* We don't have to have the cache, so no error */
+		return 0;
+
+	memcpy(lnc_node, node, zbr->len);
+	zbr->leaf = lnc_node;
+	return 0;
+}
+
+ /**
+ * lnc_add_directly - add a leaf node to the leaf-node-cache.
+ * @c: UBIFS file-system description object
+ * @zbr: zbranch of leaf node
+ * @node: leaf node
+ *
+ * This function is similar to 'lnc_add()', but it does not create a copy of
+ * @node but inserts @node to TNC directly.
+ */
+static int lnc_add_directly(struct ubifs_info *c, struct ubifs_zbranch *zbr,
+			    void *node)
+{
+	int err;
+
+	ubifs_assert(!zbr->leaf);
+	ubifs_assert(zbr->len != 0);
+
+	err = ubifs_validate_entry(c, node);
+	if (err) {
+		dbg_dump_node(c, node);
+		return err;
+	}
+
+	zbr->leaf = node;
+	return 0;
+}
+
+/**
+ * lnc_free - remove a leaf node from the leaf node cache.
+ * @zbr: zbranch of leaf node
+ * @node: leaf node
+ */
+static void lnc_free(struct ubifs_zbranch *zbr)
+{
+	if (!zbr->leaf)
+		return;
+	kfree(zbr->leaf);
+	zbr->leaf = NULL;
+}
+
+/**
+ * tnc_read_node - read a leaf node from the flash media.
+ * @c: UBIFS file-system description object
+ * @zbr: key and position of the node
+ * @node: node is returned here
+ *
+ * This function reads a node defined by @zbr from the flash media. Returns
+ * zero in case of success or a negative negative error code in case of
+ * failure.
+ */
+static int tnc_read_node(struct ubifs_info *c, struct ubifs_zbranch *zbr,
+			 void *node)
+{
+	union ubifs_key key1, *key = &zbr->key;
+	int err, type = key_type(c, key);
+	struct ubifs_wbuf *wbuf;
+
+	ubifs_assert(!zbr->leaf);
+
+	/*
+	 * 'zbr' has to point to on-flash node. The node may sit in a bud and
+	 * may even be in a write buffer, so we have to take care about this.
+	 */
+	wbuf = ubifs_get_wbuf(c, zbr->lnum);
+	if (wbuf)
+		err = ubifs_read_node_wbuf(wbuf, node, type, zbr->len,
+					   zbr->lnum, zbr->offs);
+	else
+		err = ubifs_read_node(c, node, type, zbr->len, zbr->lnum,
+				      zbr->offs);
+
+	if (err) {
+		dbg_tnc("key %s", DBGKEY(key));
+		return err;
+	}
+
+	/* Make sure the key of the read node is correct */
+	key_read(c, key, &key1);
+	if (memcmp(node + UBIFS_KEY_OFFSET, &key1, c->key_len)) {
+		ubifs_err("bad key in node at LEB %d:%d",
+			  zbr->lnum, zbr->offs);
+		dbg_tnc("looked for key %s found node's key %s",
+			DBGKEY(key), DBGKEY1(&key1));
+		dbg_dump_node(c, node);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/**
+ * tnc_read_node_nm - read a "hashed" leaf node.
+ * @c: UBIFS file-system description object
+ * @zbr: key and position of the node
+ * @node: node is returned here
+ *
+ * This function reads a "hashed" node defined by @zbr from the leaf node cache
+ * (in it is there) or from the hash media, in which case the node is also
+ * added to LNC. Returns zero in case of success or a negative negative error
+ * code in case of failure.
+ */
+static int tnc_read_node_nm(struct ubifs_info *c, struct ubifs_zbranch *zbr,
+			    void *node)
+{
+	int err;
+
+	ubifs_assert(is_hash_key(c, &zbr->key));
+
+	if (zbr->leaf) {
+		/* Read from the leaf node cache */
+		ubifs_assert(zbr->len != 0);
+		memcpy(node, zbr->leaf, zbr->len);
+		return 0;
+	}
+
+	err = tnc_read_node(c, zbr, node);
+	if (err)
+		return err;
+
+	/* Add the node to the leaf node cache */
+	err = lnc_add(c, zbr, node);
+	return err;
+}
+
+/**
+ * try_read_node - read a node if it is a node.
+ * @c: UBIFS file-system description object
+ * @buf: buffer to read to
+ * @type: node type
+ * @len: node length (not aligned)
+ * @lnum: LEB number of node to read
+ * @offs: offset of node to read
+ *
+ * This function tries to read a node of known type and length, checks it and
+ * stores it in @buf. This function returns %1 if a node is present and %0 if
+ * a node is not present. A negative error code is returned for I/O errors.
+ * This function performs that same function as ubifs_read_node except that
+ * it does not require that there is actually a node present and instead
+ * the return code indicates if a node was read.
+ */
+static int try_read_node(const struct ubifs_info *c, void *buf, int type,
+			 int len, int lnum, int offs)
+{
+	int err, node_len;
+	struct ubifs_ch *ch = buf;
+	uint32_t crc, node_crc;
+
+	dbg_io("LEB %d:%d, %s, length %d", lnum, offs, dbg_ntype(type), len);
+
+	err = ubi_read(c->ubi, lnum, buf, offs, len);
+	if (err) {
+		ubifs_err("cannot read node type %d from LEB %d:%d, error %d",
+			  type, lnum, offs, err);
+		return err;
+	}
+
+	if (le32_to_cpu(ch->magic) != UBIFS_NODE_MAGIC)
+		return 0;
+
+	if (ch->node_type != type)
+		return 0;
+
+	node_len = le32_to_cpu(ch->len);
+	if (node_len != len)
+		return 0;
+
+	crc = crc32(UBIFS_CRC32_INIT, buf + 8, node_len - 8);
+	node_crc = le32_to_cpu(ch->crc);
+	if (crc != node_crc)
+		return 0;
+
+	return 1;
+}
+
+/**
+ * fallible_read_node - try to read a leaf node.
+ * @c: UBIFS file-system description object
+ * @key:  key of node to read
+ * @zbr:  position of node
+ * @node: node returned
+ *
+ * This function tries to read a node and returns %1 if the node is read, %0
+ * if the node is not present, and a negative error code in the case of error.
+ */
+static int fallible_read_node(struct ubifs_info *c, const union ubifs_key *key,
+			      struct ubifs_zbranch *zbr, void *node)
+{
+	int ret;
+
+	dbg_tnc("LEB %d:%d, key %s", zbr->lnum, zbr->offs, DBGKEY(key));
+
+	ret = try_read_node(c, node, key_type(c, key), zbr->len, zbr->lnum,
+			    zbr->offs);
+	if (ret == 1) {
+		union ubifs_key node_key;
+		struct ubifs_dent_node *dent = node;
+
+		/* All nodes have key in the same place */
+		key_read(c, &dent->key, &node_key);
+		if (keys_cmp(c, key, &node_key) != 0)
+			ret = 0;
+	}
+	if (ret == 0)
+		dbg_mnt("dangling branch LEB %d:%d len %d, key %s",
+			zbr->lnum, zbr->offs, zbr->len, DBGKEY(key));
+	return ret;
+}
+
+/**
+ * matches_name - determine if a directory or extended attribute entry matches
+ *                a given name.
+ * @c: UBIFS file-system description object
+ * @zbr: zbranch of dent
+ * @nm: name to match
+ *
+ * This function checks if xentry/direntry referred by zbranch @zbr matches name
+ * @nm. Returns %NAME_MATCHES if it does, %NAME_LESS if the name referred by
+ * @zbr is less than @nm, and %NAME_GREATER if it is greater than @nm. In case
+ * of failure, a negative error code is returned.
+ */
+static int matches_name(struct ubifs_info *c, struct ubifs_zbranch *zbr,
+			const struct qstr *nm)
+{
+	struct ubifs_dent_node *dent;
+	int nlen, err;
+
+	/* If possible, match against the dent in the leaf node cache */
+	if (!zbr->leaf) {
+		dent = kmalloc(zbr->len, GFP_NOFS);
+		if (!dent)
+			return -ENOMEM;
+
+		err = tnc_read_node(c, zbr, dent);
+		if (err)
+			goto out_free;
+
+		/* Add the node to the leaf node cache */
+		err = lnc_add_directly(c, zbr, dent);
+		if (err)
+			goto out_free;
+	} else
+		dent = zbr->leaf;
+
+	nlen = le16_to_cpu(dent->nlen);
+	err = memcmp(dent->name, nm->name, min_t(int, nlen, nm->len));
+	if (err == 0) {
+		if (nlen == nm->len)
+			return NAME_MATCHES;
+		else if (nlen < nm->len)
+			return NAME_LESS;
+		else
+			return NAME_GREATER;
+	} else if (err < 0)
+		return NAME_LESS;
+	else
+		return NAME_GREATER;
+
+out_free:
+	kfree(dent);
+	return err;
+}
+
+/**
+ * get_znode - get a TNC znode that may not be loaded yet.
+ * @c: UBIFS file-system description object
+ * @znode: parent znode
+ * @n: znode branch slot number
+ *
+ * This function returns the znode or a negative error code.
+ */
+static struct ubifs_znode *get_znode(struct ubifs_info *c,
+				     struct ubifs_znode *znode, int n)
+{
+	struct ubifs_zbranch *zbr;
+
+	zbr = &znode->zbranch[n];
+	if (zbr->znode)
+		znode = zbr->znode;
+	else
+		znode = load_znode(c, zbr, znode, n);
+	return znode;
+}
+
+/**
+ * tnc_next - find next TNC entry.
+ * @c: UBIFS file-system description object
+ * @zn: znode is passed and returned here
+ * @n: znode branch slot number is passed and returned here
+ *
+ * This function returns %0 if the next TNC entry is found, %-ENOENT if there is
+ * no next entry, or a negative error code otherwise.
+ */
+static int tnc_next(struct ubifs_info *c, struct ubifs_znode **zn, int *n)
+{
+	struct ubifs_znode *znode = *zn;
+	int nn = *n;
+
+	nn += 1;
+	if (nn < znode->child_cnt) {
+		*n = nn;
+		return 0;
+	}
+	while (1) {
+		struct ubifs_znode *zp;
+
+		zp = znode->parent;
+		if (!zp)
+			return -ENOENT;
+		nn = znode->iip + 1;
+		znode = zp;
+		if (nn < znode->child_cnt) {
+			znode = get_znode(c, znode, nn);
+			if (IS_ERR(znode))
+				return PTR_ERR(znode);
+			while (znode->level != 0) {
+				znode = get_znode(c, znode, 0);
+				if (IS_ERR(znode))
+					return PTR_ERR(znode);
+			}
+			nn = 0;
+			break;
+		}
+	}
+	*zn = znode;
+	*n = nn;
+	return 0;
+}
+
+/**
+ * tnc_prev - find previous TNC entry.
+ * @c: UBIFS file-system description object
+ * @zn: znode is returned here
+ * @n: znode branch slot number is passed and returned here
+ *
+ * This function returns %0 if the previous TNC entry is found, %-ENOENT if
+ * there is no next entry, or a negative error code otherwise.
+ */
+static int tnc_prev(struct ubifs_info *c, struct ubifs_znode **zn, int *n)
+{
+	struct ubifs_znode *znode = *zn;
+	int nn = *n;
+
+	if (nn > 0) {
+		*n = nn - 1;
+		return 0;
+	}
+	while (1) {
+		struct ubifs_znode *zp;
+
+		zp = znode->parent;
+		if (!zp)
+			return -ENOENT;
+		nn = znode->iip - 1;
+		znode = zp;
+		if (nn >= 0) {
+			znode = get_znode(c, znode, nn);
+			if (IS_ERR(znode))
+				return PTR_ERR(znode);
+			while (znode->level != 0) {
+				nn = znode->child_cnt - 1;
+				znode = get_znode(c, znode, nn);
+				if (IS_ERR(znode))
+					return PTR_ERR(znode);
+			}
+			nn = znode->child_cnt - 1;
+			break;
+		}
+	}
+	*zn = znode;
+	*n = nn;
+	return 0;
+}
+
+/**
+ * resolve_collision - resolve a collision.
+ * @c: UBIFS file-system description object
+ * @key: key of a directory or extended attribute entry
+ * @zn: znode is returned here
+ * @n: zbranch number is passed and returned here
+ * @nm: name of the entry
+ *
+ * This function is called for "hashed" keys to make sure that the found key
+ * really corresponds to the looked up node (directory or extended attribute
+ * entry). It returns %1 and sets @zn and @n if the collision is resolved.
+ * %0 is returned if @nm is not found and @zn and @n are set to the previous
+ * entry, i.e. to the entry after which @nm could follow if it were in TNC.
+ * This means that @n may be set to %-1 if the leftmost key in @zn is the
+ * previous one. A negative error code is returned on failures.
+ */
+static int resolve_collision(struct ubifs_info *c, const union ubifs_key *key,
+			     struct ubifs_znode **zn, int *n,
+			     const struct qstr *nm)
+{
+	int err;
+
+	err = matches_name(c, &(*zn)->zbranch[*n], nm);
+	if (unlikely(err < 0))
+		return err;
+	if (err == NAME_MATCHES)
+		return 1;
+
+	if (err == NAME_GREATER) {
+		/* Look left */
+		while (1) {
+			err = tnc_prev(c, zn, n);
+			if (err == -ENOENT) {
+				ubifs_assert(*n == 0);
+				*n = -1;
+				return 0;
+			}
+			if (err < 0)
+				return err;
+			if (keys_cmp(c, &(*zn)->zbranch[*n].key, key)) {
+				/*
+				 * We have found the branch after which we would
+				 * like to insert, but inserting in this znode
+				 * may still be wrong. Consider the following 3
+				 * znodes, in the case where we are resolving a
+				 * collision with Key2.
+				 *
+				 *                  znode zp
+				 *            ----------------------
+				 * level 1     |  Key0  |  Key1  |
+				 *            -----------------------
+				 *                 |            |
+				 *       znode za  |            |  znode zb
+				 *          ------------      ------------
+				 * level 0  |  Key0  |        |  Key2  |
+				 *          ------------      ------------
+				 *
+				 * The lookup finds Key2 in znode zb. Lets say
+				 * there is no match and the name is greater so
+				 * we look left. When we find Key0, we end up
+				 * here. If we return now, we will insert into
+				 * znode za at slot n = 1.  But that is invalid
+				 * according to the parent's keys.  Key2 must
+				 * be inserted into znode zb.
+				 *
+				 * Note, this problem is not relevant for the
+				 * case when we go right, because
+				 * 'tnc_insert()' would correct the parent key.
+				 */
+				if (*n == (*zn)->child_cnt - 1) {
+					err = tnc_next(c, zn, n);
+					if (err) {
+						/* Should be impossible */
+						ubifs_assert(0);
+						if (err == -ENOENT)
+							err = -EINVAL;
+						return err;
+					}
+					ubifs_assert(*n == 0);
+					*n = -1;
+				}
+				return 0;
+			}
+			err = matches_name(c, &(*zn)->zbranch[*n], nm);
+			if (err < 0)
+				return err;
+			if (err == NAME_LESS)
+				return 0;
+			if (err == NAME_MATCHES)
+				return 1;
+			ubifs_assert(err == NAME_GREATER);
+		}
+	} else {
+		int nn = *n;
+		struct ubifs_znode *znode = *zn;
+
+		/* Look right */
+		while (1) {
+			err = tnc_next(c, &znode, &nn);
+			if (err == -ENOENT)
+				return 0;
+			if (err < 0)
+				return err;
+			if (keys_cmp(c, &znode->zbranch[nn].key, key))
+				return 0;
+			err = matches_name(c, &znode->zbranch[nn], nm);
+			if (err < 0)
+				return err;
+			if (err == NAME_GREATER)
+				return 0;
+			*zn = znode;
+			*n = nn;
+			if (err == NAME_MATCHES)
+				return 1;
+			ubifs_assert(err == NAME_LESS);
+		}
+	}
+}
+
+/**
+ * fallible_matches_name - determine if a dent matches a given name.
+ * @c: UBIFS file-system description object
+ * @zbr: zbranch of dent
+ * @nm: name to match
+ *
+ * This is a "fallible" version of 'matches_name()' function which does not
+ * panic if the direntry/xentry referred by @zbr does not exist on the media.
+ *
+ * This function checks if xentry/direntry referred by zbranch @zbr matches name
+ * @nm. Returns %NAME_MATCHES it does, %NAME_LESS if the name referred by @zbr
+ * is less than @nm, %NAME_GREATER if it is greater than @nm, and @NOT_ON_MEDIA
+ * if xentry/direntry referred by @zbr does not exist on the media. A negative
+ * error code is returned in case of failure.
+ */
+static int fallible_matches_name(struct ubifs_info *c,
+				 struct ubifs_zbranch *zbr,
+				 const struct qstr *nm)
+{
+	struct ubifs_dent_node *dent;
+	int nlen, err;
+
+	/* If possible, match against the dent in the leaf node cache */
+	if (!zbr->leaf) {
+		dent = kmalloc(zbr->len, GFP_NOFS);
+		if (!dent)
+			return -ENOMEM;
+
+		err = fallible_read_node(c, &zbr->key, zbr, dent);
+		if (err < 0)
+			goto out_free;
+		if (err == 0) {
+			/* The node was not present */
+			err = NOT_ON_MEDIA;
+			goto out_free;
+		}
+		ubifs_assert(err == 1);
+
+		err = lnc_add_directly(c, zbr, dent);
+		if (err)
+			goto out_free;
+	} else
+		dent = zbr->leaf;
+
+	nlen = le16_to_cpu(dent->nlen);
+	err = memcmp(dent->name, nm->name, min_t(int, nlen, nm->len));
+	if (err == 0) {
+		if (nlen == nm->len)
+			return NAME_MATCHES;
+		else if (nlen < nm->len)
+			return NAME_LESS;
+		else
+			return NAME_GREATER;
+	} else if (err < 0)
+		return NAME_LESS;
+	else
+		return NAME_GREATER;
+
+out_free:
+	kfree(dent);
+	return err;
+}
+
+/**
+ * fallible_resolve_collision - resolve a collision even if nodes are missing.
+ * @c: UBIFS file-system description object
+ * @key: key
+ * @zn: znode is returned here
+ * @n: branch number is passed and returned here
+ * @nm: name of directory entry
+ * @adding: indicates caller is adding a key to the TNC
+ *
+ * This is a "fallible" version of the 'resolve_collision()' function which
+ * does not panic if one of the nodes referred to by TNC does not exist on the
+ * media. This may happen when replaying the journal if a deleted node was
+ * Garbage-collected and the commit was not done. A branch that refers to a node
+ * that is not present is called a dangling branch. The following are the return
+ * codes for this function:
+ *  o if @nm was found, %1 is returned and @zn and @n are set to the found
+ *    branch;
+ *  o if we are @adding and @nm was not found, %0 is returned;
+ *  o if we are not @adding and @nm was not found, but a dangling branch was
+ *    found, then %1 is returned and @zn and @n are set to the dangling branch;
+ *  o a negative error code is returned in case of failure.
+ */
+static int fallible_resolve_collision(struct ubifs_info *c,
+				      const union ubifs_key *key,
+				      struct ubifs_znode **zn, int *n,
+				      const struct qstr *nm, int adding)
+{
+	struct ubifs_znode *o_znode = NULL, *znode = *zn;
+	int uninitialized_var(o_n), err, cmp, unsure = 0, nn = *n;
+
+	cmp = fallible_matches_name(c, &znode->zbranch[nn], nm);
+	if (unlikely(cmp < 0))
+		return cmp;
+	if (cmp == NAME_MATCHES)
+		return 1;
+	if (cmp == NOT_ON_MEDIA) {
+		o_znode = znode;
+		o_n = nn;
+		/*
+		 * We are unlucky and hit a dangling branch straight away.
+		 * Now we do not really know where to go to find the needed
+		 * branch - to the left or to the right. Well, let's try left.
+		 */
+		unsure = 1;
+	} else if (!adding)
+		unsure = 1; /* Remove a dangling branch wherever it is */
+
+	if (cmp == NAME_GREATER || unsure) {
+		/* Look left */
+		while (1) {
+			err = tnc_prev(c, zn, n);
+			if (err == -ENOENT) {
+				ubifs_assert(*n == 0);
+				*n = -1;
+				break;
+			}
+			if (err < 0)
+				return err;
+			if (keys_cmp(c, &(*zn)->zbranch[*n].key, key)) {
+				/* See comments in 'resolve_collision()' */
+				if (*n == (*zn)->child_cnt - 1) {
+					err = tnc_next(c, zn, n);
+					if (err) {
+						/* Should be impossible */
+						ubifs_assert(0);
+						if (err == -ENOENT)
+							err = -EINVAL;
+						return err;
+					}
+					ubifs_assert(*n == 0);
+					*n = -1;
+				}
+				break;
+			}
+			err = fallible_matches_name(c, &(*zn)->zbranch[*n], nm);
+			if (err < 0)
+				return err;
+			if (err == NAME_MATCHES)
+				return 1;
+			if (err == NOT_ON_MEDIA) {
+				o_znode = *zn;
+				o_n = *n;
+				continue;
+			}
+			if (!adding)
+				continue;
+			if (err == NAME_LESS)
+				break;
+			else
+				unsure = 0;
+		}
+	}
+
+	if (cmp == NAME_LESS || unsure) {
+		/* Look right */
+		*zn = znode;
+		*n = nn;
+		while (1) {
+			err = tnc_next(c, &znode, &nn);
+			if (err == -ENOENT)
+				break;
+			if (err < 0)
+				return err;
+			if (keys_cmp(c, &znode->zbranch[nn].key, key))
+				break;
+			err = fallible_matches_name(c, &znode->zbranch[nn], nm);
+			if (err < 0)
+				return err;
+			if (err == NAME_GREATER)
+				break;
+			*zn = znode;
+			*n = nn;
+			if (err == NAME_MATCHES)
+				return 1;
+			if (err == NOT_ON_MEDIA) {
+				o_znode = znode;
+				o_n = nn;
+			}
+		}
+	}
+
+	/* Never match a dangling branch when adding */
+	if (adding || !o_znode)
+		return 0;
+
+	dbg_mnt("dangling match LEB %d:%d len %d %s",
+		o_znode->zbranch[o_n].lnum, o_znode->zbranch[o_n].offs,
+		o_znode->zbranch[o_n].len, DBGKEY(key));
+	*zn = o_znode;
+	*n = o_n;
+	return 1;
+}
+
+/**
+ * matches_position - determine if a zbranch matches a given position.
+ * @zbr: zbranch of dent
+ * @lnum: LEB number of dent to match
+ * @offs: offset of dent to match
+ *
+ * This function returns %1 if @lnum:@offs matches, and %0 otherwise.
+ */
+static int matches_position(struct ubifs_zbranch *zbr, int lnum, int offs)
+{
+	if (zbr->lnum == lnum && zbr->offs == offs)
+		return 1;
+	else
+		return 0;
+}
+
+/**
+ * resolve_collision_directly - resolve a collision directly.
+ * @c: UBIFS file-system description object
+ * @key: key of directory entry
+ * @zn: znode is passed and returned here
+ * @n: zbranch number is passed and returned here
+ * @lnum: LEB number of dent node to match
+ * @offs: offset of dent node to match
+ *
+ * This function is used for "hashed" keys to make sure the found directory or
+ * extended attribute entry node is what was looked for. It is used when the
+ * flash address of the right node is known (@lnum:@offs) which makes it much
+ * easier to resolve collisions (no need to read entries and match full
+ * names). This function returns %1 and sets @zn and @n if the collision is
+ * resolved, %0 if @lnum:@offs is not found and @zn and @n are set to the
+ * previous directory entry. Otherwise a negative error code is returned.
+ */
+static int resolve_collision_directly(struct ubifs_info *c,
+				      const union ubifs_key *key,
+				      struct ubifs_znode **zn, int *n,
+				      int lnum, int offs)
+{
+	struct ubifs_znode *znode;
+	int nn, err;
+
+	znode = *zn;
+	nn = *n;
+	if (matches_position(&znode->zbranch[nn], lnum, offs))
+		return 1;
+
+	/* Look left */
+	while (1) {
+		err = tnc_prev(c, &znode, &nn);
+		if (err == -ENOENT)
+			break;
+		if (err < 0)
+			return err;
+		if (keys_cmp(c, &znode->zbranch[nn].key, key))
+			break;
+		if (matches_position(&znode->zbranch[nn], lnum, offs)) {
+			*zn = znode;
+			*n = nn;
+			return 1;
+		}
+	}
+
+	/* Look right */
+	znode = *zn;
+	nn = *n;
+	while (1) {
+		err = tnc_next(c, &znode, &nn);
+		if (err == -ENOENT)
+			return 0;
+		if (err < 0)
+			return err;
+		if (keys_cmp(c, &znode->zbranch[nn].key, key))
+			return 0;
+		*zn = znode;
+		*n = nn;
+		if (matches_position(&znode->zbranch[nn], lnum, offs))
+			return 1;
+	}
+}
+
+/**
+ * dirty_cow_bottom_up - dirty a znode and its ancestors.
+ * @c: UBIFS file-system description object
+ * @znode: znode to dirty
+ *
+ * If we do not have a unique key that resides in a znode, then we cannot
+ * dirty that znode from the top down (i.e. by using lookup_level0_dirty)
+ * This function records the path back to the last dirty ancestor, and then
+ * dirties the znodes on that path.
+ */
+static struct ubifs_znode *dirty_cow_bottom_up(struct ubifs_info *c,
+					       struct ubifs_znode *znode)
+{
+	struct ubifs_znode *zp;
+	int *path = c->bottom_up_buf, p = 0;
+
+	ubifs_assert(c->zroot.znode);
+	ubifs_assert(znode);
+	if (c->zroot.znode->level > BOTTOM_UP_HEIGHT) {
+		kfree(c->bottom_up_buf);
+		c->bottom_up_buf = kmalloc(c->zroot.znode->level * sizeof(int),
+					   GFP_NOFS);
+		if (!c->bottom_up_buf)
+			return ERR_PTR(-ENOMEM);
+		path = c->bottom_up_buf;
+	}
+	if (c->zroot.znode->level) {
+		/* Go up until parent is dirty */
+		while (1) {
+			int n;
+
+			zp = znode->parent;
+			if (!zp)
+				break;
+			n = znode->iip;
+			ubifs_assert(p < c->zroot.znode->level);
+			path[p++] = n;
+			if (!zp->cnext && ubifs_zn_dirty(znode))
+				break;
+			znode = zp;
+		}
+	}
+
+	/* Come back down, dirtying as we go */
+	while (1) {
+		struct ubifs_zbranch *zbr;
+
+		zp = znode->parent;
+		if (zp) {
+			ubifs_assert(path[p - 1] >= 0);
+			ubifs_assert(path[p - 1] < zp->child_cnt);
+			zbr = &zp->zbranch[path[--p]];
+			znode = dirty_cow_znode(c, zbr);
+		} else {
+			ubifs_assert(znode == c->zroot.znode);
+			znode = dirty_cow_znode(c, &c->zroot);
+		}
+		if (unlikely(IS_ERR(znode)) || !p)
+			break;
+		ubifs_assert(path[p - 1] >= 0);
+		ubifs_assert(path[p - 1] < znode->child_cnt);
+		znode = znode->zbranch[path[p - 1]].znode;
+	}
+
+	return znode;
+}
+
+/**
+ * lookup_level0 - search for zero-level znode.
+ * @c: UBIFS file-system description object
+ * @key:  key to lookup
+ * @zn: znode is returned here
+ * @n: znode branch slot number is returned here
+ *
+ * This function looks up the TNC tree and search for zero-level znode which
+ * refers key @key. The found zero-level znode is returned in @zn. There are 3
+ * cases:
+ *   o exact match, i.e. the found zero-level znode contains key @key, then %1
+ *     is returned and slot number of the matched branch is stored in @n;
+ *   o not exact match, which means that zero-level znode does not contain
+ *     @key, then %0 is returned and slot number of the closed branch is stored
+ *     in  @n;
+ *   o @key is so small that it is even less than the lowest key of the
+ *     leftmost zero-level node, then %0 is returned and %0 is stored in @n.
+ *
+ * Note, when the TNC tree is traversed, some znodes may be absent, then this
+ * function reads corresponding indexing nodes and inserts them to TNC. In
+ * case of failure, a negative error code is returned.
+ */
+static int lookup_level0(struct ubifs_info *c, const union ubifs_key *key,
+			 struct ubifs_znode **zn, int *n)
+{
+	int err, exact;
+	struct ubifs_znode *znode;
+	unsigned long time = get_seconds();
+
+	dbg_tnc("search key %s", DBGKEY(key));
+
+	znode = c->zroot.znode;
+	if (unlikely(!znode)) {
+		znode = load_znode(c, &c->zroot, NULL, 0);
+		if (IS_ERR(znode))
+			return PTR_ERR(znode);
+	}
+
+	znode->time = time;
+
+	while (1) {
+		struct ubifs_zbranch *zbr;
+
+		exact = ubifs_search_zbranch(c, znode, key, n);
+
+		if (znode->level == 0)
+			break;
+
+		if (*n < 0)
+			*n = 0;
+		zbr = &znode->zbranch[*n];
+
+		if (zbr->znode) {
+			znode->time = time;
+			znode = zbr->znode;
+			continue;
+		}
+
+		/* znode is not in TNC cache, load it from the media */
+		znode = load_znode(c, zbr, znode, *n);
+		if (IS_ERR(znode))
+			return PTR_ERR(znode);
+	}
+
+	*zn = znode;
+	if (exact || !is_hash_key(c, key) || *n != -1) {
+		dbg_tnc("found %d, lvl %d, n %d", exact, znode->level, *n);
+		return exact;
+	}
+
+	/*
+	 * Here is a tricky place. We have not found the key and this is a
+	 * "hashed" key, which may collide. The rest of the code deals with
+	 * situations like this:
+	 *
+	 *                  | 3 | 5 |
+	 *                  /       \
+	 *          | 3 | 5 |      | 6 | 7 | (x)
+	 *
+	 * Or more a complex example:
+	 *
+	 *                | 1 | 5 |
+	 *                /       \
+	 *       | 1 | 3 |         | 5 | 8 |
+	 *              \           /
+	 *          | 5 | 5 |   | 6 | 7 | (x)
+	 *
+	 * In the examples, if we are looking for key "5", we may reach nodes
+	 * marked with "(x)". In this case what we have do is to look at the
+	 * left and see if there is "5" key there. If there is, we have to
+	 * return it.
+	 *
+	 * Note, this whole situation is possible because we allow to have
+	 * elements which are equivalent to the next key in the parent in the
+	 * children of current znode. For example, this happens if we split a
+	 * znode like this: | 3 | 5 | 5 | 6 | 7 |, which results in something
+	 * like this:
+	 *                      | 3 | 5 |
+	 *                       /     \
+	 *                | 3 | 5 |   | 5 | 6 | 7 |
+	 *                              ^
+	 * And this becomes what is at the first "picture" after key "5" marked
+	 * with "^" is removed. What could be done is we could prohibit
+	 * splitting in the middle of the colliding sequence. Also, when
+	 * removing the leftmost key, we would have to correct the key of the
+	 * parent node, which would introduce additional complications. Namely,
+	 * if we changed the the leftmost key of the parent znode, the garbage
+	 * collector would be unable to find it (GC is doing this when GC'ing
+	 * indexing LEBs). Although we already have an additional RB-tree where
+	 * we save such changed znodes (see 'ins_clr_old_idx_znode()') until
+	 * after the commit. But anyway, this does not look easy to implement
+	 * so we did not try this.
+	 */
+	err = tnc_prev(c, &znode, n);
+	if (err == -ENOENT) {
+		dbg_tnc("found 0, lvl %d, n -1", znode->level);
+		*n = -1;
+		return 0;
+	}
+	if (unlikely(err < 0))
+		return err;
+	if (keys_cmp(c, key, &znode->zbranch[*n].key)) {
+		dbg_tnc("found 0, lvl %d, n -1", znode->level);
+		*n = -1;
+		return 0;
+	}
+
+	dbg_tnc("found 1, lvl %d, n %d", znode->level, *n);
+	*zn = znode;
+	return 1;
+}
+
+/**
+ * lookup_level0_dirty - search for zero-level znode dirtying.
+ * @c: UBIFS file-system description object
+ * @key:  key to lookup
+ * @zn: znode is returned here
+ * @n: znode branch slot number is returned here
+ *
+ * This function looks up the TNC tree and search for zero-level znode which
+ * refers key @key. The found zero-level znode is returned in @zn. There are 3
+ * cases:
+ *   o exact match, i.e. the found zero-level znode contains key @key, then %1
+ *     is returned and slot number of the matched branch is stored in @n;
+ *   o not exact match, which means that zero-level znode does not contain @key
+ *     then %0 is returned and slot number of the closed branch is stored in
+ *     @n;
+ *   o @key is so small that it is even less than the lowest key of the
+ *     leftmost zero-level node, then %0 is returned and %-1 is stored in @n.
+ *
+ * Additionally all znodes in the path from the root to the located zero-level
+ * znode are marked as dirty.
+ *
+ * Note, when the TNC tree is traversed, some znodes may be absent, then this
+ * function reads corresponding indexing nodes and inserts them to TNC. In
+ * case of failure, a negative error code is returned.
+ */
+static int lookup_level0_dirty(struct ubifs_info *c, const union ubifs_key *key,
+			       struct ubifs_znode **zn, int *n)
+{
+	int err, exact;
+	struct ubifs_znode *znode;
+	unsigned long time = get_seconds();
+
+	dbg_tnc("search and dirty key %s", DBGKEY(key));
+
+	znode = c->zroot.znode;
+	if (unlikely(!znode)) {
+		znode = load_znode(c, &c->zroot, NULL, 0);
+		if (IS_ERR(znode))
+			return PTR_ERR(znode);
+	}
+
+	znode = dirty_cow_znode(c, &c->zroot);
+	if (IS_ERR(znode))
+		return PTR_ERR(znode);
+
+	znode->time = time;
+
+	while (1) {
+		struct ubifs_zbranch *zbr;
+
+		exact = ubifs_search_zbranch(c, znode, key, n);
+
+		if (znode->level == 0)
+			break;
+
+		if (*n < 0)
+			*n = 0;
+		zbr = &znode->zbranch[*n];
+
+		if (zbr->znode) {
+			znode->time = time;
+			znode = dirty_cow_znode(c, zbr);
+			if (IS_ERR(znode))
+				return PTR_ERR(znode);
+			continue;
+		}
+
+		/* znode is not in TNC cache, load it from the media */
+		znode = load_znode(c, zbr, znode, *n);
+		if (IS_ERR(znode))
+			return PTR_ERR(znode);
+		znode = dirty_cow_znode(c, zbr);
+		if (IS_ERR(znode))
+			return PTR_ERR(znode);
+	}
+
+	*zn = znode;
+	if (exact || !is_hash_key(c, key) || *n != -1) {
+		dbg_tnc("found %d, lvl %d, n %d", exact, znode->level, *n);
+		return exact;
+	}
+
+	/*
+	 * See huge comment at 'lookup_level0_dirty()' what is the rest of the
+	 * code.
+	 */
+	err = tnc_prev(c, &znode, n);
+	if (err == -ENOENT) {
+		*n = -1;
+		dbg_tnc("found 0, lvl %d, n -1", znode->level);
+		return 0;
+	}
+	if (unlikely(err < 0))
+		return err;
+	if (keys_cmp(c, key, &znode->zbranch[*n].key)) {
+		*n = -1;
+		dbg_tnc("found 0, lvl %d, n -1", znode->level);
+		return 0;
+	}
+
+	if (znode->cnext || !ubifs_zn_dirty(znode)) {
+		znode = dirty_cow_bottom_up(c, znode);
+		if (IS_ERR(znode))
+			return PTR_ERR(znode);
+	}
+
+	dbg_tnc("found 1, lvl %d, n %d", znode->level, *n);
+	*zn = znode;
+	return 1;
+}
+
+/**
+ * ubifs_tnc_lookup - look up a file-system node.
+ * @c: UBIFS file-system description object
+ * @key: node key to lookup
+ * @node: the node is returned here
+ *
+ * This function look up and reads node with key @key. The caller has to make
+ * sure the @node buffer is large enough to fit the node. Returns zero in case
+ * of success, %-ENOENT if the node was not found, and a negative error code in
+ * case of failure.
+ */
+int ubifs_tnc_lookup(struct ubifs_info *c, const union ubifs_key *key,
+		     void *node)
+{
+	int found, n, err;
+	struct ubifs_znode *znode;
+	struct ubifs_zbranch zbr, *zt;
+
+	mutex_lock(&c->tnc_mutex);
+	found = lookup_level0(c, key, &znode, &n);
+	if (!found) {
+		err = -ENOENT;
+		goto out;
+	} else if (found < 0) {
+		err = found;
+		goto out;
+	}
+	zt = &znode->zbranch[n];
+	if (is_hash_key(c, key)) {
+		/*
+		 * In this case the leaf node cache gets used, so we pass the
+		 * address of the zbranch and keep the mutex locked
+		 */
+		err = tnc_read_node_nm(c, zt, node);
+		goto out;
+	}
+	zbr = znode->zbranch[n];
+	mutex_unlock(&c->tnc_mutex);
+
+	err = tnc_read_node(c, &zbr, node);
+	return err;
+
+out:
+	mutex_unlock(&c->tnc_mutex);
+	return err;
+}
+
+/**
+ * ubifs_tnc_locate - look up a file-system node and return it and its location.
+ * @c: UBIFS file-system description object
+ * @key: node key to lookup
+ * @node: the node is returned here
+ * @lnum: LEB number is returned here
+ * @offs: offset is returned here
+ *
+ * This function is the same as 'ubifs_tnc_lookup()' but it returns the node
+ * location also. See 'ubifs_tnc_lookup()'.
+ */
+int ubifs_tnc_locate(struct ubifs_info *c, const union ubifs_key *key,
+		     void *node, int *lnum, int *offs)
+{
+	int found, n, err;
+	struct ubifs_znode *znode;
+	struct ubifs_zbranch zbr, *zt;
+
+	mutex_lock(&c->tnc_mutex);
+	found = lookup_level0(c, key, &znode, &n);
+	if (!found) {
+		err = -ENOENT;
+		goto out;
+	} else if (found < 0) {
+		err = found;
+		goto out;
+	}
+	zt = &znode->zbranch[n];
+	if (is_hash_key(c, key)) {
+		/*
+		 * In this case the leaf node cache gets used, so we pass the
+		 * address of the zbranch and keep the mutex locked
+		 */
+		*lnum = zt->lnum;
+		*offs = zt->offs;
+		err = tnc_read_node_nm(c, zt, node);
+		goto out;
+	}
+	zbr = znode->zbranch[n];
+	mutex_unlock(&c->tnc_mutex);
+
+	*lnum = zbr.lnum;
+	*offs = zbr.offs;
+
+	err = tnc_read_node(c, &zbr, node);
+	return err;
+
+out:
+	mutex_unlock(&c->tnc_mutex);
+	return err;
+}
+
+/**
+ * do_lookup_nm- look up a "hashed" node.
+ * directory entry file-system node.
+ * @c: UBIFS file-system description object
+ * @key: node key to lookup
+ * @node: the node is returned here
+ * @nm: node name
+ *
+ * This function look up and reads a node which contains name hash in the key.
+ * Since the hash may have collisions, there may be many nodes with the same
+ * key, so we have to sequentially look to all of them until the needed one is
+ * found. This function returns zero in case of success, %-ENOENT if the node
+ * was not found, and a negative error code in case of failure.
+ */
+static int do_lookup_nm(struct ubifs_info *c, const union ubifs_key *key,
+			void *node, const struct qstr *nm)
+{
+	int found, n, err;
+	struct ubifs_znode *znode;
+	struct ubifs_zbranch zbr;
+
+	dbg_tnc("name '%.*s' key %s", nm->len, nm->name, DBGKEY(key));
+	mutex_lock(&c->tnc_mutex);
+	found = lookup_level0(c, key, &znode, &n);
+	if (!found) {
+		err = -ENOENT;
+		goto out_unlock;
+	} else if (found < 0) {
+		err = found;
+		goto out_unlock;
+	}
+
+	ubifs_assert(n >= 0);
+
+	err = resolve_collision(c, key, &znode, &n, nm);
+	dbg_tnc("rc returned %d, znode %p, n %d", err, znode, n);
+	if (unlikely(err < 0))
+		goto out_unlock;
+	if (err == 0) {
+		err = -ENOENT;
+		goto out_unlock;
+	}
+
+	zbr = znode->zbranch[n];
+	mutex_unlock(&c->tnc_mutex);
+
+	err = tnc_read_node_nm(c, &zbr, node);
+	return err;
+
+out_unlock:
+	mutex_unlock(&c->tnc_mutex);
+	return err;
+}
+
+/**
+ * ubifs_tnc_lookup_nm- look up a "hashed" node.
+ * directory entry file-system node.
+ * @c: UBIFS file-system description object
+ * @key: node key to lookup
+ * @node: the node is returned here
+ * @nm: node name
+ *
+ * This function look up and reads a node which contains name hash in the key.
+ * Since the hash may have collisions, there may be many nodes with the same
+ * key, so we have to sequentially look to all of them until the needed one is
+ * found. This function returns zero in case of success, %-ENOENT if the node
+ * was not found, and a negative error code in case of failure.
+ */
+int ubifs_tnc_lookup_nm(struct ubifs_info *c, const union ubifs_key *key,
+			void *node, const struct qstr *nm)
+{
+	int err, len;
+	const struct ubifs_dent_node *dent = node;
+
+	/*
+	 * We assume that in most of the cases there are no name collisions and
+	 * 'ubifs_tnc_lookup()' returns us the right direntry.
+	 */
+	err = ubifs_tnc_lookup(c, key, node);
+	if (err)
+		return err;
+
+	len = le16_to_cpu(dent->nlen);
+	if (nm->len == len && !memcmp(dent->name, nm->name, len))
+		return 0;
+
+	/*
+	 * Unluckily, there are hash collisions and we have to iterate over
+	 * them look at each direntry with colliding name hash sequentially.
+	 */
+	return do_lookup_nm(c, key, node, nm);
+}
+
+/**
+ * correct_parent_keys - correct parent znodes' keys.
+ * @c: UBIFS file-system description object
+ * @znode: znode to correct parent znodes for
+ *
+ * This is a helper function for 'tnc_insert()'. When the key of the leftmost
+ * zbranch changes, keys of parent znodes have to be corrected. This helper
+ * function is called in such situations and corrects the keys if needed.
+ */
+static void correct_parent_keys(const struct ubifs_info *c,
+				struct ubifs_znode *znode)
+{
+	union ubifs_key *key, *key1;
+
+	ubifs_assert(znode->parent);
+	ubifs_assert(znode->iip == 0);
+
+	key = &znode->zbranch[0].key;
+	key1 = &znode->parent->zbranch[0].key;
+
+	while (keys_cmp(c, key, key1) < 0) {
+		key_copy(c, key, key1);
+		znode = znode->parent;
+		if (!znode->parent || znode->iip)
+			break;
+		key1 = &znode->parent->zbranch[0].key;
+	}
+}
+
+/**
+ * insert_zbranch - insert a zbranch into a znode.
+ * @znode: znode into which to insert
+ * @zbr: zbranch to insert
+ * @n: slot number to insert to
+ *
+ * This is a helper function for 'tnc_insert()'. UBIFS does not allow "gaps" in
+ * znode's array of zbranches and keeps zbranches consolidated, so when a new
+ * zbranch has to be inserted to the @znode->zbranches[]' array at the @n-th
+ * slot, zbranches starting from @n have to be moved right.
+ */
+static void insert_zbranch(struct ubifs_znode *znode,
+			   const struct ubifs_zbranch *zbr, int n)
+{
+	int i;
+
+	ubifs_assert(ubifs_zn_dirty(znode));
+
+	if (znode->level) {
+		for (i = znode->child_cnt; i > n; i--) {
+			znode->zbranch[i] = znode->zbranch[i - 1];
+			if (znode->zbranch[i].znode)
+				znode->zbranch[i].znode->iip = i;
+		}
+		if (zbr->znode)
+			zbr->znode->iip = n;
+	} else
+		for (i = znode->child_cnt; i > n; i--)
+			znode->zbranch[i] = znode->zbranch[i - 1];
+
+	znode->zbranch[n] = *zbr;
+	znode->child_cnt += 1;
+
+	/*
+	 * After inserting at slot zero, the lower bound of the key range of
+	 * this znode may have changed. If this znode is subsequently split
+	 * then the upper bound of the key range may change, and furthermore
+	 * it could change to be lower than the original lower bound. If that
+	 * happens, then it will no longer be possible to find this znode in the
+	 * TNC using the key from the index node on flash. That is bad because
+	 * if it is not found, we will assume it is obsolete and may overwrite
+	 * it. Then if there is an unclean unmount, we will start using the
+	 * old index which will be broken.
+	 *
+	 * So we first mark znodes that have insertions at slot zero, and then
+	 * if they are split we add their lnum/offs to the old_idx tree.
+	 */
+	if (n == 0)
+		znode->alt = 1;
+}
+
+/**
+ * tnc_insert - insert a node into TNC.
+ * @c: UBIFS file-system description object
+ * @znode: znode to insert into
+ * @zbr: branch to insert
+ * @n: slot number to insert new zbranch to
+ *
+ * This function inserts a new node described by @zbr into znode @znode. If
+ * znode does not have a free slot for new zbranch, it is split. Parent znodes
+ * are splat as well if needed. Returns zero in case of success or a negative
+ * error code in case of failure.
+ */
+static int tnc_insert(struct ubifs_info *c, struct ubifs_znode *znode,
+		      struct ubifs_zbranch *zbr, int n)
+{
+	struct ubifs_znode *zn, *zi, *zp;
+	int i, keep, move, appending = 0;
+	union ubifs_key *key = &zbr->key;
+
+	ubifs_assert(n >= 0 && n <= c->fanout);
+
+	/* Implement naive insert for now */
+again:
+	zp = znode->parent;
+	if (znode->child_cnt < c->fanout) {
+		ubifs_assert(n != c->fanout);
+		dbg_tnc("inserted at %d level %d, key %s", n, znode->level,
+			DBGKEY(key));
+
+		insert_zbranch(znode, zbr, n);
+
+		/* Ensure parent's key is correct */
+		if (n == 0 && zp && znode->iip == 0)
+			correct_parent_keys(c, znode);
+
+		return 0;
+	}
+
+	/*
+	 * Unfortunately, @znode does not have more empty slots and we have to
+	 * split it.
+	 */
+	dbg_tnc("splitting level %d, key %s", znode->level, DBGKEY(key));
+
+	if (znode->alt)
+		/*
+		 * We can no longer be sure of finding this znode by key, so we
+		 * record it in the old_idx tree.
+		 */
+		ins_clr_old_idx_znode(c, znode);
+
+	zn = kzalloc(c->max_znode_sz, GFP_NOFS);
+	if (!zn)
+		return -ENOMEM;
+	zn->parent = zp;
+	zn->level = znode->level;
+
+	/* Decide where to split */
+	if (znode->level == 0 && n == c->fanout &&
+	    key_type(c, key) == UBIFS_DATA_KEY) {
+		union ubifs_key *key1;
+
+		/*
+		 * If this is an inode which is being appended - do not split
+		 * it because no other zbranches can be inserted between
+		 * zbranches of consecutive data nodes anyway.
+		 */
+		key1 = &znode->zbranch[n - 1].key;
+		if (key_ino(c, key1) == key_ino(c, key) &&
+		    key_type(c, key1) == UBIFS_DATA_KEY &&
+		    key_block(c, key1) == key_block(c, key) - 1)
+			appending = 1;
+	}
+
+	if (appending) {
+		keep = c->fanout;
+		move = 0;
+	} else {
+		keep = (c->fanout + 1) / 2;
+		move = c->fanout - keep;
+	}
+
+	/*
+	 * Although we don't at present, we could look at the neighbors and see
+	 * if we can move some zbranches there.
+	 */
+
+	if (n < keep) {
+		/* Insert into existing znode */
+		zi = znode;
+		move += 1;
+		keep -= 1;
+	} else {
+		/* Insert into new znode */
+		zi = zn;
+		n -= keep;
+		/* Re-parent */
+		if (zn->level != 0)
+			zbr->znode->parent = zn;
+	}
+
+	__set_bit(DIRTY_ZNODE, &zn->flags);
+	atomic_long_inc(&c->dirty_zn_cnt);
+
+	zn->child_cnt = move;
+	znode->child_cnt = keep;
+
+	dbg_tnc("moving %d, keeping %d", move, keep);
+
+	/* Move zbranch */
+	for (i = 0; i < move; i++) {
+		zn->zbranch[i] = znode->zbranch[keep + i];
+		/* Re-parent */
+		if (zn->level != 0)
+			if (zn->zbranch[i].znode) {
+				zn->zbranch[i].znode->parent = zn;
+				zn->zbranch[i].znode->iip = i;
+			}
+	}
+
+	/* Insert new key and branch */
+	dbg_tnc("inserting at %d level %d, key %s", n, zn->level, DBGKEY(key));
+
+	insert_zbranch(zi, zbr, n);
+
+	/* Insert new znode (produced by spitting) into the parent */
+	if (zp) {
+		i = n;
+		/* Locate insertion point */
+		n = znode->iip + 1;
+		if (appending && n != c->fanout)
+			appending = 0;
+
+		if (i == 0 && zi == znode && znode->iip == 0)
+			correct_parent_keys(c, znode);
+
+		/* Tail recursion */
+		zbr->key = zn->zbranch[0].key;
+		zbr->znode = zn;
+		zbr->lnum = 0;
+		zbr->offs = 0;
+		zbr->len = 0;
+		znode = zp;
+
+		goto again;
+	}
+
+	/* We have to split root znode */
+	dbg_tnc("creating new zroot at level %d", znode->level + 1);
+
+	zi = kzalloc(c->max_znode_sz, GFP_NOFS);
+	if (!zi)
+		return -ENOMEM;
+
+	zi->child_cnt = 2;
+	zi->level = znode->level + 1;
+
+	__set_bit(DIRTY_ZNODE, &zi->flags);
+	atomic_long_inc(&c->dirty_zn_cnt);
+
+	zi->zbranch[0].key = znode->zbranch[0].key;
+	zi->zbranch[0].znode = znode;
+	zi->zbranch[0].lnum = c->zroot.lnum;
+	zi->zbranch[0].offs = c->zroot.offs;
+	zi->zbranch[0].len = c->zroot.len;
+	zi->zbranch[1].key = zn->zbranch[0].key;
+	zi->zbranch[1].znode = zn;
+
+	c->zroot.lnum = 0;
+	c->zroot.offs = 0;
+	c->zroot.len = 0;
+	c->zroot.znode = zi;
+
+	zn->parent = zi;
+	zn->iip = 1;
+	znode->parent = zi;
+	znode->iip = 0;
+
+	return 0;
+}
+
+/**
+ * ubifs_tnc_add - add a node to TNC.
+ * @c: UBIFS file-system description object
+ * @key: key to add
+ * @lnum: LEB number of node
+ * @offs: node offset
+ * @len: node length
+ *
+ * This function adds a node with key @key to TNC. The node may be new or it may
+ * obsolete some existing one. Returns %0 on success or negative error code on
+ * failure.
+ */
+int ubifs_tnc_add(struct ubifs_info *c, const union ubifs_key *key, int lnum,
+		  int offs, int len)
+{
+	int found, n, err = 0;
+	struct ubifs_znode *znode;
+
+	mutex_lock(&c->tnc_mutex);
+	dbg_tnc("%d:%d, len %d, key %s", lnum, offs, len, DBGKEY(key));
+	found = lookup_level0_dirty(c, key, &znode, &n);
+	if (!found) {
+		struct ubifs_zbranch zbr;
+
+		zbr.znode = NULL;
+		zbr.lnum = lnum;
+		zbr.offs = offs;
+		zbr.len = len;
+		key_copy(c, key, &zbr.key);
+		err = tnc_insert(c, znode, &zbr, n + 1);
+	} else if (found == 1) {
+		struct ubifs_zbranch *zbr = &znode->zbranch[n];
+
+		lnc_free(zbr);
+		err = ubifs_add_dirt(c, zbr->lnum, zbr->len);
+		zbr->lnum = lnum;
+		zbr->offs = offs;
+		zbr->len = len;
+	} else
+		err = found;
+	if (!err)
+		err = dbg_check_tnc(c, 0);
+	mutex_unlock(&c->tnc_mutex);
+
+	return err;
+}
+
+/**
+ * ubifs_tnc_replace - replace a node in the TNC only if the old node is found.
+ * @c: UBIFS file-system description object
+ * @key: key to add
+ * @old_lnum: LEB number of old node
+ * @old_offs: old node offset
+ * @lnum: LEB number of node
+ * @offs: node offset
+ * @len: node length
+ *
+ * This function replaces a node with key @key in the TNC only if the old node
+ * is found.  This function is called by garbage collection when node are moved.
+ * Returns %0 on success or negative error code on failure.
+ */
+int ubifs_tnc_replace(struct ubifs_info *c, const union ubifs_key *key,
+		      int old_lnum, int old_offs, int lnum, int offs, int len)
+{
+	int found, n, err = 0;
+	struct ubifs_znode *znode;
+
+	mutex_lock(&c->tnc_mutex);
+	dbg_tnc("old LEB %d:%d, new LEB %d:%d, len %d, key %s", old_lnum,
+		old_offs, lnum, offs, len, DBGKEY(key));
+	found = lookup_level0_dirty(c, key, &znode, &n);
+	if (found < 0) {
+		err = found;
+		goto out_unlock;
+	}
+
+	if (found == 1) {
+		struct ubifs_zbranch *zbr = &znode->zbranch[n];
+
+		found = 0;
+		if (zbr->lnum == old_lnum && zbr->offs == old_offs) {
+			lnc_free(zbr);
+			err = ubifs_add_dirt(c, zbr->lnum, zbr->len);
+			if (err)
+				goto out_unlock;
+			zbr->lnum = lnum;
+			zbr->offs = offs;
+			zbr->len = len;
+			found = 1;
+		} else if (is_hash_key(c, key)) {
+			found = resolve_collision_directly(c, key, &znode, &n,
+							   old_lnum, old_offs);
+			dbg_tnc("rc returned %d, znode %p, n %d, LEB %d:%d",
+				found, znode, n, old_lnum, old_offs);
+			if (found < 0) {
+				err = found;
+				goto out_unlock;
+			}
+
+			if (found) {
+				/* Ensure the znode is dirtied */
+				if (znode->cnext || !ubifs_zn_dirty(znode)) {
+					    znode = dirty_cow_bottom_up(c,
+									znode);
+					    if (IS_ERR(znode)) {
+						    err = PTR_ERR(znode);
+						    goto out_unlock;
+					    }
+				}
+				zbr = &znode->zbranch[n];
+				lnc_free(zbr);
+				err = ubifs_add_dirt(c, zbr->lnum,
+						     zbr->len);
+				if (err)
+					goto out_unlock;
+				zbr->lnum = lnum;
+				zbr->offs = offs;
+				zbr->len = len;
+			}
+		}
+	}
+
+	if (!found)
+		err = ubifs_add_dirt(c, lnum, len);
+
+	if (!err)
+		err = dbg_check_tnc(c, 0);
+
+out_unlock:
+	mutex_unlock(&c->tnc_mutex);
+	return err;
+}
+
+/**
+ * ubifs_tnc_add_nm - add a "hashed" node to TNC.
+ * @c: UBIFS file-system description object
+ * @key: key to add
+ * @lnum: LEB number of node
+ * @offs: node offset
+ * @len: node length
+ * @nm: node name
+ *
+ * This is the same as 'ubifs_tnc_add()' but it should be used with keys which
+ * may have collisions, like directory entry keys.
+ */
+int ubifs_tnc_add_nm(struct ubifs_info *c, const union ubifs_key *key,
+		     int lnum, int offs, int len, const struct qstr *nm)
+{
+	int found, n, err = 0;
+	struct ubifs_znode *znode;
+
+	mutex_lock(&c->tnc_mutex);
+	dbg_tnc("LEB %d:%d, name '%.*s', key %s", lnum, offs, nm->len, nm->name,
+		DBGKEY(key));
+	found = lookup_level0_dirty(c, key, &znode, &n);
+	if (found < 0) {
+		err = found;
+		goto out_unlock;
+	}
+
+	if (found == 1) {
+		if (c->replaying)
+			found = fallible_resolve_collision(c, key, &znode, &n,
+							   nm, 1);
+		else
+			found = resolve_collision(c, key, &znode, &n, nm);
+		dbg_tnc("rc returned %d, znode %p, n %d", found, znode, n);
+		if (found < 0) {
+			err = found;
+			goto out_unlock;
+		}
+
+		/* Ensure the znode is dirtied */
+		if (znode->cnext || !ubifs_zn_dirty(znode)) {
+			    znode = dirty_cow_bottom_up(c, znode);
+			    if (IS_ERR(znode)) {
+				    err = PTR_ERR(znode);
+				    goto out_unlock;
+			    }
+		}
+
+		if (found == 1) {
+			struct ubifs_zbranch *zbr = &znode->zbranch[n];
+
+			lnc_free(zbr);
+			err = ubifs_add_dirt(c, zbr->lnum, zbr->len);
+			zbr->lnum = lnum;
+			zbr->offs = offs;
+			zbr->len = len;
+			goto out_unlock;
+		}
+	}
+
+	if (!found) {
+		struct ubifs_zbranch zbr;
+
+		zbr.znode = NULL;
+		zbr.lnum = lnum;
+		zbr.offs = offs;
+		zbr.len = len;
+		key_copy(c, key, &zbr.key);
+		err = tnc_insert(c, znode, &zbr, n + 1);
+		if (err)
+			goto out_unlock;
+		if (c->replaying && c->replay_sqnum < c->cs_sqnum) {
+			/*
+			 * This node was moved by garbage collection. We can
+			 * tell because it is in the journal but it has a
+			 * sequence number earlier than the last commit-start.
+			 * We did not find it in the index so there may be a
+			 * dangling branch still in the index. So we remove it
+			 * by passing 'ubifs_tnc_remove_nm()' the same key but
+			 * an unmatchable name.
+			 */
+			struct qstr noname = { .len = 0, .name = "" };
+
+			err = dbg_check_tnc(c, 0);
+			mutex_unlock(&c->tnc_mutex);
+			if (err)
+				return err;
+			return ubifs_tnc_remove_nm(c, key, &noname);
+		}
+	}
+
+out_unlock:
+	if (!err)
+		err = dbg_check_tnc(c, 0);
+	mutex_unlock(&c->tnc_mutex);
+	return err;
+}
+
+/**
+ * tnc_delete - delete a znode form TNC.
+ * @c: UBIFS file-system description object
+ * @znode: znode to delete from
+ * @n: zbranch slot number to delete
+ *
+ * This function deletes a leaf node from @n-th slot of @znode. Returns zero in
+ * case of success and a negative error code in case of failure.
+ */
+static int tnc_delete(struct ubifs_info *c, struct ubifs_znode *znode, int n)
+{
+	struct ubifs_zbranch *zbr;
+	struct ubifs_znode *zp;
+	int i, err;
+
+	/* Delete without merge for now */
+	ubifs_assert(znode->level == 0);
+	ubifs_assert(n >= 0 && n < c->fanout);
+	dbg_tnc("deleting %s", DBGKEY(&znode->zbranch[n].key));
+
+	zbr = &znode->zbranch[n];
+	lnc_free(zbr);
+
+	err = ubifs_add_dirt(c, zbr->lnum, zbr->len);
+	if (err) {
+		dbg_dump_znode(c, znode);
+		return err;
+	}
+
+	/* We do not "gap" zbranch slots */
+	for (i = n; i < znode->child_cnt - 1; i++)
+		znode->zbranch[i] = znode->zbranch[i + 1];
+	znode->child_cnt -= 1;
+
+	if (znode->child_cnt > 0)
+		return 0;
+
+	/*
+	 * This was the last zbranch, we have to delete this znode from the
+	 * parent.
+	 */
+
+	do {
+		ubifs_assert(!test_bit(OBSOLETE_ZNODE, &znode->flags));
+		ubifs_assert(ubifs_zn_dirty(znode));
+
+		zp = znode->parent;
+		n = znode->iip;
+
+		atomic_long_dec(&c->dirty_zn_cnt);
+
+		err = insert_old_idx_znode(c, znode);
+		if (err)
+			return err;
+
+		if (znode->cnext) {
+			__set_bit(OBSOLETE_ZNODE, &znode->flags);
+			atomic_long_inc(&c->clean_zn_cnt);
+			atomic_long_inc(&ubifs_clean_zn_cnt);
+		} else
+			kfree(znode);
+		znode = zp;
+	} while (znode->child_cnt == 1); /* while removing last child */
+
+	/* Remove from znode, entry n - 1 */
+	znode->child_cnt -= 1;
+	ubifs_assert(znode->level != 0);
+	for (i = n; i < znode->child_cnt; i++) {
+		znode->zbranch[i] = znode->zbranch[i + 1];
+		if (znode->zbranch[i].znode)
+			znode->zbranch[i].znode->iip = i;
+	}
+
+	/*
+	 * If this is the root and it has only 1 child then
+	 * collapse the tree.
+	 */
+	if (!znode->parent) {
+		while (znode->child_cnt == 1 && znode->level != 0) {
+			zp = znode;
+			zbr = &znode->zbranch[0];
+			znode = get_znode(c, znode, 0);
+			if (IS_ERR(znode))
+				return PTR_ERR(znode);
+			znode = dirty_cow_znode(c, zbr);
+			if (IS_ERR(znode))
+				return PTR_ERR(znode);
+			znode->parent = NULL;
+			znode->iip = 0;
+			if (c->zroot.len) {
+				err = insert_old_idx(c, c->zroot.lnum,
+						     c->zroot.offs);
+				if (err)
+					return err;
+			}
+			c->zroot.lnum = zbr->lnum;
+			c->zroot.offs = zbr->offs;
+			c->zroot.len = zbr->len;
+			c->zroot.znode = znode;
+			ubifs_assert(!test_bit(OBSOLETE_ZNODE,
+				     &zp->flags));
+			ubifs_assert(test_bit(DIRTY_ZNODE, &zp->flags));
+			atomic_long_dec(&c->dirty_zn_cnt);
+
+			if (zp->cnext) {
+				__set_bit(OBSOLETE_ZNODE, &zp->flags);
+				atomic_long_inc(&c->clean_zn_cnt);
+				atomic_long_inc(&ubifs_clean_zn_cnt);
+			} else
+				kfree(zp);
+		}
+	}
+
+	return 0;
+}
+
+/**
+ * ubifs_tnc_remove - remove an index entry of a node.
+ * @c: UBIFS file-system description object
+ * @key: key of node
+ *
+ * Returns %0 on success or negative error code on failure.
+ */
+int ubifs_tnc_remove(struct ubifs_info *c, const union ubifs_key *key)
+{
+	int found, n, err = 0;
+	struct ubifs_znode *znode;
+
+	mutex_lock(&c->tnc_mutex);
+	dbg_tnc("key %s", DBGKEY(key));
+	found = lookup_level0_dirty(c, key, &znode, &n);
+	if (found < 0) {
+		err = found;
+		goto out_unlock;
+	}
+	if (found == 1)
+		err = tnc_delete(c, znode, n);
+	if (!err)
+		err = dbg_check_tnc(c, 0);
+
+out_unlock:
+	mutex_unlock(&c->tnc_mutex);
+	return err;
+}
+
+/**
+ * ubifs_tnc_remove_nm - remove an index entry for a "hashed" node.
+ * @c: UBIFS file-system description object
+ * @key: key of node
+ * @nm: directory entry name
+ *
+ * Returns %0 on success or negative error code on failure.
+ */
+int ubifs_tnc_remove_nm(struct ubifs_info *c, const union ubifs_key *key,
+			const struct qstr *nm)
+{
+	int n, err;
+	struct ubifs_znode *znode;
+
+	mutex_lock(&c->tnc_mutex);
+	dbg_tnc("%.*s, key %s", nm->len, nm->name, DBGKEY(key));
+	err = lookup_level0_dirty(c, key, &znode, &n);
+	if (err < 0)
+		goto out_unlock;
+
+	if (err) {
+		if (c->replaying)
+			err = fallible_resolve_collision(c, key, &znode, &n,
+							 nm, 0);
+		else
+			err = resolve_collision(c, key, &znode, &n, nm);
+		dbg_tnc("rc returned %d, znode %p, n %d", err, znode, n);
+		if (err < 0)
+			goto out_unlock;
+		if (err) {
+			/* Ensure the znode is dirtied */
+			if (znode->cnext || !ubifs_zn_dirty(znode)) {
+				    znode = dirty_cow_bottom_up(c, znode);
+				    if (IS_ERR(znode)) {
+					    err = PTR_ERR(znode);
+					    goto out_unlock;
+				    }
+			}
+			err = tnc_delete(c, znode, n);
+		}
+	}
+
+out_unlock:
+	if (!err)
+		err = dbg_check_tnc(c, 0);
+	mutex_unlock(&c->tnc_mutex);
+	return err;
+}
+
+/**
+ * key_in_range - determine if a key falls within a range of keys.
+ * @c: UBIFS file-system description object
+ * @key: key to check
+ * @from_key: lowest key in range
+ * @to_key: highest key in range
+ *
+ * This function returns %1 if the key is in range and %0 otherwise.
+ */
+static int key_in_range(struct ubifs_info *c, union ubifs_key *key,
+			union ubifs_key *from_key, union ubifs_key *to_key)
+{
+	if (keys_cmp(c, key, from_key) < 0)
+		return 0;
+	if (keys_cmp(c, key, to_key) > 0)
+		return 0;
+	return 1;
+}
+
+/**
+ * ubifs_tnc_remove_range - remove index entries in range.
+ * @c: UBIFS file-system description object
+ * @from_key: lowest key to remove
+ * @to_key: highest key to remove
+ *
+ * This function removes index entries starting at @from_key and ending at
+ * @to_key.  This function returns zero in case of success and a negative error
+ * code in case of failure.
+ */
+int ubifs_tnc_remove_range(struct ubifs_info *c, union ubifs_key *from_key,
+			   union ubifs_key *to_key)
+{
+	int i, n, k, err = 0;
+	struct ubifs_znode *znode;
+	union ubifs_key *key;
+
+	mutex_lock(&c->tnc_mutex);
+	while (1) {
+		/* Find first level 0 znode that contains keys to remove */
+		err = lookup_level0(c, from_key, &znode, &n);
+		if (err < 0)
+			goto out_unlock;
+
+		if (err)
+			key = from_key;
+		else {
+			err = tnc_next(c, &znode, &n);
+			if (err == -ENOENT) {
+				err = 0;
+				goto out_unlock;
+			}
+			if (err < 0)
+				goto out_unlock;
+			key = &znode->zbranch[n].key;
+			if (!key_in_range(c, key, from_key, to_key)) {
+				err = 0;
+				goto out_unlock;
+			}
+		}
+
+		/* Ensure the znode is dirtied */
+		if (znode->cnext || !ubifs_zn_dirty(znode)) {
+			    znode = dirty_cow_bottom_up(c, znode);
+			    if (IS_ERR(znode)) {
+				    err = PTR_ERR(znode);
+				    goto out_unlock;
+			    }
+		}
+
+		/* Remove all keys in range except the first */
+		for (i = n + 1, k = 0; i < znode->child_cnt; i++, k++) {
+			key = &znode->zbranch[i].key;
+			if (!key_in_range(c, key, from_key, to_key))
+				break;
+			lnc_free(&znode->zbranch[i]);
+			err = ubifs_add_dirt(c, znode->zbranch[i].lnum,
+					     znode->zbranch[i].len);
+			if (err) {
+				dbg_dump_znode(c, znode);
+				goto out_unlock;
+			}
+			dbg_tnc("removing %s", DBGKEY(key));
+		}
+		if (k) {
+			for (i = n + 1 + k; i < znode->child_cnt; i++)
+				znode->zbranch[i - k] = znode->zbranch[i];
+			znode->child_cnt -= k;
+		}
+
+		/* Now delete the first */
+		err = tnc_delete(c, znode, n);
+		if (err)
+			goto out_unlock;
+	}
+
+out_unlock:
+	if (!err)
+		err = dbg_check_tnc(c, 0);
+	mutex_unlock(&c->tnc_mutex);
+	return err;
+}
+
+/**
+ * ubifs_tnc_remove_ino - remove an inode from TNC.
+ * @c: UBIFS file-system description object
+ * @inum: inode number to remove
+ *
+ * This function remove inode @inum and all the extended attributes associated
+ * with the anode from TNC and returns zero in case of success or a negative
+ * error code in case of failure.
+ */
+int ubifs_tnc_remove_ino(struct ubifs_info *c, ino_t inum)
+{
+	union ubifs_key key1, key2;
+	struct ubifs_dent_node *xent, *pxent = NULL;
+	struct qstr nm = { .name = NULL };
+
+	dbg_tnc("ino %lu", inum);
+
+	/*
+	 * Walk all extended attribute entries and remove them together with
+	 * corresponding extended attribute inodes.
+	 */
+	lowest_xent_key(c, &key1, inum);
+	while (1) {
+		ino_t xattr_inum;
+		int err;
+
+		xent = ubifs_tnc_next_ent(c, &key1, &nm);
+		if (IS_ERR(xent)) {
+			err = PTR_ERR(xent);
+			if (err == -ENOENT)
+				break;
+			return err;
+		}
+
+		xattr_inum = le64_to_cpu(xent->inum);
+		dbg_tnc("xent '%s', ino %lu", xent->name, xattr_inum);
+
+		nm.name = xent->name;
+		nm.len = le16_to_cpu(xent->nlen);
+		err = ubifs_tnc_remove_nm(c, &key1, &nm);
+		if (err) {
+			kfree(xent);
+			return err;
+		}
+
+		lowest_ino_key(c, &key1, xattr_inum);
+		highest_ino_key(c, &key2, xattr_inum);
+		err = ubifs_tnc_remove_range(c, &key1, &key2);
+		if (err) {
+			kfree(xent);
+			return err;
+		}
+
+		kfree(pxent);
+		pxent = xent;
+		key_read(c, &xent->key, &key1);
+	}
+
+	kfree(pxent);
+	lowest_ino_key(c, &key1, inum);
+	highest_ino_key(c, &key2, inum);
+
+	return ubifs_tnc_remove_range(c, &key1, &key2);
+}
+
+/**
+ * ubifs_tnc_next_ent - walk directory or extended attribute entries.
+ * @c: UBIFS file-system description object
+ * @key: key of last entry
+ * @nm: name of last entry found or %NULL
+ *
+ * This function finds and reads the next directory or extended attribute entry
+ * after the given key (@key) if there is one. @nm is used to resolve
+ * collisions.
+ *
+ * If the name of the current entry is not known and only the key is known,
+ * @nm->name has to be %NULL. In this case the semantics of this function is a
+ * little bit different and it returns the entry corresponding to this key, not
+ * the next one. If the key was not found, the closest "right" entry is
+ * returned.
+ *
+ * If the fist entry has to be found, @key has to contain the lowest possible
+ * key value for this inode and @name has to be %NULL.
+ *
+ * This function returns the found directory or extended attribute entry node
+ * in case of success, %-ENOENT is returned if no entry was found, and a
+ * negative error code is returned in case of failure.
+ */
+struct ubifs_dent_node *ubifs_tnc_next_ent(struct ubifs_info *c,
+					   union ubifs_key *key,
+					   const struct qstr *nm)
+{
+	int n, err, type = key_type(c, key);
+	struct ubifs_znode *znode;
+	struct ubifs_dent_node *dent;
+	struct ubifs_zbranch *zbr;
+	union ubifs_key *dkey;
+
+	dbg_tnc("%s %s", nm->name ? (char *)nm->name : "(lowest)", DBGKEY(key));
+	ubifs_assert(is_hash_key(c, key));
+
+	mutex_lock(&c->tnc_mutex);
+	err = lookup_level0(c, key, &znode, &n);
+	if (unlikely(err < 0))
+		goto out_unlock;
+
+	if (nm->name) {
+		if (err) {
+			/* Handle collisions */
+			err = resolve_collision(c, key, &znode, &n, nm);
+			dbg_tnc("rc returned %d, znode %p, n %d",
+				err, znode, n);
+			if (unlikely(err < 0))
+				goto out_unlock;
+		}
+
+		/* Now find next entry */
+		err = tnc_next(c, &znode, &n);
+		if (unlikely(err))
+			goto out_unlock;
+	} else {
+		/*
+		 * The full name of the entry was not given, in which case the
+		 * behavior of this function is a little different and it
+		 * returns current entry, not the next one.
+		 */
+		if (!err) {
+			/*
+			 * However, the given key does not exist in the TNC
+			 * tree and @znode/@n variables contain the closest
+			 * "preceding" element. Switch to the next one.
+			 */
+			err = tnc_next(c, &znode, &n);
+			if (err)
+				goto out_unlock;
+		}
+	}
+
+	zbr = &znode->zbranch[n];
+	dent = kmalloc(zbr->len, GFP_NOFS);
+	if (unlikely(!dent)) {
+		err = -ENOMEM;
+		goto out_unlock;
+	}
+
+	/*
+	 * The above 'tnc_next()' call could lead us to the next inode, check
+	 * this.
+	 */
+	dkey = &zbr->key;
+	if (key_ino(c, dkey) != key_ino(c, key) ||
+	    key_type(c, dkey) != type) {
+		err = -ENOENT;
+		goto out_free;
+	}
+
+	err = tnc_read_node_nm(c, zbr, dent);
+	if (unlikely(err))
+		goto out_free;
+
+	mutex_unlock(&c->tnc_mutex);
+	return dent;
+
+out_free:
+	kfree(dent);
+out_unlock:
+	mutex_unlock(&c->tnc_mutex);
+	return ERR_PTR(err);
+}
+
+/**
+ * tnc_destroy_cnext - destroy left-over obsolete znodes from a failed commit.
+ * @c: UBIFS file-system description object
+ *
+ * Destroy left-over obsolete znodes from a failed commit.
+ */
+static void tnc_destroy_cnext(struct ubifs_info *c)
+{
+	struct ubifs_znode *cnext;
+
+	if (!c->cnext)
+		return;
+	ubifs_assert(c->cmt_state == COMMIT_BROKEN);
+	cnext = c->cnext;
+	do {
+		struct ubifs_znode *znode = cnext;
+
+		cnext = cnext->cnext;
+		if (test_bit(OBSOLETE_ZNODE, &znode->flags))
+			kfree(znode);
+	} while (cnext && cnext != c->cnext);
+}
+
+/**
+ * ubifs_tnc_close - close TNC subsystem and free all related resources.
+ * @c: UBIFS file-system description object
+ */
+void ubifs_tnc_close(struct ubifs_info *c)
+{
+	long clean_freed;
+
+	tnc_destroy_cnext(c);
+	if (c->zroot.znode) {
+		clean_freed = ubifs_destroy_tnc_subtree(c->zroot.znode);
+		atomic_long_sub(clean_freed, &ubifs_clean_zn_cnt);
+	}
+	kfree(c->gap_lebs);
+	kfree(c->ilebs);
+	destroy_old_idx(c);
+}
+
+/**
+ * left_znode - get the znode to the left.
+ * @c: UBIFS file-system description object
+ * @znode: znode
+ *
+ * This function returns a pointer to the znode to the left of @znode or NULL if
+ * there is not one. A negative error code is returned on failure.
+ */
+static struct ubifs_znode *left_znode(struct ubifs_info *c,
+				      struct ubifs_znode *znode)
+{
+	int level = znode->level;
+
+	while (1) {
+		int n = znode->iip - 1;
+
+		/* Go up until we can go left */
+		znode = znode->parent;
+		if (!znode)
+			return NULL;
+		if (n >= 0) {
+			/* Now go down the rightmost branch to 'level' */
+			znode = get_znode(c, znode, n);
+			if (IS_ERR(znode))
+				return znode;
+			while (znode->level != level) {
+				n = znode->child_cnt - 1;
+				znode = get_znode(c, znode, n);
+				if (IS_ERR(znode))
+					return znode;
+			}
+			break;
+		}
+	}
+	return znode;
+}
+
+/**
+ * right_znode - get the znode to the right.
+ * @c: UBIFS file-system description object
+ * @znode: znode
+ *
+ * This function returns a pointer to the znode to the right of @znode or NULL
+ * if there is not one. A negative error code is returned on failure.
+ */
+static struct ubifs_znode *right_znode(struct ubifs_info *c,
+				       struct ubifs_znode *znode)
+{
+	int level = znode->level;
+
+	while (1) {
+		int n = znode->iip + 1;
+
+		/* Go up until we can go right */
+		znode = znode->parent;
+		if (!znode)
+			return NULL;
+		if (n < znode->child_cnt) {
+			/* Now go down the leftmost branch to 'level' */
+			znode = get_znode(c, znode, n);
+			if (IS_ERR(znode))
+				return znode;
+			while (znode->level != level) {
+				znode = get_znode(c, znode, 0);
+				if (IS_ERR(znode))
+					return znode;
+			}
+			break;
+		}
+	}
+	return znode;
+}
+
+/**
+ * lookup_znode - find a particular indexing node from TNC.
+ * @c: UBIFS file-system description object
+ * @key: index node key to lookup
+ * @level: index node level
+ * @lnum: index node LEB number
+ * @offs: index node offset
+ *
+ * This function searches an indexing node by its first key @key and its
+ * address @lnum:@offs. It looks up the indexing tree by pulling all indexing
+ * nodes it traverses to TNC. This function is called fro indexing nodes which
+ * were found on the media by scanning, for example when garbage-collecting or
+ * when doing in-the-gaps commit. This means that the indexing node which is
+ * looked for does not have to have exactly the same leftmost key @key, because
+ * the leftmost key may have been changed, in which case TNC will contain a
+ * dirty znode which still refers the same @lnum:@offs. This function is clever
+ * enough to recognize such indexing nodes.
+ *
+ * Note, if a znode was deleted or changed too much, then this function will
+ * not find it. For situations like this UBIFS has the old index RB-tree
+ * (indexed by @lnum:@offs).
+ *
+ * This function returns a pointer to the znode found or %NULL if it is not
+ * found. A negative error code is returned on failure.
+ */
+static struct ubifs_znode *lookup_znode(struct ubifs_info *c,
+					union ubifs_key *key, int level,
+					int lnum, int offs)
+{
+	struct ubifs_znode *znode, *zn;
+	int n, nn;
+
+	/*
+	 * The arguments have probably been read off flash, so don't assume
+	 * they are valid.
+	 */
+	if (level < 0)
+		return ERR_PTR(-EINVAL);
+
+	/* Get the root znode */
+	znode = c->zroot.znode;
+	if (!znode) {
+		znode = load_znode(c, &c->zroot, NULL, 0);
+		if (IS_ERR(znode))
+			return znode;
+	}
+	/* Check if it is the one we are looking for */
+	if (c->zroot.lnum == lnum && c->zroot.offs == offs)
+		return znode;
+	/* Descend to the parent level i.e. (level + 1) */
+	if (level >= znode->level)
+		return NULL;
+	while (1) {
+		ubifs_search_zbranch(c, znode, key, &n);
+		if (n < 0) {
+			/*
+			 * We reached a znode where the leftmost key is greater
+			 * than the key we are searching for. This is the same
+			 * situation as the one described in a huge comment at
+			 * the end of the 'lookup_level0()' function. And for
+			 * exactly the same reasons we have to try to look left
+			 * before giving up.
+			 */
+			znode = left_znode(c, znode);
+			if (!znode)
+				return NULL;
+			if (IS_ERR(znode))
+				return znode;
+			ubifs_search_zbranch(c, znode, key, &n);
+			ubifs_assert(n >= 0);
+		}
+		if (znode->level == level + 1)
+			break;
+		znode = get_znode(c, znode, n);
+		if (IS_ERR(znode))
+			return znode;
+	}
+	/* Check if the child is the one we are looking for */
+	if (znode->zbranch[n].lnum == lnum && znode->zbranch[n].offs == offs)
+		return get_znode(c, znode, n);
+	/* If the key is unique, there is nowhere else to look */
+	if (!is_hash_key(c, key))
+		return NULL;
+	/*
+	 * The key is not unique and so may be also in the znodes to either
+	 * side.
+	 */
+	zn = znode;
+	nn = n;
+	/* Look left */
+	while (1) {
+		/* Move one branch to the left */
+		if (n)
+			n -= 1;
+		else {
+			znode = left_znode(c, znode);
+			if (!znode)
+				break;
+			if (IS_ERR(znode))
+				return znode;
+			n = znode->child_cnt - 1;
+		}
+		/* Check it */
+		if (znode->zbranch[n].lnum == lnum &&
+		    znode->zbranch[n].offs == offs)
+			return get_znode(c, znode, n);
+		/* Stop if the key is less than the one we are looking for */
+		if (keys_cmp(c, &znode->zbranch[n].key, key) < 0)
+			break;
+	}
+	/* Back to the middle */
+	znode = zn;
+	n = nn;
+	/* Look right */
+	while (1) {
+		/* Move one branch to the right */
+		if (++n >= znode->child_cnt) {
+			znode = right_znode(c, znode);
+			if (!znode)
+				break;
+			if (IS_ERR(znode))
+				return znode;
+			n = 0;
+		}
+		/* Check it */
+		if (znode->zbranch[n].lnum == lnum &&
+		    znode->zbranch[n].offs == offs)
+			return get_znode(c, znode, n);
+		/* Stop if the key is greater than the one we are looking for */
+		if (keys_cmp(c, &znode->zbranch[n].key, key) > 0)
+			break;
+	}
+	return NULL;
+}
+
+/**
+ * is_idx_node_in_tnc - determine if an index node is in the TNC.
+ * @c: UBIFS file-system description object
+ * @key: key of index node
+ * @level: index node level
+ * @lnum: LEB number of index node
+ * @offs: offset of index node
+ *
+ * This function returns %0 if the index node is not referred to in the TNC, %1
+ * if the index node is referred to in the TNC and the corresponding znode is
+ * dirty, %2 if an index node is referred to in the TNC and the corresponding
+ * znode is clean, and a negative error code in case of failure.
+ *
+ * Note, the @key argument has to be the key of the first child. Also note,
+ * this function relies on the fact that 0:0 is never a valid LEB number and
+ * offset for a main-area node.
+ */
+int is_idx_node_in_tnc(struct ubifs_info *c, union ubifs_key *key, int level,
+		       int lnum, int offs)
+{
+	struct ubifs_znode *znode;
+
+	znode = lookup_znode(c, key, level, lnum, offs);
+	if (!znode)
+		return 0;
+	if (IS_ERR(znode))
+		return PTR_ERR(znode);
+
+	return ubifs_zn_dirty(znode) ? 1 : 2;
+}
+
+/**
+ * is_leaf_node_in_tnc - determine if a non-indexing not is in the TNC.
+ * @c: UBIFS file-system description object
+ * @key: node key
+ * @lnum: node LEB number
+ * @offs: node offset
+ *
+ * This function returns %1 if the node is referred to in the TNC, %0 if it is
+ * not, and a negative error code in case of failure.
+ *
+ * Note, this function relies on the fact that 0:0 is never a valid LEB number
+ * and offset for a main-area node.
+ */
+static int is_leaf_node_in_tnc(struct ubifs_info *c, union ubifs_key *key,
+			       int lnum, int offs)
+{
+	struct ubifs_zbranch *zbr;
+	struct ubifs_znode *znode, *zn;
+	int n, found, err, nn;
+	const int unique = !is_hash_key(c, key);
+
+	found = lookup_level0(c, key, &znode, &n);
+	if (found < 0)
+		return found; /* Error code */
+	if (!found)
+		return 0;
+	zbr = &znode->zbranch[n];
+	if (lnum == zbr->lnum && offs == zbr->offs)
+		return 1; /* Found it */
+	if (unique)
+		return 0;
+	/*
+	 * Because the key is not unique, we have to look left
+	 * and right as well
+	 */
+	zn = znode;
+	nn = n;
+	/* Look left */
+	while (1) {
+		err = tnc_prev(c, &znode, &n);
+		if (err == -ENOENT)
+			break;
+		if (err)
+			return err;
+		if (keys_cmp(c, key, &znode->zbranch[n].key))
+			break;
+		zbr = &znode->zbranch[n];
+		if (lnum == zbr->lnum && offs == zbr->offs)
+			return 1; /* Found it */
+	}
+	/* Look right */
+	znode = zn;
+	n = nn;
+	while (1) {
+		err = tnc_next(c, &znode, &n);
+		if (err) {
+			if (err == -ENOENT)
+				return 0;
+			return err;
+		}
+		if (keys_cmp(c, key, &znode->zbranch[n].key))
+			break;
+		zbr = &znode->zbranch[n];
+		if (lnum == zbr->lnum && offs == zbr->offs)
+			return 1; /* Found it */
+	}
+	return 0;
+}
+
+/**
+ * ubifs_tnc_has_node - determine whether a node is in the TNC.
+ * @c: UBIFS file-system description object
+ * @key: node key
+ * @level: index node level (if it is an index node)
+ * @lnum: node LEB number
+ * @offs: node offset
+ * @is_idx: non-zero if the node is an index node
+ *
+ * This function returns %1 if the node is in the TNC, %0 if it is not, and a
+ * negative error code in case of failure. For index nodes, @key has to be the
+ * key of the first child. An index node is considered to be in the TNC only if
+ * the corresponding znode is clean or has not been loaded.
+ */
+int ubifs_tnc_has_node(struct ubifs_info *c, union ubifs_key *key, int level,
+		       int lnum, int offs, int is_idx)
+{
+	int err;
+
+	mutex_lock(&c->tnc_mutex);
+	if (is_idx) {
+		err = is_idx_node_in_tnc(c, key, level, lnum, offs);
+		if (err < 0)
+			goto out_unlock;
+		if (err == 1)
+			/* The index node was found but it was dirty */
+			err = 0;
+		else if (err == 2)
+			/* The index node was found and it was clean */
+			err = 1;
+		else
+			BUG_ON(err != 0);
+	} else
+		err = is_leaf_node_in_tnc(c, key, lnum, offs);
+
+out_unlock:
+	mutex_unlock(&c->tnc_mutex);
+	return err;
+}
+
+/**
+ * ubifs_dirty_idx_node - dirty an index node.
+ * @c: UBIFS file-system description object
+ * @key: index node key
+ * @level: index node level
+ * @lnum: index node LEB number
+ * @offs: index node offset
+ *
+ * This function loads and dirties an index node so that it can be garbage
+ * collected. The @key argument has to be the key of the first child. This
+ * function relies on the fact that 0:0 is never a valid LEB number and offset
+ * for a main-area node. Returns %0 on success and a negative error code on
+ * failure.
+ */
+int ubifs_dirty_idx_node(struct ubifs_info *c, union ubifs_key *key, int level,
+			 int lnum, int offs)
+{
+	struct ubifs_znode *znode;
+	int err = 0;
+
+	mutex_lock(&c->tnc_mutex);
+	znode = lookup_znode(c, key, level, lnum, offs);
+	if (!znode)
+		goto out_unlock;
+	if (IS_ERR(znode)) {
+		err = PTR_ERR(znode);
+		goto out_unlock;
+	}
+	znode = dirty_cow_bottom_up(c, znode);
+	if (IS_ERR(znode)) {
+		err = PTR_ERR(znode);
+		goto out_unlock;
+	}
+
+out_unlock:
+	mutex_unlock(&c->tnc_mutex);
+	return err;
+}
+
+#ifdef CONFIG_UBIFS_FS_DEBUG
+
+/**
+ * dbg_walk_sub_tree - walk index subtree.
+ * @c: UBIFS file-system description object
+ * @znode: root znode of the subtree to walk
+ * @leaf_cb: called for each leaf node
+ * @znode_cb: called for each indexing node
+ * @priv: private date which is passed to callbacks
+ *
+ * This is a helper function which recursively walks the UBIFS index, reading
+ * each indexing node from the media if needed. Returns zero in case of success
+ * and a negative error code in case of failure.
+ */
+static int dbg_walk_sub_tree(struct ubifs_info *c, struct ubifs_znode *znode,
+			     dbg_leaf_callback leaf_cb,
+			     dbg_znode_callback znode_cb, void *priv)
+{
+	int n, err;
+
+	cond_resched();
+
+	if (znode_cb) {
+		err = znode_cb(c, znode, priv);
+		if (err)
+			return err;
+	}
+
+	if (znode->level == 0) {
+		if (!leaf_cb)
+			return 0;
+
+		for (n = 0; n < znode->child_cnt; n++) {
+			struct ubifs_zbranch *zbr = &znode->zbranch[n];
+
+			err = leaf_cb(c, zbr, priv);
+			if (err)
+				return err;
+		}
+	} else
+		for (n = 0; n < znode->child_cnt; n++) {
+			struct ubifs_znode *zn;
+
+			zn = get_znode(c, znode, n);
+			if (IS_ERR(zn))
+				return PTR_ERR(zn);
+			err = dbg_walk_sub_tree(c, zn, leaf_cb, znode_cb, priv);
+			if (err)
+				return err;
+		}
+
+	return 0;
+}
+
+/**
+ * dbg_walk_index - walk the on-flash index.
+ * @c: UBIFS file-system description object
+ * @leaf_cb: called for each leaf node
+ * @znode_cb: called for each indexing node
+ * @priv: private date which is passed to callbacks
+ *
+ * This function walks the UBIFS index and calls the @leaf_cb for each leaf
+ * node and @znode_cb for each indexing node. Returns zero in case of success
+ * and a negative error code in case of failure.
+ *
+ * Because 'dbg_walk_sub_tree()' is recursive, it runs the risk of exceeding the
+ * stack space.
+ *
+ * It would be better if this function removed every znode it pulled to into
+ * the TNC, so that the behavior more closely matched the non-debugging
+ * behavior.
+ */
+int dbg_walk_index(struct ubifs_info *c, dbg_leaf_callback leaf_cb,
+		   dbg_znode_callback znode_cb, void *priv)
+{
+	int err = 0;
+
+	mutex_lock(&c->tnc_mutex);
+	if (!c->zroot.znode) {
+		c->zroot.znode = load_znode(c, &c->zroot, NULL, 0);
+		if (IS_ERR(c->zroot.znode)) {
+			err = PTR_ERR(c->zroot.znode);
+			c->zroot.znode = NULL;
+			goto out_unlock;
+		}
+	}
+
+	err = dbg_walk_sub_tree(c, c->zroot.znode, leaf_cb, znode_cb, priv);
+
+out_unlock:
+	mutex_unlock(&c->tnc_mutex);
+	return err;
+}
+
+int dbg_read_leaf_nolock(struct ubifs_info *c, struct ubifs_zbranch *zbr,
+			 void *node)
+{
+	ubifs_assert(mutex_is_locked(&c->tnc_mutex));
+	if (is_hash_key(c, &zbr->key))
+		return tnc_read_node_nm(c, zbr, node);
+	return tnc_read_node(c, zbr, node);
+}
+
+#endif /* CONFIG_UBIFS_FS_DEBUG */
-- 
1.5.4.1

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