Merge tag 'kvm-s390-next-6.4-2' of https://git.kernel.org/pub/scm/linux/kernel/git...

[platform/kernel/linux-rpi.git] / fs / ubifs / tnc.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * This file is part of UBIFS.
 *
 * Copyright (C) 2006-2008 Nokia Corporation.
 *
 * 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 <linux/slab.h>
#include "ubifs.h"

static int try_read_node(const struct ubifs_info *c, void *buf, int type,
                         struct ubifs_zbranch *zbr);
static int fallible_read_node(struct ubifs_info *c, const union ubifs_key *key,
                              struct ubifs_zbranch *zbr, void *node);

/*
 * 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,
};

static void do_insert_old_idx(struct ubifs_info *c,
                              struct ubifs_old_idx *old_idx)
{
        struct ubifs_old_idx *o;
        struct rb_node **p, *parent = NULL;

        p = &c->old_idx.rb_node;
        while (*p) {
                parent = *p;
                o = rb_entry(parent, struct ubifs_old_idx, rb);
                if (old_idx->lnum < o->lnum)
                        p = &(*p)->rb_left;
                else if (old_idx->lnum > o->lnum)
                        p = &(*p)->rb_right;
                else if (old_idx->offs < o->offs)
                        p = &(*p)->rb_left;
                else if (old_idx->offs > o->offs)
                        p = &(*p)->rb_right;
                else {
                        ubifs_err(c, "old idx added twice!");
                        kfree(old_idx);
                }
        }
        rb_link_node(&old_idx->rb, parent, p);
        rb_insert_color(&old_idx->rb, &c->old_idx);
}

/**
 * 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;

        old_idx = kmalloc(sizeof(struct ubifs_old_idx), GFP_NOFS);
        if (unlikely(!old_idx))
                return -ENOMEM;
        old_idx->lnum = lnum;
        old_idx->offs = offs;
        do_insert_old_idx(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 ubifs_old_idx *old_idx, *n;

        rbtree_postorder_for_each_entry_safe(old_idx, n, &c->old_idx, rb)
                kfree(old_idx);

        c->old_idx = RB_ROOT;
}

/**
 * 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 = kmemdup(znode, c->max_znode_sz, GFP_NOFS);
        if (unlikely(!zn))
                return ERR_PTR(-ENOMEM);

        zn->cnext = NULL;
        __set_bit(DIRTY_ZNODE, &zn->flags);
        __clear_bit(COW_ZNODE, &zn->flags);

        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);
}

/**
 * replace_znode - replace old znode with new znode.
 * @c: UBIFS file-system description object
 * @new_zn: new znode
 * @old_zn: old znode
 * @zbr: the branch of parent znode
 *
 * Replace old znode with new znode in TNC.
 */
static void replace_znode(struct ubifs_info *c, struct ubifs_znode *new_zn,
                          struct ubifs_znode *old_zn, struct ubifs_zbranch *zbr)
{
        ubifs_assert(c, !ubifs_zn_obsolete(old_zn));
        __set_bit(OBSOLETE_ZNODE, &old_zn->flags);

        if (old_zn->level != 0) {
                int i;
                const int n = new_zn->child_cnt;

                /* The children now have new parent */
                for (i = 0; i < n; i++) {
                        struct ubifs_zbranch *child = &new_zn->zbranch[i];

                        if (child->znode)
                                child->znode->parent = new_zn;
                }
        }

        zbr->znode = new_zn;
        zbr->lnum = 0;
        zbr->offs = 0;
        zbr->len = 0;

        atomic_long_inc(&c->dirty_zn_cnt);
}

/**
 * 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 (!ubifs_zn_cow(znode)) {
                /* 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 (IS_ERR(zn))
                return zn;

        if (zbr->len) {
                struct ubifs_old_idx *old_idx;

                old_idx = kmalloc(sizeof(struct ubifs_old_idx), GFP_NOFS);
                if (unlikely(!old_idx)) {
                        err = -ENOMEM;
                        goto out;
                }
                old_idx->lnum = zbr->lnum;
                old_idx->offs = zbr->offs;

                err = add_idx_dirt(c, zbr->lnum, zbr->len);
                if (err) {
                        kfree(old_idx);
                        goto out;
                }

                do_insert_old_idx(c, old_idx);
        }

        replace_znode(c, zn, znode, zbr);

        return zn;

out:
        kfree(zn);
        return ERR_PTR(err);
}

/**
 * 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(c, !zbr->leaf);
        ubifs_assert(c, zbr->len != 0);
        ubifs_assert(c, is_hash_key(c, &zbr->key));

        err = ubifs_validate_entry(c, dent);
        if (err) {
                dump_stack();
                ubifs_dump_node(c, dent, zbr->len);
                return err;
        }

        lnc_node = kmemdup(node, zbr->len, GFP_NOFS);
        if (!lnc_node)
                /* We don't have to have the cache, so no error */
                return 0;

        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(c, !zbr->leaf);
        ubifs_assert(c, zbr->len != 0);

        err = ubifs_validate_entry(c, node);
        if (err) {
                dump_stack();
                ubifs_dump_node(c, node, zbr->len);
                return err;
        }

        zbr->leaf = node;
        return 0;
}

/**
 * lnc_free - remove a leaf node from the leaf node cache.
 * @zbr: zbranch of leaf node
 */
static void lnc_free(struct ubifs_zbranch *zbr)
{
        if (!zbr->leaf)
                return;
        kfree(zbr->leaf);
        zbr->leaf = NULL;
}

/**
 * tnc_read_hashed_node - 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 error
 * code in case of failure.
 */
static int tnc_read_hashed_node(struct ubifs_info *c, struct ubifs_zbranch *zbr,
                                void *node)
{
        int err;

        ubifs_assert(c, is_hash_key(c, &zbr->key));

        if (zbr->leaf) {
                /* Read from the leaf node cache */
                ubifs_assert(c, zbr->len != 0);
                memcpy(node, zbr->leaf, zbr->len);
                return 0;
        }

        if (c->replaying) {
                err = fallible_read_node(c, &zbr->key, zbr, node);
                /*
                 * When the node was not found, return -ENOENT, 0 otherwise.
                 * Negative return codes stay as-is.
                 */
                if (err == 0)
                        err = -ENOENT;
                else if (err == 1)
                        err = 0;
        } else {
                err = ubifs_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
 * @zbr: the zbranch describing the 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.
 *
 * Note, this function does not check CRC of data nodes if @c->no_chk_data_crc
 * is true (it is controlled by corresponding mount option). However, if
 * @c->mounting or @c->remounting_rw is true (we are mounting or re-mounting to
 * R/W mode), @c->no_chk_data_crc is ignored and CRC is checked. This is
 * because during mounting or re-mounting from R/O mode to R/W mode we may read
 * journal nodes (when replying the journal or doing the recovery) and the
 * journal nodes may potentially be corrupted, so checking is required.
 */
static int try_read_node(const struct ubifs_info *c, void *buf, int type,
                         struct ubifs_zbranch *zbr)
{
        int len = zbr->len;
        int lnum = zbr->lnum;
        int offs = zbr->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 = ubifs_leb_read(c, lnum, buf, offs, len, 1);
        if (err) {
                ubifs_err(c, "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;

        if (type != UBIFS_DATA_NODE || !c->no_chk_data_crc || c->mounting ||
            c->remounting_rw) {
                crc = crc32(UBIFS_CRC32_INIT, buf + 8, node_len - 8);
                node_crc = le32_to_cpu(ch->crc);
                if (crc != node_crc)
                        return 0;
        }

        err = ubifs_node_check_hash(c, buf, zbr->hash);
        if (err) {
                ubifs_bad_hash(c, buf, zbr->hash, lnum, offs);
                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_tnck(key, "LEB %d:%d, key ", zbr->lnum, zbr->offs);

        ret = try_read_node(c, node, key_type(c, key), zbr);
        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 && c->replaying)
                dbg_mntk(key, "dangling branch LEB %d:%d len %d, key ",
                        zbr->lnum, zbr->offs, zbr->len);
        return ret;
}

/**
 * matches_name - determine if a direntry or xattr 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 fscrypt_name *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 = ubifs_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, fname_name(nm), min_t(int, nlen, fname_len(nm)));
        if (err == 0) {
                if (nlen == fname_len(nm))
                        return NAME_MATCHES;
                else if (nlen < fname_len(nm))
                        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 = ubifs_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 fscrypt_name *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(c, *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(c, 0);
                                                if (err == -ENOENT)
                                                        err = -EINVAL;
                                                return err;
                                        }
                                        ubifs_assert(c, *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(c, 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(c, 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 fscrypt_name *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(c, 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, fname_name(nm), min_t(int, nlen, fname_len(nm)));
        if (err == 0) {
                if (nlen == fname_len(nm))
                        return NAME_MATCHES;
                else if (nlen < fname_len(nm))
                        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 fscrypt_name *nm,
                                      int adding)
{
        struct ubifs_znode *o_znode = NULL, *znode = *zn;
        int 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(c, *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(c, 0);
                                                if (err == -ENOENT)
                                                        err = -EINVAL;
                                                return err;
                                        }
                                        ubifs_assert(c, *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_mntk(key, "dangling match LEB %d:%d len %d key ",
                o_znode->zbranch[o_n].lnum, o_znode->zbranch[o_n].offs,
                o_znode->zbranch[o_n].len);
        *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, c->zroot.znode);
        ubifs_assert(c, znode);
        if (c->zroot.znode->level > BOTTOM_UP_HEIGHT) {
                kfree(c->bottom_up_buf);
                c->bottom_up_buf = kmalloc_array(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(c, 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(c, path[p - 1] >= 0);
                        ubifs_assert(c, path[p - 1] < zp->child_cnt);
                        zbr = &zp->zbranch[path[--p]];
                        znode = dirty_cow_znode(c, zbr);
                } else {
                        ubifs_assert(c, znode == c->zroot.znode);
                        znode = dirty_cow_znode(c, &c->zroot);
                }
                if (IS_ERR(znode) || !p)
                        break;
                ubifs_assert(c, path[p - 1] >= 0);
                ubifs_assert(c, path[p - 1] < znode->child_cnt);
                znode = znode->zbranch[path[p - 1]].znode;
        }

        return znode;
}

/**
 * ubifs_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 closest branch or %-1
 *     is stored in @n; In this case calling tnc_next() is mandatory.
 *   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.
 */
int ubifs_lookup_level0(struct ubifs_info *c, const union ubifs_key *key,
                        struct ubifs_znode **zn, int *n)
{
        int err, exact;
        struct ubifs_znode *znode;
        time64_t time = ktime_get_seconds();

        dbg_tnck(key, "search key ");
        ubifs_assert(c, key_type(c, key) < UBIFS_INVALID_KEY);

        znode = c->zroot.znode;
        if (unlikely(!znode)) {
                znode = ubifs_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 = ubifs_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 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;
        time64_t time = ktime_get_seconds();

        dbg_tnck(key, "search and dirty key ");

        znode = c->zroot.znode;
        if (unlikely(!znode)) {
                znode = ubifs_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 = ubifs_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;
}

/**
 * maybe_leb_gced - determine if a LEB may have been garbage collected.
 * @c: UBIFS file-system description object
 * @lnum: LEB number
 * @gc_seq1: garbage collection sequence number
 *
 * This function determines if @lnum may have been garbage collected since
 * sequence number @gc_seq1. If it may have been then %1 is returned, otherwise
 * %0 is returned.
 */
static int maybe_leb_gced(struct ubifs_info *c, int lnum, int gc_seq1)
{
        int gc_seq2, gced_lnum;

        gced_lnum = c->gced_lnum;
        smp_rmb();
        gc_seq2 = c->gc_seq;
        /* Same seq means no GC */
        if (gc_seq1 == gc_seq2)
                return 0;
        /* Different by more than 1 means we don't know */
        if (gc_seq1 + 1 != gc_seq2)
                return 1;
        /*
         * We have seen the sequence number has increased by 1. Now we need to
         * be sure we read the right LEB number, so read it again.
         */
        smp_rmb();
        if (gced_lnum != c->gced_lnum)
                return 1;
        /* Finally we can check lnum */
        if (gced_lnum == lnum)
                return 1;
        return 0;
}

/**
 * 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 looks 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. The node location can be returned in @lnum and @offs.
 */
int ubifs_tnc_locate(struct ubifs_info *c, const union ubifs_key *key,
                     void *node, int *lnum, int *offs)
{
        int found, n, err, safely = 0, gc_seq1;
        struct ubifs_znode *znode;
        struct ubifs_zbranch zbr, *zt;

again:
        mutex_lock(&c->tnc_mutex);
        found = ubifs_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 (lnum) {
                *lnum = zt->lnum;
                *offs = zt->offs;
        }
        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_hashed_node(c, zt, node);
                goto out;
        }
        if (safely) {
                err = ubifs_tnc_read_node(c, zt, node);
                goto out;
        }
        /* Drop the TNC mutex prematurely and race with garbage collection */
        zbr = znode->zbranch[n];
        gc_seq1 = c->gc_seq;
        mutex_unlock(&c->tnc_mutex);

        if (ubifs_get_wbuf(c, zbr.lnum)) {
                /* We do not GC journal heads */
                err = ubifs_tnc_read_node(c, &zbr, node);
                return err;
        }

        err = fallible_read_node(c, key, &zbr, node);
        if (err <= 0 || maybe_leb_gced(c, zbr.lnum, gc_seq1)) {
                /*
                 * The node may have been GC'ed out from under us so try again
                 * while keeping the TNC mutex locked.
                 */
                safely = 1;
                goto again;
        }
        return 0;

out:
        mutex_unlock(&c->tnc_mutex);
        return err;
}

/**
 * ubifs_tnc_get_bu_keys - lookup keys for bulk-read.
 * @c: UBIFS file-system description object
 * @bu: bulk-read parameters and results
 *
 * Lookup consecutive data node keys for the same inode that reside
 * consecutively in the same LEB. This function returns zero in case of success
 * and a negative error code in case of failure.
 *
 * Note, if the bulk-read buffer length (@bu->buf_len) is known, this function
 * makes sure bulk-read nodes fit the buffer. Otherwise, this function prepares
 * maximum possible amount of nodes for bulk-read.
 */
int ubifs_tnc_get_bu_keys(struct ubifs_info *c, struct bu_info *bu)
{
        int n, err = 0, lnum = -1, offs;
        int len;
        unsigned int block = key_block(c, &bu->key);
        struct ubifs_znode *znode;

        bu->cnt = 0;
        bu->blk_cnt = 0;
        bu->eof = 0;

        mutex_lock(&c->tnc_mutex);
        /* Find first key */
        err = ubifs_lookup_level0(c, &bu->key, &znode, &n);
        if (err < 0)
                goto out;
        if (err) {
                /* Key found */
                len = znode->zbranch[n].len;
                /* The buffer must be big enough for at least 1 node */
                if (len > bu->buf_len) {
                        err = -EINVAL;
                        goto out;
                }
                /* Add this key */
                bu->zbranch[bu->cnt++] = znode->zbranch[n];
                bu->blk_cnt += 1;
                lnum = znode->zbranch[n].lnum;
                offs = ALIGN(znode->zbranch[n].offs + len, 8);
        }
        while (1) {
                struct ubifs_zbranch *zbr;
                union ubifs_key *key;
                unsigned int next_block;

                /* Find next key */
                err = tnc_next(c, &znode, &n);
                if (err)
                        goto out;
                zbr = &znode->zbranch[n];
                key = &zbr->key;
                /* See if there is another data key for this file */
                if (key_inum(c, key) != key_inum(c, &bu->key) ||
                    key_type(c, key) != UBIFS_DATA_KEY) {
                        err = -ENOENT;
                        goto out;
                }
                if (lnum < 0) {
                        /* First key found */
                        lnum = zbr->lnum;
                        offs = ALIGN(zbr->offs + zbr->len, 8);
                        len = zbr->len;
                        if (len > bu->buf_len) {
                                err = -EINVAL;
                                goto out;
                        }
                } else {
                        /*
                         * The data nodes must be in consecutive positions in
                         * the same LEB.
                         */
                        if (zbr->lnum != lnum || zbr->offs != offs)
                                goto out;
                        offs += ALIGN(zbr->len, 8);
                        len = ALIGN(len, 8) + zbr->len;
                        /* Must not exceed buffer length */
                        if (len > bu->buf_len)
                                goto out;
                }
                /* Allow for holes */
                next_block = key_block(c, key);
                bu->blk_cnt += (next_block - block - 1);
                if (bu->blk_cnt >= UBIFS_MAX_BULK_READ)
                        goto out;
                block = next_block;
                /* Add this key */
                bu->zbranch[bu->cnt++] = *zbr;
                bu->blk_cnt += 1;
                /* See if we have room for more */
                if (bu->cnt >= UBIFS_MAX_BULK_READ)
                        goto out;
                if (bu->blk_cnt >= UBIFS_MAX_BULK_READ)
                        goto out;
        }
out:
        if (err == -ENOENT) {
                bu->eof = 1;
                err = 0;
        }
        bu->gc_seq = c->gc_seq;
        mutex_unlock(&c->tnc_mutex);
        if (err)
                return err;
        /*
         * An enormous hole could cause bulk-read to encompass too many
         * page cache pages, so limit the number here.
         */
        if (bu->blk_cnt > UBIFS_MAX_BULK_READ)
                bu->blk_cnt = UBIFS_MAX_BULK_READ;
        /*
         * Ensure that bulk-read covers a whole number of page cache
         * pages.
         */
        if (UBIFS_BLOCKS_PER_PAGE == 1 ||
            !(bu->blk_cnt & (UBIFS_BLOCKS_PER_PAGE - 1)))
                return 0;
        if (bu->eof) {
                /* At the end of file we can round up */
                bu->blk_cnt += UBIFS_BLOCKS_PER_PAGE - 1;
                return 0;
        }
        /* Exclude data nodes that do not make up a whole page cache page */
        block = key_block(c, &bu->key) + bu->blk_cnt;
        block &= ~(UBIFS_BLOCKS_PER_PAGE - 1);
        while (bu->cnt) {
                if (key_block(c, &bu->zbranch[bu->cnt - 1].key) < block)
                        break;
                bu->cnt -= 1;
        }
        return 0;
}

/**
 * read_wbuf - bulk-read from a LEB with a wbuf.
 * @wbuf: wbuf that may overlap the read
 * @buf: buffer into which to read
 * @len: read length
 * @lnum: LEB number from which to read
 * @offs: offset from which to read
 *
 * This functions returns %0 on success or a negative error code on failure.
 */
static int read_wbuf(struct ubifs_wbuf *wbuf, void *buf, int len, int lnum,
                     int offs)
{
        const struct ubifs_info *c = wbuf->c;
        int rlen, overlap;

        dbg_io("LEB %d:%d, length %d", lnum, offs, len);
        ubifs_assert(c, wbuf && lnum >= 0 && lnum < c->leb_cnt && offs >= 0);
        ubifs_assert(c, !(offs & 7) && offs < c->leb_size);
        ubifs_assert(c, offs + len <= c->leb_size);

        spin_lock(&wbuf->lock);
        overlap = (lnum == wbuf->lnum && offs + len > wbuf->offs);
        if (!overlap) {
                /* We may safely unlock the write-buffer and read the data */
                spin_unlock(&wbuf->lock);
                return ubifs_leb_read(c, lnum, buf, offs, len, 0);
        }

        /* Don't read under wbuf */
        rlen = wbuf->offs - offs;
        if (rlen < 0)
                rlen = 0;

        /* Copy the rest from the write-buffer */
        memcpy(buf + rlen, wbuf->buf + offs + rlen - wbuf->offs, len - rlen);
        spin_unlock(&wbuf->lock);

        if (rlen > 0)
                /* Read everything that goes before write-buffer */
                return ubifs_leb_read(c, lnum, buf, offs, rlen, 0);

        return 0;
}

/**
 * validate_data_node - validate data nodes for bulk-read.
 * @c: UBIFS file-system description object
 * @buf: buffer containing data node to validate
 * @zbr: zbranch of data node to validate
 *
 * This functions returns %0 on success or a negative error code on failure.
 */
static int validate_data_node(struct ubifs_info *c, void *buf,
                              struct ubifs_zbranch *zbr)
{
        union ubifs_key key1;
        struct ubifs_ch *ch = buf;
        int err, len;

        if (ch->node_type != UBIFS_DATA_NODE) {
                ubifs_err(c, "bad node type (%d but expected %d)",
                          ch->node_type, UBIFS_DATA_NODE);
                goto out_err;
        }

        err = ubifs_check_node(c, buf, zbr->len, zbr->lnum, zbr->offs, 0, 0);
        if (err) {
                ubifs_err(c, "expected node type %d", UBIFS_DATA_NODE);
                goto out;
        }

        err = ubifs_node_check_hash(c, buf, zbr->hash);
        if (err) {
                ubifs_bad_hash(c, buf, zbr->hash, zbr->lnum, zbr->offs);
                return err;
        }

        len = le32_to_cpu(ch->len);
        if (len != zbr->len) {
                ubifs_err(c, "bad node length %d, expected %d", len, zbr->len);
                goto out_err;
        }

        /* Make sure the key of the read node is correct */
        key_read(c, buf + UBIFS_KEY_OFFSET, &key1);
        if (!keys_eq(c, &zbr->key, &key1)) {
                ubifs_err(c, "bad key in node at LEB %d:%d",
                          zbr->lnum, zbr->offs);
                dbg_tnck(&zbr->key, "looked for key ");
                dbg_tnck(&key1, "found node's key ");
                goto out_err;
        }

        return 0;

out_err:
        err = -EINVAL;
out:
        ubifs_err(c, "bad node at LEB %d:%d", zbr->lnum, zbr->offs);
        ubifs_dump_node(c, buf, zbr->len);
        dump_stack();
        return err;
}

/**
 * ubifs_tnc_bulk_read - read a number of data nodes in one go.
 * @c: UBIFS file-system description object
 * @bu: bulk-read parameters and results
 *
 * This functions reads and validates the data nodes that were identified by the
 * 'ubifs_tnc_get_bu_keys()' function. This functions returns %0 on success,
 * -EAGAIN to indicate a race with GC, or another negative error code on
 * failure.
 */
int ubifs_tnc_bulk_read(struct ubifs_info *c, struct bu_info *bu)
{
        int lnum = bu->zbranch[0].lnum, offs = bu->zbranch[0].offs, len, err, i;
        struct ubifs_wbuf *wbuf;
        void *buf;

        len = bu->zbranch[bu->cnt - 1].offs;
        len += bu->zbranch[bu->cnt - 1].len - offs;
        if (len > bu->buf_len) {
                ubifs_err(c, "buffer too small %d vs %d", bu->buf_len, len);
                return -EINVAL;
        }

        /* Do the read */
        wbuf = ubifs_get_wbuf(c, lnum);
        if (wbuf)
                err = read_wbuf(wbuf, bu->buf, len, lnum, offs);
        else
                err = ubifs_leb_read(c, lnum, bu->buf, offs, len, 0);

        /* Check for a race with GC */
        if (maybe_leb_gced(c, lnum, bu->gc_seq))
                return -EAGAIN;

        if (err && err != -EBADMSG) {
                ubifs_err(c, "failed to read from LEB %d:%d, error %d",
                          lnum, offs, err);
                dump_stack();
                dbg_tnck(&bu->key, "key ");
                return err;
        }

        /* Validate the nodes read */
        buf = bu->buf;
        for (i = 0; i < bu->cnt; i++) {
                err = validate_data_node(c, buf, &bu->zbranch[i]);
                if (err)
                        return err;
                buf = buf + ALIGN(bu->zbranch[i].len, 8);
        }

        return 0;
}

/**
 * do_lookup_nm- look up a "hashed" node.
 * @c: UBIFS file-system description object
 * @key: node key to lookup
 * @node: the node is returned here
 * @nm: node name
 *
 * This function looks 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 fscrypt_name *nm)
{
        int found, n, err;
        struct ubifs_znode *znode;

        dbg_tnck(key, "key ");
        mutex_lock(&c->tnc_mutex);
        found = ubifs_lookup_level0(c, key, &znode, &n);
        if (!found) {
                err = -ENOENT;
                goto out_unlock;
        } else if (found < 0) {
                err = found;
                goto out_unlock;
        }

        ubifs_assert(c, 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;
        }

        err = tnc_read_hashed_node(c, &znode->zbranch[n], node);

out_unlock:
        mutex_unlock(&c->tnc_mutex);
        return err;
}

/**
 * ubifs_tnc_lookup_nm - look up a "hashed" node.
 * @c: UBIFS file-system description object
 * @key: node key to lookup
 * @node: the node is returned here
 * @nm: node name
 *
 * This function looks 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 fscrypt_name *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 (fname_len(nm) == len && !memcmp(dent->name, fname_name(nm), 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);
}

static int search_dh_cookie(struct ubifs_info *c, const union ubifs_key *key,
                            struct ubifs_dent_node *dent, uint32_t cookie,
                            struct ubifs_znode **zn, int *n, int exact)
{
        int err;
        struct ubifs_znode *znode = *zn;
        struct ubifs_zbranch *zbr;
        union ubifs_key *dkey;

        if (!exact) {
                err = tnc_next(c, &znode, n);
                if (err)
                        return err;
        }

        for (;;) {
                zbr = &znode->zbranch[*n];
                dkey = &zbr->key;

                if (key_inum(c, dkey) != key_inum(c, key) ||
                    key_type(c, dkey) != key_type(c, key)) {
                        return -ENOENT;
                }

                err = tnc_read_hashed_node(c, zbr, dent);
                if (err)
                        return err;

                if (key_hash(c, key) == key_hash(c, dkey) &&
                    le32_to_cpu(dent->cookie) == cookie) {
                        *zn = znode;
                        return 0;
                }

                err = tnc_next(c, &znode, n);
                if (err)
                        return err;
        }
}

static int do_lookup_dh(struct ubifs_info *c, const union ubifs_key *key,
                        struct ubifs_dent_node *dent, uint32_t cookie)
{
        int n, err;
        struct ubifs_znode *znode;
        union ubifs_key start_key;

        ubifs_assert(c, is_hash_key(c, key));

        lowest_dent_key(c, &start_key, key_inum(c, key));

        mutex_lock(&c->tnc_mutex);
        err = ubifs_lookup_level0(c, &start_key, &znode, &n);
        if (unlikely(err < 0))
                goto out_unlock;

        err = search_dh_cookie(c, key, dent, cookie, &znode, &n, err);

out_unlock:
        mutex_unlock(&c->tnc_mutex);
        return err;
}

/**
 * ubifs_tnc_lookup_dh - look up a "double hashed" node.
 * @c: UBIFS file-system description object
 * @key: node key to lookup
 * @node: the node is returned here
 * @cookie: node cookie for collision resolution
 *
 * This function looks 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
 * with the same cookie value 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_dh(struct ubifs_info *c, const union ubifs_key *key,
                        void *node, uint32_t cookie)
{
        int err;
        const struct ubifs_dent_node *dent = node;

        if (!c->double_hash)
                return -EOPNOTSUPP;

        /*
         * 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;

        if (le32_to_cpu(dent->cookie) == cookie)
                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_dh(c, key, node, cookie);
}

/**
 * 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(c, znode->parent);
        ubifs_assert(c, 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;
                znode->alt = 1;
                if (!znode->parent || znode->iip)
                        break;
                key1 = &znode->parent->zbranch[0].key;
        }
}

/**
 * insert_zbranch - insert a zbranch into a znode.
 * @c: UBIFS file-system description object
 * @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_info *c, struct ubifs_znode *znode,
                           const struct ubifs_zbranch *zbr, int n)
{
        int i;

        ubifs_assert(c, 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, *key1;

        ubifs_assert(c, n >= 0 && n <= c->fanout);

        /* Implement naive insert for now */
again:
        zp = znode->parent;
        if (znode->child_cnt < c->fanout) {
                ubifs_assert(c, n != c->fanout);
                dbg_tnck(key, "inserted at %d level %d, key ", n, znode->level);

                insert_zbranch(c, 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_tnck(key, "splitting level %d, key ", znode->level);

        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 && key_type(c, key) == UBIFS_DATA_KEY) {
                /* Try not to split consecutive data keys */
                if (n == c->fanout) {
                        key1 = &znode->zbranch[n - 1].key;
                        if (key_inum(c, key1) == key_inum(c, key) &&
                            key_type(c, key1) == UBIFS_DATA_KEY)
                                appending = 1;
                } else
                        goto check_split;
        } else if (appending && n != c->fanout) {
                /* Try not to split consecutive data keys */
                appending = 0;
check_split:
                if (n >= (c->fanout + 1) / 2) {
                        key1 = &znode->zbranch[0].key;
                        if (key_inum(c, key1) == key_inum(c, key) &&
                            key_type(c, key1) == UBIFS_DATA_KEY) {
                                key1 = &znode->zbranch[n].key;
                                if (key_inum(c, key1) != key_inum(c, key) ||
                                    key_type(c, key1) != UBIFS_DATA_KEY) {
                                        keep = n;
                                        move = c->fanout - keep;
                                        zi = znode;
                                        goto do_split;
                                }
                        }
                }
        }

        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;
        }

do_split:

        __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_tnck(key, "inserting at %d level %d, key ", n, zn->level);

        insert_zbranch(c, zi, zbr, n);

        /* Insert new znode (produced by spitting) into the parent */
        if (zp) {
                if (n == 0 && zi == znode && znode->iip == 0)
                        correct_parent_keys(c, znode);

                /* Locate insertion point */
                n = znode->iip + 1;

                /* 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
 * @hash: The hash over the node
 *
 * 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, const u8 *hash)
{
        int found, n, err = 0;
        struct ubifs_znode *znode;

        mutex_lock(&c->tnc_mutex);
        dbg_tnck(key, "%d:%d, len %d, key ", lnum, offs, len);
        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;
                ubifs_copy_hash(c, hash, zbr.hash);
                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;
                ubifs_copy_hash(c, hash, zbr->hash);
        } 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_tnck(key, "old LEB %d:%d, new LEB %d:%d, len %d, key ", old_lnum,
                 old_offs, lnum, offs, len);
        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
 * @hash: The hash over the node
 * @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 u8 *hash,
                     const struct fscrypt_name *nm)
{
        int found, n, err = 0;
        struct ubifs_znode *znode;

        mutex_lock(&c->tnc_mutex);
        dbg_tnck(key, "LEB %d:%d, key ", lnum, offs);
        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;
                        ubifs_copy_hash(c, hash, zbr->hash);
                        goto out_unlock;
                }
        }

        if (!found) {
                struct ubifs_zbranch zbr;

                zbr.znode = NULL;
                zbr.lnum = lnum;
                zbr.offs = offs;
                zbr.len = len;
                ubifs_copy_hash(c, hash, zbr.hash);
                key_copy(c, key, &zbr.key);
                err = tnc_insert(c, znode, &zbr, n + 1);
                if (err)
                        goto out_unlock;
                if (c->replaying) {
                        /*
                         * 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 fscrypt_name noname = { .disk_name = { .name = "", .len = 1 } };

                        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(c, znode->level == 0);
        ubifs_assert(c, n >= 0 && n < c->fanout);
        dbg_tnck(&znode->zbranch[n].key, "deleting key ");

        zbr = &znode->zbranch[n];
        lnc_free(zbr);

        err = ubifs_add_dirt(c, zbr->lnum, zbr->len);
        if (err) {
                ubifs_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(c, !ubifs_zn_obsolete(znode));
                ubifs_assert(c, 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(c, 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(c, !ubifs_zn_obsolete(zp));
                        ubifs_assert(c, ubifs_zn_dirty(zp));
                        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_tnck(key, "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 fscrypt_name *nm)
{
        int n, err;
        struct ubifs_znode *znode;

        mutex_lock(&c->tnc_mutex);
        dbg_tnck(key, "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;
}

/**
 * ubifs_tnc_remove_dh - remove an index entry for a "double hashed" node.
 * @c: UBIFS file-system description object
 * @key: key of node
 * @cookie: node cookie for collision resolution
 *
 * Returns %0 on success or negative error code on failure.
 */
int ubifs_tnc_remove_dh(struct ubifs_info *c, const union ubifs_key *key,
                        uint32_t cookie)
{
        int n, err;
        struct ubifs_znode *znode;
        struct ubifs_dent_node *dent;
        struct ubifs_zbranch *zbr;

        if (!c->double_hash)
                return -EOPNOTSUPP;

        mutex_lock(&c->tnc_mutex);
        err = lookup_level0_dirty(c, key, &znode, &n);
        if (err <= 0)
                goto out_unlock;

        zbr = &znode->zbranch[n];
        dent = kmalloc(UBIFS_MAX_DENT_NODE_SZ, GFP_NOFS);
        if (!dent) {
                err = -ENOMEM;
                goto out_unlock;
        }

        err = tnc_read_hashed_node(c, zbr, dent);
        if (err)
                goto out_free;

        /* If the cookie does not match, we're facing a hash collision. */
        if (le32_to_cpu(dent->cookie) != cookie) {
                union ubifs_key start_key;

                lowest_dent_key(c, &start_key, key_inum(c, key));

                err = ubifs_lookup_level0(c, &start_key, &znode, &n);
                if (unlikely(err < 0))
                        goto out_free;

                err = search_dh_cookie(c, key, dent, cookie, &znode, &n, err);
                if (err)
                        goto out_free;
        }

        if (znode->cnext || !ubifs_zn_dirty(znode)) {
                znode = dirty_cow_bottom_up(c, znode);
                if (IS_ERR(znode)) {
                        err = PTR_ERR(znode);
                        goto out_free;
                }
        }
        err = tnc_delete(c, znode, n);

out_free:
        kfree(dent);
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 = ubifs_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) {
                                ubifs_dump_znode(c, znode);
                                goto out_unlock;
                        }
                        dbg_tnck(key, "removing 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 fscrypt_name nm = {0};

        dbg_tnc("ino %lu", (unsigned long)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;
                        kfree(pxent);
                        return err;
                }

                xattr_inum = le64_to_cpu(xent->inum);
                dbg_tnc("xent '%s', ino %lu", xent->name,
                        (unsigned long)xattr_inum);

                ubifs_evict_xattr_inode(c, xattr_inum);

                fname_name(&nm) = xent->name;
                fname_len(&nm) = le16_to_cpu(xent->nlen);
                err = ubifs_tnc_remove_nm(c, &key1, &nm);
                if (err) {
                        kfree(pxent);
                        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(pxent);
                        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 fscrypt_name *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_tnck(key, "key ");
        ubifs_assert(c, is_hash_key(c, key));

        mutex_lock(&c->tnc_mutex);
        err = ubifs_lookup_level0(c, key, &znode, &n);
        if (unlikely(err < 0))
                goto out_unlock;

        if (fname_len(nm) > 0) {
                if (err) {
                        /* Handle collisions */
                        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 (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_inum(c, dkey) != key_inum(c, key) ||
            key_type(c, dkey) != type) {
                err = -ENOENT;
                goto out_free;
        }

        err = tnc_read_hashed_node(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, c->cmt_state == COMMIT_BROKEN);
        cnext = c->cnext;
        do {
                struct ubifs_znode *znode = cnext;

                cnext = cnext->cnext;
                if (ubifs_zn_obsolete(znode))
                        kfree(znode);
                else if (!ubifs_zn_cow(znode)) {
                        /*
                         * Don't forget to update clean znode count after
                         * committing failed, because ubifs will check this
                         * count while closing tnc. Non-obsolete znode could
                         * be re-dirtied during committing process, so dirty
                         * flag is untrustable. The flag 'COW_ZNODE' is set
                         * for each dirty znode before committing, and it is
                         * cleared as long as the znode become clean, so we
                         * can statistic clean znode count according to this
                         * flag.
                         */
                        atomic_long_inc(&c->clean_zn_cnt);
                        atomic_long_inc(&ubifs_clean_zn_cnt);
                }
        } 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)
{
        tnc_destroy_cnext(c);
        if (c->zroot.znode) {
                long n, freed;

                n = atomic_long_read(&c->clean_zn_cnt);
                freed = ubifs_destroy_tnc_subtree(c, c->zroot.znode);
                ubifs_assert(c, freed == n);
                atomic_long_sub(n, &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 for 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;

        ubifs_assert(c, key_type(c, key) < UBIFS_INVALID_KEY);

        /*
         * 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 = ubifs_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 'ubifs_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(c, 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 = ubifs_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;
}

/**
 * dbg_check_inode_size - check if inode size is correct.
 * @c: UBIFS file-system description object
 * @inode: inode to check
 * @size: inode size
 *
 * This function makes sure that the inode size (@size) is correct and it does
 * not have any pages beyond @size. Returns zero if the inode is OK, %-EINVAL
 * if it has a data page beyond @size, and other negative error code in case of
 * other errors.
 */
int dbg_check_inode_size(struct ubifs_info *c, const struct inode *inode,
                         loff_t size)
{
        int err, n;
        union ubifs_key from_key, to_key, *key;
        struct ubifs_znode *znode;
        unsigned int block;

        if (!S_ISREG(inode->i_mode))
                return 0;
        if (!dbg_is_chk_gen(c))
                return 0;

        block = (size + UBIFS_BLOCK_SIZE - 1) >> UBIFS_BLOCK_SHIFT;
        data_key_init(c, &from_key, inode->i_ino, block);
        highest_data_key(c, &to_key, inode->i_ino);

        mutex_lock(&c->tnc_mutex);
        err = ubifs_lookup_level0(c, &from_key, &znode, &n);
        if (err < 0)
                goto out_unlock;

        if (err) {
                key = &from_key;
                goto out_dump;
        }

        err = tnc_next(c, &znode, &n);
        if (err == -ENOENT) {
                err = 0;
                goto out_unlock;
        }
        if (err < 0)
                goto out_unlock;

        ubifs_assert(c, err == 0);
        key = &znode->zbranch[n].key;
        if (!key_in_range(c, key, &from_key, &to_key))
                goto out_unlock;

out_dump:
        block = key_block(c, key);
        ubifs_err(c, "inode %lu has size %lld, but there are data at offset %lld",
                  (unsigned long)inode->i_ino, size,
                  ((loff_t)block) << UBIFS_BLOCK_SHIFT);
        mutex_unlock(&c->tnc_mutex);
        ubifs_dump_inode(c, inode);
        dump_stack();
        return -EINVAL;

out_unlock:
        mutex_unlock(&c->tnc_mutex);
        return err;
}