// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2011 Red Hat, Inc.
 *
 * This file is released under the GPL.
 */

#include "dm-btree-internal.h"
#include "dm-space-map.h"
#include "dm-transaction-manager.h"

#include <linux/export.h>
#include <linux/device-mapper.h>

#define DM_MSG_PREFIX "btree"

/*
 *--------------------------------------------------------------
 * Array manipulation
 *--------------------------------------------------------------
 */
static void memcpy_disk(void *dest, const void *src, size_t len)
        __dm_written_to_disk(src)
{
        memcpy(dest, src, len);
        __dm_unbless_for_disk(src);
}

static void array_insert(void *base, size_t elt_size, unsigned int nr_elts,
                         unsigned int index, void *elt)
        __dm_written_to_disk(elt)
{
        if (index < nr_elts)
                memmove(base + (elt_size * (index + 1)),
                        base + (elt_size * index),
                        (nr_elts - index) * elt_size);

        memcpy_disk(base + (elt_size * index), elt, elt_size);
}

/*----------------------------------------------------------------*/

/* makes the assumption that no two keys are the same. */
static int bsearch(struct btree_node *n, uint64_t key, int want_hi)
{
        int lo = -1, hi = le32_to_cpu(n->header.nr_entries);

        while (hi - lo > 1) {
                int mid = lo + ((hi - lo) / 2);
                uint64_t mid_key = le64_to_cpu(n->keys[mid]);

                if (mid_key == key)
                        return mid;

                if (mid_key < key)
                        lo = mid;
                else
                        hi = mid;
        }

        return want_hi ? hi : lo;
}

int lower_bound(struct btree_node *n, uint64_t key)
{
        return bsearch(n, key, 0);
}

static int upper_bound(struct btree_node *n, uint64_t key)
{
        return bsearch(n, key, 1);
}

void inc_children(struct dm_transaction_manager *tm, struct btree_node *n,
                  struct dm_btree_value_type *vt)
{
        uint32_t nr_entries = le32_to_cpu(n->header.nr_entries);

        if (le32_to_cpu(n->header.flags) & INTERNAL_NODE)
                dm_tm_with_runs(tm, value_ptr(n, 0), nr_entries, dm_tm_inc_range);

        else if (vt->inc)
                vt->inc(vt->context, value_ptr(n, 0), nr_entries);
}

static int insert_at(size_t value_size, struct btree_node *node, unsigned int index,
                     uint64_t key, void *value)
        __dm_written_to_disk(value)
{
        uint32_t nr_entries = le32_to_cpu(node->header.nr_entries);
        uint32_t max_entries = le32_to_cpu(node->header.max_entries);
        __le64 key_le = cpu_to_le64(key);

        if (index > nr_entries ||
            index >= max_entries ||
            nr_entries >= max_entries) {
                DMERR("too many entries in btree node for insert");
                __dm_unbless_for_disk(value);
                return -ENOMEM;
        }

        __dm_bless_for_disk(&key_le);

        array_insert(node->keys, sizeof(*node->keys), nr_entries, index, &key_le);
        array_insert(value_base(node), value_size, nr_entries, index, value);
        node->header.nr_entries = cpu_to_le32(nr_entries + 1);

        return 0;
}

/*----------------------------------------------------------------*/

/*
 * We want 3n entries (for some n).  This works more nicely for repeated
 * insert remove loops than (2n + 1).
 */
static uint32_t calc_max_entries(size_t value_size, size_t block_size)
{
        uint32_t total, n;
        size_t elt_size = sizeof(uint64_t) + value_size; /* key + value */

        block_size -= sizeof(struct node_header);
        total = block_size / elt_size;
        n = total / 3;          /* rounds down */

        return 3 * n;
}

int dm_btree_empty(struct dm_btree_info *info, dm_block_t *root)
{
        int r;
        struct dm_block *b;
        struct btree_node *n;
        size_t block_size;
        uint32_t max_entries;

        r = new_block(info, &b);
        if (r < 0)
                return r;

        block_size = dm_bm_block_size(dm_tm_get_bm(info->tm));
        max_entries = calc_max_entries(info->value_type.size, block_size);

        n = dm_block_data(b);
        memset(n, 0, block_size);
        n->header.flags = cpu_to_le32(LEAF_NODE);
        n->header.nr_entries = cpu_to_le32(0);
        n->header.max_entries = cpu_to_le32(max_entries);
        n->header.value_size = cpu_to_le32(info->value_type.size);

        *root = dm_block_location(b);
        unlock_block(info, b);

        return 0;
}
EXPORT_SYMBOL_GPL(dm_btree_empty);

/*----------------------------------------------------------------*/

/*
 * Deletion uses a recursive algorithm, since we have limited stack space
 * we explicitly manage our own stack on the heap.
 */
#define MAX_SPINE_DEPTH 64
struct frame {
        struct dm_block *b;
        struct btree_node *n;
        unsigned int level;
        unsigned int nr_children;
        unsigned int current_child;
};

struct del_stack {
        struct dm_btree_info *info;
        struct dm_transaction_manager *tm;
        int top;
        struct frame spine[MAX_SPINE_DEPTH];
};

static int top_frame(struct del_stack *s, struct frame **f)
{
        if (s->top < 0) {
                DMERR("btree deletion stack empty");
                return -EINVAL;
        }

        *f = s->spine + s->top;

        return 0;
}

static int unprocessed_frames(struct del_stack *s)
{
        return s->top >= 0;
}

static void prefetch_children(struct del_stack *s, struct frame *f)
{
        unsigned int i;
        struct dm_block_manager *bm = dm_tm_get_bm(s->tm);

        for (i = 0; i < f->nr_children; i++)
                dm_bm_prefetch(bm, value64(f->n, i));
}

static bool is_internal_level(struct dm_btree_info *info, struct frame *f)
{
        return f->level < (info->levels - 1);
}

static int push_frame(struct del_stack *s, dm_block_t b, unsigned int level)
{
        int r;
        uint32_t ref_count;

        if (s->top >= MAX_SPINE_DEPTH - 1) {
                DMERR("btree deletion stack out of memory");
                return -ENOMEM;
        }

        r = dm_tm_ref(s->tm, b, &ref_count);
        if (r)
                return r;

        if (ref_count > 1)
                /*
                 * This is a shared node, so we can just decrement it's
                 * reference counter and leave the children.
                 */
                dm_tm_dec(s->tm, b);

        else {
                uint32_t flags;
                struct frame *f = s->spine + ++s->top;

                r = dm_tm_read_lock(s->tm, b, &btree_node_validator, &f->b);
                if (r) {
                        s->top--;
                        return r;
                }

                f->n = dm_block_data(f->b);
                f->level = level;
                f->nr_children = le32_to_cpu(f->n->header.nr_entries);
                f->current_child = 0;

                flags = le32_to_cpu(f->n->header.flags);
                if (flags & INTERNAL_NODE || is_internal_level(s->info, f))
                        prefetch_children(s, f);
        }

        return 0;
}

static void pop_frame(struct del_stack *s)
{
        struct frame *f = s->spine + s->top--;

        dm_tm_dec(s->tm, dm_block_location(f->b));
        dm_tm_unlock(s->tm, f->b);
}

static void unlock_all_frames(struct del_stack *s)
{
        struct frame *f;

        while (unprocessed_frames(s)) {
                f = s->spine + s->top--;
                dm_tm_unlock(s->tm, f->b);
        }
}

int dm_btree_del(struct dm_btree_info *info, dm_block_t root)
{
        int r;
        struct del_stack *s;

        /*
         * dm_btree_del() is called via an ioctl, as such should be
         * considered an FS op.  We can't recurse back into the FS, so we
         * allocate GFP_NOFS.
         */
        s = kmalloc_obj(*s, GFP_NOFS);
        if (!s)
                return -ENOMEM;
        s->info = info;
        s->tm = info->tm;
        s->top = -1;

        r = push_frame(s, root, 0);
        if (r)
                goto out;

        while (unprocessed_frames(s)) {
                uint32_t flags;
                struct frame *f;
                dm_block_t b;

                r = top_frame(s, &f);
                if (r)
                        goto out;

                if (f->current_child >= f->nr_children) {
                        pop_frame(s);
                        continue;
                }

                flags = le32_to_cpu(f->n->header.flags);
                if (flags & INTERNAL_NODE) {
                        b = value64(f->n, f->current_child);
                        f->current_child++;
                        r = push_frame(s, b, f->level);
                        if (r)
                                goto out;

                } else if (is_internal_level(info, f)) {
                        b = value64(f->n, f->current_child);
                        f->current_child++;
                        r = push_frame(s, b, f->level + 1);
                        if (r)
                                goto out;

                } else {
                        if (info->value_type.dec)
                                info->value_type.dec(info->value_type.context,
                                                     value_ptr(f->n, 0), f->nr_children);
                        pop_frame(s);
                }
        }
out:
        if (r) {
                /* cleanup all frames of del_stack */
                unlock_all_frames(s);
        }
        kfree(s);

        return r;
}
EXPORT_SYMBOL_GPL(dm_btree_del);

/*----------------------------------------------------------------*/

static int btree_lookup_raw(struct ro_spine *s, dm_block_t block, uint64_t key,
                            int (*search_fn)(struct btree_node *, uint64_t),
                            uint64_t *result_key, void *v, size_t value_size)
{
        int i, r;
        uint32_t flags, nr_entries;

        do {
                r = ro_step(s, block);
                if (r < 0)
                        return r;

                i = search_fn(ro_node(s), key);

                flags = le32_to_cpu(ro_node(s)->header.flags);
                nr_entries = le32_to_cpu(ro_node(s)->header.nr_entries);
                if (i < 0 || i >= nr_entries)
                        return -ENODATA;

                if (flags & INTERNAL_NODE)
                        block = value64(ro_node(s), i);

        } while (!(flags & LEAF_NODE));

        *result_key = le64_to_cpu(ro_node(s)->keys[i]);
        if (v)
                memcpy(v, value_ptr(ro_node(s), i), value_size);

        return 0;
}

int dm_btree_lookup(struct dm_btree_info *info, dm_block_t root,
                    uint64_t *keys, void *value_le)
{
        unsigned int level, last_level = info->levels - 1;
        int r = -ENODATA;
        uint64_t rkey;
        __le64 internal_value_le;
        struct ro_spine spine;

        init_ro_spine(&spine, info);
        for (level = 0; level < info->levels; level++) {
                size_t size;
                void *value_p;

                if (level == last_level) {
                        value_p = value_le;
                        size = info->value_type.size;

                } else {
                        value_p = &internal_value_le;
                        size = sizeof(uint64_t);
                }

                r = btree_lookup_raw(&spine, root, keys[level],
                                     lower_bound, &rkey,
                                     value_p, size);

                if (!r) {
                        if (rkey != keys[level]) {
                                exit_ro_spine(&spine);
                                return -ENODATA;
                        }
                } else {
                        exit_ro_spine(&spine);
                        return r;
                }

                root = le64_to_cpu(internal_value_le);
        }
        exit_ro_spine(&spine);

        return r;
}
EXPORT_SYMBOL_GPL(dm_btree_lookup);

static int dm_btree_lookup_next_single(struct dm_btree_info *info, dm_block_t root,
                                       uint64_t key, uint64_t *rkey, void *value_le)
{
        int r, i;
        uint32_t flags, nr_entries;
        struct dm_block *node;
        struct btree_node *n;

        r = bn_read_lock(info, root, &node);
        if (r)
                return r;

        n = dm_block_data(node);
        flags = le32_to_cpu(n->header.flags);
        nr_entries = le32_to_cpu(n->header.nr_entries);

        if (flags & INTERNAL_NODE) {
                i = lower_bound(n, key);
                if (i < 0) {
                        /*
                         * avoid early -ENODATA return when all entries are
                         * higher than the search @key.
                         */
                        i = 0;
                }
                if (i >= nr_entries) {
                        r = -ENODATA;
                        goto out;
                }

                r = dm_btree_lookup_next_single(info, value64(n, i), key, rkey, value_le);
                if (r == -ENODATA && i < (nr_entries - 1)) {
                        i++;
                        r = dm_btree_lookup_next_single(info, value64(n, i), key, rkey, value_le);
                }

        } else {
                i = upper_bound(n, key);
                if (i < 0 || i >= nr_entries) {
                        r = -ENODATA;
                        goto out;
                }

                *rkey = le64_to_cpu(n->keys[i]);
                memcpy(value_le, value_ptr(n, i), info->value_type.size);
        }
out:
        dm_tm_unlock(info->tm, node);
        return r;
}

int dm_btree_lookup_next(struct dm_btree_info *info, dm_block_t root,
                         uint64_t *keys, uint64_t *rkey, void *value_le)
{
        unsigned int level;
        int r = -ENODATA;
        __le64 internal_value_le;
        struct ro_spine spine;

        init_ro_spine(&spine, info);
        for (level = 0; level < info->levels - 1u; level++) {
                r = btree_lookup_raw(&spine, root, keys[level],
                                     lower_bound, rkey,
                                     &internal_value_le, sizeof(uint64_t));
                if (r)
                        goto out;

                if (*rkey != keys[level]) {
                        r = -ENODATA;
                        goto out;
                }

                root = le64_to_cpu(internal_value_le);
        }

        r = dm_btree_lookup_next_single(info, root, keys[level], rkey, value_le);
out:
        exit_ro_spine(&spine);
        return r;
}
EXPORT_SYMBOL_GPL(dm_btree_lookup_next);

/*----------------------------------------------------------------*/

/*
 * Copies entries from one region of a btree node to another.  The regions
 * must not overlap.
 */
static void copy_entries(struct btree_node *dest, unsigned int dest_offset,
                         struct btree_node *src, unsigned int src_offset,
                         unsigned int count)
{
        size_t value_size = le32_to_cpu(dest->header.value_size);

        memcpy(dest->keys + dest_offset, src->keys + src_offset, count * sizeof(uint64_t));
        memcpy(value_ptr(dest, dest_offset), value_ptr(src, src_offset), count * value_size);
}

/*
 * Moves entries from one region fo a btree node to another.  The regions
 * may overlap.
 */
static void move_entries(struct btree_node *dest, unsigned int dest_offset,
                         struct btree_node *src, unsigned int src_offset,
                         unsigned int count)
{
        size_t value_size = le32_to_cpu(dest->header.value_size);

        memmove(dest->keys + dest_offset, src->keys + src_offset, count * sizeof(uint64_t));
        memmove(value_ptr(dest, dest_offset), value_ptr(src, src_offset), count * value_size);
}

/*
 * Erases the first 'count' entries of a btree node, shifting following
 * entries down into their place.
 */
static void shift_down(struct btree_node *n, unsigned int count)
{
        move_entries(n, 0, n, count, le32_to_cpu(n->header.nr_entries) - count);
}

/*
 * Moves entries in a btree node up 'count' places, making space for
 * new entries at the start of the node.
 */
static void shift_up(struct btree_node *n, unsigned int count)
{
        move_entries(n, count, n, 0, le32_to_cpu(n->header.nr_entries));
}

/*
 * Redistributes entries between two btree nodes to make them
 * have similar numbers of entries.
 */
static void redistribute2(struct btree_node *left, struct btree_node *right)
{
        unsigned int nr_left = le32_to_cpu(left->header.nr_entries);
        unsigned int nr_right = le32_to_cpu(right->header.nr_entries);
        unsigned int total = nr_left + nr_right;
        unsigned int target_left = total / 2;
        unsigned int target_right = total - target_left;

        if (nr_left < target_left) {
                unsigned int delta = target_left - nr_left;

                copy_entries(left, nr_left, right, 0, delta);
                shift_down(right, delta);
        } else if (nr_left > target_left) {
                unsigned int delta = nr_left - target_left;

                if (nr_right)
                        shift_up(right, delta);
                copy_entries(right, 0, left, target_left, delta);
        }

        left->header.nr_entries = cpu_to_le32(target_left);
        right->header.nr_entries = cpu_to_le32(target_right);
}

/*
 * Redistribute entries between three nodes.  Assumes the central
 * node is empty.
 */
static void redistribute3(struct btree_node *left, struct btree_node *center,
                          struct btree_node *right)
{
        unsigned int nr_left = le32_to_cpu(left->header.nr_entries);
        unsigned int nr_center = le32_to_cpu(center->header.nr_entries);
        unsigned int nr_right = le32_to_cpu(right->header.nr_entries);
        unsigned int total, target_left, target_center, target_right;

        BUG_ON(nr_center);

        total = nr_left + nr_right;
        target_left = total / 3;
        target_center = (total - target_left) / 2;
        target_right = (total - target_left - target_center);

        if (nr_left < target_left) {
                unsigned int left_short = target_left - nr_left;

                copy_entries(left, nr_left, right, 0, left_short);
                copy_entries(center, 0, right, left_short, target_center);
                shift_down(right, nr_right - target_right);

        } else if (nr_left < (target_left + target_center)) {
                unsigned int left_to_center = nr_left - target_left;

                copy_entries(center, 0, left, target_left, left_to_center);
                copy_entries(center, left_to_center, right, 0, target_center - left_to_center);
                shift_down(right, nr_right - target_right);

        } else {
                unsigned int right_short = target_right - nr_right;

                shift_up(right, right_short);
                copy_entries(right, 0, left, nr_left - right_short, right_short);
                copy_entries(center, 0, left, target_left, nr_left - target_left);
        }

        left->header.nr_entries = cpu_to_le32(target_left);
        center->header.nr_entries = cpu_to_le32(target_center);
        right->header.nr_entries = cpu_to_le32(target_right);
}

/*
 * Splits a node by creating a sibling node and shifting half the nodes
 * contents across.  Assumes there is a parent node, and it has room for
 * another child.
 *
 * Before:
 *        +--------+
 *        | Parent |
 *        +--------+
 *           |
 *           v
 *      +----------+
 *      | A ++++++ |
 *      +----------+
 *
 *
 * After:
 *              +--------+
 *              | Parent |
 *              +--------+
 *                |     |
 *                v     +------+
 *          +---------+        |
 *          | A* +++  |        v
 *          +---------+   +-------+
 *                        | B +++ |
 *                        +-------+
 *
 * Where A* is a shadow of A.
 */
static int split_one_into_two(struct shadow_spine *s, unsigned int parent_index,
                              struct dm_btree_value_type *vt, uint64_t key)
{
        int r;
        struct dm_block *left, *right, *parent;
        struct btree_node *ln, *rn, *pn;
        __le64 location;

        left = shadow_current(s);

        r = new_block(s->info, &right);
        if (r < 0)
                return r;

        ln = dm_block_data(left);
        rn = dm_block_data(right);

        rn->header.flags = ln->header.flags;
        rn->header.nr_entries = cpu_to_le32(0);
        rn->header.max_entries = ln->header.max_entries;
        rn->header.value_size = ln->header.value_size;
        redistribute2(ln, rn);

        /* patch up the parent */
        parent = shadow_parent(s);
        pn = dm_block_data(parent);

        location = cpu_to_le64(dm_block_location(right));
        __dm_bless_for_disk(&location);
        r = insert_at(sizeof(__le64), pn, parent_index + 1,
                      le64_to_cpu(rn->keys[0]), &location);
        if (r) {
                unlock_block(s->info, right);
                return r;
        }

        /* patch up the spine */
        if (key < le64_to_cpu(rn->keys[0])) {
                unlock_block(s->info, right);
                s->nodes[1] = left;
        } else {
                unlock_block(s->info, left);
                s->nodes[1] = right;
        }

        return 0;
}

/*
 * We often need to modify a sibling node.  This function shadows a particular
 * child of the given parent node.  Making sure to update the parent to point
 * to the new shadow.
 */
static int shadow_child(struct dm_btree_info *info, struct dm_btree_value_type *vt,
                        struct btree_node *parent, unsigned int index,
                        struct dm_block **result)
{
        int r, inc;
        dm_block_t root;
        struct btree_node *node;

        root = value64(parent, index);

        r = dm_tm_shadow_block(info->tm, root, &btree_node_validator,
                               result, &inc);
        if (r)
                return r;

        node = dm_block_data(*result);

        if (inc)
                inc_children(info->tm, node, vt);

        *((__le64 *) value_ptr(parent, index)) =
                cpu_to_le64(dm_block_location(*result));

        return 0;
}

/*
 * Splits two nodes into three.  This is more work, but results in fuller
 * nodes, so saves metadata space.
 */
static int split_two_into_three(struct shadow_spine *s, unsigned int parent_index,
                                struct dm_btree_value_type *vt, uint64_t key)
{
        int r;
        unsigned int middle_index;
        struct dm_block *left, *middle, *right, *parent;
        struct btree_node *ln, *rn, *mn, *pn;
        __le64 location;

        parent = shadow_parent(s);
        pn = dm_block_data(parent);

        if (parent_index == 0) {
                middle_index = 1;
                left = shadow_current(s);
                r = shadow_child(s->info, vt, pn, parent_index + 1, &right);
                if (r)
                        return r;
        } else {
                middle_index = parent_index;
                right = shadow_current(s);
                r = shadow_child(s->info, vt, pn, parent_index - 1, &left);
                if (r)
                        return r;
        }

        r = new_block(s->info, &middle);
        if (r < 0)
                return r;

        ln = dm_block_data(left);
        mn = dm_block_data(middle);
        rn = dm_block_data(right);

        mn->header.nr_entries = cpu_to_le32(0);
        mn->header.flags = ln->header.flags;
        mn->header.max_entries = ln->header.max_entries;
        mn->header.value_size = ln->header.value_size;

        redistribute3(ln, mn, rn);

        /* patch up the parent */
        pn->keys[middle_index] = rn->keys[0];
        location = cpu_to_le64(dm_block_location(middle));
        __dm_bless_for_disk(&location);
        r = insert_at(sizeof(__le64), pn, middle_index,
                      le64_to_cpu(mn->keys[0]), &location);
        if (r) {
                if (shadow_current(s) != left)
                        unlock_block(s->info, left);

                unlock_block(s->info, middle);

                if (shadow_current(s) != right)
                        unlock_block(s->info, right);

                return r;
        }


        /* patch up the spine */
        if (key < le64_to_cpu(mn->keys[0])) {
                unlock_block(s->info, middle);
                unlock_block(s->info, right);
                s->nodes[1] = left;
        } else if (key < le64_to_cpu(rn->keys[0])) {
                unlock_block(s->info, left);
                unlock_block(s->info, right);
                s->nodes[1] = middle;
        } else {
                unlock_block(s->info, left);
                unlock_block(s->info, middle);
                s->nodes[1] = right;
        }

        return 0;
}

/*----------------------------------------------------------------*/

/*
 * Splits a node by creating two new children beneath the given node.
 *
 * Before:
 *        +----------+
 *        | A ++++++ |
 *        +----------+
 *
 *
 * After:
 *      +------------+
 *      | A (shadow) |
 *      +------------+
 *          |   |
 *   +------+   +----+
 *   |               |
 *   v               v
 * +-------+     +-------+
 * | B +++ |     | C +++ |
 * +-------+     +-------+
 */
static int btree_split_beneath(struct shadow_spine *s, uint64_t key)
{
        int r;
        size_t size;
        unsigned int nr_left, nr_right;
        struct dm_block *left, *right, *new_parent;
        struct btree_node *pn, *ln, *rn;
        __le64 val;

        new_parent = shadow_current(s);

        pn = dm_block_data(new_parent);
        size = le32_to_cpu(pn->header.flags) & INTERNAL_NODE ?
                sizeof(__le64) : s->info->value_type.size;

        /* create & init the left block */
        r = new_block(s->info, &left);
        if (r < 0)
                return r;

        ln = dm_block_data(left);
        nr_left = le32_to_cpu(pn->header.nr_entries) / 2;

        ln->header.flags = pn->header.flags;
        ln->header.nr_entries = cpu_to_le32(nr_left);
        ln->header.max_entries = pn->header.max_entries;
        ln->header.value_size = pn->header.value_size;
        memcpy(ln->keys, pn->keys, nr_left * sizeof(pn->keys[0]));
        memcpy(value_ptr(ln, 0), value_ptr(pn, 0), nr_left * size);

        /* create & init the right block */
        r = new_block(s->info, &right);
        if (r < 0) {
                unlock_block(s->info, left);
                return r;
        }

        rn = dm_block_data(right);
        nr_right = le32_to_cpu(pn->header.nr_entries) - nr_left;

        rn->header.flags = pn->header.flags;
        rn->header.nr_entries = cpu_to_le32(nr_right);
        rn->header.max_entries = pn->header.max_entries;
        rn->header.value_size = pn->header.value_size;
        memcpy(rn->keys, pn->keys + nr_left, nr_right * sizeof(pn->keys[0]));
        memcpy(value_ptr(rn, 0), value_ptr(pn, nr_left),
               nr_right * size);

        /* new_parent should just point to l and r now */
        pn->header.flags = cpu_to_le32(INTERNAL_NODE);
        pn->header.nr_entries = cpu_to_le32(2);
        pn->header.max_entries = cpu_to_le32(
                calc_max_entries(sizeof(__le64),
                                 dm_bm_block_size(
                                         dm_tm_get_bm(s->info->tm))));
        pn->header.value_size = cpu_to_le32(sizeof(__le64));

        val = cpu_to_le64(dm_block_location(left));
        __dm_bless_for_disk(&val);
        pn->keys[0] = ln->keys[0];
        memcpy_disk(value_ptr(pn, 0), &val, sizeof(__le64));

        val = cpu_to_le64(dm_block_location(right));
        __dm_bless_for_disk(&val);
        pn->keys[1] = rn->keys[0];
        memcpy_disk(value_ptr(pn, 1), &val, sizeof(__le64));

        unlock_block(s->info, left);
        unlock_block(s->info, right);
        return 0;
}

/*----------------------------------------------------------------*/

/*
 * Redistributes a node's entries with its left sibling.
 */
static int rebalance_left(struct shadow_spine *s, struct dm_btree_value_type *vt,
                          unsigned int parent_index, uint64_t key)
{
        int r;
        struct dm_block *sib;
        struct btree_node *left, *right, *parent = dm_block_data(shadow_parent(s));

        r = shadow_child(s->info, vt, parent, parent_index - 1, &sib);
        if (r)
                return r;

        left = dm_block_data(sib);
        right = dm_block_data(shadow_current(s));
        redistribute2(left, right);
        *key_ptr(parent, parent_index) = right->keys[0];

        if (key < le64_to_cpu(right->keys[0])) {
                unlock_block(s->info, s->nodes[1]);
                s->nodes[1] = sib;
        } else {
                unlock_block(s->info, sib);
        }

        return 0;
}

/*
 * Redistributes a nodes entries with its right sibling.
 */
static int rebalance_right(struct shadow_spine *s, struct dm_btree_value_type *vt,
                           unsigned int parent_index, uint64_t key)
{
        int r;
        struct dm_block *sib;
        struct btree_node *left, *right, *parent = dm_block_data(shadow_parent(s));

        r = shadow_child(s->info, vt, parent, parent_index + 1, &sib);
        if (r)
                return r;

        left = dm_block_data(shadow_current(s));
        right = dm_block_data(sib);
        redistribute2(left, right);
        *key_ptr(parent, parent_index + 1) = right->keys[0];

        if (key < le64_to_cpu(right->keys[0])) {
                unlock_block(s->info, sib);
        } else {
                unlock_block(s->info, s->nodes[1]);
                s->nodes[1] = sib;
        }

        return 0;
}

/*
 * Returns the number of spare entries in a node.
 */
static int get_node_free_space(struct dm_btree_info *info, dm_block_t b, unsigned int *space)
{
        int r;
        unsigned int nr_entries;
        struct dm_block *block;
        struct btree_node *node;

        r = bn_read_lock(info, b, &block);
        if (r)
                return r;

        node = dm_block_data(block);
        nr_entries = le32_to_cpu(node->header.nr_entries);
        *space = le32_to_cpu(node->header.max_entries) - nr_entries;

        unlock_block(info, block);
        return 0;
}

/*
 * Make space in a node, either by moving some entries to a sibling,
 * or creating a new sibling node.  SPACE_THRESHOLD defines the minimum
 * number of free entries that must be in the sibling to make the move
 * worth while.  If the siblings are shared (eg, part of a snapshot),
 * then they are not touched, since this break sharing and so consume
 * more space than we save.
 */
#define SPACE_THRESHOLD 8
static int rebalance_or_split(struct shadow_spine *s, struct dm_btree_value_type *vt,
                              unsigned int parent_index, uint64_t key)
{
        int r;
        struct btree_node *parent = dm_block_data(shadow_parent(s));
        unsigned int nr_parent = le32_to_cpu(parent->header.nr_entries);
        unsigned int free_space;
        int left_shared = 0, right_shared = 0;

        /* Should we move entries to the left sibling? */
        if (parent_index > 0) {
                dm_block_t left_b = value64(parent, parent_index - 1);

                r = dm_tm_block_is_shared(s->info->tm, left_b, &left_shared);
                if (r)
                        return r;

                if (!left_shared) {
                        r = get_node_free_space(s->info, left_b, &free_space);
                        if (r)
                                return r;

                        if (free_space >= SPACE_THRESHOLD)
                                return rebalance_left(s, vt, parent_index, key);
                }
        }

        /* Should we move entries to the right sibling? */
        if (parent_index < (nr_parent - 1)) {
                dm_block_t right_b = value64(parent, parent_index + 1);

                r = dm_tm_block_is_shared(s->info->tm, right_b, &right_shared);
                if (r)
                        return r;

                if (!right_shared) {
                        r = get_node_free_space(s->info, right_b, &free_space);
                        if (r)
                                return r;

                        if (free_space >= SPACE_THRESHOLD)
                                return rebalance_right(s, vt, parent_index, key);
                }
        }

        /*
         * We need to split the node, normally we split two nodes
         * into three.  But when inserting a sequence that is either
         * monotonically increasing or decreasing it's better to split
         * a single node into two.
         */
        if (left_shared || right_shared || (nr_parent <= 2) ||
            (parent_index == 0) || (parent_index + 1 == nr_parent)) {
                return split_one_into_two(s, parent_index, vt, key);
        } else {
                return split_two_into_three(s, parent_index, vt, key);
        }
}

/*
 * Does the node contain a particular key?
 */
static bool contains_key(struct btree_node *node, uint64_t key)
{
        int i = lower_bound(node, key);

        if (i >= 0 && le64_to_cpu(node->keys[i]) == key)
                return true;

        return false;
}

/*
 * In general we preemptively make sure there's a free entry in every
 * node on the spine when doing an insert.  But we can avoid that with
 * leaf nodes if we know it's an overwrite.
 */
static bool has_space_for_insert(struct btree_node *node, uint64_t key)
{
        if (node->header.nr_entries == node->header.max_entries) {
                if (le32_to_cpu(node->header.flags) & LEAF_NODE) {
                        /* we don't need space if it's an overwrite */
                        return contains_key(node, key);
                }

                return false;
        }

        return true;
}

static int btree_insert_raw(struct shadow_spine *s, dm_block_t root,
                            struct dm_btree_value_type *vt,
                            uint64_t key, unsigned int *index)
{
        int r, i = *index, top = 1;
        struct btree_node *node;

        for (;;) {
                r = shadow_step(s, root, vt);
                if (r < 0)
                        return r;

                node = dm_block_data(shadow_current(s));

                /*
                 * We have to patch up the parent node, ugly, but I don't
                 * see a way to do this automatically as part of the spine
                 * op.
                 */
                if (shadow_has_parent(s) && i >= 0) { /* FIXME: second clause unness. */
                        __le64 location = cpu_to_le64(dm_block_location(shadow_current(s)));

                        __dm_bless_for_disk(&location);
                        memcpy_disk(value_ptr(dm_block_data(shadow_parent(s)), i),
                                    &location, sizeof(__le64));
                }

                node = dm_block_data(shadow_current(s));

                if (!has_space_for_insert(node, key)) {
                        if (top)
                                r = btree_split_beneath(s, key);
                        else
                                r = rebalance_or_split(s, vt, i, key);

                        if (r < 0)
                                return r;

                        /* making space can cause the current node to change */
                        node = dm_block_data(shadow_current(s));
                }

                i = lower_bound(node, key);

                if (le32_to_cpu(node->header.flags) & LEAF_NODE)
                        break;

                if (i < 0) {
                        /* change the bounds on the lowest key */
                        node->keys[0] = cpu_to_le64(key);
                        i = 0;
                }

                root = value64(node, i);
                top = 0;
        }

        if (i < 0 || le64_to_cpu(node->keys[i]) != key)
                i++;

        *index = i;
        return 0;
}

static int __btree_get_overwrite_leaf(struct shadow_spine *s, dm_block_t root,
                                      uint64_t key, int *index)
{
        int r, i = -1;
        struct btree_node *node;

        *index = 0;
        for (;;) {
                r = shadow_step(s, root, &s->info->value_type);
                if (r < 0)
                        return r;

                node = dm_block_data(shadow_current(s));

                /*
                 * We have to patch up the parent node, ugly, but I don't
                 * see a way to do this automatically as part of the spine
                 * op.
                 */
                if (shadow_has_parent(s) && i >= 0) {
                        __le64 location = cpu_to_le64(dm_block_location(shadow_current(s)));

                        __dm_bless_for_disk(&location);
                        memcpy_disk(value_ptr(dm_block_data(shadow_parent(s)), i),
                                    &location, sizeof(__le64));
                }

                node = dm_block_data(shadow_current(s));
                i = lower_bound(node, key);

                BUG_ON(i < 0);
                BUG_ON(i >= le32_to_cpu(node->header.nr_entries));

                if (le32_to_cpu(node->header.flags) & LEAF_NODE) {
                        if (key != le64_to_cpu(node->keys[i]))
                                return -EINVAL;
                        break;
                }

                root = value64(node, i);
        }

        *index = i;
        return 0;
}

int btree_get_overwrite_leaf(struct dm_btree_info *info, dm_block_t root,
                             uint64_t key, int *index,
                             dm_block_t *new_root, struct dm_block **leaf)
{
        int r;
        struct shadow_spine spine;

        BUG_ON(info->levels > 1);
        init_shadow_spine(&spine, info);
        r = __btree_get_overwrite_leaf(&spine, root, key, index);
        if (!r) {
                *new_root = shadow_root(&spine);
                *leaf = shadow_current(&spine);

                /*
                 * Decrement the count so exit_shadow_spine() doesn't
                 * unlock the leaf.
                 */
                spine.count--;
        }
        exit_shadow_spine(&spine);

        return r;
}

static bool need_insert(struct btree_node *node, uint64_t *keys,
                        unsigned int level, unsigned int index)
{
        return ((index >= le32_to_cpu(node->header.nr_entries)) ||
                (le64_to_cpu(node->keys[index]) != keys[level]));
}

static int insert(struct dm_btree_info *info, dm_block_t root,
                  uint64_t *keys, void *value, dm_block_t *new_root,
                  int *inserted)
                  __dm_written_to_disk(value)
{
        int r;
        unsigned int level, index = -1, last_level = info->levels - 1;
        dm_block_t block = root;
        struct shadow_spine spine;
        struct btree_node *n;
        struct dm_btree_value_type le64_type;

        init_le64_type(info->tm, &le64_type);
        init_shadow_spine(&spine, info);

        for (level = 0; level < (info->levels - 1); level++) {
                r = btree_insert_raw(&spine, block, &le64_type, keys[level], &index);
                if (r < 0)
                        goto bad;

                n = dm_block_data(shadow_current(&spine));

                if (need_insert(n, keys, level, index)) {
                        dm_block_t new_tree;
                        __le64 new_le;

                        r = dm_btree_empty(info, &new_tree);
                        if (r < 0)
                                goto bad;

                        new_le = cpu_to_le64(new_tree);
                        __dm_bless_for_disk(&new_le);

                        r = insert_at(sizeof(uint64_t), n, index,
                                      keys[level], &new_le);
                        if (r)
                                goto bad;
                }

                if (level < last_level)
                        block = value64(n, index);
        }

        r = btree_insert_raw(&spine, block, &info->value_type,
                             keys[level], &index);
        if (r < 0)
                goto bad;

        n = dm_block_data(shadow_current(&spine));

        if (need_insert(n, keys, level, index)) {
                if (inserted)
                        *inserted = 1;

                r = insert_at(info->value_type.size, n, index,
                              keys[level], value);
                if (r)
                        goto bad_unblessed;
        } else {
                if (inserted)
                        *inserted = 0;

                if (info->value_type.dec &&
                    (!info->value_type.equal ||
                     !info->value_type.equal(
                             info->value_type.context,
                             value_ptr(n, index),
                             value))) {
                        info->value_type.dec(info->value_type.context,
                                             value_ptr(n, index), 1);
                }
                memcpy_disk(value_ptr(n, index),
                            value, info->value_type.size);
        }

        *new_root = shadow_root(&spine);
        exit_shadow_spine(&spine);

        return 0;

bad:
        __dm_unbless_for_disk(value);
bad_unblessed:
        exit_shadow_spine(&spine);
        return r;
}

int dm_btree_insert(struct dm_btree_info *info, dm_block_t root,
                    uint64_t *keys, void *value, dm_block_t *new_root)
        __dm_written_to_disk(value)
{
        return insert(info, root, keys, value, new_root, NULL);
}
EXPORT_SYMBOL_GPL(dm_btree_insert);

int dm_btree_insert_notify(struct dm_btree_info *info, dm_block_t root,
                           uint64_t *keys, void *value, dm_block_t *new_root,
                           int *inserted)
        __dm_written_to_disk(value)
{
        return insert(info, root, keys, value, new_root, inserted);
}
EXPORT_SYMBOL_GPL(dm_btree_insert_notify);

/*----------------------------------------------------------------*/

static int find_key(struct ro_spine *s, dm_block_t block, bool find_highest,
                    uint64_t *result_key, dm_block_t *next_block)
{
        int i, r;
        uint32_t flags;

        do {
                r = ro_step(s, block);
                if (r < 0)
                        return r;

                flags = le32_to_cpu(ro_node(s)->header.flags);
                i = le32_to_cpu(ro_node(s)->header.nr_entries);
                if (!i)
                        return -ENODATA;

                i--;

                if (find_highest)
                        *result_key = le64_to_cpu(ro_node(s)->keys[i]);
                else
                        *result_key = le64_to_cpu(ro_node(s)->keys[0]);

                if (next_block || flags & INTERNAL_NODE) {
                        if (find_highest)
                                block = value64(ro_node(s), i);
                        else
                                block = value64(ro_node(s), 0);
                }

        } while (flags & INTERNAL_NODE);

        if (next_block)
                *next_block = block;
        return 0;
}

static int dm_btree_find_key(struct dm_btree_info *info, dm_block_t root,
                             bool find_highest, uint64_t *result_keys)
{
        int r = 0, count = 0, level;
        struct ro_spine spine;

        init_ro_spine(&spine, info);
        for (level = 0; level < info->levels; level++) {
                r = find_key(&spine, root, find_highest, result_keys + level,
                             level == info->levels - 1 ? NULL : &root);
                if (r == -ENODATA) {
                        r = 0;
                        break;

                } else if (r)
                        break;

                count++;
        }
        exit_ro_spine(&spine);

        return r ? r : count;
}

int dm_btree_find_highest_key(struct dm_btree_info *info, dm_block_t root,
                              uint64_t *result_keys)
{
        return dm_btree_find_key(info, root, true, result_keys);
}
EXPORT_SYMBOL_GPL(dm_btree_find_highest_key);

int dm_btree_find_lowest_key(struct dm_btree_info *info, dm_block_t root,
                             uint64_t *result_keys)
{
        return dm_btree_find_key(info, root, false, result_keys);
}
EXPORT_SYMBOL_GPL(dm_btree_find_lowest_key);

/*----------------------------------------------------------------*/

/*
 * FIXME: We shouldn't use a recursive algorithm when we have limited stack
 * space.  Also this only works for single level trees.
 */
static int walk_node(struct dm_btree_info *info, dm_block_t block,
                     int (*fn)(void *context, uint64_t *keys, void *leaf),
                     void *context)
{
        int r;
        unsigned int i, nr;
        struct dm_block *node;
        struct btree_node *n;
        uint64_t keys;

        r = bn_read_lock(info, block, &node);
        if (r)
                return r;

        n = dm_block_data(node);

        nr = le32_to_cpu(n->header.nr_entries);
        for (i = 0; i < nr; i++) {
                if (le32_to_cpu(n->header.flags) & INTERNAL_NODE) {
                        r = walk_node(info, value64(n, i), fn, context);
                        if (r)
                                goto out;
                } else {
                        keys = le64_to_cpu(*key_ptr(n, i));
                        r = fn(context, &keys, value_ptr(n, i));
                        if (r)
                                goto out;
                }
        }

out:
        dm_tm_unlock(info->tm, node);
        return r;
}

int dm_btree_walk(struct dm_btree_info *info, dm_block_t root,
                  int (*fn)(void *context, uint64_t *keys, void *leaf),
                  void *context)
{
        BUG_ON(info->levels > 1);
        return walk_node(info, root, fn, context);
}
EXPORT_SYMBOL_GPL(dm_btree_walk);

/*----------------------------------------------------------------*/

static void prefetch_values(struct dm_btree_cursor *c)
{
        unsigned int i, nr;
        __le64 value_le;
        struct cursor_node *n = c->nodes + c->depth - 1;
        struct btree_node *bn = dm_block_data(n->b);
        struct dm_block_manager *bm = dm_tm_get_bm(c->info->tm);

        BUG_ON(c->info->value_type.size != sizeof(value_le));

        nr = le32_to_cpu(bn->header.nr_entries);
        for (i = 0; i < nr; i++) {
                memcpy(&value_le, value_ptr(bn, i), sizeof(value_le));
                dm_bm_prefetch(bm, le64_to_cpu(value_le));
        }
}

static bool leaf_node(struct dm_btree_cursor *c)
{
        struct cursor_node *n = c->nodes + c->depth - 1;
        struct btree_node *bn = dm_block_data(n->b);

        return le32_to_cpu(bn->header.flags) & LEAF_NODE;
}

static int push_node(struct dm_btree_cursor *c, dm_block_t b)
{
        int r;
        struct cursor_node *n = c->nodes + c->depth;

        if (c->depth >= DM_BTREE_CURSOR_MAX_DEPTH - 1) {
                DMERR("couldn't push cursor node, stack depth too high");
                return -EINVAL;
        }

        r = bn_read_lock(c->info, b, &n->b);
        if (r)
                return r;

        n->index = 0;
        c->depth++;

        if (c->prefetch_leaves || !leaf_node(c))
                prefetch_values(c);

        return 0;
}

static void pop_node(struct dm_btree_cursor *c)
{
        c->depth--;
        unlock_block(c->info, c->nodes[c->depth].b);
}

static int inc_or_backtrack(struct dm_btree_cursor *c)
{
        struct cursor_node *n;
        struct btree_node *bn;

        for (;;) {
                if (!c->depth)
                        return -ENODATA;

                n = c->nodes + c->depth - 1;
                bn = dm_block_data(n->b);

                n->index++;
                if (n->index < le32_to_cpu(bn->header.nr_entries))
                        break;

                pop_node(c);
        }

        return 0;
}

static int find_leaf(struct dm_btree_cursor *c)
{
        int r = 0;
        struct cursor_node *n;
        struct btree_node *bn;
        __le64 value_le;

        for (;;) {
                n = c->nodes + c->depth - 1;
                bn = dm_block_data(n->b);

                if (le32_to_cpu(bn->header.flags) & LEAF_NODE)
                        break;

                memcpy(&value_le, value_ptr(bn, n->index), sizeof(value_le));
                r = push_node(c, le64_to_cpu(value_le));
                if (r) {
                        DMERR("push_node failed");
                        break;
                }
        }

        if (!r && (le32_to_cpu(bn->header.nr_entries) == 0))
                return -ENODATA;

        return r;
}

int dm_btree_cursor_begin(struct dm_btree_info *info, dm_block_t root,
                          bool prefetch_leaves, struct dm_btree_cursor *c)
{
        int r;

        c->info = info;
        c->root = root;
        c->depth = 0;
        c->prefetch_leaves = prefetch_leaves;

        r = push_node(c, root);
        if (r)
                return r;

        return find_leaf(c);
}
EXPORT_SYMBOL_GPL(dm_btree_cursor_begin);

void dm_btree_cursor_end(struct dm_btree_cursor *c)
{
        while (c->depth)
                pop_node(c);
}
EXPORT_SYMBOL_GPL(dm_btree_cursor_end);

int dm_btree_cursor_next(struct dm_btree_cursor *c)
{
        int r = inc_or_backtrack(c);

        if (!r) {
                r = find_leaf(c);
                if (r)
                        DMERR("find_leaf failed");
        }

        return r;
}
EXPORT_SYMBOL_GPL(dm_btree_cursor_next);

int dm_btree_cursor_skip(struct dm_btree_cursor *c, uint32_t count)
{
        int r = 0;

        while (count-- && !r)
                r = dm_btree_cursor_next(c);

        return r;
}
EXPORT_SYMBOL_GPL(dm_btree_cursor_skip);

int dm_btree_cursor_get_value(struct dm_btree_cursor *c, uint64_t *key, void *value_le)
{
        if (c->depth) {
                struct cursor_node *n = c->nodes + c->depth - 1;
                struct btree_node *bn = dm_block_data(n->b);

                if (le32_to_cpu(bn->header.flags) & INTERNAL_NODE)
                        return -EINVAL;

                *key = le64_to_cpu(*key_ptr(bn, n->index));
                memcpy(value_le, value_ptr(bn, n->index), c->info->value_type.size);
                return 0;

        } else
                return -ENODATA;
}
EXPORT_SYMBOL_GPL(dm_btree_cursor_get_value);