// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2017 Christoph Hellwig.
 */

#include "xfs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_bit.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_inode.h"
#include "xfs_trace.h"

/*
 * In-core extent record layout:
 *
 * +-------+----------------------------+
 * | 00:53 | all 54 bits of startoff    |
 * | 54:63 | low 10 bits of startblock  |
 * +-------+----------------------------+
 * | 00:20 | all 21 bits of length      |
 * |    21 | unwritten extent bit       |
 * | 22:63 | high 42 bits of startblock |
 * +-------+----------------------------+
 */
#define XFS_IEXT_STARTOFF_MASK          xfs_mask64lo(BMBT_STARTOFF_BITLEN)
#define XFS_IEXT_LENGTH_MASK            xfs_mask64lo(BMBT_BLOCKCOUNT_BITLEN)
#define XFS_IEXT_STARTBLOCK_MASK        xfs_mask64lo(BMBT_STARTBLOCK_BITLEN)

struct xfs_iext_rec {
        uint64_t                        lo;
        uint64_t                        hi;
};

/*
 * Given that the length can't be a zero, only an empty hi value indicates an
 * unused record.
 */
static bool xfs_iext_rec_is_empty(struct xfs_iext_rec *rec)
{
        return rec->hi == 0;
}

static inline void xfs_iext_rec_clear(struct xfs_iext_rec *rec)
{
        rec->lo = 0;
        rec->hi = 0;
}

static void
xfs_iext_set(
        struct xfs_iext_rec     *rec,
        struct xfs_bmbt_irec    *irec)
{
        ASSERT((irec->br_startoff & ~XFS_IEXT_STARTOFF_MASK) == 0);
        ASSERT((irec->br_blockcount & ~XFS_IEXT_LENGTH_MASK) == 0);
        ASSERT((irec->br_startblock & ~XFS_IEXT_STARTBLOCK_MASK) == 0);

        rec->lo = irec->br_startoff & XFS_IEXT_STARTOFF_MASK;
        rec->hi = irec->br_blockcount & XFS_IEXT_LENGTH_MASK;

        rec->lo |= (irec->br_startblock << 54);
        rec->hi |= ((irec->br_startblock & ~xfs_mask64lo(10)) << (22 - 10));

        if (irec->br_state == XFS_EXT_UNWRITTEN)
                rec->hi |= (1 << 21);
}

static void
xfs_iext_get(
        struct xfs_bmbt_irec    *irec,
        struct xfs_iext_rec     *rec)
{
        irec->br_startoff = rec->lo & XFS_IEXT_STARTOFF_MASK;
        irec->br_blockcount = rec->hi & XFS_IEXT_LENGTH_MASK;

        irec->br_startblock = rec->lo >> 54;
        irec->br_startblock |= (rec->hi & xfs_mask64hi(42)) >> (22 - 10);

        if (rec->hi & (1 << 21))
                irec->br_state = XFS_EXT_UNWRITTEN;
        else
                irec->br_state = XFS_EXT_NORM;
}

enum {
        NODE_SIZE       = 256,
        KEYS_PER_NODE   = NODE_SIZE / (sizeof(uint64_t) + sizeof(void *)),
        RECS_PER_LEAF   = (NODE_SIZE - (2 * sizeof(struct xfs_iext_leaf *))) /
                                sizeof(struct xfs_iext_rec),
};

/*
 * In-core extent btree block layout:
 *
 * There are two types of blocks in the btree: leaf and inner (non-leaf) blocks.
 *
 * The leaf blocks are made up by %KEYS_PER_NODE extent records, which each
 * contain the startoffset, blockcount, startblock and unwritten extent flag.
 * See above for the exact format, followed by pointers to the previous and next
 * leaf blocks (if there are any).
 *
 * The inner (non-leaf) blocks first contain KEYS_PER_NODE lookup keys, followed
 * by an equal number of pointers to the btree blocks at the next lower level.
 *
 *              +-------+-------+-------+-------+-------+----------+----------+
 * Leaf:        | rec 1 | rec 2 | rec 3 | rec 4 | rec N | prev-ptr | next-ptr |
 *              +-------+-------+-------+-------+-------+----------+----------+
 *
 *              +-------+-------+-------+-------+-------+-------+------+-------+
 * Inner:       | key 1 | key 2 | key 3 | key N | ptr 1 | ptr 2 | ptr3 | ptr N |
 *              +-------+-------+-------+-------+-------+-------+------+-------+
 */
struct xfs_iext_node {
        uint64_t                keys[KEYS_PER_NODE];
#define XFS_IEXT_KEY_INVALID    (1ULL << 63)
        void                    *ptrs[KEYS_PER_NODE];
};

struct xfs_iext_leaf {
        struct xfs_iext_rec     recs[RECS_PER_LEAF];
        struct xfs_iext_leaf    *prev;
        struct xfs_iext_leaf    *next;
};

inline xfs_extnum_t xfs_iext_count(struct xfs_ifork *ifp)
{
        return ifp->if_bytes / sizeof(struct xfs_iext_rec);
}

static inline int xfs_iext_max_recs(struct xfs_ifork *ifp)
{
        if (ifp->if_height == 1)
                return xfs_iext_count(ifp);
        return RECS_PER_LEAF;
}

static inline struct xfs_iext_rec *cur_rec(struct xfs_iext_cursor *cur)
{
        return &cur->leaf->recs[cur->pos];
}

static inline bool xfs_iext_valid(struct xfs_ifork *ifp,
                struct xfs_iext_cursor *cur)
{
        if (!cur->leaf)
                return false;
        if (cur->pos < 0 || cur->pos >= xfs_iext_max_recs(ifp))
                return false;
        if (xfs_iext_rec_is_empty(cur_rec(cur)))
                return false;
        return true;
}

static void *
xfs_iext_find_first_leaf(
        struct xfs_ifork        *ifp)
{
        struct xfs_iext_node    *node = ifp->if_u1.if_root;
        int                     height;

        if (!ifp->if_height)
                return NULL;

        for (height = ifp->if_height; height > 1; height--) {
                node = node->ptrs[0];
                ASSERT(node);
        }

        return node;
}

static void *
xfs_iext_find_last_leaf(
        struct xfs_ifork        *ifp)
{
        struct xfs_iext_node    *node = ifp->if_u1.if_root;
        int                     height, i;

        if (!ifp->if_height)
                return NULL;

        for (height = ifp->if_height; height > 1; height--) {
                for (i = 1; i < KEYS_PER_NODE; i++)
                        if (!node->ptrs[i])
                                break;
                node = node->ptrs[i - 1];
                ASSERT(node);
        }

        return node;
}

void
xfs_iext_first(
        struct xfs_ifork        *ifp,
        struct xfs_iext_cursor  *cur)
{
        cur->pos = 0;
        cur->leaf = xfs_iext_find_first_leaf(ifp);
}

void
xfs_iext_last(
        struct xfs_ifork        *ifp,
        struct xfs_iext_cursor  *cur)
{
        int                     i;

        cur->leaf = xfs_iext_find_last_leaf(ifp);
        if (!cur->leaf) {
                cur->pos = 0;
                return;
        }

        for (i = 1; i < xfs_iext_max_recs(ifp); i++) {
                if (xfs_iext_rec_is_empty(&cur->leaf->recs[i]))
                        break;
        }
        cur->pos = i - 1;
}

void
xfs_iext_next(
        struct xfs_ifork        *ifp,
        struct xfs_iext_cursor  *cur)
{
        if (!cur->leaf) {
                ASSERT(cur->pos <= 0 || cur->pos >= RECS_PER_LEAF);
                xfs_iext_first(ifp, cur);
                return;
        }

        ASSERT(cur->pos >= 0);
        ASSERT(cur->pos < xfs_iext_max_recs(ifp));

        cur->pos++;
        if (ifp->if_height > 1 && !xfs_iext_valid(ifp, cur) &&
            cur->leaf->next) {
                cur->leaf = cur->leaf->next;
                cur->pos = 0;
        }
}

void
xfs_iext_prev(
        struct xfs_ifork        *ifp,
        struct xfs_iext_cursor  *cur)
{
        if (!cur->leaf) {
                ASSERT(cur->pos <= 0 || cur->pos >= RECS_PER_LEAF);
                xfs_iext_last(ifp, cur);
                return;
        }

        ASSERT(cur->pos >= 0);
        ASSERT(cur->pos <= RECS_PER_LEAF);

recurse:
        do {
                cur->pos--;
                if (xfs_iext_valid(ifp, cur))
                        return;
        } while (cur->pos > 0);

        if (ifp->if_height > 1 && cur->leaf->prev) {
                cur->leaf = cur->leaf->prev;
                cur->pos = RECS_PER_LEAF;
                goto recurse;
        }
}

static inline int
xfs_iext_key_cmp(
        struct xfs_iext_node    *node,
        int                     n,
        xfs_fileoff_t           offset)
{
        if (node->keys[n] > offset)
                return 1;
        if (node->keys[n] < offset)
                return -1;
        return 0;
}

static inline int
xfs_iext_rec_cmp(
        struct xfs_iext_rec     *rec,
        xfs_fileoff_t           offset)
{
        uint64_t                rec_offset = rec->lo & XFS_IEXT_STARTOFF_MASK;
        uint32_t                rec_len = rec->hi & XFS_IEXT_LENGTH_MASK;

        if (rec_offset > offset)
                return 1;
        if (rec_offset + rec_len <= offset)
                return -1;
        return 0;
}

static void *
xfs_iext_find_level(
        struct xfs_ifork        *ifp,
        xfs_fileoff_t           offset,
        int                     level)
{
        struct xfs_iext_node    *node = ifp->if_u1.if_root;
        int                     height, i;

        if (!ifp->if_height)
                return NULL;

        for (height = ifp->if_height; height > level; height--) {
                for (i = 1; i < KEYS_PER_NODE; i++)
                        if (xfs_iext_key_cmp(node, i, offset) > 0)
                                break;

                node = node->ptrs[i - 1];
                if (!node)
                        break;
        }

        return node;
}

static int
xfs_iext_node_pos(
        struct xfs_iext_node    *node,
        xfs_fileoff_t           offset)
{
        int                     i;

        for (i = 1; i < KEYS_PER_NODE; i++) {
                if (xfs_iext_key_cmp(node, i, offset) > 0)
                        break;
        }

        return i - 1;
}

static int
xfs_iext_node_insert_pos(
        struct xfs_iext_node    *node,
        xfs_fileoff_t           offset)
{
        int                     i;

        for (i = 0; i < KEYS_PER_NODE; i++) {
                if (xfs_iext_key_cmp(node, i, offset) > 0)
                        return i;
        }

        return KEYS_PER_NODE;
}

static int
xfs_iext_node_nr_entries(
        struct xfs_iext_node    *node,
        int                     start)
{
        int                     i;

        for (i = start; i < KEYS_PER_NODE; i++) {
                if (node->keys[i] == XFS_IEXT_KEY_INVALID)
                        break;
        }

        return i;
}

static int
xfs_iext_leaf_nr_entries(
        struct xfs_ifork        *ifp,
        struct xfs_iext_leaf    *leaf,
        int                     start)
{
        int                     i;

        for (i = start; i < xfs_iext_max_recs(ifp); i++) {
                if (xfs_iext_rec_is_empty(&leaf->recs[i]))
                        break;
        }

        return i;
}

static inline uint64_t
xfs_iext_leaf_key(
        struct xfs_iext_leaf    *leaf,
        int                     n)
{
        return leaf->recs[n].lo & XFS_IEXT_STARTOFF_MASK;
}

static void
xfs_iext_grow(
        struct xfs_ifork        *ifp)
{
        struct xfs_iext_node    *node = kmem_zalloc(NODE_SIZE, KM_NOFS);
        int                     i;

        if (ifp->if_height == 1) {
                struct xfs_iext_leaf *prev = ifp->if_u1.if_root;

                node->keys[0] = xfs_iext_leaf_key(prev, 0);
                node->ptrs[0] = prev;
        } else  {
                struct xfs_iext_node *prev = ifp->if_u1.if_root;

                ASSERT(ifp->if_height > 1);

                node->keys[0] = prev->keys[0];
                node->ptrs[0] = prev;
        }

        for (i = 1; i < KEYS_PER_NODE; i++)
                node->keys[i] = XFS_IEXT_KEY_INVALID;

        ifp->if_u1.if_root = node;
        ifp->if_height++;
}

static void
xfs_iext_update_node(
        struct xfs_ifork        *ifp,
        xfs_fileoff_t           old_offset,
        xfs_fileoff_t           new_offset,
        int                     level,
        void                    *ptr)
{
        struct xfs_iext_node    *node = ifp->if_u1.if_root;
        int                     height, i;

        for (height = ifp->if_height; height > level; height--) {
                for (i = 0; i < KEYS_PER_NODE; i++) {
                        if (i > 0 && xfs_iext_key_cmp(node, i, old_offset) > 0)
                                break;
                        if (node->keys[i] == old_offset)
                                node->keys[i] = new_offset;
                }
                node = node->ptrs[i - 1];
                ASSERT(node);
        }

        ASSERT(node == ptr);
}

static struct xfs_iext_node *
xfs_iext_split_node(
        struct xfs_iext_node    **nodep,
        int                     *pos,
        int                     *nr_entries)
{
        struct xfs_iext_node    *node = *nodep;
        struct xfs_iext_node    *new = kmem_zalloc(NODE_SIZE, KM_NOFS);
        const int               nr_move = KEYS_PER_NODE / 2;
        int                     nr_keep = nr_move + (KEYS_PER_NODE & 1);
        int                     i = 0;

        /* for sequential append operations just spill over into the new node */
        if (*pos == KEYS_PER_NODE) {
                *nodep = new;
                *pos = 0;
                *nr_entries = 0;
                goto done;
        }


        for (i = 0; i < nr_move; i++) {
                new->keys[i] = node->keys[nr_keep + i];
                new->ptrs[i] = node->ptrs[nr_keep + i];

                node->keys[nr_keep + i] = XFS_IEXT_KEY_INVALID;
                node->ptrs[nr_keep + i] = NULL;
        }

        if (*pos >= nr_keep) {
                *nodep = new;
                *pos -= nr_keep;
                *nr_entries = nr_move;
        } else {
                *nr_entries = nr_keep;
        }
done:
        for (; i < KEYS_PER_NODE; i++)
                new->keys[i] = XFS_IEXT_KEY_INVALID;
        return new;
}

static void
xfs_iext_insert_node(
        struct xfs_ifork        *ifp,
        uint64_t                offset,
        void                    *ptr,
        int                     level)
{
        struct xfs_iext_node    *node, *new;
        int                     i, pos, nr_entries;

again:
        if (ifp->if_height < level)
                xfs_iext_grow(ifp);

        new = NULL;
        node = xfs_iext_find_level(ifp, offset, level);
        pos = xfs_iext_node_insert_pos(node, offset);
        nr_entries = xfs_iext_node_nr_entries(node, pos);

        ASSERT(pos >= nr_entries || xfs_iext_key_cmp(node, pos, offset) != 0);
        ASSERT(nr_entries <= KEYS_PER_NODE);

        if (nr_entries == KEYS_PER_NODE)
                new = xfs_iext_split_node(&node, &pos, &nr_entries);

        /*
         * Update the pointers in higher levels if the first entry changes
         * in an existing node.
         */
        if (node != new && pos == 0 && nr_entries > 0)
                xfs_iext_update_node(ifp, node->keys[0], offset, level, node);

        for (i = nr_entries; i > pos; i--) {
                node->keys[i] = node->keys[i - 1];
                node->ptrs[i] = node->ptrs[i - 1];
        }
        node->keys[pos] = offset;
        node->ptrs[pos] = ptr;

        if (new) {
                offset = new->keys[0];
                ptr = new;
                level++;
                goto again;
        }
}

static struct xfs_iext_leaf *
xfs_iext_split_leaf(
        struct xfs_iext_cursor  *cur,
        int                     *nr_entries)
{
        struct xfs_iext_leaf    *leaf = cur->leaf;
        struct xfs_iext_leaf    *new = kmem_zalloc(NODE_SIZE, KM_NOFS);
        const int               nr_move = RECS_PER_LEAF / 2;
        int                     nr_keep = nr_move + (RECS_PER_LEAF & 1);
        int                     i;

        /* for sequential append operations just spill over into the new node */
        if (cur->pos == RECS_PER_LEAF) {
                cur->leaf = new;
                cur->pos = 0;
                *nr_entries = 0;
                goto done;
        }

        for (i = 0; i < nr_move; i++) {
                new->recs[i] = leaf->recs[nr_keep + i];
                xfs_iext_rec_clear(&leaf->recs[nr_keep + i]);
        }

        if (cur->pos >= nr_keep) {
                cur->leaf = new;
                cur->pos -= nr_keep;
                *nr_entries = nr_move;
        } else {
                *nr_entries = nr_keep;
        }
done:
        if (leaf->next)
                leaf->next->prev = new;
        new->next = leaf->next;
        new->prev = leaf;
        leaf->next = new;
        return new;
}

static void
xfs_iext_alloc_root(
        struct xfs_ifork        *ifp,
        struct xfs_iext_cursor  *cur)
{
        ASSERT(ifp->if_bytes == 0);

        ifp->if_u1.if_root = kmem_zalloc(sizeof(struct xfs_iext_rec), KM_NOFS);
        ifp->if_height = 1;

        /* now that we have a node step into it */
        cur->leaf = ifp->if_u1.if_root;
        cur->pos = 0;
}

static void
xfs_iext_realloc_root(
        struct xfs_ifork        *ifp,
        struct xfs_iext_cursor  *cur)
{
        int64_t new_size = ifp->if_bytes + sizeof(struct xfs_iext_rec);
        void *new;

        /* account for the prev/next pointers */
        if (new_size / sizeof(struct xfs_iext_rec) == RECS_PER_LEAF)
                new_size = NODE_SIZE;

        new = krealloc(ifp->if_u1.if_root, new_size, GFP_NOFS | __GFP_NOFAIL);
        memset(new + ifp->if_bytes, 0, new_size - ifp->if_bytes);
        ifp->if_u1.if_root = new;
        cur->leaf = new;
}

/*
 * Increment the sequence counter on extent tree changes. If we are on a COW
 * fork, this allows the writeback code to skip looking for a COW extent if the
 * COW fork hasn't changed. We use WRITE_ONCE here to ensure the update to the
 * sequence counter is seen before the modifications to the extent tree itself
 * take effect.
 */
static inline void xfs_iext_inc_seq(struct xfs_ifork *ifp)
{
        WRITE_ONCE(ifp->if_seq, READ_ONCE(ifp->if_seq) + 1);
}

void
xfs_iext_insert(
        struct xfs_inode        *ip,
        struct xfs_iext_cursor  *cur,
        struct xfs_bmbt_irec    *irec,
        int                     state)
{
        struct xfs_ifork        *ifp = xfs_iext_state_to_fork(ip, state);
        xfs_fileoff_t           offset = irec->br_startoff;
        struct xfs_iext_leaf    *new = NULL;
        int                     nr_entries, i;

        xfs_iext_inc_seq(ifp);

        if (ifp->if_height == 0)
                xfs_iext_alloc_root(ifp, cur);
        else if (ifp->if_height == 1)
                xfs_iext_realloc_root(ifp, cur);

        nr_entries = xfs_iext_leaf_nr_entries(ifp, cur->leaf, cur->pos);
        ASSERT(nr_entries <= RECS_PER_LEAF);
        ASSERT(cur->pos >= nr_entries ||
               xfs_iext_rec_cmp(cur_rec(cur), irec->br_startoff) != 0);

        if (nr_entries == RECS_PER_LEAF)
                new = xfs_iext_split_leaf(cur, &nr_entries);

        /*
         * Update the pointers in higher levels if the first entry changes
         * in an existing node.
         */
        if (cur->leaf != new && cur->pos == 0 && nr_entries > 0) {
                xfs_iext_update_node(ifp, xfs_iext_leaf_key(cur->leaf, 0),
                                offset, 1, cur->leaf);
        }

        for (i = nr_entries; i > cur->pos; i--)
                cur->leaf->recs[i] = cur->leaf->recs[i - 1];
        xfs_iext_set(cur_rec(cur), irec);
        ifp->if_bytes += sizeof(struct xfs_iext_rec);

        trace_xfs_iext_insert(ip, cur, state, _RET_IP_);

        if (new)
                xfs_iext_insert_node(ifp, xfs_iext_leaf_key(new, 0), new, 2);
}

static struct xfs_iext_node *
xfs_iext_rebalance_node(
        struct xfs_iext_node    *parent,
        int                     *pos,
        struct xfs_iext_node    *node,
        int                     nr_entries)
{
        /*
         * If the neighbouring nodes are completely full, or have different
         * parents, we might never be able to merge our node, and will only
         * delete it once the number of entries hits zero.
         */
        if (nr_entries == 0)
                return node;

        if (*pos > 0) {
                struct xfs_iext_node *prev = parent->ptrs[*pos - 1];
                int nr_prev = xfs_iext_node_nr_entries(prev, 0), i;

                if (nr_prev + nr_entries <= KEYS_PER_NODE) {
                        for (i = 0; i < nr_entries; i++) {
                                prev->keys[nr_prev + i] = node->keys[i];
                                prev->ptrs[nr_prev + i] = node->ptrs[i];
                        }
                        return node;
                }
        }

        if (*pos + 1 < xfs_iext_node_nr_entries(parent, *pos)) {
                struct xfs_iext_node *next = parent->ptrs[*pos + 1];
                int nr_next = xfs_iext_node_nr_entries(next, 0), i;

                if (nr_entries + nr_next <= KEYS_PER_NODE) {
                        /*
                         * Merge the next node into this node so that we don't
                         * have to do an additional update of the keys in the
                         * higher levels.
                         */
                        for (i = 0; i < nr_next; i++) {
                                node->keys[nr_entries + i] = next->keys[i];
                                node->ptrs[nr_entries + i] = next->ptrs[i];
                        }

                        ++*pos;
                        return next;
                }
        }

        return NULL;
}

static void
xfs_iext_remove_node(
        struct xfs_ifork        *ifp,
        xfs_fileoff_t           offset,
        void                    *victim)
{
        struct xfs_iext_node    *node, *parent;
        int                     level = 2, pos, nr_entries, i;

        ASSERT(level <= ifp->if_height);
        node = xfs_iext_find_level(ifp, offset, level);
        pos = xfs_iext_node_pos(node, offset);
again:
        ASSERT(node->ptrs[pos]);
        ASSERT(node->ptrs[pos] == victim);
        kmem_free(victim);

        nr_entries = xfs_iext_node_nr_entries(node, pos) - 1;
        offset = node->keys[0];
        for (i = pos; i < nr_entries; i++) {
                node->keys[i] = node->keys[i + 1];
                node->ptrs[i] = node->ptrs[i + 1];
        }
        node->keys[nr_entries] = XFS_IEXT_KEY_INVALID;
        node->ptrs[nr_entries] = NULL;

        if (pos == 0 && nr_entries > 0) {
                xfs_iext_update_node(ifp, offset, node->keys[0], level, node);
                offset = node->keys[0];
        }

        if (nr_entries >= KEYS_PER_NODE / 2)
                return;

        if (level < ifp->if_height) {
                /*
                 * If we aren't at the root yet try to find a neighbour node to
                 * merge with (or delete the node if it is empty), and then
                 * recurse up to the next level.
                 */
                level++;
                parent = xfs_iext_find_level(ifp, offset, level);
                pos = xfs_iext_node_pos(parent, offset);

                ASSERT(pos != KEYS_PER_NODE);
                ASSERT(parent->ptrs[pos] == node);

                node = xfs_iext_rebalance_node(parent, &pos, node, nr_entries);
                if (node) {
                        victim = node;
                        node = parent;
                        goto again;
                }
        } else if (nr_entries == 1) {
                /*
                 * If we are at the root and only one entry is left we can just
                 * free this node and update the root pointer.
                 */
                ASSERT(node == ifp->if_u1.if_root);
                ifp->if_u1.if_root = node->ptrs[0];
                ifp->if_height--;
                kmem_free(node);
        }
}

static void
xfs_iext_rebalance_leaf(
        struct xfs_ifork        *ifp,
        struct xfs_iext_cursor  *cur,
        struct xfs_iext_leaf    *leaf,
        xfs_fileoff_t           offset,
        int                     nr_entries)
{
        /*
         * If the neighbouring nodes are completely full we might never be able
         * to merge our node, and will only delete it once the number of
         * entries hits zero.
         */
        if (nr_entries == 0)
                goto remove_node;

        if (leaf->prev) {
                int nr_prev = xfs_iext_leaf_nr_entries(ifp, leaf->prev, 0), i;

                if (nr_prev + nr_entries <= RECS_PER_LEAF) {
                        for (i = 0; i < nr_entries; i++)
                                leaf->prev->recs[nr_prev + i] = leaf->recs[i];

                        if (cur->leaf == leaf) {
                                cur->leaf = leaf->prev;
                                cur->pos += nr_prev;
                        }
                        goto remove_node;
                }
        }

        if (leaf->next) {
                int nr_next = xfs_iext_leaf_nr_entries(ifp, leaf->next, 0), i;

                if (nr_entries + nr_next <= RECS_PER_LEAF) {
                        /*
                         * Merge the next node into this node so that we don't
                         * have to do an additional update of the keys in the
                         * higher levels.
                         */
                        for (i = 0; i < nr_next; i++) {
                                leaf->recs[nr_entries + i] =
                                        leaf->next->recs[i];
                        }

                        if (cur->leaf == leaf->next) {
                                cur->leaf = leaf;
                                cur->pos += nr_entries;
                        }

                        offset = xfs_iext_leaf_key(leaf->next, 0);
                        leaf = leaf->next;
                        goto remove_node;
                }
        }

        return;
remove_node:
        if (leaf->prev)
                leaf->prev->next = leaf->next;
        if (leaf->next)
                leaf->next->prev = leaf->prev;
        xfs_iext_remove_node(ifp, offset, leaf);
}

static void
xfs_iext_free_last_leaf(
        struct xfs_ifork        *ifp)
{
        ifp->if_height--;
        kmem_free(ifp->if_u1.if_root);
        ifp->if_u1.if_root = NULL;
}

void
xfs_iext_remove(
        struct xfs_inode        *ip,
        struct xfs_iext_cursor  *cur,
        int                     state)
{
        struct xfs_ifork        *ifp = xfs_iext_state_to_fork(ip, state);
        struct xfs_iext_leaf    *leaf = cur->leaf;
        xfs_fileoff_t           offset = xfs_iext_leaf_key(leaf, 0);
        int                     i, nr_entries;

        trace_xfs_iext_remove(ip, cur, state, _RET_IP_);

        ASSERT(ifp->if_height > 0);
        ASSERT(ifp->if_u1.if_root != NULL);
        ASSERT(xfs_iext_valid(ifp, cur));

        xfs_iext_inc_seq(ifp);

        nr_entries = xfs_iext_leaf_nr_entries(ifp, leaf, cur->pos) - 1;
        for (i = cur->pos; i < nr_entries; i++)
                leaf->recs[i] = leaf->recs[i + 1];
        xfs_iext_rec_clear(&leaf->recs[nr_entries]);
        ifp->if_bytes -= sizeof(struct xfs_iext_rec);

        if (cur->pos == 0 && nr_entries > 0) {
                xfs_iext_update_node(ifp, offset, xfs_iext_leaf_key(leaf, 0), 1,
                                leaf);
                offset = xfs_iext_leaf_key(leaf, 0);
        } else if (cur->pos == nr_entries) {
                if (ifp->if_height > 1 && leaf->next)
                        cur->leaf = leaf->next;
                else
                        cur->leaf = NULL;
                cur->pos = 0;
        }

        if (nr_entries >= RECS_PER_LEAF / 2)
                return;

        if (ifp->if_height > 1)
                xfs_iext_rebalance_leaf(ifp, cur, leaf, offset, nr_entries);
        else if (nr_entries == 0)
                xfs_iext_free_last_leaf(ifp);
}

/*
 * Lookup the extent covering bno.
 *
 * If there is an extent covering bno return the extent index, and store the
 * expanded extent structure in *gotp, and the extent cursor in *cur.
 * If there is no extent covering bno, but there is an extent after it (e.g.
 * it lies in a hole) return that extent in *gotp and its cursor in *cur
 * instead.
 * If bno is beyond the last extent return false, and return an invalid
 * cursor value.
 */
bool
xfs_iext_lookup_extent(
        struct xfs_inode        *ip,
        struct xfs_ifork        *ifp,
        xfs_fileoff_t           offset,
        struct xfs_iext_cursor  *cur,
        struct xfs_bmbt_irec    *gotp)
{
        XFS_STATS_INC(ip->i_mount, xs_look_exlist);

        cur->leaf = xfs_iext_find_level(ifp, offset, 1);
        if (!cur->leaf) {
                cur->pos = 0;
                return false;
        }

        for (cur->pos = 0; cur->pos < xfs_iext_max_recs(ifp); cur->pos++) {
                struct xfs_iext_rec *rec = cur_rec(cur);

                if (xfs_iext_rec_is_empty(rec))
                        break;
                if (xfs_iext_rec_cmp(rec, offset) >= 0)
                        goto found;
        }

        /* Try looking in the next node for an entry > offset */
        if (ifp->if_height == 1 || !cur->leaf->next)
                return false;
        cur->leaf = cur->leaf->next;
        cur->pos = 0;
        if (!xfs_iext_valid(ifp, cur))
                return false;
found:
        xfs_iext_get(gotp, cur_rec(cur));
        return true;
}

/*
 * Returns the last extent before end, and if this extent doesn't cover
 * end, update end to the end of the extent.
 */
bool
xfs_iext_lookup_extent_before(
        struct xfs_inode        *ip,
        struct xfs_ifork        *ifp,
        xfs_fileoff_t           *end,
        struct xfs_iext_cursor  *cur,
        struct xfs_bmbt_irec    *gotp)
{
        /* could be optimized to not even look up the next on a match.. */
        if (xfs_iext_lookup_extent(ip, ifp, *end - 1, cur, gotp) &&
            gotp->br_startoff <= *end - 1)
                return true;
        if (!xfs_iext_prev_extent(ifp, cur, gotp))
                return false;
        *end = gotp->br_startoff + gotp->br_blockcount;
        return true;
}

void
xfs_iext_update_extent(
        struct xfs_inode        *ip,
        int                     state,
        struct xfs_iext_cursor  *cur,
        struct xfs_bmbt_irec    *new)
{
        struct xfs_ifork        *ifp = xfs_iext_state_to_fork(ip, state);

        xfs_iext_inc_seq(ifp);

        if (cur->pos == 0) {
                struct xfs_bmbt_irec    old;

                xfs_iext_get(&old, cur_rec(cur));
                if (new->br_startoff != old.br_startoff) {
                        xfs_iext_update_node(ifp, old.br_startoff,
                                        new->br_startoff, 1, cur->leaf);
                }
        }

        trace_xfs_bmap_pre_update(ip, cur, state, _RET_IP_);
        xfs_iext_set(cur_rec(cur), new);
        trace_xfs_bmap_post_update(ip, cur, state, _RET_IP_);

}

/*
 * Return true if the cursor points at an extent and return the extent structure
 * in gotp.  Else return false.
 */
bool
xfs_iext_get_extent(
        struct xfs_ifork        *ifp,
        struct xfs_iext_cursor  *cur,
        struct xfs_bmbt_irec    *gotp)
{
        if (!xfs_iext_valid(ifp, cur))
                return false;
        xfs_iext_get(gotp, cur_rec(cur));
        return true;
}

/*
 * This is a recursive function, because of that we need to be extremely
 * careful with stack usage.
 */
static void
xfs_iext_destroy_node(
        struct xfs_iext_node    *node,
        int                     level)
{
        int                     i;

        if (level > 1) {
                for (i = 0; i < KEYS_PER_NODE; i++) {
                        if (node->keys[i] == XFS_IEXT_KEY_INVALID)
                                break;
                        xfs_iext_destroy_node(node->ptrs[i], level - 1);
                }
        }

        kmem_free(node);
}

void
xfs_iext_destroy(
        struct xfs_ifork        *ifp)
{
        xfs_iext_destroy_node(ifp->if_u1.if_root, ifp->if_height);

        ifp->if_bytes = 0;
        ifp->if_height = 0;
        ifp->if_u1.if_root = NULL;
}