/*
 * Copyright (c) 2007-2008 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@backplane.com>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * HAMMER B-Tree index
 *
 * HAMMER implements a modified B+Tree.  In documentation this will
 * simply be refered to as the HAMMER B-Tree.  Basically a HAMMER B-Tree
 * looks like a B+Tree (A B-Tree which stores its records only at the leafs
 * of the tree), but adds two additional boundary elements which describe
 * the left-most and right-most element a node is able to represent.  In
 * otherwords, we have boundary elements at the two ends of a B-Tree node
 * with no valid sub-tree pointer for the right-most element.
 *
 * A B-Tree internal node looks like this:
 *
 *      B N N N N N N B   <-- boundary and internal elements
 *       S S S S S S S    <-- subtree pointers
 *
 * A B-Tree leaf node basically looks like this:
 *
 *      L L L L L L L L   <-- leaf elemenets
 *
 * The radix for an internal node is 1 less then a leaf but we get a
 * number of significant benefits for our troubles.
 * The left-hand boundary (B in the left) is integrated into the first
 * element so it doesn't require 2 elements to accomodate boundaries.
 *
 * The big benefit to using a B-Tree containing boundary information
 * is that it is possible to cache pointers into the middle of the tree
 * and not have to start searches, insertions, OR deletions at the root
 * node.   In particular, searches are able to progress in a definitive
 * direction from any point in the tree without revisting nodes.  This
 * greatly improves the efficiency of many operations, most especially
 * record appends.
 *
 * B-Trees also make the stacking of trees fairly straightforward.
 *
 * INSERTIONS:  A search performed with the intention of doing
 * an insert will guarantee that the terminal leaf node is not full by
 * splitting full nodes.  Splits occur top-down during the dive down the
 * B-Tree.
 *
 * DELETIONS: A deletion makes no attempt to proactively balance the
 * tree and will recursively remove nodes that become empty.  If a
 * deadlock occurs a deletion may not be able to remove an empty leaf.
 * Deletions never allow internal nodes to become empty (that would blow
 * up the boundaries).
 */
#include "hammer.h"

static int btree_search(hammer_cursor_t cursor, int flags);
static int btree_split_internal(hammer_cursor_t cursor);
static int btree_split_leaf(hammer_cursor_t cursor);
static int btree_remove(hammer_cursor_t cursor, int *ndelete);
static __inline int btree_node_is_full(hammer_node_ondisk_t node);
static int hammer_btree_mirror_propagate(hammer_cursor_t cursor,
                        hammer_tid_t mirror_tid);
static void hammer_make_separator(hammer_base_elm_t key1,
                        hammer_base_elm_t key2, hammer_base_elm_t dest);
static void hammer_cursor_mirror_filter(hammer_cursor_t cursor);
static __inline void hammer_debug_btree_elm(hammer_cursor_t cursor,
                hammer_btree_elm_t elm, const char *s, int res);
static __inline void hammer_debug_btree_parent(hammer_cursor_t cursor,
                const char *s);

/*
 * Iterate records after a search.  The cursor is iterated forwards past
 * the current record until a record matching the key-range requirements
 * is found.  ENOENT is returned if the iteration goes past the ending
 * key.
 *
 * The iteration is inclusive of key_beg and can be inclusive or exclusive
 * of key_end depending on whether HAMMER_CURSOR_END_INCLUSIVE is set.
 *
 * When doing an as-of search (cursor->asof != 0), key_beg.create_tid
 * may be modified by B-Tree functions.
 *
 * cursor->key_beg may or may not be modified by this function during
 * the iteration.  XXX future - in case of an inverted lock we may have
 * to reinitiate the lookup and set key_beg to properly pick up where we
 * left off.
 *
 * If HAMMER_CURSOR_ITERATE_CHECK is set it is possible that the cursor
 * was reverse indexed due to being moved to a parent while unlocked,
 * and something else might have inserted an element outside the iteration
 * range.  When this case occurs the iterator just keeps iterating until
 * it gets back into the iteration range (instead of asserting).
 *
 * NOTE!  EDEADLK *CANNOT* be returned by this procedure.
 */
int
hammer_btree_iterate(hammer_cursor_t cursor)
{
        hammer_node_ondisk_t node;
        hammer_btree_elm_t elm;
        hammer_mount_t hmp;
        int error = 0;
        int r;
        int s;

        /*
         * Skip past the current record
         */
        hmp = cursor->trans->hmp;
        node = cursor->node->ondisk;
        if (node == NULL)
                return(ENOENT);
        if (cursor->index < node->count &&
            (cursor->flags & HAMMER_CURSOR_ATEDISK)) {
                ++cursor->index;
        }

        /*
         * HAMMER can wind up being cpu-bound.
         */
        if (++hmp->check_yield > hammer_yield_check) {
                hmp->check_yield = 0;
                lwkt_user_yield();
        }


        /*
         * Loop until an element is found or we are done.
         */
        for (;;) {
                /*
                 * We iterate up the tree and then index over one element
                 * while we are at the last element in the current node.
                 *
                 * If we are at the root of the filesystem, cursor_up
                 * returns ENOENT.
                 *
                 * XXX this could be optimized by storing the information in
                 * the parent reference.
                 *
                 * XXX we can lose the node lock temporarily, this could mess
                 * up our scan.
                 */
                ++hammer_stats_btree_iterations;
                hammer_flusher_clean_loose_ios(hmp);

                if (cursor->index == node->count) {
                        if (hammer_debug_btree) {
                                hkprintf("BRACKETU %016jx[%d] -> %016jx[%d] td=%p\n",
                                        (intmax_t)cursor->node->node_offset,
                                        cursor->index,
                                        (intmax_t)(cursor->parent ? cursor->parent->node_offset : -1),
                                        cursor->parent_index,
                                        curthread);
                        }
                        KKASSERT(cursor->parent == NULL ||
                                 cursor->parent->ondisk->elms[cursor->parent_index].internal.subtree_offset == cursor->node->node_offset);
                        error = hammer_cursor_up(cursor);
                        if (error)
                                break;
                        /* reload stale pointer */
                        node = cursor->node->ondisk;
                        KKASSERT(cursor->index != node->count);

                        /*
                         * If we are reblocking we want to return internal
                         * nodes.  Note that the internal node will be
                         * returned multiple times, on each upward recursion
                         * from its children.  The caller selects which
                         * revisit it cares about (usually first or last only).
                         */
                        if (cursor->flags & HAMMER_CURSOR_REBLOCKING) {
                                cursor->flags |= HAMMER_CURSOR_ATEDISK;
                                return(0);
                        }
                        ++cursor->index;
                        continue;
                }

                /*
                 * Check internal or leaf element.  Determine if the record
                 * at the cursor has gone beyond the end of our range.
                 *
                 * We recurse down through internal nodes.
                 */
                if (node->type == HAMMER_BTREE_TYPE_INTERNAL) {
                        elm = &node->elms[cursor->index];

                        r = hammer_btree_cmp(&cursor->key_end, &elm[0].base);
                        s = hammer_btree_cmp(&cursor->key_beg, &elm[1].base);
                        if (hammer_debug_btree) {
                                hammer_debug_btree_elm(cursor, elm, "BRACKETL", r);
                                hammer_debug_btree_elm(cursor, elm + 1, "BRACKETR", s);
                        }

                        if (r < 0) {
                                error = ENOENT;
                                break;
                        }
                        if (r == 0 && (cursor->flags &
                                       HAMMER_CURSOR_END_INCLUSIVE) == 0) {
                                error = ENOENT;
                                break;
                        }

                        /*
                         * Better not be zero
                         */
                        KKASSERT(elm->internal.subtree_offset != 0);

                        if (s <= 0) {
                                /*
                                 * If running the mirror filter see if we
                                 * can skip one or more entire sub-trees.
                                 * If we can we return the internal node
                                 * and the caller processes the skipped
                                 * range (see mirror_read).
                                 */
                                if (cursor->flags &
                                    HAMMER_CURSOR_MIRROR_FILTERED) {
                                        if (elm->internal.mirror_tid <
                                            cursor->cmirror->mirror_tid) {
                                                hammer_cursor_mirror_filter(cursor);
                                                return(0);
                                        }
                                }
                        } else {
                                /*
                                 * Normally it would be impossible for the
                                 * cursor to have gotten back-indexed,
                                 * but it can happen if a node is deleted
                                 * and the cursor is moved to its parent
                                 * internal node.  ITERATE_CHECK will be set.
                                 */
                                KKASSERT(cursor->flags &
                                         HAMMER_CURSOR_ITERATE_CHECK);
                                hdkprintf("DEBUG: Caught parent seek "
                                        "in internal iteration\n");
                        }

                        error = hammer_cursor_down(cursor);
                        if (error)
                                break;
                        KKASSERT(cursor->index == 0);
                        /* reload stale pointer */
                        node = cursor->node->ondisk;
                        continue;
                } else {
                        elm = &node->elms[cursor->index];
                        r = hammer_btree_cmp(&cursor->key_end, &elm->base);
                        if (hammer_debug_btree) {
                                hammer_debug_btree_elm(cursor, elm, "ELEMENT", r);
                        }
                        if (r < 0) {
                                error = ENOENT;
                                break;
                        }

                        /*
                         * We support both end-inclusive and
                         * end-exclusive searches.
                         */
                        if (r == 0 &&
                           (cursor->flags & HAMMER_CURSOR_END_INCLUSIVE) == 0) {
                                error = ENOENT;
                                break;
                        }

                        /*
                         * If ITERATE_CHECK is set an unlocked cursor may
                         * have been moved to a parent and the iterate can
                         * happen upon elements that are not in the requested
                         * range.
                         */
                        if (cursor->flags & HAMMER_CURSOR_ITERATE_CHECK) {
                                s = hammer_btree_cmp(&cursor->key_beg,
                                                     &elm->base);
                                if (s > 0) {
                                        hdkprintf("DEBUG: Caught parent seek "
                                                "in leaf iteration\n");
                                        ++cursor->index;
                                        continue;
                                }
                        }
                        cursor->flags &= ~HAMMER_CURSOR_ITERATE_CHECK;

                        /*
                         * Return the element
                         */
                        switch(elm->leaf.base.btype) {
                        case HAMMER_BTREE_TYPE_RECORD:
                                if ((cursor->flags & HAMMER_CURSOR_ASOF) &&
                                    hammer_btree_chkts(cursor->asof, &elm->base)) {
                                        ++cursor->index;
                                        continue;
                                }
                                error = 0;
                                break;
                        default:
                                error = EINVAL;
                                break;
                        }
                        if (error)
                                break;
                }

                /*
                 * Return entry
                 */
                if (hammer_debug_btree) {
                        elm = &cursor->node->ondisk->elms[cursor->index];
                        hammer_debug_btree_elm(cursor, elm, "ITERATE", 0xffff);
                }
                return(0);
        }
        return(error);
}

/*
 * We hit an internal element that we could skip as part of a mirroring
 * scan.  Calculate the entire range being skipped.
 *
 * It is important to include any gaps between the parent's left_bound
 * and the node's left_bound, and same goes for the right side.
 */
static void
hammer_cursor_mirror_filter(hammer_cursor_t cursor)
{
        struct hammer_cmirror *cmirror;
        hammer_node_ondisk_t ondisk;
        hammer_btree_elm_t elm;

        ondisk = cursor->node->ondisk;
        cmirror = cursor->cmirror;

        /*
         * Calculate the skipped range
         */
        elm = &ondisk->elms[cursor->index];
        if (cursor->index == 0)
                cmirror->skip_beg = *cursor->left_bound;
        else
                cmirror->skip_beg = elm->internal.base;
        while (cursor->index < ondisk->count) {
                if (elm->internal.mirror_tid >= cmirror->mirror_tid)
                        break;
                ++cursor->index;
                ++elm;
        }
        if (cursor->index == ondisk->count)
                cmirror->skip_end = *cursor->right_bound;
        else
                cmirror->skip_end = elm->internal.base;

        /*
         * clip the returned result.
         */
        if (hammer_btree_cmp(&cmirror->skip_beg, &cursor->key_beg) < 0)
                cmirror->skip_beg = cursor->key_beg;
        if (hammer_btree_cmp(&cmirror->skip_end, &cursor->key_end) > 0)
                cmirror->skip_end = cursor->key_end;
}

/*
 * Iterate in the reverse direction.  This is used by the pruning code to
 * avoid overlapping records.
 */
int
hammer_btree_iterate_reverse(hammer_cursor_t cursor)
{
        hammer_node_ondisk_t node;
        hammer_btree_elm_t elm;
        hammer_mount_t hmp;
        int error = 0;
        int r;
        int s;

        /* mirror filtering not supported for reverse iteration */
        KKASSERT ((cursor->flags & HAMMER_CURSOR_MIRROR_FILTERED) == 0);

        /*
         * Skip past the current record.  For various reasons the cursor
         * may end up set to -1 or set to point at the end of the current
         * node.  These cases must be addressed.
         */
        node = cursor->node->ondisk;
        if (node == NULL)
                return(ENOENT);
        if (cursor->index != -1 &&
            (cursor->flags & HAMMER_CURSOR_ATEDISK)) {
                --cursor->index;
        }
        if (cursor->index == cursor->node->ondisk->count)
                --cursor->index;

        /*
         * HAMMER can wind up being cpu-bound.
         */
        hmp = cursor->trans->hmp;
        if (++hmp->check_yield > hammer_yield_check) {
                hmp->check_yield = 0;
                lwkt_user_yield();
        }

        /*
         * Loop until an element is found or we are done.
         */
        for (;;) {
                ++hammer_stats_btree_iterations;
                hammer_flusher_clean_loose_ios(hmp);

                /*
                 * We iterate up the tree and then index over one element
                 * while we are at the last element in the current node.
                 */
                if (cursor->index == -1) {
                        error = hammer_cursor_up(cursor);
                        if (error) {
                                cursor->index = 0; /* sanity */
                                break;
                        }
                        /* reload stale pointer */
                        node = cursor->node->ondisk;
                        KKASSERT(cursor->index != node->count);
                        --cursor->index;
                        continue;
                }

                /*
                 * Check internal or leaf element.  Determine if the record
                 * at the cursor has gone beyond the end of our range.
                 *
                 * We recurse down through internal nodes.
                 */
                KKASSERT(cursor->index != node->count);
                if (node->type == HAMMER_BTREE_TYPE_INTERNAL) {
                        elm = &node->elms[cursor->index];

                        r = hammer_btree_cmp(&cursor->key_end, &elm[0].base);
                        s = hammer_btree_cmp(&cursor->key_beg, &elm[1].base);
                        if (hammer_debug_btree) {
                                hammer_debug_btree_elm(cursor, elm, "BRACKETL", r);
                                hammer_debug_btree_elm(cursor, elm + 1, "BRACKETR", s);
                        }

                        if (s >= 0) {
                                error = ENOENT;
                                break;
                        }

                        /*
                         * It shouldn't be possible to be seeked past key_end,
                         * even if the cursor got moved to a parent.
                         */
                        KKASSERT(r >= 0);

                        /*
                         * Better not be zero
                         */
                        KKASSERT(elm->internal.subtree_offset != 0);

                        error = hammer_cursor_down(cursor);
                        if (error)
                                break;
                        KKASSERT(cursor->index == 0);
                        /* reload stale pointer */
                        node = cursor->node->ondisk;

                        /* this can assign -1 if the leaf was empty */
                        cursor->index = node->count - 1;
                        continue;
                } else {
                        elm = &node->elms[cursor->index];
                        s = hammer_btree_cmp(&cursor->key_beg, &elm->base);
                        if (hammer_debug_btree) {
                                hammer_debug_btree_elm(cursor, elm, "ELEMENTR", s);
                        }
                        if (s > 0) {
                                error = ENOENT;
                                break;
                        }

                        /*
                         * It shouldn't be possible to be seeked past key_end,
                         * even if the cursor got moved to a parent.
                         */
                        cursor->flags &= ~HAMMER_CURSOR_ITERATE_CHECK;

                        /*
                         * Return the element
                         */
                        switch(elm->leaf.base.btype) {
                        case HAMMER_BTREE_TYPE_RECORD:
                                if ((cursor->flags & HAMMER_CURSOR_ASOF) &&
                                    hammer_btree_chkts(cursor->asof, &elm->base)) {
                                        --cursor->index;
                                        continue;
                                }
                                error = 0;
                                break;
                        default:
                                error = EINVAL;
                                break;
                        }
                        if (error)
                                break;
                }

                /*
                 * Return entry
                 */
                if (hammer_debug_btree) {
                        elm = &cursor->node->ondisk->elms[cursor->index];
                        hammer_debug_btree_elm(cursor, elm, "ITERATER", 0xffff);
                }
                return(0);
        }
        return(error);
}

/*
 * Lookup cursor->key_beg.  0 is returned on success, ENOENT if the entry
 * could not be found, EDEADLK if inserting and a retry is needed, and a
 * fatal error otherwise.  When retrying, the caller must terminate the
 * cursor and reinitialize it.  EDEADLK cannot be returned if not inserting.
 *
 * The cursor is suitably positioned for a deletion on success, and suitably
 * positioned for an insertion on ENOENT if HAMMER_CURSOR_INSERT was
 * specified.
 *
 * The cursor may begin anywhere, the search will traverse the tree in
 * either direction to locate the requested element.
 *
 * Most of the logic implementing historical searches is handled here.  We
 * do an initial lookup with create_tid set to the asof TID.  Due to the
 * way records are laid out, a backwards iteration may be required if
 * ENOENT is returned to locate the historical record.  Here's the
 * problem:
 *
 * create_tid:    10      15       20
 *                   LEAF1   LEAF2
 * records:         (11)        (18)
 *
 * Lets say we want to do a lookup AS-OF timestamp 17.  We will traverse
 * LEAF2 but the only record in LEAF2 has a create_tid of 18, which is
 * not visible and thus causes ENOENT to be returned.  We really need
 * to check record 11 in LEAF1.  If it also fails then the search fails
 * (e.g. it might represent the range 11-16 and thus still not match our
 * AS-OF timestamp of 17).  Note that LEAF1 could be empty, requiring
 * further iterations.
 *
 * If this case occurs btree_search() will set HAMMER_CURSOR_CREATE_CHECK
 * and the cursor->create_check TID if an iteration might be needed.
 * In the above example create_check would be set to 14.
 */
int
hammer_btree_lookup(hammer_cursor_t cursor)
{
        int error;

        cursor->flags &= ~HAMMER_CURSOR_ITERATE_CHECK;
        KKASSERT ((cursor->flags & HAMMER_CURSOR_INSERT) == 0 ||
                  cursor->trans->sync_lock_refs > 0);
        ++hammer_stats_btree_lookups;
        if (cursor->flags & HAMMER_CURSOR_ASOF) {
                KKASSERT((cursor->flags & HAMMER_CURSOR_INSERT) == 0);
                cursor->key_beg.create_tid = cursor->asof;
                for (;;) {
                        cursor->flags &= ~HAMMER_CURSOR_CREATE_CHECK;
                        error = btree_search(cursor, 0);
                        if (error != ENOENT ||
                            (cursor->flags & HAMMER_CURSOR_CREATE_CHECK) == 0) {
                                /*
                                 * Stop if no error.
                                 * Stop if error other then ENOENT.
                                 * Stop if ENOENT and not special case.
                                 */
                                break;
                        }
                        if (hammer_debug_btree) {
                                hkprintf("CREATE_CHECK %016jx\n",
                                        (intmax_t)cursor->create_check);
                        }
                        cursor->key_beg.create_tid = cursor->create_check;
                        /* loop */
                }
        } else {
                error = btree_search(cursor, 0);
        }
        if (error == 0)
                error = hammer_btree_extract(cursor, cursor->flags);
        return(error);
}

/*
 * Execute the logic required to start an iteration.  The first record
 * located within the specified range is returned and iteration control
 * flags are adjusted for successive hammer_btree_iterate() calls.
 *
 * Set ATEDISK so a low-level caller can call btree_first/btree_iterate
 * in a loop without worrying about it.  Higher-level merged searches will
 * adjust the flag appropriately.
 */
int
hammer_btree_first(hammer_cursor_t cursor)
{
        int error;

        error = hammer_btree_lookup(cursor);
        if (error == ENOENT) {
                cursor->flags &= ~HAMMER_CURSOR_ATEDISK;
                error = hammer_btree_iterate(cursor);
        }
        cursor->flags |= HAMMER_CURSOR_ATEDISK;
        return(error);
}

/*
 * Similarly but for an iteration in the reverse direction.
 *
 * Set ATEDISK when iterating backwards to skip the current entry,
 * which after an ENOENT lookup will be pointing beyond our end point.
 *
 * Set ATEDISK so a low-level caller can call btree_last/btree_iterate_reverse
 * in a loop without worrying about it.  Higher-level merged searches will
 * adjust the flag appropriately.
 */
int
hammer_btree_last(hammer_cursor_t cursor)
{
        struct hammer_base_elm save;
        int error;

        save = cursor->key_beg;
        cursor->key_beg = cursor->key_end;
        error = hammer_btree_lookup(cursor);
        cursor->key_beg = save;
        if (error == ENOENT ||
            (cursor->flags & HAMMER_CURSOR_END_INCLUSIVE) == 0) {
                cursor->flags |= HAMMER_CURSOR_ATEDISK;
                error = hammer_btree_iterate_reverse(cursor);
        }
        cursor->flags |= HAMMER_CURSOR_ATEDISK;
        return(error);
}

/*
 * Extract the record and/or data associated with the cursor's current
 * position.  Any prior record or data stored in the cursor is replaced.
 *
 * NOTE: All extractions occur at the leaf of the B-Tree.
 */
int
hammer_btree_extract(hammer_cursor_t cursor, int flags)
{
        hammer_node_ondisk_t node;
        hammer_btree_elm_t elm;
        hammer_off_t data_off;
        hammer_mount_t hmp;
        int32_t data_len;
        int error;

        /*
         * Certain types of corruption can result in a NULL node pointer.
         */
        if (cursor->node == NULL) {
                hkprintf("NULL cursor->node, filesystem might "
                        "have gotten corrupted\n");
                return (EINVAL);
        }

        /*
         * The case where the data reference resolves to the same buffer
         * as the record reference must be handled.
         */
        node = cursor->node->ondisk;
        elm = &node->elms[cursor->index];
        cursor->data = NULL;
        hmp = cursor->node->hmp;

        /*
         * There is nothing to extract for an internal element.
         */
        if (node->type == HAMMER_BTREE_TYPE_INTERNAL)
                return(EINVAL);

        /*
         * Only record types have data.
         */
        KKASSERT(node->type == HAMMER_BTREE_TYPE_LEAF);
        cursor->leaf = &elm->leaf;

        /*
         * Returns here unless HAMMER_CURSOR_GET_DATA is set.
         */
        if ((flags & HAMMER_CURSOR_GET_DATA) == 0)
                return(0);

        if (elm->leaf.base.btype != HAMMER_BTREE_TYPE_RECORD)
                return(EINVAL);
        data_off = elm->leaf.data_offset;
        data_len = elm->leaf.data_len;
        if (data_off == 0)
                return(0);

        /*
         * Load the data
         */
        KKASSERT(data_len >= 0 && data_len <= HAMMER_XBUFSIZE);
        cursor->data = hammer_bread_ext(hmp, data_off, data_len,
                                        &error, &cursor->data_buffer);

        /*
         * Mark the data buffer as not being meta-data if it isn't
         * meta-data (sometimes bulk data is accessed via a volume
         * block device).
         */
        if (error == 0) {
                switch(elm->leaf.base.rec_type) {
                case HAMMER_RECTYPE_DATA:
                case HAMMER_RECTYPE_DB:
                        if ((data_off & HAMMER_ZONE_LARGE_DATA) == 0)
                                break;
                        if (hammer_double_buffer == 0 ||
                            (cursor->flags & HAMMER_CURSOR_NOSWAPCACHE)) {
                                hammer_io_notmeta(cursor->data_buffer);
                        }
                        break;
                default:
                        break;
                }
        }

        /*
         * Deal with CRC errors on the extracted data.
         */
        if (error == 0 &&
            hammer_crc_test_leaf(hmp->version, cursor->data, &elm->leaf) == 0) {
                hdkprintf("CRC DATA @ %016jx/%d FAILED\n",
                        (intmax_t)elm->leaf.data_offset, elm->leaf.data_len);
                if (hammer_debug_critical)
                        Debugger("CRC FAILED: DATA");
                if (cursor->trans->flags & HAMMER_TRANSF_CRCDOM)
                        error = EDOM;   /* less critical (mirroring) */
                else
                        error = EIO;    /* critical */
        }
        return(error);
}


/*
 * Insert a leaf element into the B-Tree at the current cursor position.
 * The cursor is positioned such that the element at and beyond the cursor
 * are shifted to make room for the new record.
 *
 * The caller must call hammer_btree_lookup() with the HAMMER_CURSOR_INSERT
 * flag set and that call must return ENOENT before this function can be
 * called. ENOSPC is returned if there is no room to insert a new record.
 *
 * The caller may depend on the cursor's exclusive lock after return to
 * interlock frontend visibility (see HAMMER_RECF_CONVERT_DELETE).
 */
int
hammer_btree_insert(hammer_cursor_t cursor, hammer_btree_leaf_elm_t elm,
                    int *doprop)
{
        hammer_node_ondisk_t node;
        int i;
        int error;

        *doprop = 0;
        if ((error = hammer_cursor_upgrade_node(cursor)) != 0)
                return(error);
        ++hammer_stats_btree_inserts;

        /*
         * Insert the element at the leaf node and update the count in the
         * parent.  It is possible for parent to be NULL, indicating that
         * the filesystem's ROOT B-Tree node is a leaf itself, which is
         * possible.  The root inode can never be deleted so the leaf should
         * never be empty.
         *
         * Remember that leaf nodes do not have boundaries.
         */
        hammer_modify_node_all(cursor->trans, cursor->node);
        node = cursor->node->ondisk;
        i = cursor->index;
        KKASSERT(elm->base.btype != 0);
        KKASSERT(node->type == HAMMER_BTREE_TYPE_LEAF);
        KKASSERT(node->count < HAMMER_BTREE_LEAF_ELMS);
        if (i != node->count) {
                bcopy(&node->elms[i], &node->elms[i+1],
                      (node->count - i) * sizeof(*elm));
        }
        node->elms[i].leaf = *elm;
        ++node->count;
        hammer_cursor_inserted_element(cursor->node, i);

        /*
         * Update the leaf node's aggregate mirror_tid for mirroring
         * support.
         */
        if (node->mirror_tid < elm->base.delete_tid) {
                node->mirror_tid = elm->base.delete_tid;
                *doprop = 1;
        }
        if (node->mirror_tid < elm->base.create_tid) {
                node->mirror_tid = elm->base.create_tid;
                *doprop = 1;
        }
        hammer_modify_node_done(cursor->node);

        /*
         * Debugging sanity checks.
         */
        KKASSERT(hammer_btree_cmp(cursor->left_bound, &elm->base) <= 0);
        KKASSERT(hammer_btree_cmp(cursor->right_bound, &elm->base) > 0);
        if (i) {
                KKASSERT(hammer_btree_cmp(&node->elms[i-1].leaf.base, &elm->base) < 0);
        }
        if (i != node->count - 1)
                KKASSERT(hammer_btree_cmp(&node->elms[i+1].leaf.base, &elm->base) > 0);

        return(0);
}

/*
 * Delete a record from the B-Tree at the current cursor position.
 * The cursor is positioned such that the current element is the one
 * to be deleted.
 *
 * On return the cursor will be positioned after the deleted element and
 * MAY point to an internal node.  It will be suitable for the continuation
 * of an iteration but not for an insertion or deletion.
 *
 * Deletions will attempt to partially rebalance the B-Tree in an upward
 * direction, but will terminate rather then deadlock.  Empty internal nodes
 * are never allowed by a deletion which deadlocks may end up giving us an
 * empty leaf.  The pruner will clean up and rebalance the tree.
 *
 * This function can return EDEADLK, requiring the caller to retry the
 * operation after clearing the deadlock.
 *
 * This function will store the number of deleted btree nodes in *ndelete
 * if ndelete is not NULL.
 */
int
hammer_btree_delete(hammer_cursor_t cursor, int *ndelete)
{
        hammer_node_ondisk_t ondisk;
        hammer_node_t node;
        hammer_node_t parent __debugvar;
        int error;
        int i;

        KKASSERT (cursor->trans->sync_lock_refs > 0);
        if (ndelete)
                *ndelete = 0;
        if ((error = hammer_cursor_upgrade(cursor)) != 0)
                return(error);
        ++hammer_stats_btree_deletes;

        /*
         * Delete the element from the leaf node.
         *
         * Remember that leaf nodes do not have boundaries.
         */
        node = cursor->node;
        ondisk = node->ondisk;
        i = cursor->index;

        KKASSERT(ondisk->type == HAMMER_BTREE_TYPE_LEAF);
        KKASSERT(i >= 0 && i < ondisk->count);
        hammer_modify_node_all(cursor->trans, node);
        if (i + 1 != ondisk->count) {
                bcopy(&ondisk->elms[i+1], &ondisk->elms[i],
                      (ondisk->count - i - 1) * sizeof(ondisk->elms[0]));
        }
        --ondisk->count;
        hammer_modify_node_done(node);
        hammer_cursor_deleted_element(node, i);

        /*
         * Validate local parent
         */
        if (ondisk->parent) {
                parent = cursor->parent;

                KKASSERT(parent != NULL);
                KKASSERT(parent->node_offset == ondisk->parent);
        }

        /*
         * If the leaf becomes empty it must be detached from the parent,
         * potentially recursing through to the filesystem root.
         *
         * This may reposition the cursor at one of the parent's of the
         * current node.
         *
         * Ignore deadlock errors, that simply means that btree_remove
         * was unable to recurse and had to leave us with an empty leaf.
         */
        KKASSERT(cursor->index <= ondisk->count);
        if (ondisk->count == 0) {
                error = btree_remove(cursor, ndelete);
                if (error == EDEADLK)
                        error = 0;
        } else {
                error = 0;
        }
        KKASSERT(cursor->parent == NULL ||
                 cursor->parent_index < cursor->parent->ondisk->count);
        return(error);
}

/*
 * PRIMARY B-TREE SEARCH SUPPORT PROCEDURE
 *
 * Search the filesystem B-Tree for cursor->key_beg, return the matching node.
 *
 * The search can begin ANYWHERE in the B-Tree.  As a first step the search
 * iterates up the tree as necessary to properly position itself prior to
 * actually doing the sarch.
 *
 * INSERTIONS: The search will split full nodes and leaves on its way down
 * and guarentee that the leaf it ends up on is not full.  If we run out
 * of space the search continues to the leaf, but ENOSPC is returned.
 *
 * The search is only guarenteed to end up on a leaf if an error code of 0
 * is returned, or if inserting and an error code of ENOENT is returned.
 * Otherwise it can stop at an internal node.  On success a search returns
 * a leaf node.
 *
 * COMPLEXITY WARNING!  This is the core B-Tree search code for the entire
 * filesystem, and it is not simple code.  Please note the following facts:
 *
 * - Internal node recursions have a boundary on the left AND right.  The
 *   right boundary is non-inclusive.  The create_tid is a generic part
 *   of the key for internal nodes.
 *
 * - Filesystem lookups typically set HAMMER_CURSOR_ASOF, indicating a
 *   historical search.  ASOF and INSERT are mutually exclusive.  When
 *   doing an as-of lookup btree_search() checks for a right-edge boundary
 *   case.  If while recursing down the left-edge differs from the key
 *   by ONLY its create_tid, HAMMER_CURSOR_CREATE_CHECK is set along
 *   with cursor->create_check.  This is used by btree_lookup() to iterate.
 *   The iteration backwards because as-of searches can wind up going
 *   down the wrong branch of the B-Tree.
 */
static
int
btree_search(hammer_cursor_t cursor, int flags)
{
        hammer_node_ondisk_t node;
        hammer_btree_elm_t elm;
        int error;
        int enospc = 0;
        int i;
        int r;
        int s;

        flags |= cursor->flags;
        ++hammer_stats_btree_searches;

        if (hammer_debug_btree) {
                hammer_debug_btree_elm(cursor,
                                (hammer_btree_elm_t)&cursor->key_beg,
                                "SEARCH", 0xffff);
                if (cursor->parent)
                        hammer_debug_btree_parent(cursor, "SEARCHP");
        }

        /*
         * Move our cursor up the tree until we find a node whos range covers
         * the key we are trying to locate.
         *
         * The left bound is inclusive, the right bound is non-inclusive.
         * It is ok to cursor up too far.
         */
        for (;;) {
                r = hammer_btree_cmp(&cursor->key_beg, cursor->left_bound);
                s = hammer_btree_cmp(&cursor->key_beg, cursor->right_bound);
                if (r >= 0 && s < 0)
                        break;
                KKASSERT(cursor->parent);
                ++hammer_stats_btree_iterations;
                error = hammer_cursor_up(cursor);
                if (error)
                        goto done;
        }

        /*
         * The delete-checks below are based on node, not parent.  Set the
         * initial delete-check based on the parent.
         */
        if (r == 1) {
                KKASSERT(cursor->left_bound->create_tid != 1);
                cursor->create_check = cursor->left_bound->create_tid - 1;
                cursor->flags |= HAMMER_CURSOR_CREATE_CHECK;
        }

        /*
         * We better have ended up with a node somewhere.
         */
        KKASSERT(cursor->node != NULL);

        /*
         * If we are inserting we can't start at a full node if the parent
         * is also full (because there is no way to split the node),
         * continue running up the tree until the requirement is satisfied
         * or we hit the root of the filesystem.
         *
         * (If inserting we aren't doing an as-of search so we don't have
         *  to worry about create_check).
         */
        while (flags & HAMMER_CURSOR_INSERT) {
                if (btree_node_is_full(cursor->node->ondisk) == 0)
                        break;
                if (cursor->node->ondisk->parent == 0 ||
                    cursor->parent->ondisk->count != HAMMER_BTREE_INT_ELMS) {
                        break;
                }
                ++hammer_stats_btree_iterations;
                error = hammer_cursor_up(cursor);
                /* node may have become stale */
                if (error)
                        goto done;
        }

        /*
         * Push down through internal nodes to locate the requested key.
         */
        node = cursor->node->ondisk;
        while (node->type == HAMMER_BTREE_TYPE_INTERNAL) {
                /*
                 * Scan the node to find the subtree index to push down into.
                 * We go one-past, then back-up.
                 *
                 * We must proactively remove deleted elements which may
                 * have been left over from a deadlocked btree_remove().
                 *
                 * The left and right boundaries are included in the loop
                 * in order to detect edge cases.
                 *
                 * If the separator only differs by create_tid (r == 1)
                 * and we are doing an as-of search, we may end up going
                 * down a branch to the left of the one containing the
                 * desired key.  This requires numerous special cases.
                 */
                ++hammer_stats_btree_iterations;
                if (hammer_debug_btree) {
                        hkprintf("SEARCH-I %016jx count=%d\n",
                                (intmax_t)cursor->node->node_offset,
                                node->count);
                }

                /*
                 * Try to shortcut the search before dropping into the
                 * linear loop.  Locate the first node where r <= 1.
                 */
                i = hammer_btree_search_node(&cursor->key_beg, node);
                while (i <= node->count) {
                        ++hammer_stats_btree_elements;
                        elm = &node->elms[i];
                        r = hammer_btree_cmp(&cursor->key_beg, &elm->base);
                        if (hammer_debug_btree > 2) {
                                hkprintf(" IELM %p [%d] r=%d\n",
                                        &node->elms[i], i, r);
                        }
                        if (r < 0)
                                break;
                        if (r == 1) {
                                KKASSERT(elm->base.create_tid != 1);
                                cursor->create_check = elm->base.create_tid - 1;
                                cursor->flags |= HAMMER_CURSOR_CREATE_CHECK;
                        }
                        ++i;
                }
                if (hammer_debug_btree) {
                        hkprintf("SEARCH-I preI=%d/%d r=%d\n",
                                i, node->count, r);
                }

                /*
                 * The first two cases (i == 0 or i == node->count + 1)
                 * occur when the parent's idea of the boundary
                 * is wider then the child's idea of the boundary, and
                 * require special handling.  If not inserting we can
                 * terminate the search early for these cases but the
                 * child's boundaries cannot be unconditionally modified.
                 *
                 * The last case (neither of the above) fits in child's
                 * idea of the boundary, so we can simply push down the
                 * cursor.
                 */
                if (i == 0) {
                        /*
                         * If i == 0 the search terminated to the LEFT of the
                         * left_boundary but to the RIGHT of the parent's left
                         * boundary.
                         */
                        uint8_t save;

                        elm = &node->elms[0];

                        /*
                         * If we aren't inserting we can stop here.
                         */
                        if ((flags & (HAMMER_CURSOR_INSERT |
                                      HAMMER_CURSOR_PRUNING)) == 0) {
                                cursor->index = 0;
                                return(ENOENT);
                        }

                        /*
                         * Correct a left-hand boundary mismatch.
                         *
                         * We can only do this if we can upgrade the lock,
                         * and synchronized as a background cursor (i.e.
                         * inserting or pruning).
                         *
                         * WARNING: We can only do this if inserting, i.e.
                         * we are running on the backend.
                         */
                        if ((error = hammer_cursor_upgrade(cursor)) != 0)
                                return(error);
                        KKASSERT(cursor->flags & HAMMER_CURSOR_BACKEND);
                        hammer_modify_node_field(cursor->trans, cursor->node,
                                                 elms[0]);
                        save = node->elms[0].base.btype;
                        node->elms[0].base = *cursor->left_bound;
                        node->elms[0].base.btype = save;
                        hammer_modify_node_done(cursor->node);
                } else if (i == node->count + 1) {
                        /*
                         * If i == node->count + 1 the search terminated to
                         * the RIGHT of the right boundary but to the LEFT
                         * of the parent's right boundary.  If we aren't
                         * inserting we can stop here.
                         *
                         * Note that the last element in this case is
                         * elms[i-2] prior to adjustments to 'i'.
                         */
                        --i;
                        if ((flags & (HAMMER_CURSOR_INSERT |
                                      HAMMER_CURSOR_PRUNING)) == 0) {
                                cursor->index = i;
                                return (ENOENT);
                        }

                        /*
                         * Correct a right-hand boundary mismatch.
                         * (actual push-down record is i-2 prior to
                         * adjustments to i).
                         *
                         * We can only do this if we can upgrade the lock,
                         * and synchronized as a background cursor (i.e.
                         * inserting or pruning).
                         *
                         * WARNING: We can only do this if inserting, i.e.
                         * we are running on the backend.
                         */
                        if ((error = hammer_cursor_upgrade(cursor)) != 0)
                                return(error);
                        elm = &node->elms[i];
                        KKASSERT(cursor->flags & HAMMER_CURSOR_BACKEND);
                        hammer_modify_node(cursor->trans, cursor->node,
                                           &elm->base, sizeof(elm->base));
                        elm->base = *cursor->right_bound;
                        hammer_modify_node_done(cursor->node);
                        --i;
                } else {
                        /*
                         * The push-down index is now i - 1.  If we had
                         * terminated on the right boundary this will point
                         * us at the last element.
                         */
                        --i;
                }
                cursor->index = i;
                elm = &node->elms[i];

                if (hammer_debug_btree) {
                        hammer_debug_btree_elm(cursor, elm, "RESULT-I", 0xffff);
                }

                /*
                 * We better have a valid subtree offset.
                 */
                KKASSERT(elm->internal.subtree_offset != 0);

                /*
                 * Handle insertion and deletion requirements.
                 *
                 * If inserting split full nodes.  The split code will
                 * adjust cursor->node and cursor->index if the current
                 * index winds up in the new node.
                 *
                 * If inserting and a left or right edge case was detected,
                 * we cannot correct the left or right boundary and must
                 * prepend and append an empty leaf node in order to make
                 * the boundary correction.
                 *
                 * If we run out of space we set enospc but continue on
                 * to a leaf.
                 */
                if ((flags & HAMMER_CURSOR_INSERT) && enospc == 0) {
                        if (btree_node_is_full(node)) {
                                error = btree_split_internal(cursor);
                                if (error) {
                                        if (error != ENOSPC)
                                                goto done;
                                        enospc = 1;
                                }
                                /*
                                 * reload stale pointers
                                 */
                                i = cursor->index;
                                node = cursor->node->ondisk;
                        }
                }

                /*
                 * Push down (push into new node, existing node becomes
                 * the parent) and continue the search.
                 */
                error = hammer_cursor_down(cursor);
                /* node may have become stale */
                if (error)
                        goto done;
                node = cursor->node->ondisk;
        }

        /*
         * We are at a leaf, do a linear search of the key array.
         *
         * On success the index is set to the matching element and 0
         * is returned.
         *
         * On failure the index is set to the insertion point and ENOENT
         * is returned.
         *
         * Boundaries are not stored in leaf nodes, so the index can wind
         * up to the left of element 0 (index == 0) or past the end of
         * the array (index == node->count).  It is also possible that the
         * leaf might be empty.
         */
        ++hammer_stats_btree_iterations;
        KKASSERT (node->type == HAMMER_BTREE_TYPE_LEAF);
        KKASSERT(node->count <= HAMMER_BTREE_LEAF_ELMS);
        if (hammer_debug_btree) {
                hkprintf("SEARCH-L %016jx count=%d\n",
                        (intmax_t)cursor->node->node_offset,
                        node->count);
        }

        /*
         * Try to shortcut the search before dropping into the
         * linear loop.  Locate the first node where r <= 1.
         */
        i = hammer_btree_search_node(&cursor->key_beg, node);
        while (i < node->count) {
                ++hammer_stats_btree_elements;
                elm = &node->elms[i];

                r = hammer_btree_cmp(&cursor->key_beg, &elm->leaf.base);

                if (hammer_debug_btree > 1)
                        hkprintf(" LELM %p [%d] r=%d\n", &node->elms[i], i, r);

                /*
                 * We are at a record element.  Stop if we've flipped past
                 * key_beg, not counting the create_tid test.  Allow the
                 * r == 1 case (key_beg > element but differs only by its
                 * create_tid) to fall through to the AS-OF check.
                 */
                KKASSERT (elm->leaf.base.btype == HAMMER_BTREE_TYPE_RECORD);

                if (r < 0)
                        goto failed;
                if (r > 1) {
                        ++i;
                        continue;
                }

                /*
                 * Check our as-of timestamp against the element.
                 */
                if (flags & HAMMER_CURSOR_ASOF) {
                        if (hammer_btree_chkts(cursor->asof,
                                               &node->elms[i].base) != 0) {
                                ++i;
                                continue;
                        }
                        /* success */
                } else {
                        if (r > 0) {    /* can only be +1 */
                                ++i;
                                continue;
                        }
                        /* success */
                }
                cursor->index = i;
                error = 0;
                if (hammer_debug_btree) {
                        hkprintf("RESULT-L %016jx[%d] (SUCCESS)\n",
                                (intmax_t)cursor->node->node_offset, i);
                }
                goto done;
        }

        /*
         * The search of the leaf node failed.  i is the insertion point.
         */
failed:
        if (hammer_debug_btree) {
                hkprintf("RESULT-L %016jx[%d] (FAILED)\n",
                        (intmax_t)cursor->node->node_offset, i);
        }

        /*
         * No exact match was found, i is now at the insertion point.
         *
         * If inserting split a full leaf before returning.  This
         * may have the side effect of adjusting cursor->node and
         * cursor->index.
         */
        cursor->index = i;
        if ((flags & HAMMER_CURSOR_INSERT) && enospc == 0 &&
             btree_node_is_full(node)) {
                error = btree_split_leaf(cursor);
                if (error) {
                        if (error != ENOSPC)
                                goto done;
                        enospc = 1;
                }
                /*
                 * reload stale pointers
                 */
                /* NOT USED
                i = cursor->index;
                node = &cursor->node->internal;
                */
        }

        /*
         * We reached a leaf but did not find the key we were looking for.
         * If this is an insert we will be properly positioned for an insert
         * (ENOENT) or unable to insert (ENOSPC).
         */
        error = enospc ? ENOSPC : ENOENT;
done:
        return(error);
}

/*
 * Heuristical search for the first element whos comparison is <= 1.  May
 * return an index whos compare result is > 1 but may only return an index
 * whos compare result is <= 1 if it is the first element with that result.
 */
int
hammer_btree_search_node(hammer_base_elm_t elm, hammer_node_ondisk_t node)
{
        int b;
        int s;
        int i;
        int r;

        /*
         * Don't bother if the node does not have very many elements
         */
        b = 0;
        s = node->count;
        while (s - b > 4) {
                i = b + (s - b) / 2;
                ++hammer_stats_btree_elements;
                r = hammer_btree_cmp(elm, &node->elms[i].leaf.base);
                if (r <= 1) {
                        s = i;
                } else {
                        b = i;
                }
        }
        return(b);
}


/************************************************************************
 *                         SPLITTING AND MERGING                        *
 ************************************************************************
 *
 * These routines do all the dirty work required to split and merge nodes.
 */

/*
 * Split an internal node into two nodes and move the separator at the split
 * point to the parent.
 *
 * (cursor->node, cursor->index) indicates the element the caller intends
 * to push into.  We will adjust node and index if that element winds
 * up in the split node.
 *
 * If we are at the root of the filesystem a new root must be created with
 * two elements, one pointing to the original root and one pointing to the
 * newly allocated split node.
 */
static
int
btree_split_internal(hammer_cursor_t cursor)
{
        hammer_node_ondisk_t ondisk;
        hammer_node_t node;
        hammer_node_t parent;
        hammer_node_t new_node;
        hammer_btree_elm_t elm;
        hammer_btree_elm_t parent_elm;
        struct hammer_node_lock lockroot;
        hammer_mount_t hmp = cursor->trans->hmp;
        int parent_index;
        int made_root;
        int split;
        int error;
        int i;
        const int esize = sizeof(*elm);

        hammer_node_lock_init(&lockroot, cursor->node);
        error = hammer_btree_lock_children(cursor, 1, &lockroot, NULL);
        if (error)
                goto done;
        if ((error = hammer_cursor_upgrade(cursor)) != 0)
                goto done;
        ++hammer_stats_btree_splits;

        /*
         * Calculate the split point.  If the insertion point is at the
         * end of the leaf we adjust the split point significantly to the
         * right to try to optimize node fill and flag it.  If we hit
         * that same leaf again our heuristic failed and we don't try
         * to optimize node fill (it could lead to a degenerate case).
         */
        node = cursor->node;
        ondisk = node->ondisk;
        KKASSERT(ondisk->count > 4);
        if (cursor->index == ondisk->count &&
            (node->flags & HAMMER_NODE_NONLINEAR) == 0) {
                split = (ondisk->count + 1) * 3 / 4;
                node->flags |= HAMMER_NODE_NONLINEAR;
        } else {
                /*
                 * We are splitting but elms[split] will be promoted to
                 * the parent, leaving the right hand node with one less
                 * element.  If the insertion point will be on the
                 * left-hand side adjust the split point to give the
                 * right hand side one additional node.
                 */
                split = (ondisk->count + 1) / 2;
                if (cursor->index <= split)
                        --split;
        }

        /*
         * If we are at the root of the filesystem, create a new root node
         * with 1 element and split normally.  Avoid making major
         * modifications until we know the whole operation will work.
         */
        if (ondisk->parent == 0) {
                parent = hammer_alloc_btree(cursor->trans, 0, &error);
                if (parent == NULL)
                        goto done;
                hammer_lock_ex(&parent->lock);
                hammer_modify_node_noundo(cursor->trans, parent);
                ondisk = parent->ondisk;
                ondisk->count = 1;
                ondisk->parent = 0;
                ondisk->mirror_tid = node->ondisk->mirror_tid;
                ondisk->type = HAMMER_BTREE_TYPE_INTERNAL;
                ondisk->elms[0].base = hmp->root_btree_beg;
                ondisk->elms[0].base.btype = node->ondisk->type;
                ondisk->elms[0].internal.subtree_offset = node->node_offset;
                ondisk->elms[0].internal.mirror_tid = ondisk->mirror_tid;
                ondisk->elms[1].base = hmp->root_btree_end;
                hammer_modify_node_done(parent);
                made_root = 1;
                parent_index = 0;       /* index of current node in parent */
        } else {
                made_root = 0;
                parent = cursor->parent;
                parent_index = cursor->parent_index;
        }

        /*
         * Split node into new_node at the split point.
         *
         *  B O O O P N N B     <-- P = node->elms[split] (index 4)
         *   0 1 2 3 4 5 6      <-- subtree indices
         *
         *       x x P x x
         *        s S S s
         *         /   \
         *  B O O O B    B N N B        <--- inner boundary points are 'P'
         *   0 1 2 3      4 5 6
         */
        new_node = hammer_alloc_btree(cursor->trans, 0, &error);
        if (new_node == NULL) {
                if (made_root) {
                        hammer_unlock(&parent->lock);
                        hammer_delete_node(cursor->trans, parent);
                        hammer_rel_node(parent);
                }
                goto done;
        }
        hammer_lock_ex(&new_node->lock);

        /*
         * Create the new node.  P becomes the left-hand boundary in the
         * new node.  Copy the right-hand boundary as well.
         *
         * elm is the new separator.
         */
        hammer_modify_node_noundo(cursor->trans, new_node);
        hammer_modify_node_all(cursor->trans, node);
        ondisk = node->ondisk;
        elm = &ondisk->elms[split];
        bcopy(elm, &new_node->ondisk->elms[0],
              (ondisk->count - split + 1) * esize);  /* +1 for boundary */
        new_node->ondisk->count = ondisk->count - split;
        new_node->ondisk->parent = parent->node_offset;
        new_node->ondisk->type = HAMMER_BTREE_TYPE_INTERNAL;
        new_node->ondisk->mirror_tid = ondisk->mirror_tid;
        KKASSERT(ondisk->type == new_node->ondisk->type);
        hammer_cursor_split_node(node, new_node, split);

        /*
         * Cleanup the original node.  Elm (P) becomes the new boundary,
         * its subtree_offset was moved to the new node.  If we had created
         * a new root its parent pointer may have changed.
         */
        elm->base.btype = HAMMER_BTREE_TYPE_NONE;
        elm->internal.subtree_offset = 0;
        ondisk->count = split;

        /*
         * Insert the separator into the parent, fixup the parent's
         * reference to the original node, and reference the new node.
         * The separator is P.
         *
         * Remember that ondisk->count does not include the right-hand boundary.
         */
        hammer_modify_node_all(cursor->trans, parent);
        ondisk = parent->ondisk;
        KKASSERT(ondisk->count != HAMMER_BTREE_INT_ELMS);
        parent_elm = &ondisk->elms[parent_index+1];
        bcopy(parent_elm, parent_elm + 1,
              (ondisk->count - parent_index) * esize);

        /*
         * Why not use hammer_make_separator() here ?
         */
        parent_elm->internal.base = elm->base;  /* separator P */
        parent_elm->internal.base.btype = new_node->ondisk->type;
        parent_elm->internal.subtree_offset = new_node->node_offset;
        parent_elm->internal.mirror_tid = new_node->ondisk->mirror_tid;
        ++ondisk->count;
        hammer_modify_node_done(parent);
        hammer_cursor_inserted_element(parent, parent_index + 1);

        /*
         * The children of new_node need their parent pointer set to new_node.
         * The children have already been locked by
         * hammer_btree_lock_children().
         */
        for (i = 0; i < new_node->ondisk->count; ++i) {
                elm = &new_node->ondisk->elms[i];
                error = btree_set_parent_of_child(cursor->trans, new_node, elm);
                if (error) {
                        hpanic("btree-fixup problem");
                }
        }
        hammer_modify_node_done(new_node);

        /*
         * The filesystem's root B-Tree pointer may have to be updated.
         */
        if (made_root) {
                hammer_volume_t volume;

                volume = hammer_get_root_volume(hmp, &error);
                KKASSERT(error == 0);

                hammer_modify_volume_field(cursor->trans, volume,
                                           vol0_btree_root);
                volume->ondisk->vol0_btree_root = parent->node_offset;
                hammer_modify_volume_done(volume);
                node->ondisk->parent = parent->node_offset;
                if (cursor->parent) {
                        hammer_unlock(&cursor->parent->lock);
                        hammer_rel_node(cursor->parent);
                }
                cursor->parent = parent;        /* lock'd and ref'd */
                hammer_rel_volume(volume, 0);
        }
        hammer_modify_node_done(node);

        /*
         * Ok, now adjust the cursor depending on which element the original
         * index was pointing at.  If we are >= the split point the push node
         * is now in the new node.
         *
         * NOTE: If we are at the split point itself we cannot stay with the
         * original node because the push index will point at the right-hand
         * boundary, which is illegal.
         *
         * NOTE: The cursor's parent or parent_index must be adjusted for
         * the case where a new parent (new root) was created, and the case
         * where the cursor is now pointing at the split node.
         */
        if (cursor->index >= split) {
                cursor->parent_index = parent_index + 1;
                cursor->index -= split;
                hammer_unlock(&cursor->node->lock);
                hammer_rel_node(cursor->node);
                cursor->node = new_node;        /* locked and ref'd */
        } else {
                cursor->parent_index = parent_index;
                hammer_unlock(&new_node->lock);
                hammer_rel_node(new_node);
        }

        /*
         * Fixup left and right bounds
         */
        parent_elm = &parent->ondisk->elms[cursor->parent_index];
        cursor->left_bound = &parent_elm[0].internal.base;
        cursor->right_bound = &parent_elm[1].internal.base;
        KKASSERT(hammer_btree_cmp(cursor->left_bound,
                 &cursor->node->ondisk->elms[0].internal.base) <= 0);
        KKASSERT(hammer_btree_cmp(cursor->right_bound,
                 &cursor->node->ondisk->elms[cursor->node->ondisk->count].internal.base) >= 0);

done:
        hammer_btree_unlock_children(cursor->trans->hmp, &lockroot, NULL);
        hammer_cursor_downgrade(cursor);
        return (error);
}

/*
 * Same as the above, but splits a full leaf node.
 */
static
int
btree_split_leaf(hammer_cursor_t cursor)
{
        hammer_node_ondisk_t ondisk;
        hammer_node_t parent;
        hammer_node_t leaf;
        hammer_mount_t hmp;
        hammer_node_t new_leaf;
        hammer_btree_elm_t elm;
        hammer_btree_elm_t parent_elm;
        hammer_base_elm_t mid_boundary;
        int parent_index;
        int made_root;
        int split;
        int error;
        const size_t esize = sizeof(*elm);

        if ((error = hammer_cursor_upgrade(cursor)) != 0)
                return(error);
        ++hammer_stats_btree_splits;

        KKASSERT(hammer_btree_cmp(cursor->left_bound,
                 &cursor->node->ondisk->elms[0].leaf.base) <= 0);
        KKASSERT(hammer_btree_cmp(cursor->right_bound,
                 &cursor->node->ondisk->elms[cursor->node->ondisk->count-1].leaf.base) > 0);

        /*
         * Calculate the split point.  If the insertion point is at the
         * end of the leaf we adjust the split point significantly to the
         * right to try to optimize node fill and flag it.  If we hit
         * that same leaf again our heuristic failed and we don't try
         * to optimize node fill (it could lead to a degenerate case).
         */
        leaf = cursor->node;
        ondisk = leaf->ondisk;
        KKASSERT(ondisk->count > 4);
        if (cursor->index == ondisk->count &&
            (leaf->flags & HAMMER_NODE_NONLINEAR) == 0) {
                split = (ondisk->count + 1) * 3 / 4;
                leaf->flags |= HAMMER_NODE_NONLINEAR;
        } else {
                split = (ondisk->count + 1) / 2;
        }

#if 0
        /*
         * If the insertion point is at the split point shift the
         * split point left so we don't have to worry about
         */
        if (cursor->index == split)
                --split;
#endif
        KKASSERT(split > 0 && split < ondisk->count);

        error = 0;
        hmp = leaf->hmp;

        elm = &ondisk->elms[split];

        KKASSERT(hammer_btree_cmp(cursor->left_bound, &elm[-1].leaf.base) <= 0);
        KKASSERT(hammer_btree_cmp(cursor->left_bound, &elm->leaf.base) <= 0);
        KKASSERT(hammer_btree_cmp(cursor->right_bound, &elm->leaf.base) > 0);
        KKASSERT(hammer_btree_cmp(cursor->right_bound, &elm[1].leaf.base) > 0);

        /*
         * If we are at the root of the tree, create a new root node with
         * 1 element and split normally.  Avoid making major modifications
         * until we know the whole operation will work.
         */
        if (ondisk->parent == 0) {
                parent = hammer_alloc_btree(cursor->trans, 0, &error);
                if (parent == NULL)
                        goto done;
                hammer_lock_ex(&parent->lock);
                hammer_modify_node_noundo(cursor->trans, parent);
                ondisk = parent->ondisk;
                ondisk->count = 1;
                ondisk->parent = 0;
                ondisk->mirror_tid = leaf->ondisk->mirror_tid;
                ondisk->type = HAMMER_BTREE_TYPE_INTERNAL;
                ondisk->elms[0].base = hmp->root_btree_beg;
                ondisk->elms[0].base.btype = leaf->ondisk->type;
                ondisk->elms[0].internal.subtree_offset = leaf->node_offset;
                ondisk->elms[0].internal.mirror_tid = ondisk->mirror_tid;
                ondisk->elms[1].base = hmp->root_btree_end;
                hammer_modify_node_done(parent);
                made_root = 1;
                parent_index = 0;       /* insertion point in parent */
        } else {
                made_root = 0;
                parent = cursor->parent;
                parent_index = cursor->parent_index;
        }

        /*
         * Split leaf into new_leaf at the split point.  Select a separator
         * value in-between the two leafs but with a bent towards the right
         * leaf since comparisons use an 'elm >= separator' inequality.
         *
         *  L L L L L L L L
         *
         *       x x P x x
         *        s S S s
         *         /   \
         *  L L L L     L L L L
         */
        new_leaf = hammer_alloc_btree(cursor->trans, 0, &error);
        if (new_leaf == NULL) {
                if (made_root) {
                        hammer_unlock(&parent->lock);
                        hammer_delete_node(cursor->trans, parent);
                        hammer_rel_node(parent);
                }
                goto done;
        }
        hammer_lock_ex(&new_leaf->lock);

        /*
         * Create the new node and copy the leaf elements from the split
         * point on to the new node.
         */
        hammer_modify_node_all(cursor->trans, leaf);
        hammer_modify_node_noundo(cursor->trans, new_leaf);
        ondisk = leaf->ondisk;
        elm = &ondisk->elms[split];
        bcopy(elm, &new_leaf->ondisk->elms[0], (ondisk->count - split) * esize);
        new_leaf->ondisk->count = ondisk->count - split;
        new_leaf->ondisk->parent = parent->node_offset;
        new_leaf->ondisk->type = HAMMER_BTREE_TYPE_LEAF;
        new_leaf->ondisk->mirror_tid = ondisk->mirror_tid;
        KKASSERT(ondisk->type == new_leaf->ondisk->type);
        hammer_modify_node_done(new_leaf);
        hammer_cursor_split_node(leaf, new_leaf, split);

        /*
         * Cleanup the original node.  Because this is a leaf node and
         * leaf nodes do not have a right-hand boundary, there
         * aren't any special edge cases to clean up.  We just fixup the
         * count.
         */
        ondisk->count = split;

        /*
         * Insert the separator into the parent, fixup the parent's
         * reference to the original node, and reference the new node.
         * The separator is P.
         *
         * Remember that ondisk->count does not include the right-hand boundary.
         * We are copying parent_index+1 to parent_index+2, not +0 to +1.
         */
        hammer_modify_node_all(cursor->trans, parent);
        ondisk = parent->ondisk;
        KKASSERT(split != 0);
        KKASSERT(ondisk->count != HAMMER_BTREE_INT_ELMS);
        parent_elm = &ondisk->elms[parent_index+1];
        bcopy(parent_elm, parent_elm + 1,
              (ondisk->count - parent_index) * esize);

        /*
         * elm[-1] is the right-most elm in the original node.
         * elm[0] equals the left-most elm at index=0 in the new node.
         * parent_elm[-1] and parent_elm point to original and new node.
         * Update the parent_elm base to meet >elm[-1] and <=elm[0].
         */
        hammer_make_separator(&elm[-1].base, &elm[0].base, &parent_elm->base);
        parent_elm->internal.base.btype = new_leaf->ondisk->type;
        parent_elm->internal.subtree_offset = new_leaf->node_offset;
        parent_elm->internal.mirror_tid = new_leaf->ondisk->mirror_tid;
        mid_boundary = &parent_elm->base;
        ++ondisk->count;
        hammer_modify_node_done(parent);
        hammer_cursor_inserted_element(parent, parent_index + 1);

        /*
         * The filesystem's root B-Tree pointer may have to be updated.
         */
        if (made_root) {
                hammer_volume_t volume;

                volume = hammer_get_root_volume(hmp, &error);
                KKASSERT(error == 0);

                hammer_modify_volume_field(cursor->trans, volume,
                                           vol0_btree_root);
                volume->ondisk->vol0_btree_root = parent->node_offset;
                hammer_modify_volume_done(volume);
                leaf->ondisk->parent = parent->node_offset;
                if (cursor->parent) {
                        hammer_unlock(&cursor->parent->lock);
                        hammer_rel_node(cursor->parent);
                }
                cursor->parent = parent;        /* lock'd and ref'd */
                hammer_rel_volume(volume, 0);
        }
        hammer_modify_node_done(leaf);

        /*
         * Ok, now adjust the cursor depending on which element the original
         * index was pointing at.  If we are >= the split point the push node
         * is now in the new node.
         *
         * NOTE: If we are at the split point itself we need to select the
         * old or new node based on where key_beg's insertion point will be.
         * If we pick the wrong side the inserted element will wind up in
         * the wrong leaf node and outside that node's bounds.
         */
        if (cursor->index > split ||
            (cursor->index == split &&
             hammer_btree_cmp(&cursor->key_beg, mid_boundary) >= 0)) {
                cursor->parent_index = parent_index + 1;
                cursor->index -= split;
                hammer_unlock(&cursor->node->lock);
                hammer_rel_node(cursor->node);
                cursor->node = new_leaf;
        } else {
                cursor->parent_index = parent_index;
                hammer_unlock(&new_leaf->lock);
                hammer_rel_node(new_leaf);
        }

        /*
         * Fixup left and right bounds
         */
        parent_elm = &parent->ondisk->elms[cursor->parent_index];
        cursor->left_bound = &parent_elm[0].internal.base;
        cursor->right_bound = &parent_elm[1].internal.base;

        /*
         * Assert that the bounds are correct.
         */
        KKASSERT(hammer_btree_cmp(cursor->left_bound,
                 &cursor->node->ondisk->elms[0].leaf.base) <= 0);
        KKASSERT(hammer_btree_cmp(cursor->right_bound,
                 &cursor->node->ondisk->elms[cursor->node->ondisk->count-1].leaf.base) > 0);
        KKASSERT(hammer_btree_cmp(cursor->left_bound, &cursor->key_beg) <= 0);
        KKASSERT(hammer_btree_cmp(cursor->right_bound, &cursor->key_beg) > 0);

done:
        hammer_cursor_downgrade(cursor);
        return (error);
}


/*
 * Attempt to remove the locked, empty or want-to-be-empty B-Tree node at
 * (cursor->node).  Returns 0 on success, EDEADLK if we could not complete
 * the operation due to a deadlock, or some other error.
 *
 * This routine is initially called with an empty leaf and may be
 * recursively called with single-element internal nodes.
 *
 * It should also be noted that when removing empty leaves we must be sure
 * to test and update mirror_tid because another thread may have deadlocked
 * against us (or someone) trying to propagate it up and cannot retry once
 * the node has been deleted.
 *
 * On return the cursor may end up pointing to an internal node, suitable
 * for further iteration but not for an immediate insertion or deletion.
 */
static int
btree_remove(hammer_cursor_t cursor, int *ndelete)
{
        hammer_node_ondisk_t ondisk;
        hammer_btree_elm_t elm;
        hammer_node_t node;
        hammer_node_t parent;
        const int esize = sizeof(*elm);
        int error;

        node = cursor->node;

        /*
         * When deleting the root of the filesystem convert it to
         * an empty leaf node.  Internal nodes cannot be empty.
         */
        ondisk = node->ondisk;
        if (ondisk->parent == 0) {
                KKASSERT(cursor->parent == NULL);
                hammer_modify_node_all(cursor->trans, node);
                KKASSERT(ondisk == node->ondisk);
                ondisk->type = HAMMER_BTREE_TYPE_LEAF;
                ondisk->count = 0;
                hammer_modify_node_done(node);
                cursor->index = 0;
                return(0);
        }

        parent = cursor->parent;

        /*
         * Attempt to remove the parent's reference to the child.  If the
         * parent would become empty we have to recurse.  If we fail we
         * leave the parent pointing to an empty leaf node.
         *
         * We have to recurse successfully before we can delete the internal
         * node as it is illegal to have empty internal nodes.  Even though
         * the operation may be aborted we must still fixup any unlocked
         * cursors as if we had deleted the element prior to recursing
         * (by calling hammer_cursor_deleted_element()) so those cursors
         * are properly forced up the chain by the recursion.
         */
        if (parent->ondisk->count == 1) {
                /*
                 * This special cursor_up_locked() call leaves the original
                 * node exclusively locked and referenced, leaves the
                 * original parent locked (as the new node), and locks the
                 * new parent.  It can return EDEADLK.
                 *
                 * We cannot call hammer_cursor_removed_node() until we are
                 * actually able to remove the node.  If we did then tracked
                 * cursors in the middle of iterations could be repointed
                 * to a parent node.  If this occurs they could end up
                 * scanning newly inserted records into the node (that could
                 * not be deleted) when they push down again.
                 *
                 * Due to the way the recursion works the final parent is left
                 * in cursor->parent after the recursion returns.  Each
                 * layer on the way back up is thus able to call
                 * hammer_cursor_removed_node() and 'jump' the node up to
                 * the (same) final parent.
                 *
                 * NOTE!  The local variable 'parent' is invalid after we
                 *        call hammer_cursor_up_locked().
                 */
                error = hammer_cursor_up_locked(cursor);
                parent = NULL;

                if (error == 0) {
                        hammer_cursor_deleted_element(cursor->node, 0);
                        error = btree_remove(cursor, ndelete);
                        if (error == 0) {
                                KKASSERT(node != cursor->node);
                                hammer_cursor_removed_node(
                                        node, cursor->node, cursor->index);
                                hammer_modify_node_all(cursor->trans, node);
                                ondisk = node->ondisk;
                                ondisk->type = HAMMER_BTREE_TYPE_DELETED;
                                ondisk->count = 0;
                                hammer_modify_node_done(node);
                                hammer_flush_node(node, 0);
                                hammer_delete_node(cursor->trans, node);
                                if (ndelete)
                                        (*ndelete)++;
                        } else {
                                /*
                                 * Defer parent removal because we could not
                                 * get the lock, just let the leaf remain
                                 * empty.
                                 */
                                /*
                                 * hammer show doesn't consider this as an error.
                                 */
                        }
                        hammer_unlock(&node->lock);
                        hammer_rel_node(node);
                } else {
                        /*
                         * Defer parent removal because we could not
                         * get the lock, just let the leaf remain
                         * empty.
                         */
                        /*
                         * hammer show doesn't consider this as an error.
                         */
                }
        } else {
                KKASSERT(parent->ondisk->count > 1);

                hammer_modify_node_all(cursor->trans, parent);
                ondisk = parent->ondisk;
                KKASSERT(ondisk->type == HAMMER_BTREE_TYPE_INTERNAL);

                elm = &ondisk->elms[cursor->parent_index];
                KKASSERT(elm->internal.subtree_offset == node->node_offset);
                KKASSERT(ondisk->count > 0);

                /*
                 * We must retain the highest mirror_tid.  The deleted
                 * range is now encompassed by the element to the left.
                 * If we are already at the left edge the new left edge
                 * inherits mirror_tid.
                 *
                 * Note that bounds of the parent to our parent may create
                 * a gap to the left of our left-most node or to the right
                 * of our right-most node.  The gap is silently included
                 * in the mirror_tid's area of effect from the point of view
                 * of the scan.
                 */
                if (cursor->parent_index) {
                        if (elm[-1].internal.mirror_tid <
                            elm[0].internal.mirror_tid) {
                                elm[-1].internal.mirror_tid =
                                    elm[0].internal.mirror_tid;
                        }
                } else {
                        if (elm[1].internal.mirror_tid <
                            elm[0].internal.mirror_tid) {
                                elm[1].internal.mirror_tid =
                                    elm[0].internal.mirror_tid;
                        }
                }

                /*
                 * Delete the subtree reference in the parent.  Include
                 * boundary element at end.
                 */
                bcopy(&elm[1], &elm[0],
                      (ondisk->count - cursor->parent_index) * esize);
                --ondisk->count;
                hammer_modify_node_done(parent);
                hammer_cursor_removed_node(node, parent, cursor->parent_index);
                hammer_cursor_deleted_element(parent, cursor->parent_index);
                hammer_flush_node(node, 0);
                hammer_delete_node(cursor->trans, node);

                /*
                 * cursor->node is invalid, cursor up to make the cursor
                 * valid again.  We have to flag the condition in case
                 * another thread wiggles an insertion in during an
                 * iteration.
                 */
                cursor->flags |= HAMMER_CURSOR_ITERATE_CHECK;
                error = hammer_cursor_up(cursor);
                if (ndelete)
                        (*ndelete)++;
        }
        return (error);
}

/*
 * Propagate mirror_tid up the B-Tree starting at the current cursor.
 *
 * WARNING!  Because we push and pop the passed cursor, it may be
 *           modified by other B-Tree operations while it is unlocked
 *           and things like the node & leaf pointers, and indexes might
 *           change.
 */
void
hammer_btree_do_propagation(hammer_cursor_t cursor,
                            hammer_btree_leaf_elm_t leaf)
{
        hammer_cursor_t ncursor;
        hammer_tid_t mirror_tid;
        int error __debugvar;

        /*
         * We do not propagate a mirror_tid if the filesystem was mounted
         * in no-mirror mode.
         */
        if (cursor->trans->hmp->master_id < 0)
                return;

        /*
         * This is a bit of a hack because we cannot deadlock or return
         * EDEADLK here.  The related operation has already completed and
         * we must propagate the mirror_tid now regardless.
         *
         * Generate a new cursor which inherits the original's locks and
         * unlock the original.  Use the new cursor to propagate the
         * mirror_tid.  Then clean up the new cursor and reacquire locks
         * on the original.
         *
         * hammer_dup_cursor() cannot dup locks.  The dup inherits the
         * original's locks and the original is tracked and must be
         * re-locked.
         */
        mirror_tid = cursor->node->ondisk->mirror_tid;
        KKASSERT(mirror_tid != 0);
        ncursor = hammer_push_cursor(cursor);
        error = hammer_btree_mirror_propagate(ncursor, mirror_tid);
        KKASSERT(error == 0);
        hammer_pop_cursor(cursor, ncursor);
        /* WARNING: cursor's leaf pointer may change after pop */
}


/*
 * Propagate a mirror TID update upwards through the B-Tree to the root.
 *
 * A locked internal node must be passed in.  The node will remain locked
 * on return.
 *
 * This function syncs mirror_tid at the specified internal node's element,
 * adjusts the node's aggregation mirror_tid, and then recurses upwards.
 */
static int
hammer_btree_mirror_propagate(hammer_cursor_t cursor, hammer_tid_t mirror_tid)
{
        hammer_btree_internal_elm_t elm;
        hammer_node_t node;
        int error;

        for (;;) {
                error = hammer_cursor_up(cursor);
                if (error == 0)
                        error = hammer_cursor_upgrade(cursor);

                /*
                 * We can ignore HAMMER_CURSOR_ITERATE_CHECK, the
                 * cursor will still be properly positioned for
                 * mirror propagation, just not for iterations.
                 */
                while (error == EDEADLK) {
                        hammer_recover_cursor(cursor);
                        error = hammer_cursor_upgrade(cursor);
                }
                if (error)
                        break;

                /*
                 * If the cursor deadlocked it could end up at a leaf
                 * after we lost the lock.
                 */
                node = cursor->node;
                if (node->ondisk->type != HAMMER_BTREE_TYPE_INTERNAL)
                        continue;

                /*
                 * Adjust the node's element
                 */
                elm = &node->ondisk->elms[cursor->index].internal;
                if (elm->mirror_tid >= mirror_tid)
                        break;
                hammer_modify_node(cursor->trans, node, &elm->mirror_tid,
                                   sizeof(elm->mirror_tid));
                elm->mirror_tid = mirror_tid;
                hammer_modify_node_done(node);
                if (hammer_debug_general & 0x0002) {
                        hdkprintf("propagate %016jx @%016jx:%d\n",
                                (intmax_t)mirror_tid,
                                (intmax_t)node->node_offset,
                                cursor->index);
                }


                /*
                 * Adjust the node's mirror_tid aggregator
                 */
                if (node->ondisk->mirror_tid >= mirror_tid)
                        return(0);
                hammer_modify_node_field(cursor->trans, node, mirror_tid);
                node->ondisk->mirror_tid = mirror_tid;
                hammer_modify_node_done(node);
                if (hammer_debug_general & 0x0002) {
                        hdkprintf("propagate %016jx @%016jx\n",
                                (intmax_t)mirror_tid,
                                (intmax_t)node->node_offset);
                }
        }
        if (error == ENOENT)
                error = 0;
        return(error);
}

/*
 * Return a pointer to node's parent.  If there is no error,
 * *parent_index is set to an index of parent's elm that points
 * to this node.
 */
hammer_node_t
hammer_btree_get_parent(hammer_transaction_t trans, hammer_node_t node,
                        int *parent_indexp, int *errorp, int try_exclusive)
{
        hammer_node_t parent;
        hammer_btree_elm_t elm;
        int i;

        /*
         * Get the node
         */
        parent = hammer_get_node(trans, node->ondisk->parent, 0, errorp);
        if (*errorp) {
                KKASSERT(parent == NULL);
                return(NULL);
        }
        KKASSERT ((parent->flags & HAMMER_NODE_DELETED) == 0);

        /*
         * Lock the node
         */
        if (try_exclusive) {
                if (hammer_lock_ex_try(&parent->lock)) {
                        hammer_rel_node(parent);
                        *errorp = EDEADLK;
                        return(NULL);
                }
        } else {
                hammer_lock_sh(&parent->lock);
        }

        /*
         * Figure out which element in the parent is pointing to the
         * child.
         */
        if (node->ondisk->count) {
                i = hammer_btree_search_node(&node->ondisk->elms[0].base,
                                             parent->ondisk);
        } else {
                i = 0;
        }
        while (i < parent->ondisk->count) {
                elm = &parent->ondisk->elms[i];
                if (elm->internal.subtree_offset == node->node_offset)
                        break;
                ++i;
        }
        if (i == parent->ondisk->count) {
                hammer_unlock(&parent->lock);
                hpanic("Bad B-Tree link: parent %p node %p", parent, node);
        }
        *parent_indexp = i;
        KKASSERT(*errorp == 0);
        return(parent);
}

/*
 * The element (elm) has been moved to a new internal node (node).
 *
 * If the element represents a pointer to an internal node that node's
 * parent must be adjusted to the element's new location.
 *
 * XXX deadlock potential here with our exclusive locks
 */
int
btree_set_parent_of_child(hammer_transaction_t trans, hammer_node_t node,
                 hammer_btree_elm_t elm)
{
        hammer_node_t child;
        int error;

        error = 0;

        if (hammer_is_internal_node_elm(elm)) {
                child = hammer_get_node(trans, elm->internal.subtree_offset,
                                        0, &error);
                if (error == 0) {
                        hammer_modify_node_field(trans, child, parent);
                        child->ondisk->parent = node->node_offset;
                        hammer_modify_node_done(child);
                        hammer_rel_node(child);
                }
        }
        return(error);
}

/*
 * Initialize the root of a recursive B-Tree node lock list structure.
 */
void
hammer_node_lock_init(hammer_node_lock_t parent, hammer_node_t node)
{
        TAILQ_INIT(&parent->list);
        parent->parent = NULL;
        parent->node = node;
        parent->index = -1;
        parent->count = node->ondisk->count;
        parent->copy = NULL;
        parent->flags = 0;
}

/*
 * Initialize a cache of hammer_node_lock's including space allocated
 * for node copies.
 *
 * This is used by the rebalancing code to preallocate the copy space
 * for ~4096 B-Tree nodes (16MB of data) prior to acquiring any HAMMER
 * locks, otherwise we can blow out the pageout daemon's emergency
 * reserve and deadlock it.
 *
 * NOTE: HAMMER_NODE_LOCK_LCACHE is not set on items cached in the lcache.
 *       The flag is set when the item is pulled off the cache for use.
 */
void
hammer_btree_lcache_init(hammer_mount_t hmp, hammer_node_lock_t lcache,
                         int depth)
{
        hammer_node_lock_t item;
        int count;

        for (count = 1; depth; --depth)
                count *= HAMMER_BTREE_LEAF_ELMS;
        bzero(lcache, sizeof(*lcache));
        TAILQ_INIT(&lcache->list);
        while (count) {
                item = kmalloc(sizeof(*item), hmp->m_misc, M_WAITOK|M_ZERO);
                item->copy = kmalloc(sizeof(*item->copy),
                                     hmp->m_misc, M_WAITOK);
                TAILQ_INIT(&item->list);
                TAILQ_INSERT_TAIL(&lcache->list, item, entry);
                --count;
        }
}

void
hammer_btree_lcache_free(hammer_mount_t hmp, hammer_node_lock_t lcache)
{
        hammer_node_lock_t item;

        while ((item = TAILQ_FIRST(&lcache->list)) != NULL) {
                TAILQ_REMOVE(&lcache->list, item, entry);
                KKASSERT(item->copy);
                KKASSERT(TAILQ_EMPTY(&item->list));
                kfree(item->copy, hmp->m_misc);
                kfree(item, hmp->m_misc);
        }
        KKASSERT(lcache->copy == NULL);
}

/*
 * Exclusively lock all the children of node.  This is used by the split
 * code to prevent anyone from accessing the children of a cursor node
 * while we fix-up its parent offset.
 *
 * If we don't lock the children we can really mess up cursors which block
 * trying to cursor-up into our node.
 *
 * On failure EDEADLK (or some other error) is returned.  If a deadlock
 * error is returned the cursor is adjusted to block on termination.
 *
 * The caller is responsible for managing parent->node, the root's node
 * is usually aliased from a cursor.
 */
int
hammer_btree_lock_children(hammer_cursor_t cursor, int depth,
                           hammer_node_lock_t parent,
                           hammer_node_lock_t lcache)
{
        hammer_node_t node;
        hammer_node_lock_t item;
        hammer_node_ondisk_t ondisk;
        hammer_btree_elm_t elm;
        hammer_node_t child;
        hammer_mount_t hmp;
        int error;
        int i;

        node = parent->node;
        ondisk = node->ondisk;
        error = 0;
        hmp = cursor->trans->hmp;

        if (ondisk->type != HAMMER_BTREE_TYPE_INTERNAL)
                return(0);  /* This could return non-zero */

        /*
         * We really do not want to block on I/O with exclusive locks held,
         * pre-get the children before trying to lock the mess.  This is
         * only done one-level deep for now.
         */
        for (i = 0; i < ondisk->count; ++i) {
                ++hammer_stats_btree_elements;
                elm = &ondisk->elms[i];
                child = hammer_get_node(cursor->trans,
                                        elm->internal.subtree_offset,
                                        0, &error);
                if (child)
                        hammer_rel_node(child);
        }

        /*
         * Do it for real
         */
        for (i = 0; error == 0 && i < ondisk->count; ++i) {
                ++hammer_stats_btree_elements;
                elm = &ondisk->elms[i];

                KKASSERT(elm->internal.subtree_offset != 0);
                child = hammer_get_node(cursor->trans,
                                        elm->internal.subtree_offset,
                                        0, &error);
                if (child) {
                        if (hammer_lock_ex_try(&child->lock) != 0) {
                                if (cursor->deadlk_node == NULL) {
                                        cursor->deadlk_node = child;
                                        hammer_ref_node(cursor->deadlk_node);
                                }
                                error = EDEADLK;
                                hammer_rel_node(child);
                        } else {
                                if (lcache) {
                                        item = TAILQ_FIRST(&lcache->list);
                                        KKASSERT(item != NULL);
                                        item->flags |= HAMMER_NODE_LOCK_LCACHE;
                                        TAILQ_REMOVE(&lcache->list, item, entry);
                                } else {
                                        item = kmalloc(sizeof(*item),
                                                       hmp->m_misc,
                                                       M_WAITOK|M_ZERO);
                                        TAILQ_INIT(&item->list);
                                }

                                TAILQ_INSERT_TAIL(&parent->list, item, entry);
                                item->parent = parent;
                                item->node = child;
                                item->index = i;
                                item->count = child->ondisk->count;

                                /*
                                 * Recurse (used by the rebalancing code)
                                 */
                                if (depth > 1 && elm->base.btype == HAMMER_BTREE_TYPE_INTERNAL) {
                                        error = hammer_btree_lock_children(
                                                        cursor,
                                                        depth - 1,
                                                        item,
                                                        lcache);
                                }
                        }
                }
        }
        if (error)
                hammer_btree_unlock_children(hmp, parent, lcache);
        return(error);
}

/*
 * Create an in-memory copy of all B-Tree nodes listed, recursively,
 * including the parent.
 */
void
hammer_btree_lock_copy(hammer_cursor_t cursor, hammer_node_lock_t parent)
{
        hammer_mount_t hmp = cursor->trans->hmp;
        hammer_node_lock_t item;

        if (parent->copy == NULL) {
                KKASSERT((parent->flags & HAMMER_NODE_LOCK_LCACHE) == 0);
                parent->copy = kmalloc(sizeof(*parent->copy),
                                       hmp->m_misc, M_WAITOK);
        }
        KKASSERT((parent->flags & HAMMER_NODE_LOCK_UPDATED) == 0);
        *parent->copy = *parent->node->ondisk;
        TAILQ_FOREACH(item, &parent->list, entry) {
                hammer_btree_lock_copy(cursor, item);
        }
}

/*
 * Recursively sync modified copies to the media.
 */
int
hammer_btree_sync_copy(hammer_cursor_t cursor, hammer_node_lock_t parent)
{
        hammer_node_lock_t item;
        int count = 0;

        if (parent->flags & HAMMER_NODE_LOCK_UPDATED) {
                ++count;
                hammer_modify_node_all(cursor->trans, parent->node);
                *parent->node->ondisk = *parent->copy;
                hammer_modify_node_done(parent->node);
                if (parent->copy->type == HAMMER_BTREE_TYPE_DELETED) {
                        hammer_flush_node(parent->node, 0);
                        hammer_delete_node(cursor->trans, parent->node);
                }
        }
        TAILQ_FOREACH(item, &parent->list, entry) {
                count += hammer_btree_sync_copy(cursor, item);
        }
        return(count);
}

/*
 * Release previously obtained node locks.  The caller is responsible for
 * cleaning up parent->node itself (its usually just aliased from a cursor),
 * but this function will take care of the copies.
 *
 * NOTE: The root node is not placed in the lcache and node->copy is not
 *       deallocated when lcache != NULL.
 */
void
hammer_btree_unlock_children(hammer_mount_t hmp, hammer_node_lock_t parent,
                             hammer_node_lock_t lcache)
{
        hammer_node_lock_t item;
        hammer_node_ondisk_t copy;

        while ((item = TAILQ_FIRST(&parent->list)) != NULL) {
                TAILQ_REMOVE(&parent->list, item, entry);
                hammer_btree_unlock_children(hmp, item, lcache);
                hammer_unlock(&item->node->lock);
                hammer_rel_node(item->node);
                if (lcache) {
                        /*
                         * NOTE: When placing the item back in the lcache
                         *       the flag is cleared by the bzero().
                         *       Remaining fields are cleared as a safety
                         *       measure.
                         */
                        KKASSERT(item->flags & HAMMER_NODE_LOCK_LCACHE);
                        KKASSERT(TAILQ_EMPTY(&item->list));
                        copy = item->copy;
                        bzero(item, sizeof(*item));
                        TAILQ_INIT(&item->list);
                        item->copy = copy;
                        if (copy)
                                bzero(copy, sizeof(*copy));
                        TAILQ_INSERT_TAIL(&lcache->list, item, entry);
                } else {
                        kfree(item, hmp->m_misc);
                }
        }
        if (parent->copy && (parent->flags & HAMMER_NODE_LOCK_LCACHE) == 0) {
                kfree(parent->copy, hmp->m_misc);
                parent->copy = NULL;    /* safety */
        }
}

/************************************************************************
 *                         MISCELLANIOUS SUPPORT                        *
 ************************************************************************/

/*
 * Compare two B-Tree elements, return -N, 0, or +N (e.g. similar to strcmp).
 *
 * Note that for this particular function a return value of -1, 0, or +1
 * can denote a match if create_tid is otherwise discounted.  A create_tid
 * of zero is considered to be 'infinity' in comparisons.
 *
 * See also hammer_rec_rb_compare() and hammer_rec_cmp() in hammer_object.c.
 */
int
hammer_btree_cmp(hammer_base_elm_t key1, hammer_base_elm_t key2)
{
        if (key1->localization < key2->localization)
                return(-5);
        if (key1->localization > key2->localization)
                return(5);

        if (key1->obj_id < key2->obj_id)
                return(-4);
        if (key1->obj_id > key2->obj_id)
                return(4);

        if (key1->rec_type < key2->rec_type)
                return(-3);
        if (key1->rec_type > key2->rec_type)
                return(3);

        if (key1->key < key2->key)
                return(-2);
        if (key1->key > key2->key)
                return(2);

        /*
         * A create_tid of zero indicates a record which is undeletable
         * and must be considered to have a value of positive infinity.
         */
        if (key1->create_tid == 0) {
                if (key2->create_tid == 0)
                        return(0);
                return(1);
        }
        if (key2->create_tid == 0)
                return(-1);
        if (key1->create_tid < key2->create_tid)
                return(-1);
        if (key1->create_tid > key2->create_tid)
                return(1);
        return(0);
}

/*
 * Test a timestamp against an element to determine whether the
 * element is visible.  A timestamp of 0 means 'infinity'.
 */
int
hammer_btree_chkts(hammer_tid_t asof, hammer_base_elm_t base)
{
        if (asof == 0) {
                if (base->delete_tid)
                        return(1);
                return(0);
        }
        if (asof < base->create_tid)
                return(-1);
        if (base->delete_tid && asof >= base->delete_tid)
                return(1);
        return(0);
}

/*
 * Create a separator half way inbetween key1 and key2.  For fields just
 * one unit apart, the separator will match key2.  key1 is on the left-hand
 * side and key2 is on the right-hand side.
 *
 * key2 must be >= the separator.  It is ok for the separator to match key2.
 *
 * NOTE: Even if key1 does not match key2, the separator may wind up matching
 * key2.
 *
 * NOTE: It might be beneficial to just scrap this whole mess and just
 * set the separator to key2.
 */
#define MAKE_SEPARATOR(key1, key2, dest, field) \
        dest->field = key1->field + ((key2->field - key1->field + 1) >> 1);

static void
hammer_make_separator(hammer_base_elm_t key1, hammer_base_elm_t key2,
                      hammer_base_elm_t dest)
{
        bzero(dest, sizeof(*dest));

        dest->rec_type = key2->rec_type;
        dest->key = key2->key;
        dest->obj_id = key2->obj_id;
        dest->create_tid = key2->create_tid;

        MAKE_SEPARATOR(key1, key2, dest, localization);
        if (key1->localization == key2->localization) {
                MAKE_SEPARATOR(key1, key2, dest, obj_id);
                if (key1->obj_id == key2->obj_id) {
                        MAKE_SEPARATOR(key1, key2, dest, rec_type);
                        if (key1->rec_type == key2->rec_type) {
                                MAKE_SEPARATOR(key1, key2, dest, key);
                                /*
                                 * Don't bother creating a separator for
                                 * create_tid, which also conveniently avoids
                                 * having to handle the create_tid == 0
                                 * (infinity) case.  Just leave create_tid
                                 * set to key2.
                                 *
                                 * Worst case, dest matches key2 exactly,
                                 * which is acceptable.
                                 */
                        }
                }
        }
}

#undef MAKE_SEPARATOR

/*
 * Return whether a generic internal or leaf node is full
 */
static __inline
int
btree_node_is_full(hammer_node_ondisk_t node)
{
        int n;

        n = hammer_node_max_elements(node->type);
        if (n == -1)
                hpanic("bad type %d", node->type);

        return(n == node->count);
}

void
hammer_print_btree_node(hammer_node_ondisk_t ondisk)
{
        int i, n;

        kprintf("node %p count=%d parent=%016jx type=%c\n",
                ondisk, ondisk->count,
                (intmax_t)ondisk->parent, ondisk->type);

        switch (ondisk->type) {
        case HAMMER_BTREE_TYPE_INTERNAL:
                n = ondisk->count + 1;  /* count is NOT boundary inclusive */
                break;
        case HAMMER_BTREE_TYPE_LEAF:
                n = ondisk->count;  /* there is no boundary */
                break;
        default:
                return;  /* nothing to do */
        }

        /*
         * Dump elements including boundary.
         */
        for (i = 0; i < n; ++i) {
                kprintf("  %2d", i);
                hammer_print_btree_elm(&ondisk->elms[i]);
        }
}

void
hammer_print_btree_elm(hammer_btree_elm_t elm)
{
        kprintf("\tobj_id       = %016jx\n", (intmax_t)elm->base.obj_id);
        kprintf("\tkey          = %016jx\n", (intmax_t)elm->base.key);
        kprintf("\tcreate_tid   = %016jx\n", (intmax_t)elm->base.create_tid);
        kprintf("\tdelete_tid   = %016jx\n", (intmax_t)elm->base.delete_tid);
        kprintf("\trec_type     = %04x\n", elm->base.rec_type);
        kprintf("\tobj_type     = %02x\n", elm->base.obj_type);
        kprintf("\tbtype        = %02x (%c)\n", elm->base.btype,
                                                hammer_elm_btype(elm));
        kprintf("\tlocalization = %08x\n", elm->base.localization);

        if (hammer_is_internal_node_elm(elm)) {
                kprintf("\tsubtree_off  = %016jx\n",
                        (intmax_t)elm->internal.subtree_offset);
        } else if (hammer_is_leaf_node_elm(elm)) {
                kprintf("\tdata_offset  = %016jx\n",
                        (intmax_t)elm->leaf.data_offset);
                kprintf("\tdata_len     = %08x\n", elm->leaf.data_len);
                kprintf("\tdata_crc     = %08x\n", elm->leaf.data_crc);
        }
}

static __inline
void
hammer_debug_btree_elm(hammer_cursor_t cursor, hammer_btree_elm_t elm,
                const char *s, int res)
{
        hkprintf("%-8s %016jx[%02d] %c "
                "lo=%08x obj=%016jx rec=%02x key=%016jx tid=%016jx td=%p "
                "r=%d\n",
                s,
                (intmax_t)cursor->node->node_offset,
                cursor->index,
                hammer_elm_btype(elm),
                elm->base.localization,
                (intmax_t)elm->base.obj_id,
                elm->base.rec_type,
                (intmax_t)elm->base.key,
                (intmax_t)elm->base.create_tid,
                curthread,
                res);
}

static __inline
void
hammer_debug_btree_parent(hammer_cursor_t cursor, const char *s)
{
        hammer_btree_elm_t elm =
            &cursor->parent->ondisk->elms[cursor->parent_index];

        hkprintf("%-8s %016jx[%d] %c "
                "(%016jx/%016jx %016jx/%016jx) (%p/%p %p/%p)\n",
                s,
                (intmax_t)cursor->parent->node_offset,
                cursor->parent_index,
                hammer_elm_btype(elm),
                (intmax_t)cursor->left_bound->obj_id,
                (intmax_t)elm->internal.base.obj_id,
                (intmax_t)cursor->right_bound->obj_id,
                (intmax_t)(elm + 1)->internal.base.obj_id,
                cursor->left_bound,
                elm,
                cursor->right_bound,
                elm + 1);
}