/*
 * 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 - cursor support routines
 */
#include "hammer.h"

static int hammer_load_cursor_parent(hammer_cursor_t cursor, int try_exclusive);

/*
 * Initialize a fresh cursor using the B-Tree node cache.  If the cache
 * is not available initialize a fresh cursor at the root of the filesystem.
 */
int
hammer_init_cursor(hammer_transaction_t trans, hammer_cursor_t cursor,
                   hammer_node_cache_t cache, hammer_inode_t ip)
{
        hammer_volume_t volume;
        hammer_node_t node;
        hammer_mount_t hmp;
        u_int tticks;
        int error;

        bzero(cursor, sizeof(*cursor));

        cursor->trans = trans;
        hmp = trans->hmp;

        /*
         * As the number of inodes queued to the flusher increases we use
         * time-domain multiplexing to control read vs flush performance.
         * We have to do it here, before acquiring any ip or node locks,
         * to avoid deadlocking or excessively delaying the flusher.
         *
         * The full time period is hammer_tdmux_ticks, typically 1/5 of
         * a second.
         *
         * inode allocation begins to get restrained at 2/4 the limit
         * via the "hmrrcm" mechanism in hammer_inode.  We want to begin
         * limiting read activity before that to try to avoid processes
         * stalling out in "hmrrcm".
         */
        tticks = hammer_tdmux_ticks;
        if (trans->type != HAMMER_TRANS_FLS && tticks &&
            hmp->count_reclaims > hammer_limit_reclaims / tticks &&
            hmp->count_reclaims > hammer_autoflush * 2 &&
            hammer_flusher_running(hmp)) {
                u_int rticks;
                u_int xticks;
                u_int dummy;

                /*
                 * 0 ... xticks ... tticks
                 *
                 * rticks is the calculated position, xticks is the demarc
                 * where values below xticks are reserved for the flusher
                 * and values >= to xticks may be used by the frontend.
                 *
                 * At least one tick is always made available for the
                 * frontend.
                 */
                rticks = (u_int)ticks % tticks;
                xticks = hmp->count_reclaims * tticks / hammer_limit_reclaims;

                /*
                 * Ensure rticks and xticks are stable
                 */
                cpu_ccfence();
                if (rticks < xticks) {
                        if (hammer_debug_general & 0x0004)
                                hdkprintf("rt %3u, xt %3u, tt %3u\n",
                                        rticks, xticks, tticks);
                        tsleep(&dummy, 0, "htdmux", xticks - rticks);
                }
        }

        /*
         * If the cursor operation is on behalf of an inode, lock
         * the inode.
         *
         * When acquiring a shared lock on an inode on which the backend
         * flusher deadlocked, wait up to hammer_tdmux_ticks (1 second)
         * for the deadlock to clear.
         */
        if ((cursor->ip = ip) != NULL) {
                ++ip->cursor_ip_refs;
                if (trans->type == HAMMER_TRANS_FLS) {
                        hammer_lock_ex(&ip->lock);
                } else {
#if 0
                        if (ip->cursor_exclreq_count) {
                                tsleep(&ip->cursor_exclreq_count, 0,
                                       "hstag1", hammer_tdmux_ticks);
                        }
#endif
                        hammer_lock_sh(&ip->lock);
                }
        }

        /*
         * Step 1 - acquire a locked node from the cache if possible
         */
        if (cache && cache->node) {
                node = hammer_ref_node_safe(trans, cache, &error);
                if (error == 0) {
                        hammer_lock_sh(&node->lock);
                        if (node->flags & HAMMER_NODE_DELETED) {
                                hammer_unlock(&node->lock);
                                hammer_rel_node(node);
                                node = NULL;
                        }
                }
                if (node == NULL)
                        ++hammer_stats_btree_root_iterations;
        } else {
                node = NULL;
                ++hammer_stats_btree_root_iterations;
        }

        /*
         * Step 2 - If we couldn't get a node from the cache, get
         * the one from the root of the filesystem.
         */
        while (node == NULL) {
                volume = hammer_get_root_volume(hmp, &error);
                if (error)
                        break;
                node = hammer_get_node(trans, volume->ondisk->vol0_btree_root,
                                       0, &error);
                hammer_rel_volume(volume, 0);
                if (error)
                        break;
                /*
                 * When the frontend acquires the root b-tree node while the
                 * backend is deadlocked on it, wait up to hammer_tdmux_ticks
                 * (1 second) for the deadlock to clear.
                 */
#if 0
                if (node->cursor_exclreq_count &&
                    cursor->trans->type != HAMMER_TRANS_FLS) {
                        tsleep(&node->cursor_exclreq_count, 0,
                               "hstag3", hammer_tdmux_ticks);
                }
#endif
                hammer_lock_sh(&node->lock);

                /*
                 * If someone got in before we could lock the node, retry.
                 */
                if (node->flags & HAMMER_NODE_DELETED) {
                        hammer_unlock(&node->lock);
                        hammer_rel_node(node);
                        node = NULL;
                        continue;
                }
                if (volume->ondisk->vol0_btree_root != node->node_offset) {
                        hammer_unlock(&node->lock);
                        hammer_rel_node(node);
                        node = NULL;
                        continue;
                }
        }

        /*
         * Step 3 - finish initializing the cursor by acquiring the parent
         */
        cursor->node = node;
        if (error == 0)
                error = hammer_load_cursor_parent(cursor, 0);
        KKASSERT(error == 0);
        /* if (error) hammer_done_cursor(cursor); */
        return(error);
}

/*
 * Normalize a cursor.  Sometimes cursors can be left in a state
 * where node is NULL.  If the cursor is in this state, cursor up.
 */
void
hammer_normalize_cursor(hammer_cursor_t cursor)
{
        if (cursor->node == NULL) {
                KKASSERT(cursor->parent != NULL);
                hammer_cursor_up(cursor);
        }
}


/*
 * We are finished with a cursor.  We NULL out various fields as sanity
 * check, in case the structure is inappropriately used afterwords.
 */
void
hammer_done_cursor(hammer_cursor_t cursor)
{
        hammer_inode_t ip;

        KKASSERT((cursor->flags & HAMMER_CURSOR_TRACKED) == 0);
        if (cursor->parent) {
                hammer_unlock(&cursor->parent->lock);
                hammer_rel_node(cursor->parent);
                cursor->parent = NULL;
        }
        if (cursor->node) {
                hammer_unlock(&cursor->node->lock);
                hammer_rel_node(cursor->node);
                cursor->node = NULL;
        }
        if (cursor->data_buffer) {
                hammer_rel_buffer(cursor->data_buffer, 0);
                cursor->data_buffer = NULL;
        }
        if ((ip = cursor->ip) != NULL) {
                KKASSERT(ip->cursor_ip_refs > 0);
                --ip->cursor_ip_refs;
                hammer_unlock(&ip->lock);
                cursor->ip = NULL;
        }
        if (cursor->iprec) {
                hammer_rel_mem_record(cursor->iprec);
                cursor->iprec = NULL;
        }

        /*
         * If we deadlocked this node will be referenced.  Do a quick
         * lock/unlock to wait for the deadlock condition to clear.
         *
         * Maintain exclreq_count / wakeup as necessary to notify new
         * entrants into ip.  We continue to hold the fs_token so our
         * EDEADLK retry loop should get its chance before another thread
         * steals the lock.
         */
        if (cursor->deadlk_node) {
#if 0
                if (ip && cursor->trans->type == HAMMER_TRANS_FLS)
                        ++ip->cursor_exclreq_count;
                ++cursor->deadlk_node->cursor_exclreq_count;
#endif
                hammer_lock_ex_ident(&cursor->deadlk_node->lock, "hmrdlk");
                hammer_unlock(&cursor->deadlk_node->lock);
#if 0
                if (--cursor->deadlk_node->cursor_exclreq_count == 0)
                        wakeup(&cursor->deadlk_node->cursor_exclreq_count);
                if (ip && cursor->trans->type == HAMMER_TRANS_FLS) {
                        if (--ip->cursor_exclreq_count == 0)
                                wakeup(&ip->cursor_exclreq_count);
                }
#endif
                hammer_rel_node(cursor->deadlk_node);
                cursor->deadlk_node = NULL;
        }
        if (cursor->deadlk_rec) {
                hammer_wait_mem_record_ident(cursor->deadlk_rec, "hmmdlr");
                hammer_rel_mem_record(cursor->deadlk_rec);
                cursor->deadlk_rec = NULL;
        }

        cursor->data = NULL;
        cursor->leaf = NULL;
        cursor->left_bound = NULL;
        cursor->right_bound = NULL;
        cursor->trans = NULL;
}

/*
 * Upgrade cursor->node and cursor->parent to exclusive locks.  This
 * function can return EDEADLK.
 *
 * The lock must already be either held shared or already held exclusively
 * by us.
 *
 * We upgrade the parent first as it is the most likely to collide first
 * with the downward traversal that the frontend typically does.
 *
 * If we fail to upgrade the lock and cursor->deadlk_node is NULL,
 * we add another reference to the node that failed and set
 * cursor->deadlk_node so hammer_done_cursor() can block on it.
 */
int
hammer_cursor_upgrade(hammer_cursor_t cursor)
{
        int error;

        if (cursor->parent) {
                error = hammer_lock_upgrade(&cursor->parent->lock, 1);
                if (error && cursor->deadlk_node == NULL) {
                        cursor->deadlk_node = cursor->parent;
                        hammer_ref_node(cursor->deadlk_node);
                }
        } else {
                error = 0;
        }
        if (error == 0) {
                error = hammer_lock_upgrade(&cursor->node->lock, 1);
                if (error && cursor->deadlk_node == NULL) {
                        cursor->deadlk_node = cursor->node;
                        hammer_ref_node(cursor->deadlk_node);
                }
        }
#if 0
        error = hammer_lock_upgrade(&cursor->node->lock, 1);
        if (error && cursor->deadlk_node == NULL) {
                cursor->deadlk_node = cursor->node;
                hammer_ref_node(cursor->deadlk_node);
        } else if (error == 0 && cursor->parent) {
                error = hammer_lock_upgrade(&cursor->parent->lock, 1);
                if (error && cursor->deadlk_node == NULL) {
                        cursor->deadlk_node = cursor->parent;
                        hammer_ref_node(cursor->deadlk_node);
                }
        }
#endif
        return(error);
}

int
hammer_cursor_upgrade_node(hammer_cursor_t cursor)
{
        int error;

        error = hammer_lock_upgrade(&cursor->node->lock, 1);
        if (error && cursor->deadlk_node == NULL) {
                cursor->deadlk_node = cursor->node;
                hammer_ref_node(cursor->deadlk_node);
        }
        return(error);
}

/*
 * Downgrade cursor->node and cursor->parent to shared locks.
 */
void
hammer_cursor_downgrade(hammer_cursor_t cursor)
{
        if (hammer_lock_excl_owned(&cursor->node->lock, curthread))
                hammer_lock_downgrade(&cursor->node->lock, 1);
        if (cursor->parent &&
            hammer_lock_excl_owned(&cursor->parent->lock, curthread)) {
                hammer_lock_downgrade(&cursor->parent->lock, 1);
        }
}

/*
 * Upgrade and downgrade pairs of cursors.  This is used by the dedup
 * code which must deal with two cursors.  A special function is needed
 * because some of the nodes may be shared between the two cursors,
 * resulting in share counts > 1 which will normally cause an upgrade
 * to fail.
 */
static __noinline
int
collect_node(hammer_node_t *array, int *counts, int n, hammer_node_t node)
{
        int i;

        for (i = 0; i < n; ++i) {
                if (array[i] == node)
                        break;
        }
        if (i == n) {
                array[i] = node;
                counts[i] = 1;
                ++i;
        } else {
                ++counts[i];
        }
        return(i);
}

int
hammer_cursor_upgrade2(hammer_cursor_t cursor1, hammer_cursor_t cursor2)
{
        hammer_node_t nodes[4];
        int counts[4];
        int error;
        int i;
        int n;

        n = collect_node(nodes, counts, 0, cursor1->node);
        if (cursor1->parent)
                n = collect_node(nodes, counts, n, cursor1->parent);
        n = collect_node(nodes, counts, n, cursor2->node);
        if (cursor2->parent)
                n = collect_node(nodes, counts, n, cursor2->parent);

        error = 0;
        for (i = 0; i < n; ++i) {
                error = hammer_lock_upgrade(&nodes[i]->lock, counts[i]);
                if (error)
                        break;
        }
        if (error) {
                while (--i >= 0)
                        hammer_lock_downgrade(&nodes[i]->lock, counts[i]);
        }
        return (error);
}

void
hammer_cursor_downgrade2(hammer_cursor_t cursor1, hammer_cursor_t cursor2)
{
        hammer_node_t nodes[4];
        int counts[4];
        int i;
        int n;

        n = collect_node(nodes, counts, 0, cursor1->node);
        if (cursor1->parent)
                n = collect_node(nodes, counts, n, cursor1->parent);
        n = collect_node(nodes, counts, n, cursor2->node);
        if (cursor2->parent)
                n = collect_node(nodes, counts, n, cursor2->parent);

        for (i = 0; i < n; ++i)
                hammer_lock_downgrade(&nodes[i]->lock, counts[i]);
}

/*
 * Seek the cursor to the specified node and index.
 *
 * The caller must ref the node prior to calling this routine and release
 * it after it returns.  If the seek succeeds the cursor will gain its own
 * ref on the node.
 */
int
hammer_cursor_seek(hammer_cursor_t cursor, hammer_node_t node, int index)
{
        int error;

        hammer_cursor_downgrade(cursor);
        error = 0;

        if (cursor->node != node) {
                hammer_unlock(&cursor->node->lock);
                hammer_rel_node(cursor->node);
                cursor->node = node;
                hammer_ref_node(node);
                hammer_lock_sh(&node->lock);
                KKASSERT ((node->flags & HAMMER_NODE_DELETED) == 0);

                if (cursor->parent) {
                        hammer_unlock(&cursor->parent->lock);
                        hammer_rel_node(cursor->parent);
                        cursor->parent = NULL;
                        cursor->parent_index = 0;
                }
                error = hammer_load_cursor_parent(cursor, 0);
        }
        cursor->index = index;
        return (error);
}

/*
 * Load the parent of cursor->node into cursor->parent.
 */
static
int
hammer_load_cursor_parent(hammer_cursor_t cursor, int try_exclusive)
{
        hammer_mount_t hmp;
        hammer_node_t parent;
        hammer_node_t node;
        hammer_btree_elm_t elm;
        int error;
        int parent_index;

        hmp = cursor->trans->hmp;

        if (cursor->node->ondisk->parent) {
                node = cursor->node;
                parent = hammer_btree_get_parent(cursor->trans, node,
                                                 &parent_index,
                                                 &error, try_exclusive);
                if (error == 0) {
                        elm = &parent->ondisk->elms[parent_index];
                        cursor->parent = parent;
                        cursor->parent_index = parent_index;
                        cursor->left_bound = &elm[0].internal.base;
                        cursor->right_bound = &elm[1].internal.base;
                }
        } else {
                cursor->parent = NULL;
                cursor->parent_index = 0;
                cursor->left_bound = &hmp->root_btree_beg;
                cursor->right_bound = &hmp->root_btree_end;
                error = 0;
        }
        return(error);
}

/*
 * Cursor up to our parent node.  Return ENOENT if we are at the root of
 * the filesystem.
 */
int
hammer_cursor_up(hammer_cursor_t cursor)
{
        int error;

        hammer_cursor_downgrade(cursor);

        /*
         * If the parent is NULL we are at the root of the B-Tree and
         * return ENOENT.
         */
        if (cursor->parent == NULL)
                return (ENOENT);

        /*
         * Set the node to its parent.
         */
        hammer_unlock(&cursor->node->lock);
        hammer_rel_node(cursor->node);
        cursor->node = cursor->parent;
        cursor->index = cursor->parent_index;
        cursor->parent = NULL;
        cursor->parent_index = 0;

        error = hammer_load_cursor_parent(cursor, 0);
        return(error);
}

/*
 * Special cursor up given a locked cursor.  The orignal node is not
 * unlocked or released and the cursor is not downgraded.
 *
 * This function can fail with EDEADLK.
 *
 * This function is only run when recursively deleting parent nodes
 * to get rid of an empty leaf.
 */
int
hammer_cursor_up_locked(hammer_cursor_t cursor)
{
        hammer_node_t save;
        int error;
        int save_index;

        /*
         * If the parent is NULL we are at the root of the B-Tree and
         * return ENOENT.
         */
        if (cursor->parent == NULL)
                return (ENOENT);

        save = cursor->node;
        save_index = cursor->index;

        /*
         * Set the node to its parent.
         */
        cursor->node = cursor->parent;
        cursor->index = cursor->parent_index;
        cursor->parent = NULL;
        cursor->parent_index = 0;

        /*
         * load the new parent, attempt to exclusively lock it.  Note that
         * we are still holding the old parent (now cursor->node) exclusively
         * locked.
         *
         * This can return EDEADLK.  Undo the operation on any error.  These
         * up sequences can occur during iterations so be sure to restore
         * the index.
         */
        error = hammer_load_cursor_parent(cursor, 1);
        if (error) {
                cursor->parent = cursor->node;
                cursor->parent_index = cursor->index;
                cursor->node = save;
                cursor->index = save_index;
        }
        return(error);
}


/*
 * Cursor down through the current node, which must be an internal node.
 *
 * This routine adjusts the cursor and sets index to 0.
 */
int
hammer_cursor_down(hammer_cursor_t cursor)
{
        hammer_node_t node;
        hammer_btree_elm_t elm;
        int error;

        /*
         * The current node becomes the current parent
         */
        hammer_cursor_downgrade(cursor);
        node = cursor->node;
        KKASSERT(cursor->index >= 0 && cursor->index < node->ondisk->count);
        if (cursor->parent) {
                hammer_unlock(&cursor->parent->lock);
                hammer_rel_node(cursor->parent);
        }
        cursor->parent = node;
        cursor->parent_index = cursor->index;
        cursor->node = NULL;
        cursor->index = 0;

        /*
         * Extract element to push into at (node,index), set bounds.
         */
        elm = &node->ondisk->elms[cursor->parent_index];

        /*
         * Ok, push down into elm of an internal node.
         */
        KKASSERT(node->ondisk->type == HAMMER_BTREE_TYPE_INTERNAL);
        KKASSERT(elm->internal.subtree_offset != 0);
        cursor->left_bound = &elm[0].internal.base;
        cursor->right_bound = &elm[1].internal.base;
        node = hammer_get_node(cursor->trans,
                               elm->internal.subtree_offset, 0, &error);
        if (error == 0) {
                KASSERT(elm->base.btype == node->ondisk->type,
                        ("BTYPE MISMATCH %c %c NODE %p",
                         elm->base.btype, node->ondisk->type, node));
                if (node->ondisk->parent != cursor->parent->node_offset)
                        hpanic("node %p %016jx vs %016jx",
                                node,
                                (intmax_t)node->ondisk->parent,
                                (intmax_t)cursor->parent->node_offset);
                KKASSERT(node->ondisk->parent == cursor->parent->node_offset);
        }

        /*
         * If no error occured we can lock the new child node.  If the
         * node is deadlock flagged wait up to hammer_tdmux_ticks (1 second)
         * for the deadlock to clear.  Otherwise a large number of concurrent
         * readers can continuously stall the flusher.
         *
         * We specifically do this in the cursor_down() code in order to
         * deal with frontend top-down searches smashing against bottom-up
         * flusher-based mirror updates.  These collisions typically occur
         * above the inode in the B-Tree and are not covered by the
         * ip->cursor_exclreq_count logic.
         */
        if (error == 0) {
#if 0
                if (node->cursor_exclreq_count &&
                    cursor->trans->type != HAMMER_TRANS_FLS) {
                        tsleep(&node->cursor_exclreq_count, 0,
                               "hstag2", hammer_tdmux_ticks);
                }
#endif
                hammer_lock_sh(&node->lock);
                KKASSERT ((node->flags & HAMMER_NODE_DELETED) == 0);
                cursor->node = node;
                cursor->index = 0;
        }
        return(error);
}

/************************************************************************
 *                              DEADLOCK RECOVERY                       *
 ************************************************************************
 *
 * These are the new deadlock recovery functions.  Currently they are only
 * used for the mirror propagation and physical node removal cases but
 * ultimately the intention is to use them for all deadlock recovery
 * operations.
 *
 * WARNING!  The contents of the cursor may be modified while unlocked.
 *           passive modifications including adjusting the node, parent,
 *           indexes, and leaf pointer.
 *
 *           An outright removal of the element the cursor was pointing at
 *           will cause the HAMMER_CURSOR_TRACKED_RIPOUT flag to be set,
 *           which chains to causing the HAMMER_CURSOR_RETEST to be set
 *           when the cursor is locked again.
 */
void
hammer_unlock_cursor(hammer_cursor_t cursor)
{
        hammer_node_t node;

        KKASSERT((cursor->flags & HAMMER_CURSOR_TRACKED) == 0);
        KKASSERT(cursor->node);

        /*
         * Release the cursor's locks and track B-Tree operations on node.
         * While being tracked our cursor can be modified by other threads
         * and the node may be replaced.
         */
        if (cursor->parent) {
                hammer_unlock(&cursor->parent->lock);
                hammer_rel_node(cursor->parent);
                cursor->parent = NULL;
        }
        node = cursor->node;
        cursor->flags |= HAMMER_CURSOR_TRACKED;
        TAILQ_INSERT_TAIL(&node->cursor_list, cursor, deadlk_entry);
        hammer_unlock(&node->lock);
}

/*
 * Get the cursor heated up again.  The cursor's node may have
 * changed and we might have to locate the new parent.
 *
 * If the exact element we were on got deleted RIPOUT will be
 * set and we must clear ATEDISK so an iteration does not skip
 * the element after it.
 */
int
hammer_lock_cursor(hammer_cursor_t cursor)
{
        hammer_node_t node;
        int error;

        KKASSERT(cursor->flags & HAMMER_CURSOR_TRACKED);

        /*
         * Relock the node
         */
        for (;;) {
                node = cursor->node;
                hammer_ref_node(node);
                hammer_lock_sh(&node->lock);
                if (cursor->node == node) {
                        hammer_rel_node(node);
                        break;
                }
                hammer_unlock(&node->lock);
                hammer_rel_node(node);
        }

        /*
         * Untrack the cursor, clean up, and re-establish the parent node.
         */
        TAILQ_REMOVE(&node->cursor_list, cursor, deadlk_entry);
        cursor->flags &= ~HAMMER_CURSOR_TRACKED;

        /*
         * If a ripout has occured iterations must re-test the (new)
         * current element.  Clearing ATEDISK prevents the element from
         * being skipped and RETEST causes it to be re-tested.
         */
        if (cursor->flags & HAMMER_CURSOR_TRACKED_RIPOUT) {
                cursor->flags &= ~HAMMER_CURSOR_TRACKED_RIPOUT;
                cursor->flags &= ~HAMMER_CURSOR_ATEDISK;
                cursor->flags |= HAMMER_CURSOR_RETEST;
        }
        error = hammer_load_cursor_parent(cursor, 0);
        return(error);
}

/*
 * Recover from a deadlocked cursor, tracking any node removals or
 * replacements.  If the cursor's current node is removed by another
 * thread (via btree_remove()) the cursor will be seeked upwards.
 *
 * The caller is working a modifying operation and must be holding the
 * sync lock (shared).  We do not release the sync lock because this
 * would break atomicy.
 */
int
hammer_recover_cursor(hammer_cursor_t cursor)
{
        hammer_transaction_t trans __debugvar;
#if 0
        hammer_inode_t ip;
#endif
        int error;

        hammer_unlock_cursor(cursor);

#if 0
        ip = cursor->ip;
#endif
        trans = cursor->trans;
        KKASSERT(trans->sync_lock_refs > 0);

        /*
         * Wait for the deadlock to clear.
         *
         * Maintain exclreq_count / wakeup as necessary to notify new
         * entrants into ip.  We continue to hold the fs_token so our
         * EDEADLK retry loop should get its chance before another thread
         * steals the lock.
         */
        if (cursor->deadlk_node) {
#if 0
                if (ip && trans->type == HAMMER_TRANS_FLS)
                        ++ip->cursor_exclreq_count;
                ++cursor->deadlk_node->cursor_exclreq_count;
#endif
                hammer_lock_ex_ident(&cursor->deadlk_node->lock, "hmrdlk");
                hammer_unlock(&cursor->deadlk_node->lock);
#if 0
                if (--cursor->deadlk_node->cursor_exclreq_count == 0)
                        wakeup(&cursor->deadlk_node->cursor_exclreq_count);
                if (ip && trans->type == HAMMER_TRANS_FLS) {
                        if (--ip->cursor_exclreq_count == 0)
                                wakeup(&ip->cursor_exclreq_count);
                }
#endif
                hammer_rel_node(cursor->deadlk_node);
                cursor->deadlk_node = NULL;
        }
        if (cursor->deadlk_rec) {
                hammer_wait_mem_record_ident(cursor->deadlk_rec, "hmmdlr");
                hammer_rel_mem_record(cursor->deadlk_rec);
                cursor->deadlk_rec = NULL;
        }
        error = hammer_lock_cursor(cursor);
        return(error);
}

/*
 * Dup ocursor to ncursor.  ncursor inherits ocursor's locks and ocursor
 * is effectively unlocked and becomes tracked.  If ocursor was not locked
 * then ncursor also inherits the tracking.
 *
 * After the caller finishes working with ncursor it must be cleaned up
 * with hammer_done_cursor(), and the caller must re-lock ocursor.
 */
hammer_cursor_t
hammer_push_cursor(hammer_cursor_t ocursor)
{
        hammer_cursor_t ncursor;
        hammer_inode_t ip;
        hammer_node_t node;
        hammer_mount_t hmp;

        hmp = ocursor->trans->hmp;
        ncursor = kmalloc(sizeof(*ncursor), hmp->m_misc, M_WAITOK | M_ZERO);
        bcopy(ocursor, ncursor, sizeof(*ocursor));

        node = ocursor->node;
        hammer_ref_node(node);
        if ((ocursor->flags & HAMMER_CURSOR_TRACKED) == 0) {
                ocursor->flags |= HAMMER_CURSOR_TRACKED;
                TAILQ_INSERT_TAIL(&node->cursor_list, ocursor, deadlk_entry);
        }
        if (ncursor->parent)
                ocursor->parent = NULL;
        ocursor->data_buffer = NULL;
        ocursor->leaf = NULL;
        ocursor->data = NULL;
        if (ncursor->flags & HAMMER_CURSOR_TRACKED)
                TAILQ_INSERT_TAIL(&node->cursor_list, ncursor, deadlk_entry);
        if ((ip = ncursor->ip) != NULL) {
                ++ip->cursor_ip_refs;
        }
        if (ncursor->iprec)
                hammer_ref(&ncursor->iprec->lock);
        return(ncursor);
}

/*
 * Destroy ncursor and restore ocursor
 *
 * This is a temporary hack for the release.  We can't afford to lose
 * the IP lock until the IP object scan code is able to deal with it,
 * so have ocursor inherit it back.
 */
void
hammer_pop_cursor(hammer_cursor_t ocursor, hammer_cursor_t ncursor)
{
        hammer_mount_t hmp;
        hammer_inode_t ip;

        hmp = ncursor->trans->hmp;
        ip = ncursor->ip;
        ncursor->ip = NULL;
        if (ip)
                --ip->cursor_ip_refs;
        hammer_done_cursor(ncursor);
        kfree(ncursor, hmp->m_misc);
        KKASSERT(ocursor->ip == ip);
        hammer_lock_cursor(ocursor);
}

/*
 * onode is being replaced by nnode by the reblocking code.
 */
void
hammer_cursor_replaced_node(hammer_node_t onode, hammer_node_t nnode)
{
        hammer_cursor_t cursor;
        hammer_node_ondisk_t ondisk;
        hammer_node_ondisk_t nndisk;

        ondisk = onode->ondisk;
        nndisk = nnode->ondisk;

        while ((cursor = TAILQ_FIRST(&onode->cursor_list)) != NULL) {
                TAILQ_REMOVE(&onode->cursor_list, cursor, deadlk_entry);
                TAILQ_INSERT_TAIL(&nnode->cursor_list, cursor, deadlk_entry);
                KKASSERT(cursor->node == onode);
                if (cursor->leaf == &ondisk->elms[cursor->index].leaf)
                        cursor->leaf = &nndisk->elms[cursor->index].leaf;
                cursor->node = nnode;
                hammer_ref_node(nnode);
                hammer_rel_node(onode);
        }
}

/*
 * We have removed <node> from the parent and collapsed the parent.
 *
 * Cursors in deadlock recovery are seeked upward to the parent so the
 * btree_remove() recursion works properly even though we have marked
 * the cursor as requiring a reseek.
 *
 * This is the only cursor function which sets HAMMER_CURSOR_ITERATE_CHECK,
 * meaning the cursor is no longer definitively pointing at an element
 * within its iteration (if the cursor is being used to iterate).  The
 * iteration code will take this into account instead of asserting if the
 * cursor is outside the iteration range.
 */
void
hammer_cursor_removed_node(hammer_node_t node, hammer_node_t parent, int index)
{
        hammer_cursor_t cursor;
        hammer_node_ondisk_t ondisk;

        KKASSERT(parent != NULL);
        ondisk = node->ondisk;

        while ((cursor = TAILQ_FIRST(&node->cursor_list)) != NULL) {
                KKASSERT(cursor->node == node);
                KKASSERT(cursor->index == 0);
                TAILQ_REMOVE(&node->cursor_list, cursor, deadlk_entry);
                TAILQ_INSERT_TAIL(&parent->cursor_list, cursor, deadlk_entry);
                if (cursor->leaf == &ondisk->elms[cursor->index].leaf)
                        cursor->leaf = NULL;
                cursor->flags |= HAMMER_CURSOR_TRACKED_RIPOUT;
                cursor->flags |= HAMMER_CURSOR_ITERATE_CHECK;
                cursor->node = parent;
                cursor->index = index;
                hammer_ref_node(parent);
                hammer_rel_node(node);
        }
}

/*
 * node was split at (onode, index) with elements >= index moved to nnode.
 */
void
hammer_cursor_split_node(hammer_node_t onode, hammer_node_t nnode, int index)
{
        hammer_cursor_t cursor;
        hammer_node_ondisk_t ondisk;
        hammer_node_ondisk_t nndisk;

        ondisk = onode->ondisk;
        nndisk = nnode->ondisk;

again:
        TAILQ_FOREACH(cursor, &onode->cursor_list, deadlk_entry) {
                KKASSERT(cursor->node == onode);
                if (cursor->index < index)
                        continue;
                TAILQ_REMOVE(&onode->cursor_list, cursor, deadlk_entry);
                TAILQ_INSERT_TAIL(&nnode->cursor_list, cursor, deadlk_entry);
                if (cursor->leaf == &ondisk->elms[cursor->index].leaf)
                        cursor->leaf = &nndisk->elms[cursor->index - index].leaf;
                cursor->node = nnode;
                cursor->index -= index;
                hammer_ref_node(nnode);
                hammer_rel_node(onode);
                goto again;
        }
}

/*
 * An element was moved from one node to another or within a node.  The
 * index may also represent the end of the node (index == numelements).
 *
 * {oparent,pindex} is the parent node's pointer to onode/oindex.
 *
 * This is used by the rebalancing code.  This is not an insertion or
 * deletion and any additional elements, including the degenerate case at
 * the end of the node, will be dealt with by additional distinct calls.
 */
void
hammer_cursor_moved_element(hammer_node_t oparent, int pindex,
                            hammer_node_t onode, int oindex,
                            hammer_node_t nnode, int nindex)
{
        hammer_cursor_t cursor;
        hammer_node_ondisk_t ondisk;
        hammer_node_ondisk_t nndisk;

        /*
         * Adjust any cursors pointing at the element
         */
        ondisk = onode->ondisk;
        nndisk = nnode->ondisk;
again1:
        TAILQ_FOREACH(cursor, &onode->cursor_list, deadlk_entry) {
                KKASSERT(cursor->node == onode);
                if (cursor->index != oindex)
                        continue;
                TAILQ_REMOVE(&onode->cursor_list, cursor, deadlk_entry);
                TAILQ_INSERT_TAIL(&nnode->cursor_list, cursor, deadlk_entry);
                if (cursor->leaf == &ondisk->elms[oindex].leaf)
                        cursor->leaf = &nndisk->elms[nindex].leaf;
                cursor->node = nnode;
                cursor->index = nindex;
                hammer_ref_node(nnode);
                hammer_rel_node(onode);
                goto again1;
        }

        /*
         * When moving the first element of onode to a different node any
         * cursor which is pointing at (oparent,pindex) must be repointed
         * to nnode and ATEDISK must be cleared.
         *
         * This prevents cursors from losing track due to insertions.
         * Insertions temporarily release the cursor in order to update
         * the mirror_tids.  It primarily effects the mirror_write code.
         * The other code paths generally only do a single insertion and
         * then relookup or drop the cursor.
         */
        if (onode == nnode || oindex)
                return;
        ondisk = oparent->ondisk;
again2:
        TAILQ_FOREACH(cursor, &oparent->cursor_list, deadlk_entry) {
                KKASSERT(cursor->node == oparent);
                if (cursor->index != pindex)
                        continue;
                hkprintf("debug: shifted cursor pointing at parent\n"
                        "parent %016jx:%d onode %016jx:%d nnode %016jx:%d\n",
                        (intmax_t)oparent->node_offset, pindex,
                        (intmax_t)onode->node_offset, oindex,
                        (intmax_t)nnode->node_offset, nindex);
                TAILQ_REMOVE(&oparent->cursor_list, cursor, deadlk_entry);
                TAILQ_INSERT_TAIL(&nnode->cursor_list, cursor, deadlk_entry);
                if (cursor->leaf == &ondisk->elms[oindex].leaf)
                        cursor->leaf = &nndisk->elms[nindex].leaf;
                cursor->node = nnode;
                cursor->index = nindex;
                cursor->flags &= ~HAMMER_CURSOR_ATEDISK;
                hammer_ref_node(nnode);
                hammer_rel_node(oparent);
                goto again2;
        }
}

/*
 * The B-Tree element pointing to the specified node was moved from (oparent)
 * to (nparent, nindex).  We must locate any tracked cursors pointing at
 * node and adjust their parent accordingly.
 *
 * This is used by the rebalancing code when packing elements causes an
 * element to shift from one node to another.
 */
void
hammer_cursor_parent_changed(hammer_node_t node, hammer_node_t oparent,
                             hammer_node_t nparent, int nindex)
{
        hammer_cursor_t cursor;

again:
        TAILQ_FOREACH(cursor, &node->cursor_list, deadlk_entry) {
                KKASSERT(cursor->node == node);
                if (cursor->parent == oparent) {
                        cursor->parent = nparent;
                        cursor->parent_index = nindex;
                        hammer_ref_node(nparent);
                        hammer_rel_node(oparent);
                        goto again;
                }
        }
}

/*
 * Deleted element at (node, index)
 *
 * Shift indexes >= index
 */
void
hammer_cursor_deleted_element(hammer_node_t node, int index)
{
        hammer_cursor_t cursor;
        hammer_node_ondisk_t ondisk;

        ondisk = node->ondisk;

        TAILQ_FOREACH(cursor, &node->cursor_list, deadlk_entry) {
                KKASSERT(cursor->node == node);
                if (cursor->index == index) {
                        cursor->flags |= HAMMER_CURSOR_TRACKED_RIPOUT;
                        if (cursor->leaf == &ondisk->elms[cursor->index].leaf)
                                cursor->leaf = NULL;
                } else if (cursor->index > index) {
                        if (cursor->leaf == &ondisk->elms[cursor->index].leaf)
                                cursor->leaf = &ondisk->elms[cursor->index - 1].leaf;
                        --cursor->index;
                }
        }
}

/*
 * Inserted element at (node, index)
 *
 * Shift indexes >= index
 */
void
hammer_cursor_inserted_element(hammer_node_t node, int index)
{
        hammer_cursor_t cursor;
        hammer_node_ondisk_t ondisk;

        ondisk = node->ondisk;

        TAILQ_FOREACH(cursor, &node->cursor_list, deadlk_entry) {
                KKASSERT(cursor->node == node);
                if (cursor->index >= index) {
                        if (cursor->leaf == &ondisk->elms[cursor->index].leaf)
                                cursor->leaf = &ondisk->elms[cursor->index + 1].leaf;
                        ++cursor->index;
                }
        }
}

/*
 * Invalidate the cached data buffer associated with a cursor.
 *
 * This needs to be done when the underlying block is being freed or
 * the referenced buffer can prevent the related buffer cache buffer
 * from being properly invalidated.
 */
void
hammer_cursor_invalidate_cache(hammer_cursor_t cursor)
{
        if (cursor->data_buffer) {
                hammer_rel_buffer(cursor->data_buffer, 0);
                cursor->data_buffer = NULL;
                cursor->data = NULL;
        }
}