hammer2 - Fix upgrade deadlock

[dragonfly.git] / sys / vfs / hammer2 / hammer2_chain.c

/*
 * Copyright (c) 2011-2015 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@dragonflybsd.org>
 * and Venkatesh Srinivas <vsrinivas@dragonflybsd.org>
 *
 * 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.
 */
/*
 * This subsystem implements most of the core support functions for
 * the hammer2_chain structure.
 *
 * Chains are the in-memory version on media objects (volume header, inodes,
 * indirect blocks, data blocks, etc).  Chains represent a portion of the
 * HAMMER2 topology.
 *
 * Chains are no-longer delete-duplicated.  Instead, the original in-memory
 * chain will be moved along with its block reference (e.g. for things like
 * renames, hardlink operations, modifications, etc), and will be indexed
 * on a secondary list for flush handling instead of propagating a flag
 * upward to the root.
 *
 * Concurrent front-end operations can still run against backend flushes
 * as long as they do not cross the current flush boundary.  An operation
 * running above the current flush (in areas not yet flushed) can become
 * part of the current flush while ano peration running below the current
 * flush can become part of the next flush.
 */
#include <sys/cdefs.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/types.h>
#include <sys/lock.h>
#include <sys/kern_syscall.h>
#include <sys/uuid.h>

#include <crypto/sha2/sha2.h>

#include "hammer2.h"

static int hammer2_indirect_optimize;   /* XXX SYSCTL */

static hammer2_chain_t *hammer2_chain_create_indirect(
                hammer2_chain_t *parent,
                hammer2_key_t key, int keybits,
                hammer2_tid_t mtid, int for_type, int *errorp);
static hammer2_io_t *hammer2_chain_drop_data(hammer2_chain_t *chain,
                int lastdrop);
static hammer2_chain_t *hammer2_combined_find(
                hammer2_chain_t *parent,
                hammer2_blockref_t *base, int count,
                int *cache_indexp, hammer2_key_t *key_nextp,
                hammer2_key_t key_beg, hammer2_key_t key_end,
                hammer2_blockref_t **bresp);

/*
 * Basic RBTree for chains (core->rbtree and core->dbtree).  Chains cannot
 * overlap in the RB trees.  Deleted chains are moved from rbtree to either
 * dbtree or to dbq.
 *
 * Chains in delete-duplicate sequences can always iterate through core_entry
 * to locate the live version of the chain.
 */
RB_GENERATE(hammer2_chain_tree, hammer2_chain, rbnode, hammer2_chain_cmp);

extern int h2timer[32];
extern int h2last;
extern int h2lid;

#define TIMER(which)    do {                            \
        if (h2last)                                     \
                h2timer[h2lid] += (int)(ticks - h2last);\
        h2last = ticks;                                 \
        h2lid = which;                                  \
} while(0)

int
hammer2_chain_cmp(hammer2_chain_t *chain1, hammer2_chain_t *chain2)
{
        hammer2_key_t c1_beg;
        hammer2_key_t c1_end;
        hammer2_key_t c2_beg;
        hammer2_key_t c2_end;

        /*
         * Compare chains.  Overlaps are not supposed to happen and catch
         * any software issues early we count overlaps as a match.
         */
        c1_beg = chain1->bref.key;
        c1_end = c1_beg + ((hammer2_key_t)1 << chain1->bref.keybits) - 1;
        c2_beg = chain2->bref.key;
        c2_end = c2_beg + ((hammer2_key_t)1 << chain2->bref.keybits) - 1;

        if (c1_end < c2_beg)    /* fully to the left */
                return(-1);
        if (c1_beg > c2_end)    /* fully to the right */
                return(1);
        return(0);              /* overlap (must not cross edge boundary) */
}

static __inline
int
hammer2_isclusterable(hammer2_chain_t *chain)
{
        if (hammer2_cluster_enable) {
                if (chain->bref.type == HAMMER2_BREF_TYPE_INDIRECT ||
                    chain->bref.type == HAMMER2_BREF_TYPE_INODE ||
                    chain->bref.type == HAMMER2_BREF_TYPE_DATA) {
                        return(1);
                }
        }
        return(0);
}

/*
 * Make a chain visible to the flusher.  The flusher needs to be able to
 * do flushes of subdirectory chains or single files so it does a top-down
 * recursion using the ONFLUSH flag for the recursion.  It locates MODIFIED
 * or UPDATE chains and flushes back up the chain to the volume root.
 *
 * This routine sets ONFLUSH upward until it hits the volume root.  For
 * simplicity we ignore PFSROOT boundaries whos rules can be complex.
 * Extra ONFLUSH flagging doesn't hurt the filesystem.
 */
void
hammer2_chain_setflush(hammer2_chain_t *chain)
{
        hammer2_chain_t *parent;

        if ((chain->flags & HAMMER2_CHAIN_ONFLUSH) == 0) {
                hammer2_spin_sh(&chain->core.spin);
                while ((chain->flags & HAMMER2_CHAIN_ONFLUSH) == 0) {
                        atomic_set_int(&chain->flags, HAMMER2_CHAIN_ONFLUSH);
                        if ((parent = chain->parent) == NULL)
                                break;
                        hammer2_spin_sh(&parent->core.spin);
                        hammer2_spin_unsh(&chain->core.spin);
                        chain = parent;
                }
                hammer2_spin_unsh(&chain->core.spin);
        }
}

/*
 * Allocate a new disconnected chain element representing the specified
 * bref.  chain->refs is set to 1 and the passed bref is copied to
 * chain->bref.  chain->bytes is derived from the bref.
 *
 * chain->pmp inherits pmp unless the chain is an inode (other than the
 * super-root inode).
 *
 * NOTE: Returns a referenced but unlocked (because there is no core) chain.
 */
hammer2_chain_t *
hammer2_chain_alloc(hammer2_dev_t *hmp, hammer2_pfs_t *pmp,
                    hammer2_blockref_t *bref)
{
        hammer2_chain_t *chain;
        u_int bytes = 1U << (int)(bref->data_off & HAMMER2_OFF_MASK_RADIX);

        atomic_add_long(&hammer2_chain_allocs, 1);

        /*
         * Construct the appropriate system structure.
         */
        switch(bref->type) {
        case HAMMER2_BREF_TYPE_INODE:
        case HAMMER2_BREF_TYPE_INDIRECT:
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
        case HAMMER2_BREF_TYPE_DATA:
        case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
                /*
                 * Chain's are really only associated with the hmp but we
                 * maintain a pmp association for per-mount memory tracking
                 * purposes.  The pmp can be NULL.
                 */
                chain = kmalloc(sizeof(*chain), hmp->mchain, M_WAITOK | M_ZERO);
                break;
        case HAMMER2_BREF_TYPE_VOLUME:
        case HAMMER2_BREF_TYPE_FREEMAP:
                /*
                 * Only hammer2_chain_bulksnap() calls this function with these
                 * types.
                 */
                chain = kmalloc(sizeof(*chain), hmp->mchain, M_WAITOK | M_ZERO);
                break;
        default:
                chain = NULL;
                panic("hammer2_chain_alloc: unrecognized blockref type: %d",
                      bref->type);
        }

        /*
         * Initialize the new chain structure.  pmp must be set to NULL for
         * chains belonging to the super-root topology of a device mount.
         */
        if (pmp == hmp->spmp)
                chain->pmp = NULL;
        else
                chain->pmp = pmp;
        chain->hmp = hmp;
        chain->bref = *bref;
        chain->bytes = bytes;
        chain->refs = 1;
        chain->flags = HAMMER2_CHAIN_ALLOCATED;

        /*
         * Set the PFS boundary flag if this chain represents a PFS root.
         */
        if (bref->flags & HAMMER2_BREF_FLAG_PFSROOT)
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_PFSBOUNDARY);
        hammer2_chain_core_init(chain);

        return (chain);
}

/*
 * Initialize a chain's core structure.  This structure used to be allocated
 * but is now embedded.
 *
 * The core is not locked.  No additional refs on the chain are made.
 * (trans) must not be NULL if (core) is not NULL.
 */
void
hammer2_chain_core_init(hammer2_chain_t *chain)
{
        /*
         * Fresh core under nchain (no multi-homing of ochain's
         * sub-tree).
         */
        RB_INIT(&chain->core.rbtree);   /* live chains */
        hammer2_mtx_init(&chain->lock, "h2chain");
}

/*
 * Add a reference to a chain element, preventing its destruction.
 *
 * (can be called with spinlock held)
 */
void
hammer2_chain_ref(hammer2_chain_t *chain)
{
        if (atomic_fetchadd_int(&chain->refs, 1) == 0) {
                /*
                 * 0->non-zero transition must ensure that chain is removed
                 * from the LRU list.
                 *
                 * NOTE: Already holding lru_spin here so we cannot call
                 *       hammer2_chain_ref() to get it off lru_list, do
                 *       it manually.
                 */
                if (chain->flags & HAMMER2_CHAIN_ONLRU) {
                        hammer2_pfs_t *pmp = chain->pmp;
                        hammer2_spin_ex(&pmp->lru_spin);
                        if (chain->flags & HAMMER2_CHAIN_ONLRU) {
                                atomic_add_int(&pmp->lru_count, -1);
                                atomic_clear_int(&chain->flags,
                                                 HAMMER2_CHAIN_ONLRU);
                                TAILQ_REMOVE(&pmp->lru_list, chain, lru_node);
                        }
                        hammer2_spin_unex(&pmp->lru_spin);
                }
        }
#if 0
        kprintf("REFC %p %d %08x\n", chain, chain->refs - 1, chain->flags);
        print_backtrace(8);
#endif
}

/*
 * Insert the chain in the core rbtree.
 *
 * Normal insertions are placed in the live rbtree.  Insertion of a deleted
 * chain is a special case used by the flush code that is placed on the
 * unstaged deleted list to avoid confusing the live view.
 */
#define HAMMER2_CHAIN_INSERT_SPIN       0x0001
#define HAMMER2_CHAIN_INSERT_LIVE       0x0002
#define HAMMER2_CHAIN_INSERT_RACE       0x0004

static
int
hammer2_chain_insert(hammer2_chain_t *parent, hammer2_chain_t *chain,
                     int flags, int generation)
{
        hammer2_chain_t *xchain;
        int error = 0;

        if (flags & HAMMER2_CHAIN_INSERT_SPIN)
                hammer2_spin_ex(&parent->core.spin);

        /*
         * Interlocked by spinlock, check for race
         */
        if ((flags & HAMMER2_CHAIN_INSERT_RACE) &&
            parent->core.generation != generation) {
                error = EAGAIN;
                goto failed;
        }

        /*
         * Insert chain
         */
        xchain = RB_INSERT(hammer2_chain_tree, &parent->core.rbtree, chain);
        KASSERT(xchain == NULL,
                ("hammer2_chain_insert: collision %p %p (key=%016jx)",
                chain, xchain, chain->bref.key));
        atomic_set_int(&chain->flags, HAMMER2_CHAIN_ONRBTREE);
        chain->parent = parent;
        ++parent->core.chain_count;
        ++parent->core.generation;      /* XXX incs for _get() too, XXX */

        /*
         * We have to keep track of the effective live-view blockref count
         * so the create code knows when to push an indirect block.
         */
        if (flags & HAMMER2_CHAIN_INSERT_LIVE)
                atomic_add_int(&parent->core.live_count, 1);
failed:
        if (flags & HAMMER2_CHAIN_INSERT_SPIN)
                hammer2_spin_unex(&parent->core.spin);
        return error;
}

/*
 * Drop the caller's reference to the chain.  When the ref count drops to
 * zero this function will try to disassociate the chain from its parent and
 * deallocate it, then recursely drop the parent using the implied ref
 * from the chain's chain->parent.
 */
static hammer2_chain_t *hammer2_chain_lastdrop(hammer2_chain_t *chain);

void
hammer2_chain_drop(hammer2_chain_t *chain)
{
        u_int refs;

        if (hammer2_debug & 0x200000)
                Debugger("drop");
#if 0
        kprintf("DROP %p %d %08x\n", chain, chain->refs - 1, chain->flags);
        print_backtrace(8);
#endif

        KKASSERT(chain->refs > 0);

        while (chain) {
                refs = chain->refs;
                cpu_ccfence();
                KKASSERT(refs > 0);

                if (refs == 1) {
                        chain = hammer2_chain_lastdrop(chain);
                } else {
                        if (atomic_cmpset_int(&chain->refs, refs, refs - 1))
                                break;
                        /* retry the same chain */
                }
        }
}

/*
 * Safe handling of the 1->0 transition on chain.  Returns a chain for
 * recursive drop or NULL, possibly returning the same chain if the atomic
 * op fails.
 *
 * When two chains need to be recursively dropped we use the chain we
 * would otherwise free to placehold the additional chain.  It's a bit
 * convoluted but we can't just recurse without potentially blowing out
 * the kernel stack.
 *
 * The chain cannot be freed if it has any children.
 * The chain cannot be freed if flagged MODIFIED unless we can dispose of that.
 * The chain cannot be freed if flagged UPDATE unless we can dispose of that.
 *
 * The core spinlock is allowed nest child-to-parent (not parent-to-child).
 */
static
hammer2_chain_t *
hammer2_chain_lastdrop(hammer2_chain_t *chain)
{
        hammer2_pfs_t *pmp;
        hammer2_dev_t *hmp;
        hammer2_chain_t *parent;
        hammer2_chain_t *rdrop;
        hammer2_io_t *dio;

        /*
         * Critical field access.
         */
        hammer2_spin_ex(&chain->core.spin);

        if ((parent = chain->parent) != NULL) {
                /*
                 * If the chain has a parent the UPDATE bit prevents scrapping
                 * as the chain is needed to properly flush the parent.  Try
                 * to complete the 1->0 transition and return NULL.  Retry
                 * (return chain) if we are unable to complete the 1->0
                 * transition, else return NULL (nothing more to do).
                 *
                 * If the chain has a parent the MODIFIED bit prevents
                 * scrapping.
                 *
                 * Chains with UPDATE/MODIFIED are *not* put on the LRU list!
                 */
                if (chain->flags & (HAMMER2_CHAIN_UPDATE |
                                    HAMMER2_CHAIN_MODIFIED)) {
                        if (atomic_cmpset_int(&chain->refs, 1, 0)) {
                                dio = hammer2_chain_drop_data(chain, 0);
                                hammer2_spin_unex(&chain->core.spin);
                                if (dio)
                                        hammer2_io_bqrelse(&dio);
                                chain = NULL;
                        } else {
                                hammer2_spin_unex(&chain->core.spin);
                        }
                        return (chain);
                }
                /* spinlock still held */
        } else {
                /*
                 * The chain has no parent and can be flagged for destruction.
                 * Since it has no parent, UPDATE can also be cleared.
                 */
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_DESTROY);
                if (chain->flags & HAMMER2_CHAIN_UPDATE)
                        atomic_clear_int(&chain->flags, HAMMER2_CHAIN_UPDATE);

                /*
                 * If the chain has children or if it has been MODIFIED and
                 * also recorded for DEDUP, we must still flush the chain.
                 *
                 * In the case where it has children, the DESTROY flag test
                 * in the flush code will prevent unnecessary flushes of
                 * MODIFIED chains that are not flagged DEDUP so don't worry
                 * about that here.
                 */
                if (chain->core.chain_count ||
                    (chain->flags & (HAMMER2_CHAIN_MODIFIED |
                                     HAMMER2_CHAIN_DEDUP)) ==
                    (HAMMER2_CHAIN_MODIFIED |
                     HAMMER2_CHAIN_DEDUP)) {
                        /*
                         * Put on flushq (should ensure refs > 1), retry
                         * the drop.
                         */
                        hammer2_spin_unex(&chain->core.spin);
                        hammer2_delayed_flush(chain);
                        return(chain);  /* retry drop */
                }

                /*
                 * Otherwise we can scrap the MODIFIED bit if it is set,
                 * and continue along the freeing path.
                 */
                if (chain->flags & HAMMER2_CHAIN_MODIFIED) {
                        atomic_clear_int(&chain->flags, HAMMER2_CHAIN_MODIFIED);
                        atomic_add_long(&hammer2_count_modified_chains, -1);
                }
                /* spinlock still held */
        }

        /* spinlock still held */
        dio = NULL;

        /*
         * If any children exist we must leave the chain intact with refs == 0.
         * They exist because chains are retained below us which have refs or
         * may require flushing.  This case can occur when parent != NULL.
         *
         * Retry (return chain) if we fail to transition the refs to 0, else
         * return NULL indication nothing more to do.
         *
         * Chains with children are NOT put on the LRU list.
         */
        if (chain->core.chain_count) {
                if (parent)
                        hammer2_spin_ex(&parent->core.spin);
                if (atomic_cmpset_int(&chain->refs, 1, 0)) {
                        dio = hammer2_chain_drop_data(chain, 1);
                        hammer2_spin_unex(&chain->core.spin);
                        if (parent)
                                hammer2_spin_unex(&parent->core.spin);
                        chain = NULL;
                        if (dio)
                                hammer2_io_bqrelse(&dio);
                } else {
                        hammer2_spin_unex(&chain->core.spin);
                        if (parent)
                                hammer2_spin_unex(&parent->core.spin);
                }
                return (chain);
        }
        /* spinlock still held */
        /* no chains left under us */

        /*
         * chain->core has no children left so no accessors can get to our
         * chain from there.  Now we have to lock the parent core to interlock
         * remaining possible accessors that might bump chain's refs before
         * we can safely drop chain's refs with intent to free the chain.
         */
        hmp = chain->hmp;
        pmp = chain->pmp;       /* can be NULL */
        rdrop = NULL;

        parent = chain->parent;

        /*
         * WARNING! chain's spin lock is still held here, and other spinlocks
         *          will be acquired and released in the code below.  We
         *          cannot be making fancy procedure calls!
         */

        /*
         * We can cache the chain if it is associated with a pmp
         * and not flagged as being destroyed or requesting a full
         * release.  In this situation the chain is not removed
         * from its parent, i.e. it can still be looked up.
         *
         * We intentionally do not cache DATA chains because these
         * were likely used to load data into the logical buffer cache
         * and will not be accessed again for some time.
         */
        if ((chain->flags &
             (HAMMER2_CHAIN_DESTROY | HAMMER2_CHAIN_RELEASE)) == 0 &&
            chain->pmp &&
            chain->bref.type != HAMMER2_BREF_TYPE_DATA) {
                if (parent)
                        hammer2_spin_ex(&parent->core.spin);
                if (atomic_cmpset_int(&chain->refs, 1, 0) == 0) {
                        /*
                         * 1->0 transition failed, retry.  Do not drop
                         * the chain's data yet!
                         */
                        if (parent)
                                hammer2_spin_unex(&parent->core.spin);
                        hammer2_spin_unex(&chain->core.spin);

                        return(chain);
                }

                /*
                 * Success, be sure to clean out the chain's data
                 * before putting it on a queue that it might be
                 * reused from.
                 */
                dio = hammer2_chain_drop_data(chain, 1);

                KKASSERT((chain->flags & HAMMER2_CHAIN_ONLRU) == 0);
                hammer2_spin_ex(&pmp->lru_spin);
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_ONLRU);
                TAILQ_INSERT_TAIL(&pmp->lru_list, chain, lru_node);

                /*
                 * If we are over the LRU limit we need to drop something.
                 */
                if (pmp->lru_count > HAMMER2_LRU_LIMIT) {
                        rdrop = TAILQ_FIRST(&pmp->lru_list);
                        atomic_clear_int(&rdrop->flags, HAMMER2_CHAIN_ONLRU);
                        TAILQ_REMOVE(&pmp->lru_list, rdrop, lru_node);
                        atomic_add_int(&rdrop->refs, 1);
                        atomic_set_int(&rdrop->flags, HAMMER2_CHAIN_RELEASE);
                } else {
                        atomic_add_int(&pmp->lru_count, 1);
                }
                hammer2_spin_unex(&pmp->lru_spin);
                if (parent) {
                        hammer2_spin_unex(&parent->core.spin);
                        parent = NULL;  /* safety */
                }
                hammer2_spin_unex(&chain->core.spin);
                if (dio)
                        hammer2_io_bqrelse(&dio);

                return rdrop;
                /* NOT REACHED */
        }

        /*
         * Spinlock the parent and try to drop the last ref on chain.
         * On success determine if we should dispose of the chain
         * (remove the chain from its parent, etc).
         *
         * (normal core locks are top-down recursive but we define
         * core spinlocks as bottom-up recursive, so this is safe).
         */
        if (parent) {
                hammer2_spin_ex(&parent->core.spin);
                if (atomic_cmpset_int(&chain->refs, 1, 0) == 0) {
                        /*
                         * 1->0 transition failed, retry.
                         */
                        hammer2_spin_unex(&parent->core.spin);
                        dio = hammer2_chain_drop_data(chain, 0);
                        hammer2_spin_unex(&chain->core.spin);
                        if (dio)
                                hammer2_io_bqrelse(&dio);
                        return(chain);
                }

                /*
                 * 1->0 transition successful, remove chain from the
                 * parent.
                 */
                if (chain->flags & HAMMER2_CHAIN_ONRBTREE) {
                        RB_REMOVE(hammer2_chain_tree,
                                  &parent->core.rbtree, chain);
                        atomic_clear_int(&chain->flags, HAMMER2_CHAIN_ONRBTREE);
                        --parent->core.chain_count;
                        chain->parent = NULL;
                }

                /*
                 * If our chain was the last chain in the parent's core the
                 * core is now empty and its parent might have to be
                 * re-dropped if it has 0 refs.
                 */
                if (parent->core.chain_count == 0) {
                        rdrop = parent;
                        atomic_add_int(&rdrop->refs, 1);
                        /*
                        if (atomic_cmpset_int(&rdrop->refs, 0, 1) == 0)
                                rdrop = NULL;
                        */
                }
                hammer2_spin_unex(&parent->core.spin);
                parent = NULL;  /* safety */
                /* FALL THROUGH */
        }

        /*
         * Successful 1->0 transition and the chain can be destroyed now.
         *
         * We still have the core spinlock, and core's chain_count is 0.
         * Any parent spinlock is gone.
         */
        hammer2_spin_unex(&chain->core.spin);
        KKASSERT(RB_EMPTY(&chain->core.rbtree) &&
                 chain->core.chain_count == 0);

        /*
         * All spin locks are gone, no pointers remain to the chain, finish
         * freeing it.
         */
        KKASSERT((chain->flags & (HAMMER2_CHAIN_UPDATE |
                                  HAMMER2_CHAIN_MODIFIED)) == 0);
        dio = hammer2_chain_drop_data(chain, 1);
        if (dio)
                hammer2_io_bqrelse(&dio);

        /*
         * Once chain resources are gone we can use the now dead chain
         * structure to placehold what might otherwise require a recursive
         * drop, because we have potentially two things to drop and can only
         * return one directly.
         */
        if (chain->flags & HAMMER2_CHAIN_ALLOCATED) {
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_ALLOCATED);
                chain->hmp = NULL;
                kfree(chain, hmp->mchain);
        }

        /*
         * Possible chaining loop when parent re-drop needed.
         */
        return(rdrop);
}

/*
 * On either last lock release or last drop
 */
static hammer2_io_t *
hammer2_chain_drop_data(hammer2_chain_t *chain, int lastdrop)
{
        hammer2_io_t *dio;

        if ((dio = chain->dio) != NULL) {
                chain->dio = NULL;
                chain->data = NULL;
        } else {
                switch(chain->bref.type) {
                case HAMMER2_BREF_TYPE_VOLUME:
                case HAMMER2_BREF_TYPE_FREEMAP:
                        if (lastdrop)
                                chain->data = NULL;
                        break;
                default:
                        KKASSERT(chain->data == NULL);
                        break;
                }
        }
        return dio;
}

/*
 * Lock a referenced chain element, acquiring its data with I/O if necessary,
 * and specify how you would like the data to be resolved.
 *
 * If an I/O or other fatal error occurs, chain->error will be set to non-zero.
 *
 * The lock is allowed to recurse, multiple locking ops will aggregate
 * the requested resolve types.  Once data is assigned it will not be
 * removed until the last unlock.
 *
 * HAMMER2_RESOLVE_NEVER - Do not resolve the data element.
 *                         (typically used to avoid device/logical buffer
 *                          aliasing for data)
 *
 * HAMMER2_RESOLVE_MAYBE - Do not resolve data elements for chains in
 *                         the INITIAL-create state (indirect blocks only).
 *
 *                         Do not resolve data elements for DATA chains.
 *                         (typically used to avoid device/logical buffer
 *                          aliasing for data)
 *
 * HAMMER2_RESOLVE_ALWAYS- Always resolve the data element.
 *
 * HAMMER2_RESOLVE_SHARED- (flag) The chain is locked shared, otherwise
 *                         it will be locked exclusive.
 *
 * NOTE: Embedded elements (volume header, inodes) are always resolved
 *       regardless.
 *
 * NOTE: Specifying HAMMER2_RESOLVE_ALWAYS on a newly-created non-embedded
 *       element will instantiate and zero its buffer, and flush it on
 *       release.
 *
 * NOTE: (data) elements are normally locked RESOLVE_NEVER or RESOLVE_MAYBE
 *       so as not to instantiate a device buffer, which could alias against
 *       a logical file buffer.  However, if ALWAYS is specified the
 *       device buffer will be instantiated anyway.
 *
 * WARNING! This function blocks on I/O if data needs to be fetched.  This
 *          blocking can run concurrent with other compatible lock holders
 *          who do not need data returning.  The lock is not upgraded to
 *          exclusive during a data fetch, a separate bit is used to
 *          interlock I/O.  However, an exclusive lock holder can still count
 *          on being interlocked against an I/O fetch managed by a shared
 *          lock holder.
 */
void
hammer2_chain_lock(hammer2_chain_t *chain, int how)
{
        /*
         * Ref and lock the element.  Recursive locks are allowed.
         */
        KKASSERT(chain->refs > 0);
        atomic_add_int(&chain->lockcnt, 1);

        TIMER(20);
        /*
         * Get the appropriate lock.
         */
        if (how & HAMMER2_RESOLVE_SHARED)
                hammer2_mtx_sh(&chain->lock);
        else
                hammer2_mtx_ex(&chain->lock);
        ++curthread->td_tracker;
        TIMER(21);

        /*
         * If we already have a valid data pointer no further action is
         * necessary.
         */
        if (chain->data)
                return;
        TIMER(22);

        /*
         * Do we have to resolve the data?
         */
        switch(how & HAMMER2_RESOLVE_MASK) {
        case HAMMER2_RESOLVE_NEVER:
                return;
        case HAMMER2_RESOLVE_MAYBE:
                if (chain->flags & HAMMER2_CHAIN_INITIAL)
                        return;
                if (chain->bref.type == HAMMER2_BREF_TYPE_DATA)
                        return;
#if 0
                if (chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_NODE)
                        return;
                if (chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_LEAF)
                        return;
#endif
                /* fall through */
        case HAMMER2_RESOLVE_ALWAYS:
        default:
                break;
        }

        /*
         * Caller requires data
         */
        hammer2_chain_load_data(chain);
}

/*
 * Downgrade an exclusive chain lock to a shared chain lock.
 *
 * NOTE: There is no upgrade equivalent due to the ease of
 *       deadlocks in that direction.
 */
void
hammer2_chain_lock_downgrade(hammer2_chain_t *chain)
{
        hammer2_mtx_downgrade(&chain->lock);
}

/*
 * Obtains a second shared lock on the chain, does not account the second
 * shared lock as being owned by the current thread.
 *
 * Caller must already own a shared lock on this chain.
 *
 * The lock function is required to obtain the second shared lock without
 * blocking on pending exclusive requests.
 */
void
hammer2_chain_push_shared_lock(hammer2_chain_t *chain)
{
        hammer2_mtx_sh_again(&chain->lock);
        atomic_add_int(&chain->lockcnt, 1);
        /* do not count in td_tracker for this thread */
}

/*
 * Accounts for a shared lock that was pushed to us as being owned by our
 * thread.
 */
void
hammer2_chain_pull_shared_lock(hammer2_chain_t *chain)
{
        ++curthread->td_tracker;
}

/*
 * Issue I/O and install chain->data.  Caller must hold a chain lock, lock
 * may be of any type.
 *
 * Once chain->data is set it cannot be disposed of until all locks are
 * released.
 */
void
hammer2_chain_load_data(hammer2_chain_t *chain)
{
        hammer2_blockref_t *bref;
        hammer2_dev_t *hmp;
        char *bdata;
        int error;

        /*
         * Degenerate case, data already present.
         */
        if (chain->data)
                return;
        TIMER(23);

        hmp = chain->hmp;
        KKASSERT(hmp != NULL);

        /*
         * Gain the IOINPROG bit, interlocked block.
         */
        for (;;) {
                u_int oflags;
                u_int nflags;

                oflags = chain->flags;
                cpu_ccfence();
                if (oflags & HAMMER2_CHAIN_IOINPROG) {
                        nflags = oflags | HAMMER2_CHAIN_IOSIGNAL;
                        tsleep_interlock(&chain->flags, 0);
                        if (atomic_cmpset_int(&chain->flags, oflags, nflags)) {
                                tsleep(&chain->flags, PINTERLOCKED,
                                        "h2iocw", 0);
                        }
                        /* retry */
                } else {
                        nflags = oflags | HAMMER2_CHAIN_IOINPROG;
                        if (atomic_cmpset_int(&chain->flags, oflags, nflags)) {
                                break;
                        }
                        /* retry */
                }
        }
        TIMER(24);

        /*
         * We own CHAIN_IOINPROG
         *
         * Degenerate case if we raced another load.
         */
        if (chain->data)
                goto done;

        /*
         * We must resolve to a device buffer, either by issuing I/O or
         * by creating a zero-fill element.  We do not mark the buffer
         * dirty when creating a zero-fill element (the hammer2_chain_modify()
         * API must still be used to do that).
         *
         * The device buffer is variable-sized in powers of 2 down
         * to HAMMER2_MIN_ALLOC (typically 1K).  A 64K physical storage
         * chunk always contains buffers of the same size. (XXX)
         *
         * The minimum physical IO size may be larger than the variable
         * block size.
         */
        bref = &chain->bref;

        /*
         * The getblk() optimization can only be used on newly created
         * elements if the physical block size matches the request.
         */
        if (chain->flags & HAMMER2_CHAIN_INITIAL) {
                error = hammer2_io_new(hmp, bref->type,
                                       bref->data_off, chain->bytes,
                                       &chain->dio);
        } else {
                error = hammer2_io_bread(hmp, bref->type,
                                         bref->data_off, chain->bytes,
                                         &chain->dio);
                hammer2_adjreadcounter(&chain->bref, chain->bytes);
        }
        TIMER(25);
        if (error) {
                chain->error = HAMMER2_ERROR_IO;
                kprintf("hammer2_chain_lock: I/O error %016jx: %d\n",
                        (intmax_t)bref->data_off, error);
                hammer2_io_bqrelse(&chain->dio);
                goto done;
        }
        chain->error = 0;

        /*
         * NOTE: A locked chain's data cannot be modified without first
         *       calling hammer2_chain_modify().
         */

        /*
         * Clear INITIAL.  In this case we used io_new() and the buffer has
         * been zero'd and marked dirty.
         */
        bdata = hammer2_io_data(chain->dio, chain->bref.data_off);
        if (chain->flags & HAMMER2_CHAIN_INITIAL) {
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_INITIAL);
                chain->bref.flags |= HAMMER2_BREF_FLAG_ZERO;
        } else if (chain->flags & HAMMER2_CHAIN_MODIFIED) {
                /*
                 * check data not currently synchronized due to
                 * modification.  XXX assumes data stays in the buffer
                 * cache, which might not be true (need biodep on flush
                 * to calculate crc?  or simple crc?).
                 */
        } else if ((chain->flags & HAMMER2_CHAIN_TESTEDGOOD) == 0) {
                uint64_t mask;

        TIMER(26);
                if (hammer2_io_crc_good(chain, &mask)) {
                        atomic_set_int(&chain->flags, HAMMER2_CHAIN_TESTEDGOOD);
                } else if (hammer2_chain_testcheck(chain, bdata) == 0) {
                        kprintf("chain %016jx.%02x meth=%02x "
                                "CHECK FAIL %08x (flags=%08x)\n",
                                chain->bref.data_off,
                                chain->bref.type,
                                chain->bref.methods,
                                hammer2_icrc32(bdata, chain->bytes),
                                chain->flags);
                        chain->error = HAMMER2_ERROR_CHECK;
                } else {
                        hammer2_io_crc_setmask(chain->dio, mask);
#if 0
                        kprintf("chain %02x %016jx %u\n",
                                chain->bref.type, chain->bref.key,
                                chain->bytes);
#endif
                        atomic_set_int(&chain->flags, HAMMER2_CHAIN_TESTEDGOOD);
                }
        }
        TIMER(27);

        /*
         * Setup the data pointer, either pointing it to an embedded data
         * structure and copying the data from the buffer, or pointing it
         * into the buffer.
         *
         * The buffer is not retained when copying to an embedded data
         * structure in order to avoid potential deadlocks or recursions
         * on the same physical buffer.
         *
         * WARNING! Other threads can start using the data the instant we
         *          set chain->data non-NULL.
         */
        switch (bref->type) {
        case HAMMER2_BREF_TYPE_VOLUME:
        case HAMMER2_BREF_TYPE_FREEMAP:
                /*
                 * Copy data from bp to embedded buffer
                 */
                panic("hammer2_chain_lock: called on unresolved volume header");
                break;
        case HAMMER2_BREF_TYPE_INODE:
        case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
        case HAMMER2_BREF_TYPE_INDIRECT:
        case HAMMER2_BREF_TYPE_DATA:
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
        default:
                /*
                 * Point data at the device buffer and leave dio intact.
                 */
                chain->data = (void *)bdata;
                break;
        }

        /*
         * Release HAMMER2_CHAIN_IOINPROG and signal waiters if requested.
         */
done:
        for (;;) {
                u_int oflags;
                u_int nflags;

                oflags = chain->flags;
                nflags = oflags & ~(HAMMER2_CHAIN_IOINPROG |
                                    HAMMER2_CHAIN_IOSIGNAL);
                KKASSERT(oflags & HAMMER2_CHAIN_IOINPROG);
                if (atomic_cmpset_int(&chain->flags, oflags, nflags)) {
                        if (oflags & HAMMER2_CHAIN_IOSIGNAL)
                                wakeup(&chain->flags);
                        break;
                }
        }
        TIMER(28);
}

/*
 * Unlock and deref a chain element.
 *
 * Remember that the presence of children under chain prevent the chain's
 * destruction but do not add additional references, so the dio will still
 * be dropped.
 */
void
hammer2_chain_unlock(hammer2_chain_t *chain)
{
        u_int lockcnt;

        --curthread->td_tracker;
        /*
         * If multiple locks are present (or being attempted) on this
         * particular chain we can just unlock, drop refs, and return.
         *
         * Otherwise fall-through on the 1->0 transition.
         */
        for (;;) {
                lockcnt = chain->lockcnt;
                KKASSERT(lockcnt > 0);
                cpu_ccfence();
                if (lockcnt > 1) {
                        if (atomic_cmpset_int(&chain->lockcnt,
                                              lockcnt, lockcnt - 1)) {
                                hammer2_mtx_unlock(&chain->lock);
                                return;
                        }
                } else {
                        if (atomic_cmpset_int(&chain->lockcnt, 1, 0))
                                break;
                }
                /* retry */
        }

        /*
         * Normally we want to disassociate the data on the last unlock,
         * but leave it intact if persist_refs is non-zero.  The persist-data
         * user modifies persist_refs only while holding the chain locked
         * so there should be no race on the last unlock here.
         *
         * NOTE: If this was a shared lock we have to temporarily upgrade it
         *       to prevent data load races.  We can only do this non-blocking,
         *       and unlock/relock-excl can deadlock.  If the try fails it
         *       means someone else got a shared or exclusive lock while we
         *       we bandying about.
         */
        if (chain->persist_refs == 0) {
                hammer2_io_t *dio;

                if (hammer2_mtx_upgrade_try(&chain->lock) == 0 &&
                    chain->lockcnt == 0) {
                        dio = hammer2_chain_drop_data(chain, 0);
                        if (dio)
                                hammer2_io_bqrelse(&dio);
                }
        }
        hammer2_mtx_unlock(&chain->lock);
}

/*
 * Helper to obtain the blockref[] array base and count for a chain.
 *
 * XXX Not widely used yet, various use cases need to be validated and
 *     converted to use this function.
 */
static
hammer2_blockref_t *
hammer2_chain_base_and_count(hammer2_chain_t *parent, int *countp)
{
        hammer2_blockref_t *base;
        int count;

        if (parent->flags & HAMMER2_CHAIN_INITIAL) {
                base = NULL;

                switch(parent->bref.type) {
                case HAMMER2_BREF_TYPE_INODE:
                        count = HAMMER2_SET_COUNT;
                        break;
                case HAMMER2_BREF_TYPE_INDIRECT:
                case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                        count = parent->bytes / sizeof(hammer2_blockref_t);
                        break;
                case HAMMER2_BREF_TYPE_VOLUME:
                        count = HAMMER2_SET_COUNT;
                        break;
                case HAMMER2_BREF_TYPE_FREEMAP:
                        count = HAMMER2_SET_COUNT;
                        break;
                default:
                        panic("hammer2_chain_create_indirect: "
                              "unrecognized blockref type: %d",
                              parent->bref.type);
                        count = 0;
                        break;
                }
        } else {
                switch(parent->bref.type) {
                case HAMMER2_BREF_TYPE_INODE:
                        base = &parent->data->ipdata.u.blockset.blockref[0];
                        count = HAMMER2_SET_COUNT;
                        break;
                case HAMMER2_BREF_TYPE_INDIRECT:
                case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                        base = &parent->data->npdata[0];
                        count = parent->bytes / sizeof(hammer2_blockref_t);
                        break;
                case HAMMER2_BREF_TYPE_VOLUME:
                        base = &parent->data->voldata.
                                        sroot_blockset.blockref[0];
                        count = HAMMER2_SET_COUNT;
                        break;
                case HAMMER2_BREF_TYPE_FREEMAP:
                        base = &parent->data->blkset.blockref[0];
                        count = HAMMER2_SET_COUNT;
                        break;
                default:
                        panic("hammer2_chain_create_indirect: "
                              "unrecognized blockref type: %d",
                              parent->bref.type);
                        count = 0;
                        break;
                }
        }
        *countp = count;

        return base;
}

/*
 * This counts the number of live blockrefs in a block array and
 * also calculates the point at which all remaining blockrefs are empty.
 * This routine can only be called on a live chain (DUPLICATED flag not set).
 *
 * NOTE: Flag is not set until after the count is complete, allowing
 *       callers to test the flag without holding the spinlock.
 *
 * NOTE: If base is NULL the related chain is still in the INITIAL
 *       state and there are no blockrefs to count.
 *
 * NOTE: live_count may already have some counts accumulated due to
 *       creation and deletion and could even be initially negative.
 */
void
hammer2_chain_countbrefs(hammer2_chain_t *chain,
                         hammer2_blockref_t *base, int count)
{
        hammer2_spin_ex(&chain->core.spin);
        if ((chain->flags & HAMMER2_CHAIN_COUNTEDBREFS) == 0) {
                if (base) {
                        while (--count >= 0) {
                                if (base[count].type)
                                        break;
                        }
                        chain->core.live_zero = count + 1;
                        while (count >= 0) {
                                if (base[count].type)
                                        atomic_add_int(&chain->core.live_count,
                                                       1);
                                --count;
                        }
                } else {
                        chain->core.live_zero = 0;
                }
                /* else do not modify live_count */
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_COUNTEDBREFS);
        }
        hammer2_spin_unex(&chain->core.spin);
}

/*
 * Resize the chain's physical storage allocation in-place.  This function does
 * not adjust the data pointer and must be followed by (typically) a
 * hammer2_chain_modify() call to copy any old data over and adjust the
 * data pointer.
 *
 * Chains can be resized smaller without reallocating the storage.  Resizing
 * larger will reallocate the storage.  Excess or prior storage is reclaimed
 * asynchronously at a later time.
 *
 * Must be passed an exclusively locked parent and chain.
 *
 * This function is mostly used with DATA blocks locked RESOLVE_NEVER in order
 * to avoid instantiating a device buffer that conflicts with the vnode data
 * buffer.  However, because H2 can compress or encrypt data, the chain may
 * have a dio assigned to it in those situations, and they do not conflict.
 *
 * XXX return error if cannot resize.
 */
void
hammer2_chain_resize(hammer2_inode_t *ip,
                     hammer2_chain_t *parent, hammer2_chain_t *chain,
                     hammer2_tid_t mtid, hammer2_off_t dedup_off,
                     int nradix, int flags)
{
        hammer2_dev_t *hmp;
        size_t obytes;
        size_t nbytes;

        hmp = chain->hmp;

        /*
         * Only data and indirect blocks can be resized for now.
         * (The volu root, inodes, and freemap elements use a fixed size).
         */
        KKASSERT(chain != &hmp->vchain);
        KKASSERT(chain->bref.type == HAMMER2_BREF_TYPE_DATA ||
                 chain->bref.type == HAMMER2_BREF_TYPE_INDIRECT);
        KKASSERT(chain->parent == parent);

        /*
         * Nothing to do if the element is already the proper size
         */
        obytes = chain->bytes;
        nbytes = 1U << nradix;
        if (obytes == nbytes)
                return;

        /*
         * Make sure the old data is instantiated so we can copy it.  If this
         * is a data block, the device data may be superfluous since the data
         * might be in a logical block, but compressed or encrypted data is
         * another matter.
         *
         * NOTE: The modify will set BMAPUPD for us if BMAPPED is set.
         */
        hammer2_chain_modify(chain, mtid, dedup_off, 0);

        /*
         * Relocate the block, even if making it smaller (because different
         * block sizes may be in different regions).
         *
         * (data blocks only, we aren't copying the storage here).
         */
        hammer2_freemap_alloc(chain, nbytes);
        chain->bytes = nbytes;
        /*ip->delta_dcount += (ssize_t)(nbytes - obytes);*/ /* XXX atomic */

        /*
         * We don't want the followup chain_modify() to try to copy data
         * from the old (wrong-sized) buffer.  It won't know how much to
         * copy.  This case should only occur during writes when the
         * originator already has the data to write in-hand.
         */
        if (chain->dio) {
                KKASSERT(chain->bref.type == HAMMER2_BREF_TYPE_DATA);
                hammer2_io_brelse(&chain->dio);
                chain->data = NULL;
        }
}

/*
 * Set the chain modified so its data can be changed by the caller.
 *
 * Sets bref.modify_tid to mtid only if mtid != 0.  Note that bref.modify_tid
 * is a CLC (cluster level change) field and is not updated by parent
 * propagation during a flush.
 *
 * If the caller passes a non-zero dedup_off we assign data_off to that
 * instead of allocating a ne block.  Caller must not modify the data already
 * present at the target offset.
 */
void
hammer2_chain_modify(hammer2_chain_t *chain, hammer2_tid_t mtid,
                     hammer2_off_t dedup_off, int flags)
{
        hammer2_blockref_t obref;
        hammer2_dev_t *hmp;
        hammer2_io_t *dio;
        int error;
        int wasinitial;
        int newmod;
        char *bdata;

        hmp = chain->hmp;
        obref = chain->bref;
        KKASSERT((chain->flags & HAMMER2_CHAIN_FICTITIOUS) == 0);

        /*
         * Data is not optional for freemap chains (we must always be sure
         * to copy the data on COW storage allocations).
         */
        if (chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_NODE ||
            chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_LEAF) {
                KKASSERT((chain->flags & HAMMER2_CHAIN_INITIAL) ||
                         (flags & HAMMER2_MODIFY_OPTDATA) == 0);
        }

        /*
         * Data must be resolved if already assigned, unless explicitly
         * flagged otherwise.
         */
        if (chain->data == NULL && (flags & HAMMER2_MODIFY_OPTDATA) == 0 &&
            (chain->bref.data_off & ~HAMMER2_OFF_MASK_RADIX)) {
                hammer2_chain_load_data(chain);
        }

        /*
         * Set MODIFIED to indicate that the chain has been modified.
         * Set UPDATE to ensure that the blockref is updated in the parent.
         */
        if ((chain->flags & (HAMMER2_CHAIN_DEDUP | HAMMER2_CHAIN_MODIFIED)) ==
            (HAMMER2_CHAIN_DEDUP | HAMMER2_CHAIN_MODIFIED)) {
                /*
                 * Modified already set but a new allocation is needed
                 * anyway because we recorded this data_off for possible
                 * dedup operation.
                 */
                newmod = 1;
        } else if ((chain->flags & HAMMER2_CHAIN_MODIFIED) == 0) {
                /*
                 * Must set modified bit.
                 */
                atomic_add_long(&hammer2_count_modified_chains, 1);
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_MODIFIED);
                hammer2_pfs_memory_inc(chain->pmp);     /* can be NULL */
                newmod = 1;
        } else {
                /*
                 * Already flagged modified, no new allocation is needed.
                 */
                newmod = 0;
        }

        /*
         * Flag parent update required, clear DEDUP flag (already processed
         * above).
         */
        if ((chain->flags & HAMMER2_CHAIN_UPDATE) == 0)
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_UPDATE);
        atomic_clear_int(&chain->flags, HAMMER2_CHAIN_DEDUP);

        /*
         * The modification or re-modification requires an allocation and
         * possible COW.
         *
         * If dedup_off is non-zero, caller already has a data offset
         * containing the caller's desired data.  The dedup offset is
         * allowed to be in a partially free state and we must be sure
         * to reset it to a fully allocated state to force two bulkfree
         * passes to free it again.
         *
         * XXX can a chain already be marked MODIFIED without a data
         * assignment?  If not, assert here instead of testing the case.
         */
        if (chain != &hmp->vchain && chain != &hmp->fchain) {
                if ((chain->bref.data_off & ~HAMMER2_OFF_MASK_RADIX) == 0 ||
                     newmod
                ) {
                        if (dedup_off) {
                                chain->bref.data_off = dedup_off;
                                chain->bytes = 1 << (dedup_off &
                                                     HAMMER2_OFF_MASK_RADIX);
                                atomic_set_int(&chain->flags,
                                               HAMMER2_CHAIN_DEDUP);
                                hammer2_freemap_adjust(hmp, &chain->bref,
                                                HAMMER2_FREEMAP_DORECOVER);
                        } else {
                                hammer2_freemap_alloc(chain, chain->bytes);
                        }
                        /* XXX failed allocation */
                }
        }

        /*
         * Update mirror_tid and modify_tid.  modify_tid is only updated
         * if not passed as zero (during flushes, parent propagation passes
         * the value 0).
         *
         * NOTE: chain->pmp could be the device spmp.
         */
        chain->bref.mirror_tid = hmp->voldata.mirror_tid + 1;
        if (mtid)
                chain->bref.modify_tid = mtid;

        /*
         * Set BMAPUPD to tell the flush code that an existing blockmap entry
         * requires updating as well as to tell the delete code that the
         * chain's blockref might not exactly match (in terms of physical size
         * or block offset) the one in the parent's blocktable.  The base key
         * of course will still match.
         */
        if (chain->flags & HAMMER2_CHAIN_BMAPPED)
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_BMAPUPD);

        /*
         * Short-cut data blocks which the caller does not need an actual
         * data reference to (aka OPTDATA), as long as the chain does not
         * already have a data pointer to the data.  This generally means
         * that the modifications are being done via the logical buffer cache.
         * The INITIAL flag relates only to the device data buffer and thus
         * remains unchange in this situation.
         */
        if (chain->bref.type == HAMMER2_BREF_TYPE_DATA &&
            (flags & HAMMER2_MODIFY_OPTDATA) &&
            chain->data == NULL) {
                goto skip2;
        }

        /*
         * Clearing the INITIAL flag (for indirect blocks) indicates that
         * we've processed the uninitialized storage allocation.
         *
         * If this flag is already clear we are likely in a copy-on-write
         * situation but we have to be sure NOT to bzero the storage if
         * no data is present.
         */
        if (chain->flags & HAMMER2_CHAIN_INITIAL) {
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_INITIAL);
                wasinitial = 1;
        } else {
                wasinitial = 0;
        }

        /*
         * Instantiate data buffer and possibly execute COW operation
         */
        switch(chain->bref.type) {
        case HAMMER2_BREF_TYPE_VOLUME:
        case HAMMER2_BREF_TYPE_FREEMAP:
                /*
                 * The data is embedded, no copy-on-write operation is
                 * needed.
                 */
                KKASSERT(chain->dio == NULL);
                break;
        case HAMMER2_BREF_TYPE_INODE:
        case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
        case HAMMER2_BREF_TYPE_DATA:
        case HAMMER2_BREF_TYPE_INDIRECT:
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                /*
                 * Perform the copy-on-write operation
                 *
                 * zero-fill or copy-on-write depending on whether
                 * chain->data exists or not and set the dirty state for
                 * the new buffer.  hammer2_io_new() will handle the
                 * zero-fill.
                 *
                 * If a dedup_off was supplied this is an existing block
                 * and no COW, copy, or further modification is required.
                 */
                KKASSERT(chain != &hmp->vchain && chain != &hmp->fchain);

                if (wasinitial && dedup_off == 0) {
                        error = hammer2_io_new(hmp, chain->bref.type,
                                               chain->bref.data_off,
                                               chain->bytes, &dio);
                } else {
                        error = hammer2_io_bread(hmp, chain->bref.type,
                                                 chain->bref.data_off,
                                                 chain->bytes, &dio);
                }
                hammer2_adjreadcounter(&chain->bref, chain->bytes);

                /*
                 * If an I/O error occurs make sure callers cannot accidently
                 * modify the old buffer's contents and corrupt the filesystem.
                 */
                if (error) {
                        kprintf("hammer2_chain_modify: hmp=%p I/O error\n",
                                hmp);
                        chain->error = HAMMER2_ERROR_IO;
                        hammer2_io_brelse(&dio);
                        hammer2_io_brelse(&chain->dio);
                        chain->data = NULL;
                        break;
                }
                chain->error = 0;
                bdata = hammer2_io_data(dio, chain->bref.data_off);

                if (chain->data) {
                        /*
                         * COW (unless a dedup).
                         */
                        KKASSERT(chain->dio != NULL);
                        if (chain->data != (void *)bdata && dedup_off == 0) {
                                bcopy(chain->data, bdata, chain->bytes);
                        }
                } else if (wasinitial == 0) {
                        /*
                         * We have a problem.  We were asked to COW but
                         * we don't have any data to COW with!
                         */
                        panic("hammer2_chain_modify: having a COW %p\n",
                              chain);
                }

                /*
                 * Retire the old buffer, replace with the new.  Dirty or
                 * redirty the new buffer.
                 *
                 * WARNING! The system buffer cache may have already flushed
                 *          the buffer, so we must be sure to [re]dirty it
                 *          for further modification.
                 *
                 *          If dedup_off was supplied, the caller is not
                 *          expected to make any further modification to the
                 *          buffer.
                 */
                if (chain->dio)
                        hammer2_io_bqrelse(&chain->dio);
                chain->data = (void *)bdata;
                chain->dio = dio;
                if (dedup_off == 0)
                        hammer2_io_setdirty(dio);
                break;
        default:
                panic("hammer2_chain_modify: illegal non-embedded type %d",
                      chain->bref.type);
                break;

        }
skip2:
        /*
         * setflush on parent indicating that the parent must recurse down
         * to us.  Do not call on chain itself which might already have it
         * set.
         */
        if (chain->parent)
                hammer2_chain_setflush(chain->parent);
}

/*
 * Modify the chain associated with an inode.
 */
void
hammer2_chain_modify_ip(hammer2_inode_t *ip, hammer2_chain_t *chain,
                        hammer2_tid_t mtid, int flags)
{
        hammer2_inode_modify(ip);
        hammer2_chain_modify(chain, mtid, 0, flags);
}

/*
 * Volume header data locks
 */
void
hammer2_voldata_lock(hammer2_dev_t *hmp)
{
        lockmgr(&hmp->vollk, LK_EXCLUSIVE);
}

void
hammer2_voldata_unlock(hammer2_dev_t *hmp)
{
        lockmgr(&hmp->vollk, LK_RELEASE);
}

void
hammer2_voldata_modify(hammer2_dev_t *hmp)
{
        if ((hmp->vchain.flags & HAMMER2_CHAIN_MODIFIED) == 0) {
                atomic_add_long(&hammer2_count_modified_chains, 1);
                atomic_set_int(&hmp->vchain.flags, HAMMER2_CHAIN_MODIFIED);
                hammer2_pfs_memory_inc(hmp->vchain.pmp);
        }
}

/*
 * This function returns the chain at the nearest key within the specified
 * range.  The returned chain will be referenced but not locked.
 *
 * This function will recurse through chain->rbtree as necessary and will
 * return a *key_nextp suitable for iteration.  *key_nextp is only set if
 * the iteration value is less than the current value of *key_nextp.
 *
 * The caller should use (*key_nextp) to calculate the actual range of
 * the returned element, which will be (key_beg to *key_nextp - 1), because
 * there might be another element which is superior to the returned element
 * and overlaps it.
 *
 * (*key_nextp) can be passed as key_beg in an iteration only while non-NULL
 * chains continue to be returned.  On EOF (*key_nextp) may overflow since
 * it will wind up being (key_end + 1).
 *
 * WARNING!  Must be called with child's spinlock held.  Spinlock remains
 *           held through the operation.
 */
struct hammer2_chain_find_info {
        hammer2_chain_t         *best;
        hammer2_key_t           key_beg;
        hammer2_key_t           key_end;
        hammer2_key_t           key_next;
};

static int hammer2_chain_find_cmp(hammer2_chain_t *child, void *data);
static int hammer2_chain_find_callback(hammer2_chain_t *child, void *data);

static
hammer2_chain_t *
hammer2_chain_find(hammer2_chain_t *parent, hammer2_key_t *key_nextp,
                          hammer2_key_t key_beg, hammer2_key_t key_end)
{
        struct hammer2_chain_find_info info;

        info.best = NULL;
        info.key_beg = key_beg;
        info.key_end = key_end;
        info.key_next = *key_nextp;

        RB_SCAN(hammer2_chain_tree, &parent->core.rbtree,
                hammer2_chain_find_cmp, hammer2_chain_find_callback,
                &info);
        *key_nextp = info.key_next;
#if 0
        kprintf("chain_find %p %016jx:%016jx next=%016jx\n",
                parent, key_beg, key_end, *key_nextp);
#endif

        return (info.best);
}

static
int
hammer2_chain_find_cmp(hammer2_chain_t *child, void *data)
{
        struct hammer2_chain_find_info *info = data;
        hammer2_key_t child_beg;
        hammer2_key_t child_end;

        child_beg = child->bref.key;
        child_end = child_beg + ((hammer2_key_t)1 << child->bref.keybits) - 1;

        if (child_end < info->key_beg)
                return(-1);
        if (child_beg > info->key_end)
                return(1);
        return(0);
}

static
int
hammer2_chain_find_callback(hammer2_chain_t *child, void *data)
{
        struct hammer2_chain_find_info *info = data;
        hammer2_chain_t *best;
        hammer2_key_t child_end;

        /*
         * WARNING! Do not discard DUPLICATED chains, it is possible that
         *          we are catching an insertion half-way done.  If a
         *          duplicated chain turns out to be the best choice the
         *          caller will re-check its flags after locking it.
         *
         * WARNING! Layerq is scanned forwards, exact matches should keep
         *          the existing info->best.
         */
        if ((best = info->best) == NULL) {
                /*
                 * No previous best.  Assign best
                 */
                info->best = child;
        } else if (best->bref.key <= info->key_beg &&
                   child->bref.key <= info->key_beg) {
                /*
                 * Illegal overlap.
                 */
                KKASSERT(0);
                /*info->best = child;*/
        } else if (child->bref.key < best->bref.key) {
                /*
                 * Child has a nearer key and best is not flush with key_beg.
                 * Set best to child.  Truncate key_next to the old best key.
                 */
                info->best = child;
                if (info->key_next > best->bref.key || info->key_next == 0)
                        info->key_next = best->bref.key;
        } else if (child->bref.key == best->bref.key) {
                /*
                 * If our current best is flush with the child then this
                 * is an illegal overlap.
                 *
                 * key_next will automatically be limited to the smaller of
                 * the two end-points.
                 */
                KKASSERT(0);
                info->best = child;
        } else {
                /*
                 * Keep the current best but truncate key_next to the child's
                 * base.
                 *
                 * key_next will also automatically be limited to the smaller
                 * of the two end-points (probably not necessary for this case
                 * but we do it anyway).
                 */
                if (info->key_next > child->bref.key || info->key_next == 0)
                        info->key_next = child->bref.key;
        }

        /*
         * Always truncate key_next based on child's end-of-range.
         */
        child_end = child->bref.key + ((hammer2_key_t)1 << child->bref.keybits);
        if (child_end && (info->key_next > child_end || info->key_next == 0))
                info->key_next = child_end;

        return(0);
}

/*
 * Retrieve the specified chain from a media blockref, creating the
 * in-memory chain structure which reflects it.
 *
 * To handle insertion races pass the INSERT_RACE flag along with the
 * generation number of the core.  NULL will be returned if the generation
 * number changes before we have a chance to insert the chain.  Insert
 * races can occur because the parent might be held shared.
 *
 * Caller must hold the parent locked shared or exclusive since we may
 * need the parent's bref array to find our block.
 *
 * WARNING! chain->pmp is always set to NULL for any chain representing
 *          part of the super-root topology.
 */
hammer2_chain_t *
hammer2_chain_get(hammer2_chain_t *parent, int generation,
                  hammer2_blockref_t *bref)
{
        hammer2_dev_t *hmp = parent->hmp;
        hammer2_chain_t *chain;
        int error;

        /*
         * Allocate a chain structure representing the existing media
         * entry.  Resulting chain has one ref and is not locked.
         */
        if (bref->flags & HAMMER2_BREF_FLAG_PFSROOT)
                chain = hammer2_chain_alloc(hmp, NULL, bref);
        else
                chain = hammer2_chain_alloc(hmp, parent->pmp, bref);
        /* ref'd chain returned */

        /*
         * Flag that the chain is in the parent's blockmap so delete/flush
         * knows what to do with it.
         */
        atomic_set_int(&chain->flags, HAMMER2_CHAIN_BMAPPED);

        /*
         * Link the chain into its parent.  A spinlock is required to safely
         * access the RBTREE, and it is possible to collide with another
         * hammer2_chain_get() operation because the caller might only hold
         * a shared lock on the parent.
         *
         * NOTE: Get races can occur quite often when we distribute
         *       asynchronous read-aheads across multiple threads.
         */
        KKASSERT(parent->refs > 0);
        error = hammer2_chain_insert(parent, chain,
                                     HAMMER2_CHAIN_INSERT_SPIN |
                                     HAMMER2_CHAIN_INSERT_RACE,
                                     generation);
        if (error) {
                KKASSERT((chain->flags & HAMMER2_CHAIN_ONRBTREE) == 0);
                /*kprintf("chain %p get race\n", chain);*/
                hammer2_chain_drop(chain);
                chain = NULL;
        } else {
                KKASSERT(chain->flags & HAMMER2_CHAIN_ONRBTREE);
        }

        /*
         * Return our new chain referenced but not locked, or NULL if
         * a race occurred.
         */
        return (chain);
}

/*
 * Lookup initialization/completion API
 */
hammer2_chain_t *
hammer2_chain_lookup_init(hammer2_chain_t *parent, int flags)
{
        hammer2_chain_ref(parent);
        if (flags & HAMMER2_LOOKUP_SHARED) {
                hammer2_chain_lock(parent, HAMMER2_RESOLVE_ALWAYS |
                                           HAMMER2_RESOLVE_SHARED);
        } else {
                hammer2_chain_lock(parent, HAMMER2_RESOLVE_ALWAYS);
        }
        return (parent);
}

void
hammer2_chain_lookup_done(hammer2_chain_t *parent)
{
        if (parent) {
                hammer2_chain_unlock(parent);
                hammer2_chain_drop(parent);
        }
}

hammer2_chain_t *
hammer2_chain_getparent(hammer2_chain_t **parentp, int how)
{
        hammer2_chain_t *oparent;
        hammer2_chain_t *nparent;

        /*
         * Be careful of order, oparent must be unlocked before nparent
         * is locked below to avoid a deadlock.
         */
        oparent = *parentp;
        hammer2_spin_ex(&oparent->core.spin);
        nparent = oparent->parent;
        hammer2_chain_ref(nparent);
        hammer2_spin_unex(&oparent->core.spin);
        if (oparent) {
                hammer2_chain_unlock(oparent);
                hammer2_chain_drop(oparent);
                oparent = NULL;
        }

        hammer2_chain_lock(nparent, how);
        *parentp = nparent;

        return (nparent);
}

/*
 * Locate the first chain whos key range overlaps (key_beg, key_end) inclusive.
 * (*parentp) typically points to an inode but can also point to a related
 * indirect block and this function will recurse upwards and find the inode
 * again.
 *
 * (*parentp) must be exclusively locked and referenced and can be an inode
 * or an existing indirect block within the inode.
 *
 * On return (*parentp) will be modified to point at the deepest parent chain
 * element encountered during the search, as a helper for an insertion or
 * deletion.   The new (*parentp) will be locked and referenced and the old
 * will be unlocked and dereferenced (no change if they are both the same).
 *
 * The matching chain will be returned exclusively locked.  If NOLOCK is
 * requested the chain will be returned only referenced.  Note that the
 * parent chain must always be locked shared or exclusive, matching the
 * HAMMER2_LOOKUP_SHARED flag.  We can conceivably lock it SHARED temporarily
 * when NOLOCK is specified but that complicates matters if *parentp must
 * inherit the chain.
 *
 * NOLOCK also implies NODATA, since an unlocked chain usually has a NULL
 * data pointer or can otherwise be in flux.
 *
 * NULL is returned if no match was found, but (*parentp) will still
 * potentially be adjusted.
 *
 * If a fatal error occurs (typically an I/O error), a dummy chain is
 * returned with chain->error and error-identifying information set.  This
 * chain will assert if you try to do anything fancy with it.
 *
 * XXX Depending on where the error occurs we should allow continued iteration.
 *
 * On return (*key_nextp) will point to an iterative value for key_beg.
 * (If NULL is returned (*key_nextp) is set to (key_end + 1)).
 *
 * This function will also recurse up the chain if the key is not within the
 * current parent's range.  (*parentp) can never be set to NULL.  An iteration
 * can simply allow (*parentp) to float inside the loop.
 *
 * NOTE!  chain->data is not always resolved.  By default it will not be
 *        resolved for BREF_TYPE_DATA, FREEMAP_NODE, or FREEMAP_LEAF.  Use
 *        HAMMER2_LOOKUP_ALWAYS to force resolution (but be careful w/
 *        BREF_TYPE_DATA as the device buffer can alias the logical file
 *        buffer).
 */

hammer2_chain_t *
hammer2_chain_lookup(hammer2_chain_t **parentp, hammer2_key_t *key_nextp,
                     hammer2_key_t key_beg, hammer2_key_t key_end,
                     int *cache_indexp, int flags)
{
        hammer2_dev_t *hmp;
        hammer2_chain_t *parent;
        hammer2_chain_t *chain;
        hammer2_blockref_t *base;
        hammer2_blockref_t *bref;
        hammer2_blockref_t bcopy;
        hammer2_key_t scan_beg;
        hammer2_key_t scan_end;
        int count = 0;
        int how_always = HAMMER2_RESOLVE_ALWAYS;
        int how_maybe = HAMMER2_RESOLVE_MAYBE;
        int how;
        int generation;
        int maxloops = 300000;

        TIMER(8);

        if (flags & HAMMER2_LOOKUP_ALWAYS) {
                how_maybe = how_always;
                how = HAMMER2_RESOLVE_ALWAYS;
        } else if (flags & (HAMMER2_LOOKUP_NODATA | HAMMER2_LOOKUP_NOLOCK)) {
                how = HAMMER2_RESOLVE_NEVER;
        } else {
                how = HAMMER2_RESOLVE_MAYBE;
        }
        if (flags & HAMMER2_LOOKUP_SHARED) {
                how_maybe |= HAMMER2_RESOLVE_SHARED;
                how_always |= HAMMER2_RESOLVE_SHARED;
                how |= HAMMER2_RESOLVE_SHARED;
        }

        /*
         * Recurse (*parentp) upward if necessary until the parent completely
         * encloses the key range or we hit the inode.
         *
         * This function handles races against the flusher doing a delete-
         * duplicate above us and re-homes the parent to the duplicate in
         * that case, otherwise we'd wind up recursing down a stale chain.
         */
        parent = *parentp;
        hmp = parent->hmp;

        while (parent->bref.type == HAMMER2_BREF_TYPE_INDIRECT ||
               parent->bref.type == HAMMER2_BREF_TYPE_FREEMAP_NODE) {
                scan_beg = parent->bref.key;
                scan_end = scan_beg +
                           ((hammer2_key_t)1 << parent->bref.keybits) - 1;
                if (key_beg >= scan_beg && key_end <= scan_end)
                        break;
                parent = hammer2_chain_getparent(parentp, how_maybe);
        }

again:
        TIMER(9);
        if (--maxloops == 0)
                panic("hammer2_chain_lookup: maxloops");
        /*
         * Locate the blockref array.  Currently we do a fully associative
         * search through the array.
         */
        switch(parent->bref.type) {
        case HAMMER2_BREF_TYPE_INODE:
                /*
                 * Special shortcut for embedded data returns the inode
                 * itself.  Callers must detect this condition and access
                 * the embedded data (the strategy code does this for us).
                 *
                 * This is only applicable to regular files and softlinks.
                 */
                if (parent->data->ipdata.meta.op_flags &
                    HAMMER2_OPFLAG_DIRECTDATA) {
                        if (flags & HAMMER2_LOOKUP_NODIRECT) {
                                chain = NULL;
                                *key_nextp = key_end + 1;
                                goto done;
                        }
                        hammer2_chain_ref(parent);
                        if ((flags & HAMMER2_LOOKUP_NOLOCK) == 0)
                                hammer2_chain_lock(parent, how_always);
                        *key_nextp = key_end + 1;
                        return (parent);
                }
                base = &parent->data->ipdata.u.blockset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
        case HAMMER2_BREF_TYPE_INDIRECT:
                /*
                 * Handle MATCHIND on the parent
                 */
                if (flags & HAMMER2_LOOKUP_MATCHIND) {
                        scan_beg = parent->bref.key;
                        scan_end = scan_beg +
                               ((hammer2_key_t)1 << parent->bref.keybits) - 1;
                        if (key_beg == scan_beg && key_end == scan_end) {
                                chain = parent;
                                hammer2_chain_ref(chain);
                                hammer2_chain_lock(chain, how_maybe);
                                *key_nextp = scan_end + 1;
                                goto done;
                        }
                }
                /*
                 * Optimize indirect blocks in the INITIAL state to avoid
                 * I/O.
                 */
                if (parent->flags & HAMMER2_CHAIN_INITIAL) {
                        base = NULL;
                } else {
                        if (parent->data == NULL) {
                                kprintf("parent->data is NULL %p\n", parent);
                                while (1)
                                        tsleep(parent, 0, "xxx", 0);
                        }
                        base = &parent->data->npdata[0];
                }
                count = parent->bytes / sizeof(hammer2_blockref_t);
                break;
        case HAMMER2_BREF_TYPE_VOLUME:
                base = &parent->data->voldata.sroot_blockset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        case HAMMER2_BREF_TYPE_FREEMAP:
                base = &parent->data->blkset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        default:
                kprintf("hammer2_chain_lookup: unrecognized "
                        "blockref(B) type: %d",
                        parent->bref.type);
                while (1)
                        tsleep(&base, 0, "dead", 0);
                panic("hammer2_chain_lookup: unrecognized "
                      "blockref(B) type: %d",
                      parent->bref.type);
                base = NULL;    /* safety */
                count = 0;      /* safety */
        }
        TIMER(10);

        /*
         * Merged scan to find next candidate.
         *
         * hammer2_base_*() functions require the parent->core.live_* fields
         * to be synchronized.
         *
         * We need to hold the spinlock to access the block array and RB tree
         * and to interlock chain creation.
         */
        if ((parent->flags & HAMMER2_CHAIN_COUNTEDBREFS) == 0)
                hammer2_chain_countbrefs(parent, base, count);

        TIMER(11);

        /*
         * Combined search
         */
        hammer2_spin_ex(&parent->core.spin);
        chain = hammer2_combined_find(parent, base, count,
                                      cache_indexp, key_nextp,
                                      key_beg, key_end,
                                      &bref);
        generation = parent->core.generation;

        TIMER(12);

        /*
         * Exhausted parent chain, iterate.
         */
        if (bref == NULL) {
                TIMER(13);
                hammer2_spin_unex(&parent->core.spin);
                if (key_beg == key_end) /* short cut single-key case */
                        return (NULL);

                /*
                 * Stop if we reached the end of the iteration.
                 */
                if (parent->bref.type != HAMMER2_BREF_TYPE_INDIRECT &&
                    parent->bref.type != HAMMER2_BREF_TYPE_FREEMAP_NODE) {
                        return (NULL);
                }

                /*
                 * Calculate next key, stop if we reached the end of the
                 * iteration, otherwise go up one level and loop.
                 */
                key_beg = parent->bref.key +
                          ((hammer2_key_t)1 << parent->bref.keybits);
                if (key_beg == 0 || key_beg > key_end)
                        return (NULL);
                parent = hammer2_chain_getparent(parentp, how_maybe);
                goto again;
        }

        /*
         * Selected from blockref or in-memory chain.
         */
        if (chain == NULL) {
                TIMER(14);
                bcopy = *bref;
                hammer2_spin_unex(&parent->core.spin);
                chain = hammer2_chain_get(parent, generation,
                                          &bcopy);
                if (chain == NULL) {
                        /*
                        kprintf("retry lookup parent %p keys %016jx:%016jx\n",
                                parent, key_beg, key_end);
                        */
                        goto again;
                }
                if (bcmp(&bcopy, bref, sizeof(bcopy))) {
                        hammer2_chain_drop(chain);
                        goto again;
                }
        } else {
                TIMER(15);
                hammer2_chain_ref(chain);
                hammer2_spin_unex(&parent->core.spin);
        }

        TIMER(16);
        /*
         * chain is referenced but not locked.  We must lock the chain
         * to obtain definitive DUPLICATED/DELETED state
         */
        if (chain->bref.type == HAMMER2_BREF_TYPE_INDIRECT ||
            chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_NODE) {
                hammer2_chain_lock(chain, how_maybe);
        } else {
                hammer2_chain_lock(chain, how);
        }
        TIMER(17);

        /*
         * Skip deleted chains (XXX cache 'i' end-of-block-array? XXX)
         *
         * NOTE: Chain's key range is not relevant as there might be
         *       one-offs within the range that are not deleted.
         *
         * NOTE: Lookups can race delete-duplicate because
         *       delete-duplicate does not lock the parent's core
         *       (they just use the spinlock on the core).  We must
         *       check for races by comparing the DUPLICATED flag before
         *       releasing the spinlock with the flag after locking the
         *       chain.
         */
        if (chain->flags & HAMMER2_CHAIN_DELETED) {
                hammer2_chain_unlock(chain);
                hammer2_chain_drop(chain);
                key_beg = *key_nextp;
                if (key_beg == 0 || key_beg > key_end)
                        return(NULL);
                goto again;
        }
        TIMER(18);

        /*
         * If the chain element is an indirect block it becomes the new
         * parent and we loop on it.  We must maintain our top-down locks
         * to prevent the flusher from interfering (i.e. doing a
         * delete-duplicate and leaving us recursing down a deleted chain).
         *
         * The parent always has to be locked with at least RESOLVE_MAYBE
         * so we can access its data.  It might need a fixup if the caller
         * passed incompatible flags.  Be careful not to cause a deadlock
         * as a data-load requires an exclusive lock.
         *
         * If HAMMER2_LOOKUP_MATCHIND is set and the indirect block's key
         * range is within the requested key range we return the indirect
         * block and do NOT loop.  This is usually only used to acquire
         * freemap nodes.
         */
        if (chain->bref.type == HAMMER2_BREF_TYPE_INDIRECT ||
            chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_NODE) {
                hammer2_chain_unlock(parent);
                hammer2_chain_drop(parent);
                *parentp = parent = chain;
                goto again;
        }
        TIMER(19);
done:
        /*
         * All done, return the chain.
         *
         * If the caller does not want a locked chain, replace the lock with
         * a ref.  Perhaps this can eventually be optimized to not obtain the
         * lock in the first place for situations where the data does not
         * need to be resolved.
         */
        if (chain) {
                if (flags & HAMMER2_LOOKUP_NOLOCK)
                        hammer2_chain_unlock(chain);
        }
        TIMER(20);

        return (chain);
}

/*
 * After having issued a lookup we can iterate all matching keys.
 *
 * If chain is non-NULL we continue the iteration from just after it's index.
 *
 * If chain is NULL we assume the parent was exhausted and continue the
 * iteration at the next parent.
 *
 * If a fatal error occurs (typically an I/O error), a dummy chain is
 * returned with chain->error and error-identifying information set.  This
 * chain will assert if you try to do anything fancy with it.
 *
 * XXX Depending on where the error occurs we should allow continued iteration.
 *
 * parent must be locked on entry and remains locked throughout.  chain's
 * lock status must match flags.  Chain is always at least referenced.
 *
 * WARNING!  The MATCHIND flag does not apply to this function.
 */
hammer2_chain_t *
hammer2_chain_next(hammer2_chain_t **parentp, hammer2_chain_t *chain,
                   hammer2_key_t *key_nextp,
                   hammer2_key_t key_beg, hammer2_key_t key_end,
                   int *cache_indexp, int flags)
{
        hammer2_chain_t *parent;
        int how_maybe;

        /*
         * Calculate locking flags for upward recursion.
         */
        how_maybe = HAMMER2_RESOLVE_MAYBE;
        if (flags & HAMMER2_LOOKUP_SHARED)
                how_maybe |= HAMMER2_RESOLVE_SHARED;

        parent = *parentp;

        /*
         * Calculate the next index and recalculate the parent if necessary.
         */
        if (chain) {
                key_beg = chain->bref.key +
                          ((hammer2_key_t)1 << chain->bref.keybits);
                if ((flags & (HAMMER2_LOOKUP_NOLOCK |
                              HAMMER2_LOOKUP_NOUNLOCK)) == 0) {
                        hammer2_chain_unlock(chain);
                }
                hammer2_chain_drop(chain);

                /*
                 * chain invalid past this point, but we can still do a
                 * pointer comparison w/parent.
                 *
                 * Any scan where the lookup returned degenerate data embedded
                 * in the inode has an invalid index and must terminate.
                 */
                if (chain == parent)
                        return(NULL);
                if (key_beg == 0 || key_beg > key_end)
                        return(NULL);
                chain = NULL;
        } else if (parent->bref.type != HAMMER2_BREF_TYPE_INDIRECT &&
                   parent->bref.type != HAMMER2_BREF_TYPE_FREEMAP_NODE) {
                /*
                 * We reached the end of the iteration.
                 */
                return (NULL);
        } else {
                /*
                 * Continue iteration with next parent unless the current
                 * parent covers the range.
                 */
                key_beg = parent->bref.key +
                          ((hammer2_key_t)1 << parent->bref.keybits);
                if (key_beg == 0 || key_beg > key_end)
                        return (NULL);
                parent = hammer2_chain_getparent(parentp, how_maybe);
        }

        /*
         * And execute
         */
        return (hammer2_chain_lookup(parentp, key_nextp,
                                     key_beg, key_end,
                                     cache_indexp, flags));
}

/*
 * The raw scan function is similar to lookup/next but does not seek to a key.
 * Blockrefs are iterated via first_bref = (parent, NULL) and
 * next_chain = (parent, bref).
 *
 * The passed-in parent must be locked and its data resolved.  The function
 * nominally returns a locked and referenced *chainp != NULL for chains
 * the caller might need to recurse on (and will dipose of any *chainp passed
 * in).  The caller must check the chain->bref.type either way.
 *
 * *chainp is not set for leaf elements.
 *
 * This function takes a pointer to a stack-based bref structure whos
 * contents is updated for each iteration.  The same pointer is returned,
 * or NULL when the iteration is complete.  *firstp must be set to 1 for
 * the first ieration.  This function will set it to 0.
 */
hammer2_blockref_t *
hammer2_chain_scan(hammer2_chain_t *parent, hammer2_chain_t **chainp,
                   hammer2_blockref_t *bref, int *firstp,
                   int *cache_indexp, int flags)
{
        hammer2_dev_t *hmp;
        hammer2_blockref_t *base;
        hammer2_blockref_t *bref_ptr;
        hammer2_key_t key;
        hammer2_key_t next_key;
        hammer2_chain_t *chain = NULL;
        int count = 0;
        int how_always = HAMMER2_RESOLVE_ALWAYS;
        int how_maybe = HAMMER2_RESOLVE_MAYBE;
        int how;
        int generation;
        int maxloops = 300000;

        hmp = parent->hmp;

        /*
         * Scan flags borrowed from lookup.
         */
        if (flags & HAMMER2_LOOKUP_ALWAYS) {
                how_maybe = how_always;
                how = HAMMER2_RESOLVE_ALWAYS;
        } else if (flags & (HAMMER2_LOOKUP_NODATA | HAMMER2_LOOKUP_NOLOCK)) {
                how = HAMMER2_RESOLVE_NEVER;
        } else {
                how = HAMMER2_RESOLVE_MAYBE;
        }
        if (flags & HAMMER2_LOOKUP_SHARED) {
                how_maybe |= HAMMER2_RESOLVE_SHARED;
                how_always |= HAMMER2_RESOLVE_SHARED;
                how |= HAMMER2_RESOLVE_SHARED;
        }

        /*
         * Calculate key to locate first/next element, unlocking the previous
         * element as we go.  Be careful, the key calculation can overflow.
         *
         * (also reset bref to NULL)
         */
        if (*firstp) {
                key = 0;
                *firstp = 0;
        } else {
                key = bref->key + ((hammer2_key_t)1 << bref->keybits);
                if ((chain = *chainp) != NULL) {
                        *chainp = NULL;
                        hammer2_chain_unlock(chain);
                        hammer2_chain_drop(chain);
                        chain = NULL;
                }
                if (key == 0) {
                        bref = NULL;
                        goto done;
                }
        }

again:
        KKASSERT(parent->error == 0);   /* XXX case not handled yet */
        if (--maxloops == 0)
                panic("hammer2_chain_scan: maxloops");
        /*
         * Locate the blockref array.  Currently we do a fully associative
         * search through the array.
         */
        switch(parent->bref.type) {
        case HAMMER2_BREF_TYPE_INODE:
                /*
                 * An inode with embedded data has no sub-chains.
                 *
                 * WARNING! Bulk scan code may pass a static chain marked
                 *          as BREF_TYPE_INODE with a copy of the volume
                 *          root blockset to snapshot the volume.
                 */
                if (parent->data->ipdata.meta.op_flags &
                    HAMMER2_OPFLAG_DIRECTDATA) {
                        bref = NULL;
                        goto done;
                }
                base = &parent->data->ipdata.u.blockset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
        case HAMMER2_BREF_TYPE_INDIRECT:
                /*
                 * Optimize indirect blocks in the INITIAL state to avoid
                 * I/O.
                 */
                if (parent->flags & HAMMER2_CHAIN_INITIAL) {
                        base = NULL;
                } else {
                        if (parent->data == NULL)
                                panic("parent->data is NULL");
                        base = &parent->data->npdata[0];
                }
                count = parent->bytes / sizeof(hammer2_blockref_t);
                break;
        case HAMMER2_BREF_TYPE_VOLUME:
                base = &parent->data->voldata.sroot_blockset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        case HAMMER2_BREF_TYPE_FREEMAP:
                base = &parent->data->blkset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        default:
                panic("hammer2_chain_lookup: unrecognized blockref type: %d",
                      parent->bref.type);
                base = NULL;    /* safety */
                count = 0;      /* safety */
        }

        /*
         * Merged scan to find next candidate.
         *
         * hammer2_base_*() functions require the parent->core.live_* fields
         * to be synchronized.
         *
         * We need to hold the spinlock to access the block array and RB tree
         * and to interlock chain creation.
         */
        if ((parent->flags & HAMMER2_CHAIN_COUNTEDBREFS) == 0)
                hammer2_chain_countbrefs(parent, base, count);

        next_key = 0;
        bref_ptr = NULL;
        hammer2_spin_ex(&parent->core.spin);
        chain = hammer2_combined_find(parent, base, count,
                                      cache_indexp, &next_key,
                                      key, HAMMER2_KEY_MAX,
                                      &bref_ptr);
        generation = parent->core.generation;

        /*
         * Exhausted parent chain, we're done.
         */
        if (bref_ptr == NULL) {
                hammer2_spin_unex(&parent->core.spin);
                KKASSERT(chain == NULL);
                bref = NULL;
                goto done;
        }

        /*
         * Copy into the supplied stack-based blockref.
         */
        *bref = *bref_ptr;

        /*
         * Selected from blockref or in-memory chain.
         */
        if (chain == NULL) {
                switch(bref->type) {
                case HAMMER2_BREF_TYPE_INODE:
                case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                case HAMMER2_BREF_TYPE_INDIRECT:
                case HAMMER2_BREF_TYPE_VOLUME:
                case HAMMER2_BREF_TYPE_FREEMAP:
                        /*
                         * Recursion, always get the chain
                         */
                        hammer2_spin_unex(&parent->core.spin);
                        chain = hammer2_chain_get(parent, generation, bref);
                        if (chain == NULL) {
                                kprintf("retry scan parent %p keys %016jx\n",
                                        parent, key);
                                goto again;
                        }
                        if (bcmp(bref, bref_ptr, sizeof(*bref))) {
                                hammer2_chain_drop(chain);
                                chain = NULL;
                                goto again;
                        }
                        break;
                default:
                        /*
                         * No recursion, do not waste time instantiating
                         * a chain, just iterate using the bref.
                         */
                        hammer2_spin_unex(&parent->core.spin);
                        break;
                }
        } else {
                /*
                 * Recursion or not we need the chain in order to supply
                 * the bref.
                 */
                hammer2_chain_ref(chain);
                hammer2_spin_unex(&parent->core.spin);
        }

        /*
         * chain is referenced but not locked.  We must lock the chain
         * to obtain definitive DUPLICATED/DELETED state
         */
        if (chain)
                hammer2_chain_lock(chain, how);

        /*
         * Skip deleted chains (XXX cache 'i' end-of-block-array? XXX)
         *
         * NOTE: chain's key range is not relevant as there might be
         *       one-offs within the range that are not deleted.
         *
         * NOTE: XXX this could create problems with scans used in
         *       situations other than mount-time recovery.
         *
         * NOTE: Lookups can race delete-duplicate because
         *       delete-duplicate does not lock the parent's core
         *       (they just use the spinlock on the core).  We must
         *       check for races by comparing the DUPLICATED flag before
         *       releasing the spinlock with the flag after locking the
         *       chain.
         */
        if (chain && (chain->flags & HAMMER2_CHAIN_DELETED)) {
                hammer2_chain_unlock(chain);
                hammer2_chain_drop(chain);
                chain = NULL;

                key = next_key;
                if (key == 0) {
                        bref = NULL;
                        goto done;
                }
                goto again;
        }

done:
        /*
         * All done, return the bref or NULL, supply chain if necessary.
         */
        if (chain)
                *chainp = chain;
        return (bref);
}

/*
 * Create and return a new hammer2 system memory structure of the specified
 * key, type and size and insert it under (*parentp).  This is a full
 * insertion, based on the supplied key/keybits, and may involve creating
 * indirect blocks and moving other chains around via delete/duplicate.
 *
 * THE CALLER MUST HAVE ALREADY PROPERLY SEEKED (*parentp) TO THE INSERTION
 * POINT SANS ANY REQUIRED INDIRECT BLOCK CREATIONS DUE TO THE ARRAY BEING
 * FULL.  This typically means that the caller is creating the chain after
 * doing a hammer2_chain_lookup().
 *
 * (*parentp) must be exclusive locked and may be replaced on return
 * depending on how much work the function had to do.
 *
 * (*parentp) must not be errored or this function will assert.
 *
 * (*chainp) usually starts out NULL and returns the newly created chain,
 * but if the caller desires the caller may allocate a disconnected chain
 * and pass it in instead.
 *
 * This function should NOT be used to insert INDIRECT blocks.  It is
 * typically used to create/insert inodes and data blocks.
 *
 * Caller must pass-in an exclusively locked parent the new chain is to
 * be inserted under, and optionally pass-in a disconnected, exclusively
 * locked chain to insert (else we create a new chain).  The function will
 * adjust (*parentp) as necessary, create or connect the chain, and
 * return an exclusively locked chain in *chainp.
 *
 * When creating a PFSROOT inode under the super-root, pmp is typically NULL
 * and will be reassigned.
 */
int
hammer2_chain_create(hammer2_chain_t **parentp,
                     hammer2_chain_t **chainp, hammer2_pfs_t *pmp,
                     hammer2_key_t key, int keybits, int type, size_t bytes,
                     hammer2_tid_t mtid, hammer2_off_t dedup_off, int flags)
{
        hammer2_dev_t *hmp;
        hammer2_chain_t *chain;
        hammer2_chain_t *parent;
        hammer2_blockref_t *base;
        hammer2_blockref_t dummy;
        int allocated = 0;
        int error = 0;
        int count;
        int maxloops = 300000;

        /*
         * Topology may be crossing a PFS boundary.
         */
        parent = *parentp;
        KKASSERT(hammer2_mtx_owned(&parent->lock));
        KKASSERT(parent->error == 0);
        hmp = parent->hmp;
        chain = *chainp;

        if (chain == NULL) {
                /*
                 * First allocate media space and construct the dummy bref,
                 * then allocate the in-memory chain structure.  Set the
                 * INITIAL flag for fresh chains which do not have embedded
                 * data.
                 *
                 * XXX for now set the check mode of the child based on
                 *     the parent or, if the parent is an inode, the
                 *     specification in the inode.
                 */
                bzero(&dummy, sizeof(dummy));
                dummy.type = type;
                dummy.key = key;
                dummy.keybits = keybits;
                dummy.data_off = hammer2_getradix(bytes);
                dummy.methods = parent->bref.methods;
                if (parent->bref.type == HAMMER2_BREF_TYPE_INODE &&
                    parent->data) {
                        dummy.methods &= ~HAMMER2_ENC_CHECK(-1);
                        dummy.methods |= HAMMER2_ENC_CHECK(
                                          parent->data->ipdata.meta.check_algo);
                }

                chain = hammer2_chain_alloc(hmp, pmp, &dummy);

                /*
                 * Lock the chain manually, chain_lock will load the chain
                 * which we do NOT want to do.  (note: chain->refs is set
                 * to 1 by chain_alloc() for us, but lockcnt is not).
                 */
                chain->lockcnt = 1;
                hammer2_mtx_ex(&chain->lock);
                allocated = 1;
                ++curthread->td_tracker;

                /*
                 * Set INITIAL to optimize I/O.  The flag will generally be
                 * processed when we call hammer2_chain_modify().
                 *
                 * Recalculate bytes to reflect the actual media block
                 * allocation.
                 */
                bytes = (hammer2_off_t)1 <<
                        (int)(chain->bref.data_off & HAMMER2_OFF_MASK_RADIX);
                chain->bytes = bytes;

                switch(type) {
                case HAMMER2_BREF_TYPE_VOLUME:
                case HAMMER2_BREF_TYPE_FREEMAP:
                        panic("hammer2_chain_create: called with volume type");
                        break;
                case HAMMER2_BREF_TYPE_INDIRECT:
                        panic("hammer2_chain_create: cannot be used to"
                              "create indirect block");
                        break;
                case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                        panic("hammer2_chain_create: cannot be used to"
                              "create freemap root or node");
                        break;
                case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
                        KKASSERT(bytes == sizeof(chain->data->bmdata));
                        /* fall through */
                case HAMMER2_BREF_TYPE_INODE:
                case HAMMER2_BREF_TYPE_DATA:
                default:
                        /*
                         * leave chain->data NULL, set INITIAL
                         */
                        KKASSERT(chain->data == NULL);
                        atomic_set_int(&chain->flags, HAMMER2_CHAIN_INITIAL);
                        break;
                }
        } else {
                /*
                 * We are reattaching a previously deleted chain, possibly
                 * under a new parent and possibly with a new key/keybits.
                 * The chain does not have to be in a modified state.  The
                 * UPDATE flag will be set later on in this routine.
                 *
                 * Do NOT mess with the current state of the INITIAL flag.
                 */
                chain->bref.key = key;
                chain->bref.keybits = keybits;
                if (chain->flags & HAMMER2_CHAIN_DELETED)
                        atomic_clear_int(&chain->flags, HAMMER2_CHAIN_DELETED);
                KKASSERT(chain->parent == NULL);
        }
        if (flags & HAMMER2_INSERT_PFSROOT)
                chain->bref.flags |= HAMMER2_BREF_FLAG_PFSROOT;
        else
                chain->bref.flags &= ~HAMMER2_BREF_FLAG_PFSROOT;

        /*
         * Calculate how many entries we have in the blockref array and
         * determine if an indirect block is required.
         */
again:
        if (--maxloops == 0)
                panic("hammer2_chain_create: maxloops");

        switch(parent->bref.type) {
        case HAMMER2_BREF_TYPE_INODE:
                if ((parent->data->ipdata.meta.op_flags &
                     HAMMER2_OPFLAG_DIRECTDATA) != 0) {
                        kprintf("hammer2: parent set for direct-data! "
                                "pkey=%016jx ckey=%016jx\n",
                                parent->bref.key,
                                chain->bref.key);
                }
                KKASSERT((parent->data->ipdata.meta.op_flags &
                          HAMMER2_OPFLAG_DIRECTDATA) == 0);
                KKASSERT(parent->data != NULL);
                base = &parent->data->ipdata.u.blockset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        case HAMMER2_BREF_TYPE_INDIRECT:
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                if (parent->flags & HAMMER2_CHAIN_INITIAL)
                        base = NULL;
                else
                        base = &parent->data->npdata[0];
                count = parent->bytes / sizeof(hammer2_blockref_t);
                break;
        case HAMMER2_BREF_TYPE_VOLUME:
                KKASSERT(parent->data != NULL);
                base = &parent->data->voldata.sroot_blockset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        case HAMMER2_BREF_TYPE_FREEMAP:
                KKASSERT(parent->data != NULL);
                base = &parent->data->blkset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        default:
                panic("hammer2_chain_create: unrecognized blockref type: %d",
                      parent->bref.type);
                base = NULL;
                count = 0;
                break;
        }

        /*
         * Make sure we've counted the brefs
         */
        if ((parent->flags & HAMMER2_CHAIN_COUNTEDBREFS) == 0)
                hammer2_chain_countbrefs(parent, base, count);

        KKASSERT(parent->core.live_count >= 0 &&
                 parent->core.live_count <= count);

        /*
         * If no free blockref could be found we must create an indirect
         * block and move a number of blockrefs into it.  With the parent
         * locked we can safely lock each child in order to delete+duplicate
         * it without causing a deadlock.
         *
         * This may return the new indirect block or the old parent depending
         * on where the key falls.  NULL is returned on error.
         */
        if (parent->core.live_count == count) {
                hammer2_chain_t *nparent;

                nparent = hammer2_chain_create_indirect(parent, key, keybits,
                                                        mtid, type, &error);
                if (nparent == NULL) {
                        if (allocated)
                                hammer2_chain_drop(chain);
                        chain = NULL;
                        goto done;
                }
                if (parent != nparent) {
                        hammer2_chain_unlock(parent);
                        hammer2_chain_drop(parent);
                        parent = *parentp = nparent;
                }
                goto again;
        }

        /*
         * Link the chain into its parent.
         */
        if (chain->parent != NULL)
                panic("hammer2: hammer2_chain_create: chain already connected");
        KKASSERT(chain->parent == NULL);
        hammer2_chain_insert(parent, chain,
                             HAMMER2_CHAIN_INSERT_SPIN |
                             HAMMER2_CHAIN_INSERT_LIVE,
                             0);

        if (allocated) {
                /*
                 * Mark the newly created chain modified.  This will cause
                 * UPDATE to be set and process the INITIAL flag.
                 *
                 * Device buffers are not instantiated for DATA elements
                 * as these are handled by logical buffers.
                 *
                 * Indirect and freemap node indirect blocks are handled
                 * by hammer2_chain_create_indirect() and not by this
                 * function.
                 *
                 * Data for all other bref types is expected to be
                 * instantiated (INODE, LEAF).
                 */
                switch(chain->bref.type) {
                case HAMMER2_BREF_TYPE_DATA:
                case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
                case HAMMER2_BREF_TYPE_INODE:
                        hammer2_chain_modify(chain, mtid, dedup_off,
                                             HAMMER2_MODIFY_OPTDATA);
                        break;
                default:
                        /*
                         * Remaining types are not supported by this function.
                         * In particular, INDIRECT and LEAF_NODE types are
                         * handled by create_indirect().
                         */
                        panic("hammer2_chain_create: bad type: %d",
                              chain->bref.type);
                        /* NOT REACHED */
                        break;
                }
        } else {
                /*
                 * When reconnecting a chain we must set UPDATE and
                 * setflush so the flush recognizes that it must update
                 * the bref in the parent.
                 */
                if ((chain->flags & HAMMER2_CHAIN_UPDATE) == 0)
                        atomic_set_int(&chain->flags, HAMMER2_CHAIN_UPDATE);
        }

        /*
         * We must setflush(parent) to ensure that it recurses through to
         * chain.  setflush(chain) might not work because ONFLUSH is possibly
         * already set in the chain (so it won't recurse up to set it in the
         * parent).
         */
        hammer2_chain_setflush(parent);

done:
        *chainp = chain;

        return (error);
}

/*
 * Move the chain from its old parent to a new parent.  The chain must have
 * already been deleted or already disconnected (or never associated) with
 * a parent.  The chain is reassociated with the new parent and the deleted
 * flag will be cleared (no longer deleted).  The chain's modification state
 * is not altered.
 *
 * THE CALLER MUST HAVE ALREADY PROPERLY SEEKED (parent) TO THE INSERTION
 * POINT SANS ANY REQUIRED INDIRECT BLOCK CREATIONS DUE TO THE ARRAY BEING
 * FULL.  This typically means that the caller is creating the chain after
 * doing a hammer2_chain_lookup().
 *
 * A non-NULL bref is typically passed when key and keybits must be overridden.
 * Note that hammer2_cluster_duplicate() *ONLY* uses the key and keybits fields
 * from a passed-in bref and uses the old chain's bref for everything else.
 *
 * Neither (parent) or (chain) can be errored.
 *
 * If (parent) is non-NULL then the new duplicated chain is inserted under
 * the parent.
 *
 * If (parent) is NULL then the newly duplicated chain is not inserted
 * anywhere, similar to if it had just been chain_alloc()'d (suitable for
 * passing into hammer2_chain_create() after this function returns).
 *
 * WARNING! This function calls create which means it can insert indirect
 *          blocks.  This can cause other unrelated chains in the parent to
 *          be moved to a newly inserted indirect block in addition to the
 *          specific chain.
 */
void
hammer2_chain_rename(hammer2_blockref_t *bref,
                     hammer2_chain_t **parentp, hammer2_chain_t *chain,
                     hammer2_tid_t mtid, int flags)
{
        hammer2_dev_t *hmp;
        hammer2_chain_t *parent;
        size_t bytes;

        /*
         * WARNING!  We should never resolve DATA to device buffers
         *           (XXX allow it if the caller did?), and since
         *           we currently do not have the logical buffer cache
         *           buffer in-hand to fix its cached physical offset
         *           we also force the modify code to not COW it. XXX
         */
        hmp = chain->hmp;
        KKASSERT(chain->parent == NULL);
        KKASSERT(chain->error == 0);

        /*
         * Now create a duplicate of the chain structure, associating
         * it with the same core, making it the same size, pointing it
         * to the same bref (the same media block).
         */
        if (bref == NULL)
                bref = &chain->bref;
        bytes = (hammer2_off_t)1 <<
                (int)(bref->data_off & HAMMER2_OFF_MASK_RADIX);

        /*
         * If parent is not NULL the duplicated chain will be entered under
         * the parent and the UPDATE bit set to tell flush to update
         * the blockref.
         *
         * We must setflush(parent) to ensure that it recurses through to
         * chain.  setflush(chain) might not work because ONFLUSH is possibly
         * already set in the chain (so it won't recurse up to set it in the
         * parent).
         *
         * Having both chains locked is extremely important for atomicy.
         */
        if (parentp && (parent = *parentp) != NULL) {
                KKASSERT(hammer2_mtx_owned(&parent->lock));
                KKASSERT(parent->refs > 0);
                KKASSERT(parent->error == 0);

                hammer2_chain_create(parentp, &chain, chain->pmp,
                                     bref->key, bref->keybits, bref->type,
                                     chain->bytes, mtid, 0, flags);
                KKASSERT(chain->flags & HAMMER2_CHAIN_UPDATE);
                hammer2_chain_setflush(*parentp);
        }
}

/*
 * Helper function for deleting chains.
 *
 * The chain is removed from the live view (the RBTREE) as well as the parent's
 * blockmap.  Both chain and its parent must be locked.
 *
 * parent may not be errored.  chain can be errored.
 */
static void
_hammer2_chain_delete_helper(hammer2_chain_t *parent, hammer2_chain_t *chain,
                             hammer2_tid_t mtid, int flags)
{
        hammer2_dev_t *hmp;

        KKASSERT((chain->flags & (HAMMER2_CHAIN_DELETED |
                                  HAMMER2_CHAIN_FICTITIOUS)) == 0);
        KKASSERT(chain->parent == parent);
        hmp = chain->hmp;

        if (chain->flags & HAMMER2_CHAIN_BMAPPED) {
                /*
                 * Chain is blockmapped, so there must be a parent.
                 * Atomically remove the chain from the parent and remove
                 * the blockmap entry.  The parent must be set modified
                 * to remove the blockmap entry.
                 */
                hammer2_blockref_t *base;
                int count;

                KKASSERT(parent != NULL);
                KKASSERT(parent->error == 0);
                KKASSERT((parent->flags & HAMMER2_CHAIN_INITIAL) == 0);
                hammer2_chain_modify(parent, mtid, 0, HAMMER2_MODIFY_OPTDATA);

                /*
                 * Calculate blockmap pointer
                 */
                KKASSERT(chain->flags & HAMMER2_CHAIN_ONRBTREE);
                hammer2_spin_ex(&parent->core.spin);

                atomic_set_int(&chain->flags, HAMMER2_CHAIN_DELETED);
                atomic_add_int(&parent->core.live_count, -1);
                ++parent->core.generation;
                RB_REMOVE(hammer2_chain_tree, &parent->core.rbtree, chain);
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_ONRBTREE);
                --parent->core.chain_count;
                chain->parent = NULL;

                switch(parent->bref.type) {
                case HAMMER2_BREF_TYPE_INODE:
                        /*
                         * Access the inode's block array.  However, there
                         * is no block array if the inode is flagged
                         * DIRECTDATA.  The DIRECTDATA case typicaly only
                         * occurs when a hardlink has been shifted up the
                         * tree and the original inode gets replaced with
                         * an OBJTYPE_HARDLINK placeholding inode.
                         */
                        if (parent->data &&
                            (parent->data->ipdata.meta.op_flags &
                             HAMMER2_OPFLAG_DIRECTDATA) == 0) {
                                base =
                                   &parent->data->ipdata.u.blockset.blockref[0];
                        } else {
                                base = NULL;
                        }
                        count = HAMMER2_SET_COUNT;
                        break;
                case HAMMER2_BREF_TYPE_INDIRECT:
                case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                        if (parent->data)
                                base = &parent->data->npdata[0];
                        else
                                base = NULL;
                        count = parent->bytes / sizeof(hammer2_blockref_t);
                        break;
                case HAMMER2_BREF_TYPE_VOLUME:
                        base = &parent->data->voldata.
                                        sroot_blockset.blockref[0];
                        count = HAMMER2_SET_COUNT;
                        break;
                case HAMMER2_BREF_TYPE_FREEMAP:
                        base = &parent->data->blkset.blockref[0];
                        count = HAMMER2_SET_COUNT;
                        break;
                default:
                        base = NULL;
                        count = 0;
                        panic("hammer2_flush_pass2: "
                              "unrecognized blockref type: %d",
                              parent->bref.type);
                }

                /*
                 * delete blockmapped chain from its parent.
                 *
                 * The parent is not affected by any statistics in chain
                 * which are pending synchronization.  That is, there is
                 * nothing to undo in the parent since they have not yet
                 * been incorporated into the parent.
                 *
                 * The parent is affected by statistics stored in inodes.
                 * Those have already been synchronized, so they must be
                 * undone.  XXX split update possible w/delete in middle?
                 */
                if (base) {
                        int cache_index = -1;
                        hammer2_base_delete(parent, base, count,
                                            &cache_index, chain);
                }
                hammer2_spin_unex(&parent->core.spin);
        } else if (chain->flags & HAMMER2_CHAIN_ONRBTREE) {
                /*
                 * Chain is not blockmapped but a parent is present.
                 * Atomically remove the chain from the parent.  There is
                 * no blockmap entry to remove.
                 *
                 * Because chain was associated with a parent but not
                 * synchronized, the chain's *_count_up fields contain
                 * inode adjustment statistics which must be undone.
                 */
                hammer2_spin_ex(&parent->core.spin);
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_DELETED);
                atomic_add_int(&parent->core.live_count, -1);
                ++parent->core.generation;
                RB_REMOVE(hammer2_chain_tree, &parent->core.rbtree, chain);
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_ONRBTREE);
                --parent->core.chain_count;
                chain->parent = NULL;
                hammer2_spin_unex(&parent->core.spin);
        } else {
                /*
                 * Chain is not blockmapped and has no parent.  This
                 * is a degenerate case.
                 */
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_DELETED);
        }
}

/*
 * Create an indirect block that covers one or more of the elements in the
 * current parent.  Either returns the existing parent with no locking or
 * ref changes or returns the new indirect block locked and referenced
 * and leaving the original parent lock/ref intact as well.
 *
 * If an error occurs, NULL is returned and *errorp is set to the error.
 *
 * The returned chain depends on where the specified key falls.
 *
 * The key/keybits for the indirect mode only needs to follow three rules:
 *
 * (1) That all elements underneath it fit within its key space and
 *
 * (2) That all elements outside it are outside its key space.
 *
 * (3) When creating the new indirect block any elements in the current
 *     parent that fit within the new indirect block's keyspace must be
 *     moved into the new indirect block.
 *
 * (4) The keyspace chosen for the inserted indirect block CAN cover a wider
 *     keyspace the the current parent, but lookup/iteration rules will
 *     ensure (and must ensure) that rule (2) for all parents leading up
 *     to the nearest inode or the root volume header is adhered to.  This
 *     is accomplished by always recursing through matching keyspaces in
 *     the hammer2_chain_lookup() and hammer2_chain_next() API.
 *
 * The current implementation calculates the current worst-case keyspace by
 * iterating the current parent and then divides it into two halves, choosing
 * whichever half has the most elements (not necessarily the half containing
 * the requested key).
 *
 * We can also opt to use the half with the least number of elements.  This
 * causes lower-numbered keys (aka logical file offsets) to recurse through
 * fewer indirect blocks and higher-numbered keys to recurse through more.
 * This also has the risk of not moving enough elements to the new indirect
 * block and being forced to create several indirect blocks before the element
 * can be inserted.
 *
 * Must be called with an exclusively locked parent.
 */
static int hammer2_chain_indkey_freemap(hammer2_chain_t *parent,
                                hammer2_key_t *keyp, int keybits,
                                hammer2_blockref_t *base, int count);
static int hammer2_chain_indkey_normal(hammer2_chain_t *parent,
                                hammer2_key_t *keyp, int keybits,
                                hammer2_blockref_t *base, int count);
static
hammer2_chain_t *
hammer2_chain_create_indirect(hammer2_chain_t *parent,
                              hammer2_key_t create_key, int create_bits,
                              hammer2_tid_t mtid, int for_type, int *errorp)
{
        hammer2_dev_t *hmp;
        hammer2_blockref_t *base;
        hammer2_blockref_t *bref;
        hammer2_blockref_t bcopy;
        hammer2_chain_t *chain;
        hammer2_chain_t *ichain;
        hammer2_chain_t dummy;
        hammer2_key_t key = create_key;
        hammer2_key_t key_beg;
        hammer2_key_t key_end;
        hammer2_key_t key_next;
        int keybits = create_bits;
        int count;
        int nbytes;
        int cache_index;
        int loops;
        int reason;
        int generation;
        int maxloops = 300000;

        /*
         * Calculate the base blockref pointer or NULL if the chain
         * is known to be empty.  We need to calculate the array count
         * for RB lookups either way.
         */
        hmp = parent->hmp;
        *errorp = 0;
        KKASSERT(hammer2_mtx_owned(&parent->lock));

        /*hammer2_chain_modify(&parent, HAMMER2_MODIFY_OPTDATA);*/
        base = hammer2_chain_base_and_count(parent, &count);

        /*
         * dummy used in later chain allocation (no longer used for lookups).
         */
        bzero(&dummy, sizeof(dummy));

        /*
         * When creating an indirect block for a freemap node or leaf
         * the key/keybits must be fitted to static radix levels because
         * particular radix levels use particular reserved blocks in the
         * related zone.
         *
         * This routine calculates the key/radix of the indirect block
         * we need to create, and whether it is on the high-side or the
         * low-side.
         */
        if (for_type == HAMMER2_BREF_TYPE_FREEMAP_NODE ||
            for_type == HAMMER2_BREF_TYPE_FREEMAP_LEAF) {
                keybits = hammer2_chain_indkey_freemap(parent, &key, keybits,
                                                       base, count);
        } else {
                keybits = hammer2_chain_indkey_normal(parent, &key, keybits,
                                                      base, count);
        }

        /*
         * Normalize the key for the radix being represented, keeping the
         * high bits and throwing away the low bits.
         */
        key &= ~(((hammer2_key_t)1 << keybits) - 1);

        /*
         * How big should our new indirect block be?  It has to be at least
         * as large as its parent.
         *
         * The freemap uses a specific indirect block size.
         *
         * The first indirect block level down from an inode typically
         * uses LBUFSIZE (16384), else it uses PBUFSIZE (65536).
         */
        if (for_type == HAMMER2_BREF_TYPE_FREEMAP_NODE ||
            for_type == HAMMER2_BREF_TYPE_FREEMAP_LEAF) {
                nbytes = HAMMER2_FREEMAP_LEVELN_PSIZE;
        } else if (parent->bref.type == HAMMER2_BREF_TYPE_INODE) {
                nbytes = HAMMER2_IND_BYTES_MIN;
        } else {
                nbytes = HAMMER2_IND_BYTES_MAX;
        }
        if (nbytes < count * sizeof(hammer2_blockref_t)) {
                KKASSERT(for_type != HAMMER2_BREF_TYPE_FREEMAP_NODE &&
                         for_type != HAMMER2_BREF_TYPE_FREEMAP_LEAF);
                nbytes = count * sizeof(hammer2_blockref_t);
        }

        /*
         * Ok, create our new indirect block
         */
        if (for_type == HAMMER2_BREF_TYPE_FREEMAP_NODE ||
            for_type == HAMMER2_BREF_TYPE_FREEMAP_LEAF) {
                dummy.bref.type = HAMMER2_BREF_TYPE_FREEMAP_NODE;
        } else {
                dummy.bref.type = HAMMER2_BREF_TYPE_INDIRECT;
        }
        dummy.bref.key = key;
        dummy.bref.keybits = keybits;
        dummy.bref.data_off = hammer2_getradix(nbytes);
        dummy.bref.methods = parent->bref.methods;

        ichain = hammer2_chain_alloc(hmp, parent->pmp, &dummy.bref);
        atomic_set_int(&ichain->flags, HAMMER2_CHAIN_INITIAL);
        hammer2_chain_lock(ichain, HAMMER2_RESOLVE_MAYBE);
        /* ichain has one ref at this point */

        /*
         * We have to mark it modified to allocate its block, but use
         * OPTDATA to allow it to remain in the INITIAL state.  Otherwise
         * it won't be acted upon by the flush code.
         */
        hammer2_chain_modify(ichain, mtid, 0, HAMMER2_MODIFY_OPTDATA);

        /*
         * Iterate the original parent and move the matching brefs into
         * the new indirect block.
         *
         * XXX handle flushes.
         */
        key_beg = 0;
        key_end = HAMMER2_KEY_MAX;
        cache_index = 0;
        hammer2_spin_ex(&parent->core.spin);
        loops = 0;
        reason = 0;

        for (;;) {
                /*
                 * Parent may have been modified, relocating its block array.
                 * Reload the base pointer.
                 */
                base = hammer2_chain_base_and_count(parent, &count);

                if (++loops > 100000) {
                    hammer2_spin_unex(&parent->core.spin);
                    panic("excessive loops r=%d p=%p base/count %p:%d %016jx\n",
                          reason, parent, base, count, key_next);
                }

                /*
                 * NOTE: spinlock stays intact, returned chain (if not NULL)
                 *       is not referenced or locked which means that we
                 *       cannot safely check its flagged / deletion status
                 *       until we lock it.
                 */
                chain = hammer2_combined_find(parent, base, count,
                                              &cache_index, &key_next,
                                              key_beg, key_end,
                                              &bref);
                generation = parent->core.generation;
                if (bref == NULL)
                        break;
                key_next = bref->key + ((hammer2_key_t)1 << bref->keybits);

                /*
                 * Skip keys that are not within the key/radix of the new
                 * indirect block.  They stay in the parent.
                 */
                if ((~(((hammer2_key_t)1 << keybits) - 1) &
                    (key ^ bref->key)) != 0) {
                        goto next_key_spinlocked;
                }

                /*
                 * Load the new indirect block by acquiring the related
                 * chains (potentially from media as it might not be
                 * in-memory).  Then move it to the new parent (ichain)
                 * via DELETE-DUPLICATE.
                 *
                 * chain is referenced but not locked.  We must lock the
                 * chain to obtain definitive DUPLICATED/DELETED state
                 */
                if (chain) {
                        /*
                         * Use chain already present in the RBTREE
                         */
                        hammer2_chain_ref(chain);
                        hammer2_spin_unex(&parent->core.spin);
                        hammer2_chain_lock(chain, HAMMER2_RESOLVE_NEVER);
                } else {
                        /*
                         * Get chain for blockref element.  _get returns NULL
                         * on insertion race.
                         */
                        bcopy = *bref;
                        hammer2_spin_unex(&parent->core.spin);
                        chain = hammer2_chain_get(parent, generation, &bcopy);
                        if (chain == NULL) {
                                reason = 1;
                                hammer2_spin_ex(&parent->core.spin);
                                continue;
                        }
                        if (bcmp(&bcopy, bref, sizeof(bcopy))) {
                                kprintf("REASON 2\n");
                                reason = 2;
                                hammer2_chain_drop(chain);
                                hammer2_spin_ex(&parent->core.spin);
                                continue;
                        }
                        hammer2_chain_lock(chain, HAMMER2_RESOLVE_NEVER);
                }

                /*
                 * This is always live so if the chain has been deleted
                 * we raced someone and we have to retry.
                 *
                 * NOTE: Lookups can race delete-duplicate because
                 *       delete-duplicate does not lock the parent's core
                 *       (they just use the spinlock on the core).  We must
                 *       check for races by comparing the DUPLICATED flag before
                 *       releasing the spinlock with the flag after locking the
                 *       chain.
                 *
                 *       (note reversed logic for this one)
                 */
                if (chain->flags & HAMMER2_CHAIN_DELETED) {
                        hammer2_chain_unlock(chain);
                        hammer2_chain_drop(chain);
                        goto next_key;
                }

                /*
                 * Shift the chain to the indirect block.
                 *
                 * WARNING! No reason for us to load chain data, pass NOSTATS
                 *          to prevent delete/insert from trying to access
                 *          inode stats (and thus asserting if there is no
                 *          chain->data loaded).
                 *
                 * WARNING! The (parent, chain) deletion may modify the parent
                 *          and invalidate the base pointer.
                 */
                hammer2_chain_delete(parent, chain, mtid, 0);
                hammer2_chain_rename(NULL, &ichain, chain, mtid, 0);
                hammer2_chain_unlock(chain);
                hammer2_chain_drop(chain);
                KKASSERT(parent->refs > 0);
                chain = NULL;
                base = NULL;    /* safety */
next_key:
                hammer2_spin_ex(&parent->core.spin);
next_key_spinlocked:
                if (--maxloops == 0)
                        panic("hammer2_chain_create_indirect: maxloops");
                reason = 4;
                if (key_next == 0 || key_next > key_end)
                        break;
                key_beg = key_next;
                /* loop */
        }
        hammer2_spin_unex(&parent->core.spin);

        /*
         * Insert the new indirect block into the parent now that we've
         * cleared out some entries in the parent.  We calculated a good
         * insertion index in the loop above (ichain->index).
         *
         * We don't have to set UPDATE here because we mark ichain
         * modified down below (so the normal modified -> flush -> set-moved
         * sequence applies).
         *
         * The insertion shouldn't race as this is a completely new block
         * and the parent is locked.
         */
        base = NULL;    /* safety, parent modify may change address */
        KKASSERT((ichain->flags & HAMMER2_CHAIN_ONRBTREE) == 0);
        hammer2_chain_insert(parent, ichain,
                             HAMMER2_CHAIN_INSERT_SPIN |
                             HAMMER2_CHAIN_INSERT_LIVE,
                             0);

        /*
         * Make sure flushes propogate after our manual insertion.
         */
        hammer2_chain_setflush(ichain);
        hammer2_chain_setflush(parent);

        /*
         * Figure out what to return.
         */
        if (~(((hammer2_key_t)1 << keybits) - 1) &
                   (create_key ^ key)) {
                /*
                 * Key being created is outside the key range,
                 * return the original parent.
                 */
                hammer2_chain_unlock(ichain);
                hammer2_chain_drop(ichain);
        } else {
                /*
                 * Otherwise its in the range, return the new parent.
                 * (leave both the new and old parent locked).
                 */
                parent = ichain;
        }

        return(parent);
}

/*
 * Calculate the keybits and highside/lowside of the freemap node the
 * caller is creating.
 *
 * This routine will specify the next higher-level freemap key/radix
 * representing the lowest-ordered set.  By doing so, eventually all
 * low-ordered sets will be moved one level down.
 *
 * We have to be careful here because the freemap reserves a limited
 * number of blocks for a limited number of levels.  So we can't just
 * push indiscriminately.
 */
int
hammer2_chain_indkey_freemap(hammer2_chain_t *parent, hammer2_key_t *keyp,
                             int keybits, hammer2_blockref_t *base, int count)
{
        hammer2_chain_t *chain;
        hammer2_blockref_t *bref;
        hammer2_key_t key;
        hammer2_key_t key_beg;
        hammer2_key_t key_end;
        hammer2_key_t key_next;
        int cache_index;
        int locount;
        int hicount;
        int maxloops = 300000;

        key = *keyp;
        locount = 0;
        hicount = 0;
        keybits = 64;

        /*
         * Calculate the range of keys in the array being careful to skip
         * slots which are overridden with a deletion.
         */
        key_beg = 0;
        key_end = HAMMER2_KEY_MAX;
        cache_index = 0;
        hammer2_spin_ex(&parent->core.spin);

        for (;;) {
                if (--maxloops == 0) {
                        panic("indkey_freemap shit %p %p:%d\n",
                              parent, base, count);
                }
                chain = hammer2_combined_find(parent, base, count,
                                              &cache_index, &key_next,
                                              key_beg, key_end,
                                              &bref);

                /*
                 * Exhausted search
                 */
                if (bref == NULL)
                        break;

                /*
                 * Skip deleted chains.
                 */
                if (chain && (chain->flags & HAMMER2_CHAIN_DELETED)) {
                        if (key_next == 0 || key_next > key_end)
                                break;
                        key_beg = key_next;
                        continue;
                }

                /*
                 * Use the full live (not deleted) element for the scan
                 * iteration.  HAMMER2 does not allow partial replacements.
                 *
                 * XXX should be built into hammer2_combined_find().
                 */
                key_next = bref->key + ((hammer2_key_t)1 << bref->keybits);

                if (keybits > bref->keybits) {
                        key = bref->key;
                        keybits = bref->keybits;
                } else if (keybits == bref->keybits && bref->key < key) {
                        key = bref->key;
                }
                if (key_next == 0)
                        break;
                key_beg = key_next;
        }
        hammer2_spin_unex(&parent->core.spin);

        /*
         * Return the keybits for a higher-level FREEMAP_NODE covering
         * this node.
         */
        switch(keybits) {
        case HAMMER2_FREEMAP_LEVEL0_RADIX:
                keybits = HAMMER2_FREEMAP_LEVEL1_RADIX;
                break;
        case HAMMER2_FREEMAP_LEVEL1_RADIX:
                keybits = HAMMER2_FREEMAP_LEVEL2_RADIX;
                break;
        case HAMMER2_FREEMAP_LEVEL2_RADIX:
                keybits = HAMMER2_FREEMAP_LEVEL3_RADIX;
                break;
        case HAMMER2_FREEMAP_LEVEL3_RADIX:
                keybits = HAMMER2_FREEMAP_LEVEL4_RADIX;
                break;
        case HAMMER2_FREEMAP_LEVEL4_RADIX:
                keybits = HAMMER2_FREEMAP_LEVEL5_RADIX;
                break;
        case HAMMER2_FREEMAP_LEVEL5_RADIX:
                panic("hammer2_chain_indkey_freemap: level too high");
                break;
        default:
                panic("hammer2_chain_indkey_freemap: bad radix");
                break;
        }
        *keyp = key;

        return (keybits);
}

/*
 * Calculate the keybits and highside/lowside of the indirect block the
 * caller is creating.
 */
static int
hammer2_chain_indkey_normal(hammer2_chain_t *parent, hammer2_key_t *keyp,
                            int keybits, hammer2_blockref_t *base, int count)
{
        hammer2_blockref_t *bref;
        hammer2_chain_t *chain;
        hammer2_key_t key_beg;
        hammer2_key_t key_end;
        hammer2_key_t key_next;
        hammer2_key_t key;
        int nkeybits;
        int locount;
        int hicount;
        int cache_index;
        int maxloops = 300000;

        key = *keyp;
        locount = 0;
        hicount = 0;

        /*
         * Calculate the range of keys in the array being careful to skip
         * slots which are overridden with a deletion.  Once the scan
         * completes we will cut the key range in half and shift half the
         * range into the new indirect block.
         */
        key_beg = 0;
        key_end = HAMMER2_KEY_MAX;
        cache_index = 0;
        hammer2_spin_ex(&parent->core.spin);

        for (;;) {
                if (--maxloops == 0) {
                        panic("indkey_freemap shit %p %p:%d\n",
                              parent, base, count);
                }
                chain = hammer2_combined_find(parent, base, count,
                                              &cache_index, &key_next,
                                              key_beg, key_end,
                                              &bref);

                /*
                 * Exhausted search
                 */
                if (bref == NULL)
                        break;

                /*
                 * NOTE: No need to check DUPLICATED here because we do
                 *       not release the spinlock.
                 */
                if (chain && (chain->flags & HAMMER2_CHAIN_DELETED)) {
                        if (key_next == 0 || key_next > key_end)
                                break;
                        key_beg = key_next;
                        continue;
                }

                /*
                 * Use the full live (not deleted) element for the scan
                 * iteration.  HAMMER2 does not allow partial replacements.
                 *
                 * XXX should be built into hammer2_combined_find().
                 */
                key_next = bref->key + ((hammer2_key_t)1 << bref->keybits);

                /*
                 * Expand our calculated key range (key, keybits) to fit
                 * the scanned key.  nkeybits represents the full range
                 * that we will later cut in half (two halves @ nkeybits - 1).
                 */
                nkeybits = keybits;
                if (nkeybits < bref->keybits) {
                        if (bref->keybits > 64) {
                                kprintf("bad bref chain %p bref %p\n",
                                        chain, bref);
                                Debugger("fubar");
                        }
                        nkeybits = bref->keybits;
                }
                while (nkeybits < 64 &&
                       (~(((hammer2_key_t)1 << nkeybits) - 1) &
                        (key ^ bref->key)) != 0) {
                        ++nkeybits;
                }

                /*
                 * If the new key range is larger we have to determine
                 * which side of the new key range the existing keys fall
                 * under by checking the high bit, then collapsing the
                 * locount into the hicount or vise-versa.
                 */
                if (keybits != nkeybits) {
                        if (((hammer2_key_t)1 << (nkeybits - 1)) & key) {
                                hicount += locount;
                                locount = 0;
                        } else {
                                locount += hicount;
                                hicount = 0;
                        }
                        keybits = nkeybits;
                }

                /*
                 * The newly scanned key will be in the lower half or the
                 * upper half of the (new) key range.
                 */
                if (((hammer2_key_t)1 << (nkeybits - 1)) & bref->key)
                        ++hicount;
                else
                        ++locount;

                if (key_next == 0)
                        break;
                key_beg = key_next;
        }
        hammer2_spin_unex(&parent->core.spin);
        bref = NULL;    /* now invalid (safety) */

        /*
         * Adjust keybits to represent half of the full range calculated
         * above (radix 63 max)
         */
        --keybits;

        /*
         * Select whichever half contains the most elements.  Theoretically
         * we can select either side as long as it contains at least one
         * element (in order to ensure that a free slot is present to hold
         * the indirect block).
         */
        if (hammer2_indirect_optimize) {
                /*
                 * Insert node for least number of keys, this will arrange
                 * the first few blocks of a large file or the first few
                 * inodes in a directory with fewer indirect blocks when
                 * created linearly.
                 */
                if (hicount < locount && hicount != 0)
                        key |= (hammer2_key_t)1 << keybits;
                else
                        key &= ~(hammer2_key_t)1 << keybits;
        } else {
                /*
                 * Insert node for most number of keys, best for heavily
                 * fragmented files.
                 */
                if (hicount > locount)
                        key |= (hammer2_key_t)1 << keybits;
                else
                        key &= ~(hammer2_key_t)1 << keybits;
        }
        *keyp = key;

        return (keybits);
}

/*
 * Sets CHAIN_DELETED and remove the chain's blockref from the parent if
 * it exists.
 *
 * Both parent and chain must be locked exclusively.
 *
 * This function will modify the parent if the blockref requires removal
 * from the parent's block table.
 *
 * This function is NOT recursive.  Any entity already pushed into the
 * chain (such as an inode) may still need visibility into its contents,
 * as well as the ability to read and modify the contents.  For example,
 * for an unlinked file which is still open.
 */
void
hammer2_chain_delete(hammer2_chain_t *parent, hammer2_chain_t *chain,
                     hammer2_tid_t mtid, int flags)
{
        KKASSERT(hammer2_mtx_owned(&chain->lock));

        /*
         * Nothing to do if already marked.
         *
         * We need the spinlock on the core whos RBTREE contains chain
         * to protect against races.
         */
        if ((chain->flags & HAMMER2_CHAIN_DELETED) == 0) {
                KKASSERT((chain->flags & HAMMER2_CHAIN_DELETED) == 0 &&
                         chain->parent == parent);
                _hammer2_chain_delete_helper(parent, chain, mtid, flags);
        }

        /*
         * Permanent deletions mark the chain as destroyed.
         */
        if (flags & HAMMER2_DELETE_PERMANENT) {
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_DESTROY);
        } else {
                /* XXX might not be needed */
                hammer2_chain_setflush(chain);
        }
}

/*
 * Returns the index of the nearest element in the blockref array >= elm.
 * Returns (count) if no element could be found.
 *
 * Sets *key_nextp to the next key for loop purposes but does not modify
 * it if the next key would be higher than the current value of *key_nextp.
 * Note that *key_nexp can overflow to 0, which should be tested by the
 * caller.
 *
 * (*cache_indexp) is a heuristic and can be any value without effecting
 * the result.
 *
 * WARNING!  Must be called with parent's spinlock held.  Spinlock remains
 *           held through the operation.
 */
static int
hammer2_base_find(hammer2_chain_t *parent,
                  hammer2_blockref_t *base, int count,
                  int *cache_indexp, hammer2_key_t *key_nextp,
                  hammer2_key_t key_beg, hammer2_key_t key_end)
{
        hammer2_blockref_t *scan;
        hammer2_key_t scan_end;
        int i;
        int limit;

        /*
         * Require the live chain's already have their core's counted
         * so we can optimize operations.
         */
        KKASSERT(parent->flags & HAMMER2_CHAIN_COUNTEDBREFS);

        /*
         * Degenerate case
         */
        if (count == 0 || base == NULL)
                return(count);

        /*
         * Sequential optimization using *cache_indexp.  This is the most
         * likely scenario.
         *
         * We can avoid trailing empty entries on live chains, otherwise
         * we might have to check the whole block array.
         */
        i = *cache_indexp;
        cpu_ccfence();
        limit = parent->core.live_zero;
        if (i >= limit)
                i = limit - 1;
        if (i < 0)
                i = 0;
        KKASSERT(i < count);

        /*
         * Search backwards
         */
        scan = &base[i];
        while (i > 0 && (scan->type == 0 || scan->key > key_beg)) {
                --scan;
                --i;
        }
        *cache_indexp = i;

        /*
         * Search forwards, stop when we find a scan element which
         * encloses the key or until we know that there are no further
         * elements.
         */
        while (i < count) {
                if (scan->type != 0) {
                        scan_end = scan->key +
                                   ((hammer2_key_t)1 << scan->keybits) - 1;
                        if (scan->key > key_beg || scan_end >= key_beg)
                                break;
                }
                if (i >= limit)
                        return (count);
                ++scan;
                ++i;
        }
        if (i != count) {
                *cache_indexp = i;
                if (i >= limit) {
                        i = count;
                } else {
                        scan_end = scan->key +
                                   ((hammer2_key_t)1 << scan->keybits);
                        if (scan_end && (*key_nextp > scan_end ||
                                         *key_nextp == 0)) {
                                *key_nextp = scan_end;
                        }
                }
        }
        return (i);
}

/*
 * Do a combined search and return the next match either from the blockref
 * array or from the in-memory chain.  Sets *bresp to the returned bref in
 * both cases, or sets it to NULL if the search exhausted.  Only returns
 * a non-NULL chain if the search matched from the in-memory chain.
 *
 * When no in-memory chain has been found and a non-NULL bref is returned
 * in *bresp.
 *
 *
 * The returned chain is not locked or referenced.  Use the returned bref
 * to determine if the search exhausted or not.  Iterate if the base find
 * is chosen but matches a deleted chain.
 *
 * WARNING!  Must be called with parent's spinlock held.  Spinlock remains
 *           held through the operation.
 */
static hammer2_chain_t *
hammer2_combined_find(hammer2_chain_t *parent,
                      hammer2_blockref_t *base, int count,
                      int *cache_indexp, hammer2_key_t *key_nextp,
                      hammer2_key_t key_beg, hammer2_key_t key_end,
                      hammer2_blockref_t **bresp)
{
        hammer2_blockref_t *bref;
        hammer2_chain_t *chain;
        int i;

        /*
         * Lookup in block array and in rbtree.
         */
        *key_nextp = key_end + 1;
        i = hammer2_base_find(parent, base, count, cache_indexp,
                              key_nextp, key_beg, key_end);
        chain = hammer2_chain_find(parent, key_nextp, key_beg, key_end);

        /*
         * Neither matched
         */
        if (i == count && chain == NULL) {
                *bresp = NULL;
                return(NULL);
        }

        /*
         * Only chain matched.
         */
        if (i == count) {
                bref = &chain->bref;
                goto found;
        }

        /*
         * Only blockref matched.
         */
        if (chain == NULL) {
                bref = &base[i];
                goto found;
        }

        /*
         * Both in-memory and blockref matched, select the nearer element.
         *
         * If both are flush with the left-hand side or both are the
         * same distance away, select the chain.  In this situation the
         * chain must have been loaded from the matching blockmap.
         */
        if ((chain->bref.key <= key_beg && base[i].key <= key_beg) ||
            chain->bref.key == base[i].key) {
                KKASSERT(chain->bref.key == base[i].key);
                bref = &chain->bref;
                goto found;
        }

        /*
         * Select the nearer key
         */
        if (chain->bref.key < base[i].key) {
                bref = &chain->bref;
        } else {
                bref = &base[i];
                chain = NULL;
        }

        /*
         * If the bref is out of bounds we've exhausted our search.
         */
found:
        if (bref->key > key_end) {
                *bresp = NULL;
                chain = NULL;
        } else {
                *bresp = bref;
        }
        return(chain);
}

/*
 * Locate the specified block array element and delete it.  The element
 * must exist.
 *
 * The spin lock on the related chain must be held.
 *
 * NOTE: live_count was adjusted when the chain was deleted, so it does not
 *       need to be adjusted when we commit the media change.
 */
void
hammer2_base_delete(hammer2_chain_t *parent,
                    hammer2_blockref_t *base, int count,
                    int *cache_indexp, hammer2_chain_t *chain)
{
        hammer2_blockref_t *elm = &chain->bref;
        hammer2_key_t key_next;
        int i;

        /*
         * Delete element.  Expect the element to exist.
         *
         * XXX see caller, flush code not yet sophisticated enough to prevent
         *     re-flushed in some cases.
         */
        key_next = 0; /* max range */
        i = hammer2_base_find(parent, base, count, cache_indexp,
                              &key_next, elm->key, elm->key);
        if (i == count || base[i].type == 0 ||
            base[i].key != elm->key ||
            ((chain->flags & HAMMER2_CHAIN_BMAPUPD) == 0 &&
             base[i].keybits != elm->keybits)) {
                hammer2_spin_unex(&parent->core.spin);
                panic("delete base %p element not found at %d/%d elm %p\n",
                      base, i, count, elm);
                return;
        }

        /*
         * Update stats and zero the entry
         */
        parent->bref.data_count -= base[i].data_count;
        parent->bref.data_count -= (hammer2_off_t)1 <<
                        (int)(base[i].data_off & HAMMER2_OFF_MASK_RADIX);
        parent->bref.inode_count -= base[i].inode_count;
        if (base[i].type == HAMMER2_BREF_TYPE_INODE)
                parent->bref.inode_count -= 1;

        bzero(&base[i], sizeof(*base));

        /*
         * We can only optimize parent->core.live_zero for live chains.
         */
        if (parent->core.live_zero == i + 1) {
                while (--i >= 0 && base[i].type == 0)
                        ;
                parent->core.live_zero = i + 1;
        }

        /*
         * Clear appropriate blockmap flags in chain.
         */
        atomic_clear_int(&chain->flags, HAMMER2_CHAIN_BMAPPED |
                                        HAMMER2_CHAIN_BMAPUPD);
}

/*
 * Insert the specified element.  The block array must not already have the
 * element and must have space available for the insertion.
 *
 * The spin lock on the related chain must be held.
 *
 * NOTE: live_count was adjusted when the chain was deleted, so it does not
 *       need to be adjusted when we commit the media change.
 */
void
hammer2_base_insert(hammer2_chain_t *parent,
                    hammer2_blockref_t *base, int count,
                    int *cache_indexp, hammer2_chain_t *chain)
{
        hammer2_blockref_t *elm = &chain->bref;
        hammer2_key_t key_next;
        hammer2_key_t xkey;
        int i;
        int j;
        int k;
        int l;
        int u = 1;

        /*
         * Insert new element.  Expect the element to not already exist
         * unless we are replacing it.
         *
         * XXX see caller, flush code not yet sophisticated enough to prevent
         *     re-flushed in some cases.
         */
        key_next = 0; /* max range */
        i = hammer2_base_find(parent, base, count, cache_indexp,
                              &key_next, elm->key, elm->key);

        /*
         * Shortcut fill optimization, typical ordered insertion(s) may not
         * require a search.
         */
        KKASSERT(i >= 0 && i <= count);

        /*
         * Set appropriate blockmap flags in chain.
         */
        atomic_set_int(&chain->flags, HAMMER2_CHAIN_BMAPPED);

        /*
         * Update stats and zero the entry
         */
        parent->bref.data_count += elm->data_count;
        parent->bref.data_count += (hammer2_off_t)1 <<
                        (int)(elm->data_off & HAMMER2_OFF_MASK_RADIX);
        parent->bref.inode_count += elm->inode_count;
        if (elm->type == HAMMER2_BREF_TYPE_INODE)
                parent->bref.inode_count += 1;


        /*
         * We can only optimize parent->core.live_zero for live chains.
         */
        if (i == count && parent->core.live_zero < count) {
                i = parent->core.live_zero++;
                base[i] = *elm;
                return;
        }

        xkey = elm->key + ((hammer2_key_t)1 << elm->keybits) - 1;
        if (i != count && (base[i].key < elm->key || xkey >= base[i].key)) {
                hammer2_spin_unex(&parent->core.spin);
                panic("insert base %p overlapping elements at %d elm %p\n",
                      base, i, elm);
        }

        /*
         * Try to find an empty slot before or after.
         */
        j = i;
        k = i;
        while (j > 0 || k < count) {
                --j;
                if (j >= 0 && base[j].type == 0) {
                        if (j == i - 1) {
                                base[j] = *elm;
                        } else {
                                bcopy(&base[j+1], &base[j],
                                      (i - j - 1) * sizeof(*base));
                                base[i - 1] = *elm;
                        }
                        goto validate;
                }
                ++k;
                if (k < count && base[k].type == 0) {
                        bcopy(&base[i], &base[i+1],
                              (k - i) * sizeof(hammer2_blockref_t));
                        base[i] = *elm;

                        /*
                         * We can only update parent->core.live_zero for live
                         * chains.
                         */
                        if (parent->core.live_zero <= k)
                                parent->core.live_zero = k + 1;
                        u = 2;
                        goto validate;
                }
        }
        panic("hammer2_base_insert: no room!");

        /*
         * Debugging
         */
validate:
        key_next = 0;
        for (l = 0; l < count; ++l) {
                if (base[l].type) {
                        key_next = base[l].key +
                                   ((hammer2_key_t)1 << base[l].keybits) - 1;
                        break;
                }
        }
        while (++l < count) {
                if (base[l].type) {
                        if (base[l].key <= key_next)
                                panic("base_insert %d %d,%d,%d fail %p:%d", u, i, j, k, base, l);
                        key_next = base[l].key +
                                   ((hammer2_key_t)1 << base[l].keybits) - 1;

                }
        }

}

#if 0

/*
 * Sort the blockref array for the chain.  Used by the flush code to
 * sort the blockref[] array.
 *
 * The chain must be exclusively locked AND spin-locked.
 */
typedef hammer2_blockref_t *hammer2_blockref_p;

static
int
hammer2_base_sort_callback(const void *v1, const void *v2)
{
        hammer2_blockref_p bref1 = *(const hammer2_blockref_p *)v1;
        hammer2_blockref_p bref2 = *(const hammer2_blockref_p *)v2;

        /*
         * Make sure empty elements are placed at the end of the array
         */
        if (bref1->type == 0) {
                if (bref2->type == 0)
                        return(0);
                return(1);
        } else if (bref2->type == 0) {
                return(-1);
        }

        /*
         * Sort by key
         */
        if (bref1->key < bref2->key)
                return(-1);
        if (bref1->key > bref2->key)
                return(1);
        return(0);
}

void
hammer2_base_sort(hammer2_chain_t *chain)
{
        hammer2_blockref_t *base;
        int count;

        switch(chain->bref.type) {
        case HAMMER2_BREF_TYPE_INODE:
                /*
                 * Special shortcut for embedded data returns the inode
                 * itself.  Callers must detect this condition and access
                 * the embedded data (the strategy code does this for us).
                 *
                 * This is only applicable to regular files and softlinks.
                 */
                if (chain->data->ipdata.meta.op_flags &
                    HAMMER2_OPFLAG_DIRECTDATA) {
                        return;
                }
                base = &chain->data->ipdata.u.blockset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
        case HAMMER2_BREF_TYPE_INDIRECT:
                /*
                 * Optimize indirect blocks in the INITIAL state to avoid
                 * I/O.
                 */
                KKASSERT((chain->flags & HAMMER2_CHAIN_INITIAL) == 0);
                base = &chain->data->npdata[0];
                count = chain->bytes / sizeof(hammer2_blockref_t);
                break;
        case HAMMER2_BREF_TYPE_VOLUME:
                base = &chain->data->voldata.sroot_blockset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        case HAMMER2_BREF_TYPE_FREEMAP:
                base = &chain->data->blkset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        default:
                kprintf("hammer2_chain_lookup: unrecognized "
                        "blockref(A) type: %d",
                        chain->bref.type);
                while (1)
                        tsleep(&base, 0, "dead", 0);
                panic("hammer2_chain_lookup: unrecognized "
                      "blockref(A) type: %d",
                      chain->bref.type);
                base = NULL;    /* safety */
                count = 0;      /* safety */
        }
        kqsort(base, count, sizeof(*base), hammer2_base_sort_callback);
}

#endif

/*
 * Chain memory management
 */
void
hammer2_chain_wait(hammer2_chain_t *chain)
{
        tsleep(chain, 0, "chnflw", 1);
}

const hammer2_media_data_t *
hammer2_chain_rdata(hammer2_chain_t *chain)
{
        KKASSERT(chain->data != NULL);
        return (chain->data);
}

hammer2_media_data_t *
hammer2_chain_wdata(hammer2_chain_t *chain)
{
        KKASSERT(chain->data != NULL);
        return (chain->data);
}

/*
 * Set the check data for a chain.  This can be a heavy-weight operation
 * and typically only runs on-flush.  For file data check data is calculated
 * when the logical buffers are flushed.
 */
void
hammer2_chain_setcheck(hammer2_chain_t *chain, void *bdata)
{
        chain->bref.flags &= ~HAMMER2_BREF_FLAG_ZERO;

        switch(HAMMER2_DEC_CHECK(chain->bref.methods)) {
        case HAMMER2_CHECK_NONE:
                break;
        case HAMMER2_CHECK_DISABLED:
                break;
        case HAMMER2_CHECK_ISCSI32:
                chain->bref.check.iscsi32.value =
                        hammer2_icrc32(bdata, chain->bytes);
                break;
        case HAMMER2_CHECK_XXHASH64:
                chain->bref.check.xxhash64.value =
                        XXH64(bdata, chain->bytes, XXH_HAMMER2_SEED);
                break;
        case HAMMER2_CHECK_SHA192:
                {
                        SHA256_CTX hash_ctx;
                        union {
                                uint8_t digest[SHA256_DIGEST_LENGTH];
                                uint64_t digest64[SHA256_DIGEST_LENGTH/8];
                        } u;

                        SHA256_Init(&hash_ctx);
                        SHA256_Update(&hash_ctx, bdata, chain->bytes);
                        SHA256_Final(u.digest, &hash_ctx);
                        u.digest64[2] ^= u.digest64[3];
                        bcopy(u.digest,
                              chain->bref.check.sha192.data,
                              sizeof(chain->bref.check.sha192.data));
                }
                break;
        case HAMMER2_CHECK_FREEMAP:
                chain->bref.check.freemap.icrc32 =
                        hammer2_icrc32(bdata, chain->bytes);
                break;
        default:
                kprintf("hammer2_chain_setcheck: unknown check type %02x\n",
                        chain->bref.methods);
                break;
        }
}

int
hammer2_chain_testcheck(hammer2_chain_t *chain, void *bdata)
{
        int r;

        if (chain->bref.flags & HAMMER2_BREF_FLAG_ZERO)
                return 1;

        switch(HAMMER2_DEC_CHECK(chain->bref.methods)) {
        case HAMMER2_CHECK_NONE:
                r = 1;
                break;
        case HAMMER2_CHECK_DISABLED:
                r = 1;
                break;
        case HAMMER2_CHECK_ISCSI32:
                r = (chain->bref.check.iscsi32.value ==
                     hammer2_icrc32(bdata, chain->bytes));
                hammer2_check_icrc32 += chain->bytes;
                break;
        case HAMMER2_CHECK_XXHASH64:
                r = (chain->bref.check.xxhash64.value ==
                     XXH64(bdata, chain->bytes, XXH_HAMMER2_SEED));
                hammer2_check_xxhash64 += chain->bytes;
                break;
        case HAMMER2_CHECK_SHA192:
                {
                        SHA256_CTX hash_ctx;
                        union {
                                uint8_t digest[SHA256_DIGEST_LENGTH];
                                uint64_t digest64[SHA256_DIGEST_LENGTH/8];
                        } u;

                        SHA256_Init(&hash_ctx);
                        SHA256_Update(&hash_ctx, bdata, chain->bytes);
                        SHA256_Final(u.digest, &hash_ctx);
                        u.digest64[2] ^= u.digest64[3];
                        if (bcmp(u.digest,
                                 chain->bref.check.sha192.data,
                                 sizeof(chain->bref.check.sha192.data)) == 0) {
                                r = 1;
                        } else {
                                r = 0;
                        }
                }
                break;
        case HAMMER2_CHECK_FREEMAP:
                r = (chain->bref.check.freemap.icrc32 ==
                     hammer2_icrc32(bdata, chain->bytes));
                if (r == 0) {
                        kprintf("freemap.icrc %08x icrc32 %08x (%d)\n",
                                chain->bref.check.freemap.icrc32,
                                hammer2_icrc32(bdata, chain->bytes), chain->bytes);
                        if (chain->dio)
                                kprintf("dio %p buf %016jx,%d bdata %p/%p\n",
                                        chain->dio, chain->dio->bp->b_loffset, chain->dio->bp->b_bufsize, bdata, chain->dio->bp->b_data);
                }

                break;
        default:
                kprintf("hammer2_chain_setcheck: unknown check type %02x\n",
                        chain->bref.methods);
                r = 1;
                break;
        }
        return r;
}

/*
 * The caller presents a shared-locked (parent, chain) where the chain
 * is of type HAMMER2_OBJTYPE_HARDLINK.  The caller must hold the ip
 * structure representing the inode locked to prevent
 * consolidation/deconsolidation races.
 *
 * The flags passed in are LOOKUP flags, not RESOLVE flags.  Only
 * HAMMER2_LOOKUP_SHARED is supported.
 *
 * We locate the hardlink in the current or a common parent directory.
 *
 * If we are unable to locate the hardlink, EIO is returned and
 * (*chainp) is unlocked and dropped.
 */
int
hammer2_chain_hardlink_find(hammer2_inode_t *dip,
                        hammer2_chain_t **parentp,
                        hammer2_chain_t **chainp,
                        int flags)
{
        hammer2_chain_t *parent;
        hammer2_chain_t *rchain;
        hammer2_key_t key_dummy;
        hammer2_key_t lhc;
        int cache_index = -1;
        int resolve_flags;

        resolve_flags = (flags & HAMMER2_LOOKUP_SHARED) ?
                        HAMMER2_RESOLVE_SHARED : 0;

        /*
         * Obtain the key for the hardlink from *chainp.
         */
        rchain = *chainp;
        lhc = rchain->data->ipdata.meta.inum;
        hammer2_chain_unlock(rchain);
        hammer2_chain_drop(rchain);
        rchain = NULL;

        for (;;) {
                int again;

                rchain = hammer2_chain_lookup(parentp, &key_dummy,
                                              lhc, lhc,
                                              &cache_index, flags);
                if (rchain)
                        break;

                /*
                 * Iterate parents, handle parent rename races by retrying
                 * the operation.
                 */
                again = 0;
                for (;;) {
                        parent = *parentp;
                        if (parent->bref.type == HAMMER2_BREF_TYPE_INODE) {
                                if (again == 1)
                                        break;
                                ++again;
                        }
                        if (parent->bref.flags & HAMMER2_BREF_FLAG_PFSROOT)
                                goto done;
                        for (;;) {
                                if (parent->parent == NULL)
                                        goto done;
                                parent = parent->parent;
                                hammer2_chain_ref(parent);
                                hammer2_chain_unlock(*parentp);
                                hammer2_chain_lock(parent,
                                                   HAMMER2_RESOLVE_ALWAYS |
                                                   resolve_flags);
                                if ((*parentp)->parent == parent) {
                                        hammer2_chain_drop(*parentp);
                                        *parentp = parent;
                                        break;
                                }
                                hammer2_chain_unlock(parent);
                                hammer2_chain_drop(parent);
                                hammer2_chain_lock(*parentp,
                                                   HAMMER2_RESOLVE_ALWAYS |
                                                   resolve_flags);
                                parent = *parentp;
                        }
                }
        }
done:

        *chainp = rchain;
        return (rchain ? 0 : EINVAL);
}

/*
 * Used by the bulkscan code to snapshot the synchronized storage for
 * a volume, allowing it to be scanned concurrently against normal
 * operation.
 */
hammer2_chain_t *
hammer2_chain_bulksnap(hammer2_chain_t *chain)
{
        hammer2_chain_t *copy;

        copy = hammer2_chain_alloc(chain->hmp, chain->pmp, &chain->bref);
        switch(chain->bref.type) {
        case HAMMER2_BREF_TYPE_VOLUME:
                copy->data = kmalloc(sizeof(copy->data->voldata),
                                     chain->hmp->mchain,
                                     M_WAITOK | M_ZERO);
                hammer2_spin_ex(&chain->core.spin);
                copy->data->voldata = chain->data->voldata;
                hammer2_spin_unex(&chain->core.spin);
                break;
        case HAMMER2_BREF_TYPE_FREEMAP:
                copy->data = kmalloc(sizeof(hammer2_blockset_t),
                                     chain->hmp->mchain,
                                     M_WAITOK | M_ZERO);
                hammer2_spin_ex(&chain->core.spin);
                copy->data->blkset = chain->data->blkset;
                hammer2_spin_unex(&chain->core.spin);
                break;
        default:
                break;
        }
        return copy;
}

void
hammer2_chain_bulkdrop(hammer2_chain_t *copy)
{
        switch(copy->bref.type) {
        case HAMMER2_BREF_TYPE_VOLUME:
        case HAMMER2_BREF_TYPE_FREEMAP:
                KKASSERT(copy->data);
                kfree(copy->data, copy->hmp->mchain);
                copy->data = NULL;
                atomic_add_long(&hammer2_chain_allocs, -1);
                break;
        default:
                break;
        }
        hammer2_chain_drop(copy);
}

/*
 * Create a snapshot of the specified {parent, ochain} with the specified
 * label.  The originating hammer2_inode must be exclusively locked for
 * safety.
 *
 * The ioctl code has already synced the filesystem.
 */
int
hammer2_chain_snapshot(hammer2_chain_t *chain, hammer2_ioc_pfs_t *pmp,
                       hammer2_tid_t mtid)
{
        hammer2_dev_t *hmp;
        const hammer2_inode_data_t *ripdata;
        hammer2_inode_data_t *wipdata;
        hammer2_chain_t *nchain;
        hammer2_inode_t *nip;
        size_t name_len;
        hammer2_key_t lhc;
        struct vattr vat;
#if 0
        uuid_t opfs_clid;
#endif
        int error;

        kprintf("snapshot %s\n", pmp->name);

        name_len = strlen(pmp->name);
        lhc = hammer2_dirhash(pmp->name, name_len);

        /*
         * Get the clid
         */
        ripdata = &chain->data->ipdata;
#if 0
        opfs_clid = ripdata->meta.pfs_clid;
#endif
        hmp = chain->hmp;

        /*
         * Create the snapshot directory under the super-root
         *
         * Set PFS type, generate a unique filesystem id, and generate
         * a cluster id.  Use the same clid when snapshotting a PFS root,
         * which theoretically allows the snapshot to be used as part of
         * the same cluster (perhaps as a cache).
         *
         * Copy the (flushed) blockref array.  Theoretically we could use
         * chain_duplicate() but it becomes difficult to disentangle
         * the shared core so for now just brute-force it.
         */
        VATTR_NULL(&vat);
        vat.va_type = VDIR;
        vat.va_mode = 0755;
        nip = hammer2_inode_create(hmp->spmp->iroot, &vat, proc0.p_ucred,
                                   pmp->name, name_len, 0,
                                   1, 0, 0,
                                   HAMMER2_INSERT_PFSROOT, &error);

        if (nip) {
                hammer2_inode_modify(nip);
                nchain = hammer2_inode_chain(nip, 0, HAMMER2_RESOLVE_ALWAYS);
                hammer2_chain_modify(nchain, mtid, 0, 0);
                wipdata = &nchain->data->ipdata;

                nip->meta.pfs_type = HAMMER2_PFSTYPE_MASTER;
                nip->meta.pfs_subtype = HAMMER2_PFSSUBTYPE_SNAPSHOT;
                nip->meta.op_flags |= HAMMER2_OPFLAG_PFSROOT;
                kern_uuidgen(&nip->meta.pfs_fsid, 1);

                /*
                 * Give the snapshot its own private cluster id.  As a
                 * snapshot no further synchronization with the original
                 * cluster will be done.
                 */
#if 0
                if (chain->flags & HAMMER2_CHAIN_PFSBOUNDARY)
                        nip->meta.pfs_clid = opfs_clid;
                else
                        kern_uuidgen(&nip->meta.pfs_clid, 1);
#endif
                kern_uuidgen(&nip->meta.pfs_clid, 1);
                nchain->bref.flags |= HAMMER2_BREF_FLAG_PFSROOT;

                /* XXX hack blockset copy */
                /* XXX doesn't work with real cluster */
                wipdata->meta = nip->meta;
                wipdata->u.blockset = ripdata->u.blockset;
                hammer2_flush(nchain, 1);
                hammer2_chain_unlock(nchain);
                hammer2_chain_drop(nchain);
                hammer2_inode_unlock(nip);
        }
        return (error);
}