hammer2 - Major restructuring, part 3/several

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

/*
 * Copyright (c) 2011-2013 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@dragonflybsd.org>
 * by 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 and hammer2_chain_core structures.
 *
 * Chains represent the filesystem media topology in-memory.  Any given
 * chain can represent an inode, indirect block, data, or other types
 * of blocks.
 *
 * This module provides APIs for direct and indirect block searches,
 * iterations, recursions, creation, deletion, replication, and snapshot
 * views (used by the flush and snapshot code).
 *
 * Generally speaking any modification made to a chain must propagate all
 * the way back to the volume header, issuing copy-on-write updates to the
 * blockref tables all the way up.  Any chain except the volume header itself
 * can be flushed to disk at any time, in any order.  None of it matters
 * until we get to the point where we want to synchronize the volume header
 * (see the flush code).
 *
 * The chain structure supports snapshot views in time, which are primarily
 * used until the related data and meta-data is flushed to allow the
 * filesystem to make snapshots without requiring it to first flush,
 * and to allow the filesystem flush and modify the filesystem concurrently
 * with minimal or no stalls.
 */
#include <sys/cdefs.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/types.h>
#include <sys/lock.h>
#include <sys/uuid.h>

#include "hammer2.h"

static int hammer2_indirect_optimize;   /* XXX SYSCTL */

static hammer2_chain_t *hammer2_chain_create_indirect(
                hammer2_trans_t *trans, hammer2_chain_t *parent,
                hammer2_key_t key, int keybits, int *errorp);

/*
 * We use a red-black tree to guarantee safe lookups under shared locks.
 *
 * Chains can be overloaded onto the same index, creating a different
 * view of a blockref table based on a transaction id.  The RBTREE
 * deconflicts the view by sub-sorting on delete_tid.
 *
 * NOTE: Any 'current' chain which is not yet deleted will have a
 *       delete_tid of HAMMER2_MAX_TID (0xFFF....FFFLLU).
 */
RB_GENERATE(hammer2_chain_tree, hammer2_chain, rbnode, hammer2_chain_cmp);

int
hammer2_chain_cmp(hammer2_chain_t *chain1, hammer2_chain_t *chain2)
{
        if (chain1->index < chain2->index)
                return(-1);
        if (chain1->index > chain2->index)
                return(1);
        if (chain1->delete_tid < chain2->delete_tid)
                return(-1);
        if (chain1->delete_tid > chain2->delete_tid)
                return(1);
        return(0);
}

/*
 * Flag chain->parent SUBMODIFIED recursively up to the root.  The
 * recursion can terminate when a parent is encountered with SUBMODIFIED
 * already set.  The flag is NOT set on the passed-in chain.
 *
 * This can be confusing because even though chains are multi-homed,
 * each chain has a specific idea of its parent (chain->parent) which
 * is singly-homed.
 *
 * This flag is used by the flusher's downward recursion to detect
 * modifications and can only be cleared bottom-up.
 *
 * The parent pointer is protected by all the modified children below it
 * and cannot be changed until they have all been flushed.  However, setsubmod
 * operations on new modifications can race flushes in progress, so we use
 * the chain->core->cst.spin lock to handle collisions.
 */
void
hammer2_chain_parent_setsubmod(hammer2_chain_t *chain)
{
        hammer2_chain_t *parent;
        hammer2_chain_core_t *core;

        while ((parent = chain->parent) != NULL) {
                core = parent->core;
                spin_lock(&core->cst.spin);
                while (parent->duplink)
                        parent = parent->duplink;
                if (parent->flags & HAMMER2_CHAIN_SUBMODIFIED) {
                        spin_unlock(&core->cst.spin);
                        break;
                }
                atomic_set_int(&parent->flags, HAMMER2_CHAIN_SUBMODIFIED);
                spin_unlock(&core->cst.spin);
                chain = parent;
        }
}

/*
 * 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->core is NOT allocated and the media data and bp pointers are left
 * NULL.  The caller must call chain_core_alloc() to allocate or associate
 * a core with the chain.
 *
 * NOTE: Returns a referenced but unlocked (because there is no core) chain.
 */
hammer2_chain_t *
hammer2_chain_alloc(hammer2_mount_t *hmp, hammer2_blockref_t *bref)
{
        hammer2_chain_t *chain;
        u_int bytes = 1U << (int)(bref->data_off & HAMMER2_OFF_MASK_RADIX);

        /*
         * Construct the appropriate system structure.
         */
        switch(bref->type) {
        case HAMMER2_BREF_TYPE_INODE:
        case HAMMER2_BREF_TYPE_INDIRECT:
        case HAMMER2_BREF_TYPE_FREEMAP_ROOT:
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
        case HAMMER2_BREF_TYPE_DATA:
        case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
                chain = kmalloc(sizeof(*chain), hmp->mchain, M_WAITOK | M_ZERO);
                break;
        case HAMMER2_BREF_TYPE_VOLUME:
                chain = NULL;
                panic("hammer2_chain_alloc volume type illegal for op");
        default:
                chain = NULL;
                panic("hammer2_chain_alloc: unrecognized blockref type: %d",
                      bref->type);
        }

        chain->hmp = hmp;
        chain->bref = *bref;
        chain->index = -1;              /* not yet assigned */
        chain->bytes = bytes;
        chain->refs = 1;
        chain->flags = HAMMER2_CHAIN_ALLOCATED;
        chain->delete_tid = HAMMER2_MAX_TID;

        return (chain);
}

/*
 * Associate an existing core with the chain or allocate a new core.
 *
 * The core is not locked.  No additional refs on the chain are made.
 */
void
hammer2_chain_core_alloc(hammer2_chain_t *chain, hammer2_chain_core_t *core)
{
        KKASSERT(chain->core == NULL);

        if (core == NULL) {
                core = kmalloc(sizeof(*core), chain->hmp->mchain,
                               M_WAITOK | M_ZERO);
                RB_INIT(&core->rbtree);
                core->sharecnt = 1;
                chain->core = core;
                ccms_cst_init(&core->cst, chain);
        } else {
                atomic_add_int(&core->sharecnt, 1);
                chain->core = core;
        }
}

/*
 * Deallocate a chain after the caller has transitioned its refs to 0
 * and disassociated it from its parent.
 *
 * We must drop sharecnt on the core (if any) and handle its 1->0 transition
 * too.
 */
static void
hammer2_chain_dealloc(hammer2_chain_t *chain)
{
        hammer2_chain_core_t *core;

        /*
         * Chain's flags are expected to be sane.
         */
        KKASSERT((chain->flags & (HAMMER2_CHAIN_MOVED |
                                  HAMMER2_CHAIN_MODIFIED |
                                  HAMMER2_CHAIN_ONRBTREE)) == 0);
        KKASSERT(chain->duplink == NULL);

        /*
         * Disconnect chain->core from chain and free core if it was the
         * last core.  If any children are present in the core's rbtree
         * they cannot have a pointer to our chain by definition because
         * our chain's refs have dropped to 0.  If this is the last sharecnt
         * on core, then core's rbtree must be empty by definition.
         */
        if ((core = chain->core) != NULL) {
                /*
                 * Other chains may reference the same core so the core's
                 * spinlock is needed to safely disconnect it.
                 */
                spin_lock(&core->cst.spin);
                chain->core = NULL;
                if (atomic_fetchadd_int(&core->sharecnt, -1) == 1) {
                        spin_unlock(&core->cst.spin);
                        KKASSERT(RB_EMPTY(&core->rbtree));
                        KKASSERT(core->cst.count == 0);
                        KKASSERT(core->cst.upgrade == 0);
                        kfree(core, chain->hmp->mchain);
                } else {
                        spin_unlock(&core->cst.spin);
                }
                core = NULL;            /* safety */
        }

        /*
         * Finally free the structure and return for possible recursion.
         */
        hammer2_chain_free(chain);
}

/*
 * Free a disconnected chain element.
 */
void
hammer2_chain_free(hammer2_chain_t *chain)
{
        hammer2_mount_t *hmp = chain->hmp;

        switch(chain->bref.type) {
        case HAMMER2_BREF_TYPE_VOLUME:
                chain->data = NULL;
                break;
        case HAMMER2_BREF_TYPE_INODE:
                if (chain->data) {
                        kfree(chain->data, hmp->minode);
                        chain->data = NULL;
                }
                break;
        default:
                KKASSERT(chain->data == NULL);
                break;
        }

        KKASSERT(chain->core == NULL);
        KKASSERT(chain->bp == NULL);
        chain->hmp = NULL;

        if (chain->flags & HAMMER2_CHAIN_ALLOCATED)
                kfree(chain, hmp->mchain);
}

/*
 * Add a reference to a chain element, preventing its destruction.
 */
void
hammer2_chain_ref(hammer2_chain_t *chain)
{
        atomic_add_int(&chain->refs, 1);
}

/*
 * Drop the caller's reference to the chain.  When the ref count drops to
 * zero this function will disassociate the chain from its parent and
 * deallocate it, then recursely drop the parent using the implied ref
 * from the chain's chain->parent.
 *
 * WARNING! Just because we are able to deallocate a chain doesn't mean
 *          that chain->core->rbtree is empty.  There can still be a sharecnt
 *          on chain->core and RBTREE entries that refer to different parents.
 */
static hammer2_chain_t *hammer2_chain_lastdrop(hammer2_chain_t *chain);

void
hammer2_chain_drop(hammer2_chain_t *chain)
{
        u_int refs;
        u_int need = 0;

#if 1
        if (chain->flags & HAMMER2_CHAIN_MOVED)
                ++need;
        if (chain->flags & HAMMER2_CHAIN_MODIFIED)
                ++need;
        KKASSERT(chain->refs > need);
#endif

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

                if (refs == 1) {
                        if (chain->parent) {
                                chain = hammer2_chain_lastdrop(chain);
                                /* recursively drop parent or retry same */
                        } else if (atomic_cmpset_int(&chain->refs, 1, 0)) {
                                hammer2_chain_dealloc(chain);
                                chain = NULL;
                                /* no parent to recurse on */
                        } else {
                                /* retry the same 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 when the chain has a
 * parent.
 *
 * NOTE: A chain can only be removed from its parent core's RBTREE on
 *       the 1->0 transition by definition.  No other code is allowed
 *       to remove chain from its RBTREE, so no race is possible.
 */
static
hammer2_chain_t *
hammer2_chain_lastdrop(hammer2_chain_t *chain)
{
        hammer2_chain_t *parent;
        hammer2_chain_core_t *parent_core;

        parent = chain->parent;
        parent_core = parent->core;
        KKASSERT(chain->flags & HAMMER2_CHAIN_ONRBTREE);

        spin_lock(&parent_core->cst.spin);
        if (atomic_cmpset_int(&chain->refs, 1, 0)) {
                RB_REMOVE(hammer2_chain_tree, &parent_core->rbtree, chain);
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_ONRBTREE);
                chain->parent = NULL;   /* NULL field, must drop implied ref */
                spin_unlock(&parent_core->cst.spin);
                if (chain->duplink) {
                        hammer2_chain_drop(chain->duplink);
                        chain->duplink = NULL;
                }
                hammer2_chain_dealloc(chain);
                chain = parent;         /* recursively drop parent */
        } else {
                spin_unlock(&parent_core->cst.spin);
        }
        return (chain);
}

/*
 * Ref and lock a chain element, acquiring its data with I/O if necessary,
 * and specify how you would like the data to be resolved.
 *
 * Returns 0 on success or an error code if the data could not be acquired.
 * The chain element is locked either way.
 *
 * 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! If data must be fetched a shared lock will temporarily be
 *          upgraded to exclusive.  However, a deadlock can occur if
 *          the caller owns more than one shared lock.
 */
int
hammer2_chain_lock(hammer2_chain_t *chain, int how)
{
        hammer2_mount_t *hmp;
        hammer2_chain_core_t *core;
        hammer2_blockref_t *bref;
        hammer2_off_t pbase;
        hammer2_off_t peof;
        ccms_state_t ostate;
        size_t boff;
        size_t bbytes;
        int error;
        char *bdata;

        /*
         * Ref and lock the element.  Recursive locks are allowed.
         */
        if ((how & HAMMER2_RESOLVE_NOREF) == 0)
                hammer2_chain_ref(chain);
        hmp = chain->hmp;
        KKASSERT(hmp != NULL);

        /*
         * Get the appropriate lock.
         */
        core = chain->core;
        if (how & HAMMER2_RESOLVE_SHARED)
                ccms_thread_lock(&core->cst, CCMS_STATE_SHARED);
        else
                ccms_thread_lock(&core->cst, CCMS_STATE_EXCLUSIVE);

        /*
         * If we already have a valid data pointer no further action is
         * necessary.
         */
        if (chain->data)
                return (0);

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

        /*
         * Upgrade to an exclusive lock so we can safely manipulate the
         * buffer cache.  If another thread got to it before us we
         * can just return.
         */
        ostate = ccms_thread_lock_upgrade(&core->cst);
        if (chain->data) {
                ccms_thread_lock_restore(&core->cst, ostate);
                return (0);
        }

        /*
         * 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_MINALLOCSIZE (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;

        if ((bbytes = chain->bytes) < HAMMER2_MINIOSIZE)
                bbytes = HAMMER2_MINIOSIZE;
        pbase = bref->data_off & ~(hammer2_off_t)(bbytes - 1);
        peof = (pbase + HAMMER2_PBUFSIZE64) & ~HAMMER2_PBUFMASK64;
        boff = bref->data_off & HAMMER2_OFF_MASK & (bbytes - 1);
        KKASSERT(pbase != 0);

        /*
         * 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) &&
            chain->bytes == bbytes) {
                chain->bp = getblk(hmp->devvp, pbase, bbytes, 0, 0);
                error = 0;
        } else if (hammer2_cluster_enable) {
                error = cluster_read(hmp->devvp, peof, pbase, bbytes,
                                     HAMMER2_PBUFSIZE, HAMMER2_PBUFSIZE,
                                     &chain->bp);
        } else {
                error = bread(hmp->devvp, pbase, bbytes, &chain->bp);
        }

        if (error) {
                kprintf("hammer2_chain_get: I/O error %016jx: %d\n",
                        (intmax_t)pbase, error);
                bqrelse(chain->bp);
                chain->bp = NULL;
                ccms_thread_lock_restore(&core->cst, ostate);
                return (error);
        }

        /*
         * Zero the data area if the chain is in the INITIAL-create state.
         * Mark the buffer for bdwrite().
         */
        bdata = (char *)chain->bp->b_data + boff;
        if (chain->flags & HAMMER2_CHAIN_INITIAL) {
                bzero(bdata, chain->bytes);
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_DIRTYBP);
        }

        /*
         * 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.
         */
        switch (bref->type) {
        case HAMMER2_BREF_TYPE_VOLUME:
                /*
                 * Copy data from bp to embedded buffer
                 */
                panic("hammer2_chain_lock: called on unresolved volume header");
#if 0
                /* NOT YET */
                KKASSERT(pbase == 0);
                KKASSERT(chain->bytes == HAMMER2_PBUFSIZE);
                bcopy(bdata, &hmp->voldata, chain->bytes);
                chain->data = (void *)&hmp->voldata;
                bqrelse(chain->bp);
                chain->bp = NULL;
#endif
                break;
        case HAMMER2_BREF_TYPE_INODE:
                /*
                 * Copy data from bp to embedded buffer, do not retain the
                 * device buffer.
                 */
                KKASSERT(chain->bytes == sizeof(chain->data->ipdata));
                chain->data = kmalloc(sizeof(chain->data->ipdata),
                                      hmp->minode, M_WAITOK | M_ZERO);
                bcopy(bdata, &chain->data->ipdata, chain->bytes);
                bqrelse(chain->bp);
                chain->bp = NULL;
                break;
        case HAMMER2_BREF_TYPE_INDIRECT:
        case HAMMER2_BREF_TYPE_DATA:
        case HAMMER2_BREF_TYPE_FREEMAP_ROOT:
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
        case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
        default:
                /*
                 * Point data at the device buffer and leave bp intact.
                 */
                chain->data = (void *)bdata;
                break;
        }

        /*
         * Make sure the bp is not specifically owned by this thread before
         * restoring to a possibly shared lock, so another hammer2 thread
         * can release it.
         */
        if (chain->bp)
                BUF_KERNPROC(chain->bp);
        ccms_thread_lock_restore(&core->cst, ostate);
        return (0);
}

/*
 * Unlock and deref a chain element.
 *
 * On the last lock release any non-embedded data (chain->bp) will be
 * retired.
 */
void
hammer2_chain_unlock(hammer2_chain_t *chain)
{
        hammer2_chain_core_t *core = chain->core;
        long *counterp;

        /*
         * Release the CST lock but with a special 1->0 transition case
         * to also drop the refs on chain.  Multiple CST locks only
         *
         * Returns non-zero if lock references remain.  When zero is
         * returned the last lock reference is retained and any shared
         * lock is upgraded to an exclusive lock for final disposition.
         */
        if (ccms_thread_unlock_zero(&core->cst)) {
                KKASSERT(chain->refs > 1);
                atomic_add_int(&chain->refs, -1);
                return;
        }

        /*
         * Shortcut the case if the data is embedded or not resolved.
         *
         * Do NOT NULL out chain->data (e.g. inode data), it might be
         * dirty.
         *
         * The DIRTYBP flag is non-applicable in this situation and can
         * be cleared to keep the flags state clean.
         */
        if (chain->bp == NULL) {
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_DIRTYBP);
                ccms_thread_unlock(&core->cst);
                hammer2_chain_drop(chain);
                return;
        }

        /*
         * Statistics
         */
        if ((chain->flags & HAMMER2_CHAIN_DIRTYBP) == 0) {
                ;
        } else if (chain->flags & HAMMER2_CHAIN_IOFLUSH) {
                switch(chain->bref.type) {
                case HAMMER2_BREF_TYPE_DATA:
                        counterp = &hammer2_ioa_file_write;
                        break;
                case HAMMER2_BREF_TYPE_INODE:
                        counterp = &hammer2_ioa_meta_write;
                        break;
                case HAMMER2_BREF_TYPE_INDIRECT:
                        counterp = &hammer2_ioa_indr_write;
                        break;
                case HAMMER2_BREF_TYPE_FREEMAP_ROOT:
                case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
                        counterp = &hammer2_ioa_fmap_write;
                        break;
                default:
                        counterp = &hammer2_ioa_volu_write;
                        break;
                }
                ++*counterp;
        } else {
                switch(chain->bref.type) {
                case HAMMER2_BREF_TYPE_DATA:
                        counterp = &hammer2_iod_file_write;
                        break;
                case HAMMER2_BREF_TYPE_INODE:
                        counterp = &hammer2_iod_meta_write;
                        break;
                case HAMMER2_BREF_TYPE_INDIRECT:
                        counterp = &hammer2_iod_indr_write;
                        break;
                case HAMMER2_BREF_TYPE_FREEMAP_ROOT:
                case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
                        counterp = &hammer2_iod_fmap_write;
                        break;
                default:
                        counterp = &hammer2_iod_volu_write;
                        break;
                }
                ++*counterp;
        }

        /*
         * Clean out the bp.
         *
         * If a device buffer was used for data be sure to destroy the
         * buffer when we are done to avoid aliases (XXX what about the
         * underlying VM pages?).
         *
         * NOTE: Freemap leaf's use reserved blocks and thus no aliasing
         *       is possible.
         */
        if (chain->bref.type == HAMMER2_BREF_TYPE_DATA)
                chain->bp->b_flags |= B_RELBUF;

        /*
         * The DIRTYBP flag tracks whether we have to bdwrite() the buffer
         * or not.  The flag will get re-set when chain_modify() is called,
         * even if MODIFIED is already set, allowing the OS to retire the
         * buffer independent of a hammer2 flus.
         */
        chain->data = NULL;
        if (chain->flags & HAMMER2_CHAIN_DIRTYBP) {
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_DIRTYBP);
                if (chain->flags & HAMMER2_CHAIN_IOFLUSH) {
                        atomic_clear_int(&chain->flags,
                                         HAMMER2_CHAIN_IOFLUSH);
                        chain->bp->b_flags |= B_RELBUF;
                        cluster_awrite(chain->bp);
                } else {
                        chain->bp->b_flags |= B_CLUSTEROK;
                        bdwrite(chain->bp);
                }
        } else {
                if (chain->flags & HAMMER2_CHAIN_IOFLUSH) {
                        atomic_clear_int(&chain->flags,
                                         HAMMER2_CHAIN_IOFLUSH);
                        chain->bp->b_flags |= B_RELBUF;
                        brelse(chain->bp);
                } else {
                        /* bp might still be dirty */
                        bqrelse(chain->bp);
                }
        }
        chain->bp = NULL;
        ccms_thread_unlock(&core->cst);
        hammer2_chain_drop(chain);
}

/*
 * Resize the chain's physical storage allocation in-place.  This may
 * replace the passed-in chain with a new chain.
 *
 * Chains can be resized smaller without reallocating the storage.
 * Resizing larger will reallocate the storage.
 *
 * Must be passed an exclusively locked parent and chain, returns a new
 * exclusively locked chain at the same index and unlocks the old chain.
 * Flushes the buffer if necessary.
 *
 * If you want the resize code to copy the data to the new block then the
 * caller should lock the chain RESOLVE_MAYBE or RESOLVE_ALWAYS.
 *
 * If the caller already holds a logical buffer containing the data and
 * intends to bdwrite() that buffer resolve with RESOLVE_NEVER.  The resize
 * operation will then not copy the (stale) data from the media.
 *
 * 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.
 *
 * XXX flags currently ignored, uses chain->bp to detect data/no-data.
 * XXX return error if cannot resize.
 */
void
hammer2_chain_resize(hammer2_trans_t *trans, hammer2_inode_t *ip,
                     struct buf *bp,
                     hammer2_chain_t *parent, hammer2_chain_t **chainp,
                     int nradix, int flags)
{
        hammer2_mount_t *hmp = trans->hmp;
        hammer2_chain_t *chain = *chainp;
        struct buf *nbp;
        hammer2_off_t pbase;
        size_t obytes;
        size_t nbytes;
        size_t bbytes;
        int boff;
        char *bdata;
        int error;

        /*
         * 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);

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

        /*
         * Delete the old chain and duplicate it at the same (parent, index),
         * returning a new chain.  This allows the old chain to still be
         * used by the flush code.  Duplication occurs in-place.
         *
         * NOTE: If we are not crossing a synchronization point the
         *       duplication code will simply reuse the existing chain
         *       structure.
         */
        hammer2_chain_delete(trans, parent, chain);
        hammer2_chain_duplicate(trans, parent, chain->index, &chain, NULL);

        /*
         * Set MODIFIED and add a chain ref to prevent destruction.  Both
         * modified flags share the same ref.  (duplicated chains do not
         * start out MODIFIED unless possibly if the duplication code
         * decided to reuse the existing chain as-is).
         *
         * If the chain is already marked MODIFIED then we can safely
         * return the previous allocation to the pool without having to
         * worry about snapshots.  XXX check flush synchronization.
         */
        if ((chain->flags & HAMMER2_CHAIN_MODIFIED) == 0) {
                atomic_set_int(&ip->flags, HAMMER2_INODE_MODIFIED);
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_MODIFIED);
                hammer2_chain_ref(chain);
        } else {
                hammer2_freemap_free(hmp, chain->bref.data_off,
                                     chain->bref.type);
        }

        /*
         * Relocate the block, even if making it smaller (because different
         * block sizes may be in different regions).
         */
        chain->bref.data_off = hammer2_freemap_alloc(hmp, chain->bref.type,
                                                     nbytes);
        chain->bytes = nbytes;
        /*ip->delta_dcount += (ssize_t)(nbytes - obytes);*/ /* XXX atomic */

        /*
         * The device buffer may be larger than the allocation size.
         */
        if ((bbytes = chain->bytes) < HAMMER2_MINIOSIZE)
                bbytes = HAMMER2_MINIOSIZE;
        pbase = chain->bref.data_off & ~(hammer2_off_t)(bbytes - 1);
        boff = chain->bref.data_off & HAMMER2_OFF_MASK & (bbytes - 1);

        /*
         * Only copy the data if resolved, otherwise the caller is
         * responsible.
         */
        if (chain->bp) {
                KKASSERT(chain->bref.type == HAMMER2_BREF_TYPE_INDIRECT ||
                         chain->bref.type == HAMMER2_BREF_TYPE_DATA);
                KKASSERT(chain != &hmp->vchain);        /* safety */

                /*
                 * The getblk() optimization can only be used if the
                 * physical block size matches the request.
                 */
                if (nbytes == bbytes) {
                        nbp = getblk(hmp->devvp, pbase, bbytes, 0, 0);
                        error = 0;
                } else {
                        error = bread(hmp->devvp, pbase, bbytes, &nbp);
                        KKASSERT(error == 0);
                }
                bdata = (char *)nbp->b_data + boff;

                /*
                 * chain->bp and chain->data represent the on-disk version
                 * of the data, where as the passed-in bp is usually a
                 * more up-to-date logical buffer.  However, there is no
                 * need to synchronize the more up-to-date data in (bp)
                 * as it will do that on its own when it flushes.
                 */
                if (nbytes < obytes) {
                        bcopy(chain->data, bdata, nbytes);
                } else {
                        bcopy(chain->data, bdata, obytes);
                        bzero(bdata + obytes, nbytes - obytes);
                }

                /*
                 * NOTE: The INITIAL state of the chain is left intact.
                 *       We depend on hammer2_chain_modify() to do the
                 *       right thing.
                 *
                 * NOTE: We set B_NOCACHE to throw away the previous bp and
                 *       any VM backing store, even if it was dirty.
                 *       Otherwise we run the risk of a logical/device
                 *       conflict on reallocation.
                 */
                chain->bp->b_flags |= B_RELBUF | B_NOCACHE;
                brelse(chain->bp);
                chain->bp = nbp;
                chain->data = (void *)bdata;
                hammer2_chain_modify(trans, chain, 0);
        }

        /*
         * Make sure the chain is marked MOVED and SUBMOD is set in the
         * parent(s) so the adjustments are picked up by flush.
         */
        if ((chain->flags & HAMMER2_CHAIN_MOVED) == 0) {
                hammer2_chain_ref(chain);
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_MOVED);
        }
        hammer2_chain_parent_setsubmod(chain);
        *chainp = chain;
}

/*
 * Convert a locked chain that was retrieved read-only to read-write,
 * duplicating it if necessary to satisfy active flush points.
 *
 * If not already marked modified a new physical block will be allocated
 * and assigned to the bref.
 *
 * If already modified and the new modification crosses a synchronization
 * point the chain is duplicated in order to allow the flush to synchronize
 * the old chain.  The new chain replaces the old.
 *
 * Non-data blocks - The chain should be locked to at least the RESOLVE_MAYBE
 *                   level or the COW operation will not work.
 *
 * Data blocks     - The chain is usually locked RESOLVE_NEVER so as not to
 *                   run the data through the device buffers.
 *
 * This function may return a different chain than was passed, in which case
 * the old chain will be unlocked and the new chain will be locked.
 */
hammer2_inode_data_t *
hammer2_chain_modify_ip(hammer2_trans_t *trans, hammer2_inode_t *ip,
                             int flags)
{
#if 0
        hammer2_chain_t *ochain;

        ochain = ip->chain;
#endif
        hammer2_chain_modify(trans, ip->chain, flags);
#if 0
        if (ochain != ip->chain) {
                hammer2_chain_ref(ip->chain);
                hammer2_chain_drop(ochain);
        }
#endif
        return(&ip->chain->data->ipdata);
}

void
hammer2_chain_modify(hammer2_trans_t *trans, hammer2_chain_t *chain, int flags)
{
        hammer2_mount_t *hmp = trans->hmp;
        hammer2_off_t pbase;
        struct buf *nbp;
        int error;
        size_t bbytes;
        size_t boff;
        void *bdata;

        /*
         * modify_tid is only update for primary modifications, not for
         * propagated brefs.  mirror_tid will be updated regardless during
         * the flush, no need to set it here.
         */
        if ((flags & HAMMER2_MODIFY_NO_MODIFY_TID) == 0)
                chain->bref.modify_tid = trans->sync_tid;

        /*
         * If the chain is already marked MODIFIED we can usually just
         * return.
         *
         * WARNING!  It is possible that a prior lock/modify sequence
         *           retired the buffer.  During this lock/modify sequence
         *           MODIFIED may still be set but the buffer could wind up
         *           clean.  Since the caller is going to modify the buffer
         *           further we have to be sure that DIRTYBP is set again.
         *
         * WARNING!  Currently the caller is responsible for handling
         *           any delete/duplication roll of the chain to account
         *           for modifications crossing synchronization points.
         */
        if (chain->flags & HAMMER2_CHAIN_MODIFIED) {
                if ((flags & HAMMER2_MODIFY_OPTDATA) == 0 &&
                    chain->bp == NULL) {
                        goto skip1;
                }
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_DIRTYBP);
                return;
        }

        /*
         * Set MODIFIED and add a chain ref to prevent destruction.  Both
         * modified flags share the same ref.
         */
        atomic_set_int(&chain->flags, HAMMER2_CHAIN_MODIFIED);
        hammer2_chain_ref(chain);

        /*
         * Adjust chain->modify_tid so the flusher knows when the
         * modification occurred.
         */
        chain->modify_tid = trans->sync_tid;

        /*
         * We must allocate the copy-on-write block.
         *
         * If the data is embedded no other action is required.
         *
         * If the data is not embedded we acquire and clear the
         * new block.  If chain->data is not NULL we then do the
         * copy-on-write.  chain->data will then be repointed to the new
         * buffer and the old buffer will be released.
         *
         * For newly created elements with no prior allocation we go
         * through the copy-on-write steps except without the copying part.
         */
        if (chain != &hmp->vchain) {
                if ((hammer2_debug & 0x0001) &&
                    (chain->bref.data_off & HAMMER2_OFF_MASK)) {
                        kprintf("Replace %d\n", chain->bytes);
                }
                chain->bref.data_off =
                        hammer2_freemap_alloc(hmp, chain->bref.type,
                                              chain->bytes);
                /* XXX failed allocation */
        }

        /*
         * If data instantiation is optional and the chain has no current
         * data association (typical for DATA and newly-created INDIRECT
         * elements), don't instantiate the buffer now.
         */
        if ((flags & HAMMER2_MODIFY_OPTDATA) && chain->bp == NULL)
                goto skip2;

skip1:
        /*
         * Setting the DIRTYBP flag will cause the buffer to be dirtied or
         * written-out on unlock.  This bit is independent of the MODIFIED
         * bit because the chain may still need meta-data adjustments done
         * by virtue of MODIFIED for its parent, and the buffer can be
         * flushed out (possibly multiple times) by the OS before that.
         *
         * Clearing the INITIAL flag (for indirect blocks) indicates that
         * a zero-fill buffer has been instantiated.
         */
        atomic_set_int(&chain->flags, HAMMER2_CHAIN_DIRTYBP);
        atomic_clear_int(&chain->flags, HAMMER2_CHAIN_INITIAL);

        /*
         * We currently should never instantiate a device buffer for a
         * file data chain.  (We definitely can for a freemap chain).
         */
        KKASSERT(chain->bref.type != HAMMER2_BREF_TYPE_DATA);

        /*
         * Execute COW operation
         */
        switch(chain->bref.type) {
        case HAMMER2_BREF_TYPE_VOLUME:
        case HAMMER2_BREF_TYPE_INODE:
                /*
                 * The data is embedded, no copy-on-write operation is
                 * needed.
                 */
                KKASSERT(chain->bp == NULL);
                break;
        case HAMMER2_BREF_TYPE_DATA:
        case HAMMER2_BREF_TYPE_INDIRECT:
        case HAMMER2_BREF_TYPE_FREEMAP_ROOT:
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
        case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
                /*
                 * Perform the copy-on-write operation
                 */
                KKASSERT(chain != &hmp->vchain);        /* safety */
                /*
                 * The device buffer may be larger than the allocation size.
                 */
                if ((bbytes = chain->bytes) < HAMMER2_MINIOSIZE)
                        bbytes = HAMMER2_MINIOSIZE;
                pbase = chain->bref.data_off & ~(hammer2_off_t)(bbytes - 1);
                boff = chain->bref.data_off & HAMMER2_OFF_MASK & (bbytes - 1);

                /*
                 * The getblk() optimization can only be used if the
                 * physical block size matches the request.
                 */
                if (chain->bytes == bbytes) {
                        nbp = getblk(hmp->devvp, pbase, bbytes, 0, 0);
                        error = 0;
                } else {
                        error = bread(hmp->devvp, pbase, bbytes, &nbp);
                        KKASSERT(error == 0);
                }
                bdata = (char *)nbp->b_data + boff;

                /*
                 * Copy or zero-fill on write depending on whether
                 * chain->data exists or not.
                 */
                if (chain->data) {
                        bcopy(chain->data, bdata, chain->bytes);
                        KKASSERT(chain->bp != NULL);
                } else {
                        bzero(bdata, chain->bytes);
                }
                if (chain->bp) {
                        chain->bp->b_flags |= B_RELBUF;
                        brelse(chain->bp);
                }
                chain->bp = nbp;
                chain->data = bdata;
                break;
        default:
                panic("hammer2_chain_modify: illegal non-embedded type %d",
                      chain->bref.type);
                break;

        }
skip2:
        if ((flags & HAMMER2_MODIFY_NOSUB) == 0)
                hammer2_chain_parent_setsubmod(chain);
}

/*
 * Mark the volume as having been modified.  This short-cut version
 * does not have to lock the volume's chain, which allows the ioctl
 * code to make adjustments to connections without deadlocking.  XXX
 *
 * No ref is made on vchain when flagging it MODIFIED.
 */
void
hammer2_modify_volume(hammer2_mount_t *hmp)
{
        hammer2_voldata_lock(hmp);
        hammer2_voldata_unlock(hmp, 1);
}

/*
 * Locate an in-memory chain.  The parent must be locked.  The in-memory
 * chain is returned with a reference and without a lock, or NULL
 * if not found.
 *
 * This function returns the chain at the specified index with the highest
 * delete_tid.  The caller must check whether the chain is flagged
 * CHAIN_DELETED or not.
 *
 * NOTE: If no chain is found the caller usually must check the on-media
 *       array to determine if a blockref exists at the index.
 */
struct hammer2_chain_find_info {
        hammer2_chain_t *best;
        hammer2_tid_t   delete_tid;
        int index;
};

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

        if (child->index < info->index)
                return(-1);
        if (child->index > info->index)
                return(1);
        return(0);
}

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

        if (info->delete_tid < child->delete_tid) {
                info->delete_tid = child->delete_tid;
                info->best = child;
        }
        return(0);
}

static
hammer2_chain_t *
hammer2_chain_find_locked(hammer2_chain_t *parent, int index)
{
        struct hammer2_chain_find_info info;

        info.index = index;
        info.delete_tid = 0;
        info.best = NULL;

        RB_SCAN(hammer2_chain_tree, &parent->core->rbtree,
                hammer2_chain_find_cmp, hammer2_chain_find_callback,
                &info);

        return (info.best);
}

hammer2_chain_t *
hammer2_chain_find(hammer2_chain_t *parent, int index)
{
        hammer2_chain_t *chain;

        spin_lock(&parent->core->cst.spin);
        chain = hammer2_chain_find_locked(parent, index);
        if (chain)
                hammer2_chain_ref(chain);
        spin_unlock(&parent->core->cst.spin);

        return (chain);
}

/*
 * Return a locked chain structure with all associated data acquired.
 * (if LOOKUP_NOLOCK is requested the returned chain is only referenced).
 *
 * Caller must hold the parent locked shared or exclusive since we may
 * need the parent's bref array to find our block.
 *
 * The returned child is locked as requested.  If NOLOCK, the returned
 * child is still at least referenced.
 */
hammer2_chain_t *
hammer2_chain_get(hammer2_chain_t *parent, int index, int flags)
{
        hammer2_blockref_t *bref;
        hammer2_mount_t *hmp = parent->hmp;
        hammer2_chain_t *chain;
        hammer2_chain_t dummy;
        int how;

        /*
         * Figure out how to lock.  MAYBE can be used to optimized
         * the initial-create state for indirect blocks.
         */
        if (flags & (HAMMER2_LOOKUP_NODATA | HAMMER2_LOOKUP_NOLOCK))
                how = HAMMER2_RESOLVE_NEVER;
        else
                how = HAMMER2_RESOLVE_MAYBE;
        if (flags & (HAMMER2_LOOKUP_SHARED | HAMMER2_LOOKUP_NOLOCK))
                how |= HAMMER2_RESOLVE_SHARED;

retry:
        /*
         * First see if we have a (possibly modified) chain element cached
         * for this (parent, index).  Acquire the data if necessary.
         *
         * If chain->data is non-NULL the chain should already be marked
         * modified.
         */
        dummy.flags = 0;
        dummy.index = index;
        dummy.delete_tid = HAMMER2_MAX_TID;
        spin_lock(&parent->core->cst.spin);
        chain = RB_FIND(hammer2_chain_tree, &parent->core->rbtree, &dummy);
        if (chain) {
                hammer2_chain_ref(chain);
                spin_unlock(&parent->core->cst.spin);
                if ((flags & HAMMER2_LOOKUP_NOLOCK) == 0)
                        hammer2_chain_lock(chain, how | HAMMER2_RESOLVE_NOREF);
                return(chain);
        }
        spin_unlock(&parent->core->cst.spin);

        /*
         * The parent chain must not be in the INITIAL state.
         */
        if (parent->flags & HAMMER2_CHAIN_INITIAL) {
                panic("hammer2_chain_get: Missing bref(1)");
                /* NOT REACHED */
        }

        /*
         * No RBTREE entry found, lookup the bref and issue I/O (switch on
         * the parent's bref to determine where and how big the array is).
         */
        switch(parent->bref.type) {
        case HAMMER2_BREF_TYPE_INODE:
                KKASSERT(index >= 0 && index < HAMMER2_SET_COUNT);
                bref = &parent->data->ipdata.u.blockset.blockref[index];
                break;
        case HAMMER2_BREF_TYPE_INDIRECT:
        case HAMMER2_BREF_TYPE_FREEMAP_ROOT:
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                KKASSERT(parent->data != NULL);
                KKASSERT(index >= 0 &&
                         index < parent->bytes / sizeof(hammer2_blockref_t));
                bref = &parent->data->npdata.blockref[index];
                break;
        case HAMMER2_BREF_TYPE_VOLUME:
                KKASSERT(index >= 0 && index < HAMMER2_SET_COUNT);
                bref = &hmp->voldata.sroot_blockset.blockref[index];
                break;
        default:
                bref = NULL;
                panic("hammer2_chain_get: unrecognized blockref type: %d",
                      parent->bref.type);
        }
        if (bref->type == 0) {
                panic("hammer2_chain_get: Missing bref(2)");
                /* NOT REACHED */
        }

        /*
         * Allocate a chain structure representing the existing media
         * entry.  Resulting chain has one ref and is not locked.
         *
         * The locking operation we do later will issue I/O to read it.
         */
        chain = hammer2_chain_alloc(hmp, bref);
        hammer2_chain_core_alloc(chain, NULL);  /* ref'd chain returned */

        /*
         * 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.
         */
        KKASSERT(parent->refs > 0);
        spin_lock(&parent->core->cst.spin);
        chain->parent = parent;
        chain->index = index;
        if (RB_INSERT(hammer2_chain_tree, &parent->core->rbtree, chain)) {
                chain->parent = NULL;
                chain->index = -1;
                spin_unlock(&parent->core->cst.spin);
                hammer2_chain_drop(chain);
                goto retry;
        }
        atomic_set_int(&chain->flags, HAMMER2_CHAIN_ONRBTREE);
        hammer2_chain_ref(parent);              /* chain->parent ref */
        spin_unlock(&parent->core->cst.spin);

        /*
         * Our new chain is referenced but NOT locked.  Lock the chain
         * below.  The locking operation also resolves its data.
         *
         * If NOLOCK is set the release will release the one-and-only lock.
         */
        if ((flags & HAMMER2_LOOKUP_NOLOCK) == 0) {
                hammer2_chain_lock(chain, how); /* recusive lock */
                hammer2_chain_drop(chain);      /* excess ref */
        }
        return (chain);
}

/*
 * Lookup initialization/completion API
 */
hammer2_chain_t *
hammer2_chain_lookup_init(hammer2_chain_t *parent, int flags)
{
        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);
}


/*
 * Locate any key between key_beg and 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.
 *
 * WARNING!  THIS DOES NOT RETURN KEYS IN LOGICAL KEY ORDER!  ANY KEY
 *           WITHIN THE RANGE CAN BE RETURNED.  HOWEVER, AN ITERATION
 *           WHICH PICKS UP WHERE WE LEFT OFF WILL CONTINUE THE SCAN.
 *
 * (*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.
 *
 * NULL is returned if no match was found, but (*parentp) will still
 * potentially be adjusted.
 *
 * 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.
 */
hammer2_chain_t *
hammer2_chain_lookup(hammer2_chain_t **parentp,
                     hammer2_key_t key_beg, hammer2_key_t key_end,
                     int flags)
{
        hammer2_mount_t *hmp;
        hammer2_chain_t *parent;
        hammer2_chain_t *chain;
        hammer2_chain_t *tmp;
        hammer2_blockref_t *base;
        hammer2_blockref_t *bref;
        hammer2_key_t scan_beg;
        hammer2_key_t scan_end;
        int count = 0;
        int i;
        int how_always = HAMMER2_RESOLVE_ALWAYS;
        int how_maybe = HAMMER2_RESOLVE_MAYBE;

        if (flags & (HAMMER2_LOOKUP_SHARED | HAMMER2_LOOKUP_NOLOCK)) {
                how_maybe |= HAMMER2_RESOLVE_SHARED;
                how_always |= HAMMER2_RESOLVE_SHARED;
        }

        /*
         * Recurse (*parentp) upward if necessary until the parent completely
         * encloses the key range or we hit the inode.
         */
        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;
                hammer2_chain_ref(parent);              /* ref old parent */
                hammer2_chain_unlock(parent);           /* unlock old parent */
                parent = parent->parent;
                while (parent->duplink)
                        parent = parent->duplink;

                                                        /* lock new parent */
                hammer2_chain_lock(parent, how_maybe);
                hammer2_chain_drop(*parentp);           /* drop old parent */
                *parentp = parent;                      /* new parent */
        }

again:
        /*
         * 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.op_flags & HAMMER2_OPFLAG_DIRECTDATA) {
                        if (flags & HAMMER2_LOOKUP_NOLOCK)
                                hammer2_chain_ref(parent);
                        else
                                hammer2_chain_lock(parent, how_always);
                        return (parent);
                }
                base = &parent->data->ipdata.u.blockset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        case HAMMER2_BREF_TYPE_INDIRECT:
        case HAMMER2_BREF_TYPE_FREEMAP_ROOT:
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                /*
                 * 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.blockref[0];
                }
                count = parent->bytes / sizeof(hammer2_blockref_t);
                break;
        case HAMMER2_BREF_TYPE_VOLUME:
                base = &hmp->voldata.sroot_blockset.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 */
        }

        /*
         * If the element and key overlap we use the element.
         *
         * NOTE! Deleted elements are effectively invisible.  Deletions
         *       proactively clear the parent bref to the deleted child
         *       so we do not try to shadow here to avoid parent updates
         *       (which would be difficult since multiple deleted elements
         *       might represent different flush synchronization points).
         */
        bref = NULL;
        for (i = 0; i < count; ++i) {
                tmp = hammer2_chain_find(parent, i);
                if (tmp) {
                        if (tmp->flags & HAMMER2_CHAIN_DELETED)
                                continue;
                        bref = &tmp->bref;
                        KKASSERT(bref->type != 0);
                } else if (base == NULL || base[i].type == 0) {
                        continue;
                } else {
                        bref = &base[i];
                }
                scan_beg = bref->key;
                scan_end = scan_beg + ((hammer2_key_t)1 << bref->keybits) - 1;
                if (tmp)
                        hammer2_chain_drop(tmp);
                if (key_beg <= scan_end && key_end >= scan_beg)
                        break;
        }
        if (i == count) {
                if (key_beg == key_end)
                        return (NULL);
                return (hammer2_chain_next(parentp, NULL,
                                           key_beg, key_end, flags));
        }

        /*
         * Acquire the new chain element.  If the chain element is an
         * indirect block we must search recursively.
         *
         * It is possible for the tmp chain above to be removed from
         * the RBTREE but the parent lock ensures it would not have been
         * destroyed from the media, so the chain_get() code will simply
         * reload it from the media in that case.
         */
        chain = hammer2_chain_get(parent, i, flags);
        if (chain == NULL)
                return (NULL);

        /*
         * If the chain element is an indirect block it becomes the new
         * parent and we loop on it.
         *
         * 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 (chain->bref.type == HAMMER2_BREF_TYPE_INDIRECT ||
            chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_NODE) {
                hammer2_chain_unlock(parent);
                *parentp = parent = chain;
                if (flags & HAMMER2_LOOKUP_NOLOCK) {
                        hammer2_chain_lock(chain, how_maybe);
                        hammer2_chain_drop(chain);      /* excess ref */
                } else if ((flags & HAMMER2_LOOKUP_NODATA) &&
                           chain->data == NULL) {
                        hammer2_chain_ref(chain);
                        hammer2_chain_unlock(chain);
                        hammer2_chain_lock(chain, how_maybe |
                                                  HAMMER2_RESOLVE_NOREF);
                }
                goto again;
        }

        /*
         * All done, return the chain
         */
        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.
 *
 * parent must be locked on entry and remains locked throughout.  chain's
 * lock status must match flags.  Chain is always at least referenced.
 */
hammer2_chain_t *
hammer2_chain_next(hammer2_chain_t **parentp, hammer2_chain_t *chain,
                   hammer2_key_t key_beg, hammer2_key_t key_end,
                   int flags)
{
        hammer2_mount_t *hmp;
        hammer2_chain_t *parent;
        hammer2_chain_t *tmp;
        hammer2_blockref_t *base;
        hammer2_blockref_t *bref;
        hammer2_key_t scan_beg;
        hammer2_key_t scan_end;
        int i;
        int how_maybe = HAMMER2_RESOLVE_MAYBE;
        int count;

        if (flags & (HAMMER2_LOOKUP_SHARED | HAMMER2_LOOKUP_NOLOCK))
                how_maybe |= HAMMER2_RESOLVE_SHARED;

        parent = *parentp;
        hmp = parent->hmp;

again:
        /*
         * Calculate the next index and recalculate the parent if necessary.
         */
        if (chain) {
                /*
                 * Continue iteration within current parent.  If not NULL
                 * the passed-in chain may or may not be locked, based on
                 * the LOOKUP_NOLOCK flag (passed in as returned from lookup
                 * or a prior next).
                 */
                i = chain->index + 1;
                if (flags & HAMMER2_LOOKUP_NOLOCK)
                        hammer2_chain_drop(chain);
                else
                        hammer2_chain_unlock(chain);

                /*
                 * Any scan where the lookup returned degenerate data embedded
                 * in the inode has an invalid index and must terminate.
                 */
                if (chain == parent)
                        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.
                 */
                hammer2_chain_t *nparent;

                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)
                        return (NULL);

                i = parent->index + 1;
                nparent = parent->parent;
                while (nparent->duplink)
                        nparent = nparent->duplink;
                hammer2_chain_ref(nparent);     /* ref new parent */
                hammer2_chain_unlock(parent);   /* unlock old parent */
                                                /* lock new parent */
                hammer2_chain_lock(nparent, how_maybe);
                hammer2_chain_drop(nparent);    /* drop excess ref */
                *parentp = parent = nparent;
        }

again2:
        /*
         * Locate the blockref array.  Currently we do a fully associative
         * search through the array.
         */
        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_ROOT:
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                if (parent->flags & HAMMER2_CHAIN_INITIAL) {
                        base = NULL;
                } else {
                        KKASSERT(parent->data != NULL);
                        base = &parent->data->npdata.blockref[0];
                }
                count = parent->bytes / sizeof(hammer2_blockref_t);
                break;
        case HAMMER2_BREF_TYPE_VOLUME:
                base = &hmp->voldata.sroot_blockset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        default:
                panic("hammer2_chain_next: unrecognized blockref type: %d",
                      parent->bref.type);
                base = NULL;    /* safety */
                count = 0;      /* safety */
                break;
        }
        KKASSERT(i <= count);

        /*
         * Look for the key.  If we are unable to find a match and an exact
         * match was requested we return NULL.  If a range was requested we
         * run hammer2_chain_next() to iterate.
         *
         * NOTE! Deleted elements are effectively invisible.  Deletions
         *       proactively clear the parent bref to the deleted child
         *       so we do not try to shadow here to avoid parent updates
         *       (which would be difficult since multiple deleted elements
         *       might represent different flush synchronization points).
         */
        bref = NULL;
        while (i < count) {
                tmp = hammer2_chain_find(parent, i);
                if (tmp) {
                        if (tmp->flags & HAMMER2_CHAIN_DELETED) {
                                ++i;
                                continue;
                        }
                        bref = &tmp->bref;
                } else if (base == NULL || base[i].type == 0) {
                        ++i;
                        continue;
                } else {
                        bref = &base[i];
                }
                scan_beg = bref->key;
                scan_end = scan_beg + ((hammer2_key_t)1 << bref->keybits) - 1;
                if (tmp)
                        hammer2_chain_drop(tmp);
                if (key_beg <= scan_end && key_end >= scan_beg)
                        break;
                ++i;
        }

        /*
         * If we couldn't find a match recurse up a parent to continue the
         * search.
         */
        if (i == count)
                goto again;

        /*
         * Acquire the new chain element.  If the chain element is an
         * indirect block we must search recursively.
         */
        chain = hammer2_chain_get(parent, i, flags);
        if (chain == NULL)
                return (NULL);

        /*
         * If the chain element is an indirect block it becomes the new
         * parent and we loop on it.
         *
         * 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 (chain->bref.type == HAMMER2_BREF_TYPE_INDIRECT ||
            chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_NODE) {
                hammer2_chain_unlock(parent);
                *parentp = parent = chain;
                chain = NULL;
                if (flags & HAMMER2_LOOKUP_NOLOCK) {
                        hammer2_chain_lock(parent, how_maybe);
                        hammer2_chain_drop(parent);     /* excess ref */
                } else if ((flags & HAMMER2_LOOKUP_NODATA) &&
                           parent->data == NULL) {
                        hammer2_chain_ref(parent);
                        hammer2_chain_unlock(parent);
                        hammer2_chain_lock(parent, how_maybe |
                                                   HAMMER2_RESOLVE_NOREF);
                }
                i = 0;
                goto again2;
        }

        /*
         * All done, return chain
         */
        return (chain);
}

/*
 * Create and return a new hammer2 system memory structure of the specified
 * key, type and size and insert it RELATIVE TO (PARENT).
 *
 * (parent) is typically either an inode or an indirect block, acquired
 * acquired as a side effect of issuing a prior failed lookup.  parent
 * must be locked and held.  Do not pass the inode chain to this function
 * unless that is the chain returned by the failed lookup.
 *
 * (*chainp) is either NULL, a newly allocated chain, or a chain allocated
 * via hammer2_chain_duplicate().  When not NULL, the passed-in chain must
 * NOT be attached to any parent, and will be attached by this function.
 * This mechanic is used by the rename code.
 *
 * Non-indirect types will automatically allocate indirect blocks as required
 * if the new item does not fit in the current (parent).
 *
 * Indirect types will move a portion of the existing blockref array in
 * (parent) into the new indirect type and then use one of the free slots
 * to emplace the new indirect type.
 *
 * A new locked chain element is returned of the specified type.  The
 * element may or may not have a data area associated with it:
 *
 *      VOLUME          not allowed here
 *      INODE           kmalloc()'d data area is set up
 *      INDIRECT        not allowed here
 *      DATA            no data area will be set-up (caller is expected
 *                      to have logical buffers, we don't want to alias
 *                      the data onto device buffers!).
 *
 * Requires an exclusively locked parent.
 */
int
hammer2_chain_create(hammer2_trans_t *trans, hammer2_chain_t *parent,
                     hammer2_chain_t **chainp,
                     hammer2_key_t key, int keybits, int type, size_t bytes)
{
        hammer2_mount_t *hmp;
        hammer2_chain_t *chain;
        hammer2_chain_t *child;
        hammer2_blockref_t dummy;
        hammer2_blockref_t *base;
        int unlock_parent = 0;
        int allocated = 0;
        int error = 0;
        int count;
        int i;

        KKASSERT(ccms_thread_lock_owned(&parent->core->cst));
        hmp = parent->hmp;
        chain = *chainp;

        if (chain == NULL) {
                /*
                 * First allocate media space and construct the dummy bref,
                 * then allocate the in-memory chain structure.
                 */
                bzero(&dummy, sizeof(dummy));
                dummy.type = type;
                dummy.key = key;
                dummy.keybits = keybits;
                dummy.data_off = hammer2_allocsize(bytes);
                dummy.methods = parent->bref.methods;
                chain = hammer2_chain_alloc(hmp, &dummy);
                hammer2_chain_core_alloc(chain, NULL);
                ccms_thread_lock(&chain->core->cst, CCMS_STATE_EXCLUSIVE);
                allocated = 1;

                /*
                 * We do NOT set INITIAL here (yet).  INITIAL is only
                 * used for indirect blocks.
                 *
                 * 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:
                        panic("hammer2_chain_create: called with volume type");
                        break;
                case HAMMER2_BREF_TYPE_INODE:
                        KKASSERT(bytes == HAMMER2_INODE_BYTES);
                        chain->data = kmalloc(sizeof(chain->data->ipdata),
                                              hmp->minode, M_WAITOK | M_ZERO);
                        break;
                case HAMMER2_BREF_TYPE_INDIRECT:
                        panic("hammer2_chain_create: cannot be used to"
                              "create indirect block");
                        break;
                case HAMMER2_BREF_TYPE_FREEMAP_ROOT:
                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:
                case HAMMER2_BREF_TYPE_DATA:
                default:
                        /* leave chain->data NULL */
                        KKASSERT(chain->data == NULL);
                        break;
                }
        } else {
                /*
                 * Potentially update the chain's key/keybits.
                 */
                chain->bref.key = key;
                chain->bref.keybits = keybits;
        }

again:
        /*
         * Locate a free blockref in the parent's array
         */
        switch(parent->bref.type) {
        case HAMMER2_BREF_TYPE_INODE:
                KKASSERT((parent->data->ipdata.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_ROOT:
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                if (parent->flags & HAMMER2_CHAIN_INITIAL) {
                        base = NULL;
                } else {
                        KKASSERT(parent->data != NULL);
                        base = &parent->data->npdata.blockref[0];
                }
                count = parent->bytes / sizeof(hammer2_blockref_t);
                break;
        case HAMMER2_BREF_TYPE_VOLUME:
                KKASSERT(parent->data != NULL);
                base = &hmp->voldata.sroot_blockset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        default:
                panic("hammer2_chain_create: unrecognized blockref type: %d",
                      parent->bref.type);
                count = 0;
                break;
        }

        /*
         * Scan for an unallocated bref, also skipping any slots occupied
         * by in-memory chain elements that may not yet have been updated
         * in the parent's bref array.
         *
         * We don't have to hold the spinlock to save an empty slot as
         * new slots can only transition from empty if the parent is
         * locked exclusively.
         */

        spin_lock(&parent->core->cst.spin);
        for (i = 0; i < count; ++i) {
                child = hammer2_chain_find_locked(parent, i);
                if (child) {
                        if (child->flags & HAMMER2_CHAIN_DELETED)
                                break;
                        continue;
                }
                if (base == NULL)
                        break;
                if (base[i].type == 0)
                        break;
        }
        spin_unlock(&parent->core->cst.spin);

        /*
         * 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 move 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 (i == count) {
                hammer2_chain_t *nparent;

                nparent = hammer2_chain_create_indirect(trans, parent,
                                                        key, keybits,
                                                        &error);
                if (nparent == NULL) {
                        if (allocated)
                                hammer2_chain_free(chain);
                        chain = NULL;
                        goto done;
                }
                if (parent != nparent) {
                        if (unlock_parent)
                                hammer2_chain_unlock(parent);
                        parent = nparent;
                        unlock_parent = 1;
                }
                goto again;
        }

        /*
         * Link the chain into its parent.  Later on we will have to set
         * the MOVED bit in situations where we don't mark the new chain
         * as being modified.
         */
        if (chain->parent != NULL)
                panic("hammer2: hammer2_chain_create: chain already connected");
        KKASSERT(chain->parent == NULL);
        KKASSERT((chain->flags & HAMMER2_CHAIN_DELETED) == 0);

        chain->parent = parent;
        chain->index = i;
        KKASSERT(parent->refs > 0);
        spin_lock(&parent->core->cst.spin);
        if (RB_INSERT(hammer2_chain_tree, &parent->core->rbtree, chain))
                panic("hammer2_chain_link: collision");
        atomic_set_int(&chain->flags, HAMMER2_CHAIN_ONRBTREE);
        hammer2_chain_ref(parent);              /* chain->parent ref */
        spin_unlock(&parent->core->cst.spin);

        /*
         * (allocated) indicates that this is a newly-created chain element
         * rather than a renamed chain element.
         *
         * In this situation we want to place the chain element in
         * the MODIFIED state.  The caller expects it to NOT be in the
         * INITIAL state.
         *
         * The data area will be set up as follows:
         *
         *      VOLUME          not allowed here.
         *
         *      INODE           embedded data are will be set-up.
         *
         *      INDIRECT        not allowed here.
         *
         *      DATA            no data area will be set-up (caller is expected
         *                      to have logical buffers, we don't want to alias
         *                      the data onto device buffers!).
         */
        if (allocated) {
                switch(chain->bref.type) {
                case HAMMER2_BREF_TYPE_DATA:
                case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
                        hammer2_chain_modify(trans, chain,
                                             HAMMER2_MODIFY_OPTDATA);
                        break;
                case HAMMER2_BREF_TYPE_INDIRECT:
                case HAMMER2_BREF_TYPE_FREEMAP_ROOT:
                case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                        /* not supported in this function */
                        panic("hammer2_chain_create: bad type");
                        atomic_set_int(&chain->flags, HAMMER2_CHAIN_INITIAL);
                        hammer2_chain_modify(trans, chain,
                                             HAMMER2_MODIFY_OPTDATA);
                        break;
                default:
                        hammer2_chain_modify(trans, chain, 0);
                        break;
                }
        } else {
                /*
                 * When reconnecting a chain we must set MOVED and setsubmod
                 * so the flush recognizes that it must update the bref in
                 * the parent.
                 */
                if ((chain->flags & HAMMER2_CHAIN_MOVED) == 0) {
                        hammer2_chain_ref(chain);
                        atomic_set_int(&chain->flags, HAMMER2_CHAIN_MOVED);
                }
                hammer2_chain_parent_setsubmod(chain);
        }

done:
        *chainp = chain;
        if (unlock_parent)
                hammer2_chain_unlock(parent);
        return (error);
}

/*
 * Replace (*chainp) with a duplicate.  The original *chainp is unlocked
 * and the replacement will be returned locked.  Both the original and the
 * new chain will share the same RBTREE (have the same chain->core), with
 * the new chain becoming the 'current' chain (meaning it is the first in
 * the linked list at core->chain_first).
 *
 * If (parent, i) then the new duplicated chain is inserted under the parent
 * at the specified index (the parent must not have a ref at that index).
 *
 * If (NULL, -1) then the new 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).
 *
 * NOTE! Duplication is used in order to retain the original topology to
 *       support flush synchronization points.  Both the original and the
 *       new chain will have the same transaction id and thus the operation
 *       appears atomic on the media.
 */
void
hammer2_chain_duplicate(hammer2_trans_t *trans, hammer2_chain_t *parent, int i,
                        hammer2_chain_t **chainp, hammer2_blockref_t *bref)
{
        hammer2_mount_t *hmp = trans->hmp;
        hammer2_blockref_t *base;
        hammer2_chain_t *ochain;
        hammer2_chain_t *nchain;
        hammer2_chain_t *scan;
        size_t bytes;
        int count;

        /*
         * First 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), and copying any inline
         * data.
         */
        ochain = *chainp;
        if (bref == NULL)
                bref = &ochain->bref;
        nchain = hammer2_chain_alloc(hmp, bref);
        hammer2_chain_core_alloc(nchain, ochain->core);

        bytes = (hammer2_off_t)1 <<
                (int)(bref->data_off & HAMMER2_OFF_MASK_RADIX);
        nchain->bytes = bytes;

        /*
         * Be sure to copy the INITIAL flag as well or we could end up
         * loading garbage from the bref.
         */
        if (ochain->flags & HAMMER2_CHAIN_INITIAL)
                atomic_set_int(&nchain->flags, HAMMER2_CHAIN_INITIAL);

        /*
         * If the old chain is modified the new one must be too,
         * but we only want to allocate a new bref.
         */
        if (ochain->flags & HAMMER2_CHAIN_MODIFIED) {
                /*
                 * When duplicating chains the MODIFIED state is inherited.
                 * A new bref typically must be allocated.  However, file
                 * data chains may already have the data offset assigned
                 * to a logical buffer cache buffer so we absolutely cannot
                 * allocate a new bref here for TYPE_DATA.
                 *
                 * Basically the flusher core only dumps media topology
                 * and meta-data, not file data.  The VOP_FSYNC code deals
                 * with the file data.  XXX need back-pointer to inode.
                 */
                if (nchain->bref.type == HAMMER2_BREF_TYPE_DATA) {
                        atomic_set_int(&nchain->flags, HAMMER2_CHAIN_MODIFIED);
                        hammer2_chain_ref(nchain);
                } else {
                        hammer2_chain_modify(trans, nchain,
                                             HAMMER2_MODIFY_OPTDATA);
                }
        } else if (nchain->flags & HAMMER2_CHAIN_INITIAL) {
                /*
                 * When duplicating chains in the INITITAL state we need
                 * to ensure that the chain is marked modified so a
                 * block is properly assigned to it, otherwise the MOVED
                 * bit won't do the right thing.
                 */
                KKASSERT (nchain->bref.type != HAMMER2_BREF_TYPE_DATA);
                hammer2_chain_modify(trans, nchain, HAMMER2_MODIFY_OPTDATA);
        }
        if (parent || (ochain->flags & HAMMER2_CHAIN_MOVED)) {
                atomic_set_int(&nchain->flags, HAMMER2_CHAIN_MOVED);
                hammer2_chain_ref(nchain);
        }
        atomic_set_int(&nchain->flags, HAMMER2_CHAIN_SUBMODIFIED);

        switch(nchain->bref.type) {
        case HAMMER2_BREF_TYPE_VOLUME:
                panic("hammer2_chain_duplicate: cannot be called w/volhdr");
                break;
        case HAMMER2_BREF_TYPE_INODE:
                KKASSERT(bytes == HAMMER2_INODE_BYTES);
                if (ochain->data) {
                        nchain->data = kmalloc(sizeof(nchain->data->ipdata),
                                              hmp->minode, M_WAITOK | M_ZERO);
                        nchain->data->ipdata = ochain->data->ipdata;
                }
                break;
        case HAMMER2_BREF_TYPE_INDIRECT:
                if ((nchain->flags & HAMMER2_CHAIN_MODIFIED) &&
                    nchain->data) {
                        bcopy(ochain->data, nchain->data,
                              nchain->bytes);
                }
                break;
        case HAMMER2_BREF_TYPE_FREEMAP_ROOT:
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                panic("hammer2_chain_duplicate: cannot be used to"
                      "create a freemap root or node");
                break;
        case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
        case HAMMER2_BREF_TYPE_DATA:
        default:
                if ((nchain->flags & HAMMER2_CHAIN_MODIFIED) &&
                    nchain->data) {
                        bcopy(ochain->data, nchain->data,
                              nchain->bytes);
                }
                /* leave chain->data NULL */
                KKASSERT(nchain->data == NULL);
                break;
        }

        /*
         * Both chains must be locked for us to be able to set the
         * duplink.  The caller may expect valid data.
         *
         * Unmodified duplicated blocks may have the same bref, we
         * must be careful to avoid buffer cache deadlocks so we
         * unlock the old chain before resolving the new one.
         *
         * Insert nchain at the end of the duplication list.
         */
        hammer2_chain_lock(nchain, HAMMER2_RESOLVE_NEVER);

        for (;;) {
                for (scan = ochain; scan->duplink; scan = scan->duplink)
                        ;
                spin_lock(&scan->core->cst.spin);
                if (scan->duplink == NULL) {
                        /* inherits excess ref from alloc */
                        scan->duplink = nchain;
                        spin_unlock(&scan->core->cst.spin);
                        break;
                }
                spin_unlock(&scan->core->cst.spin);
        }

        hammer2_chain_unlock(ochain);
        *chainp = nchain;
        hammer2_chain_lock(nchain, HAMMER2_RESOLVE_MAYBE);
        hammer2_chain_unlock(nchain);

        /*
         * If parent is not NULL, insert into the parent at the requested
         * index.  The newly duplicated chain must be marked MOVED and
         * SUBMODIFIED set in its parent(s).
         */
        if (parent) {
                /*
                 * Locate a free blockref in the parent's array
                 */
                KKASSERT(ccms_thread_lock_owned(&parent->core->cst));
                switch(parent->bref.type) {
                case HAMMER2_BREF_TYPE_INODE:
                        KKASSERT((parent->data->ipdata.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_ROOT:
                case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                        if (parent->flags & HAMMER2_CHAIN_INITIAL) {
                                base = NULL;
                        } else {
                                KKASSERT(parent->data != NULL);
                                base = &parent->data->npdata.blockref[0];
                        }
                        count = parent->bytes / sizeof(hammer2_blockref_t);
                        break;
                case HAMMER2_BREF_TYPE_VOLUME:
                        KKASSERT(parent->data != NULL);
                        base = &hmp->voldata.sroot_blockset.blockref[0];
                        count = HAMMER2_SET_COUNT;
                        break;
                default:
                        panic("hammer2_chain_create: unrecognized "
                              "blockref type: %d",
                              parent->bref.type);
                        count = 0;
                        break;
                }
                KKASSERT(i >= 0 && i < count);
                KKASSERT(base == NULL || base[i].type == 0);

                nchain->parent = parent;
                nchain->index = i;
                KKASSERT((nchain->flags & HAMMER2_CHAIN_DELETED) == 0);
                KKASSERT(parent->refs > 0);
                spin_lock(&parent->core->cst.spin);
                if (RB_INSERT(hammer2_chain_tree, &parent->core->rbtree, nchain))
                        panic("hammer2_chain_link: collision");
                atomic_set_int(&nchain->flags, HAMMER2_CHAIN_ONRBTREE);
                hammer2_chain_ref(parent);      /* nchain->parent ref */
                spin_unlock(&parent->core->cst.spin);

                if ((nchain->flags & HAMMER2_CHAIN_MOVED) == 0) {
                        hammer2_chain_ref(nchain);
                        atomic_set_int(&nchain->flags, HAMMER2_CHAIN_MOVED);
                }
                hammer2_chain_parent_setsubmod(nchain);
        }
}

/*
 * 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
hammer2_chain_t *
hammer2_chain_create_indirect(hammer2_trans_t *trans, hammer2_chain_t *parent,
                              hammer2_key_t create_key, int create_bits,
                              int *errorp)
{
        hammer2_mount_t *hmp = trans->hmp;
        hammer2_blockref_t *base;
        hammer2_blockref_t *bref;
        hammer2_chain_t *chain;
        hammer2_chain_t *child;
        hammer2_chain_t *ichain;
        hammer2_chain_t dummy;
        hammer2_key_t key = create_key;
        int keybits = create_bits;
        int locount = 0;
        int hicount = 0;
        int count;
        int nbytes;
        int i;

        /*
         * 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.
         */
        KKASSERT(ccms_thread_lock_owned(&parent->core->cst));
        *errorp = 0;

        /*hammer2_chain_modify(trans, parent, HAMMER2_MODIFY_OPTDATA);*/
        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_ROOT:
                case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                        count = parent->bytes / sizeof(hammer2_blockref_t);
                        break;
                case HAMMER2_BREF_TYPE_VOLUME:
                        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_ROOT:
                case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                        base = &parent->data->npdata.blockref[0];
                        count = parent->bytes / sizeof(hammer2_blockref_t);
                        break;
                case HAMMER2_BREF_TYPE_VOLUME:
                        base = &hmp->voldata.sroot_blockset.blockref[0];
                        count = HAMMER2_SET_COUNT;
                        break;
                default:
                        panic("hammer2_chain_create_indirect: "
                              "unrecognized blockref type: %d",
                              parent->bref.type);
                        count = 0;
                        break;
                }
        }

        /*
         * Scan for an unallocated bref, also skipping any slots occupied
         * by in-memory chain elements which may not yet have been updated
         * in the parent's bref array.
         *
         * Deleted elements are ignored.
         */
        bzero(&dummy, sizeof(dummy));
        dummy.delete_tid = HAMMER2_MAX_TID;

        spin_lock(&parent->core->cst.spin);
        for (i = 0; i < count; ++i) {
                int nkeybits;

                child = hammer2_chain_find_locked(parent, i);
                if (child) {
                        if (child->flags & HAMMER2_CHAIN_DELETED)
                                continue;
                        bref = &child->bref;
                } else if (base && base[i].type) {
                        bref = &base[i];
                } else {
                        continue;
                }

                /*
                 * 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 index %d chain %p bref %p\n", i, 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
                 * higher half of the (new) key range.
                 */
                if (((hammer2_key_t)1 << (nkeybits - 1)) & bref->key)
                        ++hicount;
                else
                        ++locount;
        }
        spin_unlock(&parent->core->cst.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).
         */
        key &= ~(((hammer2_key_t)1 << keybits) - 1);
        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;
        }

        /*
         * How big should our new indirect block be?  It has to be at least
         * as large as its parent.
         */
        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))
                nbytes = count * sizeof(hammer2_blockref_t);

        /*
         * Ok, create our new indirect block
         */
        switch(parent->bref.type) {
        case HAMMER2_BREF_TYPE_FREEMAP_ROOT:
        case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                dummy.bref.type = HAMMER2_BREF_TYPE_FREEMAP_NODE;
                break;
        default:
                dummy.bref.type = HAMMER2_BREF_TYPE_INDIRECT;
                break;
        }
        dummy.bref.key = key;
        dummy.bref.keybits = keybits;
        dummy.bref.data_off = hammer2_allocsize(nbytes);
        dummy.bref.methods = parent->bref.methods;

        ichain = hammer2_chain_alloc(hmp, &dummy.bref);
        atomic_set_int(&ichain->flags, HAMMER2_CHAIN_INITIAL);
        hammer2_chain_core_alloc(ichain, NULL);
        hammer2_chain_lock(ichain, HAMMER2_RESOLVE_MAYBE);
        hammer2_chain_drop(ichain);     /* excess ref from alloc */

        /*
         * 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(trans, ichain, HAMMER2_MODIFY_OPTDATA);

        /*
         * Iterate the original parent and move the matching brefs into
         * the new indirect block.
         *
         * XXX handle flushes.
         */
        spin_lock(&parent->core->cst.spin);
        for (i = 0; i < count; ++i) {
                /*
                 * For keying purposes access the bref from the media or
                 * from our in-memory cache.  In cases where the in-memory
                 * cache overrides the media the keyrefs will be the same
                 * anyway so we can avoid checking the cache when the media
                 * has a key.
                 */
                child = hammer2_chain_find_locked(parent, i);
                if (child) {
                        if (child->flags & HAMMER2_CHAIN_DELETED) {
                                if (ichain->index < 0)
                                        ichain->index = i;
                                continue;
                        }
                        bref = &child->bref;
                } else if (base && base[i].type) {
                        bref = &base[i];
                } else {
                        if (ichain->index < 0)
                                ichain->index = i;
                        continue;
                }

                /*
                 * Skip keys not in the chosen half (low or high), only bit
                 * (keybits - 1) needs to be compared but for safety we
                 * will compare all msb bits plus that bit again.
                 */
                if ((~(((hammer2_key_t)1 << keybits) - 1) &
                    (key ^ bref->key)) != 0) {
                        continue;
                }

                /*
                 * This element is being moved from the parent, its slot
                 * is available for our new indirect block.
                 */
                if (ichain->index < 0)
                        ichain->index = i;

                /*
                 * Load the new indirect block by acquiring or allocating
                 * the related chain entries, then move them to the new
                 * parent (ichain) by deleting them from their old location
                 * and inserting a duplicate of the chain and any modified
                 * sub-chain in the new location.
                 *
                 * We must set MOVED in the chain being duplicated and
                 * SUBMODIFIED in the parent(s) so the flush code knows
                 * what is going on.  The latter is done after the loop.
                 *
                 * WARNING! chain->cst.spin must be held when chain->parent is
                 *          modified, even though we own the full blown lock,
                 *          to deal with setsubmod and rename races.
                 *          (XXX remove this req).
                 */
                spin_unlock(&parent->core->cst.spin);
                chain = hammer2_chain_get(parent, i, HAMMER2_LOOKUP_NODATA);
                hammer2_chain_delete(trans, parent, chain);
                hammer2_chain_duplicate(trans, ichain, i, &chain, NULL);

                hammer2_chain_unlock(chain);
                KKASSERT(parent->refs > 0);
                chain = NULL;
                spin_lock(&parent->core->cst.spin);
        }
        spin_unlock(&parent->core->cst.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 MOVED 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.
         */
        if (ichain->index < 0)
                kprintf("indirect parent %p count %d key %016jx/%d\n",
                        parent, count, (intmax_t)key, keybits);
        KKASSERT(ichain->index >= 0);
        KKASSERT((ichain->flags & HAMMER2_CHAIN_ONRBTREE) == 0);
        spin_lock(&parent->core->cst.spin);
        if (RB_INSERT(hammer2_chain_tree, &parent->core->rbtree, ichain))
                panic("hammer2_chain_create_indirect: ichain insertion");
        atomic_set_int(&ichain->flags, HAMMER2_CHAIN_ONRBTREE);
        ichain->parent = parent;
        hammer2_chain_ref(parent);      /* ichain->parent ref */
        spin_unlock(&parent->core->cst.spin);
        KKASSERT(parent->duplink == NULL); /* XXX mus be inside spin */

        /*
         * Mark the new indirect block modified after insertion, which
         * will propagate up through parent all the way to the root and
         * also allocate the physical block in ichain for our caller,
         * and assign ichain->data to a pre-zero'd space (because there
         * is not prior data to copy into it).
         *
         * We have to set SUBMODIFIED in ichain's flags manually so the
         * flusher knows it has to recurse through it to get to all of
         * our moved blocks, then call setsubmod() to set the bit
         * recursively.
         */
        /*hammer2_chain_modify(trans, ichain, HAMMER2_MODIFY_OPTDATA);*/
        hammer2_chain_parent_setsubmod(ichain);
        atomic_set_int(&ichain->flags, HAMMER2_CHAIN_SUBMODIFIED);

        /*
         * Figure out what to return.
         */
        if (create_bits > keybits) {
                /*
                 * Key being created is way outside the key range,
                 * return the original parent.
                 */
                hammer2_chain_unlock(ichain);
        } else 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);
        } else {
                /*
                 * Otherwise its in the range, return the new parent.
                 * (leave both the new and old parent locked).
                 */
                parent = ichain;
        }

        return(parent);
}

/*
 * Sets CHAIN_DELETED and CHAIN_MOVED in the chain being deleted and
 * set chain->delete_tid.
 *
 * This function does NOT generate a modification to the parent.  Such
 * modifications are handled by the flush code and are properly merged
 * using the flush synchronization point.  The find/get code will
 * properly overload the RBTREE check on top of the bref check to detect
 * deleted entries prior to flush.
 *
 * 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.
 *
 * NOTE: This function does NOT set chain->modify_tid, allowing future
 *       code to distinguish between live and deleted chains by testing
 *       sync_tid.
 */
void
hammer2_chain_delete(hammer2_trans_t *trans, hammer2_chain_t *parent,
                     hammer2_chain_t *chain)
{
        if (chain->parent->core != parent->core)
                panic("hammer2_chain_delete: parent mismatch");
        if (parent->duplink)
                panic("hammer2_chain_delete: deleting via stale path");
        KKASSERT(ccms_thread_lock_owned(&parent->core->cst));

        /*
         * Nothing to do if already marked.
         */
        if (chain->flags & HAMMER2_CHAIN_DELETED)
                return;

        /*
         * We must set MOVED along with DELETED for the flush code to
         * recognize the operation and properly disconnect the chain
         * in-memory.
         *
         * The setting of DELETED causes finds, lookups, and _next iterations
         * to no longer recognize the chain.  RB_SCAN()s will still have
         * visibility (needed for flush serialization points).
         */
        atomic_set_int(&chain->flags, HAMMER2_CHAIN_DELETED);
        if ((chain->flags & HAMMER2_CHAIN_MOVED) == 0) {
                hammer2_chain_ref(chain);
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_MOVED);
        }
        chain->delete_tid = trans->sync_tid;
        hammer2_chain_parent_setsubmod(chain);
}

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