hammer2 - serialized flush work part 4

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

/*
 * Copyright (c) 2011-2012 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 handles direct and indirect block searches, recursions,
 * creation, and deletion.  Chains of blockrefs are tracked and modifications
 * are flagged for propagation... eventually all the way back to the volume
 * header.  Any chain except the volume header can be flushed to disk at
 * any time... none of it matters until the volume header is dealt with
 * (which is not here, see hammer2_vfsops.c for the volume header disk
 * sequencing).
 *
 * Serialized flushes are not handled here, see hammer2_flush.c.  This module
 * can essentially work on the current version of data, which can be in memory
 * as well as on-disk due to the above.  However, we are responsible for
 * making a copy of the state when a modified chain is part of a flush
 * and we attempt to modify it again before the flush gets to it.  In that
 * situation we create an allocated copy of the state that the flush can
 * deal with.  If a chain undergoing deletion is part of a flush it is
 * marked DELETED and its bref index is kept intact for the flush, but the
 * chain is thereafter ignored by this module's because it is no longer
 * current.
 */
#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_mount_t *hmp, 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.
 */
RB_GENERATE(hammer2_chain_tree, hammer2_chain, rbnode, hammer2_chain_cmp);

int
hammer2_chain_cmp(hammer2_chain_t *chain1, hammer2_chain_t *chain2)
{
        return(chain2->index - chain1->index);
}

/*
 * Recursively mark the parent chain elements so flushes can find
 * modified elements.  Stop when we hit a chain already flagged
 * SUBMODIFIED, but ignore the SUBMODIFIED bit that might be set
 * in chain itself.
 *
 * SUBMODIFIED is not set on the chain passed in.
 *
 * The chain->cst.spin lock can be held to stabilize the chain->parent
 * pointer.  The first parent is stabilized by virtue of chain being
 * fully locked.
 */
void
hammer2_chain_parent_setsubmod(hammer2_mount_t *hmp, hammer2_chain_t *chain)
{
        hammer2_chain_t *parent;

        parent = chain->parent;
        if (parent && (parent->flags & HAMMER2_CHAIN_SUBMODIFIED) == 0) {
                spin_lock(&parent->cst.spin);
                for (;;) {
                        atomic_set_int(&parent->flags,
                                       HAMMER2_CHAIN_SUBMODIFIED);
                        if ((chain = parent->parent) == NULL)
                                break;
                        spin_lock(&chain->cst.spin);    /* upward interlock */
                        spin_unlock(&parent->cst.spin);
                        parent = chain;
                }
                spin_unlock(&parent->cst.spin);
        }
}

/*
 * Allocate a new disconnected chain element representing the specified
 * bref.  The chain element is locked exclusively and refs is set to 1.
 * Media data (data) and meta-structure (u) pointers are left NULL.
 *
 * This essentially allocates a system memory structure representing one
 * of the media structure types, including inodes.
 */
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);
        }

        /*
         * Only set bref_flush if the bref has a real media offset, otherwise
         * the caller has to wait for the chain to be modified/block-allocated
         * before a blockref can be synchronized with its (future) parent.
         */
        chain->bref = *bref;
        if (bref->data_off & ~HAMMER2_OFF_MASK_RADIX)
                chain->bref_flush = *bref;
        chain->index = -1;              /* not yet assigned */
        chain->refs = 1;
        chain->bytes = bytes;
        ccms_cst_init(&chain->cst, chain);
        ccms_thread_lock(&chain->cst, CCMS_STATE_EXCLUSIVE);

        return (chain);
}

/*
 * Deallocate a chain (the step before freeing it).  Remove the chain from
 * its parent's tree.
 *
 * Caller must hold the parent and the chain exclusively locked, and
 * chain->refs must be 0.
 *
 * This function unlocks, removes, and destroys chain, and will recursively
 * destroy any sub-chains under chain (whos refs must also be 0 at this
 * point).
 *
 * parent can be NULL.
 */
static void
hammer2_chain_dealloc(hammer2_mount_t *hmp, hammer2_chain_t *chain)
{
        hammer2_chain_t *parent;
        hammer2_chain_t *child;

        KKASSERT(chain->refs == 0);
        KKASSERT(chain->flushing == 0);
        KKASSERT((chain->flags &
                  (HAMMER2_CHAIN_MOVED | HAMMER2_CHAIN_MODIFIED)) == 0);

        /*
         * If the sub-tree is not empty all the elements on it must have
         * 0 refs and be deallocatable.
         */
        while ((child = RB_ROOT(&chain->rbhead)) != NULL) {
                ccms_thread_lock(&child->cst, CCMS_STATE_EXCLUSIVE);
                hammer2_chain_dealloc(hmp, child);
        }

        /*
         * If the DELETED flag is not set the chain must be removed from
         * its parent's tree.
         *
         * 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.
         */
        if (chain->flags & HAMMER2_CHAIN_ONRBTREE) {
                spin_lock(&chain->cst.spin);    /* shouldn't be needed */
                parent = chain->parent;
                RB_REMOVE(hammer2_chain_tree, &parent->rbhead, chain);
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_ONRBTREE);
                chain->parent = NULL;
                spin_unlock(&chain->cst.spin);
        }
        hammer2_chain_free(hmp, chain);
}

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

        ccms_thread_unlock(&chain->cst);
        KKASSERT(chain->cst.count == 0);
        KKASSERT(chain->cst.upgrade == 0);

        kfree(chain, hmp->mchain);
}

/*
 * Add a reference to a chain element, preventing its destruction.
 *
 * The parent chain must be locked shared or exclusive or otherwise be
 * stable and already have a reference.
 */
void
hammer2_chain_ref(hammer2_mount_t *hmp, hammer2_chain_t *chain)
{
        u_int refs;

        while (chain) {
                refs = chain->refs;
                KKASSERT(chain->refs >= 0);
                cpu_ccfence();
                if (refs == 0) {
                        /*
                         * 0 -> 1 transition must bump the refs on the parent
                         * too.  The caller has stabilized the parent.
                         */
                        if (atomic_cmpset_int(&chain->refs, 0, 1)) {
                                chain = chain->parent;
                                KKASSERT(chain == NULL || chain->refs > 0);
                        }
                        /* retry or continue along the parent chain */
                } else {
                        /*
                         * N -> N+1
                         */
                        if (atomic_cmpset_int(&chain->refs, refs, refs + 1))
                                break;
                        /* retry */
                }
        }
}

/*
 * Drop the callers reference to the chain element.  If the ref count
 * reaches zero we attempt to recursively drop the parent.
 *
 * MOVED and MODIFIED elements hold additional references so it should not
 * be possible for the count on a modified element to drop to 0.
 *
 * The chain element must NOT be locked by the caller on the 1->0 transition.
 *
 * The parent might or might not be locked by the caller.  If we are unable
 * to lock the parent on the 1->0 transition the destruction of the chain
 * will be deferred but we still recurse upward and drop the ref on the
 * parent (see the lastdrop() function)
 */
static hammer2_chain_t *hammer2_chain_lastdrop(hammer2_mount_t *hmp,
                                                hammer2_chain_t *chain);

void
hammer2_chain_drop(hammer2_mount_t *hmp, hammer2_chain_t *chain)
{
        u_int refs;

        while (chain) {
                refs = chain->refs;
                cpu_ccfence();
                KKASSERT(refs > 0);
                if (refs == 1) {
                        /*
                         * (1) lastdrop successfully drops the chain to 0
                         *     refs and may may not have destroyed it.
                         *     lastdrop will return the parent so we can
                         *     recursively drop the implied ref from the
                         *     1->0 transition.
                         *
                         * (2) lastdrop fails to transition refs from 1 to 0
                         *     and returns the same chain, we retry.
                         */
                        chain = hammer2_chain_lastdrop(hmp, chain);
                } else {
                        if (atomic_cmpset_int(&chain->refs, refs, refs - 1)) {
                                /*
                                 * Succeeded, count did not reach zero so
                                 * cut out of the loop.
                                 */
                                break;
                        }
                        /* retry the same chain */
                }
        }
}

/*
 * Handle SMP races during the last drop.  We must obtain a lock on
 * chain->parent to stabilize the last pointer reference to chain
 * (if applicable).  This reference does not have a parallel ref count,
 * that is idle chains in the topology can have a ref count of 0.
 *
 * The 1->0 transition implies a ref on the parent.
 */
static
hammer2_chain_t *
hammer2_chain_lastdrop(hammer2_mount_t *hmp, hammer2_chain_t *chain)
{
        hammer2_chain_t *parent;

        /*
         * Stablize chain->parent with the chain cst's spinlock.
         * (parent can be NULL here).
         *
         * cst.spin locks are allowed to be nested bottom-up (the reverse
         * of the normal top-down for full-blown cst locks), so this also
         * allows us to attempt to obtain the parent's cst lock non-blocking
         * (which must acquire the parent's spinlock unconditionally) while
         * we are still holding the chain's spinlock.
         */
        spin_lock(&chain->cst.spin);
        parent = chain->parent;

        /*
         * If chain->flushing is non-zero we cannot deallocate the chain
         * here.  The flushing field will be serialized for the inline
         * unlock made by the flusher itself and we don't care about races
         * in any other situation because the thread lock on the parent
         * will fail in other situations.
         *
         * If we have a non-NULL parent but cannot acquire its thread
         * lock, we also cannot deallocate the chain.
         */
        if (chain->flushing ||
            (parent && ccms_thread_lock_nonblock(&parent->cst,
                                                 CCMS_STATE_EXCLUSIVE))) {
                if (atomic_cmpset_int(&chain->refs, 1, 0)) {
                        spin_unlock(&chain->cst.spin);  /* success */
                        return(parent);
                } else {
                        spin_unlock(&chain->cst.spin);  /* failure */
                        return(chain);
                }
        }
        spin_unlock(&chain->cst.spin);

        /*
         * With the parent now held we control the last pointer reference
         * to chain ONLY IF this is the 1->0 drop.  If we fail to transition
         * from 1->0 we raced a refs change and must retry at chain.
         */
        if (atomic_cmpset_int(&chain->refs, 1, 0) == 0) {
                /* failure */
                if (parent)
                        ccms_thread_unlock(&parent->cst);
                return(chain);
        }

        /*
         * Ok, we succeeded.  We now own the implied ref on the parent
         * associated with the 1->0 transition of the child.  It should not
         * be possible for ANYTHING to access the child now, as we own the
         * lock on the parent, so we should be able to safely lock the
         * child and destroy it.
         */
        ccms_thread_lock(&chain->cst, CCMS_STATE_EXCLUSIVE);
        hammer2_chain_dealloc(hmp, chain);

        /*
         * We want to return parent with its implied ref to the caller
         * to recurse and drop the parent.
         */
        if (parent)
                ccms_thread_unlock(&parent->cst);
        return (parent);
}

/*
 * 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.
 */
int
hammer2_chain_lock(hammer2_mount_t *hmp, hammer2_chain_t *chain, int how)
{
        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.
         */
        hammer2_chain_ref(hmp, chain);
        if (how & HAMMER2_RESOLVE_SHARED)
                ccms_thread_lock(&chain->cst, CCMS_STATE_SHARED);
        else
                ccms_thread_lock(&chain->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(&chain->cst);
        if (chain->data) {
                ccms_thread_lock_restore(&chain->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(&chain->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(&chain->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_mount_t *hmp, hammer2_chain_t *chain)
{
        long *counterp;

        /*
         * Release the CST lock but with a special 1->0 transition case.
         *
         * 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(&chain->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(&chain->cst);
                hammer2_chain_drop(hmp, 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(&chain->cst);
        hammer2_chain_drop(hmp, chain);
}

/*
 * Resize the chain's physical storage allocation.  Chains can be resized
 * smaller without reallocating the storage.  Resizing larger will reallocate
 * the storage.
 *
 * Must be passed a locked chain.
 *
 * 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 data.
 *
 * 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.
 */
void
hammer2_chain_resize(hammer2_inode_t *ip, hammer2_chain_t *chain,
                     int nradix, int flags)
{
        hammer2_mount_t *hmp = ip->hmp;
        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;

        /*
         * Set MODIFIED and add a chain ref to prevent destruction.  Both
         * modified flags share the same ref.
         *
         * If the chain is already marked MODIFIED then we can safely
         * return the previous allocation to the pool without having to
         * worry about snapshots.
         */
        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_MODIFY_TID);
                hammer2_chain_ref(hmp, 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;

                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(hmp, 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(hmp, chain);
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_MOVED);
        }
        hammer2_chain_parent_setsubmod(hmp, chain);
}

/*
 * Convert a locked chain that was retrieved read-only to read-write.
 *
 * If not already marked modified a new physical block will be allocated
 * and assigned to the bref.
 *
 * 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.
 */
void
hammer2_chain_modify(hammer2_mount_t *hmp, hammer2_chain_t *chain, int flags)
{
        struct buf *nbp;
        int error;
        hammer2_off_t pbase;
        size_t bbytes;
        size_t boff;
        void *bdata;

        /*
         * Tells flush that modify_tid must be updated, otherwise only
         * mirror_tid is updated.  This is the default.
         */
        if ((flags & HAMMER2_MODIFY_NO_MODIFY_TID) == 0)
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_MODIFY_TID);

        /*
         * If the chain is already marked MODIFIED we can just return.
         *
         * However, 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.
         */
        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(hmp, chain);

        /*
         * 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(hmp, 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.
 */
void
hammer2_modify_volume(hammer2_mount_t *hmp)
{
        hammer2_voldata_lock(hmp);
        atomic_set_int(&hmp->vchain.flags, HAMMER2_CHAIN_MODIFIED_AUX);
        hammer2_voldata_unlock(hmp);
}

/*
 * Locate an in-memory chain.  The parent must be locked.  The in-memory
 * chain is returned or NULL if no in-memory chain is present.
 *
 * NOTE: A chain on-media might exist for this index when NULL is returned.
 */
hammer2_chain_t *
hammer2_chain_find(hammer2_mount_t *hmp, hammer2_chain_t *parent, int index)
{
        hammer2_chain_t dummy;
        hammer2_chain_t *chain;

        dummy.index = index;
        chain = RB_FIND(hammer2_chain_tree, &parent->rbhead, &dummy);
        return (chain);
}

/*
 * Return a locked chain structure with all associated data acquired.
 *
 * Caller must lock the parent on call, the returned child will be locked.
 */
hammer2_chain_t *
hammer2_chain_get(hammer2_mount_t *hmp, hammer2_chain_t *parent,
                  int index, int flags)
{
        hammer2_blockref_t *bref;
        hammer2_chain_t *chain;
        hammer2_chain_t dummy;
        int how;
        ccms_state_t ostate;

        /*
         * 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;

        /*
         * 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.index = index;
        chain = RB_FIND(hammer2_chain_tree, &parent->rbhead, &dummy);
        if (chain) {
                if (flags & HAMMER2_LOOKUP_NOLOCK)
                        hammer2_chain_ref(hmp, chain);
                else
                        hammer2_chain_lock(hmp, chain, how);
                return(chain);
        }

        /*
         * Upgrade our thread lock and handle any race that may have
         * occurred.  Leave the lock upgraded for the rest of the get.
         * We have to do this because we will be modifying the chain
         * structure.
         */
        ostate = ccms_thread_lock_upgrade(&parent->cst);
        chain = RB_FIND(hammer2_chain_tree, &parent->rbhead, &dummy);
        if (chain) {
                if (flags & HAMMER2_LOOKUP_NOLOCK)
                        hammer2_chain_ref(hmp, chain);
                else
                        hammer2_chain_lock(hmp, chain, how);
                ccms_thread_lock_restore(&parent->cst, ostate);
                return(chain);
        }

        /*
         * The get function must always succeed, panic if there's no
         * data to index.
         */
        if (parent->flags & HAMMER2_CHAIN_INITIAL) {
                ccms_thread_lock_restore(&parent->cst, ostate);
                panic("hammer2_chain_get: Missing bref(1)");
                /* NOT REACHED */
        }

        /*
         * Otherwise lookup the bref and issue I/O (switch on the parent)
         */
        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.
         *
         * The locking operation we do later will issue I/O to read it.
         */
        chain = hammer2_chain_alloc(hmp, bref);

        /*
         * Link the chain into its parent.  Caller is expected to hold an
         * exclusive lock on the parent.
         */
        chain->parent = parent;
        chain->index = index;
        if (RB_INSERT(hammer2_chain_tree, &parent->rbhead, chain))
                panic("hammer2_chain_link: collision");
        atomic_set_int(&chain->flags, HAMMER2_CHAIN_ONRBTREE);
        KKASSERT(parent->refs > 0);
        atomic_add_int(&parent->refs, 1);       /* for red-black entry */
        ccms_thread_lock_restore(&parent->cst, ostate);

        /*
         * Our new chain structure has already been referenced and locked
         * but the lock code handles the I/O so call it to resolve the data.
         * Then release one of our two exclusive locks.
         *
         * If NOLOCK is set the release will release the one-and-only lock.
         */
        if ((flags & HAMMER2_LOOKUP_NOLOCK) == 0) {
                hammer2_chain_lock(hmp, chain, how);    /* recusive lock */
                hammer2_chain_drop(hmp, chain);         /* excess ref */
        }
        ccms_thread_unlock(&chain->cst);                        /* from alloc */

        return (chain);
}

/*
 * 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 and 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_mount_t *hmp, hammer2_chain_t **parentp,
                     hammer2_key_t key_beg, hammer2_key_t key_end,
                     int flags)
{
        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;
        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(hmp, parent);         /* ref old parent */
                hammer2_chain_unlock(hmp, parent);      /* unlock old parent */
                parent = parent->parent;
                                                        /* lock new parent */
                hammer2_chain_lock(hmp, parent, how_maybe);
                hammer2_chain_drop(hmp, *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(hmp, parent);
                        else
                                hammer2_chain_lock(hmp, 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.  A Deleted
         *        elements covers (makes invisible) any original media
         *        data.
         */
        bref = NULL;
        for (i = 0; i < count; ++i) {
                tmp = hammer2_chain_find(hmp, 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 (key_beg <= scan_end && key_end >= scan_beg)
                        break;
        }
        if (i == count) {
                if (key_beg == key_end)
                        return (NULL);
                return (hammer2_chain_next(hmp, parentp, NULL,
                                           key_beg, key_end, flags));
        }

        /*
         * Acquire the new chain element.  If the chain element is an
         * indirect block we must search recursively.
         */
        chain = hammer2_chain_get(hmp, 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 it might need a fixup if the caller passed incompatible flags.
         */
        if (chain->bref.type == HAMMER2_BREF_TYPE_INDIRECT ||
            chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_NODE) {
                hammer2_chain_unlock(hmp, parent);
                *parentp = parent = chain;
                if (flags & HAMMER2_LOOKUP_NOLOCK) {
                        hammer2_chain_lock(hmp, chain, how_maybe);
                        hammer2_chain_drop(hmp, chain); /* excess ref */
                } else if (flags & HAMMER2_LOOKUP_NODATA) {
                        hammer2_chain_lock(hmp, chain, how_maybe);
                        hammer2_chain_unlock(hmp, chain);
                }
                goto again;
        }

        /*
         * All done, return 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.
 */
hammer2_chain_t *
hammer2_chain_next(hammer2_mount_t *hmp, hammer2_chain_t **parentp,
                   hammer2_chain_t *chain,
                   hammer2_key_t key_beg, hammer2_key_t key_end,
                   int flags)
{
        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;

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(hmp, chain);
                else
                        hammer2_chain_unlock(hmp, 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;
                hammer2_chain_ref(hmp, nparent);        /* ref new parent */
                hammer2_chain_unlock(hmp, parent);      /* unlock old parent */
                                                        /* lock new parent */
                hammer2_chain_lock(hmp, nparent, how_maybe);
                hammer2_chain_drop(hmp, 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.  A Deleted
         *        elements covers (makes invisible) any original media
         *        data.
         */
        bref = NULL;
        while (i < count) {
                tmp = hammer2_chain_find(hmp, 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 (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(hmp, 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 it might need a fixup if the caller passed incompatible flags.
         */
        if (chain->bref.type == HAMMER2_BREF_TYPE_INDIRECT ||
            chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_NODE) {
                hammer2_chain_unlock(hmp, parent);
                *parentp = parent = chain;
                chain = NULL;
                if (flags & HAMMER2_LOOKUP_NOLOCK) {
                        hammer2_chain_lock(hmp, parent, how_maybe);
                        hammer2_chain_drop(hmp, parent);        /* excess ref */
                } else if (flags & HAMMER2_LOOKUP_NODATA) {
                        hammer2_chain_lock(hmp, parent, how_maybe);
                        hammer2_chain_unlock(hmp, parent);
                }
                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.
 *
 * 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, referenced 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.
 */
hammer2_chain_t *
hammer2_chain_create(hammer2_mount_t *hmp, hammer2_chain_t *parent,
                     hammer2_chain_t *chain,
                     hammer2_key_t key, int keybits, int type, size_t bytes,
                     int *errorp)
{
        hammer2_blockref_t dummy;
        hammer2_blockref_t *base;
        hammer2_chain_t dummy_chain;
        int unlock_parent = 0;
        int allocated = 0;
        int count;
        int i;

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

        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);
                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.
         */
        bzero(&dummy_chain, sizeof(dummy_chain));
        for (i = 0; i < count; ++i) {
                if (base == NULL) {
                        dummy_chain.index = i;
                        if (RB_FIND(hammer2_chain_tree,
                                    &parent->rbhead, &dummy_chain) == NULL) {
                                break;
                        }
                } else if (base[i].type == 0) {
                        dummy_chain.index = i;
                        if (RB_FIND(hammer2_chain_tree,
                                    &parent->rbhead, &dummy_chain) == NULL) {
                                break;
                        }
                }
        }

        /*
         * 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.  The most
         * typical error is EAGAIN (flush conflict during chain move).
         */
        if (i == count) {
                hammer2_chain_t *nparent;

                nparent = hammer2_chain_create_indirect(hmp, parent,
                                                        key, keybits,
                                                        errorp);
                if (nparent == NULL) {
                        if (allocated)
                                hammer2_chain_free(hmp, chain);
                        chain = NULL;
                        goto done;
                }
                if (parent != nparent) {
                        if (unlock_parent)
                                hammer2_chain_unlock(hmp, 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);
        chain->parent = parent;
        chain->index = i;
        if (RB_INSERT(hammer2_chain_tree, &parent->rbhead, chain))
                panic("hammer2_chain_link: collision");
        atomic_set_int(&chain->flags, HAMMER2_CHAIN_ONRBTREE);
        KKASSERT((chain->flags & HAMMER2_CHAIN_DELETED) == 0);
        KKASSERT(parent->refs > 0);
        atomic_add_int(&parent->refs, 1);

        /*
         * (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 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(hmp, 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(hmp, chain,
                                             HAMMER2_MODIFY_OPTDATA);
                        break;
                default:
                        hammer2_chain_modify(hmp, chain, 0);
                        break;
                }
        } else {
                /*
                 * When reconnecting inodes we have to call setsubmod()
                 * to ensure that its state propagates up the newly
                 * connected parent.
                 *
                 * Make sure MOVED is set but do not update bref_flush.  If
                 * the chain is undergoing modification bref_flush will be
                 * updated when it gets flushed.  If it is not then the
                 * bref may not have been flushed yet and we do not want to
                 * set MODIFIED here as this could result in unnecessary
                 * reallocations.
                 */
                if ((chain->flags & HAMMER2_CHAIN_MOVED) == 0) {
                        hammer2_chain_ref(hmp, chain);
                        atomic_set_int(&chain->flags, HAMMER2_CHAIN_MOVED);
                }
                hammer2_chain_parent_setsubmod(hmp, chain);
        }

done:
        if (unlock_parent)
                hammer2_chain_unlock(hmp, parent);
        return (chain);
}

/*
 * 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.
 * EAGAIN can be returned to indicate a flush collision which requires the
 * caller to retry.
 *
 * 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_mount_t *hmp, hammer2_chain_t *parent,
                              hammer2_key_t create_key, int create_bits,
                              int *errorp)
{
        hammer2_blockref_t *base;
        hammer2_blockref_t *bref;
        hammer2_chain_t *chain;
        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->cst));
        *errorp = 0;

        hammer2_chain_modify(hmp, 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.
         */
        bzero(&dummy, sizeof(dummy));
        for (i = 0; i < count; ++i) {
                int nkeybits;

                dummy.index = i;
                chain = RB_FIND(hammer2_chain_tree, &parent->rbhead, &dummy);
                if (chain) {
                        /*
                         * NOTE! CHAIN_DELETED elements have to be adjusted
                         *       too, they cannot be ignored.
                         */
                        bref = &chain->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)
                        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;
        }

        /*
         * 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);

        /*
         * Iterate the original parent and move the matching brefs into
         * the new indirect block.
         */
        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.
                 */
                dummy.index = i;
                chain = RB_FIND(hammer2_chain_tree, &parent->rbhead, &dummy);
                if (chain) {
                        /*
                         * NOTE! CHAIN_DELETED elements have to be adjusted
                         *       too, they cannot be ignored.
                         */
                        bref = &chain->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 simply move them to the
                 * new parent (ichain).  We cannot move chains which are
                 * undergoing flushing and will break out of the loop in
                 * that case.
                 *
                 * When adjusting the parent/child relationship we must
                 * set the MOVED bit but we do NOT update bref_flush
                 * because otherwise we might synchronize a bref that has
                 * not yet been flushed.  We depend on chain's bref_flush
                 * either being correct or the chain being in a MODIFIED
                 * state.
                 *
                 * We do not want to set MODIFIED here as this would result
                 * in unnecessary reallocations.
                 *
                 * We must still set SUBMODIFIED in the parent but we do
                 * that 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.
                 */
                chain = hammer2_chain_get(hmp, parent, i,
                                          HAMMER2_LOOKUP_NODATA);
                if (chain->flushing) {
                        hammer2_chain_unlock(hmp, chain);
                        break;
                }

                spin_lock(&chain->cst.spin);
                RB_REMOVE(hammer2_chain_tree, &parent->rbhead, chain);
                if (RB_INSERT(hammer2_chain_tree, &ichain->rbhead, chain))
                        panic("hammer2_chain_create_indirect: collision");
                chain->parent = ichain;
                spin_unlock(&chain->cst.spin);

                if (base)
                        bzero(&base[i], sizeof(base[i]));
                atomic_add_int(&parent->refs, -1);
                atomic_add_int(&ichain->refs, 1);
                if ((chain->flags & HAMMER2_CHAIN_MOVED) == 0) {
                        hammer2_chain_ref(hmp, chain);
                        atomic_set_int(&chain->flags, HAMMER2_CHAIN_MOVED);
                }
                hammer2_chain_unlock(hmp, chain);
                KKASSERT(parent->refs > 0);
                chain = NULL;
        }

        /*
         * If we hit a chain that is undergoing flushing we're screwed and
         * we have to undo the whole mess.  Since ichain has not been linked
         * in yet, the moved chains are not reachable and will not have been
         * disposed of.
         *
         * WARNING! This code is pretty hairy because the flusher is sitting
         *          on the parent processing one of the children that we
         *          haven't yet moved, and will do a RB_NEXT loop on that
         *          child.  So the children we're moving back have to be
         *          returned to the same place in the iteration that they
         *          were removed from.
         */
        if (i != count) {
                kprintf("hammer2_chain_create_indirect: EAGAIN\n");
                *errorp = EAGAIN;
                while ((chain = RB_ROOT(&ichain->rbhead)) != NULL) {
                        hammer2_chain_lock(hmp, chain, HAMMER2_RESOLVE_NEVER);
                        KKASSERT(chain->flushing == 0);
                        RB_REMOVE(hammer2_chain_tree, &ichain->rbhead, chain);
                        if (RB_INSERT(hammer2_chain_tree, &parent->rbhead, chain))
                                panic("hammer2_chain_create_indirect: collision");
                        chain->parent = parent;
                        atomic_add_int(&parent->refs, 1);
                        atomic_add_int(&ichain->refs, -1);
                        /* MOVED bit might have been inherited, cannot undo */
                        hammer2_chain_unlock(hmp, chain);
                }
                hammer2_chain_free(hmp, ichain);
                return(NULL);
        }

        /*
         * 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).
         */
        KKASSERT(ichain->index >= 0);
        if (RB_INSERT(hammer2_chain_tree, &parent->rbhead, ichain))
                panic("hammer2_chain_create_indirect: ichain insertion");
        atomic_set_int(&ichain->flags, HAMMER2_CHAIN_ONRBTREE);
        ichain->parent = parent;
        atomic_add_int(&parent->refs, 1);

        /*
         * 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(hmp, ichain, HAMMER2_MODIFY_OPTDATA);
        hammer2_chain_parent_setsubmod(hmp, 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(hmp, 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(hmp, ichain);
        } else {
                /*
                 * Otherwise its in the range, return the new parent.
                 * (leave both the new and old parent locked).
                 */
                parent = ichain;
        }

        return(parent);
}

/*
 * Physically delete the specified chain element.  Note that inodes with
 * open descriptors should not be deleted (as with other filesystems) until
 * the last open descriptor is closed.
 *
 * This routine will remove the chain element from its parent and potentially
 * also recurse upward and delete indirect blocks which become empty as a
 * side effect.
 *
 * The caller must pass a pointer to the chain's parent, also locked and
 * referenced.  (*parentp) will be modified in a manner similar to a lookup
 * or iteration when indirect blocks are also deleted as a side effect.
 *
 * Must be called with an exclusively locked parent and chain.  parent and
 * chain are both left locked on return.
 *
 * XXX This currently does not adhere to the MOVED flag protocol in that
 *     the removal is immediately indicated in the parent's blockref[]
 *     array.
 */
void
hammer2_chain_delete(hammer2_mount_t *hmp, hammer2_chain_t *parent,
                     hammer2_chain_t *chain, int retain)
{
        hammer2_blockref_t *base;
        int count;

        if (chain->parent != parent)
                panic("hammer2_chain_delete: parent mismatch");
        KKASSERT(ccms_thread_lock_owned(&parent->cst));

        /*
         * Mark the parent modified so our base[] pointer remains valid
         * while we move entries.  For the optimized indirect block
         * case mark the parent moved instead.
         *
         * Calculate the blockref reference in the parent
         */
        switch(parent->bref.type) {
        case HAMMER2_BREF_TYPE_INODE:
                hammer2_chain_modify(hmp, parent, HAMMER2_MODIFY_NO_MODIFY_TID);
                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:
                hammer2_chain_modify(hmp, parent, HAMMER2_MODIFY_OPTDATA |
                                                  HAMMER2_MODIFY_NO_MODIFY_TID);
                if (parent->flags & HAMMER2_CHAIN_INITIAL)
                        base = NULL;
                else
                        base = &parent->data->npdata.blockref[0];
                count = parent->bytes / sizeof(hammer2_blockref_t);
                break;
        case HAMMER2_BREF_TYPE_VOLUME:
                hammer2_chain_modify(hmp, parent, HAMMER2_MODIFY_NO_MODIFY_TID);
                base = &hmp->voldata.sroot_blockset.blockref[0];
                count = HAMMER2_SET_COUNT;
                break;
        default:
                panic("hammer2_chain_delete: unrecognized blockref type: %d",
                      parent->bref.type);
                count = 0;
                break;
        }
        KKASSERT(chain->index >= 0 && chain->index < count);

        /*
         * We may not be able to immediately disconnect the chain if a
         * flush is in progress.  If retain is non-zero we MUST disconnect
         * the chain now and callers are responsible for making sure that
         * flushing is zero.
         */
        spin_lock(&chain->cst.spin);
        if ((retain || chain->flushing == 0) &&
            (chain->flags & HAMMER2_CHAIN_ONRBTREE)) {
                if (base)
                        bzero(&base[chain->index], sizeof(*base));
                KKASSERT(chain->flushing == 0);
                RB_REMOVE(hammer2_chain_tree, &parent->rbhead, chain);
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_ONRBTREE);
                atomic_add_int(&parent->refs, -1);   /* for red-black entry */
                chain->index = -1;
                chain->parent = NULL;
        }
        spin_unlock(&chain->cst.spin);

        /*
         * Cumulative adjustments must be propagated to the parent inode
         * when deleting and synchronized to ip.  This occurs even if we
         * cannot detach the chain from its parent.
         *
         * NOTE:  We do not propagate ip->delta_*count to the parent because
         *        these represent adjustments that have not yet been
         *        propagated upward, so we don't need to remove them from
         *        the parent.
         *
         * Clear the pointer to the parent inode.
         */
        if ((chain->flags & HAMMER2_CHAIN_DELETED) == 0 &&
            chain->bref.type == HAMMER2_BREF_TYPE_INODE) {
                /* XXX */
        }

        /*
         * If retain is 0 the deletion is permanent.  Because the chain is
         * no longer connected to the topology a flush will have no
         * visibility into it.  We must dispose of the references related
         * to the MODIFIED and MOVED flags, otherwise the ref count will
         * never transition to 0.
         *
         * If retain is non-zero the deleted element is likely an inode
         * which the vnops frontend will mark DESTROYED and flush.  In that
         * situation we must retain the flags for any open file descriptors
         * on the (removed) inode.  The final close will destroy the
         * disconnected chain.
         */
        if (retain == 0) {
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_DELETED);
                if (chain->flags & HAMMER2_CHAIN_MODIFIED) {
                        atomic_clear_int(&chain->flags, HAMMER2_CHAIN_MODIFIED);
                        hammer2_chain_drop(hmp, chain);
                }
                if (chain->flags & HAMMER2_CHAIN_MOVED) {
                        atomic_clear_int(&chain->flags, HAMMER2_CHAIN_MOVED);
                        hammer2_chain_drop(hmp, chain);
                }
        }

        /*
         * The chain is still likely referenced, possibly even by a vnode
         * (if an inode), so defer further action until the chain gets
         * dropped.
         */
}

void
hammer2_chain_wait(hammer2_mount_t *hmp, hammer2_chain_t *chain)
{
        tsleep(chain, 0, "chnflw", 1);
}