text: /*
   * Copyright (c) 2011-2020 The DragonFly Project.  All rights reserved.
   *
   * This code is derived from software contributed to The DragonFly Project
   * by Matthew Dillon <dillon@dragonflybsd.org>
   * and Venkatesh Srinivas <vsrinivas@dragonflybsd.org>
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   * 3. Neither the name of The DragonFly Project nor the names of its
   *    contributors may be used to endorse or promote products derived
   *    from this software without specific, prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
   * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
   * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
   * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
   * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   */
  /*
   * This subsystem implements most of the core support functions for
   * the hammer2_chain structure.
   *
   * Chains are the in-memory version on media objects (volume header, inodes,
   * indirect blocks, data blocks, etc).  Chains represent a portion of the
   * HAMMER2 topology.
   *
   * Chains are no-longer delete-duplicated.  Instead, the original in-memory
   * chain will be moved along with its block reference (e.g. for things like
   * renames, hardlink operations, modifications, etc), and will be indexed
   * on a secondary list for flush handling instead of propagating a flag
   * upward to the root.
   *
   * Concurrent front-end operations can still run against backend flushes
   * as long as they do not cross the current flush boundary.  An operation
   * running above the current flush (in areas not yet flushed) can become
   * part of the current flush while ano peration running below the current
   * flush can become part of the next flush.
   */
  #include <sys/cdefs.h>
  #include <sys/param.h>
  #include <sys/systm.h>
  #include <sys/types.h>
  #include <sys/lock.h>
  #include <sys/buf.h>
  
  #include <crypto/sha2/sha2.h>
  
  #include "hammer2.h"
  
  static hammer2_chain_t *hammer2_chain_create_indirect(
  		hammer2_chain_t *parent,
  		hammer2_key_t key, int keybits,
  		hammer2_tid_t mtid, int for_type, int *errorp);
  static int hammer2_chain_delete_obref(hammer2_chain_t *parent,
  		hammer2_chain_t *chain,
  		hammer2_tid_t mtid, int flags,
  		hammer2_blockref_t *obref);
  static hammer2_chain_t *hammer2_combined_find(
  		hammer2_chain_t *parent,
  		hammer2_blockref_t *base, int count,
  		hammer2_key_t *key_nextp,
  		hammer2_key_t key_beg, hammer2_key_t key_end,
  		hammer2_blockref_t **bresp);
  static hammer2_chain_t *hammer2_chain_lastdrop(hammer2_chain_t *chain,
  				int depth);
  static void hammer2_chain_lru_flush(hammer2_pfs_t *pmp);
  
  /*
   * There are many degenerate situations where an extreme rate of console
   * output can occur from warnings and errors.  Make sure this output does
   * not impede operations.
   */
  static struct krate krate_h2chk = { .freq = 5 };
  static struct krate krate_h2me = { .freq = 1 };
  static struct krate krate_h2em = { .freq = 1 };
  
  /*
   * Basic RBTree for chains (core.rbtree).
   */
  RB_GENERATE(hammer2_chain_tree, hammer2_chain, rbnode, hammer2_chain_cmp);
  
  int
  hammer2_chain_cmp(hammer2_chain_t *chain1, hammer2_chain_t *chain2)
  {
  	hammer2_key_t c1_beg;
  	hammer2_key_t c1_end;
  	hammer2_key_t c2_beg;
  	hammer2_key_t c2_end;
  
  	/*
  	 * Compare chains.  Overlaps are not supposed to happen and catch
  	 * any software issues early we count overlaps as a match.
  	 */
  	c1_beg = chain1->bref.key;
  	c1_end = c1_beg + ((hammer2_key_t)1 << chain1->bref.keybits) - 1;
  	c2_beg = chain2->bref.key;
  	c2_end = c2_beg + ((hammer2_key_t)1 << chain2->bref.keybits) - 1;
  
  	if (c1_end < c2_beg)	/* fully to the left */
  		return(-1);
  	if (c1_beg > c2_end)	/* fully to the right */
  		return(1);
  	return(0);		/* overlap (must not cross edge boundary) */
  }
  
  /*
   * Assert that a chain has no media data associated with it.
   */
  static __inline void
  hammer2_chain_assert_no_data(hammer2_chain_t *chain)
  {
  	KKASSERT(chain->dio == NULL);
  	if (chain->bref.type != HAMMER2_BREF_TYPE_VOLUME &&
  	    chain->bref.type != HAMMER2_BREF_TYPE_FREEMAP &&
  	    chain->data) {
  		panic("hammer2_chain_assert_no_data: chain %p still has data",
  		    chain);
  	}
  }
  
  /*
   * Make a chain visible to the flusher.  The flusher operates using a top-down
   * recursion based on the ONFLUSH flag.  It locates MODIFIED and UPDATE chains,
   * flushes them, and updates blocks back to the volume root.
   *
   * This routine sets the ONFLUSH flag upward from the triggering chain until
   * it hits an inode root or the volume root.  Inode chains serve as inflection
   * points, requiring the flusher to bridge across trees.  Inodes include
   * regular inodes, PFS roots (pmp->iroot), and the media super root
   * (spmp->iroot).
   */
  void
  hammer2_chain_setflush(hammer2_chain_t *chain)
  {
  	hammer2_chain_t *parent;
  
  	if ((chain->flags & HAMMER2_CHAIN_ONFLUSH) == 0) {
  		hammer2_spin_sh(&chain->core.spin);
  		while ((chain->flags & HAMMER2_CHAIN_ONFLUSH) == 0) {
  			atomic_set_int(&chain->flags, HAMMER2_CHAIN_ONFLUSH);
  			if (chain->bref.type == HAMMER2_BREF_TYPE_INODE)
  				break;
  			if ((parent = chain->parent) == NULL)
  				break;
  			hammer2_spin_sh(&parent->core.spin);
  			hammer2_spin_unsh(&chain->core.spin);
  			chain = parent;
  		}
  		hammer2_spin_unsh(&chain->core.spin);
  	}
  }
  
  /*
   * Allocate a new disconnected chain element representing the specified
   * bref.  chain->refs is set to 1 and the passed bref is copied to
   * chain->bref.  chain->bytes is derived from the bref.
   *
   * chain->pmp inherits pmp unless the chain is an inode (other than the
   * super-root inode).
   *
   * NOTE: Returns a referenced but unlocked (because there is no core) chain.
   */
  hammer2_chain_t *
  hammer2_chain_alloc(hammer2_dev_t *hmp, hammer2_pfs_t *pmp,
  		    hammer2_blockref_t *bref)
  {
  	hammer2_chain_t *chain;
  	u_int bytes;
  
  	/*
  	 * Special case - radix of 0 indicates a chain that does not
  	 * need a data reference (context is completely embedded in the
  	 * bref).
  	 */
  	if ((int)(bref->data_off & HAMMER2_OFF_MASK_RADIX))
  		bytes = 1U << (int)(bref->data_off & HAMMER2_OFF_MASK_RADIX);
  	else
  		bytes = 0;
  
  	switch(bref->type) {
  	case HAMMER2_BREF_TYPE_INODE:
  	case HAMMER2_BREF_TYPE_INDIRECT:
  	case HAMMER2_BREF_TYPE_DATA:
  	case HAMMER2_BREF_TYPE_DIRENT:
  	case HAMMER2_BREF_TYPE_FREEMAP_NODE:
  	case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
  	case HAMMER2_BREF_TYPE_FREEMAP:
  	case HAMMER2_BREF_TYPE_VOLUME:
  		chain = kmalloc_obj(sizeof(*chain), hmp->mchain,
  				    M_WAITOK | M_ZERO);
  		atomic_add_long(&hammer2_chain_allocs, 1);
  		break;
  	case HAMMER2_BREF_TYPE_EMPTY:
  	default:
  		panic("hammer2_chain_alloc: unrecognized blockref type: %d",
  		      bref->type);
  		break;
  	}
  
  	/*
  	 * Initialize the new chain structure.  pmp must be set to NULL for
  	 * chains belonging to the super-root topology of a device mount.
  	 */
  	if (pmp == hmp->spmp)
  		chain->pmp = NULL;
  	else
  		chain->pmp = pmp;
  
  	chain->hmp = hmp;
  	chain->bref = *bref;
  	chain->bytes = bytes;
  	chain->refs = 1;
  	chain->flags = HAMMER2_CHAIN_ALLOCATED;
  	lockinit(&chain->diolk, "chdio", 0, 0);
  
  	/*
  	 * Set the PFS boundary flag if this chain represents a PFS root.
  	 */
  	if (bref->flags & HAMMER2_BREF_FLAG_PFSROOT)
  		atomic_set_int(&chain->flags, HAMMER2_CHAIN_PFSBOUNDARY);
  	hammer2_chain_core_init(chain);
  
  	return (chain);
  }
  
  /*
   * Initialize a chain's core structure.  This structure used to be allocated
   * but is now embedded.
   *
   * The core is not locked.  No additional refs on the chain are made.
   * (trans) must not be NULL if (core) is not NULL.
   */
  void
  hammer2_chain_core_init(hammer2_chain_t *chain)
  {
  	/*
  	 * Fresh core under nchain (no multi-homing of ochain's
  	 * sub-tree).
  	 */
  	RB_INIT(&chain->core.rbtree);	/* live chains */
  	hammer2_mtx_init(&chain->lock, "h2chain");
  }
  
  /*
   * Add a reference to a chain element, preventing its destruction.
   *
   * (can be called with spinlock held)
   */
  void
  hammer2_chain_ref(hammer2_chain_t *chain)
  {
  	if (atomic_fetchadd_int(&chain->refs, 1) == 0) {
  		/*
  		 * Just flag that the chain was used and should be recycled
  		 * on the LRU if it encounters it later.
  		 */
  		if (chain->flags & HAMMER2_CHAIN_ONLRU)
  			atomic_set_int(&chain->flags, HAMMER2_CHAIN_LRUHINT);
  
  #if 0
  		/*
  		 * REMOVED - reduces contention, lru_list is more heuristical
  		 * now.
  		 *
  		 * 0->non-zero transition must ensure that chain is removed
  		 * from the LRU list.
  		 *
  		 * NOTE: Already holding lru_spin here so we cannot call
  		 *	 hammer2_chain_ref() to get it off lru_list, do
  		 *	 it manually.
  		 */
  		if (chain->flags & HAMMER2_CHAIN_ONLRU) {
  			hammer2_pfs_t *pmp = chain->pmp;
  			hammer2_spin_ex(&pmp->lru_spin);
  			if (chain->flags & HAMMER2_CHAIN_ONLRU) {
  				atomic_add_int(&pmp->lru_count, -1);
  				atomic_clear_int(&chain->flags,
  						 HAMMER2_CHAIN_ONLRU);
  				TAILQ_REMOVE(&pmp->lru_list, chain, lru_node);
  			}
  			hammer2_spin_unex(&pmp->lru_spin);
  		}
  #endif
  	}
  }
  
  /*
   * Ref a locked chain and force the data to be held across an unlock.
   * Chain must be currently locked.  The user of the chain who desires
   * to release the hold must call hammer2_chain_lock_unhold() to relock
   * and unhold the chain, then unlock normally, or may simply call
   * hammer2_chain_drop_unhold() (which is safer against deadlocks).
   */
  void
  hammer2_chain_ref_hold(hammer2_chain_t *chain)
  {
  	atomic_add_int(&chain->lockcnt, 1);
  	hammer2_chain_ref(chain);
  }
  
  /*
   * Insert the chain in the core rbtree.
   *
   * Normal insertions are placed in the live rbtree.  Insertion of a deleted
   * chain is a special case used by the flush code that is placed on the
   * unstaged deleted list to avoid confusing the live view.
   */
  #define HAMMER2_CHAIN_INSERT_SPIN	0x0001
  #define HAMMER2_CHAIN_INSERT_LIVE	0x0002
  #define HAMMER2_CHAIN_INSERT_RACE	0x0004
  
  static
  int
  hammer2_chain_insert(hammer2_chain_t *parent, hammer2_chain_t *chain,
  		     int flags, int generation)
  {
  	hammer2_chain_t *xchain;
  	int error = 0;
  
  	if (flags & HAMMER2_CHAIN_INSERT_SPIN)
  		hammer2_spin_ex(&parent->core.spin);
  
  	/*
  	 * Interlocked by spinlock, check for race
  	 */
  	if ((flags & HAMMER2_CHAIN_INSERT_RACE) &&
  	    parent->core.generation != generation) {
  		error = HAMMER2_ERROR_EAGAIN;
  		goto failed;
  	}
  
  	/*
  	 * Insert chain
  	 */
  	xchain = RB_INSERT(hammer2_chain_tree, &parent->core.rbtree, chain);
  	KASSERT(xchain == NULL,
  		("hammer2_chain_insert: collision %p %p (key=%016jx)",
  		chain, xchain, chain->bref.key));
  	atomic_set_int(&chain->flags, HAMMER2_CHAIN_ONRBTREE);
  	chain->parent = parent;
  	++parent->core.chain_count;
  	++parent->core.generation;	/* XXX incs for _get() too, XXX */
  
  	/*
  	 * We have to keep track of the effective live-view blockref count
  	 * so the create code knows when to push an indirect block.
  	 */
  	if (flags & HAMMER2_CHAIN_INSERT_LIVE)
  		atomic_add_int(&parent->core.live_count, 1);
  failed:
  	if (flags & HAMMER2_CHAIN_INSERT_SPIN)
  		hammer2_spin_unex(&parent->core.spin);
  	return error;
  }
  
  /*
   * Drop the caller's reference to the chain.  When the ref count drops to
   * zero this function will try to disassociate the chain from its parent and
   * deallocate it, then recursely drop the parent using the implied ref
   * from the chain's chain->parent.
   *
   * Nobody should own chain's mutex on the 1->0 transition, unless this drop
   * races an acquisition by another cpu.  Therefore we can loop if we are
   * unable to acquire the mutex, and refs is unlikely to be 1 unless we again
   * race against another drop.
   */
  void
  hammer2_chain_drop(hammer2_chain_t *chain)
  {
  	u_int refs;
  
  	KKASSERT(chain->refs > 0);
  
  	while (chain) {
  		refs = chain->refs;
  		cpu_ccfence();
  		KKASSERT(refs > 0);
  
  		if (refs == 1) {
  			if (hammer2_mtx_ex_try(&chain->lock) == 0)
  				chain = hammer2_chain_lastdrop(chain, 0);
  			/* retry the same chain, or chain from lastdrop */
  		} else {
  			if (atomic_cmpset_int(&chain->refs, refs, refs - 1))
  				break;
  			/* retry the same chain */
  		}
  		cpu_pause();
  	}
  }
  
  /*
   * Unhold a held and probably not-locked chain, ensure that the data is
   * dropped on the 1->0 transition of lockcnt by obtaining an exclusive
   * lock and then simply unlocking the chain.
   */
  void
  hammer2_chain_unhold(hammer2_chain_t *chain)
  {
  	u_int lockcnt;
  	int iter = 0;
  
  	for (;;) {
  		lockcnt = chain->lockcnt;
  		cpu_ccfence();
  		if (lockcnt > 1) {
  			if (atomic_cmpset_int(&chain->lockcnt,
  					      lockcnt, lockcnt - 1)) {
  				break;
  			}
  		} else if (hammer2_mtx_ex_try(&chain->lock) == 0) {
  			hammer2_chain_unlock(chain);
  			break;
  		} else {
  			/*
  			 * This situation can easily occur on SMP due to
  			 * the gap inbetween the 1->0 transition and the
  			 * final unlock.  We cannot safely block on the
  			 * mutex because lockcnt might go above 1.
  			 *
  			 * XXX Sleep for one tick if it takes too long.
  			 */
  			if (++iter > 1000) {
  				if (iter > 1000 + hz) {
  					kprintf("hammer2: h2race1 %p\n", chain);
  					iter = 1000;
  				}
  				tsleep(&iter, 0, "h2race1", 1);
  			}
  			cpu_pause();
  		}
  	}
  }
  
  void
  hammer2_chain_drop_unhold(hammer2_chain_t *chain)
  {
  	hammer2_chain_unhold(chain);
  	hammer2_chain_drop(chain);
  }
  
  void
  hammer2_chain_rehold(hammer2_chain_t *chain)
  {
  	hammer2_chain_lock(chain, HAMMER2_RESOLVE_SHARED);
  	atomic_add_int(&chain->lockcnt, 1);
  	hammer2_chain_unlock(chain);
  }
  
  /*
   * Handles the (potential) last drop of chain->refs from 1->0.  Called with
   * the mutex exclusively locked, refs == 1, and lockcnt 0.  SMP races are
   * possible against refs and lockcnt.  We must dispose of the mutex on chain.
   *
   * This function returns an unlocked chain for recursive drop or NULL.  It
   * can return the same chain if it determines it has raced another ref.
   *
   * --
   *
   * When two chains need to be recursively dropped we use the chain we
   * would otherwise free to placehold the additional chain.  It's a bit
   * convoluted but we can't just recurse without potentially blowing out
   * the kernel stack.
   *
   * The chain cannot be freed if it has any children.
   * The chain cannot be freed if flagged MODIFIED unless we can dispose of it.
   * The chain cannot be freed if flagged UPDATE unless we can dispose of it.
   * Any dedup registration can remain intact.
   *
   * The core spinlock is allowed to nest child-to-parent (not parent-to-child).
   */
  static
  hammer2_chain_t *
  hammer2_chain_lastdrop(hammer2_chain_t *chain, int depth)
  {
  	hammer2_pfs_t *pmp;
  	hammer2_dev_t *hmp;
  	hammer2_chain_t *parent;
  	hammer2_chain_t *rdrop;
  
  	/*
  	 * We need chain's spinlock to interlock the sub-tree test.
  	 * We already have chain's mutex, protecting chain->parent.
  	 *
  	 * Remember that chain->refs can be in flux.
  	 */
  	hammer2_spin_ex(&chain->core.spin);
  
  	if (chain->parent != NULL) {
  		/*
  		 * If the chain has a parent the UPDATE bit prevents scrapping
  		 * as the chain is needed to properly flush the parent.  Try
  		 * to complete the 1->0 transition and return NULL.  Retry
  		 * (return chain) if we are unable to complete the 1->0
  		 * transition, else return NULL (nothing more to do).
  		 *
  		 * If the chain has a parent the MODIFIED bit prevents
  		 * scrapping.
  		 *
  		 * Chains with UPDATE/MODIFIED are *not* put on the LRU list!
  		 */
  		if (chain->flags & (HAMMER2_CHAIN_UPDATE |
  				    HAMMER2_CHAIN_MODIFIED)) {
  			if (atomic_cmpset_int(&chain->refs, 1, 0)) {
  				hammer2_spin_unex(&chain->core.spin);
  				hammer2_chain_assert_no_data(chain);
  				hammer2_mtx_unlock(&chain->lock);
  				chain = NULL;
  			} else {
  				hammer2_spin_unex(&chain->core.spin);
  				hammer2_mtx_unlock(&chain->lock);
  			}
  			return (chain);
  		}
  		/* spinlock still held */
  	} else if (chain->bref.type == HAMMER2_BREF_TYPE_VOLUME ||
  		   chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP) {
  		/*
  		 * Retain the static vchain and fchain.  Clear bits that
  		 * are not relevant.  Do not clear the MODIFIED bit,
  		 * and certainly do not put it on the delayed-flush queue.
  		 */
  		atomic_clear_int(&chain->flags, HAMMER2_CHAIN_UPDATE);
  	} else {
  		/*
  		 * The chain has no parent and can be flagged for destruction.
  		 * Since it has no parent, UPDATE can also be cleared.
  		 */
  		atomic_set_int(&chain->flags, HAMMER2_CHAIN_DESTROY);
  		if (chain->flags & HAMMER2_CHAIN_UPDATE)
  			atomic_clear_int(&chain->flags, HAMMER2_CHAIN_UPDATE);
  
  		/*
  		 * If the chain has children we must propagate the DESTROY
  		 * flag downward and rip the disconnected topology apart.
  		 * This is accomplished by calling hammer2_flush() on the
  		 * chain.
  		 *
  		 * Any dedup is already handled by the underlying DIO, so
  		 * we do not have to specifically flush it here.
  		 */
  		if (chain->core.chain_count) {
  			hammer2_spin_unex(&chain->core.spin);
  			hammer2_flush(chain, HAMMER2_FLUSH_TOP |
  					     HAMMER2_FLUSH_ALL);
  			hammer2_mtx_unlock(&chain->lock);
  
  			return(chain);	/* retry drop */
  		}
  
  		/*
  		 * Otherwise we can scrap the MODIFIED bit if it is set,
  		 * and continue along the freeing path.
  		 *
  		 * Be sure to clean-out any dedup bits.  Without a parent
  		 * this chain will no longer be visible to the flush code.
  		 * Easy check data_off to avoid the volume root.
  		 */
  		if (chain->flags & HAMMER2_CHAIN_MODIFIED) {
  			atomic_clear_int(&chain->flags, HAMMER2_CHAIN_MODIFIED);
  			atomic_add_long(&hammer2_count_modified_chains, -1);
  			if (chain->pmp)
  				hammer2_pfs_memory_wakeup(chain->pmp, -1);
  		}
  		/* spinlock still held */
  	}
  
  	/* spinlock still held */
  
  	/*
  	 * If any children exist we must leave the chain intact with refs == 0.
  	 * They exist because chains are retained below us which have refs or
  	 * may require flushing.
  	 *
  	 * Retry (return chain) if we fail to transition the refs to 0, else
  	 * return NULL indication nothing more to do.
  	 *
  	 * Chains with children are NOT put on the LRU list.
  	 */
  	if (chain->core.chain_count) {
  		if (atomic_cmpset_int(&chain->refs, 1, 0)) {
  			hammer2_spin_unex(&chain->core.spin);
  			hammer2_chain_assert_no_data(chain);
  			hammer2_mtx_unlock(&chain->lock);
  			chain = NULL;
  		} else {
  			hammer2_spin_unex(&chain->core.spin);
  			hammer2_mtx_unlock(&chain->lock);
  		}
  		return (chain);
  	}
  	/* spinlock still held */
  	/* no chains left under us */
  
  	/*
  	 * chain->core has no children left so no accessors can get to our
  	 * chain from there.  Now we have to lock the parent core to interlock
  	 * remaining possible accessors that might bump chain's refs before
  	 * we can safely drop chain's refs with intent to free the chain.
  	 */
  	hmp = chain->hmp;
  	pmp = chain->pmp;	/* can be NULL */
  	rdrop = NULL;
  
  	parent = chain->parent;
  
  	/*
  	 * WARNING! chain's spin lock is still held here, and other spinlocks
  	 *	    will be acquired and released in the code below.  We
  	 *	    cannot be making fancy procedure calls!
  	 */
  
  	/*
  	 * We can cache the chain if it is associated with a pmp
  	 * and not flagged as being destroyed or requesting a full
  	 * release.  In this situation the chain is not removed
  	 * from its parent, i.e. it can still be looked up.
  	 *
  	 * We intentionally do not cache DATA chains because these
  	 * were likely used to load data into the logical buffer cache
  	 * and will not be accessed again for some time.
  	 */
  	if ((chain->flags &
  	     (HAMMER2_CHAIN_DESTROY | HAMMER2_CHAIN_RELEASE)) == 0 &&
  	    chain->pmp &&
  	    chain->bref.type != HAMMER2_BREF_TYPE_DATA) {
  		if (parent)
  			hammer2_spin_ex(&parent->core.spin);
  		if (atomic_cmpset_int(&chain->refs, 1, 0) == 0) {
  			/*
  			 * 1->0 transition failed, retry.  Do not drop
  			 * the chain's data yet!
  			 */
  			if (parent)
  				hammer2_spin_unex(&parent->core.spin);
  			hammer2_spin_unex(&chain->core.spin);
  			hammer2_mtx_unlock(&chain->lock);
  
  			return(chain);
  		}
  
  		/*
  		 * Success
  		 */
  		hammer2_chain_assert_no_data(chain);
  
  		/*
  		 * Make sure we are on the LRU list, clean up excessive
  		 * LRU entries.  We can only really drop one but there might
  		 * be other entries that we can remove from the lru_list
  		 * without dropping.
  		 *
  		 * NOTE: HAMMER2_CHAIN_ONLRU may only be safely set when
  		 *	 chain->core.spin AND pmp->lru_spin are held, but
  		 *	 can be safely cleared only holding pmp->lru_spin.
  		 */
  		if ((chain->flags & HAMMER2_CHAIN_ONLRU) == 0) {
  			hammer2_spin_ex(&pmp->lru_spin);
  			if ((chain->flags & HAMMER2_CHAIN_ONLRU) == 0) {
  				atomic_set_int(&chain->flags,
  					       HAMMER2_CHAIN_ONLRU);
  				TAILQ_INSERT_TAIL(&pmp->lru_list,
  						  chain, lru_node);
  				atomic_add_int(&pmp->lru_count, 1);
  			}
  			if (pmp->lru_count < HAMMER2_LRU_LIMIT)
  				depth = 1;	/* disable lru_list flush */
  			hammer2_spin_unex(&pmp->lru_spin);
  		} else {
  			/* disable lru flush */
  			depth = 1;
  		}
  
  		if (parent) {
  			hammer2_spin_unex(&parent->core.spin);
  			parent = NULL;	/* safety */
  		}
  		hammer2_spin_unex(&chain->core.spin);
  		hammer2_mtx_unlock(&chain->lock);
  
  		/*
  		 * lru_list hysteresis (see above for depth overrides).
  		 * Note that depth also prevents excessive lastdrop recursion.
  		 */
  		if (depth == 0)
  			hammer2_chain_lru_flush(pmp);
  
  		return NULL;
  		/* NOT REACHED */
  	}
  
  	/*
  	 * Make sure we are not on the LRU list.
  	 */
  	if (chain->flags & HAMMER2_CHAIN_ONLRU) {
  		hammer2_spin_ex(&pmp->lru_spin);
  		if (chain->flags & HAMMER2_CHAIN_ONLRU) {
  			atomic_add_int(&pmp->lru_count, -1);
  			atomic_clear_int(&chain->flags, HAMMER2_CHAIN_ONLRU);
  			TAILQ_REMOVE(&pmp->lru_list, chain, lru_node);
  		}
  		hammer2_spin_unex(&pmp->lru_spin);
  	}
  
  	/*
  	 * Spinlock the parent and try to drop the last ref on chain.
  	 * On success determine if we should dispose of the chain
  	 * (remove the chain from its parent, etc).
  	 *
  	 * (normal core locks are top-down recursive but we define
  	 * core spinlocks as bottom-up recursive, so this is safe).
  	 */
  	if (parent) {
  		hammer2_spin_ex(&parent->core.spin);
  		if (atomic_cmpset_int(&chain->refs, 1, 0) == 0) {
  			/*
  			 * 1->0 transition failed, retry.
  			 */
  			hammer2_spin_unex(&parent->core.spin);
  			hammer2_spin_unex(&chain->core.spin);
  			hammer2_mtx_unlock(&chain->lock);
  
  			return(chain);
  		}
  
  		/*
  		 * 1->0 transition successful, parent spin held to prevent
  		 * new lookups, chain spinlock held to protect parent field.
  		 * Remove chain from the parent.
  		 *
  		 * If the chain is being removed from the parent's btree but
  		 * is not blkmapped, we have to adjust live_count downward.  If
  		 * it is blkmapped then the blockref is retained in the parent
  		 * as is its associated live_count.  This case can occur when
  		 * a chain added to the topology is unable to flush and is
  		 * then later deleted.
  		 */
  		if (chain->flags & HAMMER2_CHAIN_ONRBTREE) {
  			if ((parent->flags & HAMMER2_CHAIN_COUNTEDBREFS) &&
  			    (chain->flags & HAMMER2_CHAIN_BLKMAPPED) == 0) {
  				atomic_add_int(&parent->core.live_count, -1);
  			}
  			RB_REMOVE(hammer2_chain_tree,
  				  &parent->core.rbtree, chain);
  			atomic_clear_int(&chain->flags, HAMMER2_CHAIN_ONRBTREE);
  			--parent->core.chain_count;
  			chain->parent = NULL;
  		}
  
  		/*
  		 * If our chain was the last chain in the parent's core the
  		 * core is now empty and its parent might have to be
  		 * re-dropped if it has 0 refs.
  		 */
  		if (parent->core.chain_count == 0) {
  			rdrop = parent;
  			atomic_add_int(&rdrop->refs, 1);
  			/*
  			if (atomic_cmpset_int(&rdrop->refs, 0, 1) == 0)
  				rdrop = NULL;
  			*/
  		}
  		hammer2_spin_unex(&parent->core.spin);
  		parent = NULL;	/* safety */
  		/* FALL THROUGH */
  	} else {
  		/*
  		 * No-parent case.
  		 */
  		if (atomic_cmpset_int(&chain->refs, 1, 0) == 0) {
  			/*
  			 * 1->0 transition failed, retry.
  			 */
  			hammer2_spin_unex(&parent->core.spin);
  			hammer2_spin_unex(&chain->core.spin);
  			hammer2_mtx_unlock(&chain->lock);
  
  			return(chain);
  		}
  	}
  
  	/*
  	 * Successful 1->0 transition, no parent, no children... no way for
  	 * anyone to ref this chain any more.  We can clean-up and free it.
  	 *
  	 * We still have the core spinlock, and core's chain_count is 0.
  	 * Any parent spinlock is gone.
  	 */
  	hammer2_spin_unex(&chain->core.spin);
  	hammer2_chain_assert_no_data(chain);
  	hammer2_mtx_unlock(&chain->lock);
  	KKASSERT(RB_EMPTY(&chain->core.rbtree) &&
  		 chain->core.chain_count == 0);
  
  	/*
  	 * All locks are gone, no pointers remain to the chain, finish
  	 * freeing it.
  	 */
  	KKASSERT((chain->flags & (HAMMER2_CHAIN_UPDATE |
  				  HAMMER2_CHAIN_MODIFIED)) == 0);
  
  	/*
  	 * Once chain resources are gone we can use the now dead chain
  	 * structure to placehold what might otherwise require a recursive
  	 * drop, because we have potentially two things to drop and can only
  	 * return one directly.
  	 */
  	if (chain->flags & HAMMER2_CHAIN_ALLOCATED) {
  		atomic_clear_int(&chain->flags, HAMMER2_CHAIN_ALLOCATED);
  		chain->hmp = NULL;
  		kfree_obj(chain, hmp->mchain);
  	}
  
  	/*
  	 * Possible chaining loop when parent re-drop needed.
  	 */
  	return(rdrop);
  }
  
  /*
   * Heuristical flush of the LRU, try to reduce the number of entries
   * on the LRU to (HAMMER2_LRU_LIMIT * 2 / 3).  This procedure is called
   * only when lru_count exceeds HAMMER2_LRU_LIMIT.
   */
  static
  void
  hammer2_chain_lru_flush(hammer2_pfs_t *pmp)
  {
  	hammer2_chain_t *chain;
  
  again:
  	chain = NULL;
  	hammer2_spin_ex(&pmp->lru_spin);
  	while (pmp->lru_count > HAMMER2_LRU_LIMIT * 2 / 3) {
  		/*
  		 * Pick a chain off the lru_list, just recycle it quickly
  		 * if LRUHINT is set (the chain was ref'd but left on
  		 * the lru_list, so cycle to the end).
  		 */
  		chain = TAILQ_FIRST(&pmp->lru_list);
  		TAILQ_REMOVE(&pmp->lru_list, chain, lru_node);
  
  		if (chain->flags & HAMMER2_CHAIN_LRUHINT) {
  			atomic_clear_int(&chain->flags, HAMMER2_CHAIN_LRUHINT);
  			TAILQ_INSERT_TAIL(&pmp->lru_list, chain, lru_node);
  			chain = NULL;
  			continue;
  		}
  
  		/*
  		 * Ok, we are off the LRU.  We must adjust refs before we
  		 * can safely clear the ONLRU flag.
  		 */
  		atomic_add_int(&pmp->lru_count, -1);
  		if (atomic_cmpset_int(&chain->refs, 0, 1)) {
  			atomic_clear_int(&chain->flags, HAMMER2_CHAIN_ONLRU);
  			atomic_set_int(&chain->flags, HAMMER2_CHAIN_RELEASE);
  			break;
  		}
  		atomic_clear_int(&chain->flags, HAMMER2_CHAIN_ONLRU);
  		chain = NULL;
  	}
  	hammer2_spin_unex(&pmp->lru_spin);
  	if (chain == NULL)
  		return;
  
  	/*
  	 * If we picked a chain off the lru list we may be able to lastdrop
  	 * it.  Use a depth of 1 to prevent excessive lastdrop recursion.
  	 */
  	while (chain) {
  		u_int refs;
  
  		refs = chain->refs;
  		cpu_ccfence();
  		KKASSERT(refs > 0);
  
  		if (refs == 1) {
  			if (hammer2_mtx_ex_try(&chain->lock) == 0)
  				chain = hammer2_chain_lastdrop(chain, 1);
  			/* retry the same chain, or chain from lastdrop */
  		} else {
  			if (atomic_cmpset_int(&chain->refs, refs, refs - 1))
  				break;
  			/* retry the same chain */
  		}
  		cpu_pause();
  	}
  	goto again;
  }
  
  /*
   * On last lock release.
   */
  static hammer2_io_t *
  hammer2_chain_drop_data(hammer2_chain_t *chain)
  {
  	hammer2_io_t *dio;
  
  	if ((dio = chain->dio) != NULL) {
  		chain->dio = NULL;
  		chain->data = NULL;
  	} else {
  		switch(chain->bref.type) {
  		case HAMMER2_BREF_TYPE_VOLUME:
  		case HAMMER2_BREF_TYPE_FREEMAP:
  			break;
  		default:
  			if (chain->data != NULL) {
  				hammer2_spin_unex(&chain->core.spin);
  				panic("chain data not null: "
  				      "chain %p bref %016jx.%02x "
  				      "refs %d parent %p dio %p data %p",
  				      chain, chain->bref.data_off,
  				      chain->bref.type, chain->refs,
  				      chain->parent,
  				      chain->dio, chain->data);
  			}
  			KKASSERT(chain->data == NULL);
  			break;
  		}
  	}
  	return dio;
  }
  
  /*
   * Lock a referenced chain element, acquiring its data with I/O if necessary,
   * and specify how you would like the data to be resolved.
   *
   * If an I/O or other fatal error occurs, chain->error will be set to non-zero.
   *
   * The lock is allowed to recurse, multiple locking ops will aggregate
   * the requested resolve types.  Once data is assigned it will not be
   * removed until the last unlock.
   *
   * HAMMER2_RESOLVE_NEVER - Do not resolve the data element.
   *			   (typically used to avoid device/logical buffer
   *			    aliasing for data)
   *
   * HAMMER2_RESOLVE_MAYBE - Do not resolve data elements for chains in
   *			   the INITIAL-create state (indirect blocks only).
   *
   *			   Do not resolve data elements for DATA chains.
   *			   (typically used to avoid device/logical buffer
   *			    aliasing for data)
   *
   * HAMMER2_RESOLVE_ALWAYS- Always resolve the data element.
   *
   * HAMMER2_RESOLVE_SHARED- (flag) The chain is locked shared, otherwise
   *			   it will be locked exclusive.
   *
   * HAMMER2_RESOLVE_NONBLOCK- (flag) The chain is locked non-blocking.  If
   *			   the lock fails, EAGAIN is returned.
   *
   * 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.
   *
   * NOTE: The return value is always 0 unless NONBLOCK is specified, in which
   *	 case it can be either 0 or EAGAIN.
   *
   * WARNING! This function blocks on I/O if data needs to be fetched.  This
   *	    blocking can run concurrent with other compatible lock holders
   *	    who do not need data returning.  The lock is not upgraded to
   *	    exclusive during a data fetch, a separate bit is used to
   *	    interlock I/O.  However, an exclusive lock holder can still count
   *	    on being interlocked against an I/O fetch managed by a shared
   *	    lock holder.
   */
  int
  hammer2_chain_lock(hammer2_chain_t *chain, int how)
  {
  	KKASSERT(chain->refs > 0);
  
  	if (how & HAMMER2_RESOLVE_NONBLOCK) {
  		/*
  		 * We still have to bump lockcnt before acquiring the lock,
  		 * even for non-blocking operation, because the unlock code
  		 * live-loops on lockcnt == 1 when dropping the last lock.
  		 *
  		 * If the non-blocking operation fails we have to use an
  		 * unhold sequence to undo the mess.
  		 *
  		 * NOTE: LOCKAGAIN must always succeed without blocking,
  		 *	 even if NONBLOCK is specified.
  		 */
  		atomic_add_int(&chain->lockcnt, 1);
  		if (how & HAMMER2_RESOLVE_SHARED) {
  			if (how & HAMMER2_RESOLVE_LOCKAGAIN) {
  				hammer2_mtx_sh_again(&chain->lock);
  			} else {
  				if (hammer2_mtx_sh_try(&chain->lock) != 0) {
  					hammer2_chain_unhold(chain);
  					return EAGAIN;
  				}
  			}
  		} else {
  			if (hammer2_mtx_ex_try(&chain->lock) != 0) {
  				hammer2_chain_unhold(chain);
  				return EAGAIN;
  			}
  		}
  	} else {
  		/*
  		 * Get the appropriate lock.  If LOCKAGAIN is flagged with
  		 * SHARED the caller expects a shared lock to already be
  		 * present and we are giving it another ref.  This case must
  		 * importantly not block if there is a pending exclusive lock
  		 * request.
  		 */
  		atomic_add_int(&chain->lockcnt, 1);
  		if (how & HAMMER2_RESOLVE_SHARED) {
  			if (how & HAMMER2_RESOLVE_LOCKAGAIN) {
  				hammer2_mtx_sh_again(&chain->lock);
  			} else {
  				hammer2_mtx_sh(&chain->lock);
  			}
  		} else {
  			hammer2_mtx_ex(&chain->lock);
  		}
  	}
  
  	/*
  	 * If we already have a valid data pointer make sure the data is
  	 * synchronized to the current cpu, and then no further action is
  	 * necessary.
  	 */
  	if (chain->data) {
  		if (chain->dio)
  			hammer2_io_bkvasync(chain->dio);
  		return 0;
  	}
  
  	/*
  	 * Do we have to resolve the data?  This is generally only
  	 * applicable to HAMMER2_BREF_TYPE_DATA which is special-cased.
  	 * Other BREF types expects the data to be there.
  	 */
  	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 0
  		if (chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_NODE)
  			return 0;
  		if (chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_LEAF)
  			return 0;
  #endif
  		/* fall through */
  	case HAMMER2_RESOLVE_ALWAYS:
  	default:
  		break;
  	}
  
  	/*
  	 * Caller requires data
  	 */
  	hammer2_chain_load_data(chain);
  
  	return 0;
  }
  
  /*
   * Lock the chain, retain the hold, and drop the data persistence count.
   * The data should remain valid because we never transitioned lockcnt
   * through 0.
   */
  void
  hammer2_chain_lock_unhold(hammer2_chain_t *chain, int how)
  {
  	hammer2_chain_lock(chain, how);
  	atomic_add_int(&chain->lockcnt, -1);
  }
  
  #if 0
  /*
   * Downgrade an exclusive chain lock to a shared chain lock.
   *
   * NOTE: There is no upgrade equivalent due to the ease of
   *	 deadlocks in that direction.
   */
  void
  hammer2_chain_lock_downgrade(hammer2_chain_t *chain)
  {
  	hammer2_mtx_downgrade(&chain->lock);
  }
  #endif
  
  /*
   * Issue I/O and install chain->data.  Caller must hold a chain lock, lock
   * may be of any type.
   *
   * Once chain->data is set it cannot be disposed of until all locks are
   * released.
   *
   * Make sure the data is synchronized to the current cpu.
   */
  void
  hammer2_chain_load_data(hammer2_chain_t *chain)
  {
  	hammer2_blockref_t *bref;
  	hammer2_dev_t *hmp;
  	hammer2_io_t *dio;
  	char *bdata;
  	int error;
  
  	/*
  	 * Degenerate case, data already present, or chain has no media
  	 * reference to load.
  	 */
  	KKASSERT(chain->lock.mtx_lock & MTX_MASK);
  	if (chain->data) {
  		if (chain->dio)
  			hammer2_io_bkvasync(chain->dio);
  		return;
  	}
  	if ((chain->bref.data_off & ~HAMMER2_OFF_MASK_RADIX) == 0)
  		return;
  
  	hmp = chain->hmp;
  	KKASSERT(hmp != NULL);
  
  	/*
  	 * Gain the IOINPROG bit, interlocked block.
  	 */
  	for (;;) {
  		u_int oflags;
  		u_int nflags;
  
  		oflags = chain->flags;
  		cpu_ccfence();
  		if (oflags & HAMMER2_CHAIN_IOINPROG) {
  			nflags = oflags | HAMMER2_CHAIN_IOSIGNAL;
  			tsleep_interlock(&chain->flags, 0);
  			if (atomic_cmpset_int(&chain->flags, oflags, nflags)) {
  				tsleep(&chain->flags, PINTERLOCKED,
  					"h2iocw", 0);
  			}
  			/* retry */
  		} else {
  			nflags = oflags | HAMMER2_CHAIN_IOINPROG;
  			if (atomic_cmpset_int(&chain->flags, oflags, nflags)) {
  				break;
  			}
  			/* retry */
  		}
  	}
  
  	/*
  	 * We own CHAIN_IOINPROG
  	 *
  	 * Degenerate case if we raced another load.
  	 */
  	if (chain->data) {
  		if (chain->dio)
  			hammer2_io_bkvasync(chain->dio);
  		goto done;
  	}
  
  	/*
  	 * We must resolve to a device buffer, either by issuing I/O or
  	 * by creating a zero-fill element.  We do not mark the buffer
  	 * dirty when creating a zero-fill element (the hammer2_chain_modify()
  	 * API must still be used to do that).
  	 *
  	 * The device buffer is variable-sized in powers of 2 down
  	 * to HAMMER2_MIN_ALLOC (typically 1K).  A 64K physical storage
  	 * chunk always contains buffers of the same size. (XXX)
  	 *
  	 * The minimum physical IO size may be larger than the variable
  	 * block size.
  	 */
  	bref = &chain->bref;
  
  	/*
  	 * The getblk() optimization can only be used on newly created
  	 * elements if the physical block size matches the request.
  	 */
  	if (chain->flags & HAMMER2_CHAIN_INITIAL) {
  		error = hammer2_io_new(hmp, bref->type,
  				       bref->data_off, chain->bytes,
  				       &chain->dio);
  	} else {
  		error = hammer2_io_bread(hmp, bref->type,
  					 bref->data_off, chain->bytes,
  					 &chain->dio);
  		hammer2_adjreadcounter(chain->bref.type, chain->bytes);
  	}
  	if (error) {
  		chain->error = HAMMER2_ERROR_EIO;
  		kprintf("hammer2_chain_load_data: I/O error %016jx: %d\n",
  			(intmax_t)bref->data_off, error);
  		hammer2_io_bqrelse(&chain->dio);
  		goto done;
  	}
  	chain->error = 0;
  
  	/*
  	 * This isn't perfect and can be ignored on OSs which do not have
  	 * an indication as to whether a buffer is coming from cache or
  	 * if I/O was actually issued for the read.  TESTEDGOOD will work
  	 * pretty well without the B_IOISSUED logic because chains are
  	 * cached, but in that situation (without B_IOISSUED) it will not
  	 * detect whether a re-read via I/O is corrupted verses the original
  	 * read.
  	 *
  	 * We can't re-run the CRC on every fresh lock.  That would be
  	 * insanely expensive.
  	 *
  	 * If the underlying kernel buffer covers the entire chain we can
  	 * use the B_IOISSUED indication to determine if we have to re-run
  	 * the CRC on chain data for chains that managed to stay cached
  	 * across the kernel disposal of the original buffer.
  	 */
  	if ((dio = chain->dio) != NULL && dio->bp) {
  		struct buf *bp = dio->bp;
  
  		if (dio->psize == chain->bytes &&
  		    (bp->b_flags & B_IOISSUED)) {
  			atomic_clear_int(&chain->flags,
  					 HAMMER2_CHAIN_TESTEDGOOD);
  			bp->b_flags &= ~B_IOISSUED;
  		}
  	}
  
  	/*
  	 * NOTE: A locked chain's data cannot be modified without first
  	 *	 calling hammer2_chain_modify().
  	 */
  
  	/*
  	 * NOTE: hammer2_io_data() call issues bkvasync()
  	 */
  	bdata = hammer2_io_data(chain->dio, chain->bref.data_off);
  
  	if (chain->flags & HAMMER2_CHAIN_INITIAL) {
  		/*
  		 * Clear INITIAL.  In this case we used io_new() and the
  		 * buffer has been zero'd and marked dirty.
  		 *
  		 * CHAIN_MODIFIED has not been set yet, and we leave it
  		 * that way for now.  Set a temporary CHAIN_NOTTESTED flag
  		 * to prevent hammer2_chain_testcheck() from trying to match
  		 * a check code that has not yet been generated.  This bit
  		 * should NOT end up on the actual media.
  		 */
  		atomic_clear_int(&chain->flags, HAMMER2_CHAIN_INITIAL);
  		atomic_set_int(&chain->flags, HAMMER2_CHAIN_NOTTESTED);
  	} else if (chain->flags & HAMMER2_CHAIN_MODIFIED) {
  		/*
  		 * check data not currently synchronized due to
  		 * modification.  XXX assumes data stays in the buffer
  		 * cache, which might not be true (need biodep on flush
  		 * to calculate crc?  or simple crc?).
  		 */
  	} else if ((chain->flags & HAMMER2_CHAIN_TESTEDGOOD) == 0) {
  		if (hammer2_chain_testcheck(chain, bdata) == 0) {
  			chain->error = HAMMER2_ERROR_CHECK;
  		} else {
  			atomic_set_int(&chain->flags, HAMMER2_CHAIN_TESTEDGOOD);
  		}
  	}
  
  	/*
  	 * Setup the data pointer, either pointing it to an embedded data
  	 * structure and copying the data from the buffer, or pointing it
  	 * into the buffer.
  	 *
  	 * The buffer is not retained when copying to an embedded data
  	 * structure in order to avoid potential deadlocks or recursions
  	 * on the same physical buffer.
  	 *
  	 * WARNING! Other threads can start using the data the instant we
  	 *	    set chain->data non-NULL.
  	 */
  	switch (bref->type) {
  	case HAMMER2_BREF_TYPE_VOLUME:
  	case HAMMER2_BREF_TYPE_FREEMAP:
  		/*
  		 * Copy data from bp to embedded buffer
  		 */
  		panic("hammer2_chain_load_data: unresolved volume header");
  		break;
  	case HAMMER2_BREF_TYPE_DIRENT:
  		KKASSERT(chain->bytes != 0);
  		/* fall through */
  	case HAMMER2_BREF_TYPE_INODE:
  	case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
  	case HAMMER2_BREF_TYPE_INDIRECT:
  	case HAMMER2_BREF_TYPE_DATA:
  	case HAMMER2_BREF_TYPE_FREEMAP_NODE:
  	default:
  		/*
  		 * Point data at the device buffer and leave dio intact.
  		 */
  		chain->data = (void *)bdata;
  		break;
  	}
  
  	/*
  	 * Release HAMMER2_CHAIN_IOINPROG and signal waiters if requested.
  	 */
  done:
  	for (;;) {
  		u_int oflags;
  		u_int nflags;
  
  		oflags = chain->flags;
  		nflags = oflags & ~(HAMMER2_CHAIN_IOINPROG |
  				    HAMMER2_CHAIN_IOSIGNAL);
  		KKASSERT(oflags & HAMMER2_CHAIN_IOINPROG);
  		if (atomic_cmpset_int(&chain->flags, oflags, nflags)) {
  			if (oflags & HAMMER2_CHAIN_IOSIGNAL)
  				wakeup(&chain->flags);
  			break;
  		}
  	}
  }
  
  /*
   * Unlock and deref a chain element.
   *
   * Remember that the presence of children under chain prevent the chain's
   * destruction but do not add additional references, so the dio will still
   * be dropped.
   */
  void
  hammer2_chain_unlock(hammer2_chain_t *chain)
  {
  	hammer2_io_t *dio;
  	u_int lockcnt;
  	int iter = 0;
  
  	/*
  	 * If multiple locks are present (or being attempted) on this
  	 * particular chain we can just unlock, drop refs, and return.
  	 *
  	 * Otherwise fall-through on the 1->0 transition.
  	 */
  	for (;;) {
  		lockcnt = chain->lockcnt;
  		KKASSERT(lockcnt > 0);
  		cpu_ccfence();
  		if (lockcnt > 1) {
  			if (atomic_cmpset_int(&chain->lockcnt,
  					      lockcnt, lockcnt - 1)) {
  				hammer2_mtx_unlock(&chain->lock);
  				return;
  			}
  		} else if (hammer2_mtx_upgrade_try(&chain->lock) == 0) {
  			/* while holding the mutex exclusively */
  			if (atomic_cmpset_int(&chain->lockcnt, 1, 0))
  				break;
  		} else {
  			/*
  			 * This situation can easily occur on SMP due to
  			 * the gap inbetween the 1->0 transition and the
  			 * final unlock.  We cannot safely block on the
  			 * mutex because lockcnt might go above 1.
  			 *
  			 * XXX Sleep for one tick if it takes too long.
  			 */
  			if (++iter > 1000) {
  				if (iter > 1000 + hz) {
  					kprintf("hammer2: h2race2 %p\n", chain);
  					iter = 1000;
  				}
  				tsleep(&iter, 0, "h2race2", 1);
  			}
  			cpu_pause();
  		}
  		/* retry */
  	}
  
  	/*
  	 * Last unlock / mutex upgraded to exclusive.  Drop the data
  	 * reference.
  	 */
  	dio = hammer2_chain_drop_data(chain);
  	if (dio)
  		hammer2_io_bqrelse(&dio);
  	hammer2_mtx_unlock(&chain->lock);
  }
  
  /*
   * Unlock and hold chain data intact
   */
  void
  hammer2_chain_unlock_hold(hammer2_chain_t *chain)
  {
  	atomic_add_int(&chain->lockcnt, 1);
  	hammer2_chain_unlock(chain);
  }
  
  /*
   * Helper to obtain the blockref[] array base and count for a chain.
   *
   * XXX Not widely used yet, various use cases need to be validated and
   *     converted to use this function.
   */
  static
  hammer2_blockref_t *
  hammer2_chain_base_and_count(hammer2_chain_t *parent, int *countp)
  {
  	hammer2_blockref_t *base;
  	int count;
  
  	if (parent->flags & HAMMER2_CHAIN_INITIAL) {
  		base = NULL;
  
  		switch(parent->bref.type) {
  		case HAMMER2_BREF_TYPE_INODE:
  			count = HAMMER2_SET_COUNT;
  			break;
  		case HAMMER2_BREF_TYPE_INDIRECT:
  		case HAMMER2_BREF_TYPE_FREEMAP_NODE:
  			count = parent->bytes / sizeof(hammer2_blockref_t);
  			break;
  		case HAMMER2_BREF_TYPE_VOLUME:
  			count = HAMMER2_SET_COUNT;
  			break;
  		case HAMMER2_BREF_TYPE_FREEMAP:
  			count = HAMMER2_SET_COUNT;
  			break;
  		default:
  			panic("hammer2_chain_base_and_count: "
  			      "unrecognized blockref type: %d",
  			      parent->bref.type);
  			count = 0;
  			break;
  		}
  	} else {
  		switch(parent->bref.type) {
  		case HAMMER2_BREF_TYPE_INODE:
  			base = &parent->data->ipdata.u.blockset.blockref[0];
  			count = HAMMER2_SET_COUNT;
  			break;
  		case HAMMER2_BREF_TYPE_INDIRECT:
  		case HAMMER2_BREF_TYPE_FREEMAP_NODE:
  			base = &parent->data->npdata[0];
  			count = parent->bytes / sizeof(hammer2_blockref_t);
  			break;
  		case HAMMER2_BREF_TYPE_VOLUME:
  			base = &parent->data->voldata.
  					sroot_blockset.blockref[0];
  			count = HAMMER2_SET_COUNT;
  			break;
  		case HAMMER2_BREF_TYPE_FREEMAP:
  			base = &parent->data->blkset.blockref[0];
  			count = HAMMER2_SET_COUNT;
  			break;
  		default:
  			panic("hammer2_chain_base_and_count: "
  			      "unrecognized blockref type: %d",
  			      parent->bref.type);
  			base = NULL;
  			count = 0;
  			break;
  		}
  	}
  	*countp = count;
  
  	return base;
  }
  
  /*
   * This counts the number of live blockrefs in a block array and
   * also calculates the point at which all remaining blockrefs are empty.
   * This routine can only be called on a live chain.
   *
   * Caller holds the chain locked, but possibly with a shared lock.  We
   * must use an exclusive spinlock to prevent corruption.
   *
   * NOTE: Flag is not set until after the count is complete, allowing
   *	 callers to test the flag without holding the spinlock.
   *
   * NOTE: If base is NULL the related chain is still in the INITIAL
   *	 state and there are no blockrefs to count.
   *
   * NOTE: live_count may already have some counts accumulated due to
   *	 creation and deletion and could even be initially negative.
   */
  void
  hammer2_chain_countbrefs(hammer2_chain_t *chain,
  			 hammer2_blockref_t *base, int count)
  {
  	hammer2_spin_ex(&chain->core.spin);
          if ((chain->flags & HAMMER2_CHAIN_COUNTEDBREFS) == 0) {
  		if (base) {
  			while (--count >= 0) {
  				if (base[count].type != HAMMER2_BREF_TYPE_EMPTY)
  					break;
  			}
  			chain->core.live_zero = count + 1;
  			while (count >= 0) {
  				if (base[count].type != HAMMER2_BREF_TYPE_EMPTY)
  					atomic_add_int(&chain->core.live_count,
  						       1);
  				--count;
  			}
  		} else {
  			chain->core.live_zero = 0;
  		}
  		/* else do not modify live_count */
  		atomic_set_int(&chain->flags, HAMMER2_CHAIN_COUNTEDBREFS);
  	}
  	hammer2_spin_unex(&chain->core.spin);
  }
  
  /*
   * Resize the chain's physical storage allocation in-place.  This function does
   * not usually adjust the data pointer and must be followed by (typically) a
   * hammer2_chain_modify() call to copy any old data over and adjust the
   * data pointer.
   *
   * Chains can be resized smaller without reallocating the storage.  Resizing
   * larger will reallocate the storage.  Excess or prior storage is reclaimed
   * asynchronously at a later time.
   *
   * An nradix value of 0 is special-cased to mean that the storage should
   * be disassociated, that is the chain is being resized to 0 bytes (not 1
   * byte).
   *
   * Must be passed an exclusively locked parent and chain.
   *
   * This function is mostly used with DATA blocks locked RESOLVE_NEVER in order
   * to avoid instantiating a device buffer that conflicts with the vnode data
   * buffer.  However, because H2 can compress or encrypt data, the chain may
   * have a dio assigned to it in those situations, and they do not conflict.
   *
   * XXX return error if cannot resize.
   */
  int
  hammer2_chain_resize(hammer2_chain_t *chain,
  		     hammer2_tid_t mtid, hammer2_off_t dedup_off,
  		     int nradix, int flags)
  {
  	hammer2_dev_t *hmp;
  	size_t obytes;
  	size_t nbytes;
  	int error;
  
  	hmp = chain->hmp;
  
  	/*
  	 * Only data and indirect blocks can be resized for now.
  	 * (The volu root, inodes, and freemap elements use a fixed size).
  	 */
  	KKASSERT(chain != &hmp->vchain);
  	KKASSERT(chain->bref.type == HAMMER2_BREF_TYPE_DATA ||
  		 chain->bref.type == HAMMER2_BREF_TYPE_INDIRECT ||
  		 chain->bref.type == HAMMER2_BREF_TYPE_DIRENT);
  
  	/*
  	 * Nothing to do if the element is already the proper size
  	 */
  	obytes = chain->bytes;
  	nbytes = (nradix) ? (1U << nradix) : 0;
  	if (obytes == nbytes)
  		return (chain->error);
  
  	/*
  	 * Make sure the old data is instantiated so we can copy it.  If this
  	 * is a data block, the device data may be superfluous since the data
  	 * might be in a logical block, but compressed or encrypted data is
  	 * another matter.
  	 *
  	 * NOTE: The modify will set BLKMAPUPD for us if BLKMAPPED is set.
  	 */
  	error = hammer2_chain_modify(chain, mtid, dedup_off, 0);
  	if (error)
  		return error;
  
  	/*
  	 * Reallocate the block, even if making it smaller (because different
  	 * block sizes may be in different regions).
  	 *
  	 * NOTE: Operation does not copy the data and may only be used
  	 *	 to resize data blocks in-place, or directory entry blocks
  	 *	 which are about to be modified in some manner.
  	 */
  	error = hammer2_freemap_alloc(chain, nbytes);
  	if (error)
  		return error;
  
  	chain->bytes = nbytes;
  
  	/*
  	 * We don't want the followup chain_modify() to try to copy data
  	 * from the old (wrong-sized) buffer.  It won't know how much to
  	 * copy.  This case should only occur during writes when the
  	 * originator already has the data to write in-hand.
  	 */
  	if (chain->dio) {
  		KKASSERT(chain->bref.type == HAMMER2_BREF_TYPE_DATA ||
  			 chain->bref.type == HAMMER2_BREF_TYPE_DIRENT);
  		hammer2_io_brelse(&chain->dio);
  		chain->data = NULL;
  	}
  	return (chain->error);
  }
  
  /*
   * Set the chain modified so its data can be changed by the caller, or
   * install deduplicated data.  The caller must call this routine for each
   * set of modifications it makes, even if the chain is already flagged
   * MODIFIED.
   *
   * Sets bref.modify_tid to mtid only if mtid != 0.  Note that bref.modify_tid
   * is a CLC (cluster level change) field and is not updated by parent
   * propagation during a flush.
   *
   * Returns an appropriate HAMMER2_ERROR_* code, which will generally reflect
   * chain->error except for HAMMER2_ERROR_ENOSPC.  If the allocation fails
   * due to no space available, HAMMER2_ERROR_ENOSPC is returned and the chain
   * remains unmodified with its old data ref intact and chain->error
   * unchanged.
   *
   *				 Dedup Handling
   *
   * If the DEDUPABLE flag is set in the chain the storage must be reallocated
   * even if the chain is still flagged MODIFIED.  In this case the chain's
   * DEDUPABLE flag will be cleared once the new storage has been assigned.
   *
   * If the caller passes a non-zero dedup_off we will use it to assign the
   * new storage.  The MODIFIED flag will be *CLEARED* in this case, and
   * DEDUPABLE will be set (NOTE: the UPDATE flag is always set).  The caller
   * must not modify the data content upon return.
   */
  int
  hammer2_chain_modify(hammer2_chain_t *chain, hammer2_tid_t mtid,
  		     hammer2_off_t dedup_off, int flags)
  {
  	hammer2_blockref_t obref;
  	hammer2_dev_t *hmp;
  	hammer2_io_t *dio;
  	int error;
  	int wasinitial;
  	int setmodified;
  	int setupdate;
  	int newmod;
  	char *bdata;
  
  	hmp = chain->hmp;
  	obref = chain->bref;
  	KKASSERT(chain->lock.mtx_lock & MTX_EXCLUSIVE);
  
  	/*
  	 * Data is not optional for freemap chains (we must always be sure
  	 * to copy the data on COW storage allocations).
  	 */
  	if (chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_NODE ||
  	    chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_LEAF) {
  		KKASSERT((chain->flags & HAMMER2_CHAIN_INITIAL) ||
  			 (flags & HAMMER2_MODIFY_OPTDATA) == 0);
  	}
  
  	/*
  	 * Data must be resolved if already assigned, unless explicitly
  	 * flagged otherwise.  If we cannot safety load the data the
  	 * modification fails and we return early.
  	 */
  	if (chain->data == NULL && chain->bytes != 0 &&
  	    (flags & HAMMER2_MODIFY_OPTDATA) == 0 &&
  	    (chain->bref.data_off & ~HAMMER2_OFF_MASK_RADIX)) {
  		hammer2_chain_load_data(chain);
  		if (chain->error)
  			return (chain->error);
  	}
  	error = 0;
  
  	/*
  	 * Set MODIFIED to indicate that the chain has been modified.  A new
  	 * allocation is required when modifying a chain.
  	 *
  	 * Set UPDATE to ensure that the blockref is updated in the parent.
  	 *
  	 * If MODIFIED is already set determine if we can reuse the assigned
  	 * data block or if we need a new data block.
  	 */
  	if ((chain->flags & HAMMER2_CHAIN_MODIFIED) == 0) {
  		/*
  		 * Must set modified bit.
  		 */
  		atomic_add_long(&hammer2_count_modified_chains, 1);
  		atomic_set_int(&chain->flags, HAMMER2_CHAIN_MODIFIED);
  		hammer2_pfs_memory_inc(chain->pmp);  /* can be NULL */
  		setmodified = 1;
  
  		/*
  		 * We may be able to avoid a copy-on-write if the chain's
  		 * check mode is set to NONE and the chain's current
  		 * modify_tid is beyond the last explicit snapshot tid.
  		 *
  		 * This implements HAMMER2's overwrite-in-place feature.
  		 *
  		 * NOTE! This data-block cannot be used as a de-duplication
  		 *	 source when the check mode is set to NONE.
  		 */
  		if ((chain->bref.type == HAMMER2_BREF_TYPE_DATA ||
  		     chain->bref.type == HAMMER2_BREF_TYPE_DIRENT) &&
  		    (chain->flags & HAMMER2_CHAIN_INITIAL) == 0 &&
  		    (chain->flags & HAMMER2_CHAIN_DEDUPABLE) == 0 &&
  		    HAMMER2_DEC_CHECK(chain->bref.methods) ==
  		     HAMMER2_CHECK_NONE &&
  		    chain->pmp &&
  		    chain->bref.modify_tid >
  		     chain->pmp->iroot->meta.pfs_lsnap_tid) {
  			/*
  			 * Sector overwrite allowed.
  			 */
  			newmod = 0;
  		} else if ((hmp->hflags & HMNT2_EMERG) &&
  			   chain->pmp &&
  			   chain->bref.modify_tid >
  			    chain->pmp->iroot->meta.pfs_lsnap_tid) {
  			/*
  			 * If in emergency delete mode then do a modify-in-
  			 * place on any chain type belonging to the PFS as
  			 * long as it doesn't mess up a snapshot.  We might
  			 * be forced to do this anyway a little further down
  			 * in the code if the allocation fails.
  			 *
  			 * Also note that in emergency mode, these modify-in-
  			 * place operations are NOT SAFE.  A storage failure,
  			 * power failure, or panic can corrupt the filesystem.
  			 */
  			newmod = 0;
  		} else {
  			/*
  			 * Sector overwrite not allowed, must copy-on-write.
  			 */
  			newmod = 1;
  		}
  	} else if (chain->flags & HAMMER2_CHAIN_DEDUPABLE) {
  		/*
  		 * If the modified chain was registered for dedup we need
  		 * a new allocation.  This only happens for delayed-flush
  		 * chains (i.e. which run through the front-end buffer
  		 * cache).
  		 */
  		newmod = 1;
  		setmodified = 0;
  	} else {
  		/*
  		 * Already flagged modified, no new allocation is needed.
  		 */
  		newmod = 0;
  		setmodified = 0;
  	}
  
  	/*
  	 * Flag parent update required.
  	 */
  	if ((chain->flags & HAMMER2_CHAIN_UPDATE) == 0) {
  		atomic_set_int(&chain->flags, HAMMER2_CHAIN_UPDATE);
  		setupdate = 1;
  	} else {
  		setupdate = 0;
  	}
  
  	/*
  	 * The XOP code returns held but unlocked focus chains.  This
  	 * prevents the chain from being destroyed but does not prevent
  	 * it from being modified.  diolk is used to interlock modifications
  	 * against XOP frontend accesses to the focus.
  	 *
  	 * This allows us to theoretically avoid deadlocking the frontend
  	 * if one of the backends lock up by not formally locking the
  	 * focused chain in the frontend.  In addition, the synchronization
  	 * code relies on this mechanism to avoid deadlocking concurrent
  	 * synchronization threads.
  	 */
  	lockmgr(&chain->diolk, LK_EXCLUSIVE);
  
  	/*
  	 * The modification or re-modification requires an allocation and
  	 * possible COW.  If an error occurs, the previous content and data
  	 * reference is retained and the modification fails.
  	 *
  	 * If dedup_off is non-zero, the caller is requesting a deduplication
  	 * rather than a modification.  The MODIFIED bit is not set and the
  	 * data offset is set to the deduplication offset.  The data cannot
  	 * be modified.
  	 *
  	 * NOTE: The dedup offset is allowed to be in a partially free state
  	 *	 and we must be sure to reset it to a fully allocated state
  	 *	 to force two bulkfree passes to free it again.
  	 *
  	 * NOTE: Only applicable when chain->bytes != 0.
  	 *
  	 * XXX can a chain already be marked MODIFIED without a data
  	 * assignment?  If not, assert here instead of testing the case.
  	 */
  	if (chain != &hmp->vchain && chain != &hmp->fchain &&
  	    chain->bytes) {
  		if ((chain->bref.data_off & ~HAMMER2_OFF_MASK_RADIX) == 0 ||
  		    newmod
  		) {
  			/*
  			 * NOTE: We do not have to remove the dedup
  			 *	 registration because the area is still
  			 *	 allocated and the underlying DIO will
  			 *	 still be flushed.
  			 */
  			if (dedup_off) {
  				chain->bref.data_off = dedup_off;
  				if ((int)(dedup_off & HAMMER2_OFF_MASK_RADIX))
  					chain->bytes = 1 <<
  						(int)(dedup_off &
  						HAMMER2_OFF_MASK_RADIX);
  				else
  					chain->bytes = 0;
  				chain->error = 0;
  				atomic_clear_int(&chain->flags,
  						 HAMMER2_CHAIN_MODIFIED);
  				atomic_add_long(&hammer2_count_modified_chains,
  						-1);
  				if (chain->pmp) {
  					hammer2_pfs_memory_wakeup(
  						chain->pmp, -1);
  				}
  				hammer2_freemap_adjust(hmp, &chain->bref,
  						HAMMER2_FREEMAP_DORECOVER);
  				atomic_set_int(&chain->flags,
  						HAMMER2_CHAIN_DEDUPABLE);
  			} else {
  				error = hammer2_freemap_alloc(chain,
  							      chain->bytes);
  				atomic_clear_int(&chain->flags,
  						HAMMER2_CHAIN_DEDUPABLE);
  
  				/*
  				 * If we are unable to allocate a new block
  				 * but we are in emergency mode, issue a
  				 * warning to the console and reuse the same
  				 * block.
  				 *
  				 * We behave as if the allocation were
  				 * successful.
  				 *
  				 * THIS IS IMPORTANT: These modifications
  				 * are virtually guaranteed to corrupt any
  				 * snapshots related to this filesystem.
  				 */
  				if (error && (hmp->hflags & HMNT2_EMERG)) {
  					error = 0;
  					chain->bref.flags |=
  						HAMMER2_BREF_FLAG_EMERG_MIP;
  
  					krateprintf(&krate_h2em,
  					    "hammer2: Emergency Mode WARNING: "
  					    "Operation will likely corrupt "
  					    "related snapshot: "
  					    "%016jx.%02x key=%016jx\n",
  					    chain->bref.data_off,
  					    chain->bref.type,
  					    chain->bref.key);
  				} else if (error == 0) {
  					chain->bref.flags &=
  						~HAMMER2_BREF_FLAG_EMERG_MIP;
  				}
  			}
  		}
  	}
  
  	/*
  	 * Stop here if error.  We have to undo any flag bits we might
  	 * have set above.
  	 */
  	if (error) {
  		if (setmodified) {
  			atomic_clear_int(&chain->flags, HAMMER2_CHAIN_MODIFIED);
  			atomic_add_long(&hammer2_count_modified_chains, -1);
  			if (chain->pmp)
  				hammer2_pfs_memory_wakeup(chain->pmp, -1);
  		}
  		if (setupdate) {
  			atomic_clear_int(&chain->flags, HAMMER2_CHAIN_UPDATE);
  		}
  		lockmgr(&chain->diolk, LK_RELEASE);
  
  		return error;
  	}
  
  	/*
  	 * Update mirror_tid and modify_tid.  modify_tid is only updated
  	 * if not passed as zero (during flushes, parent propagation passes
  	 * the value 0).
  	 *
  	 * NOTE: chain->pmp could be the device spmp.
  	 */
  	chain->bref.mirror_tid = hmp->voldata.mirror_tid + 1;
  	if (mtid)
  		chain->bref.modify_tid = mtid;
  
  	/*
  	 * Set BLKMAPUPD to tell the flush code that an existing blockmap entry
  	 * requires updating as well as to tell the delete code that the
  	 * chain's blockref might not exactly match (in terms of physical size
  	 * or block offset) the one in the parent's blocktable.  The base key
  	 * of course will still match.
  	 */
  	if (chain->flags & HAMMER2_CHAIN_BLKMAPPED)
  		atomic_set_int(&chain->flags, HAMMER2_CHAIN_BLKMAPUPD);
  
  	/*
  	 * Short-cut data block handling when the caller does not need an
  	 * actual data reference to (aka OPTDATA), as long as the chain does
  	 * not already have a data pointer to the data and no de-duplication
  	 * occurred.
  	 *
  	 * This generally means that the modifications are being done via the
  	 * logical buffer cache.
  	 *
  	 * NOTE: If deduplication occurred we have to run through the data
  	 *	 stuff to clear INITIAL, and the caller will likely want to
  	 *	 assign the check code anyway.  Leaving INITIAL set on a
  	 *	 dedup can be deadly (it can cause the block to be zero'd!).
  	 *
  	 * This code also handles bytes == 0 (most dirents).
  	 */
  	if (chain->bref.type == HAMMER2_BREF_TYPE_DATA &&
  	    (flags & HAMMER2_MODIFY_OPTDATA) &&
  	    chain->data == NULL) {
  		if (dedup_off == 0) {
  			KKASSERT(chain->dio == NULL);
  			goto skip2;
  		}
  	}
  
  	/*
  	 * Clearing the INITIAL flag (for indirect blocks) indicates that
  	 * we've processed the uninitialized storage allocation.
  	 *
  	 * If this flag is already clear we are likely in a copy-on-write
  	 * situation but we have to be sure NOT to bzero the storage if
  	 * no data is present.
  	 *
  	 * Clearing of NOTTESTED is allowed if the MODIFIED bit is set,
  	 */
  	if (chain->flags & HAMMER2_CHAIN_INITIAL) {
  		atomic_clear_int(&chain->flags, HAMMER2_CHAIN_INITIAL);
  		wasinitial = 1;
  	} else {
  		wasinitial = 0;
  	}
  
  	/*
  	 * Instantiate data buffer and possibly execute COW operation
  	 */
  	switch(chain->bref.type) {
  	case HAMMER2_BREF_TYPE_VOLUME:
  	case HAMMER2_BREF_TYPE_FREEMAP:
  		/*
  		 * The data is embedded, no copy-on-write operation is
  		 * needed.
  		 */
  		KKASSERT(chain->dio == NULL);
  		break;
  	case HAMMER2_BREF_TYPE_DIRENT:
  		/*
  		 * The data might be fully embedded.
  		 */
  		if (chain->bytes == 0) {
  			KKASSERT(chain->dio == NULL);
  			break;
  		}
  		/* fall through */
  	case HAMMER2_BREF_TYPE_INODE:
  	case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
  	case HAMMER2_BREF_TYPE_DATA:
  	case HAMMER2_BREF_TYPE_INDIRECT:
  	case HAMMER2_BREF_TYPE_FREEMAP_NODE:
  		/*
  		 * Perform the copy-on-write operation
  		 *
  		 * zero-fill or copy-on-write depending on whether
  		 * chain->data exists or not and set the dirty state for
  		 * the new buffer.  hammer2_io_new() will handle the
  		 * zero-fill.
  		 *
  		 * If a dedup_off was supplied this is an existing block
  		 * and no COW, copy, or further modification is required.
  		 */
  		KKASSERT(chain != &hmp->vchain && chain != &hmp->fchain);
  
  		if (wasinitial && dedup_off == 0) {
  			error = hammer2_io_new(hmp, chain->bref.type,
  					       chain->bref.data_off,
  					       chain->bytes, &dio);
  		} else {
  			error = hammer2_io_bread(hmp, chain->bref.type,
  						 chain->bref.data_off,
  						 chain->bytes, &dio);
  		}
  		hammer2_adjreadcounter(chain->bref.type, chain->bytes);
  
  		/*
  		 * If an I/O error occurs make sure callers cannot accidently
  		 * modify the old buffer's contents and corrupt the filesystem.
  		 *
  		 * NOTE: hammer2_io_data() call issues bkvasync()
  		 */
  		if (error) {
  			kprintf("hammer2_chain_modify: hmp=%p I/O error\n",
  				hmp);
  			chain->error = HAMMER2_ERROR_EIO;
  			hammer2_io_brelse(&dio);
  			hammer2_io_brelse(&chain->dio);
  			chain->data = NULL;
  			break;
  		}
  		chain->error = 0;
  		bdata = hammer2_io_data(dio, chain->bref.data_off);
  
  		if (chain->data) {
  			/*
  			 * COW (unless a dedup).
  			 */
  			KKASSERT(chain->dio != NULL);
  			if (chain->data != (void *)bdata && dedup_off == 0) {
  				bcopy(chain->data, bdata, chain->bytes);
  			}
  		} else if (wasinitial == 0 && dedup_off == 0) {
  			/*
  			 * We have a problem.  We were asked to COW but
  			 * we don't have any data to COW with!
  			 */
  			panic("hammer2_chain_modify: having a COW %p\n",
  			      chain);
  		}
  
  		/*
  		 * Retire the old buffer, replace with the new.  Dirty or
  		 * redirty the new buffer.
  		 *
  		 * WARNING! The system buffer cache may have already flushed
  		 *	    the buffer, so we must be sure to [re]dirty it
  		 *	    for further modification.
  		 *
  		 *	    If dedup_off was supplied, the caller is not
  		 *	    expected to make any further modification to the
  		 *	    buffer.
  		 *
  		 * WARNING! hammer2_get_gdata() assumes dio never transitions
  		 *	    through NULL in order to optimize away unnecessary
  		 *	    diolk operations.
  		 */
  		{
  			hammer2_io_t *tio;
  
  			if ((tio = chain->dio) != NULL)
  				hammer2_io_bqrelse(&tio);
  			chain->data = (void *)bdata;
  			chain->dio = dio;
  			if (dedup_off == 0)
  				hammer2_io_setdirty(dio);
  		}
  		break;
  	default:
  		panic("hammer2_chain_modify: illegal non-embedded type %d",
  		      chain->bref.type);
  		break;
  
  	}
  skip2:
  	/*
  	 * setflush on parent indicating that the parent must recurse down
  	 * to us.  Do not call on chain itself which might already have it
  	 * set.
  	 */
  	if (chain->parent)
  		hammer2_chain_setflush(chain->parent);
  	lockmgr(&chain->diolk, LK_RELEASE);
  
  	return (chain->error);
  }
  
  /*
   * Modify the chain associated with an inode.
   */
  int
  hammer2_chain_modify_ip(hammer2_inode_t *ip, hammer2_chain_t *chain,
  			hammer2_tid_t mtid, int flags)
  {
  	int error;
  
  	hammer2_inode_modify(ip);
  	error = hammer2_chain_modify(chain, mtid, 0, flags);
  
  	return error;
  }
  
  /*
   * This function returns the chain at the nearest key within the specified
   * range.  The returned chain will be referenced but not locked.
   *
   * This function will recurse through chain->rbtree as necessary and will
   * return a *key_nextp suitable for iteration.  *key_nextp is only set if
   * the iteration value is less than the current value of *key_nextp.
   *
   * The caller should use (*key_nextp) to calculate the actual range of
   * the returned element, which will be (key_beg to *key_nextp - 1), because
   * there might be another element which is superior to the returned element
   * and overlaps it.
   *
   * (*key_nextp) can be passed as key_beg in an iteration only while non-NULL
   * chains continue to be returned.  On EOF (*key_nextp) may overflow since
   * it will wind up being (key_end + 1).
   *
   * WARNING!  Must be called with child's spinlock held.  Spinlock remains
   *	     held through the operation.
   */
  struct hammer2_chain_find_info {
  	hammer2_chain_t		*best;
  	hammer2_key_t		key_beg;
  	hammer2_key_t		key_end;
  	hammer2_key_t		key_next;
  };
  
  static int hammer2_chain_find_cmp(hammer2_chain_t *child, void *data);
  static int hammer2_chain_find_callback(hammer2_chain_t *child, void *data);
  
  static
  hammer2_chain_t *
  hammer2_chain_find(hammer2_chain_t *parent, hammer2_key_t *key_nextp,
  			  hammer2_key_t key_beg, hammer2_key_t key_end)
  {
  	struct hammer2_chain_find_info info;
  
  	info.best = NULL;
  	info.key_beg = key_beg;
  	info.key_end = key_end;
  	info.key_next = *key_nextp;
  
  	RB_SCAN(hammer2_chain_tree, &parent->core.rbtree,
  		hammer2_chain_find_cmp, hammer2_chain_find_callback,
  		&info);
  	*key_nextp = info.key_next;
  #if 0
  	kprintf("chain_find %p %016jx:%016jx next=%016jx\n",
  		parent, key_beg, key_end, *key_nextp);
  #endif
  
  	return (info.best);
  }
  
  static
  int
  hammer2_chain_find_cmp(hammer2_chain_t *child, void *data)
  {
  	struct hammer2_chain_find_info *info = data;
  	hammer2_key_t child_beg;
  	hammer2_key_t child_end;
  
  	child_beg = child->bref.key;
  	child_end = child_beg + ((hammer2_key_t)1 << child->bref.keybits) - 1;
  
  	if (child_end < info->key_beg)
  		return(-1);
  	if (child_beg > info->key_end)
  		return(1);
  	return(0);
  }
  
  static
  int
  hammer2_chain_find_callback(hammer2_chain_t *child, void *data)
  {
  	struct hammer2_chain_find_info *info = data;
  	hammer2_chain_t *best;
  	hammer2_key_t child_end;
  
  	/*
  	 * WARNING! Layerq is scanned forwards, exact matches should keep
  	 *	    the existing info->best.
  	 */
  	if ((best = info->best) == NULL) {
  		/*
  		 * No previous best.  Assign best
  		 */
  		info->best = child;
  	} else if (best->bref.key <= info->key_beg &&
  		   child->bref.key <= info->key_beg) {
  		/*
  		 * Illegal overlap.
  		 */
  		KKASSERT(0);
  		/*info->best = child;*/
  	} else if (child->bref.key < best->bref.key) {
  		/*
  		 * Child has a nearer key and best is not flush with key_beg.
  		 * Set best to child.  Truncate key_next to the old best key.
  		 */
  		info->best = child;
  		if (info->key_next > best->bref.key || info->key_next == 0)
  			info->key_next = best->bref.key;
  	} else if (child->bref.key == best->bref.key) {
  		/*
  		 * If our current best is flush with the child then this
  		 * is an illegal overlap.
  		 *
  		 * key_next will automatically be limited to the smaller of
  		 * the two end-points.
  		 */
  		KKASSERT(0);
  		info->best = child;
  	} else {
  		/*
  		 * Keep the current best but truncate key_next to the child's
  		 * base.
  		 *
  		 * key_next will also automatically be limited to the smaller
  		 * of the two end-points (probably not necessary for this case
  		 * but we do it anyway).
  		 */
  		if (info->key_next > child->bref.key || info->key_next == 0)
  			info->key_next = child->bref.key;
  	}
  
  	/*
  	 * Always truncate key_next based on child's end-of-range.
  	 */
  	child_end = child->bref.key + ((hammer2_key_t)1 << child->bref.keybits);
  	if (child_end && (info->key_next > child_end || info->key_next == 0))
  		info->key_next = child_end;
  
  	return(0);
  }
  
  /*
   * Retrieve the specified chain from a media blockref, creating the
   * in-memory chain structure which reflects it.  The returned chain is
   * held and locked according to (how) (HAMMER2_RESOLVE_*).  The caller must
   * handle crc-checks and so forth, and should check chain->error before
   * assuming that the data is good.
   *
   * To handle insertion races pass the INSERT_RACE flag along with the
   * generation number of the core.  NULL will be returned if the generation
   * number changes before we have a chance to insert the chain.  Insert
   * races can occur because the parent might be held shared.
   *
   * Caller must hold the parent locked shared or exclusive since we may
   * need the parent's bref array to find our block.
   *
   * WARNING! chain->pmp is always set to NULL for any chain representing
   *	    part of the super-root topology.
   */
  hammer2_chain_t *
  hammer2_chain_get(hammer2_chain_t *parent, int generation,
  		  hammer2_blockref_t *bref, int how)
  {
  	hammer2_dev_t *hmp = parent->hmp;
  	hammer2_chain_t *chain;
  	int error;
  
  	/*
  	 * Allocate a chain structure representing the existing media
  	 * entry.  Resulting chain has one ref and is not locked.
  	 */
  	if (bref->flags & HAMMER2_BREF_FLAG_PFSROOT)
  		chain = hammer2_chain_alloc(hmp, NULL, bref);
  	else
  		chain = hammer2_chain_alloc(hmp, parent->pmp, bref);
  	/* ref'd chain returned */
  
  	/*
  	 * Flag that the chain is in the parent's blockmap so delete/flush
  	 * knows what to do with it.
  	 */
  	atomic_set_int(&chain->flags, HAMMER2_CHAIN_BLKMAPPED);
  
  	/*
  	 * chain must be locked to avoid unexpected ripouts
  	 */
  	hammer2_chain_lock(chain, how);
  
  	/*
  	 * Link the chain into its parent.  A spinlock is required to safely
  	 * access the RBTREE, and it is possible to collide with another
  	 * hammer2_chain_get() operation because the caller might only hold
  	 * a shared lock on the parent.
  	 *
  	 * NOTE: Get races can occur quite often when we distribute
  	 *	 asynchronous read-aheads across multiple threads.
  	 */
  	KKASSERT(parent->refs > 0);
  	error = hammer2_chain_insert(parent, chain,
  				     HAMMER2_CHAIN_INSERT_SPIN |
  				     HAMMER2_CHAIN_INSERT_RACE,
  				     generation);
  	if (error) {
  		KKASSERT((chain->flags & HAMMER2_CHAIN_ONRBTREE) == 0);
  		/*kprintf("chain %p get race\n", chain);*/
  		hammer2_chain_unlock(chain);
  		hammer2_chain_drop(chain);
  		chain = NULL;
  	} else {
  		KKASSERT(chain->flags & HAMMER2_CHAIN_ONRBTREE);
  	}
  
  	/*
  	 * Return our new chain referenced but not locked, or NULL if
  	 * a race occurred.
  	 */
  	return (chain);
  }
  
  /*
   * Lookup initialization/completion API
   */
  hammer2_chain_t *
  hammer2_chain_lookup_init(hammer2_chain_t *parent, int flags)
  {
  	hammer2_chain_ref(parent);
  	if (flags & HAMMER2_LOOKUP_SHARED) {
  		hammer2_chain_lock(parent, HAMMER2_RESOLVE_ALWAYS |
  					   HAMMER2_RESOLVE_SHARED);
  	} else {
  		hammer2_chain_lock(parent, HAMMER2_RESOLVE_ALWAYS);
  	}
  	return (parent);
  }
  
  void
  hammer2_chain_lookup_done(hammer2_chain_t *parent)
  {
  	if (parent) {
  		hammer2_chain_unlock(parent);
  		hammer2_chain_drop(parent);
  	}
  }
  
  /*
   * Take the locked chain and return a locked parent.  The chain remains
   * locked on return, but may have to be temporarily unlocked to acquire
   * the parent.  Because of this, (chain) must be stable and cannot be
   * deleted while it was temporarily unlocked (typically means that (chain)
   * is an inode).
   *
   * Pass HAMMER2_RESOLVE_* flags in flags.
   *
   * This will work even if the chain is errored, and the caller can check
   * parent->error on return if desired since the parent will be locked.
   *
   * This function handles the lock order reversal.
   */
  hammer2_chain_t *
  hammer2_chain_getparent(hammer2_chain_t *chain, int flags)
  {
  	hammer2_chain_t *parent;
  
  	/*
  	 * Be careful of order, chain must be unlocked before parent
  	 * is locked below to avoid a deadlock.  Try it trivially first.
  	 */
  	parent = chain->parent;
  	if (parent == NULL)
  		panic("hammer2_chain_getparent: no parent");
  	hammer2_chain_ref(parent);
  	if (hammer2_chain_lock(parent, flags|HAMMER2_RESOLVE_NONBLOCK) == 0)
  		return parent;
  
  	for (;;) {
  		hammer2_chain_unlock(chain);
  		hammer2_chain_lock(parent, flags);
  		hammer2_chain_lock(chain, flags);
  
  		/*
  		 * Parent relinking races are quite common.  We have to get
  		 * it right or we will blow up the block table.
  		 */
  		if (chain->parent == parent)
  			break;
  		hammer2_chain_unlock(parent);
  		hammer2_chain_drop(parent);
  		cpu_ccfence();
  		parent = chain->parent;
  		if (parent == NULL)
  			panic("hammer2_chain_getparent: no parent");
  		hammer2_chain_ref(parent);
  	}
  	return parent;
  }
  
  /*
   * Take the locked chain and return a locked parent.  The chain is unlocked
   * and dropped.  *chainp is set to the returned parent as a convenience.
   * Pass HAMMER2_RESOLVE_* flags in flags.
   *
   * This will work even if the chain is errored, and the caller can check
   * parent->error on return if desired since the parent will be locked.
   *
   * The chain does NOT need to be stable.  We use a tracking structure
   * to track the expected parent if the chain is deleted out from under us.
   *
   * This function handles the lock order reversal.
   */
  hammer2_chain_t *
  hammer2_chain_repparent(hammer2_chain_t **chainp, int flags)
  {
  	hammer2_chain_t *chain;
  	hammer2_chain_t *parent;
  	struct hammer2_reptrack reptrack;
  	struct hammer2_reptrack **repp;
  
  	/*
  	 * Be careful of order, chain must be unlocked before parent
  	 * is locked below to avoid a deadlock.  Try it trivially first.
  	 */
  	chain = *chainp;
  	parent = chain->parent;
  	if (parent == NULL) {
  		hammer2_spin_unex(&chain->core.spin);
  		panic("hammer2_chain_repparent: no parent");
  	}
  	hammer2_chain_ref(parent);
  	if (hammer2_chain_lock(parent, flags|HAMMER2_RESOLVE_NONBLOCK) == 0) {
  		hammer2_chain_unlock(chain);
  		hammer2_chain_drop(chain);
  		*chainp = parent;
  
  		return parent;
  	}
  
  	/*
  	 * Ok, now it gets a bit nasty.  There are multiple situations where
  	 * the parent might be in the middle of a deletion, or where the child
  	 * (chain) might be deleted the instant we let go of its lock.
  	 * We can potentially end up in a no-win situation!
  	 *
  	 * In particular, the indirect_maintenance() case can cause these
  	 * situations.
  	 *
  	 * To deal with this we install a reptrack structure in the parent
  	 * This reptrack structure 'owns' the parent ref and will automatically
  	 * migrate to the parent's parent if the parent is deleted permanently.
  	 */
  	hammer2_spin_init(&reptrack.spin, "h2reptrk");
  	reptrack.chain = parent;
  	hammer2_chain_ref(parent);		/* for the reptrack */
  
  	hammer2_spin_ex(&parent->core.spin);
  	reptrack.next = parent->core.reptrack;
  	parent->core.reptrack = &reptrack;
  	hammer2_spin_unex(&parent->core.spin);
  
  	hammer2_chain_unlock(chain);
  	hammer2_chain_drop(chain);
  	chain = NULL;	/* gone */
  
  	/*
  	 * At the top of this loop, chain is gone and parent is refd both
  	 * by us explicitly AND via our reptrack.  We are attempting to
  	 * lock parent.
  	 */
  	for (;;) {
  		hammer2_chain_lock(parent, flags);
  
  		if (reptrack.chain == parent)
  			break;
  		hammer2_chain_unlock(parent);
  		hammer2_chain_drop(parent);
  
  		kprintf("hammer2: debug REPTRACK %p->%p\n",
  			parent, reptrack.chain);
  		hammer2_spin_ex(&reptrack.spin);
  		parent = reptrack.chain;
  		hammer2_chain_ref(parent);
  		hammer2_spin_unex(&reptrack.spin);
  	}
  
  	/*
  	 * Once parent is locked and matches our reptrack, our reptrack
  	 * will be stable and we have our parent.  We can unlink our
  	 * reptrack.
  	 *
  	 * WARNING!  Remember that the chain lock might be shared.  Chains
  	 *	     locked shared have stable parent linkages.
  	 */
  	hammer2_spin_ex(&parent->core.spin);
  	repp = &parent->core.reptrack;
  	while (*repp != &reptrack)
  		repp = &(*repp)->next;
  	*repp = reptrack.next;
  	hammer2_spin_unex(&parent->core.spin);
  
  	hammer2_chain_drop(parent);	/* reptrack ref */
  	*chainp = parent;		/* return parent lock+ref */
  
  	return parent;
  }
  
  /*
   * Dispose of any linked reptrack structures in (chain) by shifting them to
   * (parent).  Both (chain) and (parent) must be exclusively locked.
   *
   * This is interlocked against any children of (chain) on the other side.
   * No children so remain as-of when this is called so we can test
   * core.reptrack without holding the spin-lock.
   *
   * Used whenever the caller intends to permanently delete chains related
   * to topological recursions (BREF_TYPE_INDIRECT, BREF_TYPE_FREEMAP_NODE),
   * where the chains underneath the node being deleted are given a new parent
   * above the node being deleted.
   */
  static
  void
  hammer2_chain_repchange(hammer2_chain_t *parent, hammer2_chain_t *chain)
  {
  	struct hammer2_reptrack *reptrack;
  
  	KKASSERT(chain->core.live_count == 0 && RB_EMPTY(&chain->core.rbtree));
  	while (chain->core.reptrack) {
  		hammer2_spin_ex(&parent->core.spin);
  		hammer2_spin_ex(&chain->core.spin);
  		reptrack = chain->core.reptrack;
  		if (reptrack == NULL) {
  			hammer2_spin_unex(&chain->core.spin);
  			hammer2_spin_unex(&parent->core.spin);
  			break;
  		}
  		hammer2_spin_ex(&reptrack->spin);
  		chain->core.reptrack = reptrack->next;
  		reptrack->chain = parent;
  		reptrack->next = parent->core.reptrack;
  		parent->core.reptrack = reptrack;
  		hammer2_chain_ref(parent);		/* reptrack */
  
  		hammer2_spin_unex(&chain->core.spin);
  		hammer2_spin_unex(&parent->core.spin);
  		kprintf("hammer2: debug repchange %p %p->%p\n",
  			reptrack, chain, parent);
  		hammer2_chain_drop(chain);		/* reptrack */
  	}
  }
  
  /*
   * Locate the first chain whos key range overlaps (key_beg, key_end) inclusive.
   * (*parentp) typically points to an inode but can also point to a related
   * indirect block and this function will recurse upwards and find the inode
   * or the nearest undeleted indirect block covering the key range.
   *
   * This function unconditionally sets *errorp, replacing any previous value.
   *
   * (*parentp) must be exclusive or shared locked (depending on flags) and
   * referenced and can be an inode or an existing indirect block within the
   * inode.
   *
   * If (*parent) is errored out, this function will not attempt to recurse
   * the radix tree and will return NULL along with an appropriate *errorp.
   * If NULL is returned and *errorp is 0, the requested lookup could not be
   * located.
   *
   * 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 shared or exclusive (depending on flags),
   * and referenced, and the old will be unlocked and dereferenced (no change
   * if they are both the same).  This is particularly important if the caller
   * wishes to insert a new chain, (*parentp) will be set properly even if NULL
   * is returned, as long as no error occurred.
   *
   * The matching chain will be returned locked according to flags.
   *
   * --
   *
   * NULL is returned if no match was found, but (*parentp) will still
   * potentially be adjusted.
   *
   * On return (*key_nextp) will point to an iterative value for key_beg.
   * (If NULL is returned (*key_nextp) is set to (key_end + 1)).
   *
   * This function will also recurse up the chain if the key is not within the
   * current parent's range.  (*parentp) can never be set to NULL.  An iteration
   * can simply allow (*parentp) to float inside the loop.
   *
   * NOTE!  chain->data is not always resolved.  By default it will not be
   *	  resolved for BREF_TYPE_DATA, FREEMAP_NODE, or FREEMAP_LEAF.  Use
   *	  HAMMER2_LOOKUP_ALWAYS to force resolution (but be careful w/
   *	  BREF_TYPE_DATA as the device buffer can alias the logical file
   *	  buffer).
   */
  
  hammer2_chain_t *
  hammer2_chain_lookup(hammer2_chain_t **parentp, hammer2_key_t *key_nextp,
  		     hammer2_key_t key_beg, hammer2_key_t key_end,
  		     int *errorp, int flags)
  {
  	hammer2_dev_t *hmp;
  	hammer2_chain_t *parent;
  	hammer2_chain_t *chain;
  	hammer2_blockref_t *base;
  	hammer2_blockref_t *bref;
  	hammer2_blockref_t bsave;
  	hammer2_key_t scan_beg;
  	hammer2_key_t scan_end;
  	int count = 0;
  	int how_always = HAMMER2_RESOLVE_ALWAYS;
  	int how_maybe = HAMMER2_RESOLVE_MAYBE;
  	int how;
  	int generation;
  	int maxloops = 300000;
  	volatile hammer2_mtx_t save_mtx;
  
  	if (flags & HAMMER2_LOOKUP_ALWAYS) {
  		how_maybe = how_always;
  		how = HAMMER2_RESOLVE_ALWAYS;
  	} else if (flags & HAMMER2_LOOKUP_NODATA) {
  		how = HAMMER2_RESOLVE_NEVER;
  	} else {
  		how = HAMMER2_RESOLVE_MAYBE;
  	}
  	if (flags & HAMMER2_LOOKUP_SHARED) {
  		how_maybe |= HAMMER2_RESOLVE_SHARED;
  		how_always |= HAMMER2_RESOLVE_SHARED;
  		how |= HAMMER2_RESOLVE_SHARED;
  	}
  
  	/*
  	 * Recurse (*parentp) upward if necessary until the parent completely
  	 * encloses the key range or we hit the inode.
  	 *
  	 * Handle races against the flusher deleting indirect nodes on its
  	 * way back up by continuing to recurse upward past the deletion.
  	 */
  	parent = *parentp;
  	hmp = parent->hmp;
  	*errorp = 0;
  
  	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 ((parent->flags & HAMMER2_CHAIN_DELETED) == 0) {
  			if (key_beg >= scan_beg && key_end <= scan_end)
  				break;
  		}
  		parent = hammer2_chain_repparent(parentp, how_maybe);
  	}
  again:
  	if (--maxloops == 0)
  		panic("hammer2_chain_lookup: maxloops");
  
  	/*
  	 * MATCHIND case that does not require parent->data (do prior to
  	 * parent->error check).
  	 */
  	switch(parent->bref.type) {
  	case HAMMER2_BREF_TYPE_FREEMAP_NODE:
  	case HAMMER2_BREF_TYPE_INDIRECT:
  		if (flags & HAMMER2_LOOKUP_MATCHIND) {
  			scan_beg = parent->bref.key;
  			scan_end = scan_beg +
  			       ((hammer2_key_t)1 << parent->bref.keybits) - 1;
  			if (key_beg == scan_beg && key_end == scan_end) {
  				chain = parent;
  				hammer2_chain_ref(chain);
  				hammer2_chain_lock(chain, how_maybe);
  				*key_nextp = scan_end + 1;
  				goto done;
  			}
  		}
  		break;
  	default:
  		break;
  	}
  
  	/*
  	 * No lookup is possible if the parent is errored.  We delayed
  	 * this check as long as we could to ensure that the parent backup,
  	 * embedded data, and MATCHIND code could still execute.
  	 */
  	if (parent->error) {
  		*errorp = parent->error;
  		return NULL;
  	}
  
  	/*
  	 * 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.
  		 *
  		 * We need a second lock on parent.  Since we already have
  		 * a lock we must pass LOCKAGAIN to prevent unexpected
  		 * blocking (we don't want to block on a second shared
  		 * ref if an exclusive lock is pending)
  		 */
  		if (parent->data->ipdata.meta.op_flags &
  		    HAMMER2_OPFLAG_DIRECTDATA) {
  			if (flags & HAMMER2_LOOKUP_NODIRECT) {
  				chain = NULL;
  				*key_nextp = key_end + 1;
  				goto done;
  			}
  			hammer2_chain_ref(parent);
  			hammer2_chain_lock(parent, how_always |
  						   HAMMER2_RESOLVE_LOCKAGAIN);
  			*key_nextp = key_end + 1;
  			return (parent);
  		}
  		base = &parent->data->ipdata.u.blockset.blockref[0];
  		count = HAMMER2_SET_COUNT;
  		break;
  	case HAMMER2_BREF_TYPE_FREEMAP_NODE:
  	case HAMMER2_BREF_TYPE_INDIRECT:
  		/*
  		 * Optimize indirect blocks in the INITIAL state to avoid
  		 * I/O.
  		 *
  		 * Debugging: Enter permanent wait state instead of
  		 * panicing on unexpectedly NULL data for the moment.
  		 */
  		if (parent->flags & HAMMER2_CHAIN_INITIAL) {
  			base = NULL;
  		} else {
  			if (parent->data == NULL) {
  				kprintf("hammer2: unexpected NULL data "
  					"on %p\n", parent);
  				while (1)
  					tsleep(parent, 0, "xxx", 0);
  			}
  			base = &parent->data->npdata[0];
  		}
  		count = parent->bytes / sizeof(hammer2_blockref_t);
  		break;
  	case HAMMER2_BREF_TYPE_VOLUME:
  		base = &parent->data->voldata.sroot_blockset.blockref[0];
  		count = HAMMER2_SET_COUNT;
  		break;
  	case HAMMER2_BREF_TYPE_FREEMAP:
  		base = &parent->data->blkset.blockref[0];
  		count = HAMMER2_SET_COUNT;
  		break;
  	default:
  		panic("hammer2_chain_lookup: unrecognized "
  		      "blockref(B) type: %d",
  		      parent->bref.type);
  		base = NULL;	/* safety */
  		count = 0;	/* safety */
  		break;
  	}
  
  	/*
  	 * Merged scan to find next candidate.
  	 *
  	 * hammer2_base_*() functions require the parent->core.live_* fields
  	 * to be synchronized.
  	 *
  	 * We need to hold the spinlock to access the block array and RB tree
  	 * and to interlock chain creation.
  	 */
  	if ((parent->flags & HAMMER2_CHAIN_COUNTEDBREFS) == 0)
  		hammer2_chain_countbrefs(parent, base, count);
  
  	/*
  	 * Combined search
  	 */
  	hammer2_spin_ex(&parent->core.spin);
  	chain = hammer2_combined_find(parent, base, count,
  				      key_nextp,
  				      key_beg, key_end,
  				      &bref);
  	generation = parent->core.generation;
  
  	/*
  	 * Exhausted parent chain, iterate.
  	 */
  	if (bref == NULL) {
  		KKASSERT(chain == NULL);
  		hammer2_spin_unex(&parent->core.spin);
  		if (key_beg == key_end)	/* short cut single-key case */
  			return (NULL);
  
  		/*
  		 * Stop if we reached the end of the iteration.
  		 */
  		if (parent->bref.type != HAMMER2_BREF_TYPE_INDIRECT &&
  		    parent->bref.type != HAMMER2_BREF_TYPE_FREEMAP_NODE) {
  			return (NULL);
  		}
  
  		/*
  		 * Calculate next key, stop if we reached the end of the
  		 * iteration, otherwise go up one level and loop.
  		 */
  		key_beg = parent->bref.key +
  			  ((hammer2_key_t)1 << parent->bref.keybits);
  		if (key_beg == 0 || key_beg > key_end)
  			return (NULL);
  		parent = hammer2_chain_repparent(parentp, how_maybe);
  		goto again;
  	}
  
  	/*
  	 * Selected from blockref or in-memory chain.
  	 */
  	bsave = *bref;
  	if (chain == NULL) {
  		hammer2_spin_unex(&parent->core.spin);
  		if (bsave.type == HAMMER2_BREF_TYPE_INDIRECT ||
  		    bsave.type == HAMMER2_BREF_TYPE_FREEMAP_NODE) {
  			chain = hammer2_chain_get(parent, generation,
  						  &bsave, how_maybe);
  		} else {
  			chain = hammer2_chain_get(parent, generation,
  						  &bsave, how);
  		}
  		if (chain == NULL)
  			goto again;
  	} else {
  		hammer2_chain_ref(chain);
  		hammer2_spin_unex(&parent->core.spin);
  
  		/*
  		 * chain is referenced but not locked.  We must lock the
  		 * chain to obtain definitive state.
  		 */
  		if (bsave.type == HAMMER2_BREF_TYPE_INDIRECT ||
  		    bsave.type == HAMMER2_BREF_TYPE_FREEMAP_NODE) {
  			hammer2_chain_lock(chain, how_maybe);
  		} else {
  			hammer2_chain_lock(chain, how);
  		}
  		KKASSERT(chain->parent == parent);
  	}
  	if (bcmp(&bsave, &chain->bref, sizeof(bsave)) ||
  	    chain->parent != parent) {
  		hammer2_chain_unlock(chain);
  		hammer2_chain_drop(chain);
  		chain = NULL;	/* SAFETY */
  		goto again;
  	}
  
  
  	/*
  	 * Skip deleted chains (XXX cache 'i' end-of-block-array? XXX)
  	 *
  	 * NOTE: Chain's key range is not relevant as there might be
  	 *	 one-offs within the range that are not deleted.
  	 *
  	 * NOTE: Lookups can race delete-duplicate because
  	 *	 delete-duplicate does not lock the parent's core
  	 *	 (they just use the spinlock on the core).
  	 */
  	if (chain->flags & HAMMER2_CHAIN_DELETED) {
  		kprintf("skip deleted chain %016jx.%02x key=%016jx\n",
  			chain->bref.data_off, chain->bref.type,
  			chain->bref.key);
  		hammer2_chain_unlock(chain);
  		hammer2_chain_drop(chain);
  		chain = NULL;	/* SAFETY */
  		key_beg = *key_nextp;
  		if (key_beg == 0 || key_beg > key_end)
  			return(NULL);
  		goto again;
  	}
  
  	/*
  	 * If the chain element is an indirect block it becomes the new
  	 * parent and we loop on it.  We must maintain our top-down locks
  	 * to prevent the flusher from interfering (i.e. doing a
  	 * delete-duplicate and leaving us recursing down a deleted chain).
  	 *
  	 * The parent always has to be locked with at least RESOLVE_MAYBE
  	 * so we can access its data.  It might need a fixup if the caller
  	 * passed incompatible flags.  Be careful not to cause a deadlock
  	 * as a data-load requires an exclusive lock.
  	 *
  	 * If HAMMER2_LOOKUP_MATCHIND is set and the indirect block's key
  	 * range is within the requested key range we return the indirect
  	 * block and do NOT loop.  This is usually only used to acquire
  	 * freemap nodes.
  	 */
  	if (chain->bref.type == HAMMER2_BREF_TYPE_INDIRECT ||
  	    chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_NODE) {
  		save_mtx = parent->lock;
  		hammer2_chain_unlock(parent);
  		hammer2_chain_drop(parent);
  		*parentp = parent = chain;
  		chain = NULL;	/* SAFETY */
  		goto again;
  	}
  done:
  	/*
  	 * All done, return the locked chain.
  	 *
  	 * If the caller does not want a locked chain, replace the lock with
  	 * a ref.  Perhaps this can eventually be optimized to not obtain the
  	 * lock in the first place for situations where the data does not
  	 * need to be resolved.
  	 *
  	 * NOTE! A chain->error must be tested by the caller upon return.
  	 *	 *errorp is only set based on issues which occur while
  	 *	 trying to reach the chain.
  	 */
  	return (chain);
  }
  
  /*
   * After having issued a lookup we can iterate all matching keys.
   *
   * If chain is non-NULL we continue the iteration from just after it's index.
   *
   * If chain is NULL we assume the parent was exhausted and continue the
   * iteration at the next parent.
   *
   * If a fatal error occurs (typically an I/O error), a dummy chain is
   * returned with chain->error and error-identifying information set.  This
   * chain will assert if you try to do anything fancy with it.
   *
   * XXX Depending on where the error occurs we should allow continued iteration.
   *
   * parent must be locked on entry and remains locked throughout.  chain's
   * lock status must match flags.  Chain is always at least referenced.
   *
   * WARNING!  The MATCHIND flag does not apply to this function.
   */
  hammer2_chain_t *
  hammer2_chain_next(hammer2_chain_t **parentp, hammer2_chain_t *chain,
  		   hammer2_key_t *key_nextp,
  		   hammer2_key_t key_beg, hammer2_key_t key_end,
  		   int *errorp, int flags)
  {
  	hammer2_chain_t *parent;
  	int how_maybe;
  
  	/*
  	 * Calculate locking flags for upward recursion.
  	 */
  	how_maybe = HAMMER2_RESOLVE_MAYBE;
  	if (flags & HAMMER2_LOOKUP_SHARED)
  		how_maybe |= HAMMER2_RESOLVE_SHARED;
  
  	parent = *parentp;
  	*errorp = 0;
  
  	/*
  	 * Calculate the next index and recalculate the parent if necessary.
  	 */
  	if (chain) {
  		key_beg = chain->bref.key +
  			  ((hammer2_key_t)1 << chain->bref.keybits);
  		hammer2_chain_unlock(chain);
  		hammer2_chain_drop(chain);
  
  		/*
  		 * chain invalid past this point, but we can still do a
  		 * pointer comparison w/parent.
  		 *
  		 * Any scan where the lookup returned degenerate data embedded
  		 * in the inode has an invalid index and must terminate.
  		 */
  		if (chain == parent)
  			return(NULL);
  		if (key_beg == 0 || key_beg > key_end)
  			return(NULL);
  		chain = NULL;
  	} else if (parent->bref.type != HAMMER2_BREF_TYPE_INDIRECT &&
  		   parent->bref.type != HAMMER2_BREF_TYPE_FREEMAP_NODE) {
  		/*
  		 * We reached the end of the iteration.
  		 */
  		return (NULL);
  	} else {
  		/*
  		 * Continue iteration with next parent unless the current
  		 * parent covers the range.
  		 *
  		 * (This also handles the case of a deleted, empty indirect
  		 * node).
  		 */
  		key_beg = parent->bref.key +
  			  ((hammer2_key_t)1 << parent->bref.keybits);
  		if (key_beg == 0 || key_beg > key_end)
  			return (NULL);
  		parent = hammer2_chain_repparent(parentp, how_maybe);
  	}
  
  	/*
  	 * And execute
  	 */
  	return (hammer2_chain_lookup(parentp, key_nextp,
  				     key_beg, key_end,
  				     errorp, flags));
  }
  
  /*
   * Caller wishes to iterate chains under parent, loading new chains into
   * chainp.  Caller must initialize *chainp to NULL and *firstp to 1, and
   * then call hammer2_chain_scan() repeatedly until a non-zero return.
   * During the scan, *firstp will be set to 0 and (*chainp) will be replaced
   * with the returned chain for the scan.  The returned *chainp will be
   * locked and referenced.  Any prior contents will be unlocked and dropped.
   *
   * Caller should check the return value.  A normal scan EOF will return
   * exactly HAMMER2_ERROR_EOF.  Any other non-zero value indicates an
   * error trying to access parent data.  Any error in the returned chain
   * must be tested separately by the caller.
   *
   * (*chainp) is dropped on each scan, but will only be set if the returned
   * element itself can recurse.  Leaf elements are NOT resolved, loaded, or
   * returned via *chainp.  The caller will get their bref only.
   *
   * The raw scan function is similar to lookup/next but does not seek to a key.
   * Blockrefs are iterated via first_bref = (parent, NULL) and
   * next_chain = (parent, bref).
   *
   * The passed-in parent must be locked and its data resolved.  The function
   * nominally returns a locked and referenced *chainp != NULL for chains
   * the caller might need to recurse on (and will dipose of any *chainp passed
   * in).  The caller must check the chain->bref.type either way.
   */
  int
  hammer2_chain_scan(hammer2_chain_t *parent, hammer2_chain_t **chainp,
  		   hammer2_blockref_t *bref, int *firstp,
  		   int flags)
  {
  	hammer2_dev_t *hmp;
  	hammer2_blockref_t *base;
  	hammer2_blockref_t *bref_ptr;
  	hammer2_key_t key;
  	hammer2_key_t next_key;
  	hammer2_chain_t *chain = NULL;
  	int count = 0;
  	int how_always = HAMMER2_RESOLVE_ALWAYS;
  	int how_maybe = HAMMER2_RESOLVE_MAYBE;
  	int how;
  	int generation;
  	int maxloops = 300000;
  	int error;
  
  	hmp = parent->hmp;
  	error = 0;
  
  	/*
  	 * Scan flags borrowed from lookup.
  	 */
  	if (flags & HAMMER2_LOOKUP_ALWAYS) {
  		how_maybe = how_always;
  		how = HAMMER2_RESOLVE_ALWAYS;
  	} else if (flags & HAMMER2_LOOKUP_NODATA) {
  		how = HAMMER2_RESOLVE_NEVER;
  	} else {
  		how = HAMMER2_RESOLVE_MAYBE;
  	}
  	if (flags & HAMMER2_LOOKUP_SHARED) {
  		how_maybe |= HAMMER2_RESOLVE_SHARED;
  		how_always |= HAMMER2_RESOLVE_SHARED;
  		how |= HAMMER2_RESOLVE_SHARED;
  	}
  
  	/*
  	 * Calculate key to locate first/next element, unlocking the previous
  	 * element as we go.  Be careful, the key calculation can overflow.
  	 *
  	 * (also reset bref to NULL)
  	 */
  	if (*firstp) {
  		key = 0;
  		*firstp = 0;
  	} else {
  		key = bref->key + ((hammer2_key_t)1 << bref->keybits);
  		if ((chain = *chainp) != NULL) {
  			*chainp = NULL;
  			hammer2_chain_unlock(chain);
  			hammer2_chain_drop(chain);
  			chain = NULL;
  		}
  		if (key == 0) {
  			error |= HAMMER2_ERROR_EOF;
  			goto done;
  		}
  	}
  
  again:
  	if (parent->error) {
  		error = parent->error;
  		goto done;
  	}
  	if (--maxloops == 0)
  		panic("hammer2_chain_scan: maxloops");
  
  	/*
  	 * Locate the blockref array.  Currently we do a fully associative
  	 * search through the array.
  	 */
  	switch(parent->bref.type) {
  	case HAMMER2_BREF_TYPE_INODE:
  		/*
  		 * An inode with embedded data has no sub-chains.
  		 *
  		 * WARNING! Bulk scan code may pass a static chain marked
  		 *	    as BREF_TYPE_INODE with a copy of the volume
  		 *	    root blockset to snapshot the volume.
  		 */
  		if (parent->data->ipdata.meta.op_flags &
  		    HAMMER2_OPFLAG_DIRECTDATA) {
  			error |= HAMMER2_ERROR_EOF;
  			goto done;
  		}
  		base = &parent->data->ipdata.u.blockset.blockref[0];
  		count = HAMMER2_SET_COUNT;
  		break;
  	case HAMMER2_BREF_TYPE_FREEMAP_NODE:
  	case HAMMER2_BREF_TYPE_INDIRECT:
  		/*
  		 * Optimize indirect blocks in the INITIAL state to avoid
  		 * I/O.
  		 */
  		if (parent->flags & HAMMER2_CHAIN_INITIAL) {
  			base = NULL;
  		} else {
  			if (parent->data == NULL)
  				panic("parent->data is NULL");
  			base = &parent->data->npdata[0];
  		}
  		count = parent->bytes / sizeof(hammer2_blockref_t);
  		break;
  	case HAMMER2_BREF_TYPE_VOLUME:
  		base = &parent->data->voldata.sroot_blockset.blockref[0];
  		count = HAMMER2_SET_COUNT;
  		break;
  	case HAMMER2_BREF_TYPE_FREEMAP:
  		base = &parent->data->blkset.blockref[0];
  		count = HAMMER2_SET_COUNT;
  		break;
  	default:
  		panic("hammer2_chain_scan: unrecognized blockref type: %d",
  		      parent->bref.type);
  		base = NULL;	/* safety */
  		count = 0;	/* safety */
  		break;
  	}
  
  	/*
  	 * Merged scan to find next candidate.
  	 *
  	 * hammer2_base_*() functions require the parent->core.live_* fields
  	 * to be synchronized.
  	 *
  	 * We need to hold the spinlock to access the block array and RB tree
  	 * and to interlock chain creation.
  	 */
  	if ((parent->flags & HAMMER2_CHAIN_COUNTEDBREFS) == 0)
  		hammer2_chain_countbrefs(parent, base, count);
  
  	next_key = 0;
  	bref_ptr = NULL;
  	hammer2_spin_ex(&parent->core.spin);
  	chain = hammer2_combined_find(parent, base, count,
  				      &next_key,
  				      key, HAMMER2_KEY_MAX,
  				      &bref_ptr);
  	generation = parent->core.generation;
  
  	/*
  	 * Exhausted parent chain, we're done.
  	 */
  	if (bref_ptr == NULL) {
  		hammer2_spin_unex(&parent->core.spin);
  		KKASSERT(chain == NULL);
  		error |= HAMMER2_ERROR_EOF;
  		goto done;
  	}
  
  	/*
  	 * Copy into the supplied stack-based blockref.
  	 */
  	*bref = *bref_ptr;
  
  	/*
  	 * Selected from blockref or in-memory chain.
  	 */
  	if (chain == NULL) {
  		switch(bref->type) {
  		case HAMMER2_BREF_TYPE_INODE:
  		case HAMMER2_BREF_TYPE_FREEMAP_NODE:
  		case HAMMER2_BREF_TYPE_INDIRECT:
  		case HAMMER2_BREF_TYPE_VOLUME:
  		case HAMMER2_BREF_TYPE_FREEMAP:
  			/*
  			 * Recursion, always get the chain
  			 */
  			hammer2_spin_unex(&parent->core.spin);
  			chain = hammer2_chain_get(parent, generation,
  						  bref, how);
  			if (chain == NULL)
  				goto again;
  			break;
  		default:
  			/*
  			 * No recursion, do not waste time instantiating
  			 * a chain, just iterate using the bref.
  			 */
  			hammer2_spin_unex(&parent->core.spin);
  			break;
  		}
  	} else {
  		/*
  		 * Recursion or not we need the chain in order to supply
  		 * the bref.
  		 */
  		hammer2_chain_ref(chain);
  		hammer2_spin_unex(&parent->core.spin);
  		hammer2_chain_lock(chain, how);
  	}
  	if (chain &&
  	    (bcmp(bref, &chain->bref, sizeof(*bref)) ||
  	     chain->parent != parent)) {
  		hammer2_chain_unlock(chain);
  		hammer2_chain_drop(chain);
  		chain = NULL;
  		goto again;
  	}
  
  	/*
  	 * Skip deleted chains (XXX cache 'i' end-of-block-array? XXX)
  	 *
  	 * NOTE: chain's key range is not relevant as there might be
  	 *	 one-offs within the range that are not deleted.
  	 *
  	 * NOTE: XXX this could create problems with scans used in
  	 *	 situations other than mount-time recovery.
  	 *
  	 * NOTE: Lookups can race delete-duplicate because
  	 *	 delete-duplicate does not lock the parent's core
  	 *	 (they just use the spinlock on the core).
  	 */
  	if (chain && (chain->flags & HAMMER2_CHAIN_DELETED)) {
  		hammer2_chain_unlock(chain);
  		hammer2_chain_drop(chain);
  		chain = NULL;
  
  		key = next_key;
  		if (key == 0) {
  			error |= HAMMER2_ERROR_EOF;
  			goto done;
  		}
  		goto again;
  	}
  
  done:
  	/*
  	 * All done, return the bref or NULL, supply chain if necessary.
  	 */
  	if (chain)
  		*chainp = chain;
  	return (error);
  }
  
  /*
   * Create and return a new hammer2 system memory structure of the specified
   * key, type and size and insert it under (*parentp).  This is a full
   * insertion, based on the supplied key/keybits, and may involve creating
   * indirect blocks and moving other chains around via delete/duplicate.
   *
   * This call can be made with parent == NULL as long as a non -1 methods
   * is supplied.  hmp must also be supplied in this situation (otherwise
   * hmp is extracted from the supplied parent).  The chain will be detached
   * from the topology.  A later call with both parent and chain can be made
   * to attach it.
   *
   * THE CALLER MUST HAVE ALREADY PROPERLY SEEKED (*parentp) TO THE INSERTION
   * POINT SANS ANY REQUIRED INDIRECT BLOCK CREATIONS DUE TO THE ARRAY BEING
   * FULL.  This typically means that the caller is creating the chain after
   * doing a hammer2_chain_lookup().
   *
   * (*parentp) must be exclusive locked and may be replaced on return
   * depending on how much work the function had to do.
   *
   * (*parentp) must not be errored or this function will assert.
   *
   * (*chainp) usually starts out NULL and returns the newly created chain,
   * but if the caller desires the caller may allocate a disconnected chain
   * and pass it in instead.
   *
   * This function should NOT be used to insert INDIRECT blocks.  It is
   * typically used to create/insert inodes and data blocks.
   *
   * Caller must pass-in an exclusively locked parent the new chain is to
   * be inserted under, and optionally pass-in a disconnected, exclusively
   * locked chain to insert (else we create a new chain).  The function will
   * adjust (*parentp) as necessary, create or connect the chain, and
   * return an exclusively locked chain in *chainp.
   *
   * When creating a PFSROOT inode under the super-root, pmp is typically NULL
   * and will be reassigned.
   *
   * NOTE: returns HAMMER_ERROR_* flags
   */
  int
  hammer2_chain_create(hammer2_chain_t **parentp, hammer2_chain_t **chainp,
  		     hammer2_dev_t *hmp, hammer2_pfs_t *pmp, int methods,
  		     hammer2_key_t key, int keybits, int type, size_t bytes,
  		     hammer2_tid_t mtid, hammer2_off_t dedup_off, int flags)
  {
  	hammer2_chain_t *chain;
  	hammer2_chain_t *parent;
  	hammer2_blockref_t *base;
  	hammer2_blockref_t dummy;
  	int allocated = 0;
  	int error = 0;
  	int count;
  	int maxloops = 300000;
  
  	/*
  	 * Topology may be crossing a PFS boundary.
  	 */
  	parent = *parentp;
  	if (parent) {
  		KKASSERT(hammer2_mtx_owned(&parent->lock));
  		KKASSERT(parent->error == 0);
  		hmp = parent->hmp;
  	}
  	chain = *chainp;
  
  	if (chain == NULL) {
  		/*
  		 * First allocate media space and construct the dummy bref,
  		 * then allocate the in-memory chain structure.  Set the
  		 * INITIAL flag for fresh chains which do not have embedded
  		 * data.
  		 */
  		bzero(&dummy, sizeof(dummy));
  		dummy.type = type;
  		dummy.key = key;
  		dummy.keybits = keybits;
  		dummy.data_off = hammer2_getradix(bytes);
  
  		/*
  		 * Inherit methods from parent by default.  Primarily used
  		 * for BREF_TYPE_DATA.  Non-data types *must* be set to
  		 * a non-NONE check algorithm.
  		 */
  		if (methods == -1)
  			dummy.methods = parent->bref.methods;
  		else
  			dummy.methods = (uint8_t)methods;
  
  		if (type != HAMMER2_BREF_TYPE_DATA &&
  		    HAMMER2_DEC_CHECK(dummy.methods) == HAMMER2_CHECK_NONE) {
  			dummy.methods |=
  				HAMMER2_ENC_CHECK(HAMMER2_CHECK_DEFAULT);
  		}
  
  		chain = hammer2_chain_alloc(hmp, pmp, &dummy);
  
  		/*
  		 * Lock the chain manually, chain_lock will load the chain
  		 * which we do NOT want to do.  (note: chain->refs is set
  		 * to 1 by chain_alloc() for us, but lockcnt is not).
  		 */
  		chain->lockcnt = 1;
  		hammer2_mtx_ex(&chain->lock);
  		allocated = 1;
  
  		/*
  		 * Set INITIAL to optimize I/O.  The flag will generally be
  		 * processed when we call hammer2_chain_modify().
  		 */
  		switch(type) {
  		case HAMMER2_BREF_TYPE_VOLUME:
  		case HAMMER2_BREF_TYPE_FREEMAP:
  			panic("hammer2_chain_create: called with volume type");
  			break;
  		case HAMMER2_BREF_TYPE_INDIRECT:
  			panic("hammer2_chain_create: cannot be used to"
  			      "create indirect block");
  			break;
  		case HAMMER2_BREF_TYPE_FREEMAP_NODE:
  			panic("hammer2_chain_create: cannot be used to"
  			      "create freemap root or node");
  			break;
  		case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
  			KKASSERT(bytes == sizeof(chain->data->bmdata));
  			/* fall through */
  		case HAMMER2_BREF_TYPE_DIRENT:
  		case HAMMER2_BREF_TYPE_INODE:
  		case HAMMER2_BREF_TYPE_DATA:
  		default:
  			/*
  			 * leave chain->data NULL, set INITIAL
  			 */
  			KKASSERT(chain->data == NULL);
  			atomic_set_int(&chain->flags, HAMMER2_CHAIN_INITIAL);
  			break;
  		}
  	} else {
  		/*
  		 * We are reattaching a previously deleted chain, possibly
  		 * under a new parent and possibly with a new key/keybits.
  		 * The chain does not have to be in a modified state.  The
  		 * UPDATE flag will be set later on in this routine.
  		 *
  		 * Do NOT mess with the current state of the INITIAL flag.
  		 */
  		chain->bref.key = key;
  		chain->bref.keybits = keybits;
  		if (chain->flags & HAMMER2_CHAIN_DELETED)
  			atomic_clear_int(&chain->flags, HAMMER2_CHAIN_DELETED);
  		KKASSERT(chain->parent == NULL);
  	}
  
  	/*
  	 * Set the appropriate bref flag if requested.
  	 *
  	 * NOTE! Callers can call this function to move chains without
  	 *	 knowing about special flags, so don't clear bref flags
  	 *	 here!
  	 */
  	if (flags & HAMMER2_INSERT_PFSROOT)
  		chain->bref.flags |= HAMMER2_BREF_FLAG_PFSROOT;
  
  	if (parent == NULL)
  		goto skip;
  
  	/*
  	 * Calculate how many entries we have in the blockref array and
  	 * determine if an indirect block is required when inserting into
  	 * the parent.
  	 */
  again:
  	if (--maxloops == 0)
  		panic("hammer2_chain_create: maxloops");
  
  	switch(parent->bref.type) {
  	case HAMMER2_BREF_TYPE_INODE:
  		if ((parent->data->ipdata.meta.op_flags &
  		     HAMMER2_OPFLAG_DIRECTDATA) != 0) {
  			kprintf("hammer2: parent set for direct-data! "
  				"pkey=%016jx ckey=%016jx\n",
  				parent->bref.key,
  				chain->bref.key);
  	        }
  		KKASSERT((parent->data->ipdata.meta.op_flags &
  			  HAMMER2_OPFLAG_DIRECTDATA) == 0);
  		KKASSERT(parent->data != NULL);
  		base = &parent->data->ipdata.u.blockset.blockref[0];
  		count = HAMMER2_SET_COUNT;
  		break;
  	case HAMMER2_BREF_TYPE_INDIRECT:
  	case HAMMER2_BREF_TYPE_FREEMAP_NODE:
  		if (parent->flags & HAMMER2_CHAIN_INITIAL)
  			base = NULL;
  		else
  			base = &parent->data->npdata[0];
  		count = parent->bytes / sizeof(hammer2_blockref_t);
  		break;
  	case HAMMER2_BREF_TYPE_VOLUME:
  		KKASSERT(parent->data != NULL);
  		base = &parent->data->voldata.sroot_blockset.blockref[0];
  		count = HAMMER2_SET_COUNT;
  		break;
  	case HAMMER2_BREF_TYPE_FREEMAP:
  		KKASSERT(parent->data != NULL);
  		base = &parent->data->blkset.blockref[0];
  		count = HAMMER2_SET_COUNT;
  		break;
  	default:
  		panic("hammer2_chain_create: unrecognized blockref type: %d",
  		      parent->bref.type);
  		base = NULL;
  		count = 0;
  		break;
  	}
  
  	/*
  	 * Make sure we've counted the brefs
  	 */
  	if ((parent->flags & HAMMER2_CHAIN_COUNTEDBREFS) == 0)
  		hammer2_chain_countbrefs(parent, base, count);
  
  	KASSERT(parent->core.live_count >= 0 &&
  		parent->core.live_count <= count,
  		("bad live_count %d/%d (%02x, %d)",
  			parent->core.live_count, count,
  			parent->bref.type, parent->bytes));
  
  	/*
  	 * If no free blockref could be found we must create an indirect
  	 * block and move a number of blockrefs into it.  With the parent
  	 * locked we can safely lock each child in order to delete+duplicate
  	 * it without causing a deadlock.
  	 *
  	 * This may return the new indirect block or the old parent depending
  	 * on where the key falls.  NULL is returned on error.
  	 */
  	if (parent->core.live_count == count) {
  		hammer2_chain_t *nparent;
  
  		KKASSERT((flags & HAMMER2_INSERT_SAMEPARENT) == 0);
  
  		nparent = hammer2_chain_create_indirect(parent, key, keybits,
  							mtid, type, &error);
  		if (nparent == NULL) {
  			if (allocated)
  				hammer2_chain_drop(chain);
  			chain = NULL;
  			goto done;
  		}
  		if (parent != nparent) {
  			hammer2_chain_unlock(parent);
  			hammer2_chain_drop(parent);
  			parent = *parentp = nparent;
  		}
  		goto again;
  	}
  
  	/*
  	 * fall through if parent, or skip to here if no parent.
  	 */
  skip:
  	if (chain->flags & HAMMER2_CHAIN_DELETED)
  		kprintf("Inserting deleted chain @%016jx\n",
  			chain->bref.key);
  
  	/*
  	 * Link the chain into its parent.
  	 */
  	if (chain->parent != NULL)
  		panic("hammer2: hammer2_chain_create: chain already connected");
  	KKASSERT(chain->parent == NULL);
  	if (parent) {
  		KKASSERT(parent->core.live_count < count);
  		hammer2_chain_insert(parent, chain,
  				     HAMMER2_CHAIN_INSERT_SPIN |
  				     HAMMER2_CHAIN_INSERT_LIVE,
  				     0);
  	}
  
  	if (allocated) {
  		/*
  		 * Mark the newly created chain modified.  This will cause
  		 * UPDATE to be set and process the INITIAL flag.
  		 *
  		 * Device buffers are not instantiated for DATA elements
  		 * as these are handled by logical buffers.
  		 *
  		 * Indirect and freemap node indirect blocks are handled
  		 * by hammer2_chain_create_indirect() and not by this
  		 * function.
  		 *
  		 * Data for all other bref types is expected to be
  		 * instantiated (INODE, LEAF).
  		 */
  		switch(chain->bref.type) {
  		case HAMMER2_BREF_TYPE_DATA:
  		case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
  		case HAMMER2_BREF_TYPE_DIRENT:
  		case HAMMER2_BREF_TYPE_INODE:
  			error = hammer2_chain_modify(chain, mtid, dedup_off,
  						     HAMMER2_MODIFY_OPTDATA);
  			break;
  		default:
  			/*
  			 * Remaining types are not supported by this function.
  			 * In particular, INDIRECT and LEAF_NODE types are
  			 * handled by create_indirect().
  			 */
  			panic("hammer2_chain_create: bad type: %d",
  			      chain->bref.type);
  			/* NOT REACHED */
  			break;
  		}
  	} else {
  		/*
  		 * When reconnecting a chain we must set UPDATE and
  		 * setflush so the flush recognizes that it must update
  		 * the bref in the parent.
  		 */
  		if ((chain->flags & HAMMER2_CHAIN_UPDATE) == 0)
  			atomic_set_int(&chain->flags, HAMMER2_CHAIN_UPDATE);
  	}
  
  	/*
  	 * We must setflush(parent) to ensure that it recurses through to
  	 * chain.  setflush(chain) might not work because ONFLUSH is possibly
  	 * already set in the chain (so it won't recurse up to set it in the
  	 * parent).
  	 */
  	if (parent)
  		hammer2_chain_setflush(parent);
  
  done:
  	*chainp = chain;
  
  	return (error);
  }
  
  /*
   * Move the chain from its old parent to a new parent.  The chain must have
   * already been deleted or already disconnected (or never associated) with
   * a parent.  The chain is reassociated with the new parent and the deleted
   * flag will be cleared (no longer deleted).  The chain's modification state
   * is not altered.
   *
   * THE CALLER MUST HAVE ALREADY PROPERLY SEEKED (parent) TO THE INSERTION
   * POINT SANS ANY REQUIRED INDIRECT BLOCK CREATIONS DUE TO THE ARRAY BEING
   * FULL.  This typically means that the caller is creating the chain after
   * doing a hammer2_chain_lookup().
   *
   * Neither (parent) or (chain) can be errored.
   *
   * If (parent) is non-NULL then the chain is inserted under the parent.
   *
   * If (parent) is NULL then the newly duplicated chain is not inserted
   * anywhere, similar to if it had just been chain_alloc()'d (suitable for
   * passing into hammer2_chain_create() after this function returns).
   *
   * WARNING! This function calls create which means it can insert indirect
   *	    blocks.  This can cause other unrelated chains in the parent to
   *	    be moved to a newly inserted indirect block in addition to the
   *	    specific chain.
   */
  void
  hammer2_chain_rename(hammer2_chain_t **parentp, hammer2_chain_t *chain,
  		     hammer2_tid_t mtid, int flags)
  {
  	hammer2_blockref_t *bref;
  	hammer2_dev_t *hmp;
  	hammer2_chain_t *parent;
  
  	/*
  	 * WARNING!  We should never resolve DATA to device buffers
  	 *	     (XXX allow it if the caller did?), and since
  	 *	     we currently do not have the logical buffer cache
  	 *	     buffer in-hand to fix its cached physical offset
  	 *	     we also force the modify code to not COW it. XXX
  	 *
  	 * NOTE!     We allow error'd chains to be renamed.  The bref itself
  	 *	     is good and can be renamed.  The content, however, may
  	 *	     be inaccessible.
  	 */
  	hmp = chain->hmp;
  	KKASSERT(chain->parent == NULL);
  	/*KKASSERT(chain->error == 0); allow */
  	bref = &chain->bref;
  
  	/*
  	 * If parent is not NULL the duplicated chain will be entered under
  	 * the parent and the UPDATE bit set to tell flush to update
  	 * the blockref.
  	 *
  	 * We must setflush(parent) to ensure that it recurses through to
  	 * chain.  setflush(chain) might not work because ONFLUSH is possibly
  	 * already set in the chain (so it won't recurse up to set it in the
  	 * parent).
  	 *
  	 * Having both chains locked is extremely important for atomicy.
  	 */
  	if (parentp && (parent = *parentp) != NULL) {
  		KKASSERT(hammer2_mtx_owned(&parent->lock));
  		KKASSERT(parent->refs > 0);
  		KKASSERT(parent->error == 0);
  
  		hammer2_chain_create(parentp, &chain, NULL, chain->pmp,
  				     HAMMER2_METH_DEFAULT,
  				     bref->key, bref->keybits, bref->type,
  				     chain->bytes, mtid, 0, flags);
  		KKASSERT(chain->flags & HAMMER2_CHAIN_UPDATE);
  		hammer2_chain_setflush(*parentp);
  	}
  }
  
  /*
   * This works in tandem with delete_obref() to install a blockref in
   * (typically) an indirect block that is associated with the chain being
   * moved to *parentp.
   *
   * The reason we need this function is that the caller needs to maintain
   * the blockref as it was, and not generate a new blockref for what might
   * be a modified chain.  Otherwise stuff will leak into the flush that
   * the flush code's FLUSH_INODE_STOP flag is unable to catch.
   *
   * It is EXTREMELY important that we properly set CHAIN_BLKMAPUPD and
   * CHAIN_UPDATE.  We must set BLKMAPUPD if the bref does not match, and
   * we must clear CHAIN_UPDATE (that was likely set by the chain_rename) if
   * it does.  Otherwise we can end up in a situation where H2 is unable to
   * clean up the in-memory chain topology.
   *
   * The reason for this is that flushes do not generally flush through
   * BREF_TYPE_INODE chains and depend on a hammer2_inode_t queued to syncq
   * or sideq to properly flush and dispose of the related inode chain's flags.
   * Situations where the inode is not actually modified by the frontend,
   * but where we have to move the related chains around as we insert or cleanup
   * indirect blocks, can leave us with a 'dirty' (non-disposable) in-memory
   * inode chain that does not have a hammer2_inode_t associated with it.
   */
  static void
  hammer2_chain_rename_obref(hammer2_chain_t **parentp, hammer2_chain_t *chain,
  			   hammer2_tid_t mtid, int flags,
  			   hammer2_blockref_t *obref)
  {
  	hammer2_chain_rename(parentp, chain, mtid, flags);
  
  	if (obref->type != HAMMER2_BREF_TYPE_EMPTY) {
  		hammer2_blockref_t *tbase;
  		int tcount;
  
  		KKASSERT((chain->flags & HAMMER2_CHAIN_BLKMAPPED) == 0);
  		hammer2_chain_modify(*parentp, mtid, 0, 0);
  		tbase = hammer2_chain_base_and_count(*parentp, &tcount);
  		hammer2_base_insert(*parentp, tbase, tcount, chain, obref);
  		if (bcmp(obref, &chain->bref, sizeof(chain->bref))) {
  			atomic_set_int(&chain->flags, HAMMER2_CHAIN_BLKMAPUPD |
  						      HAMMER2_CHAIN_UPDATE);
  		} else {
  			atomic_clear_int(&chain->flags, HAMMER2_CHAIN_UPDATE);
  		}
  	}
  }
  
  /*
   * Helper function for deleting chains.
   *
   * The chain is removed from the live view (the RBTREE) as well as the parent's
   * blockmap.  Both chain and its parent must be locked.
   *
   * parent may not be errored.  chain can be errored.
   */
  static int
  _hammer2_chain_delete_helper(hammer2_chain_t *parent, hammer2_chain_t *chain,
  			     hammer2_tid_t mtid, int flags,
  			     hammer2_blockref_t *obref)
  {
  	hammer2_dev_t *hmp;
  	int error = 0;
  
  	KKASSERT((chain->flags & HAMMER2_CHAIN_DELETED) == 0);
  	KKASSERT(chain->parent == parent);
  	hmp = chain->hmp;
  
  	if (chain->flags & HAMMER2_CHAIN_BLKMAPPED) {
  		/*
  		 * Chain is blockmapped, so there must be a parent.
  		 * Atomically remove the chain from the parent and remove
  		 * the blockmap entry.  The parent must be set modified
  		 * to remove the blockmap entry.
  		 */
  		hammer2_blockref_t *base;
  		int count;
  
  		KKASSERT(parent != NULL);
  		KKASSERT(parent->error == 0);
  		KKASSERT((parent->flags & HAMMER2_CHAIN_INITIAL) == 0);
  		error = hammer2_chain_modify(parent, mtid, 0, 0);
  		if (error)
  			goto done;
  
  		/*
  		 * Calculate blockmap pointer
  		 */
  		KKASSERT(chain->flags & HAMMER2_CHAIN_ONRBTREE);
  		hammer2_spin_ex(&chain->core.spin);
  		hammer2_spin_ex(&parent->core.spin);
  
  		atomic_set_int(&chain->flags, HAMMER2_CHAIN_DELETED);
  		atomic_add_int(&parent->core.live_count, -1);
  		++parent->core.generation;
  		RB_REMOVE(hammer2_chain_tree, &parent->core.rbtree, chain);
  		atomic_clear_int(&chain->flags, HAMMER2_CHAIN_ONRBTREE);
  		--parent->core.chain_count;
  		chain->parent = NULL;
  
  		switch(parent->bref.type) {
  		case HAMMER2_BREF_TYPE_INODE:
  			/*
  			 * Access the inode's block array.  However, there
  			 * is no block array if the inode is flagged
  			 * DIRECTDATA.
  			 */
  			if (parent->data &&
  			    (parent->data->ipdata.meta.op_flags &
  			     HAMMER2_OPFLAG_DIRECTDATA) == 0) {
  				base =
  				   &parent->data->ipdata.u.blockset.blockref[0];
  			} else {
  				base = NULL;
  			}
  			count = HAMMER2_SET_COUNT;
  			break;
  		case HAMMER2_BREF_TYPE_INDIRECT:
  		case HAMMER2_BREF_TYPE_FREEMAP_NODE:
  			if (parent->data)
  				base = &parent->data->npdata[0];
  			else
  				base = NULL;
  			count = parent->bytes / sizeof(hammer2_blockref_t);
  			break;
  		case HAMMER2_BREF_TYPE_VOLUME:
  			base = &parent->data->voldata.
  					sroot_blockset.blockref[0];
  			count = HAMMER2_SET_COUNT;
  			break;
  		case HAMMER2_BREF_TYPE_FREEMAP:
  			base = &parent->data->blkset.blockref[0];
  			count = HAMMER2_SET_COUNT;
  			break;
  		default:
  			base = NULL;
  			count = 0;
  			panic("_hammer2_chain_delete_helper: "
  			      "unrecognized blockref type: %d",
  			      parent->bref.type);
  			break;
  		}
  
  		/*
  		 * delete blockmapped chain from its parent.
  		 *
  		 * The parent is not affected by any statistics in chain
  		 * which are pending synchronization.  That is, there is
  		 * nothing to undo in the parent since they have not yet
  		 * been incorporated into the parent.
  		 *
  		 * The parent is affected by statistics stored in inodes.
  		 * Those have already been synchronized, so they must be
  		 * undone.  XXX split update possible w/delete in middle?
  		 */
  		if (base) {
  			hammer2_base_delete(parent, base, count, chain, obref);
  		}
  		hammer2_spin_unex(&parent->core.spin);
  		hammer2_spin_unex(&chain->core.spin);
  	} else if (chain->flags & HAMMER2_CHAIN_ONRBTREE) {
  		/*
  		 * Chain is not blockmapped but a parent is present.
  		 * Atomically remove the chain from the parent.  There is
  		 * no blockmap entry to remove.
  		 *
  		 * Because chain was associated with a parent but not
  		 * synchronized, the chain's *_count_up fields contain
  		 * inode adjustment statistics which must be undone.
  		 */
  		hammer2_spin_ex(&chain->core.spin);
  		hammer2_spin_ex(&parent->core.spin);
  		atomic_set_int(&chain->flags, HAMMER2_CHAIN_DELETED);
  		atomic_add_int(&parent->core.live_count, -1);
  		++parent->core.generation;
  		RB_REMOVE(hammer2_chain_tree, &parent->core.rbtree, chain);
  		atomic_clear_int(&chain->flags, HAMMER2_CHAIN_ONRBTREE);
  		--parent->core.chain_count;
  		chain->parent = NULL;
  		hammer2_spin_unex(&parent->core.spin);
  		hammer2_spin_unex(&chain->core.spin);
  	} else {
  		/*
  		 * Chain is not blockmapped and has no parent.  This
  		 * is a degenerate case.
  		 */
  		atomic_set_int(&chain->flags, HAMMER2_CHAIN_DELETED);
  	}
  done:
  	return error;
  }
  
  /*
   * 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 H2 error.
   *
   * The returned chain depends on where the specified key falls.
   *
   * The key/keybits for the indirect mode only needs to follow three rules:
   *
   * (1) That all elements underneath it fit within its key space and
   *
   * (2) That all elements outside it are outside its key space.
   *
   * (3) When creating the new indirect block any elements in the current
   *     parent that fit within the new indirect block's keyspace must be
   *     moved into the new indirect block.
   *
   * (4) The keyspace chosen for the inserted indirect block CAN cover a wider
   *     keyspace the the current parent, but lookup/iteration rules will
   *     ensure (and must ensure) that rule (2) for all parents leading up
   *     to the nearest inode or the root volume header is adhered to.  This
   *     is accomplished by always recursing through matching keyspaces in
   *     the hammer2_chain_lookup() and hammer2_chain_next() API.
   *
   * The current implementation calculates the current worst-case keyspace by
   * iterating the current parent and then divides it into two halves, choosing
   * whichever half has the most elements (not necessarily the half containing
   * the requested key).
   *
   * We can also opt to use the half with the least number of elements.  This
   * causes lower-numbered keys (aka logical file offsets) to recurse through
   * fewer indirect blocks and higher-numbered keys to recurse through more.
   * This also has the risk of not moving enough elements to the new indirect
   * block and being forced to create several indirect blocks before the element
   * can be inserted.
   *
   * Must be called with an exclusively locked parent.
   *
   * NOTE: *errorp set to HAMMER_ERROR_* flags
   */
  static int hammer2_chain_indkey_freemap(hammer2_chain_t *parent,
  				hammer2_key_t *keyp, int keybits,
  				hammer2_blockref_t *base, int count);
  static int hammer2_chain_indkey_file(hammer2_chain_t *parent,
  				hammer2_key_t *keyp, int keybits,
  				hammer2_blockref_t *base, int count,
  				int ncount);
  static int hammer2_chain_indkey_dir(hammer2_chain_t *parent,
  				hammer2_key_t *keyp, int keybits,
  				hammer2_blockref_t *base, int count,
  				int ncount);
  static
  hammer2_chain_t *
  hammer2_chain_create_indirect(hammer2_chain_t *parent,
  			      hammer2_key_t create_key, int create_bits,
  			      hammer2_tid_t mtid, int for_type, int *errorp)
  {
  	hammer2_dev_t *hmp;
  	hammer2_blockref_t *base;
  	hammer2_blockref_t *bref;
  	hammer2_blockref_t bsave;
  	hammer2_blockref_t dummy;
  	hammer2_chain_t *chain;
  	hammer2_chain_t *ichain;
  	hammer2_key_t key = create_key;
  	hammer2_key_t key_beg;
  	hammer2_key_t key_end;
  	hammer2_key_t key_next;
  	int keybits = create_bits;
  	int count;
  	int ncount;
  	int nbytes;
  	int loops;
  	int error;
  	int reason;
  	int generation;
  	int maxloops = 300000;
  
  	/*
  	 * Calculate the base blockref pointer or NULL if the chain
  	 * is known to be empty.  We need to calculate the array count
  	 * for RB lookups either way.
  	 */
  	hmp = parent->hmp;
  	KKASSERT(hammer2_mtx_owned(&parent->lock));
  
  	/*
  	 * Pre-modify the parent now to avoid having to deal with error
  	 * processing if we tried to later (in the middle of our loop).
  	 *
  	 * We are going to be moving bref's around, the indirect blocks
  	 * cannot be in an initial state.  Do not pass MODIFY_OPTDATA.
  	 */
  	*errorp = hammer2_chain_modify(parent, mtid, 0, 0);
  	if (*errorp) {
  		kprintf("hammer2_chain_create_indirect: error %08x %s\n",
  			*errorp, hammer2_error_str(*errorp));
  		return NULL;
  	}
  	KKASSERT((parent->flags & HAMMER2_CHAIN_INITIAL) == 0);
  
  	/*hammer2_chain_modify(&parent, HAMMER2_MODIFY_OPTDATA);*/
  	base = hammer2_chain_base_and_count(parent, &count);
  
  	/*
  	 * How big should our new indirect block be?  It has to be at least
  	 * as large as its parent for splits to work properly.
  	 *
  	 * The freemap uses a specific indirect block size.  The number of
  	 * levels are built dynamically and ultimately depend on the size
  	 * volume.  Because freemap blocks are taken from the reserved areas
  	 * of the volume our goal is efficiency (fewer levels) and not so
  	 * much to save disk space.
  	 *
  	 * The first indirect block level for a directory usually uses
  	 * HAMMER2_IND_BYTES_MIN (4KB = 32 directory entries).  Due to
  	 * the hash mechanism, this typically gives us a nominal
  	 * 32 * 4 entries with one level of indirection.
  	 *
  	 * We use HAMMER2_IND_BYTES_NOM (16KB = 128 blockrefs) for FILE
  	 * indirect blocks.  The initial 4 entries in the inode gives us
  	 * 256KB.  Up to 4 indirect blocks gives us 32MB.  Three levels
  	 * of indirection gives us 137GB, and so forth.  H2 can support
  	 * huge file sizes but they are not typical, so we try to stick
  	 * with compactness and do not use a larger indirect block size.
  	 *
  	 * We could use 64KB (PBUFSIZE), giving us 512 blockrefs, but
  	 * due to the way indirect blocks are created this usually winds
  	 * up being extremely inefficient for small files.  Even though
  	 * 16KB requires more levels of indirection for very large files,
  	 * the 16KB records can be ganged together into 64KB DIOs.
  	 */
  	if (for_type == HAMMER2_BREF_TYPE_FREEMAP_NODE ||
  	    for_type == HAMMER2_BREF_TYPE_FREEMAP_LEAF) {
  		nbytes = HAMMER2_FREEMAP_LEVELN_PSIZE;
  	} else if (parent->bref.type == HAMMER2_BREF_TYPE_INODE) {
  		if (parent->data->ipdata.meta.type ==
  		    HAMMER2_OBJTYPE_DIRECTORY)
  			nbytes = HAMMER2_IND_BYTES_MIN;	/* 4KB = 32 entries */
  		else
  			nbytes = HAMMER2_IND_BYTES_NOM;	/* 16KB = ~8MB file */
  
  	} else {
  		nbytes = HAMMER2_IND_BYTES_NOM;
  	}
  	if (nbytes < count * sizeof(hammer2_blockref_t)) {
  		KKASSERT(for_type != HAMMER2_BREF_TYPE_FREEMAP_NODE &&
  			 for_type != HAMMER2_BREF_TYPE_FREEMAP_LEAF);
  		nbytes = count * sizeof(hammer2_blockref_t);
  	}
  	ncount = nbytes / sizeof(hammer2_blockref_t);
  
  	/*
  	 * When creating an indirect block for a freemap node or leaf
  	 * the key/keybits must be fitted to static radix levels because
  	 * particular radix levels use particular reserved blocks in the
  	 * related zone.
  	 *
  	 * This routine calculates the key/radix of the indirect block
  	 * we need to create, and whether it is on the high-side or the
  	 * low-side.
  	 */
  	switch(for_type) {
  	case HAMMER2_BREF_TYPE_FREEMAP_NODE:
  	case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
  		keybits = hammer2_chain_indkey_freemap(parent, &key, keybits,
  						       base, count);
  		break;
  	case HAMMER2_BREF_TYPE_DATA:
  		keybits = hammer2_chain_indkey_file(parent, &key, keybits,
  						    base, count, ncount);
  		break;
  	case HAMMER2_BREF_TYPE_DIRENT:
  	case HAMMER2_BREF_TYPE_INODE:
  		keybits = hammer2_chain_indkey_dir(parent, &key, keybits,
  						   base, count, ncount);
  		break;
  	default:
  		panic("illegal indirect block for bref type %d", for_type);
  		break;
  	}
  
  	/*
  	 * Normalize the key for the radix being represented, keeping the
  	 * high bits and throwing away the low bits.
  	 */
  	key &= ~(((hammer2_key_t)1 << keybits) - 1);
  
  	/*
  	 * Ok, create our new indirect block
  	 */
  	bzero(&dummy, sizeof(dummy));
  	if (for_type == HAMMER2_BREF_TYPE_FREEMAP_NODE ||
  	    for_type == HAMMER2_BREF_TYPE_FREEMAP_LEAF) {
  		dummy.type = HAMMER2_BREF_TYPE_FREEMAP_NODE;
  	} else {
  		dummy.type = HAMMER2_BREF_TYPE_INDIRECT;
  	}
  	dummy.key = key;
  	dummy.keybits = keybits;
  	dummy.data_off = hammer2_getradix(nbytes);
  	dummy.methods =
  		HAMMER2_ENC_CHECK(HAMMER2_DEC_CHECK(parent->bref.methods)) |
  		HAMMER2_ENC_COMP(HAMMER2_COMP_NONE);
  
  	ichain = hammer2_chain_alloc(hmp, parent->pmp, &dummy);
  	atomic_set_int(&ichain->flags, HAMMER2_CHAIN_INITIAL);
  	hammer2_chain_lock(ichain, HAMMER2_RESOLVE_MAYBE);
  	/* ichain has one ref at this point */
  
  	/*
  	 * We have to mark it modified to allocate its block, but use
  	 * OPTDATA to allow it to remain in the INITIAL state.  Otherwise
  	 * it won't be acted upon by the flush code.
  	 *
  	 * XXX remove OPTDATA, we need a fully initialized indirect block to
  	 * be able to move the original blockref.
  	 */
  	*errorp = hammer2_chain_modify(ichain, mtid, 0, 0);
  	if (*errorp) {
  		kprintf("hammer2_chain_create_indirect: error %08x %s\n",
  			*errorp, hammer2_error_str(*errorp));
  		hammer2_chain_unlock(ichain);
  		hammer2_chain_drop(ichain);
  		return NULL;
  	}
  	KKASSERT((ichain->flags & HAMMER2_CHAIN_INITIAL) == 0);
  
  	/*
  	 * Iterate the original parent and move the matching brefs into
  	 * the new indirect block.
  	 *
  	 * XXX handle flushes.
  	 */
  	key_beg = 0;
  	key_end = HAMMER2_KEY_MAX;
  	key_next = 0;	/* avoid gcc warnings */
  	hammer2_spin_ex(&parent->core.spin);
  	loops = 0;
  	reason = 0;
  
  	for (;;) {
  		/*
  		 * Parent may have been modified, relocating its block array.
  		 * Reload the base pointer.
  		 */
  		base = hammer2_chain_base_and_count(parent, &count);
  
  		if (++loops > 100000) {
  		    hammer2_spin_unex(&parent->core.spin);
  		    panic("excessive loops r=%d p=%p base/count %p:%d %016jx\n",
  			  reason, parent, base, count, key_next);
  		}
  
  		/*
  		 * NOTE: spinlock stays intact, returned chain (if not NULL)
  		 *	 is not referenced or locked which means that we
  		 *	 cannot safely check its flagged / deletion status
  		 *	 until we lock it.
  		 */
  		chain = hammer2_combined_find(parent, base, count,
  					      &key_next,
  					      key_beg, key_end,
  					      &bref);
  		generation = parent->core.generation;
  		if (bref == NULL)
  			break;
  		key_next = bref->key + ((hammer2_key_t)1 << bref->keybits);
  
  		/*
  		 * Skip keys that are not within the key/radix of the new
  		 * indirect block.  They stay in the parent.
  		 */
  		if (rounddown2(key ^ bref->key, (hammer2_key_t)1 << keybits) != 0) {
  			goto next_key_spinlocked;
  		}
  
  		/*
  		 * Load the new indirect block by acquiring the related
  		 * chains (potentially from media as it might not be
  		 * in-memory).  Then move it to the new parent (ichain).
  		 *
  		 * chain is referenced but not locked.  We must lock the
  		 * chain to obtain definitive state.
  		 */
  		bsave = *bref;
  		if (chain) {
  			/*
  			 * Use chain already present in the RBTREE
  			 */
  			hammer2_chain_ref(chain);
  			hammer2_spin_unex(&parent->core.spin);
  			hammer2_chain_lock(chain, HAMMER2_RESOLVE_NEVER);
  		} else {
  			/*
  			 * Get chain for blockref element.  _get returns NULL
  			 * on insertion race.
  			 */
  			hammer2_spin_unex(&parent->core.spin);
  			chain = hammer2_chain_get(parent, generation, &bsave,
  						  HAMMER2_RESOLVE_NEVER);
  			if (chain == NULL) {
  				reason = 1;
  				hammer2_spin_ex(&parent->core.spin);
  				continue;
  			}
  		}
  
  		/*
  		 * This is always live so if the chain has been deleted
  		 * we raced someone and we have to retry.
  		 *
  		 * NOTE: Lookups can race delete-duplicate because
  		 *	 delete-duplicate does not lock the parent's core
  		 *	 (they just use the spinlock on the core).
  		 *
  		 *	 (note reversed logic for this one)
  		 */
  		if (bcmp(&bsave, &chain->bref, sizeof(bsave)) ||
  		    chain->parent != parent ||
  		    (chain->flags & HAMMER2_CHAIN_DELETED)) {
  			hammer2_chain_unlock(chain);
  			hammer2_chain_drop(chain);
  			if (hammer2_debug & 0x0040) {
  				kprintf("LOST PARENT RETRY "
  				"RETRY (%p,%p)->%p %08x\n",
  				parent, chain->parent, chain, chain->flags);
  			}
  			hammer2_spin_ex(&parent->core.spin);
  			continue;
  		}
  
  		/*
  		 * Shift the chain to the indirect block.
  		 *
  		 * WARNING! No reason for us to load chain data, pass NOSTATS
  		 *	    to prevent delete/insert from trying to access
  		 *	    inode stats (and thus asserting if there is no
  		 *	    chain->data loaded).
  		 *
  		 * WARNING! The (parent, chain) deletion may modify the parent
  		 *	    and invalidate the base pointer.
  		 *
  		 * WARNING! Parent must already be marked modified, so we
  		 *	    can assume that chain_delete always suceeds.
  		 *
  		 * WARNING! hammer2_chain_repchange() does not have to be
  		 *	    called (and doesn't work anyway because we are
  		 *	    only doing a partial shift).  A recursion that is
  		 *	    in-progress can continue at the current parent
  		 *	    and will be able to properly find its next key.
  		 */
  		error = hammer2_chain_delete_obref(parent, chain, mtid, 0,
  						   &bsave);
  		KKASSERT(error == 0);
  		hammer2_chain_rename_obref(&ichain, chain, mtid, 0, &bsave);
  		hammer2_chain_unlock(chain);
  		hammer2_chain_drop(chain);
  		KKASSERT(parent->refs > 0);
  		chain = NULL;
  		base = NULL;	/* safety */
  		hammer2_spin_ex(&parent->core.spin);
  next_key_spinlocked:
  		if (--maxloops == 0)
  			panic("hammer2_chain_create_indirect: maxloops");
  		reason = 4;
  		if (key_next == 0 || key_next > key_end)
  			break;
  		key_beg = key_next;
  		/* loop */
  	}
  	hammer2_spin_unex(&parent->core.spin);
  
  	/*
  	 * Insert the new indirect block into the parent now that we've
  	 * cleared out some entries in the parent.  We calculated a good
  	 * insertion index in the loop above (ichain->index).
  	 *
  	 * We don't have to set UPDATE here because we mark ichain
  	 * modified down below (so the normal modified -> flush -> set-moved
  	 * sequence applies).
  	 *
  	 * The insertion shouldn't race as this is a completely new block
  	 * and the parent is locked.
  	 */
  	base = NULL;	/* safety, parent modify may change address */
  	KKASSERT((ichain->flags & HAMMER2_CHAIN_ONRBTREE) == 0);
  	KKASSERT(parent->core.live_count < count);
  	hammer2_chain_insert(parent, ichain,
  			     HAMMER2_CHAIN_INSERT_SPIN |
  			     HAMMER2_CHAIN_INSERT_LIVE,
  			     0);
  
  	/*
  	 * Make sure flushes propogate after our manual insertion.
  	 */
  	hammer2_chain_setflush(ichain);
  	hammer2_chain_setflush(parent);
  
  	/*
  	 * Figure out what to return.
  	 */
  	if (rounddown2(create_key ^ key, (hammer2_key_t)1 << keybits)) {
  		/*
  		 * Key being created is outside the key range,
  		 * return the original parent.
  		 */
  		hammer2_chain_unlock(ichain);
  		hammer2_chain_drop(ichain);
  	} else {
  		/*
  		 * Otherwise its in the range, return the new parent.
  		 * (leave both the new and old parent locked).
  		 */
  		parent = ichain;
  	}
  
  	return(parent);
  }
  
  /*
   * Do maintenance on an indirect chain.  Both parent and chain are locked.
   *
   * Returns non-zero if (chain) is deleted, either due to being empty or
   * because its children were safely moved into the parent.
   */
  int
  hammer2_chain_indirect_maintenance(hammer2_chain_t *parent,
  				   hammer2_chain_t *chain)
  {
  	hammer2_blockref_t *chain_base;
  	hammer2_blockref_t *base;
  	hammer2_blockref_t *bref;
  	hammer2_blockref_t bsave;
  	hammer2_key_t key_next;
  	hammer2_key_t key_beg;
  	hammer2_key_t key_end;
  	hammer2_chain_t *sub;
  	int chain_count;
  	int count;
  	int error;
  	int generation;
  
  	/*
  	 * Make sure we have an accurate live_count
  	 */
  	if ((chain->flags & (HAMMER2_CHAIN_INITIAL |
  			     HAMMER2_CHAIN_COUNTEDBREFS)) == 0) {
  		base = &chain->data->npdata[0];
  		count = chain->bytes / sizeof(hammer2_blockref_t);
  		hammer2_chain_countbrefs(chain, base, count);
  	}
  
  	/*
  	 * If the indirect block is empty we can delete it.
  	 * (ignore deletion error)
  	 */
  	if (chain->core.live_count == 0 && RB_EMPTY(&chain->core.rbtree)) {
  		hammer2_chain_delete(parent, chain,
  				     chain->bref.modify_tid,
  				     HAMMER2_DELETE_PERMANENT);
  		hammer2_chain_repchange(parent, chain);
  		return 1;
  	}
  
  	base = hammer2_chain_base_and_count(parent, &count);
  
  	if ((parent->flags & (HAMMER2_CHAIN_INITIAL |
  			     HAMMER2_CHAIN_COUNTEDBREFS)) == 0) {
  		hammer2_chain_countbrefs(parent, base, count);
  	}
  
  	/*
  	 * Determine if we can collapse chain into parent, calculate
  	 * hysteresis for chain emptiness.
  	 */
  	if (parent->core.live_count + chain->core.live_count - 1 > count)
  		return 0;
  	chain_count = chain->bytes / sizeof(hammer2_blockref_t);
  	if (chain->core.live_count > chain_count * 3 / 4)
  		return 0;
  
  	/*
  	 * Ok, theoretically we can collapse chain's contents into
  	 * parent.  chain is locked, but any in-memory children of chain
  	 * are not.  For this to work, we must be able to dispose of any
  	 * in-memory children of chain.
  	 *
  	 * For now require that there are no in-memory children of chain.
  	 *
  	 * WARNING! Both chain and parent must remain locked across this
  	 *	    entire operation.
  	 */
  
  	/*
  	 * Parent must be marked modified.  Don't try to collapse it if we
  	 * can't mark it modified.  Once modified, destroy chain to make room
  	 * and to get rid of what will be a conflicting key (this is included
  	 * in the calculation above).  Finally, move the children of chain
  	 * into chain's parent.
  	 *
  	 * This order creates an accounting problem for bref.embed.stats
  	 * because we destroy chain before we remove its children.  Any
  	 * elements whos blockref is already synchronized will be counted
  	 * twice.  To deal with the problem we clean out chain's stats prior
  	 * to deleting it.
  	 */
  	error = hammer2_chain_modify(parent, 0, 0, 0);
  	if (error) {
  		krateprintf(&krate_h2me, "hammer2: indirect_maint: %s\n",
  			    hammer2_error_str(error));
  		return 0;
  	}
  	error = hammer2_chain_modify(chain, chain->bref.modify_tid, 0, 0);
  	if (error) {
  		krateprintf(&krate_h2me, "hammer2: indirect_maint: %s\n",
  			    hammer2_error_str(error));
  		return 0;
  	}
  
  	chain->bref.embed.stats.inode_count = 0;
  	chain->bref.embed.stats.data_count = 0;
  	error = hammer2_chain_delete(parent, chain,
  				     chain->bref.modify_tid,
  				     HAMMER2_DELETE_PERMANENT);
  	KKASSERT(error == 0);
  
  	/*
  	 * The combined_find call requires core.spin to be held.  One would
  	 * think there wouldn't be any conflicts since we hold chain
  	 * exclusively locked, but the caching mechanism for 0-ref children
  	 * does not require a chain lock.
  	 */
  	hammer2_spin_ex(&chain->core.spin);
  
  	key_next = 0;
  	key_beg = 0;
  	key_end = HAMMER2_KEY_MAX;
  	for (;;) {
  		chain_base = &chain->data->npdata[0];
  		chain_count = chain->bytes / sizeof(hammer2_blockref_t);
  		sub = hammer2_combined_find(chain, chain_base, chain_count,
  					    &key_next,
  					    key_beg, key_end,
  					    &bref);
  		generation = chain->core.generation;
  		if (bref == NULL)
  			break;
  		key_next = bref->key + ((hammer2_key_t)1 << bref->keybits);
  
  		bsave = *bref;
  		if (sub) {
  			hammer2_chain_ref(sub);
  			hammer2_spin_unex(&chain->core.spin);
  			hammer2_chain_lock(sub, HAMMER2_RESOLVE_NEVER);
  		} else {
  			hammer2_spin_unex(&chain->core.spin);
  			sub = hammer2_chain_get(chain, generation, &bsave,
  						HAMMER2_RESOLVE_NEVER);
  			if (sub == NULL) {
  				hammer2_spin_ex(&chain->core.spin);
  				continue;
  			}
  		}
  		if (bcmp(&bsave, &sub->bref, sizeof(bsave)) ||
  		    sub->parent != chain ||
  		    (sub->flags & HAMMER2_CHAIN_DELETED)) {
  			hammer2_chain_unlock(sub);
  			hammer2_chain_drop(sub);
  			hammer2_spin_ex(&chain->core.spin);
  			sub = NULL;	/* safety */
  			continue;
  		}
  		error = hammer2_chain_delete_obref(chain, sub,
  						   sub->bref.modify_tid, 0,
  						   &bsave);
  		KKASSERT(error == 0);
  		hammer2_chain_rename_obref(&parent, sub,
  				     sub->bref.modify_tid,
  				     HAMMER2_INSERT_SAMEPARENT, &bsave);
  		hammer2_chain_unlock(sub);
  		hammer2_chain_drop(sub);
  		hammer2_spin_ex(&chain->core.spin);
  
  		if (key_next == 0)
  			break;
  		key_beg = key_next;
  	}
  	hammer2_spin_unex(&chain->core.spin);
  
  	hammer2_chain_repchange(parent, chain);
  
  	return 1;
  }
  
  /*
   * Freemap indirect blocks
   *
   * Calculate the keybits and highside/lowside of the freemap node the
   * caller is creating.
   *
   * This routine will specify the next higher-level freemap key/radix
   * representing the lowest-ordered set.  By doing so, eventually all
   * low-ordered sets will be moved one level down.
   *
   * We have to be careful here because the freemap reserves a limited
   * number of blocks for a limited number of levels.  So we can't just
   * push indiscriminately.
   */
  int
  hammer2_chain_indkey_freemap(hammer2_chain_t *parent, hammer2_key_t *keyp,
  			     int keybits, hammer2_blockref_t *base, int count)
  {
  	hammer2_chain_t *chain;
  	hammer2_blockref_t *bref;
  	hammer2_key_t key;
  	hammer2_key_t key_beg;
  	hammer2_key_t key_end;
  	hammer2_key_t key_next;
  	int locount;
  	int hicount;
  	int maxloops = 300000;
  
  	key = *keyp;
  	locount = 0;
  	hicount = 0;
  	keybits = 64;
  
  	/*
  	 * Calculate the range of keys in the array being careful to skip
  	 * slots which are overridden with a deletion.
  	 */
  	key_beg = 0;
  	key_end = HAMMER2_KEY_MAX;
  	hammer2_spin_ex(&parent->core.spin);
  
  	for (;;) {
  		if (--maxloops == 0) {
  			panic("indkey_freemap shit %p %p:%d\n",
  			      parent, base, count);
  		}
  		chain = hammer2_combined_find(parent, base, count,
  					      &key_next,
  					      key_beg, key_end,
  					      &bref);
  
  		/*
  		 * Exhausted search
  		 */
  		if (bref == NULL)
  			break;
  
  		/*
  		 * Skip deleted chains.
  		 */
  		if (chain && (chain->flags & HAMMER2_CHAIN_DELETED)) {
  			if (key_next == 0 || key_next > key_end)
  				break;
  			key_beg = key_next;
  			continue;
  		}
  
  		/*
  		 * Use the full live (not deleted) element for the scan
  		 * iteration.  HAMMER2 does not allow partial replacements.
  		 *
  		 * XXX should be built into hammer2_combined_find().
  		 */
  		key_next = bref->key + ((hammer2_key_t)1 << bref->keybits);
  
  		if (keybits > bref->keybits) {
  			key = bref->key;
  			keybits = bref->keybits;
  		} else if (keybits == bref->keybits && bref->key < key) {
  			key = bref->key;
  		}
  		if (key_next == 0)
  			break;
  		key_beg = key_next;
  	}
  	hammer2_spin_unex(&parent->core.spin);
  
  	/*
  	 * Return the keybits for a higher-level FREEMAP_NODE covering
  	 * this node.
  	 */
  	switch(keybits) {
  	case HAMMER2_FREEMAP_LEVEL0_RADIX:
  		keybits = HAMMER2_FREEMAP_LEVEL1_RADIX;
  		break;
  	case HAMMER2_FREEMAP_LEVEL1_RADIX:
  		keybits = HAMMER2_FREEMAP_LEVEL2_RADIX;
  		break;
  	case HAMMER2_FREEMAP_LEVEL2_RADIX:
  		keybits = HAMMER2_FREEMAP_LEVEL3_RADIX;
  		break;
  	case HAMMER2_FREEMAP_LEVEL3_RADIX:
  		keybits = HAMMER2_FREEMAP_LEVEL4_RADIX;
  		break;
  	case HAMMER2_FREEMAP_LEVEL4_RADIX:
  		keybits = HAMMER2_FREEMAP_LEVEL5_RADIX;
  		break;
  	case HAMMER2_FREEMAP_LEVEL5_RADIX:
  		panic("hammer2_chain_indkey_freemap: level too high");
  		break;
  	default:
  		panic("hammer2_chain_indkey_freemap: bad radix");
  		break;
  	}
  	*keyp = key;
  
  	return (keybits);
  }
  
  /*
   * File indirect blocks
   *
   * Calculate the key/keybits for the indirect block to create by scanning
   * existing keys.  The key being created is also passed in *keyp and can be
   * inside or outside the indirect block.  Regardless, the indirect block
   * must hold at least two keys in order to guarantee sufficient space.
   *
   * We use a modified version of the freemap's fixed radix tree, but taylored
   * for file data.  Basically we configure an indirect block encompassing the
   * smallest key.
   */
  static int
  hammer2_chain_indkey_file(hammer2_chain_t *parent, hammer2_key_t *keyp,
  			    int keybits, hammer2_blockref_t *base, int count,
  			    int ncount)
  {
  	hammer2_chain_t *chain;
  	hammer2_blockref_t *bref;
  	hammer2_key_t key;
  	hammer2_key_t key_beg;
  	hammer2_key_t key_end;
  	hammer2_key_t key_next;
  	int nradix;
  	int locount;
  	int hicount;
  	int maxloops = 300000;
  
  	key = *keyp;
  	locount = 0;
  	hicount = 0;
  	keybits = 64;
  
  	/*
  	 * Calculate the range of keys in the array being careful to skip
  	 * slots which are overridden with a deletion.
  	 *
  	 * Locate the smallest key.
  	 */
  	key_beg = 0;
  	key_end = HAMMER2_KEY_MAX;
  	hammer2_spin_ex(&parent->core.spin);
  
  	for (;;) {
  		if (--maxloops == 0) {
  			panic("indkey_freemap shit %p %p:%d\n",
  			      parent, base, count);
  		}
  		chain = hammer2_combined_find(parent, base, count,
  					      &key_next,
  					      key_beg, key_end,
  					      &bref);
  
  		/*
  		 * Exhausted search
  		 */
  		if (bref == NULL)
  			break;
  
  		/*
  		 * Skip deleted chains.
  		 */
  		if (chain && (chain->flags & HAMMER2_CHAIN_DELETED)) {
  			if (key_next == 0 || key_next > key_end)
  				break;
  			key_beg = key_next;
  			continue;
  		}
  
  		/*
  		 * Use the full live (not deleted) element for the scan
  		 * iteration.  HAMMER2 does not allow partial replacements.
  		 *
  		 * XXX should be built into hammer2_combined_find().
  		 */
  		key_next = bref->key + ((hammer2_key_t)1 << bref->keybits);
  
  		if (keybits > bref->keybits) {
  			key = bref->key;
  			keybits = bref->keybits;
  		} else if (keybits == bref->keybits && bref->key < key) {
  			key = bref->key;
  		}
  		if (key_next == 0)
  			break;
  		key_beg = key_next;
  	}
  	hammer2_spin_unex(&parent->core.spin);
  
  	/*
  	 * Calculate the static keybits for a higher-level indirect block
  	 * that contains the key.
  	 */
  	*keyp = key;
  
  	switch(ncount) {
  	case HAMMER2_IND_COUNT_MIN:
  		nradix = HAMMER2_IND_RADIX_MIN - HAMMER2_BLOCKREF_RADIX;
  		break;
  	case HAMMER2_IND_COUNT_NOM:
  		nradix = HAMMER2_IND_RADIX_NOM - HAMMER2_BLOCKREF_RADIX;
  		break;
  	case HAMMER2_IND_COUNT_MAX:
  		nradix = HAMMER2_IND_RADIX_MAX - HAMMER2_BLOCKREF_RADIX;
  		break;
  	default:
  		panic("bad ncount %d\n", ncount);
  		nradix = 0;
  		break;
  	}
  
  	/*
  	 * The largest radix that can be returned for an indirect block is
  	 * 63 bits.  (The largest practical indirect block radix is actually
  	 * 62 bits because the top-level inode or volume root contains four
  	 * entries, but allow 63 to be returned).
  	 */
  	if (nradix >= 64)
  		nradix = 63;
  
  	return keybits + nradix;
  }
  
  #if 1
  
  /*
   * Directory indirect blocks.
   *
   * Covers both the inode index (directory of inodes), and directory contents
   * (filenames hardlinked to inodes).
   *
   * Because directory keys are hashed we generally try to cut the space in
   * half.  We accomodate the inode index (which tends to have linearly
   * increasing inode numbers) by ensuring that the keyspace is at least large
   * enough to fill up the indirect block being created.
   */
  static int
  hammer2_chain_indkey_dir(hammer2_chain_t *parent, hammer2_key_t *keyp,
  			 int keybits, hammer2_blockref_t *base, int count,
  			 int ncount)
  {
  	hammer2_blockref_t *bref;
  	hammer2_chain_t	*chain;
  	hammer2_key_t key_beg;
  	hammer2_key_t key_end;
  	hammer2_key_t key_next;
  	hammer2_key_t key;
  	int nkeybits;
  	int locount;
  	int hicount;
  	int maxloops = 300000;
  
  	/*
  	 * NOTE: We can't take a shortcut here anymore for inodes because
  	 *	 the root directory can contain a mix of inodes and directory
  	 *	 entries (we used to just return 63 if parent->bref.type was
  	 *	 HAMMER2_BREF_TYPE_INODE.
  	 */
  	key = *keyp;
  	locount = 0;
  	hicount = 0;
  
  	/*
  	 * Calculate the range of keys in the array being careful to skip
  	 * slots which are overridden with a deletion.
  	 */
  	key_beg = 0;
  	key_end = HAMMER2_KEY_MAX;
  	hammer2_spin_ex(&parent->core.spin);
  
  	for (;;) {
  		if (--maxloops == 0) {
  			panic("indkey_freemap shit %p %p:%d\n",
  			      parent, base, count);
  		}
  		chain = hammer2_combined_find(parent, base, count,
  					      &key_next,
  					      key_beg, key_end,
  					      &bref);
  
  		/*
  		 * Exhausted search
  		 */
  		if (bref == NULL)
  			break;
  
  		/*
  		 * Deleted object
  		 */
  		if (chain && (chain->flags & HAMMER2_CHAIN_DELETED)) {
  			if (key_next == 0 || key_next > key_end)
  				break;
  			key_beg = key_next;
  			continue;
  		}
  
  		/*
  		 * Use the full live (not deleted) element for the scan
  		 * iteration.  HAMMER2 does not allow partial replacements.
  		 *
  		 * XXX should be built into hammer2_combined_find().
  		 */
  		key_next = bref->key + ((hammer2_key_t)1 << bref->keybits);
  
  		/*
  		 * Expand our calculated key range (key, keybits) to fit
  		 * the scanned key.  nkeybits represents the full range
  		 * that we will later cut in half (two halves @ nkeybits - 1).
  		 */
  		nkeybits = keybits;
  		if (nkeybits < bref->keybits) {
  			if (bref->keybits > 64) {
  				kprintf("bad bref chain %p bref %p\n",
  					chain, bref);
  				Debugger("fubar");
  			}
  			nkeybits = bref->keybits;
  		}
  		while (nkeybits < 64 &&
  		       rounddown2(key ^ bref->key, (hammer2_key_t)1 << nkeybits) != 0) {
  			++nkeybits;
  		}
  
  		/*
  		 * If the new key range is larger we have to determine
  		 * which side of the new key range the existing keys fall
  		 * under by checking the high bit, then collapsing the
  		 * locount into the hicount or vise-versa.
  		 */
  		if (keybits != nkeybits) {
  			if (((hammer2_key_t)1 << (nkeybits - 1)) & key) {
  				hicount += locount;
  				locount = 0;
  			} else {
  				locount += hicount;
  				hicount = 0;
  			}
  			keybits = nkeybits;
  		}
  
  		/*
  		 * The newly scanned key will be in the lower half or the
  		 * upper half of the (new) key range.
  		 */
  		if (((hammer2_key_t)1 << (nkeybits - 1)) & bref->key)
  			++hicount;
  		else
  			++locount;
  
  		if (key_next == 0)
  			break;
  		key_beg = key_next;
  	}
  	hammer2_spin_unex(&parent->core.spin);
  	bref = NULL;	/* now invalid (safety) */
  
  	/*
  	 * Adjust keybits to represent half of the full range calculated
  	 * above (radix 63 max) for our new indirect block.
  	 */
  	--keybits;
  
  	/*
  	 * Expand keybits to hold at least ncount elements.  ncount will be
  	 * a power of 2.  This is to try to completely fill leaf nodes (at
  	 * least for keys which are not hashes).
  	 *
  	 * We aren't counting 'in' or 'out', we are counting 'high side'
  	 * and 'low side' based on the bit at (1LL << keybits).  We want
  	 * everything to be inside in these cases so shift it all to
  	 * the low or high side depending on the new high bit.
  	 */
  	while (((hammer2_key_t)1 << keybits) < ncount) {
  		++keybits;
  		if (key & ((hammer2_key_t)1 << keybits)) {
  			hicount += locount;
  			locount = 0;
  		} else {
  			locount += hicount;
  			hicount = 0;
  		}
  	}
  
  	if (hicount > locount)
  		key |= (hammer2_key_t)1 << keybits;
  	else
  		key &= ~(hammer2_key_t)1 << keybits;
  
  	*keyp = key;
  
  	return (keybits);
  }
  
  #else
  
  /*
   * Directory indirect blocks.
   *
   * Covers both the inode index (directory of inodes), and directory contents
   * (filenames hardlinked to inodes).
   *
   * Because directory keys are hashed we generally try to cut the space in
   * half.  We accomodate the inode index (which tends to have linearly
   * increasing inode numbers) by ensuring that the keyspace is at least large
   * enough to fill up the indirect block being created.
   */
  static int
  hammer2_chain_indkey_dir(hammer2_chain_t *parent, hammer2_key_t *keyp,
  			 int keybits, hammer2_blockref_t *base, int count,
  			 int ncount)
  {
  	hammer2_blockref_t *bref;
  	hammer2_chain_t	*chain;
  	hammer2_key_t key_beg;
  	hammer2_key_t key_end;
  	hammer2_key_t key_next;
  	hammer2_key_t key;
  	int nkeybits;
  	int locount;
  	int hicount;
  	int maxloops = 300000;
  
  	/*
  	 * Shortcut if the parent is the inode.  In this situation the
  	 * parent has 4+1 directory entries and we are creating an indirect
  	 * block capable of holding many more.
  	 */
  	if (parent->bref.type == HAMMER2_BREF_TYPE_INODE) {
  		return 63;
  	}
  
  	key = *keyp;
  	locount = 0;
  	hicount = 0;
  
  	/*
  	 * Calculate the range of keys in the array being careful to skip
  	 * slots which are overridden with a deletion.
  	 */
  	key_beg = 0;
  	key_end = HAMMER2_KEY_MAX;
  	hammer2_spin_ex(&parent->core.spin);
  
  	for (;;) {
  		if (--maxloops == 0) {
  			panic("indkey_freemap shit %p %p:%d\n",
  			      parent, base, count);
  		}
  		chain = hammer2_combined_find(parent, base, count,
  					      &key_next,
  					      key_beg, key_end,
  					      &bref);
  
  		/*
  		 * Exhausted search
  		 */
  		if (bref == NULL)
  			break;
  
  		/*
  		 * Deleted object
  		 */
  		if (chain && (chain->flags & HAMMER2_CHAIN_DELETED)) {
  			if (key_next == 0 || key_next > key_end)
  				break;
  			key_beg = key_next;
  			continue;
  		}
  
  		/*
  		 * Use the full live (not deleted) element for the scan
  		 * iteration.  HAMMER2 does not allow partial replacements.
  		 *
  		 * XXX should be built into hammer2_combined_find().
  		 */
  		key_next = bref->key + ((hammer2_key_t)1 << bref->keybits);
  
  		/*
  		 * Expand our calculated key range (key, keybits) to fit
  		 * the scanned key.  nkeybits represents the full range
  		 * that we will later cut in half (two halves @ nkeybits - 1).
  		 */
  		nkeybits = keybits;
  		if (nkeybits < bref->keybits) {
  			if (bref->keybits > 64) {
  				kprintf("bad bref chain %p bref %p\n",
  					chain, bref);
  				Debugger("fubar");
  			}
  			nkeybits = bref->keybits;
  		}
  		while (nkeybits < 64 &&
  		       (~(((hammer2_key_t)1 << nkeybits) - 1) &
  		        (key ^ bref->key)) != 0) {
  			++nkeybits;
  		}
  
  		/*
  		 * If the new key range is larger we have to determine
  		 * which side of the new key range the existing keys fall
  		 * under by checking the high bit, then collapsing the
  		 * locount into the hicount or vise-versa.
  		 */
  		if (keybits != nkeybits) {
  			if (((hammer2_key_t)1 << (nkeybits - 1)) & key) {
  				hicount += locount;
  				locount = 0;
  			} else {
  				locount += hicount;
  				hicount = 0;
  			}
  			keybits = nkeybits;
  		}
  
  		/*
  		 * The newly scanned key will be in the lower half or the
  		 * upper half of the (new) key range.
  		 */
  		if (((hammer2_key_t)1 << (nkeybits - 1)) & bref->key)
  			++hicount;
  		else
  			++locount;
  
  		if (key_next == 0)
  			break;
  		key_beg = key_next;
  	}
  	hammer2_spin_unex(&parent->core.spin);
  	bref = NULL;	/* now invalid (safety) */
  
  	/*
  	 * Adjust keybits to represent half of the full range calculated
  	 * above (radix 63 max) for our new indirect block.
  	 */
  	--keybits;
  
  	/*
  	 * Expand keybits to hold at least ncount elements.  ncount will be
  	 * a power of 2.  This is to try to completely fill leaf nodes (at
  	 * least for keys which are not hashes).
  	 *
  	 * We aren't counting 'in' or 'out', we are counting 'high side'
  	 * and 'low side' based on the bit at (1LL << keybits).  We want
  	 * everything to be inside in these cases so shift it all to
  	 * the low or high side depending on the new high bit.
  	 */
  	while (((hammer2_key_t)1 << keybits) < ncount) {
  		++keybits;
  		if (key & ((hammer2_key_t)1 << keybits)) {
  			hicount += locount;
  			locount = 0;
  		} else {
  			locount += hicount;
  			hicount = 0;
  		}
  	}
  
  	if (hicount > locount)
  		key |= (hammer2_key_t)1 << keybits;
  	else
  		key &= ~(hammer2_key_t)1 << keybits;
  
  	*keyp = key;
  
  	return (keybits);
  }
  
  #endif
  
  /*
   * Sets CHAIN_DELETED and remove the chain's blockref from the parent if
   * it exists.
   *
   * Both parent and chain must be locked exclusively.
   *
   * This function will modify the parent if the blockref requires removal
   * from the parent's block table.
   *
   * This function is NOT recursive.  Any entity already pushed into the
   * chain (such as an inode) may still need visibility into its contents,
   * as well as the ability to read and modify the contents.  For example,
   * for an unlinked file which is still open.
   *
   * Also note that the flusher is responsible for cleaning up empty
   * indirect blocks.
   */
  int
  hammer2_chain_delete(hammer2_chain_t *parent, hammer2_chain_t *chain,
  		     hammer2_tid_t mtid, int flags)
  {
  	int error = 0;
  
  	KKASSERT(hammer2_mtx_owned(&chain->lock));
  
  	/*
  	 * Nothing to do if already marked.
  	 *
  	 * We need the spinlock on the core whos RBTREE contains chain
  	 * to protect against races.
  	 */
  	if ((chain->flags & HAMMER2_CHAIN_DELETED) == 0) {
  		KKASSERT((chain->flags & HAMMER2_CHAIN_DELETED) == 0 &&
  			 chain->parent == parent);
  		error = _hammer2_chain_delete_helper(parent, chain,
  						     mtid, flags, NULL);
  	}
  
  	/*
  	 * Permanent deletions mark the chain as destroyed.
  	 *
  	 * NOTE: We do not setflush the chain unless the deletion is
  	 *	 permanent, since the deletion of a chain does not actually
  	 *	 require it to be flushed.
  	 */
  	if (error == 0) {
  		if (flags & HAMMER2_DELETE_PERMANENT) {
  			atomic_set_int(&chain->flags, HAMMER2_CHAIN_DESTROY);
  			hammer2_chain_setflush(chain);
  		}
  	}
  
  	return error;
  }
  
  static int
  hammer2_chain_delete_obref(hammer2_chain_t *parent, hammer2_chain_t *chain,
  		     hammer2_tid_t mtid, int flags,
  		     hammer2_blockref_t *obref)
  {
  	int error = 0;
  
  	KKASSERT(hammer2_mtx_owned(&chain->lock));
  
  	/*
  	 * Nothing to do if already marked.
  	 *
  	 * We need the spinlock on the core whos RBTREE contains chain
  	 * to protect against races.
  	 */
  	obref->type = HAMMER2_BREF_TYPE_EMPTY;
  	if ((chain->flags & HAMMER2_CHAIN_DELETED) == 0) {
  		KKASSERT((chain->flags & HAMMER2_CHAIN_DELETED) == 0 &&
  			 chain->parent == parent);
  		error = _hammer2_chain_delete_helper(parent, chain,
  						     mtid, flags, obref);
  	}
  
  	/*
  	 * Permanent deletions mark the chain as destroyed.
  	 *
  	 * NOTE: We do not setflush the chain unless the deletion is
  	 *	 permanent, since the deletion of a chain does not actually
  	 *	 require it to be flushed.
  	 */
  	if (error == 0) {
  		if (flags & HAMMER2_DELETE_PERMANENT) {
  			atomic_set_int(&chain->flags, HAMMER2_CHAIN_DESTROY);
  			hammer2_chain_setflush(chain);
  		}
  	}
  
  	return error;
  }
  
  /*
   * Returns the index of the nearest element in the blockref array >= elm.
   * Returns (count) if no element could be found.
   *
   * Sets *key_nextp to the next key for loop purposes but does not modify
   * it if the next key would be higher than the current value of *key_nextp.
   * Note that *key_nexp can overflow to 0, which should be tested by the
   * caller.
   *
   * WARNING!  Must be called with parent's spinlock held.  Spinlock remains
   *	     held through the operation.
   */
  static int
  hammer2_base_find(hammer2_chain_t *parent,
  		  hammer2_blockref_t *base, int count,
  		  hammer2_key_t *key_nextp,
  		  hammer2_key_t key_beg, hammer2_key_t key_end)
  {
  	hammer2_blockref_t *scan;
  	hammer2_key_t scan_end;
  	int i;
  	int limit;
  
  	/*
  	 * Require the live chain's already have their core's counted
  	 * so we can optimize operations.
  	 */
          KKASSERT(parent->flags & HAMMER2_CHAIN_COUNTEDBREFS);
  
  	/*
  	 * Degenerate case
  	 */
  	if (count == 0 || base == NULL)
  		return(count);
  
  	/*
  	 * Sequential optimization using parent->cache_index.  This is
  	 * the most likely scenario.
  	 *
  	 * We can avoid trailing empty entries on live chains, otherwise
  	 * we might have to check the whole block array.
  	 */
  	i = parent->cache_index;	/* SMP RACE OK */
  	cpu_ccfence();
  	limit = parent->core.live_zero;
  	if (i >= limit)
  		i = limit - 1;
  	if (i < 0)
  		i = 0;
  	KKASSERT(i < count);
  
  	/*
  	 * Search backwards
  	 */
  	scan = &base[i];
  	while (i > 0 && (scan->type == HAMMER2_BREF_TYPE_EMPTY ||
  	    scan->key > key_beg)) {
  		--scan;
  		--i;
  	}
  	parent->cache_index = i;
  
  	/*
  	 * Search forwards, stop when we find a scan element which
  	 * encloses the key or until we know that there are no further
  	 * elements.
  	 */
  	while (i < count) {
  		if (scan->type != HAMMER2_BREF_TYPE_EMPTY) {
  			scan_end = scan->key +
  				   ((hammer2_key_t)1 << scan->keybits) - 1;
  			if (scan->key > key_beg || scan_end >= key_beg)
  				break;
  		}
  		if (i >= limit)
  			return (count);
  		++scan;
  		++i;
  	}
  	if (i != count) {
  		parent->cache_index = i;
  		if (i >= limit) {
  			i = count;
  		} else {
  			scan_end = scan->key +
  				   ((hammer2_key_t)1 << scan->keybits);
  			if (scan_end && (*key_nextp > scan_end ||
  					 *key_nextp == 0)) {
  				*key_nextp = scan_end;
  			}
  		}
  	}
  	return (i);
  }
  
  /*
   * Do a combined search and return the next match either from the blockref
   * array or from the in-memory chain.  Sets *bresp to the returned bref in
   * both cases, or sets it to NULL if the search exhausted.  Only returns
   * a non-NULL chain if the search matched from the in-memory chain.
   *
   * When no in-memory chain has been found and a non-NULL bref is returned
   * in *bresp.
   *
   *
   * The returned chain is not locked or referenced.  Use the returned bref
   * to determine if the search exhausted or not.  Iterate if the base find
   * is chosen but matches a deleted chain.
   *
   * WARNING!  Must be called with parent's spinlock held.  Spinlock remains
   *	     held through the operation.
   */
  hammer2_chain_t *
  hammer2_combined_find(hammer2_chain_t *parent,
  		      hammer2_blockref_t *base, int count,
  		      hammer2_key_t *key_nextp,
  		      hammer2_key_t key_beg, hammer2_key_t key_end,
  		      hammer2_blockref_t **bresp)
  {
  	hammer2_blockref_t *bref;
  	hammer2_chain_t *chain;
  	int i;
  
  	/*
  	 * Lookup in block array and in rbtree.
  	 */
  	*key_nextp = key_end + 1;
  	i = hammer2_base_find(parent, base, count, key_nextp,
  			      key_beg, key_end);
  	chain = hammer2_chain_find(parent, key_nextp, key_beg, key_end);
  
  	/*
  	 * Neither matched
  	 */
  	if (i == count && chain == NULL) {
  		*bresp = NULL;
  		return(NULL);
  	}
  
  	/*
  	 * Only chain matched.
  	 */
  	if (i == count) {
  		bref = &chain->bref;
  		goto found;
  	}
  
  	/*
  	 * Only blockref matched.
  	 */
  	if (chain == NULL) {
  		bref = &base[i];
  		goto found;
  	}
  
  	/*
  	 * Both in-memory and blockref matched, select the nearer element.
  	 *
  	 * If both are flush with the left-hand side or both are the
  	 * same distance away, select the chain.  In this situation the
  	 * chain must have been loaded from the matching blockmap.
  	 */
  	if ((chain->bref.key <= key_beg && base[i].key <= key_beg) ||
  	    chain->bref.key == base[i].key) {
  		KKASSERT(chain->bref.key == base[i].key);
  		bref = &chain->bref;
  		goto found;
  	}
  
  	/*
  	 * Select the nearer key
  	 */
  	if (chain->bref.key < base[i].key) {
  		bref = &chain->bref;
  	} else {
  		bref = &base[i];
  		chain = NULL;
  	}
  
  	/*
  	 * If the bref is out of bounds we've exhausted our search.
  	 */
  found:
  	if (bref->key > key_end) {
  		*bresp = NULL;
  		chain = NULL;
  	} else {
  		*bresp = bref;
  	}
  	return(chain);
  }
  
  /*
   * Locate the specified block array element and delete it.  The element
   * must exist.
   *
   * The spin lock on the related chain must be held.
   *
   * NOTE: live_count was adjusted when the chain was deleted, so it does not
   *	 need to be adjusted when we commit the media change.
   */
  void
  hammer2_base_delete(hammer2_chain_t *parent,
  		    hammer2_blockref_t *base, int count,
  		    hammer2_chain_t *chain,
  		    hammer2_blockref_t *obref)
  {
  	hammer2_blockref_t *elm = &chain->bref;
  	hammer2_blockref_t *scan;
  	hammer2_key_t key_next;
  	int i;
  
  	/*
  	 * Delete element.  Expect the element to exist.
  	 *
  	 * XXX see caller, flush code not yet sophisticated enough to prevent
  	 *     re-flushed in some cases.
  	 */
  	key_next = 0; /* max range */
  	i = hammer2_base_find(parent, base, count, &key_next,
  			      elm->key, elm->key);
  	scan = &base[i];
  	if (i == count || scan->type == HAMMER2_BREF_TYPE_EMPTY ||
  	    scan->key != elm->key ||
  	    ((chain->flags & HAMMER2_CHAIN_BLKMAPUPD) == 0 &&
  	     scan->keybits != elm->keybits)) {
  		hammer2_spin_unex(&parent->core.spin);
  		panic("delete base %p element not found at %d/%d elm %p\n",
  		      base, i, count, elm);
  		return;
  	}
  
  	/*
  	 * Update stats and zero the entry.
  	 *
  	 * NOTE: Handle radix == 0 (0 bytes) case.
  	 */
  	if ((int)(scan->data_off & HAMMER2_OFF_MASK_RADIX)) {
  		parent->bref.embed.stats.data_count -= (hammer2_off_t)1 <<
  				(int)(scan->data_off & HAMMER2_OFF_MASK_RADIX);
  	}
  	switch(scan->type) {
  	case HAMMER2_BREF_TYPE_INODE:
  		--parent->bref.embed.stats.inode_count;
  		/* fall through */
  	case HAMMER2_BREF_TYPE_DATA:
  		if (parent->bref.leaf_count == HAMMER2_BLOCKREF_LEAF_MAX) {
  			atomic_set_int(&chain->flags,
  				       HAMMER2_CHAIN_HINT_LEAF_COUNT);
  		} else {
  			if (parent->bref.leaf_count)
  				--parent->bref.leaf_count;
  		}
  		/* fall through */
  	case HAMMER2_BREF_TYPE_INDIRECT:
  		if (scan->type != HAMMER2_BREF_TYPE_DATA) {
  			parent->bref.embed.stats.data_count -=
  				scan->embed.stats.data_count;
  			parent->bref.embed.stats.inode_count -=
  				scan->embed.stats.inode_count;
  		}
  		if (scan->type == HAMMER2_BREF_TYPE_INODE)
  			break;
  		if (parent->bref.leaf_count == HAMMER2_BLOCKREF_LEAF_MAX) {
  			atomic_set_int(&chain->flags,
  				       HAMMER2_CHAIN_HINT_LEAF_COUNT);
  		} else {
  			if (parent->bref.leaf_count <= scan->leaf_count)
  				parent->bref.leaf_count = 0;
  			else
  				parent->bref.leaf_count -= scan->leaf_count;
  		}
  		break;
  	case HAMMER2_BREF_TYPE_DIRENT:
  		if (parent->bref.leaf_count == HAMMER2_BLOCKREF_LEAF_MAX) {
  			atomic_set_int(&chain->flags,
  				       HAMMER2_CHAIN_HINT_LEAF_COUNT);
  		} else {
  			if (parent->bref.leaf_count)
  				--parent->bref.leaf_count;
  		}
  	default:
  		break;
  	}
  
  	if (obref)
  		*obref = *scan;
  	bzero(scan, sizeof(*scan));
  
  	/*
  	 * We can only optimize parent->core.live_zero for live chains.
  	 */
  	if (parent->core.live_zero == i + 1) {
  		while (--i >= 0 && base[i].type == HAMMER2_BREF_TYPE_EMPTY)
  			;
  		parent->core.live_zero = i + 1;
  	}
  
  	/*
  	 * Clear appropriate blockmap flags in chain.
  	 */
  	atomic_clear_int(&chain->flags, HAMMER2_CHAIN_BLKMAPPED |
  					HAMMER2_CHAIN_BLKMAPUPD);
  }
  
  /*
   * Insert the specified element.  The block array must not already have the
   * element and must have space available for the insertion.
   *
   * The spin lock on the related chain must be held.
   *
   * NOTE: live_count was adjusted when the chain was deleted, so it does not
   *	 need to be adjusted when we commit the media change.
   */
  void
  hammer2_base_insert(hammer2_chain_t *parent,
  		    hammer2_blockref_t *base, int count,
  		    hammer2_chain_t *chain, hammer2_blockref_t *elm)
  {
  	hammer2_key_t key_next;
  	hammer2_key_t xkey;
  	int i;
  	int j;
  	int k;
  	int l;
  	int u = 1;
  
  	/*
  	 * Insert new element.  Expect the element to not already exist
  	 * unless we are replacing it.
  	 *
  	 * XXX see caller, flush code not yet sophisticated enough to prevent
  	 *     re-flushed in some cases.
  	 */
  	key_next = 0; /* max range */
  	i = hammer2_base_find(parent, base, count, &key_next,
  			      elm->key, elm->key);
  
  	/*
  	 * Shortcut fill optimization, typical ordered insertion(s) may not
  	 * require a search.
  	 */
  	KKASSERT(i >= 0 && i <= count);
  
  	/*
  	 * Set appropriate blockmap flags in chain (if not NULL)
  	 */
  	if (chain)
  		atomic_set_int(&chain->flags, HAMMER2_CHAIN_BLKMAPPED);
  
  	/*
  	 * Update stats and zero the entry
  	 */
  	if ((int)(elm->data_off & HAMMER2_OFF_MASK_RADIX)) {
  		parent->bref.embed.stats.data_count += (hammer2_off_t)1 <<
  				(int)(elm->data_off & HAMMER2_OFF_MASK_RADIX);
  	}
  	switch(elm->type) {
  	case HAMMER2_BREF_TYPE_INODE:
  		++parent->bref.embed.stats.inode_count;
  		/* fall through */
  	case HAMMER2_BREF_TYPE_DATA:
  		if (parent->bref.leaf_count != HAMMER2_BLOCKREF_LEAF_MAX)
  			++parent->bref.leaf_count;
  		/* fall through */
  	case HAMMER2_BREF_TYPE_INDIRECT:
  		if (elm->type != HAMMER2_BREF_TYPE_DATA) {
  			parent->bref.embed.stats.data_count +=
  				elm->embed.stats.data_count;
  			parent->bref.embed.stats.inode_count +=
  				elm->embed.stats.inode_count;
  		}
  		if (elm->type == HAMMER2_BREF_TYPE_INODE)
  			break;
  		if (parent->bref.leaf_count + elm->leaf_count <
  		    HAMMER2_BLOCKREF_LEAF_MAX) {
  			parent->bref.leaf_count += elm->leaf_count;
  		} else {
  			parent->bref.leaf_count = HAMMER2_BLOCKREF_LEAF_MAX;
  		}
  		break;
  	case HAMMER2_BREF_TYPE_DIRENT:
  		if (parent->bref.leaf_count != HAMMER2_BLOCKREF_LEAF_MAX)
  			++parent->bref.leaf_count;
  		break;
  	default:
  		break;
  	}
  
  
  	/*
  	 * We can only optimize parent->core.live_zero for live chains.
  	 */
  	if (i == count && parent->core.live_zero < count) {
  		i = parent->core.live_zero++;
  		base[i] = *elm;
  		return;
  	}
  
  	xkey = elm->key + ((hammer2_key_t)1 << elm->keybits) - 1;
  	if (i != count && (base[i].key < elm->key || xkey >= base[i].key)) {
  		hammer2_spin_unex(&parent->core.spin);
  		panic("insert base %p overlapping elements at %d elm %p\n",
  		      base, i, elm);
  	}
  
  	/*
  	 * Try to find an empty slot before or after.
  	 */
  	j = i;
  	k = i;
  	while (j > 0 || k < count) {
  		--j;
  		if (j >= 0 && base[j].type == HAMMER2_BREF_TYPE_EMPTY) {
  			if (j == i - 1) {
  				base[j] = *elm;
  			} else {
  				bcopy(&base[j+1], &base[j],
  				      (i - j - 1) * sizeof(*base));
  				base[i - 1] = *elm;
  			}
  			goto validate;
  		}
  		++k;
  		if (k < count && base[k].type == HAMMER2_BREF_TYPE_EMPTY) {
  			bcopy(&base[i], &base[i+1],
  			      (k - i) * sizeof(hammer2_blockref_t));
  			base[i] = *elm;
  
  			/*
  			 * We can only update parent->core.live_zero for live
  			 * chains.
  			 */
  			if (parent->core.live_zero <= k)
  				parent->core.live_zero = k + 1;
  			u = 2;
  			goto validate;
  		}
  	}
  	panic("hammer2_base_insert: no room!");
  
  	/*
  	 * Debugging
  	 */
  validate:
  	key_next = 0;
  	for (l = 0; l < count; ++l) {
  		if (base[l].type != HAMMER2_BREF_TYPE_EMPTY) {
  			key_next = base[l].key +
  				   ((hammer2_key_t)1 << base[l].keybits) - 1;
  			break;
  		}
  	}
  	while (++l < count) {
  		if (base[l].type != HAMMER2_BREF_TYPE_EMPTY) {
  			if (base[l].key <= key_next)
  				panic("base_insert %d %d,%d,%d fail %p:%d", u, i, j, k, base, l);
  			key_next = base[l].key +
  				   ((hammer2_key_t)1 << base[l].keybits) - 1;
  
  		}
  	}
  
  }
  
  #if 0
  
  /*
   * Sort the blockref array for the chain.  Used by the flush code to
   * sort the blockref[] array.
   *
   * The chain must be exclusively locked AND spin-locked.
   */
  typedef hammer2_blockref_t *hammer2_blockref_p;
  
  static
  int
  hammer2_base_sort_callback(const void *v1, const void *v2)
  {
  	hammer2_blockref_p bref1 = *(const hammer2_blockref_p *)v1;
  	hammer2_blockref_p bref2 = *(const hammer2_blockref_p *)v2;
  
  	/*
  	 * Make sure empty elements are placed at the end of the array
  	 */
  	if (bref1->type == HAMMER2_BREF_TYPE_EMPTY) {
  		if (bref2->type == HAMMER2_BREF_TYPE_EMPTY)
  			return(0);
  		return(1);
  	} else if (bref2->type == HAMMER2_BREF_TYPE_EMPTY) {
  		return(-1);
  	}
  
  	/*
  	 * Sort by key
  	 */
  	if (bref1->key < bref2->key)
  		return(-1);
  	if (bref1->key > bref2->key)
  		return(1);
  	return(0);
  }
  
  void
  hammer2_base_sort(hammer2_chain_t *chain)
  {
  	hammer2_blockref_t *base;
  	int count;
  
  	switch(chain->bref.type) {
  	case HAMMER2_BREF_TYPE_INODE:
  		/*
  		 * Special shortcut for embedded data returns the inode
  		 * itself.  Callers must detect this condition and access
  		 * the embedded data (the strategy code does this for us).
  		 *
  		 * This is only applicable to regular files and softlinks.
  		 */
  		if (chain->data->ipdata.meta.op_flags &
  		    HAMMER2_OPFLAG_DIRECTDATA) {
  			return;
  		}
  		base = &chain->data->ipdata.u.blockset.blockref[0];
  		count = HAMMER2_SET_COUNT;
  		break;
  	case HAMMER2_BREF_TYPE_FREEMAP_NODE:
  	case HAMMER2_BREF_TYPE_INDIRECT:
  		/*
  		 * Optimize indirect blocks in the INITIAL state to avoid
  		 * I/O.
  		 */
  		KKASSERT((chain->flags & HAMMER2_CHAIN_INITIAL) == 0);
  		base = &chain->data->npdata[0];
  		count = chain->bytes / sizeof(hammer2_blockref_t);
  		break;
  	case HAMMER2_BREF_TYPE_VOLUME:
  		base = &chain->data->voldata.sroot_blockset.blockref[0];
  		count = HAMMER2_SET_COUNT;
  		break;
  	case HAMMER2_BREF_TYPE_FREEMAP:
  		base = &chain->data->blkset.blockref[0];
  		count = HAMMER2_SET_COUNT;
  		break;
  	default:
  		panic("hammer2_base_sort: unrecognized "
  		      "blockref(A) type: %d",
  		      chain->bref.type);
  		base = NULL;	/* safety */
  		count = 0;	/* safety */
  		break;
  	}
  	kqsort(base, count, sizeof(*base), hammer2_base_sort_callback);
  }
  
  #endif
  
  /*
   * Set the check data for a chain.  This can be a heavy-weight operation
   * and typically only runs on-flush.  For file data check data is calculated
   * when the logical buffers are flushed.
   */
  void
  hammer2_chain_setcheck(hammer2_chain_t *chain, void *bdata)
  {
  	atomic_clear_int(&chain->flags, HAMMER2_CHAIN_NOTTESTED);
  
  	switch(HAMMER2_DEC_CHECK(chain->bref.methods)) {
  	case HAMMER2_CHECK_NONE:
  		break;
  	case HAMMER2_CHECK_DISABLED:
  		break;
  	case HAMMER2_CHECK_ISCSI32:
  		chain->bref.check.iscsi32.value =
  			hammer2_icrc32(bdata, chain->bytes);
  		break;
  	case HAMMER2_CHECK_XXHASH64:
  		chain->bref.check.xxhash64.value =
  			XXH64(bdata, chain->bytes, XXH_HAMMER2_SEED);
  		break;
  	case HAMMER2_CHECK_SHA192:
  		{
  			SHA256_CTX hash_ctx;
  			union {
  				uint8_t digest[SHA256_DIGEST_LENGTH];
  				uint64_t digest64[SHA256_DIGEST_LENGTH/8];
  			} u;
  
  			SHA256_Init(&hash_ctx);
  			SHA256_Update(&hash_ctx, bdata, chain->bytes);
  			SHA256_Final(u.digest, &hash_ctx);
  			u.digest64[2] ^= u.digest64[3];
  			bcopy(u.digest,
  			      chain->bref.check.sha192.data,
  			      sizeof(chain->bref.check.sha192.data));
  		}
  		break;
  	case HAMMER2_CHECK_FREEMAP:
  		chain->bref.check.freemap.icrc32 =
  			hammer2_icrc32(bdata, chain->bytes);
  		break;
  	default:
  		kprintf("hammer2_chain_setcheck: unknown check type %02x\n",
  			chain->bref.methods);
  		break;
  	}
  }
  
  /*
   * Characterize a failed check code and try to trace back to the inode.
   */
  static void
  hammer2_characterize_failed_chain(hammer2_chain_t *chain, uint64_t check,
  				  int bits)
  {
  	hammer2_chain_t *lchain;
  	hammer2_chain_t *ochain;
  	int did;
  
  	did = krateprintf(&krate_h2chk,
  		"chain %016jx.%02x (%s) meth=%02x CHECK FAIL "
  		"(flags=%08x, bref/data ",
  		chain->bref.data_off,
  		chain->bref.type,
  		hammer2_bref_type_str(chain->bref.type),
  		chain->bref.methods,
  		chain->flags);
  	if (did == 0)
  		return;
  
  	if (bits == 32) {
  		kprintf("%08x/%08x)\n",
  			chain->bref.check.iscsi32.value,
  			(uint32_t)check);
  	} else {
  		kprintf("%016jx/%016jx)\n",
  			chain->bref.check.xxhash64.value,
  			check);
  	}
  
  	/*
  	 * Run up the chains to try to find the governing inode so we
  	 * can report it.
  	 *
  	 * XXX This error reporting is not really MPSAFE
  	 */
  	ochain = chain;
  	lchain = chain;
  	while (chain && chain->bref.type != HAMMER2_BREF_TYPE_INODE) {
  		lchain = chain;
  		chain = chain->parent;
  	}
  
  	if (chain && chain->bref.type == HAMMER2_BREF_TYPE_INODE &&
  	    ((chain->bref.flags & HAMMER2_BREF_FLAG_PFSROOT) == 0 ||
  	     (lchain->bref.key & HAMMER2_DIRHASH_VISIBLE))) {
  		kprintf("   Resides at/in inode %ld\n",
  			chain->bref.key);
  	} else if (chain && chain->bref.type == HAMMER2_BREF_TYPE_INODE) {
  		kprintf("   Resides in inode index - CRITICAL!!!\n");
  	} else {
  		kprintf("   Resides in root index - CRITICAL!!!\n");
  	}
  	if (ochain->hmp) {
  		const char *pfsname = "UNKNOWN";
  		int i;
  
  		if (ochain->pmp) {
  			for (i = 0; i < HAMMER2_MAXCLUSTER; ++i) {
  				if (ochain->pmp->pfs_hmps[i] == ochain->hmp &&
  				    ochain->pmp->pfs_names[i]) {
  					pfsname = ochain->pmp->pfs_names[i];
  					break;
  				}
  			}
  		}
  		kprintf("   In pfs %s on device %s\n",
  			pfsname, ochain->hmp->devrepname);
  	}
  }
  
  /*
   * Returns non-zero on success, 0 on failure.
   */
  int
  hammer2_chain_testcheck(hammer2_chain_t *chain, void *bdata)
  {
  	uint32_t check32;
  	uint64_t check64;
  	int r;
  
  	if (chain->flags & HAMMER2_CHAIN_NOTTESTED)
  		return 1;
  
  	switch(HAMMER2_DEC_CHECK(chain->bref.methods)) {
  	case HAMMER2_CHECK_NONE:
  		r = 1;
  		break;
  	case HAMMER2_CHECK_DISABLED:
  		r = 1;
  		break;
  	case HAMMER2_CHECK_ISCSI32:
  		check32 = hammer2_icrc32(bdata, chain->bytes);
  		r = (chain->bref.check.iscsi32.value == check32);
  		if (r == 0) {
  			hammer2_characterize_failed_chain(chain, check32, 32);
  		}
  		hammer2_process_icrc32 += chain->bytes;
  		break;
  	case HAMMER2_CHECK_XXHASH64:
  		check64 = XXH64(bdata, chain->bytes, XXH_HAMMER2_SEED);
  		r = (chain->bref.check.xxhash64.value == check64);
  		if (r == 0) {
  			hammer2_characterize_failed_chain(chain, check64, 64);
  		}
  		hammer2_process_xxhash64 += chain->bytes;
  		break;
  	case HAMMER2_CHECK_SHA192:
  		{
  			SHA256_CTX hash_ctx;
  			union {
  				uint8_t digest[SHA256_DIGEST_LENGTH];
  				uint64_t digest64[SHA256_DIGEST_LENGTH/8];
  			} u;
  
  			SHA256_Init(&hash_ctx);
  			SHA256_Update(&hash_ctx, bdata, chain->bytes);
  			SHA256_Final(u.digest, &hash_ctx);
  			u.digest64[2] ^= u.digest64[3];
  			if (bcmp(u.digest,
  				 chain->bref.check.sha192.data,
  			         sizeof(chain->bref.check.sha192.data)) == 0) {
  				r = 1;
  			} else {
  				r = 0;
  				krateprintf(&krate_h2chk,
  					"chain %016jx.%02x meth=%02x "
  					"CHECK FAIL\n",
  					chain->bref.data_off,
  					chain->bref.type,
  					chain->bref.methods);
  			}
  		}
  		break;
  	case HAMMER2_CHECK_FREEMAP:
  		r = (chain->bref.check.freemap.icrc32 ==
  		     hammer2_icrc32(bdata, chain->bytes));
  		if (r == 0) {
  			int did;
  
  			did = krateprintf(&krate_h2chk,
  					  "chain %016jx.%02x meth=%02x "
  					  "CHECK FAIL\n",
  					  chain->bref.data_off,
  					  chain->bref.type,
  					  chain->bref.methods);
  			if (did) {
  				kprintf("freemap.icrc %08x icrc32 %08x (%d)\n",
  					chain->bref.check.freemap.icrc32,
  					hammer2_icrc32(bdata, chain->bytes),
  					chain->bytes);
  				if (chain->dio) {
  					kprintf("dio %p buf %016jx,%d "
  						"bdata %p/%p\n",
  						chain->dio,
  						chain->dio->bp->b_loffset,
  						chain->dio->bp->b_bufsize,
  						bdata,
  						chain->dio->bp->b_data);
  				}
  			}
  		}
  		break;
  	default:
  		kprintf("hammer2_chain_testcheck: unknown check type %02x\n",
  			chain->bref.methods);
  		r = 1;
  		break;
  	}
  	return r;
  }
  
  /*
   * Acquire the chain and parent representing the specified inode for the
   * device at the specified cluster index.
   *
   * The flags passed in are LOOKUP flags, not RESOLVE flags.
   *
   * If we are unable to locate the inode, HAMMER2_ERROR_EIO is returned and
   * *chainp will be NULL.  *parentp may still be set error or not, or NULL
   * if the parent itself could not be resolved.
   *
   * The caller may pass-in a locked *parentp and/or *chainp, or neither.
   * They will be unlocked and released by this function.  The *parentp and
   * *chainp representing the located inode are returned locked.
   */
  int
  hammer2_chain_inode_find(hammer2_pfs_t *pmp, hammer2_key_t inum,
  			 int clindex, int flags,
  			 hammer2_chain_t **parentp, hammer2_chain_t **chainp)
  {
  	hammer2_chain_t *parent;
  	hammer2_chain_t *rchain;
  	hammer2_key_t key_dummy;
  	hammer2_inode_t *ip;
  	int resolve_flags;
  	int error;
  
  	resolve_flags = (flags & HAMMER2_LOOKUP_SHARED) ?
  			HAMMER2_RESOLVE_SHARED : 0;
  
  	/*
  	 * Caller expects us to replace these.
  	 */
  	if (*chainp) {
  		hammer2_chain_unlock(*chainp);
  		hammer2_chain_drop(*chainp);
  		*chainp = NULL;
  	}
  	if (*parentp) {
  		hammer2_chain_unlock(*parentp);
  		hammer2_chain_drop(*parentp);
  		*parentp = NULL;
  	}
  
  	/*
  	 * Be very careful, this is a backend function and we CANNOT
  	 * lock any frontend inode structure we find.  But we have to
  	 * look the inode up this way first in case it exists but is
  	 * detached from the radix tree.
  	 */
  	ip = hammer2_inode_lookup(pmp, inum);
  	if (ip) {
  		*chainp = hammer2_inode_chain_and_parent(ip, clindex,
  						       parentp,
  						       resolve_flags);
  		hammer2_inode_drop(ip);
  		if (*chainp)
  			return 0;
  		hammer2_chain_unlock(*chainp);
  		hammer2_chain_drop(*chainp);
  		*chainp = NULL;
  		if (*parentp) {
  			hammer2_chain_unlock(*parentp);
  			hammer2_chain_drop(*parentp);
  			*parentp = NULL;
  		}
  	}
  
  	/*
  	 * Inodes hang off of the iroot (bit 63 is clear, differentiating
  	 * inodes from root directory entries in the key lookup).
  	 */
  	parent = hammer2_inode_chain(pmp->iroot, clindex, resolve_flags);
  	rchain = NULL;
  	if (parent) {
  		rchain = hammer2_chain_lookup(&parent, &key_dummy,
  					      inum, inum,
  					      &error, flags);
  	} else {
  		error = HAMMER2_ERROR_EIO;
  	}
  	*parentp = parent;
  	*chainp = rchain;
  
  	return error;
  }
  
  /*
   * Used by the bulkscan code to snapshot the synchronized storage for
   * a volume, allowing it to be scanned concurrently against normal
   * operation.
   */
  hammer2_chain_t *
  hammer2_chain_bulksnap(hammer2_dev_t *hmp)
  {
  	hammer2_chain_t *copy;
  
  	copy = hammer2_chain_alloc(hmp, hmp->spmp, &hmp->vchain.bref);
  	copy->data = kmalloc(sizeof(copy->data->voldata),
  			     hmp->mmsg, M_WAITOK | M_ZERO);
  	hammer2_voldata_lock(hmp);
  	copy->data->voldata = hmp->volsync;
  	hammer2_voldata_unlock(hmp);
  
  	return copy;
  }
  
  void
  hammer2_chain_bulkdrop(hammer2_chain_t *copy)
  {
  	KKASSERT(copy->bref.type == HAMMER2_BREF_TYPE_VOLUME);
  	KKASSERT(copy->data);
  	kfree(copy->data, copy->hmp->mmsg);
  	copy->data = NULL;
  	atomic_add_long(&hammer2_chain_allocs, -1);
  	hammer2_chain_drop(copy);
  }
  
  /*
   * Returns non-zero if the chain (INODE or DIRENT) matches the
   * filename.
   */
  int
  hammer2_chain_dirent_test(hammer2_chain_t *chain, const char *name,
  			  size_t name_len)
  {
  	const hammer2_inode_data_t *ripdata;
  
  	if (chain->bref.type == HAMMER2_BREF_TYPE_INODE) {
  		ripdata = &chain->data->ipdata;
  		if (ripdata->meta.name_len == name_len &&
  		    bcmp(ripdata->filename, name, name_len) == 0) {
  			return 1;
  		}
  	}
  	if (chain->bref.type == HAMMER2_BREF_TYPE_DIRENT &&
  	    chain->bref.embed.dirent.namlen == name_len) {
  		if (name_len > sizeof(chain->bref.check.buf) &&
  		    bcmp(chain->data->buf, name, name_len) == 0) {
  			return 1;
  		}
  		if (name_len <= sizeof(chain->bref.check.buf) &&
  		    bcmp(chain->bref.check.buf, name, name_len) == 0) {
  			return 1;
  		}
  	}
  	return 0;
  }
  