hammer2 - Stabilization pass

[dragonfly.git] / sys / vfs / hammer2 / hammer2_flush.c

/*
 * Copyright (c) 2011-2014 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@dragonflybsd.org>
 * by Venkatesh Srinivas <vsrinivas@dragonflybsd.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
/*
 *                      TRANSACTION AND FLUSH HANDLING
 *
 * Deceptively simple but actually fairly difficult to implement properly is
 * how I would describe it.
 *
 * Flushing generally occurs bottom-up but requires a top-down scan to
 * locate chains with MODIFIED and/or UPDATE bits set.  The ONFLUSH flag
 * tells how to recurse downward to find these chains.
 */

#include <sys/cdefs.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/types.h>
#include <sys/lock.h>
#include <sys/uuid.h>

#include "hammer2.h"

#define FLUSH_DEBUG 0

#define HAMMER2_FLUSH_DEPTH_LIMIT       10      /* stack recursion limit */


/*
 * Recursively flush the specified chain.  The chain is locked and
 * referenced by the caller and will remain so on return.  The chain
 * will remain referenced throughout but can temporarily lose its
 * lock during the recursion to avoid unnecessarily stalling user
 * processes.
 */
struct hammer2_flush_info {
        hammer2_chain_t *parent;
        hammer2_trans_t *trans;
        int             depth;
        int             diddeferral;
        int             cache_index;
        struct h2_flush_list flushq;
        hammer2_xid_t   sync_xid;       /* memory synchronization point */
        hammer2_chain_t *debug;
};

typedef struct hammer2_flush_info hammer2_flush_info_t;

static void hammer2_flush_core(hammer2_flush_info_t *info,
                                hammer2_chain_t *chain, int deleting);
static int hammer2_flush_recurse(hammer2_chain_t *child, void *data);

/*
 * For now use a global transaction manager.  What we ultimately want to do
 * is give each non-overlapping hmp/pmp group its own transaction manager.
 *
 * Transactions govern XID tracking on the physical media (the hmp), but they
 * also govern TID tracking which is per-PFS and thus might cross multiple
 * hmp's.  So we can't just stuff tmanage into hammer2_dev or
 * hammer2_pfs.
 */
void
hammer2_trans_manage_init(hammer2_trans_manage_t *tman)
{
        lockinit(&tman->translk, "h2trans", 0, 0);
        TAILQ_INIT(&tman->transq);
        tman->flush_xid = 1;
        tman->alloc_xid = tman->flush_xid + 1;
}

hammer2_xid_t
hammer2_trans_newxid(hammer2_pfs_t *pmp)
{
        hammer2_xid_t xid;

        for (;;) {
                xid = atomic_fetchadd_int(&pmp->tmanage.alloc_xid, 1);
                if (xid)
                        break;
        }
        return xid;
}

/*
 * Transaction support functions for writing to the filesystem.
 *
 * Initializing a new transaction allocates a transaction ID.  Typically
 * passed a pmp (hmp passed as NULL), indicating a cluster transaction.  Can
 * be passed a NULL pmp and non-NULL hmp to indicate a transaction on a single
 * media target.  The latter mode is used by the recovery code.
 *
 * TWO TRANSACTION IDs can run concurrently, where one is a flush and the
 * other is a set of any number of concurrent filesystem operations.  We
 * can either have <running_fs_ops> + <waiting_flush> + <blocked_fs_ops>
 * or we can have <running_flush> + <concurrent_fs_ops>.
 *
 * During a flush, new fs_ops are only blocked until the fs_ops prior to
 * the flush complete.  The new fs_ops can then run concurrent with the flush.
 *
 * Buffer-cache transactions operate as fs_ops but never block.  A
 * buffer-cache flush will run either before or after the current pending
 * flush depending on its state.
 */
void
hammer2_trans_init(hammer2_trans_t *trans, hammer2_pfs_t *pmp, int flags)
{
        hammer2_trans_manage_t *tman;
        hammer2_trans_t *head;

        tman = &pmp->tmanage;

        bzero(trans, sizeof(*trans));
        trans->pmp = pmp;
        trans->flags = flags;
        trans->td = curthread;

        lockmgr(&tman->translk, LK_EXCLUSIVE);

        if (flags & HAMMER2_TRANS_ISFLUSH) {
                /*
                 * If multiple flushes are trying to run we have to
                 * wait until it is our turn.  All flushes are serialized.
                 *
                 * We queue ourselves and then wait to become the head
                 * of the queue, allowing all prior flushes to complete.
                 *
                 * Multiple normal transactions can share the current
                 * transaction id but a flush transaction needs its own
                 * unique TID for proper block table update accounting.
                 */
                ++tman->flushcnt;
                ++pmp->modify_tid;
                tman->flush_xid = hammer2_trans_newxid(pmp);
                trans->sync_xid = tman->flush_xid;
                trans->modify_tid = pmp->modify_tid;
                TAILQ_INSERT_TAIL(&tman->transq, trans, entry);
                if (TAILQ_FIRST(&tman->transq) != trans) {
                        trans->blocked = 1;
                        while (trans->blocked) {
                                lksleep(&trans->sync_xid, &tman->translk,
                                        0, "h2multf", hz);
                        }
                }
        } else if (tman->flushcnt == 0) {
                /*
                 * No flushes are pending, we can go.  Use prior flush_xid + 1.
                 *
                 * WARNING!  Also see hammer2_chain_setflush()
                 */
                TAILQ_INSERT_TAIL(&tman->transq, trans, entry);
                trans->sync_xid = tman->flush_xid + 1;

                /* XXX improve/optimize inode allocation */
        } else if (trans->flags & HAMMER2_TRANS_BUFCACHE) {
                /*
                 * A buffer cache transaction is requested while a flush
                 * is in progress.  The flush's PREFLUSH flag must be set
                 * in this situation.
                 *
                 * The buffer cache flush takes on the main flush's
                 * transaction id.
                 */
                TAILQ_FOREACH(head, &tman->transq, entry) {
                        if (head->flags & HAMMER2_TRANS_ISFLUSH)
                                break;
                }
                KKASSERT(head);
                KKASSERT(head->flags & HAMMER2_TRANS_PREFLUSH);
                trans->flags |= HAMMER2_TRANS_PREFLUSH;
                TAILQ_INSERT_AFTER(&tman->transq, head, trans, entry);
                trans->sync_xid = head->sync_xid;
                trans->modify_tid = head->modify_tid;
                trans->flags |= HAMMER2_TRANS_CONCURRENT;
                /* not allowed to block */
        } else {
                /*
                 * A normal transaction is requested while a flush is in
                 * progress.  We insert after the current flush and may
                 * block.
                 *
                 * WARNING!  Also see hammer2_chain_setflush()
                 */
                TAILQ_FOREACH(head, &tman->transq, entry) {
                        if (head->flags & HAMMER2_TRANS_ISFLUSH)
                                break;
                }
                KKASSERT(head);
                TAILQ_INSERT_AFTER(&tman->transq, head, trans, entry);
                trans->sync_xid = head->sync_xid + 1;
                trans->flags |= HAMMER2_TRANS_CONCURRENT;

                /*
                 * XXX for now we must block new transactions, synchronous
                 * flush mode is on by default.
                 *
                 * If synchronous flush mode is enabled concurrent
                 * frontend transactions during the flush are not
                 * allowed (except we don't have a choice for buffer
                 * cache ops).
                 */
                if (hammer2_synchronous_flush > 0 ||
                    TAILQ_FIRST(&tman->transq) != head) {
                        trans->blocked = 1;
                        while (trans->blocked) {
                                lksleep(&trans->sync_xid, &tman->translk,
                                        0, "h2multf", hz);
                        }
                }
        }
        if (flags & HAMMER2_TRANS_NEWINODE) {
                if (pmp->spmp_hmp) {
                        /*
                         * Super-root transaction, all new inodes have an
                         * inode number of 1.  Normal pfs inode cache
                         * semantics are not used.
                         */
                        trans->inode_tid = 1;
                } else {
                        /*
                         * Normal transaction
                         */
                        if (pmp->inode_tid < HAMMER2_INODE_START)
                                pmp->inode_tid = HAMMER2_INODE_START;
                        trans->inode_tid = pmp->inode_tid++;
                }
        }

        lockmgr(&tman->translk, LK_RELEASE);
}

void
hammer2_trans_assert_strategy(hammer2_pfs_t *pmp)
{
        hammer2_trans_manage_t *tman;
        hammer2_trans_t *head;

        tman = &pmp->tmanage;
        lockmgr(&tman->translk, LK_EXCLUSIVE);
        if (tman->flushcnt) {
                TAILQ_FOREACH(head, &tman->transq, entry) {
                        if (head->flags & HAMMER2_TRANS_ISFLUSH)
                                break;
                }
                KKASSERT(head);
                KKASSERT(head->flags & HAMMER2_TRANS_PREFLUSH);
        }
        lockmgr(&tman->translk, LK_RELEASE);
}

void
hammer2_trans_done(hammer2_trans_t *trans)
{
        hammer2_trans_manage_t *tman;
        hammer2_trans_t *head;
        hammer2_trans_t *scan;

        tman = &trans->pmp->tmanage;

        /*
         * Remove.
         */
        lockmgr(&tman->translk, LK_EXCLUSIVE);
        TAILQ_REMOVE(&tman->transq, trans, entry);
        head = TAILQ_FIRST(&tman->transq);

        /*
         * Adjust flushcnt if this was a flush, clear TRANS_CONCURRENT
         * up through the next flush.  (If the head is a flush then we
         * stop there, unlike the unblock code following this section).
         */
        if (trans->flags & HAMMER2_TRANS_ISFLUSH) {
                --tman->flushcnt;
                scan = head;
                while (scan && (scan->flags & HAMMER2_TRANS_ISFLUSH) == 0) {
                        atomic_clear_int(&scan->flags,
                                         HAMMER2_TRANS_CONCURRENT);
                        scan = TAILQ_NEXT(scan, entry);
                }
        }

        /*
         * Unblock the head of the queue and any additional transactions
         * up to the next flush.  The head can be a flush and it will be
         * unblocked along with the non-flush transactions following it
         * (which are allowed to run concurrently with it).
         *
         * In synchronous flush mode we stop if the head transaction is
         * a flush.
         */
        if (head && head->blocked) {
                head->blocked = 0;
                wakeup(&head->sync_xid);

                if (hammer2_synchronous_flush > 0)
                        scan = head;
                else
                        scan = TAILQ_NEXT(head, entry);
                while (scan && (scan->flags & HAMMER2_TRANS_ISFLUSH) == 0) {
                        if (scan->blocked) {
                                scan->blocked = 0;
                                wakeup(&scan->sync_xid);
                        }
                        scan = TAILQ_NEXT(scan, entry);
                }
        }
        lockmgr(&tman->translk, LK_RELEASE);
}

/*
 * Chains undergoing destruction are removed from the in-memory topology.
 * To avoid getting lost these chains are placed on the delayed flush
 * queue which will properly dispose of them.
 *
 * We do this instead of issuing an immediate flush in order to give
 * recursive deletions (rm -rf, etc) a chance to remove more of the
 * hierarchy, potentially allowing an enormous amount of write I/O to
 * be avoided.
 */
void
hammer2_delayed_flush(hammer2_trans_t *trans, hammer2_chain_t *chain)
{
        if ((chain->flags & HAMMER2_CHAIN_DELAYED) == 0) {
                hammer2_spin_ex(&chain->hmp->list_spin);
                if ((chain->flags & (HAMMER2_CHAIN_DELAYED |
                                     HAMMER2_CHAIN_DEFERRED)) == 0) {
                        atomic_set_int(&chain->flags, HAMMER2_CHAIN_DELAYED |
                                                      HAMMER2_CHAIN_DEFERRED);
                        TAILQ_INSERT_TAIL(&chain->hmp->flushq,
                                          chain, flush_node);
                        hammer2_chain_ref(chain);
                }
                hammer2_spin_unex(&chain->hmp->list_spin);
        }
}

/*
 * Flush the chain and all modified sub-chains through the specified
 * synchronization point, propagating parent chain modifications, modify_tid,
 * and mirror_tid updates back up as needed.
 *
 * Caller must have interlocked against any non-flush-related modifying
 * operations in progress whos XXX values are less than or equal
 * to the passed sync_xid.
 *
 * Caller must have already vetted synchronization points to ensure they
 * are properly flushed.  Only snapshots and cluster flushes can create
 * these sorts of synchronization points.
 *
 * This routine can be called from several places but the most important
 * is from VFS_SYNC.
 *
 * chain is locked on call and will remain locked on return.  The chain's
 * UPDATE flag indicates that its parent's block table (which is not yet
 * part of the flush) should be updated.  The chain may be replaced by
 * the call if it was modified.
 */
void
hammer2_flush(hammer2_trans_t *trans, hammer2_chain_t *chain, int istop)
{
        hammer2_chain_t *scan;
        hammer2_flush_info_t info;
        hammer2_dev_t *hmp;
        int loops;

        /*
         * Execute the recursive flush and handle deferrals.
         *
         * Chains can be ridiculously long (thousands deep), so to
         * avoid blowing out the kernel stack the recursive flush has a
         * depth limit.  Elements at the limit are placed on a list
         * for re-execution after the stack has been popped.
         */
        bzero(&info, sizeof(info));
        TAILQ_INIT(&info.flushq);
        info.trans = trans;
        info.sync_xid = trans->sync_xid;
        info.cache_index = -1;

        /*
         * Calculate parent (can be NULL), if not NULL the flush core
         * expects the parent to be referenced so it can easily lock/unlock
         * it without it getting ripped up.
         */
        if ((info.parent = chain->parent) != NULL)
                hammer2_chain_ref(info.parent);

        /*
         * Extra ref needed because flush_core expects it when replacing
         * chain.
         */
        hammer2_chain_ref(chain);
        hmp = chain->hmp;
        loops = 0;

        for (;;) {
                /*
                 * Move hmp->flushq to info.flushq if non-empty so it can
                 * be processed.
                 */
                if (TAILQ_FIRST(&hmp->flushq) != NULL) {
                        hammer2_spin_ex(&chain->hmp->list_spin);
                        TAILQ_CONCAT(&info.flushq, &hmp->flushq, flush_node);
                        hammer2_spin_unex(&chain->hmp->list_spin);
                }

                /*
                 * Unwind deep recursions which had been deferred.  This
                 * can leave the FLUSH_* bits set for these chains, which
                 * will be handled when we [re]flush chain after the unwind.
                 */
                while ((scan = TAILQ_FIRST(&info.flushq)) != NULL) {
                        KKASSERT(scan->flags & HAMMER2_CHAIN_DEFERRED);
                        TAILQ_REMOVE(&info.flushq, scan, flush_node);
                        atomic_clear_int(&scan->flags, HAMMER2_CHAIN_DEFERRED |
                                                       HAMMER2_CHAIN_DELAYED);

                        /*
                         * Now that we've popped back up we can do a secondary
                         * recursion on the deferred elements.
                         *
                         * NOTE: hammer2_flush() may replace scan.
                         */
                        if (hammer2_debug & 0x0040)
                                kprintf("deferred flush %p\n", scan);
                        hammer2_chain_lock(scan, HAMMER2_RESOLVE_MAYBE);
                        hammer2_flush(trans, scan, 0);
                        hammer2_chain_unlock(scan);
                        hammer2_chain_drop(scan);       /* ref from deferral */
                }

                /*
                 * [re]flush chain.
                 */
                info.diddeferral = 0;
                hammer2_flush_core(&info, chain, istop);

                /*
                 * Only loop if deep recursions have been deferred.
                 */
                if (TAILQ_EMPTY(&info.flushq))
                        break;

                if (++loops % 1000 == 0) {
                        kprintf("hammer2_flush: excessive loops on %p\n",
                                chain);
                        if (hammer2_debug & 0x100000)
                                Debugger("hell4");
                }
        }
        hammer2_chain_drop(chain);
        if (info.parent)
                hammer2_chain_drop(info.parent);
}

/*
 * This is the core of the chain flushing code.  The chain is locked by the
 * caller and must also have an extra ref on it by the caller, and remains
 * locked and will have an extra ref on return.  Upon return, the caller can
 * test the UPDATE bit on the child to determine if the parent needs updating.
 *
 * (1) Determine if this node is a candidate for the flush, return if it is
 *     not.  fchain and vchain are always candidates for the flush.
 *
 * (2) If we recurse too deep the chain is entered onto the deferral list and
 *     the current flush stack is aborted until after the deferral list is
 *     run.
 *
 * (3) Recursively flush live children (rbtree).  This can create deferrals.
 *     A successful flush clears the MODIFIED and UPDATE bits on the children
 *     and typically causes the parent to be marked MODIFIED as the children
 *     update the parent's block table.  A parent might already be marked
 *     MODIFIED due to a deletion (whos blocktable update in the parent is
 *     handled by the frontend), or if the parent itself is modified by the
 *     frontend for other reasons.
 *
 * (4) Permanently disconnected sub-trees are cleaned up by the front-end.
 *     Deleted-but-open inodes can still be individually flushed via the
 *     filesystem syncer.
 *
 * (5) Note that an unmodified child may still need the block table in its
 *     parent updated (e.g. rename/move).  The child will have UPDATE set
 *     in this case.
 *
 *                      WARNING ON BREF MODIFY_TID/MIRROR_TID
 *
 * blockref.modify_tid is consistent only within a PFS, and will not be
 * consistent during synchronization.  mirror_tid is consistent across the
 * block device regardless of the PFS.
 */
static void
hammer2_flush_core(hammer2_flush_info_t *info, hammer2_chain_t *chain,
                   int istop)
{
        hammer2_chain_t *parent;
        hammer2_dev_t *hmp;
        int diddeferral;

        /*
         * (1) Optimize downward recursion to locate nodes needing action.
         *     Nothing to do if none of these flags are set.
         */
        if ((chain->flags & HAMMER2_CHAIN_FLUSH_MASK) == 0) {
                if (hammer2_debug & 0x200) {
                        if (info->debug == NULL)
                                info->debug = chain;
                } else {
                        return;
                }
        }

        hmp = chain->hmp;
        diddeferral = info->diddeferral;
        parent = info->parent;          /* can be NULL */

        /*
         * Downward search recursion
         */
        if (chain->flags & (HAMMER2_CHAIN_DEFERRED | HAMMER2_CHAIN_DELAYED)) {
                /*
                 * Already deferred.
                 */
                ++info->diddeferral;
        } else if (info->depth == HAMMER2_FLUSH_DEPTH_LIMIT) {
                /*
                 * Recursion depth reached.
                 */
                KKASSERT((chain->flags & HAMMER2_CHAIN_DELAYED) == 0);
                hammer2_chain_ref(chain);
                TAILQ_INSERT_TAIL(&info->flushq, chain, flush_node);
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_DEFERRED);
                ++info->diddeferral;
        } else if ((chain->flags & HAMMER2_CHAIN_PFSBOUNDARY) && istop == 0) {
                /*
                 * We do not recurse through PFSROOTs.  PFSROOT flushes are
                 * handled by the related pmp's (whether mounted or not,
                 * including during recovery).
                 *
                 * But we must still process the PFSROOT chains for block
                 * table updates in their parent (which IS part of our flush).
                 *
                 * Note that the volume root, vchain, does not set this flag.
                 */
                ;
        } else if (chain->flags & HAMMER2_CHAIN_ONFLUSH) {
                /*
                 * Downward recursion search (actual flush occurs bottom-up).
                 * pre-clear ONFLUSH.  It can get set again due to races,
                 * which we want so the scan finds us again in the next flush.
                 * These races can also include 
                 *
                 * Flush recursions stop at PFSROOT boundaries.  Each PFS
                 * must be individually flushed and then the root must
                 * be flushed.
                 */
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_ONFLUSH);
                info->parent = chain;
                hammer2_spin_ex(&chain->core.spin);
                RB_SCAN(hammer2_chain_tree, &chain->core.rbtree,
                        NULL, hammer2_flush_recurse, info);
                hammer2_spin_unex(&chain->core.spin);
                info->parent = parent;
                if (info->diddeferral)
                        hammer2_chain_setflush(info->trans, chain);
        }

        /*
         * Now we are in the bottom-up part of the recursion.
         *
         * Do not update chain if lower layers were deferred.
         */
        if (info->diddeferral)
                goto done;

        /*
         * Propagate the DESTROY flag downwards.  This dummies up the flush
         * code and tries to invalidate related buffer cache buffers to
         * avoid the disk write.
         */
        if (parent && (parent->flags & HAMMER2_CHAIN_DESTROY))
                atomic_set_int(&chain->flags, HAMMER2_CHAIN_DESTROY);

        /*
         * Chain was already modified or has become modified, flush it out.
         */
again:
        if ((hammer2_debug & 0x200) &&
            info->debug &&
            (chain->flags & (HAMMER2_CHAIN_MODIFIED | HAMMER2_CHAIN_UPDATE))) {
                hammer2_chain_t *scan = chain;

                kprintf("DISCONNECTED FLUSH %p->%p\n", info->debug, chain);
                while (scan) {
                        kprintf("    chain %p [%08x] bref=%016jx:%02x\n",
                                scan, scan->flags,
                                scan->bref.key, scan->bref.type);
                        if (scan == info->debug)
                                break;
                        scan = scan->parent;
                }
        }

        if (chain->flags & HAMMER2_CHAIN_MODIFIED) {
                /*
                 * Dispose of the modified bit.
                 *
                 * UPDATE should already be set.
                 * bref.mirror_tid should already be set.
                 */
                KKASSERT((chain->flags & HAMMER2_CHAIN_UPDATE) ||
                         chain == &hmp->vchain);
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_MODIFIED);

                /*
                 * Manage threads waiting for excessive dirty memory to
                 * be retired.
                 */
                if (chain->pmp)
                        hammer2_pfs_memory_wakeup(chain->pmp);

                if ((chain->flags & HAMMER2_CHAIN_UPDATE) ||
                    chain == &hmp->vchain ||
                    chain == &hmp->fchain) {
                        /*
                         * Drop the ref from the MODIFIED bit we cleared,
                         * net -1 ref.
                         */
                        hammer2_chain_drop(chain);
                } else {
                        /*
                         * Drop the ref from the MODIFIED bit we cleared and
                         * set a ref for the UPDATE bit we are setting.  Net
                         * 0 refs.
                         */
                        atomic_set_int(&chain->flags, HAMMER2_CHAIN_UPDATE);
                }

                /*
                 * Issue the flush.  This is indirect via the DIO.
                 *
                 * NOTE: A DELETED node that reaches this point must be
                 *       flushed for synchronization point consistency.
                 *
                 * NOTE: Even though MODIFIED was already set, the related DIO
                 *       might not be dirty due to a system buffer cache
                 *       flush and must be set dirty if we are going to make
                 *       further modifications to the buffer.  Chains with
                 *       embedded data don't need this.
                 */
                if (hammer2_debug & 0x1000) {
                        kprintf("Flush %p.%d %016jx/%d sync_xid=%08x "
                                "data=%016jx\n",
                                chain, chain->bref.type,
                                chain->bref.key, chain->bref.keybits,
                                info->sync_xid,
                                chain->bref.data_off);
                }
                if (hammer2_debug & 0x2000) {
                        Debugger("Flush hell");
                }

                /*
                 * Update chain CRCs for flush.
                 *
                 * NOTE: Volume headers are NOT flushed here as they require
                 *       special processing.
                 */
                switch(chain->bref.type) {
                case HAMMER2_BREF_TYPE_FREEMAP:
                        /*
                         * Update the volume header's freemap_tid to the
                         * freemap's flushing mirror_tid.
                         *
                         * (note: embedded data, do not call setdirty)
                         */
                        KKASSERT(hmp->vchain.flags & HAMMER2_CHAIN_MODIFIED);
                        KKASSERT(chain == &hmp->fchain);
                        hmp->voldata.freemap_tid = chain->bref.mirror_tid;
                        kprintf("sync freemap mirror_tid %08jx\n",
                                (intmax_t)chain->bref.mirror_tid);

                        /*
                         * The freemap can be flushed independently of the
                         * main topology, but for the case where it is
                         * flushed in the same transaction, and flushed
                         * before vchain (a case we want to allow for
                         * performance reasons), make sure modifications
                         * made during the flush under vchain use a new
                         * transaction id.
                         *
                         * Otherwise the mount recovery code will get confused.
                         */
                        ++hmp->voldata.mirror_tid;
                        break;
                case HAMMER2_BREF_TYPE_VOLUME:
                        /*
                         * The free block table is flushed by
                         * hammer2_vfs_sync() before it flushes vchain.
                         * We must still hold fchain locked while copying
                         * voldata to volsync, however.
                         *
                         * (note: embedded data, do not call setdirty)
                         */
                        hammer2_chain_lock(&hmp->fchain,
                                           HAMMER2_RESOLVE_ALWAYS);
                        hammer2_voldata_lock(hmp);
                        kprintf("sync volume  mirror_tid %08jx\n",
                                (intmax_t)chain->bref.mirror_tid);

                        /*
                         * Update the volume header's mirror_tid to the
                         * main topology's flushing mirror_tid.  It is
                         * possible that voldata.mirror_tid is already
                         * beyond bref.mirror_tid due to the bump we made
                         * above in BREF_TYPE_FREEMAP.
                         */
                        if (hmp->voldata.mirror_tid < chain->bref.mirror_tid) {
                                hmp->voldata.mirror_tid =
                                        chain->bref.mirror_tid;
                        }

                        /*
                         * The volume header is flushed manually by the
                         * syncer, not here.  All we do here is adjust the
                         * crc's.
                         */
                        KKASSERT(chain->data != NULL);
                        KKASSERT(chain->dio == NULL);

                        hmp->voldata.icrc_sects[HAMMER2_VOL_ICRC_SECT1]=
                                hammer2_icrc32(
                                        (char *)&hmp->voldata +
                                         HAMMER2_VOLUME_ICRC1_OFF,
                                        HAMMER2_VOLUME_ICRC1_SIZE);
                        hmp->voldata.icrc_sects[HAMMER2_VOL_ICRC_SECT0]=
                                hammer2_icrc32(
                                        (char *)&hmp->voldata +
                                         HAMMER2_VOLUME_ICRC0_OFF,
                                        HAMMER2_VOLUME_ICRC0_SIZE);
                        hmp->voldata.icrc_volheader =
                                hammer2_icrc32(
                                        (char *)&hmp->voldata +
                                         HAMMER2_VOLUME_ICRCVH_OFF,
                                        HAMMER2_VOLUME_ICRCVH_SIZE);

                        kprintf("syncvolhdr %016jx %016jx\n",
                                hmp->voldata.mirror_tid,
                                hmp->vchain.bref.mirror_tid);
                        hmp->volsync = hmp->voldata;
                        atomic_set_int(&chain->flags, HAMMER2_CHAIN_VOLUMESYNC);
                        hammer2_voldata_unlock(hmp);
                        hammer2_chain_unlock(&hmp->fchain);
                        break;
                case HAMMER2_BREF_TYPE_DATA:
                        /*
                         * Data elements have already been flushed via the
                         * logical file buffer cache.  Their hash was set in
                         * the bref by the vop_write code.  Do not re-dirty.
                         *
                         * Make sure any device buffer(s) have been flushed
                         * out here (there aren't usually any to flush) XXX.
                         */
                        break;
                case HAMMER2_BREF_TYPE_INDIRECT:
                case HAMMER2_BREF_TYPE_FREEMAP_NODE:
                case HAMMER2_BREF_TYPE_FREEMAP_LEAF:
                        /*
                         * Buffer I/O will be cleaned up when the volume is
                         * flushed (but the kernel is free to flush it before
                         * then, as well).
                         */
                        KKASSERT((chain->flags & HAMMER2_CHAIN_EMBEDDED) == 0);
                        hammer2_chain_setcheck(chain, chain->data);
                        break;
                case HAMMER2_BREF_TYPE_INODE:
                        /*
                         * NOTE: We must call io_setdirty() to make any late
                         *       changes to the inode data, the system might
                         *       have already flushed the buffer.
                         */
                        if (chain->data->ipdata.op_flags &
                            HAMMER2_OPFLAG_PFSROOT) {
                                /*
                                 * non-NULL pmp if mounted as a PFS.  We must
                                 * sync fields cached in the pmp? XXX
                                 */
                                hammer2_inode_data_t *ipdata;

                                hammer2_io_setdirty(chain->dio);
                                ipdata = &chain->data->ipdata;
                                if (chain->pmp) {
                                        ipdata->pfs_inum =
                                                chain->pmp->inode_tid;
                                }
                        } else {
                                /* can't be mounted as a PFS */
                        }

                        KKASSERT((chain->flags & HAMMER2_CHAIN_EMBEDDED) == 0);
                        hammer2_chain_setcheck(chain, chain->data);
                        break;
                default:
                        KKASSERT(chain->flags & HAMMER2_CHAIN_EMBEDDED);
                        panic("hammer2_flush_core: unsupported "
                              "embedded bref %d",
                              chain->bref.type);
                        /* NOT REACHED */
                }

                /*
                 * If the chain was destroyed try to avoid unnecessary I/O.
                 * (this only really works if the DIO system buffer is the
                 * same size as chain->bytes).
                 */
                if ((chain->flags & HAMMER2_CHAIN_DESTROY) && chain->dio) {
                        hammer2_io_setinval(chain->dio, chain->bytes);
                }
        }

        /*
         * If UPDATE is set the parent block table may need to be updated.
         *
         * NOTE: UPDATE may be set on vchain or fchain in which case
         *       parent could be NULL.  It's easiest to allow the case
         *       and test for NULL.  parent can also wind up being NULL
         *       due to a deletion so we need to handle the case anyway.
         *
         * If no parent exists we can just clear the UPDATE bit.  If the
         * chain gets reattached later on the bit will simply get set
         * again.
         */
        if ((chain->flags & HAMMER2_CHAIN_UPDATE) && parent == NULL) {
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_UPDATE);
                hammer2_chain_drop(chain);
        }

        /*
         * The chain may need its blockrefs updated in the parent.  This
         * requires some fancy footwork.
         */
        if (chain->flags & HAMMER2_CHAIN_UPDATE) {
                hammer2_blockref_t *base;
                int count;

                /*
                 * Both parent and chain must be locked.  This requires
                 * temporarily unlocking the chain.  We have to deal with
                 * the case where the chain might be reparented or modified
                 * while it was unlocked.
                 */
                hammer2_chain_unlock(chain);
                hammer2_chain_lock(parent, HAMMER2_RESOLVE_ALWAYS);
                hammer2_chain_lock(chain, HAMMER2_RESOLVE_MAYBE);
                if (chain->parent != parent) {
                        kprintf("PARENT MISMATCH ch=%p p=%p/%p\n",
                                chain, chain->parent, parent);
                        hammer2_chain_unlock(parent);
                        goto done;
                }

                /*
                 * Check race condition.  If someone got in and modified
                 * it again while it was unlocked, we have to loop up.
                 */
                if (chain->flags & HAMMER2_CHAIN_MODIFIED) {
                        hammer2_chain_unlock(parent);
                        kprintf("hammer2_flush: chain %p flush-mod race\n",
                                chain);
                        goto again;
                }

                /*
                 * Clear UPDATE flag, mark parent modified, update its
                 * modify_tid if necessary, and adjust the parent blockmap.
                 */
                if (chain->flags & HAMMER2_CHAIN_UPDATE) {
                        atomic_clear_int(&chain->flags, HAMMER2_CHAIN_UPDATE);
                        hammer2_chain_drop(chain);
                }

                /*
                 * (optional code)
                 *
                 * Avoid actually modifying and updating the parent if it
                 * was flagged for destruction.  This can greatly reduce
                 * disk I/O in large tree removals because the
                 * hammer2_io_setinval() call in the upward recursion
                 * (see MODIFIED code above) can only handle a few cases.
                 */
                if (parent->flags & HAMMER2_CHAIN_DESTROY) {
                        if (parent->bref.modify_tid < chain->bref.modify_tid) {
                                parent->bref.modify_tid =
                                        chain->bref.modify_tid;
                        }
                        atomic_clear_int(&chain->flags, HAMMER2_CHAIN_BMAPPED |
                                                        HAMMER2_CHAIN_BMAPUPD);
                        hammer2_chain_unlock(parent);
                        goto skipupdate;
                }

                /*
                 * We are updating the parent's blockmap, the parent must
                 * be set modified.
                 */
                hammer2_chain_modify(info->trans, parent, 0);
                if (parent->bref.modify_tid < chain->bref.modify_tid)
                        parent->bref.modify_tid = chain->bref.modify_tid;

                /*
                 * Calculate blockmap pointer
                 */
                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.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 = &chain->hmp->voldata.sroot_blockset.blockref[0];
                        count = HAMMER2_SET_COUNT;
                        break;
                case HAMMER2_BREF_TYPE_FREEMAP:
                        base = &parent->data->npdata[0];
                        count = HAMMER2_SET_COUNT;
                        break;
                default:
                        base = NULL;
                        count = 0;
                        panic("hammer2_flush_core: "
                              "unrecognized blockref type: %d",
                              parent->bref.type);
                }

                /*
                 * Blocktable updates
                 *
                 * We synchronize pending statistics at this time.  Delta
                 * adjustments designated for the current and upper level
                 * are synchronized.
                 */
                if (base && (chain->flags & HAMMER2_CHAIN_BMAPUPD)) {
                        if (chain->flags & HAMMER2_CHAIN_BMAPPED) {
                                hammer2_spin_ex(&parent->core.spin);
                                hammer2_base_delete(info->trans, parent,
                                                    base, count,
                                                    &info->cache_index, chain);
                                hammer2_spin_unex(&parent->core.spin);
                                /* base_delete clears both bits */
                        } else {
                                atomic_clear_int(&chain->flags,
                                                 HAMMER2_CHAIN_BMAPUPD);
                        }
                }
                if (base && (chain->flags & HAMMER2_CHAIN_BMAPPED) == 0) {
                        hammer2_spin_ex(&parent->core.spin);
                        hammer2_base_insert(info->trans, parent,
                                            base, count,
                                            &info->cache_index, chain);
                        hammer2_spin_unex(&parent->core.spin);
                        /* base_insert sets BMAPPED */
                }
                hammer2_chain_unlock(parent);
        }
skipupdate:
        ;

        /*
         * Final cleanup after flush
         */
done:
        KKASSERT(chain->refs > 0);
        if (hammer2_debug & 0x200) {
                if (info->debug == chain)
                        info->debug = NULL;
        }
}

/*
 * Flush recursion helper, called from flush_core, calls flush_core.
 *
 * Flushes the children of the caller's chain (info->parent), restricted
 * by sync_tid.  Set info->domodify if the child's blockref must propagate
 * back up to the parent.
 *
 * Ripouts can move child from rbtree to dbtree or dbq but the caller's
 * flush scan order prevents any chains from being lost.  A child can be
 * executes more than once.
 *
 * WARNING! If we do not call hammer2_flush_core() we must update
 *          bref.mirror_tid ourselves to indicate that the flush has
 *          processed the child.
 *
 * WARNING! parent->core spinlock is held on entry and return.
 */
static int
hammer2_flush_recurse(hammer2_chain_t *child, void *data)
{
        hammer2_flush_info_t *info = data;
        /*hammer2_trans_t *trans = info->trans;*/
        hammer2_chain_t *parent = info->parent;

        /*
         * (child can never be fchain or vchain so a special check isn't
         *  needed).
         *
         * We must ref the child before unlocking the spinlock.
         *
         * The caller has added a ref to the parent so we can temporarily
         * unlock it in order to lock the child.
         */
        hammer2_chain_ref(child);
        hammer2_spin_unex(&parent->core.spin);

        hammer2_chain_unlock(parent);
        hammer2_chain_lock(child, HAMMER2_RESOLVE_MAYBE);

        /*
         * Recurse and collect deferral data.  We're in the media flush,
         * this can cross PFS boundaries.
         */
        if (child->flags & HAMMER2_CHAIN_FLUSH_MASK) {
                ++info->depth;
                hammer2_flush_core(info, child, 0);
                --info->depth;
        } else if (hammer2_debug & 0x200) {
                if (info->debug == NULL)
                        info->debug = child;
                ++info->depth;
                hammer2_flush_core(info, child, 0);
                --info->depth;
                if (info->debug == child)
                        info->debug = NULL;
        }

        /*
         * Relock to continue the loop
         */
        hammer2_chain_unlock(child);
        hammer2_chain_lock(parent, HAMMER2_RESOLVE_MAYBE);
        hammer2_chain_drop(child);
        KKASSERT(info->parent == parent);
        hammer2_spin_ex(&parent->core.spin);

        return (0);
}