HAMMER VFS: Add missing hammer_rel_volume() call in deadlock/retry case.

[dragonfly.git] / sys / vfs / hammer / hammer_ondisk.c

/*
 * Copyright (c) 2007-2008 The DragonFly Project.  All rights reserved.
 * 
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@backplane.com>
 * 
 * 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.
 * 
 * $DragonFly: src/sys/vfs/hammer/hammer_ondisk.c,v 1.76 2008/08/29 20:19:08 dillon Exp $
 */
/*
 * Manage HAMMER's on-disk structures.  These routines are primarily
 * responsible for interfacing with the kernel's I/O subsystem and for
 * managing in-memory structures.
 */

#include "hammer.h"
#include <sys/fcntl.h>
#include <sys/nlookup.h>
#include <sys/buf.h>
#include <sys/buf2.h>

static void hammer_free_volume(hammer_volume_t volume);
static int hammer_load_volume(hammer_volume_t volume);
static int hammer_load_buffer(hammer_buffer_t buffer, int isnew);
static int hammer_load_node(hammer_node_t node, int isnew);

static int
hammer_vol_rb_compare(hammer_volume_t vol1, hammer_volume_t vol2)
{
        if (vol1->vol_no < vol2->vol_no)
                return(-1);
        if (vol1->vol_no > vol2->vol_no)
                return(1);
        return(0);
}

/*
 * hammer_buffer structures are indexed via their zoneX_offset, not
 * their zone2_offset.
 */
static int
hammer_buf_rb_compare(hammer_buffer_t buf1, hammer_buffer_t buf2)
{
        if (buf1->zoneX_offset < buf2->zoneX_offset)
                return(-1);
        if (buf1->zoneX_offset > buf2->zoneX_offset)
                return(1);
        return(0);
}

static int
hammer_nod_rb_compare(hammer_node_t node1, hammer_node_t node2)
{
        if (node1->node_offset < node2->node_offset)
                return(-1);
        if (node1->node_offset > node2->node_offset)
                return(1);
        return(0);
}

RB_GENERATE2(hammer_vol_rb_tree, hammer_volume, rb_node,
             hammer_vol_rb_compare, int32_t, vol_no);
RB_GENERATE2(hammer_buf_rb_tree, hammer_buffer, rb_node,
             hammer_buf_rb_compare, hammer_off_t, zoneX_offset);
RB_GENERATE2(hammer_nod_rb_tree, hammer_node, rb_node,
             hammer_nod_rb_compare, hammer_off_t, node_offset);

/************************************************************************
 *                              VOLUMES                                 *
 ************************************************************************
 *
 * Load a HAMMER volume by name.  Returns 0 on success or a positive error
 * code on failure.  Volumes must be loaded at mount time, get_volume() will
 * not load a new volume.
 *
 * Calls made to hammer_load_volume() or single-threaded
 */
int
hammer_install_volume(struct hammer_mount *hmp, const char *volname,
                      struct vnode *devvp)
{
        struct mount *mp;
        hammer_volume_t volume;
        struct hammer_volume_ondisk *ondisk;
        struct nlookupdata nd;
        struct buf *bp = NULL;
        int error;
        int ronly;
        int setmp = 0;

        mp = hmp->mp;
        ronly = ((mp->mnt_flag & MNT_RDONLY) ? 1 : 0);

        /*
         * Allocate a volume structure
         */
        ++hammer_count_volumes;
        volume = kmalloc(sizeof(*volume), hmp->m_misc, M_WAITOK|M_ZERO);
        volume->vol_name = kstrdup(volname, hmp->m_misc);
        volume->io.hmp = hmp;   /* bootstrap */
        hammer_io_init(&volume->io, volume, HAMMER_STRUCTURE_VOLUME);
        volume->io.offset = 0LL;
        volume->io.bytes = HAMMER_BUFSIZE;

        /*
         * Get the device vnode
         */
        if (devvp == NULL) {
                error = nlookup_init(&nd, volume->vol_name, UIO_SYSSPACE, NLC_FOLLOW);
                if (error == 0)
                        error = nlookup(&nd);
                if (error == 0)
                        error = cache_vref(&nd.nl_nch, nd.nl_cred, &volume->devvp);
                nlookup_done(&nd);
        } else {
                error = 0;
                volume->devvp = devvp;
        }

        if (error == 0) {
                if (vn_isdisk(volume->devvp, &error)) {
                        error = vfs_mountedon(volume->devvp);
                }
        }
        if (error == 0 &&
            count_udev(volume->devvp->v_umajor, volume->devvp->v_uminor) > 0) {
                error = EBUSY;
        }
        if (error == 0) {
                vn_lock(volume->devvp, LK_EXCLUSIVE | LK_RETRY);
                error = vinvalbuf(volume->devvp, V_SAVE, 0, 0);
                if (error == 0) {
                        error = VOP_OPEN(volume->devvp, 
                                         (ronly ? FREAD : FREAD|FWRITE),
                                         FSCRED, NULL);
                }
                vn_unlock(volume->devvp);
        }
        if (error) {
                hammer_free_volume(volume);
                return(error);
        }
        volume->devvp->v_rdev->si_mountpoint = mp;
        setmp = 1;

        /*
         * Extract the volume number from the volume header and do various
         * sanity checks.
         */
        error = bread(volume->devvp, 0LL, HAMMER_BUFSIZE, &bp);
        if (error)
                goto late_failure;
        ondisk = (void *)bp->b_data;
        if (ondisk->vol_signature != HAMMER_FSBUF_VOLUME) {
                kprintf("hammer_mount: volume %s has an invalid header\n",
                        volume->vol_name);
                error = EFTYPE;
                goto late_failure;
        }
        volume->vol_no = ondisk->vol_no;
        volume->buffer_base = ondisk->vol_buf_beg;
        volume->vol_flags = ondisk->vol_flags;
        volume->nblocks = ondisk->vol_nblocks; 
        volume->maxbuf_off = HAMMER_ENCODE_RAW_BUFFER(volume->vol_no,
                                    ondisk->vol_buf_end - ondisk->vol_buf_beg);
        volume->maxraw_off = ondisk->vol_buf_end;

        if (RB_EMPTY(&hmp->rb_vols_root)) {
                hmp->fsid = ondisk->vol_fsid;
        } else if (bcmp(&hmp->fsid, &ondisk->vol_fsid, sizeof(uuid_t))) {
                kprintf("hammer_mount: volume %s's fsid does not match "
                        "other volumes\n", volume->vol_name);
                error = EFTYPE;
                goto late_failure;
        }

        /*
         * Insert the volume structure into the red-black tree.
         */
        if (RB_INSERT(hammer_vol_rb_tree, &hmp->rb_vols_root, volume)) {
                kprintf("hammer_mount: volume %s has a duplicate vol_no %d\n",
                        volume->vol_name, volume->vol_no);
                error = EEXIST;
        }

        /*
         * Set the root volume .  HAMMER special cases rootvol the structure.
         * We do not hold a ref because this would prevent related I/O
         * from being flushed.
         */
        if (error == 0 && ondisk->vol_rootvol == ondisk->vol_no) {
                hmp->rootvol = volume;
                hmp->nvolumes = ondisk->vol_count;
                if (bp) {
                        brelse(bp);
                        bp = NULL;
                }
                hmp->mp->mnt_stat.f_blocks += ondisk->vol0_stat_bigblocks *
                        (HAMMER_LARGEBLOCK_SIZE / HAMMER_BUFSIZE);
                hmp->mp->mnt_vstat.f_blocks += ondisk->vol0_stat_bigblocks *
                        (HAMMER_LARGEBLOCK_SIZE / HAMMER_BUFSIZE);
        }
late_failure:
        if (bp)
                brelse(bp);
        if (error) {
                /*vinvalbuf(volume->devvp, V_SAVE, 0, 0);*/
                if (setmp)
                        volume->devvp->v_rdev->si_mountpoint = NULL;
                VOP_CLOSE(volume->devvp, ronly ? FREAD : FREAD|FWRITE);
                hammer_free_volume(volume);
        }
        return (error);
}

/*
 * This is called for each volume when updating the mount point from
 * read-write to read-only or vise-versa.
 */
int
hammer_adjust_volume_mode(hammer_volume_t volume, void *data __unused)
{
        if (volume->devvp) {
                vn_lock(volume->devvp, LK_EXCLUSIVE | LK_RETRY);
                if (volume->io.hmp->ronly) {
                        /* do not call vinvalbuf */
                        VOP_OPEN(volume->devvp, FREAD, FSCRED, NULL);
                        VOP_CLOSE(volume->devvp, FREAD|FWRITE);
                } else {
                        /* do not call vinvalbuf */
                        VOP_OPEN(volume->devvp, FREAD|FWRITE, FSCRED, NULL);
                        VOP_CLOSE(volume->devvp, FREAD);
                }
                vn_unlock(volume->devvp);
        }
        return(0);
}

/*
 * Unload and free a HAMMER volume.  Must return >= 0 to continue scan
 * so returns -1 on failure.
 */
int
hammer_unload_volume(hammer_volume_t volume, void *data __unused)
{
        hammer_mount_t hmp = volume->io.hmp;
        int ronly = ((hmp->mp->mnt_flag & MNT_RDONLY) ? 1 : 0);
        struct buf *bp;

        /*
         * Clean up the root volume pointer, which is held unlocked in hmp.
         */
        if (hmp->rootvol == volume)
                hmp->rootvol = NULL;

        /*
         * We must not flush a dirty buffer to disk on umount.  It should
         * have already been dealt with by the flusher, or we may be in
         * catastrophic failure.
         */
        hammer_io_clear_modify(&volume->io, 1);
        volume->io.waitdep = 1;
        bp = hammer_io_release(&volume->io, 1);

        /*
         * Clean up the persistent ref ioerror might have on the volume
         */
        if (volume->io.ioerror) {
                volume->io.ioerror = 0;
                hammer_unref(&volume->io.lock);
        }

        /*
         * There should be no references on the volume, no clusters, and
         * no super-clusters.
         */
        KKASSERT(volume->io.lock.refs == 0);
        if (bp)
                brelse(bp);

        volume->ondisk = NULL;
        if (volume->devvp) {
                if (volume->devvp->v_rdev &&
                    volume->devvp->v_rdev->si_mountpoint == hmp->mp
                ) {
                        volume->devvp->v_rdev->si_mountpoint = NULL;
                }
                if (ronly) {
                        /*
                         * Make sure we don't sync anything to disk if we
                         * are in read-only mode (1) or critically-errored
                         * (2).  Note that there may be dirty buffers in
                         * normal read-only mode from crash recovery.
                         */
                        vinvalbuf(volume->devvp, 0, 0, 0);
                        VOP_CLOSE(volume->devvp, FREAD);
                } else {
                        /*
                         * Normal termination, save any dirty buffers
                         * (XXX there really shouldn't be any).
                         */
                        vinvalbuf(volume->devvp, V_SAVE, 0, 0);
                        VOP_CLOSE(volume->devvp, FREAD|FWRITE);
                }
        }

        /*
         * Destroy the structure
         */
        RB_REMOVE(hammer_vol_rb_tree, &hmp->rb_vols_root, volume);
        hammer_free_volume(volume);
        return(0);
}

static
void
hammer_free_volume(hammer_volume_t volume)
{
        hammer_mount_t hmp = volume->io.hmp;

        if (volume->vol_name) {
                kfree(volume->vol_name, hmp->m_misc);
                volume->vol_name = NULL;
        }
        if (volume->devvp) {
                vrele(volume->devvp);
                volume->devvp = NULL;
        }
        --hammer_count_volumes;
        kfree(volume, hmp->m_misc);
}

/*
 * Get a HAMMER volume.  The volume must already exist.
 */
hammer_volume_t
hammer_get_volume(struct hammer_mount *hmp, int32_t vol_no, int *errorp)
{
        struct hammer_volume *volume;

        /*
         * Locate the volume structure
         */
        volume = RB_LOOKUP(hammer_vol_rb_tree, &hmp->rb_vols_root, vol_no);
        if (volume == NULL) {
                *errorp = ENOENT;
                return(NULL);
        }
        hammer_ref(&volume->io.lock);

        /*
         * Deal with on-disk info
         */
        if (volume->ondisk == NULL || volume->io.loading) {
                *errorp = hammer_load_volume(volume);
                if (*errorp) {
                        hammer_rel_volume(volume, 1);
                        volume = NULL;
                }
        } else {
                *errorp = 0;
        }
        return(volume);
}

int
hammer_ref_volume(hammer_volume_t volume)
{
        int error;

        hammer_ref(&volume->io.lock);

        /*
         * Deal with on-disk info
         */
        if (volume->ondisk == NULL || volume->io.loading) {
                error = hammer_load_volume(volume);
                if (error)
                        hammer_rel_volume(volume, 1);
        } else {
                error = 0;
        }
        return (error);
}

hammer_volume_t
hammer_get_root_volume(struct hammer_mount *hmp, int *errorp)
{
        hammer_volume_t volume;

        volume = hmp->rootvol;
        KKASSERT(volume != NULL);
        hammer_ref(&volume->io.lock);

        /*
         * Deal with on-disk info
         */
        if (volume->ondisk == NULL || volume->io.loading) {
                *errorp = hammer_load_volume(volume);
                if (*errorp) {
                        hammer_rel_volume(volume, 1);
                        volume = NULL;
                }
        } else {
                *errorp = 0;
        }
        return (volume);
}

/*
 * Load a volume's on-disk information.  The volume must be referenced and
 * not locked.  We temporarily acquire an exclusive lock to interlock
 * against releases or multiple get's.
 */
static int
hammer_load_volume(hammer_volume_t volume)
{
        int error;

        ++volume->io.loading;
        hammer_lock_ex(&volume->io.lock);

        if (volume->ondisk == NULL) {
                error = hammer_io_read(volume->devvp, &volume->io,
                                       volume->maxraw_off);
                if (error == 0)
                        volume->ondisk = (void *)volume->io.bp->b_data;
        } else {
                error = 0;
        }
        --volume->io.loading;
        hammer_unlock(&volume->io.lock);
        return(error);
}

/*
 * Release a volume.  Call hammer_io_release on the last reference.  We have
 * to acquire an exclusive lock to interlock against volume->ondisk tests
 * in hammer_load_volume(), and hammer_io_release() also expects an exclusive
 * lock to be held.
 *
 * Volumes are not unloaded from memory during normal operation.
 */
void
hammer_rel_volume(hammer_volume_t volume, int flush)
{
        struct buf *bp = NULL;

        crit_enter();
        if (volume->io.lock.refs == 1) {
                ++volume->io.loading;
                hammer_lock_ex(&volume->io.lock);
                if (volume->io.lock.refs == 1) {
                        volume->ondisk = NULL;
                        bp = hammer_io_release(&volume->io, flush);
                }
                --volume->io.loading;
                hammer_unlock(&volume->io.lock);
        }
        hammer_unref(&volume->io.lock);
        if (bp)
                brelse(bp);
        crit_exit();
}

int
hammer_mountcheck_volumes(struct hammer_mount *hmp)
{
        hammer_volume_t vol;
        int i;

        for (i = 0; i < hmp->nvolumes; ++i) {
                vol = RB_LOOKUP(hammer_vol_rb_tree, &hmp->rb_vols_root, i);
                if (vol == NULL)
                        return(EINVAL);
        }
        return(0);
}

/************************************************************************
 *                              BUFFERS                                 *
 ************************************************************************
 *
 * Manage buffers.  Currently all blockmap-backed zones are direct-mapped
 * to zone-2 buffer offsets, without a translation stage.  However, the
 * hammer_buffer structure is indexed by its zoneX_offset, not its
 * zone2_offset.
 *
 * The proper zone must be maintained throughout the code-base all the way
 * through to the big-block allocator, or routines like hammer_del_buffers()
 * will not be able to locate all potentially conflicting buffers.
 */
hammer_buffer_t
hammer_get_buffer(hammer_mount_t hmp, hammer_off_t buf_offset,
                  int bytes, int isnew, int *errorp)
{
        hammer_buffer_t buffer;
        hammer_volume_t volume;
        hammer_off_t    zone2_offset;
        hammer_io_type_t iotype;
        int vol_no;
        int zone;

        buf_offset &= ~HAMMER_BUFMASK64;
again:
        /*
         * Shortcut if the buffer is already cached
         */
        buffer = RB_LOOKUP(hammer_buf_rb_tree, &hmp->rb_bufs_root, buf_offset);
        if (buffer) {
                if (buffer->io.lock.refs == 0)
                        ++hammer_count_refedbufs;
                hammer_ref(&buffer->io.lock);

                /*
                 * Once refed the ondisk field will not be cleared by
                 * any other action.
                 */
                if (buffer->ondisk && buffer->io.loading == 0) {
                        *errorp = 0;
                        return(buffer);
                }

                /*
                 * The buffer is no longer loose if it has a ref, and
                 * cannot become loose once it gains a ref.  Loose
                 * buffers will never be in a modified state.  This should
                 * only occur on the 0->1 transition of refs.
                 *
                 * lose_list can be modified via a biodone() interrupt.
                 */
                if (buffer->io.mod_list == &hmp->lose_list) {
                        crit_enter();   /* biodone race against list */
                        TAILQ_REMOVE(buffer->io.mod_list, &buffer->io,
                                     mod_entry);
                        crit_exit();
                        buffer->io.mod_list = NULL;
                        KKASSERT(buffer->io.modified == 0);
                }
                goto found;
        }

        /*
         * What is the buffer class?
         */
        zone = HAMMER_ZONE_DECODE(buf_offset);

        switch(zone) {
        case HAMMER_ZONE_LARGE_DATA_INDEX:
        case HAMMER_ZONE_SMALL_DATA_INDEX:
                iotype = HAMMER_STRUCTURE_DATA_BUFFER;
                break;
        case HAMMER_ZONE_UNDO_INDEX:
                iotype = HAMMER_STRUCTURE_UNDO_BUFFER;
                break;
        case HAMMER_ZONE_META_INDEX:
        default:
                /*
                 * NOTE: inode data and directory entries are placed in this
                 * zone.  inode atime/mtime is updated in-place and thus
                 * buffers containing inodes must be synchronized as
                 * meta-buffers, same as buffers containing B-Tree info.
                 */
                iotype = HAMMER_STRUCTURE_META_BUFFER;
                break;
        }

        /*
         * Handle blockmap offset translations
         */
        if (zone >= HAMMER_ZONE_BTREE_INDEX) {
                zone2_offset = hammer_blockmap_lookup(hmp, buf_offset, errorp);
        } else if (zone == HAMMER_ZONE_UNDO_INDEX) {
                zone2_offset = hammer_undo_lookup(hmp, buf_offset, errorp);
        } else {
                KKASSERT(zone == HAMMER_ZONE_RAW_BUFFER_INDEX);
                zone2_offset = buf_offset;
                *errorp = 0;
        }
        if (*errorp)
                return(NULL);

        /*
         * NOTE: zone2_offset and maxbuf_off are both full zone-2 offset
         * specifications.
         */
        KKASSERT((zone2_offset & HAMMER_OFF_ZONE_MASK) ==
                 HAMMER_ZONE_RAW_BUFFER);
        vol_no = HAMMER_VOL_DECODE(zone2_offset);
        volume = hammer_get_volume(hmp, vol_no, errorp);
        if (volume == NULL)
                return(NULL);

        KKASSERT(zone2_offset < volume->maxbuf_off);

        /*
         * Allocate a new buffer structure.  We will check for races later.
         */
        ++hammer_count_buffers;
        buffer = kmalloc(sizeof(*buffer), hmp->m_misc,
                         M_WAITOK|M_ZERO|M_USE_RESERVE);
        buffer->zone2_offset = zone2_offset;
        buffer->zoneX_offset = buf_offset;

        hammer_io_init(&buffer->io, volume, iotype);
        buffer->io.offset = volume->ondisk->vol_buf_beg +
                            (zone2_offset & HAMMER_OFF_SHORT_MASK);
        buffer->io.bytes = bytes;
        TAILQ_INIT(&buffer->clist);
        hammer_ref(&buffer->io.lock);

        /*
         * Insert the buffer into the RB tree and handle late collisions.
         */
        if (RB_INSERT(hammer_buf_rb_tree, &hmp->rb_bufs_root, buffer)) {
                hammer_unref(&buffer->io.lock); /* safety */
                --hammer_count_buffers;
                hammer_rel_volume(volume, 0);
                buffer->io.volume = NULL;       /* safety */
                kfree(buffer, hmp->m_misc);
                goto again;
        }
        ++hammer_count_refedbufs;
found:

        /*
         * Deal with on-disk info and loading races.
         */
        if (buffer->ondisk == NULL || buffer->io.loading) {
                *errorp = hammer_load_buffer(buffer, isnew);
                if (*errorp) {
                        hammer_rel_buffer(buffer, 1);
                        buffer = NULL;
                }
        } else {
                *errorp = 0;
        }
        return(buffer);
}

/*
 * This is used by the direct-read code to deal with large-data buffers
 * created by the reblocker and mirror-write code.  The direct-read code
 * bypasses the HAMMER buffer subsystem and so any aliased dirty or write-
 * running hammer buffers must be fully synced to disk before we can issue
 * the direct-read.
 *
 * This code path is not considered critical as only the rebocker and
 * mirror-write code will create large-data buffers via the HAMMER buffer
 * subsystem.  They do that because they operate at the B-Tree level and
 * do not access the vnode/inode structures.
 */
void
hammer_sync_buffers(hammer_mount_t hmp, hammer_off_t base_offset, int bytes)
{
        hammer_buffer_t buffer;
        int error;

        KKASSERT((base_offset & HAMMER_OFF_ZONE_MASK) ==
                 HAMMER_ZONE_LARGE_DATA);

        while (bytes > 0) {
                buffer = RB_LOOKUP(hammer_buf_rb_tree, &hmp->rb_bufs_root,
                                   base_offset);
                if (buffer && (buffer->io.modified || buffer->io.running)) {
                        error = hammer_ref_buffer(buffer);
                        if (error == 0) {
                                hammer_io_wait(&buffer->io);
                                if (buffer->io.modified) {
                                        hammer_io_write_interlock(&buffer->io);
                                        hammer_io_flush(&buffer->io);
                                        hammer_io_done_interlock(&buffer->io);
                                        hammer_io_wait(&buffer->io);
                                }
                                hammer_rel_buffer(buffer, 0);
                        }
                }
                base_offset += HAMMER_BUFSIZE;
                bytes -= HAMMER_BUFSIZE;
        }
}

/*
 * Destroy all buffers covering the specified zoneX offset range.  This
 * is called when the related blockmap layer2 entry is freed or when
 * a direct write bypasses our buffer/buffer-cache subsystem.
 *
 * The buffers may be referenced by the caller itself.  Setting reclaim
 * will cause the buffer to be destroyed when it's ref count reaches zero.
 *
 * Return 0 on success, EAGAIN if some buffers could not be destroyed due
 * to additional references held by other threads, or some other (typically
 * fatal) error.
 */
int
hammer_del_buffers(hammer_mount_t hmp, hammer_off_t base_offset,
                   hammer_off_t zone2_offset, int bytes,
                   int report_conflicts)
{
        hammer_buffer_t buffer;
        hammer_volume_t volume;
        int vol_no;
        int error;
        int ret_error;

        vol_no = HAMMER_VOL_DECODE(zone2_offset);
        volume = hammer_get_volume(hmp, vol_no, &ret_error);
        KKASSERT(ret_error == 0);

        while (bytes > 0) {
                buffer = RB_LOOKUP(hammer_buf_rb_tree, &hmp->rb_bufs_root,
                                   base_offset);
                if (buffer) {
                        error = hammer_ref_buffer(buffer);
                        if (error == 0 && buffer->io.lock.refs != 1) {
                                error = EAGAIN;
                                hammer_rel_buffer(buffer, 0);
                        }
                        if (error == 0) {
                                KKASSERT(buffer->zone2_offset == zone2_offset);
                                hammer_io_clear_modify(&buffer->io, 1);
                                buffer->io.reclaim = 1;
                                buffer->io.waitdep = 1;
                                KKASSERT(buffer->io.volume == volume);
                                hammer_rel_buffer(buffer, 0);
                        }
                } else {
                        error = hammer_io_inval(volume, zone2_offset);
                }
                if (error) {
                        ret_error = error;
                        if (report_conflicts || (hammer_debug_general & 0x8000))
                                kprintf("hammer_del_buffers: unable to invalidate %016llx buffer=%p rep=%d\n", base_offset, buffer, report_conflicts);
                }
                base_offset += HAMMER_BUFSIZE;
                zone2_offset += HAMMER_BUFSIZE;
                bytes -= HAMMER_BUFSIZE;
        }
        hammer_rel_volume(volume, 0);
        return (ret_error);
}

static int
hammer_load_buffer(hammer_buffer_t buffer, int isnew)
{
        hammer_volume_t volume;
        int error;

        /*
         * Load the buffer's on-disk info
         */
        volume = buffer->io.volume;
        ++buffer->io.loading;
        hammer_lock_ex(&buffer->io.lock);

        if (hammer_debug_io & 0x0001) {
                kprintf("load_buffer %016llx %016llx isnew=%d od=%p\n",
                        buffer->zoneX_offset, buffer->zone2_offset, isnew,
                        buffer->ondisk);
        }

        if (buffer->ondisk == NULL) {
                if (isnew) {
                        error = hammer_io_new(volume->devvp, &buffer->io);
                } else {
                        error = hammer_io_read(volume->devvp, &buffer->io,
                                               volume->maxraw_off);
                }
                if (error == 0)
                        buffer->ondisk = (void *)buffer->io.bp->b_data;
        } else if (isnew) {
                error = hammer_io_new(volume->devvp, &buffer->io);
        } else {
                error = 0;
        }
        --buffer->io.loading;
        hammer_unlock(&buffer->io.lock);
        return (error);
}

/*
 * NOTE: Called from RB_SCAN, must return >= 0 for scan to continue.
 * This routine is only called during unmount.
 */
int
hammer_unload_buffer(hammer_buffer_t buffer, void *data __unused)
{
        /*
         * Clean up the persistent ref ioerror might have on the buffer
         * and acquire a ref (steal ioerror's if we can).
         */
        if (buffer->io.ioerror) {
                buffer->io.ioerror = 0;
        } else {
                if (buffer->io.lock.refs == 0)
                        ++hammer_count_refedbufs;
                hammer_ref(&buffer->io.lock);
        }

        /*
         * We must not flush a dirty buffer to disk on umount.  It should
         * have already been dealt with by the flusher, or we may be in
         * catastrophic failure.
         */
        hammer_io_clear_modify(&buffer->io, 1);
        hammer_flush_buffer_nodes(buffer);
        KKASSERT(buffer->io.lock.refs == 1);
        hammer_rel_buffer(buffer, 2);
        return(0);
}

/*
 * Reference a buffer that is either already referenced or via a specially
 * handled pointer (aka cursor->buffer).
 */
int
hammer_ref_buffer(hammer_buffer_t buffer)
{
        int error;

        if (buffer->io.lock.refs == 0)
                ++hammer_count_refedbufs;
        hammer_ref(&buffer->io.lock);

        /*
         * At this point a biodone() will not touch the buffer other then
         * incidental bits.  However, lose_list can be modified via
         * a biodone() interrupt.
         *
         * No longer loose
         */
        if (buffer->io.mod_list == &buffer->io.hmp->lose_list) {
                crit_enter();
                TAILQ_REMOVE(buffer->io.mod_list, &buffer->io, mod_entry);
                buffer->io.mod_list = NULL;
                crit_exit();
        }

        if (buffer->ondisk == NULL || buffer->io.loading) {
                error = hammer_load_buffer(buffer, 0);
                if (error) {
                        hammer_rel_buffer(buffer, 1);
                        /*
                         * NOTE: buffer pointer can become stale after
                         * the above release.
                         */
                }
        } else {
                error = 0;
        }
        return(error);
}

/*
 * Release a buffer.  We have to deal with several places where
 * another thread can ref the buffer.
 *
 * Only destroy the structure itself if the related buffer cache buffer
 * was disassociated from it.  This ties the management of the structure
 * to the buffer cache subsystem.  buffer->ondisk determines whether the
 * embedded io is referenced or not.
 */
void
hammer_rel_buffer(hammer_buffer_t buffer, int flush)
{
        hammer_volume_t volume;
        hammer_mount_t hmp;
        struct buf *bp = NULL;
        int freeme = 0;

        hmp = buffer->io.hmp;

        crit_enter();
        if (buffer->io.lock.refs == 1) {
                ++buffer->io.loading;   /* force interlock check */
                hammer_lock_ex(&buffer->io.lock);
                if (buffer->io.lock.refs == 1) {
                        bp = hammer_io_release(&buffer->io, flush);

                        if (buffer->io.lock.refs == 1)
                                --hammer_count_refedbufs;

                        if (buffer->io.bp == NULL &&
                            buffer->io.lock.refs == 1) {
                                /*
                                 * Final cleanup
                                 *
                                 * NOTE: It is impossible for any associated
                                 * B-Tree nodes to have refs if the buffer
                                 * has no additional refs.
                                 */
                                RB_REMOVE(hammer_buf_rb_tree,
                                          &buffer->io.hmp->rb_bufs_root,
                                          buffer);
                                volume = buffer->io.volume;
                                buffer->io.volume = NULL; /* sanity */
                                hammer_rel_volume(volume, 0);
                                hammer_io_clear_modlist(&buffer->io);
                                hammer_flush_buffer_nodes(buffer);
                                KKASSERT(TAILQ_EMPTY(&buffer->clist));
                                freeme = 1;
                        }
                }
                --buffer->io.loading;
                hammer_unlock(&buffer->io.lock);
        }
        hammer_unref(&buffer->io.lock);
        crit_exit();
        if (bp)
                brelse(bp);
        if (freeme) {
                --hammer_count_buffers;
                kfree(buffer, hmp->m_misc);
        }
}

/*
 * Access the filesystem buffer containing the specified hammer offset.
 * buf_offset is a conglomeration of the volume number and vol_buf_beg
 * relative buffer offset.  It must also have bit 55 set to be valid.
 * (see hammer_off_t in hammer_disk.h).
 *
 * Any prior buffer in *bufferp will be released and replaced by the
 * requested buffer.
 *
 * NOTE: The buffer is indexed via its zoneX_offset but we allow the
 * passed cached *bufferp to match against either zoneX or zone2.
 */
static __inline
void *
_hammer_bread(hammer_mount_t hmp, hammer_off_t buf_offset, int bytes,
             int *errorp, struct hammer_buffer **bufferp)
{
        hammer_buffer_t buffer;
        int32_t xoff = (int32_t)buf_offset & HAMMER_BUFMASK;

        buf_offset &= ~HAMMER_BUFMASK64;
        KKASSERT((buf_offset & HAMMER_OFF_ZONE_MASK) != 0);

        buffer = *bufferp;
        if (buffer == NULL || (buffer->zone2_offset != buf_offset &&
                               buffer->zoneX_offset != buf_offset)) {
                if (buffer)
                        hammer_rel_buffer(buffer, 0);
                buffer = hammer_get_buffer(hmp, buf_offset, bytes, 0, errorp);
                *bufferp = buffer;
        } else {
                *errorp = 0;
        }

        /*
         * Return a pointer to the buffer data.
         */
        if (buffer == NULL)
                return(NULL);
        else
                return((char *)buffer->ondisk + xoff);
}

void *
hammer_bread(hammer_mount_t hmp, hammer_off_t buf_offset,
             int *errorp, struct hammer_buffer **bufferp)
{
        return(_hammer_bread(hmp, buf_offset, HAMMER_BUFSIZE, errorp, bufferp));
}

void *
hammer_bread_ext(hammer_mount_t hmp, hammer_off_t buf_offset, int bytes,
                 int *errorp, struct hammer_buffer **bufferp)
{
        bytes = (bytes + HAMMER_BUFMASK) & ~HAMMER_BUFMASK;
        return(_hammer_bread(hmp, buf_offset, bytes, errorp, bufferp));
}

/*
 * Access the filesystem buffer containing the specified hammer offset.
 * No disk read operation occurs.  The result buffer may contain garbage.
 *
 * Any prior buffer in *bufferp will be released and replaced by the
 * requested buffer.
 *
 * This function marks the buffer dirty but does not increment its
 * modify_refs count.
 */
static __inline
void *
_hammer_bnew(hammer_mount_t hmp, hammer_off_t buf_offset, int bytes,
             int *errorp, struct hammer_buffer **bufferp)
{
        hammer_buffer_t buffer;
        int32_t xoff = (int32_t)buf_offset & HAMMER_BUFMASK;

        buf_offset &= ~HAMMER_BUFMASK64;

        buffer = *bufferp;
        if (buffer == NULL || (buffer->zone2_offset != buf_offset &&
                               buffer->zoneX_offset != buf_offset)) {
                if (buffer)
                        hammer_rel_buffer(buffer, 0);
                buffer = hammer_get_buffer(hmp, buf_offset, bytes, 1, errorp);
                *bufferp = buffer;
        } else {
                *errorp = 0;
        }

        /*
         * Return a pointer to the buffer data.
         */
        if (buffer == NULL)
                return(NULL);
        else
                return((char *)buffer->ondisk + xoff);
}

void *
hammer_bnew(hammer_mount_t hmp, hammer_off_t buf_offset,
             int *errorp, struct hammer_buffer **bufferp)
{
        return(_hammer_bnew(hmp, buf_offset, HAMMER_BUFSIZE, errorp, bufferp));
}

void *
hammer_bnew_ext(hammer_mount_t hmp, hammer_off_t buf_offset, int bytes,
                int *errorp, struct hammer_buffer **bufferp)
{
        bytes = (bytes + HAMMER_BUFMASK) & ~HAMMER_BUFMASK;
        return(_hammer_bnew(hmp, buf_offset, bytes, errorp, bufferp));
}

/************************************************************************
 *                              NODES                                   *
 ************************************************************************
 *
 * Manage B-Tree nodes.  B-Tree nodes represent the primary indexing
 * method used by the HAMMER filesystem.
 *
 * Unlike other HAMMER structures, a hammer_node can be PASSIVELY
 * associated with its buffer, and will only referenced the buffer while
 * the node itself is referenced.
 *
 * A hammer_node can also be passively associated with other HAMMER
 * structures, such as inodes, while retaining 0 references.  These
 * associations can be cleared backwards using a pointer-to-pointer in
 * the hammer_node.
 *
 * This allows the HAMMER implementation to cache hammer_nodes long-term
 * and short-cut a great deal of the infrastructure's complexity.  In
 * most cases a cached node can be reacquired without having to dip into
 * either the buffer or cluster management code.
 *
 * The caller must pass a referenced cluster on call and will retain
 * ownership of the reference on return.  The node will acquire its own
 * additional references, if necessary.
 */
hammer_node_t
hammer_get_node(hammer_transaction_t trans, hammer_off_t node_offset,
                int isnew, int *errorp)
{
        hammer_mount_t hmp = trans->hmp;
        hammer_node_t node;

        KKASSERT((node_offset & HAMMER_OFF_ZONE_MASK) == HAMMER_ZONE_BTREE);

        /*
         * Locate the structure, allocating one if necessary.
         */
again:
        node = RB_LOOKUP(hammer_nod_rb_tree, &hmp->rb_nods_root, node_offset);
        if (node == NULL) {
                ++hammer_count_nodes;
                node = kmalloc(sizeof(*node), hmp->m_misc, M_WAITOK|M_ZERO|M_USE_RESERVE);
                node->node_offset = node_offset;
                node->hmp = hmp;
                TAILQ_INIT(&node->cursor_list);
                TAILQ_INIT(&node->cache_list);
                if (RB_INSERT(hammer_nod_rb_tree, &hmp->rb_nods_root, node)) {
                        --hammer_count_nodes;
                        kfree(node, hmp->m_misc);
                        goto again;
                }
        }
        hammer_ref(&node->lock);
        if (node->ondisk) {
                *errorp = 0;
        } else {
                *errorp = hammer_load_node(node, isnew);
                trans->flags |= HAMMER_TRANSF_DIDIO;
        }
        if (*errorp) {
                hammer_rel_node(node);
                node = NULL;
        }
        return(node);
}

/*
 * Reference an already-referenced node.
 */
void
hammer_ref_node(hammer_node_t node)
{
        KKASSERT(node->lock.refs > 0 && node->ondisk != NULL);
        hammer_ref(&node->lock);
}

/*
 * Load a node's on-disk data reference.
 */
static int
hammer_load_node(hammer_node_t node, int isnew)
{
        hammer_buffer_t buffer;
        hammer_off_t buf_offset;
        int error;

        error = 0;
        ++node->loading;
        hammer_lock_ex(&node->lock);
        if (node->ondisk == NULL) {
                /*
                 * This is a little confusing but the jist is that
                 * node->buffer determines whether the node is on
                 * the buffer's clist and node->ondisk determines
                 * whether the buffer is referenced.
                 *
                 * We could be racing a buffer release, in which case
                 * node->buffer may become NULL while we are blocked
                 * referencing the buffer.
                 */
                if ((buffer = node->buffer) != NULL) {
                        error = hammer_ref_buffer(buffer);
                        if (error == 0 && node->buffer == NULL) {
                                TAILQ_INSERT_TAIL(&buffer->clist,
                                                  node, entry);
                                node->buffer = buffer;
                        }
                } else {
                        buf_offset = node->node_offset & ~HAMMER_BUFMASK64;
                        buffer = hammer_get_buffer(node->hmp, buf_offset,
                                                   HAMMER_BUFSIZE, 0, &error);
                        if (buffer) {
                                KKASSERT(error == 0);
                                TAILQ_INSERT_TAIL(&buffer->clist,
                                                  node, entry);
                                node->buffer = buffer;
                        }
                }
                if (error)
                        goto failed;
                node->ondisk = (void *)((char *)buffer->ondisk +
                                        (node->node_offset & HAMMER_BUFMASK));
                if (isnew == 0 && 
                    (node->flags & HAMMER_NODE_CRCGOOD) == 0) {
                        if (hammer_crc_test_btree(node->ondisk) == 0)
                                Debugger("CRC FAILED: B-TREE NODE");
                        node->flags |= HAMMER_NODE_CRCGOOD;
                }
        }
failed:
        --node->loading;
        hammer_unlock(&node->lock);
        return (error);
}

/*
 * Safely reference a node, interlock against flushes via the IO subsystem.
 */
hammer_node_t
hammer_ref_node_safe(struct hammer_mount *hmp, hammer_node_cache_t cache,
                     int *errorp)
{
        hammer_node_t node;

        node = cache->node;
        if (node != NULL) {
                hammer_ref(&node->lock);
                if (node->ondisk)
                        *errorp = 0;
                else
                        *errorp = hammer_load_node(node, 0);
                if (*errorp) {
                        hammer_rel_node(node);
                        node = NULL;
                }
        } else {
                *errorp = ENOENT;
        }
        return(node);
}

/*
 * Release a hammer_node.  On the last release the node dereferences
 * its underlying buffer and may or may not be destroyed.
 */
void
hammer_rel_node(hammer_node_t node)
{
        hammer_buffer_t buffer;

        /*
         * If this isn't the last ref just decrement the ref count and
         * return.
         */
        if (node->lock.refs > 1) {
                hammer_unref(&node->lock);
                return;
        }

        /*
         * If there is no ondisk info or no buffer the node failed to load,
         * remove the last reference and destroy the node.
         */
        if (node->ondisk == NULL) {
                hammer_unref(&node->lock);
                hammer_flush_node(node);
                /* node is stale now */
                return;
        }

        /*
         * Do not disassociate the node from the buffer if it represents
         * a modified B-Tree node that still needs its crc to be generated.
         */
        if (node->flags & HAMMER_NODE_NEEDSCRC)
                return;

        /*
         * Do final cleanups and then either destroy the node and leave it
         * passively cached.  The buffer reference is removed regardless.
         */
        buffer = node->buffer;
        node->ondisk = NULL;

        if ((node->flags & HAMMER_NODE_FLUSH) == 0) {
                hammer_unref(&node->lock);
                hammer_rel_buffer(buffer, 0);
                return;
        }

        /*
         * Destroy the node.
         */
        hammer_unref(&node->lock);
        hammer_flush_node(node);
        /* node is stale */
        hammer_rel_buffer(buffer, 0);
}

/*
 * Free space on-media associated with a B-Tree node.
 */
void
hammer_delete_node(hammer_transaction_t trans, hammer_node_t node)
{
        KKASSERT((node->flags & HAMMER_NODE_DELETED) == 0);
        node->flags |= HAMMER_NODE_DELETED;
        hammer_blockmap_free(trans, node->node_offset, sizeof(*node->ondisk));
}

/*
 * Passively cache a referenced hammer_node.  The caller may release
 * the node on return.
 */
void
hammer_cache_node(hammer_node_cache_t cache, hammer_node_t node)
{
        /*
         * If the node doesn't exist, or is being deleted, don't cache it!
         *
         * The node can only ever be NULL in the I/O failure path.
         */
        if (node == NULL || (node->flags & HAMMER_NODE_DELETED))
                return;
        if (cache->node == node)
                return;
        while (cache->node)
                hammer_uncache_node(cache);
        if (node->flags & HAMMER_NODE_DELETED)
                return;
        cache->node = node;
        TAILQ_INSERT_TAIL(&node->cache_list, cache, entry);
}

void
hammer_uncache_node(hammer_node_cache_t cache)
{
        hammer_node_t node;

        if ((node = cache->node) != NULL) {
                TAILQ_REMOVE(&node->cache_list, cache, entry);
                cache->node = NULL;
                if (TAILQ_EMPTY(&node->cache_list))
                        hammer_flush_node(node);
        }
}

/*
 * Remove a node's cache references and destroy the node if it has no
 * other references or backing store.
 */
void
hammer_flush_node(hammer_node_t node)
{
        hammer_node_cache_t cache;
        hammer_buffer_t buffer;
        hammer_mount_t hmp = node->hmp;

        while ((cache = TAILQ_FIRST(&node->cache_list)) != NULL) {
                TAILQ_REMOVE(&node->cache_list, cache, entry);
                cache->node = NULL;
        }
        if (node->lock.refs == 0 && node->ondisk == NULL) {
                KKASSERT((node->flags & HAMMER_NODE_NEEDSCRC) == 0);
                RB_REMOVE(hammer_nod_rb_tree, &node->hmp->rb_nods_root, node);
                if ((buffer = node->buffer) != NULL) {
                        node->buffer = NULL;
                        TAILQ_REMOVE(&buffer->clist, node, entry);
                        /* buffer is unreferenced because ondisk is NULL */
                }
                --hammer_count_nodes;
                kfree(node, hmp->m_misc);
        }
}

/*
 * Flush passively cached B-Tree nodes associated with this buffer.
 * This is only called when the buffer is about to be destroyed, so
 * none of the nodes should have any references.  The buffer is locked.
 *
 * We may be interlocked with the buffer.
 */
void
hammer_flush_buffer_nodes(hammer_buffer_t buffer)
{
        hammer_node_t node;

        while ((node = TAILQ_FIRST(&buffer->clist)) != NULL) {
                KKASSERT(node->ondisk == NULL);
                KKASSERT((node->flags & HAMMER_NODE_NEEDSCRC) == 0);

                if (node->lock.refs == 0) {
                        hammer_ref(&node->lock);
                        node->flags |= HAMMER_NODE_FLUSH;
                        hammer_rel_node(node);
                } else {
                        KKASSERT(node->loading != 0);
                        KKASSERT(node->buffer != NULL);
                        buffer = node->buffer;
                        node->buffer = NULL;
                        TAILQ_REMOVE(&buffer->clist, node, entry);
                        /* buffer is unreferenced because ondisk is NULL */
                }
        }
}


/************************************************************************
 *                              ALLOCATORS                              *
 ************************************************************************/

/*
 * Allocate a B-Tree node.
 */
hammer_node_t
hammer_alloc_btree(hammer_transaction_t trans, int *errorp)
{
        hammer_buffer_t buffer = NULL;
        hammer_node_t node = NULL;
        hammer_off_t node_offset;

        node_offset = hammer_blockmap_alloc(trans, HAMMER_ZONE_BTREE_INDEX,
                                            sizeof(struct hammer_node_ondisk),
                                            errorp);
        if (*errorp == 0) {
                node = hammer_get_node(trans, node_offset, 1, errorp);
                hammer_modify_node_noundo(trans, node);
                bzero(node->ondisk, sizeof(*node->ondisk));
                hammer_modify_node_done(node);
        }
        if (buffer)
                hammer_rel_buffer(buffer, 0);
        return(node);
}

/*
 * Allocate data.  If the address of a data buffer is supplied then
 * any prior non-NULL *data_bufferp will be released and *data_bufferp
 * will be set to the related buffer.  The caller must release it when
 * finally done.  The initial *data_bufferp should be set to NULL by
 * the caller.
 *
 * The caller is responsible for making hammer_modify*() calls on the
 * *data_bufferp.
 */
void *
hammer_alloc_data(hammer_transaction_t trans, int32_t data_len, 
                  u_int16_t rec_type, hammer_off_t *data_offsetp,
                  struct hammer_buffer **data_bufferp, int *errorp)
{
        void *data;
        int zone;

        /*
         * Allocate data
         */
        if (data_len) {
                switch(rec_type) {
                case HAMMER_RECTYPE_INODE:
                case HAMMER_RECTYPE_DIRENTRY:
                case HAMMER_RECTYPE_EXT:
                case HAMMER_RECTYPE_FIX:
                case HAMMER_RECTYPE_PFS:
                        zone = HAMMER_ZONE_META_INDEX;
                        break;
                case HAMMER_RECTYPE_DATA:
                case HAMMER_RECTYPE_DB:
                        if (data_len <= HAMMER_BUFSIZE / 2) {
                                zone = HAMMER_ZONE_SMALL_DATA_INDEX;
                        } else {
                                data_len = (data_len + HAMMER_BUFMASK) &
                                           ~HAMMER_BUFMASK;
                                zone = HAMMER_ZONE_LARGE_DATA_INDEX;
                        }
                        break;
                default:
                        panic("hammer_alloc_data: rec_type %04x unknown",
                              rec_type);
                        zone = 0;       /* NOT REACHED */
                        break;
                }
                *data_offsetp = hammer_blockmap_alloc(trans, zone,
                                                      data_len, errorp);
        } else {
                *data_offsetp = 0;
        }
        if (*errorp == 0 && data_bufferp) {
                if (data_len) {
                        data = hammer_bread_ext(trans->hmp, *data_offsetp,
                                                data_len, errorp, data_bufferp);
                } else {
                        data = NULL;
                }
        } else {
                data = NULL;
        }
        return(data);
}

/*
 * Sync dirty buffers to the media and clean-up any loose ends.
 *
 * These functions do not start the flusher going, they simply
 * queue everything up to the flusher.
 */
static int hammer_sync_scan1(struct mount *mp, struct vnode *vp, void *data);
static int hammer_sync_scan2(struct mount *mp, struct vnode *vp, void *data);

int
hammer_queue_inodes_flusher(hammer_mount_t hmp, int waitfor)
{
        struct hammer_sync_info info;

        info.error = 0;
        info.waitfor = waitfor;
        if (waitfor == MNT_WAIT) {
                vmntvnodescan(hmp->mp, VMSC_GETVP|VMSC_ONEPASS,
                              hammer_sync_scan1, hammer_sync_scan2, &info);
        } else {
                vmntvnodescan(hmp->mp, VMSC_GETVP|VMSC_ONEPASS|VMSC_NOWAIT,
                              hammer_sync_scan1, hammer_sync_scan2, &info);
        }
        return(info.error);
}

/*
 * Filesystem sync.  If doing a synchronous sync make a second pass on
 * the vnodes in case any were already flushing during the first pass,
 * and activate the flusher twice (the second time brings the UNDO FIFO's
 * start position up to the end position after the first call).
 */
int
hammer_sync_hmp(hammer_mount_t hmp, int waitfor)
{
        struct hammer_sync_info info;

        info.error = 0;
        info.waitfor = MNT_NOWAIT;
        vmntvnodescan(hmp->mp, VMSC_GETVP|VMSC_NOWAIT,
                      hammer_sync_scan1, hammer_sync_scan2, &info);
        if (info.error == 0 && waitfor == MNT_WAIT) {
                info.waitfor = waitfor;
                vmntvnodescan(hmp->mp, VMSC_GETVP,
                              hammer_sync_scan1, hammer_sync_scan2, &info);
        }
        if (waitfor == MNT_WAIT) {
                hammer_flusher_sync(hmp);
                hammer_flusher_sync(hmp);
        } else {
                hammer_flusher_async(hmp, NULL);
                hammer_flusher_async(hmp, NULL);
        }
        return(info.error);
}

static int
hammer_sync_scan1(struct mount *mp, struct vnode *vp, void *data)
{
        struct hammer_inode *ip;

        ip = VTOI(vp);
        if (vp->v_type == VNON || ip == NULL ||
            ((ip->flags & HAMMER_INODE_MODMASK) == 0 &&
             RB_EMPTY(&vp->v_rbdirty_tree))) {
                return(-1);
        }
        return(0);
}

static int
hammer_sync_scan2(struct mount *mp, struct vnode *vp, void *data)
{
        struct hammer_sync_info *info = data;
        struct hammer_inode *ip;
        int error;

        ip = VTOI(vp);
        if (vp->v_type == VNON || vp->v_type == VBAD ||
            ((ip->flags & HAMMER_INODE_MODMASK) == 0 &&
             RB_EMPTY(&vp->v_rbdirty_tree))) {
                return(0);
        }
        error = VOP_FSYNC(vp, MNT_NOWAIT);
        if (error)
                info->error = error;
        return(0);
}