[apple/xnu.git] / bsd / vfs / vfs_journal.c

/*
 * Copyright (c) 2002-2012 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
//
// This file implements a simple write-ahead journaling layer.  
// In theory any file system can make use of it by calling these 
// functions when the fs wants to modify meta-data blocks.  See
// vfs_journal.h for a more detailed description of the api and
// data structures.
//
// Dominic Giampaolo (dbg@apple.com)
//

#ifdef KERNEL

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/file_internal.h>
#include <sys/stat.h>
#include <sys/buf_internal.h>
#include <sys/proc_internal.h>
#include <sys/mount_internal.h>
#include <sys/namei.h>
#include <sys/vnode_internal.h>
#include <sys/ioctl.h>
#include <sys/tty.h>
#include <sys/ubc.h>
#include <sys/malloc.h>
#include <kern/task.h>
#include <kern/thread.h>
#include <kern/kalloc.h>
#include <sys/disk.h>
#include <sys/kdebug.h>
#include <miscfs/specfs/specdev.h>
#include <libkern/OSAtomic.h>   /* OSAddAtomic */

kern_return_t   thread_terminate(thread_t);

/*
 * Set sysctl vfs.generic.jnl.kdebug.trim=1 to enable KERNEL_DEBUG_CONSTANT
 * logging of trim-related calls within the journal.  (They're
 * disabled by default because there can be a lot of these events,
 * and we don't want to overwhelm the kernel debug buffer.  If you
 * want to watch these events in particular, just set the sysctl.)
 */
static int jnl_kdebug = 0;
SYSCTL_DECL(_vfs_generic);
SYSCTL_NODE(_vfs_generic, OID_AUTO, jnl, CTLFLAG_RW|CTLFLAG_LOCKED, 0, "Journal");
SYSCTL_NODE(_vfs_generic_jnl, OID_AUTO, kdebug, CTLFLAG_RW|CTLFLAG_LOCKED, 0, "Journal kdebug");
SYSCTL_INT(_vfs_generic_jnl_kdebug, OID_AUTO, trim, CTLFLAG_RW|CTLFLAG_LOCKED, &jnl_kdebug, 0, "Enable kdebug logging for journal TRIM");

#define DBG_JOURNAL_FLUSH                       FSDBG_CODE(DBG_JOURNAL, 1)
#define DBG_JOURNAL_TRIM_ADD            FSDBG_CODE(DBG_JOURNAL, 2)
#define DBG_JOURNAL_TRIM_REMOVE         FSDBG_CODE(DBG_JOURNAL, 3)
#define DBG_JOURNAL_TRIM_REMOVE_PENDING FSDBG_CODE(DBG_JOURNAL, 4)
#define DBG_JOURNAL_TRIM_REALLOC        FSDBG_CODE(DBG_JOURNAL, 5)
#define DBG_JOURNAL_TRIM_FLUSH          FSDBG_CODE(DBG_JOURNAL, 6)
#define DBG_JOURNAL_TRIM_UNMAP          FSDBG_CODE(DBG_JOURNAL, 7)

/* 
 * Cap the journal max size to 2GB.  On HFS, it will attempt to occupy
 * a full allocation block if the current size is smaller than the allocation
 * block on which it resides.  Once we hit the exabyte filesystem range, then
 * it will use 2GB allocation blocks.  As a result, make the cap 2GB.
 */
#define MAX_JOURNAL_SIZE 0x80000000U

#include <sys/sdt.h> /* DTRACE_IO1 */
#else

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdarg.h>
#include <sys/types.h>
#include "compat.h"

#endif   /* KERNEL */

#include "vfs_journal.h"

#include <sys/kdebug.h>

#if 0
#undef KERNEL_DEBUG
#define KERNEL_DEBUG KERNEL_DEBUG_CONSTANT
#endif


#ifndef CONFIG_HFS_TRIM
#define CONFIG_HFS_TRIM 0
#endif


#if JOURNALING

//
// By default, we grow the list of extents to trim by one page at a time.
// We'll opt to flush a transaction if it contains at least
// JOURNAL_FLUSH_TRIM_EXTENTS extents to be trimmed (even if the number
// of modified blocks is small).
//
enum {
    JOURNAL_DEFAULT_TRIM_BYTES = PAGE_SIZE,
    JOURNAL_DEFAULT_TRIM_EXTENTS = JOURNAL_DEFAULT_TRIM_BYTES / sizeof(dk_extent_t),
    JOURNAL_FLUSH_TRIM_EXTENTS = JOURNAL_DEFAULT_TRIM_EXTENTS * 15 / 16
};

unsigned int jnl_trim_flush_limit = JOURNAL_FLUSH_TRIM_EXTENTS;
SYSCTL_UINT (_kern, OID_AUTO, jnl_trim_flush, CTLFLAG_RW, &jnl_trim_flush_limit, 0, "number of trimmed extents to cause a journal flush");

/* XXX next prototype should be from libsa/stdlib.h> but conflicts libkern */
__private_extern__ void qsort(
        void * array,
        size_t nmembers,
        size_t member_size,
        int (*)(const void *, const void *));



// number of bytes to checksum in a block_list_header
// NOTE: this should be enough to clear out the header
//       fields as well as the first entry of binfo[]
#define BLHDR_CHECKSUM_SIZE 32

static void lock_condition(journal *jnl, boolean_t *condition, const char *condition_name);
static void wait_condition(journal *jnl, boolean_t *condition, const char *condition_name);
static void unlock_condition(journal *jnl, boolean_t *condition);
static void finish_end_thread(transaction *tr);
static void write_header_thread(journal *jnl);
static int finish_end_transaction(transaction *tr, errno_t (*callback)(void*), void *callback_arg);
static int end_transaction(transaction *tr, int force_it, errno_t (*callback)(void*), void *callback_arg, boolean_t drop_lock, boolean_t must_wait);
static void abort_transaction(journal *jnl, transaction *tr);
static void dump_journal(journal *jnl);

static __inline__ void  lock_journal(journal *jnl);
static __inline__ void  unlock_journal(journal *jnl);
static __inline__ void  lock_oldstart(journal *jnl);
static __inline__ void  unlock_oldstart(journal *jnl);
static __inline__ void  lock_flush(journal *jnl);
static __inline__ void  unlock_flush(journal *jnl);


//
// 3105942 - Coalesce writes to the same block on journal replay
//

typedef struct bucket {
        off_t     block_num;
        uint32_t  jnl_offset;
        uint32_t  block_size;
        int32_t   cksum;
} bucket;

#define STARTING_BUCKETS 256

static int add_block(journal *jnl, struct bucket **buf_ptr, off_t block_num, size_t size, size_t offset, int32_t cksum, int *num_buckets_ptr, int *num_full_ptr);
static int grow_table(struct bucket **buf_ptr, int num_buckets, int new_size);
static int lookup_bucket(struct bucket **buf_ptr, off_t block_num, int num_full);
static int do_overlap(journal *jnl, struct bucket **buf_ptr, int blk_index, off_t block_num, size_t size, size_t offset, int32_t cksum, int *num_buckets_ptr, int *num_full_ptr);
static int insert_block(journal *jnl, struct bucket **buf_ptr, int blk_index, off_t num, size_t size, size_t offset, int32_t cksum, int *num_buckets_ptr, int *num_full_ptr, int overwriting);

#define CHECK_JOURNAL(jnl) \
        do {               \
        if (jnl == NULL) {                                      \
                panic("%s:%d: null journal ptr?\n", __FILE__, __LINE__); \
        }                                                               \
        if (jnl->jdev == NULL) {                                \
                panic("%s:%d: jdev is null!\n", __FILE__, __LINE__); \
        }                                                       \
        if (jnl->fsdev == NULL) {                               \
                panic("%s:%d: fsdev is null!\n", __FILE__, __LINE__);   \
        }                                                               \
        if (jnl->jhdr->magic != JOURNAL_HEADER_MAGIC) {                 \
                panic("%s:%d: jhdr magic corrupted (0x%x != 0x%x)\n",   \
                      __FILE__, __LINE__, jnl->jhdr->magic, JOURNAL_HEADER_MAGIC); \
        }                                                               \
        if (   jnl->jhdr->start <= 0                                    \
               || jnl->jhdr->start > jnl->jhdr->size) {                 \
                panic("%s:%d: jhdr start looks bad (0x%llx max size 0x%llx)\n", \
                      __FILE__, __LINE__, jnl->jhdr->start, jnl->jhdr->size); \
        }                                                               \
        if (   jnl->jhdr->end <= 0                                      \
               || jnl->jhdr->end > jnl->jhdr->size) {                   \
                panic("%s:%d: jhdr end looks bad (0x%llx max size 0x%llx)\n", \
                      __FILE__, __LINE__, jnl->jhdr->end, jnl->jhdr->size); \
        }                                                               \
        } while(0)

#define CHECK_TRANSACTION(tr) \
        do {                  \
        if (tr == NULL) {                                       \
                panic("%s:%d: null transaction ptr?\n", __FILE__, __LINE__); \
        }                                                               \
        if (tr->jnl == NULL) {                                          \
                panic("%s:%d: null tr->jnl ptr?\n", __FILE__, __LINE__); \
        }                                                               \
        if (tr->blhdr != (block_list_header *)tr->tbuffer) {            \
                panic("%s:%d: blhdr (%p) != tbuffer (%p)\n", __FILE__, __LINE__, tr->blhdr, tr->tbuffer); \
        }                                                               \
        if (tr->total_bytes < 0) {                                      \
                panic("%s:%d: tr total_bytes looks bad: %d\n", __FILE__, __LINE__, tr->total_bytes); \
        }                                                               \
        if (tr->journal_start < 0) {                                    \
                panic("%s:%d: tr journal start looks bad: 0x%llx\n", __FILE__, __LINE__, tr->journal_start); \
        }                                                               \
        if (tr->journal_end < 0) {                                      \
                panic("%s:%d: tr journal end looks bad: 0x%llx\n", __FILE__, __LINE__, tr->journal_end); \
        }                                                               \
        if (tr->blhdr && (tr->blhdr->max_blocks <= 0 || tr->blhdr->max_blocks > (tr->jnl->jhdr->size/tr->jnl->jhdr->jhdr_size))) { \
                panic("%s:%d: tr blhdr max_blocks looks bad: %d\n", __FILE__, __LINE__, tr->blhdr->max_blocks); \
        }                                                               \
        } while(0)



//
// this isn't a great checksum routine but it will do for now.
// we use it to checksum the journal header and the block list
// headers that are at the start of each transaction.
//
static unsigned int
calc_checksum(char *ptr, int len)
{
        int i;
        unsigned int cksum=0;

        // this is a lame checksum but for now it'll do
        for(i = 0; i < len; i++, ptr++) {
                cksum = (cksum << 8) ^ (cksum + *(unsigned char *)ptr);
        }

        return (~cksum);
}

//
// Journal Locking
//
lck_grp_attr_t *  jnl_group_attr;
lck_attr_t *      jnl_lock_attr;
lck_grp_t *       jnl_mutex_group;

void
journal_init(void)
{
        jnl_lock_attr    = lck_attr_alloc_init();
        jnl_group_attr   = lck_grp_attr_alloc_init();
        jnl_mutex_group  = lck_grp_alloc_init("jnl-mutex", jnl_group_attr);
}

static __inline__ void
lock_journal(journal *jnl)
{
        lck_mtx_lock(&jnl->jlock);
}

static __inline__ void
unlock_journal(journal *jnl)
{
        lck_mtx_unlock(&jnl->jlock);
}

static __inline__ void
lock_flush(journal *jnl)
{
        lck_mtx_lock(&jnl->flock);
}

static __inline__ void
unlock_flush(journal *jnl)
{
        lck_mtx_unlock(&jnl->flock);
}

static __inline__ void
lock_oldstart(journal *jnl)
{
        lck_mtx_lock(&jnl->old_start_lock);
}

static __inline__ void
unlock_oldstart(journal *jnl)
{
        lck_mtx_unlock(&jnl->old_start_lock);
}



#define JNL_WRITE    0x0001
#define JNL_READ     0x0002
#define JNL_HEADER   0x8000

//
// This function sets up a fake buf and passes it directly to the
// journal device strategy routine (so that it won't get cached in
// the block cache.
//
// It also handles range checking the i/o so that we don't write
// outside the journal boundaries and it will wrap the i/o back
// to the beginning if necessary (skipping over the journal header)
// 
static size_t
do_journal_io(journal *jnl, off_t *offset, void *data, size_t len, int direction)
{
        int     err, curlen=len;
        size_t  io_sz = 0;
        buf_t   bp;
        off_t   max_iosize;

        if (*offset < 0 || *offset > jnl->jhdr->size) {
                panic("jnl: do_jnl_io: bad offset 0x%llx (max 0x%llx)\n", *offset, jnl->jhdr->size);
        }
        
        if (direction & JNL_WRITE)
                max_iosize = jnl->max_write_size;
        else if (direction & JNL_READ)
                max_iosize = jnl->max_read_size;
        else
                max_iosize = 128 * 1024;

again:
        bp = alloc_io_buf(jnl->jdev, 1);

        if (*offset + (off_t)curlen > jnl->jhdr->size && *offset != 0 && jnl->jhdr->size != 0) {
                if (*offset == jnl->jhdr->size) {
                        *offset = jnl->jhdr->jhdr_size;
                } else {
                        curlen = (off_t)jnl->jhdr->size - *offset;
                }
        }

        if (curlen > max_iosize) {
                curlen = max_iosize;
        }

        if (curlen <= 0) {
                panic("jnl: do_jnl_io: curlen == %d, offset 0x%llx len %zd\n", curlen, *offset, len);
        }

        if (*offset == 0 && (direction & JNL_HEADER) == 0) {
                panic("jnl: request for i/o to jnl-header without JNL_HEADER flag set! (len %d, data %p)\n", curlen, data);
        }

        if (direction & JNL_READ)
                buf_setflags(bp, B_READ);
        else {
                /*
                 * don't have to set any flags
                 */
                vnode_startwrite(jnl->jdev);
        }
        buf_setsize(bp, curlen);
        buf_setcount(bp, curlen);
        buf_setdataptr(bp, (uintptr_t)data);
        buf_setblkno(bp, (daddr64_t) ((jnl->jdev_offset + *offset) / (off_t)jnl->jhdr->jhdr_size));
        buf_setlblkno(bp, (daddr64_t) ((jnl->jdev_offset + *offset) / (off_t)jnl->jhdr->jhdr_size));

        if ((direction & JNL_WRITE) && (jnl->flags & JOURNAL_DO_FUA_WRITES)) {
                buf_markfua(bp);
        }

        DTRACE_IO1(journal__start, buf_t, bp);
        err = VNOP_STRATEGY(bp);
        if (!err) {
                err = (int)buf_biowait(bp);
        }
        DTRACE_IO1(journal__done, buf_t, bp);
        free_io_buf(bp);

        if (err) {
                printf("jnl: %s: do_jnl_io: strategy err 0x%x\n", jnl->jdev_name, err);
                return 0;
        }

        *offset += curlen;
        io_sz   += curlen;

        if (io_sz != len) {
                // handle wrap-around
                data    = (char *)data + curlen;
                curlen  = len - io_sz;
                if (*offset >= jnl->jhdr->size) {
                        *offset = jnl->jhdr->jhdr_size;
                }
                goto again;
        }

        return io_sz;
}

static size_t
read_journal_data(journal *jnl, off_t *offset, void *data, size_t len)
{
        return do_journal_io(jnl, offset, data, len, JNL_READ);
}

static size_t
write_journal_data(journal *jnl, off_t *offset, void *data, size_t len)
{
        return do_journal_io(jnl, offset, data, len, JNL_WRITE);
}


static size_t
read_journal_header(journal *jnl, void *data, size_t len)
{
        off_t hdr_offset = 0;
        
        return do_journal_io(jnl, &hdr_offset, data, len, JNL_READ|JNL_HEADER);
}

static int
write_journal_header(journal *jnl, int updating_start, uint32_t sequence_num)
{
        static int num_err_prints = 0;
        int ret=0;
        off_t jhdr_offset = 0;
        struct vfs_context context;

        context.vc_thread = current_thread();
        context.vc_ucred = NOCRED;
        // 
        // Flush the track cache if we're not doing force-unit-access
        // writes.
        //
        if (!updating_start && (jnl->flags & JOURNAL_DO_FUA_WRITES) == 0) {
                ret = VNOP_IOCTL(jnl->jdev, DKIOCSYNCHRONIZECACHE, NULL, FWRITE, &context);
        }
        if (ret != 0) {
                //
                // Only print this error if it's a different error than the
                // previous one, or if it's the first time for this device
                // or if the total number of printfs is less than 25.  We
                // allow for up to 25 printfs to insure that some make it
                // into the on-disk syslog.  Otherwise if we only printed
                // one, it's possible it would never make it to the syslog
                // for the root volume and that makes debugging hard.
                //
                if (   ret != jnl->last_flush_err
                       || (jnl->flags & JOURNAL_FLUSHCACHE_ERR) == 0
                       || num_err_prints++ < 25) {
            
                        printf("jnl: %s: flushing fs disk buffer returned 0x%x\n", jnl->jdev_name, ret);
            
                        jnl->flags |= JOURNAL_FLUSHCACHE_ERR;
                        jnl->last_flush_err = ret;
                }
        }

        jnl->jhdr->sequence_num = sequence_num;
        jnl->jhdr->checksum = 0;
        jnl->jhdr->checksum = calc_checksum((char *)jnl->jhdr, JOURNAL_HEADER_CKSUM_SIZE);

        if (do_journal_io(jnl, &jhdr_offset, jnl->header_buf, jnl->jhdr->jhdr_size, JNL_WRITE|JNL_HEADER) != (size_t)jnl->jhdr->jhdr_size) {
                printf("jnl: %s: write_journal_header: error writing the journal header!\n", jnl->jdev_name);
                jnl->flags |= JOURNAL_INVALID;
                return -1;
        }       

        // If we're not doing force-unit-access writes, then we
        // have to flush after writing the journal header so that
        // a future transaction doesn't sneak out to disk before
        // the header does and thus overwrite data that the old
        // journal header refers to.  Saw this exact case happen
        // on an IDE bus analyzer with Larry Barras so while it
        // may seem obscure, it's not.
        //
        if (updating_start && (jnl->flags & JOURNAL_DO_FUA_WRITES) == 0) {
                VNOP_IOCTL(jnl->jdev, DKIOCSYNCHRONIZECACHE, NULL, FWRITE, &context);
        }

        return 0;
}



//
// this is a work function used to free up transactions that
// completed. they can't be free'd from buffer_flushed_callback
// because it is called from deep with the disk driver stack
// and thus can't do something that would potentially cause
// paging.  it gets called by each of the journal api entry
// points so stuff shouldn't hang around for too long.
//
static void
free_old_stuff(journal *jnl)
{
        transaction *tr, *next;
        block_list_header  *blhdr=NULL, *next_blhdr=NULL;

        if (jnl->tr_freeme == NULL)
                return;

        lock_oldstart(jnl);
        tr = jnl->tr_freeme;
        jnl->tr_freeme = NULL;
        unlock_oldstart(jnl);

        for(; tr; tr=next) {
                for (blhdr = tr->blhdr; blhdr; blhdr = next_blhdr) {
                        next_blhdr = (block_list_header *)((long)blhdr->binfo[0].bnum);
                        blhdr->binfo[0].bnum = 0xdeadc0de;
                    
                        kmem_free(kernel_map, (vm_offset_t)blhdr, tr->tbuffer_size);

                        KERNEL_DEBUG(0xbbbbc01c, jnl, tr, tr->tbuffer_size, 0, 0);
                }
                next = tr->next;
                FREE_ZONE(tr, sizeof(transaction), M_JNL_TR);
        }
}



//
// This is our callback that lets us know when a buffer has been
// flushed to disk.  It's called from deep within the driver stack
// and thus is quite limited in what it can do.  Notably, it can
// not initiate any new i/o's or allocate/free memory.
//
static void
buffer_flushed_callback(struct buf *bp, void *arg)
{
        transaction  *tr;
        journal      *jnl;
        transaction  *ctr, *prev=NULL, *next;
        size_t        i;
        int           bufsize, amt_flushed, total_bytes;


        //printf("jnl: buf flush: bp @ 0x%x l/blkno %qd/%qd vp 0x%x tr @ 0x%x\n",
        //         bp, buf_lblkno(bp), buf_blkno(bp), buf_vnode(bp), arg);

        // snarf out the bits we want
        bufsize = buf_size(bp);
        tr      = (transaction *)arg;

        // then we've already seen it
        if (tr == NULL) {
                return;
        }

        CHECK_TRANSACTION(tr);

        jnl = tr->jnl;
        if (jnl->flags & JOURNAL_INVALID) {
                return;
        }

        CHECK_JOURNAL(jnl);

        amt_flushed = tr->num_killed;
        total_bytes = tr->total_bytes;
    
        // update the number of blocks that have been flushed.
        // this buf may represent more than one block so take
        // that into account.
        //
        // OSAddAtomic() returns the value of tr->num_flushed before the add
        //
        amt_flushed += OSAddAtomic(bufsize, &tr->num_flushed);


        // if this transaction isn't done yet, just return as
        // there is nothing to do.
        //
        // NOTE: we are careful to not reference anything through
        //       the tr pointer after doing the OSAddAtomic().  if
        //       this if statement fails then we are the last one
        //       and then it's ok to dereference "tr".
        //
        if ((amt_flushed + bufsize) < total_bytes) {
                return;
        }

        // this will single thread checking the transaction
        lock_oldstart(jnl);

        if (tr->total_bytes == (int)0xfbadc0de) {
                // then someone beat us to it...
                unlock_oldstart(jnl);
                return;
        }

        // mark this so that we're the owner of dealing with the
        // cleanup for this transaction
        tr->total_bytes = 0xfbadc0de;

        //printf("jnl: tr 0x%x (0x%llx 0x%llx) in jnl 0x%x completed.\n",
        //   tr, tr->journal_start, tr->journal_end, jnl);

        // find this entry in the old_start[] index and mark it completed
        for(i = 0; i < sizeof(jnl->old_start)/sizeof(jnl->old_start[0]); i++) {
        
                if ((off_t)(jnl->old_start[i] & ~(0x8000000000000000ULL)) == tr->journal_start) {
                        jnl->old_start[i] &= ~(0x8000000000000000ULL);
                        break;
                }
        }

        if (i >= sizeof(jnl->old_start)/sizeof(jnl->old_start[0])) {
                panic("jnl: buffer_flushed: did not find tr w/start @ %lld (tr %p, jnl %p)\n",
                      tr->journal_start, tr, jnl);
        }


        // if we are here then we need to update the journal header
        // to reflect that this transaction is complete
        if (tr->journal_start == jnl->active_start) {
                jnl->active_start = tr->journal_end;
                tr->journal_start = tr->journal_end = (off_t)0;
        }

        // go through the completed_trs list and try to coalesce
        // entries, restarting back at the beginning if we have to.
        for (ctr = jnl->completed_trs; ctr; prev=ctr, ctr=next) {
                if (ctr->journal_start == jnl->active_start) {
                        jnl->active_start = ctr->journal_end;
                        if (prev) {
                                prev->next = ctr->next;
                        }
                        if (ctr == jnl->completed_trs) {
                                jnl->completed_trs = ctr->next;
                        }
            
                        next           = jnl->completed_trs;   // this starts us over again
                        ctr->next      = jnl->tr_freeme;
                        jnl->tr_freeme = ctr;
                        ctr            = NULL;
                } else if (tr->journal_end == ctr->journal_start) {
                        ctr->journal_start = tr->journal_start;
                        next               = jnl->completed_trs;  // this starts us over again
                        ctr                = NULL;
                        tr->journal_start  = tr->journal_end = (off_t)0;
                } else if (tr->journal_start == ctr->journal_end) {
                        ctr->journal_end  = tr->journal_end;
                        next              = ctr->next;
                        tr->journal_start = tr->journal_end = (off_t)0;
                } else if (ctr->next && ctr->journal_end == ctr->next->journal_start) {
                        // coalesce the next entry with this one and link the next
                        // entry in at the head of the tr_freeme list
                        next              = ctr->next;           // temporarily use the "next" variable
                        ctr->journal_end  = next->journal_end;
                        ctr->next         = next->next;
                        next->next        = jnl->tr_freeme;      // link in the next guy at the head of the tr_freeme list
                        jnl->tr_freeme    = next;

                        next              = jnl->completed_trs;  // this starts us over again
                        ctr               = NULL;
                } else {
                        next = ctr->next;
                }
        }
    
        // if this is true then we didn't merge with anyone
        // so link ourselves in at the head of the completed
        // transaction list.
        if (tr->journal_start != 0) {
                // put this entry into the correct sorted place
                // in the list instead of just at the head.
                //
        
                prev = NULL;
                for (ctr = jnl->completed_trs; ctr && tr->journal_start > ctr->journal_start; prev=ctr, ctr=ctr->next) {
                        // just keep looping
                }

                if (ctr == NULL && prev == NULL) {
                        jnl->completed_trs = tr;
                        tr->next = NULL;
                } else if (ctr == jnl->completed_trs) {
                        tr->next = jnl->completed_trs;
                        jnl->completed_trs = tr;
                } else {
                        tr->next = prev->next;
                        prev->next = tr;
                }
        } else {
                // if we're here this tr got merged with someone else so
                // put it on the list to be free'd
                tr->next       = jnl->tr_freeme;
                jnl->tr_freeme = tr;
        }
        unlock_oldstart(jnl);

        unlock_condition(jnl, &jnl->asyncIO);
}


#include <libkern/OSByteOrder.h>

#define SWAP16(x) OSSwapInt16(x)
#define SWAP32(x) OSSwapInt32(x)
#define SWAP64(x) OSSwapInt64(x)


static void
swap_journal_header(journal *jnl)
{
        jnl->jhdr->magic      = SWAP32(jnl->jhdr->magic);
        jnl->jhdr->endian     = SWAP32(jnl->jhdr->endian);
        jnl->jhdr->start      = SWAP64(jnl->jhdr->start);
        jnl->jhdr->end        = SWAP64(jnl->jhdr->end);
        jnl->jhdr->size       = SWAP64(jnl->jhdr->size);
        jnl->jhdr->blhdr_size = SWAP32(jnl->jhdr->blhdr_size);
        jnl->jhdr->checksum   = SWAP32(jnl->jhdr->checksum);
        jnl->jhdr->jhdr_size  = SWAP32(jnl->jhdr->jhdr_size);
        jnl->jhdr->sequence_num  = SWAP32(jnl->jhdr->sequence_num);
}

static void
swap_block_list_header(journal *jnl, block_list_header *blhdr)
{
        int i;
    
        blhdr->max_blocks = SWAP16(blhdr->max_blocks);
        blhdr->num_blocks = SWAP16(blhdr->num_blocks);
        blhdr->bytes_used = SWAP32(blhdr->bytes_used);
        blhdr->checksum   = SWAP32(blhdr->checksum);
        blhdr->flags      = SWAP32(blhdr->flags);

        if (blhdr->num_blocks >= ((jnl->jhdr->blhdr_size / sizeof(block_info)) - 1)) {
                printf("jnl: %s: blhdr num blocks looks suspicious (%d / blhdr size %d).  not swapping.\n", jnl->jdev_name, blhdr->num_blocks, jnl->jhdr->blhdr_size);
                return;
        }

        for(i = 0; i < blhdr->num_blocks; i++) {
                blhdr->binfo[i].bnum    = SWAP64(blhdr->binfo[i].bnum);
                blhdr->binfo[i].u.bi.bsize   = SWAP32(blhdr->binfo[i].u.bi.bsize);
                blhdr->binfo[i].u.bi.b.cksum = SWAP32(blhdr->binfo[i].u.bi.b.cksum);
        }
}


static int
update_fs_block(journal *jnl, void *block_ptr, off_t fs_block, size_t bsize)
{
        int             ret;
        struct buf *oblock_bp=NULL;
    
        // first read the block we want.
        ret = buf_meta_bread(jnl->fsdev, (daddr64_t)fs_block, bsize, NOCRED, &oblock_bp);
        if (ret != 0) {
                printf("jnl: %s: update_fs_block: error reading fs block # %lld! (ret %d)\n", jnl->jdev_name, fs_block, ret);

                if (oblock_bp) {
                        buf_brelse(oblock_bp);
                        oblock_bp = NULL;
                }

                // let's try to be aggressive here and just re-write the block
                oblock_bp = buf_getblk(jnl->fsdev, (daddr64_t)fs_block, bsize, 0, 0, BLK_META);
                if (oblock_bp == NULL) {
                        printf("jnl: %s: update_fs_block: buf_getblk() for %lld failed! failing update.\n", jnl->jdev_name, fs_block);
                        return -1;
                }
        }
            
        // make sure it's the correct size.
        if (buf_size(oblock_bp) != bsize) {
                buf_brelse(oblock_bp);
                return -1;
        }

        // copy the journal data over top of it
        memcpy((char *)buf_dataptr(oblock_bp), block_ptr, bsize);

        if ((ret = VNOP_BWRITE(oblock_bp)) != 0) {
                printf("jnl: %s: update_fs_block: failed to update block %lld (ret %d)\n", jnl->jdev_name, fs_block,ret);
                return ret;
        }

        // and now invalidate it so that if someone else wants to read
        // it in a different size they'll be able to do it.
        ret = buf_meta_bread(jnl->fsdev, (daddr64_t)fs_block, bsize, NOCRED, &oblock_bp);
        if (oblock_bp) {
                buf_markinvalid(oblock_bp);
                buf_brelse(oblock_bp);
        }
            
        return 0;
}

static int
grow_table(struct bucket **buf_ptr, int num_buckets, int new_size)
{
        struct bucket *newBuf;
        int current_size = num_buckets, i;
    
        // return if newsize is less than the current size
        if (new_size < num_buckets) {
                return current_size;
        }
    
        if ((MALLOC(newBuf, struct bucket *, new_size*sizeof(struct bucket), M_TEMP, M_WAITOK)) == NULL) {
                printf("jnl: grow_table: no memory to expand coalesce buffer!\n");
                return -1;
        }
    
        //  printf("jnl: lookup_bucket: expanded co_buf to %d elems\n", new_size);
    
        // copy existing elements 
        bcopy(*buf_ptr, newBuf, num_buckets*sizeof(struct bucket));
    
        // initialize the new ones
        for(i = num_buckets; i < new_size; i++) {
                newBuf[i].block_num = (off_t)-1;
        }
    
        // free the old container
        FREE(*buf_ptr, M_TEMP);
    
        // reset the buf_ptr
        *buf_ptr = newBuf;
    
        return new_size;
}

static int
lookup_bucket(struct bucket **buf_ptr, off_t block_num, int num_full)
{
        int lo, hi, index, matches, i;
    
        if (num_full == 0) {
                return 0; // table is empty, so insert at index=0
        }
    
        lo = 0;
        hi = num_full - 1;
        index = -1;
    
        // perform binary search for block_num
        do {
                int mid = (hi - lo)/2 + lo;
                off_t this_num = (*buf_ptr)[mid].block_num;
        
                if (block_num == this_num) {
                        index = mid;
                        break;
                }
        
                if (block_num < this_num) {
                        hi = mid;
                        continue;
                }
        
                if (block_num > this_num) {
                        lo = mid + 1;
                        continue;
                }
        } while (lo < hi);
    
        // check if lo and hi converged on the match
        if (block_num == (*buf_ptr)[hi].block_num) {
                index = hi;
        }
    
        // if no existing entry found, find index for new one
        if (index == -1) {
                index = (block_num < (*buf_ptr)[hi].block_num) ? hi : hi + 1;
        } else {
                // make sure that we return the right-most index in the case of multiple matches
                matches = 0;
                i = index + 1;
                while (i < num_full && block_num == (*buf_ptr)[i].block_num) {
                        matches++;
                        i++;
                }

                index += matches;
        }
    
        return index;
}

static int
insert_block(journal *jnl, struct bucket **buf_ptr, int blk_index, off_t num, size_t size, size_t offset, int32_t cksum, int *num_buckets_ptr, int *num_full_ptr, int overwriting)
{
        if (!overwriting) {
                // grow the table if we're out of space
                if (*num_full_ptr >= *num_buckets_ptr) {
                        int new_size = *num_buckets_ptr * 2;
                        int grow_size = grow_table(buf_ptr, *num_buckets_ptr, new_size);
            
                        if (grow_size < new_size) {
                                printf("jnl: %s: add_block: grow_table returned an error!\n", jnl->jdev_name);
                                return -1;
                        }
            
                        *num_buckets_ptr = grow_size; //update num_buckets to reflect the new size
                }
        
                // if we're not inserting at the end, we need to bcopy
                if (blk_index != *num_full_ptr) {
                        bcopy( (*buf_ptr)+(blk_index), (*buf_ptr)+(blk_index+1), (*num_full_ptr-blk_index)*sizeof(struct bucket) );
                }
        
                (*num_full_ptr)++; // increment only if we're not overwriting
        }

        // sanity check the values we're about to add
        if ((off_t)offset >= jnl->jhdr->size) {
                offset = jnl->jhdr->jhdr_size + (offset - jnl->jhdr->size);
        }
        if (size <= 0) {
                panic("jnl: insert_block: bad size in insert_block (%zd)\n", size);
        }        

        (*buf_ptr)[blk_index].block_num = num;
        (*buf_ptr)[blk_index].block_size = size;
        (*buf_ptr)[blk_index].jnl_offset = offset;
        (*buf_ptr)[blk_index].cksum = cksum;
    
        return blk_index;
}

static int
do_overlap(journal *jnl, struct bucket **buf_ptr, int blk_index, off_t block_num, size_t size, __unused size_t offset, int32_t cksum, int *num_buckets_ptr, int *num_full_ptr)
{
        int     num_to_remove, index, i, overwrite, err;
        size_t  jhdr_size = jnl->jhdr->jhdr_size, new_offset;
        off_t   overlap, block_start, block_end;

        block_start = block_num*jhdr_size;
        block_end = block_start + size;
        overwrite = (block_num == (*buf_ptr)[blk_index].block_num && size >= (*buf_ptr)[blk_index].block_size);

        // first, eliminate any overlap with the previous entry
        if (blk_index != 0 && !overwrite) {
                off_t prev_block_start = (*buf_ptr)[blk_index-1].block_num*jhdr_size;
                off_t prev_block_end = prev_block_start + (*buf_ptr)[blk_index-1].block_size;
                overlap = prev_block_end - block_start;
                if (overlap > 0) {
                        if (overlap % jhdr_size != 0) {
                                panic("jnl: do_overlap: overlap with previous entry not a multiple of %zd\n", jhdr_size);
                        }

                        // if the previous entry completely overlaps this one, we need to break it into two pieces.
                        if (prev_block_end > block_end) {
                                off_t new_num = block_end / jhdr_size;
                                size_t new_size = prev_block_end - block_end;

                                new_offset = (*buf_ptr)[blk_index-1].jnl_offset + (block_end - prev_block_start);
                
                                err = insert_block(jnl, buf_ptr, blk_index, new_num, new_size, new_offset, cksum, num_buckets_ptr, num_full_ptr, 0);
                                if (err < 0) {
                                        panic("jnl: do_overlap: error inserting during pre-overlap\n");
                                }
                        }
            
                        // Regardless, we need to truncate the previous entry to the beginning of the overlap
                        (*buf_ptr)[blk_index-1].block_size = block_start - prev_block_start;
                        (*buf_ptr)[blk_index-1].cksum = 0;   // have to blow it away because there's no way to check it
                }
        }

        // then, bail out fast if there's no overlap with the entries that follow
        if (!overwrite && block_end <= (off_t)((*buf_ptr)[blk_index].block_num*jhdr_size)) {
                return 0; // no overlap, no overwrite
        } else if (overwrite && (blk_index + 1 >= *num_full_ptr || block_end <= (off_t)((*buf_ptr)[blk_index+1].block_num*jhdr_size))) {

                (*buf_ptr)[blk_index].cksum = cksum;   // update this
                return 1; // simple overwrite
        }
    
        // Otherwise, find all cases of total and partial overlap. We use the special
        // block_num of -2 to designate entries that are completely overlapped and must
        // be eliminated. The block_num, size, and jnl_offset of partially overlapped
        // entries must be adjusted to keep the array consistent.
        index = blk_index;
        num_to_remove = 0;
        while (index < *num_full_ptr && block_end > (off_t)((*buf_ptr)[index].block_num*jhdr_size)) {
                if (block_end >= (off_t)(((*buf_ptr)[index].block_num*jhdr_size + (*buf_ptr)[index].block_size))) {
                        (*buf_ptr)[index].block_num = -2; // mark this for deletion
                        num_to_remove++;
                } else {
                        overlap = block_end - (*buf_ptr)[index].block_num*jhdr_size;
                        if (overlap > 0) {
                                if (overlap % jhdr_size != 0) {
                                        panic("jnl: do_overlap: overlap of %lld is not multiple of %zd\n", overlap, jhdr_size);
                                }
                                
                                // if we partially overlap this entry, adjust its block number, jnl offset, and size
                                (*buf_ptr)[index].block_num += (overlap / jhdr_size); // make sure overlap is multiple of jhdr_size, or round up
                                (*buf_ptr)[index].cksum = 0;
                
                                new_offset = (*buf_ptr)[index].jnl_offset + overlap; // check for wrap-around
                                if ((off_t)new_offset >= jnl->jhdr->size) {
                                        new_offset = jhdr_size + (new_offset - jnl->jhdr->size);
                                }
                                (*buf_ptr)[index].jnl_offset = new_offset;
                
                                (*buf_ptr)[index].block_size -= overlap; // sanity check for negative value
                                if ((*buf_ptr)[index].block_size <= 0) {
                                        panic("jnl: do_overlap: after overlap, new block size is invalid (%u)\n", (*buf_ptr)[index].block_size);
                                        // return -1; // if above panic is removed, return -1 for error
                                }
                        }
                        
                }

                index++;
        }

        // bcopy over any completely overlapped entries, starting at the right (where the above loop broke out)
        index--; // start with the last index used within the above loop
        while (index >= blk_index) {
                if ((*buf_ptr)[index].block_num == -2) {
                        if (index == *num_full_ptr-1) {
                                (*buf_ptr)[index].block_num = -1; // it's the last item in the table... just mark as free
                        } else {
                                bcopy( (*buf_ptr)+(index+1), (*buf_ptr)+(index), (*num_full_ptr - (index + 1)) * sizeof(struct bucket) );
                        }
                        (*num_full_ptr)--;
                }
                index--;
        }

        // eliminate any stale entries at the end of the table
        for(i = *num_full_ptr; i < (*num_full_ptr + num_to_remove); i++) {
                (*buf_ptr)[i].block_num = -1;
        }
    
        return 0; // if we got this far, we need to insert the entry into the table (rather than overwrite) 
}

// PR-3105942: Coalesce writes to the same block in journal replay
// We coalesce writes by maintaining a dynamic sorted array of physical disk blocks
// to be replayed and the corresponding location in the journal which contains
// the most recent data for those blocks. The array is "played" once the all the
// blocks in the journal have been coalesced. The code for the case of conflicting/
// overlapping writes to a single block is the most dense. Because coalescing can
// disrupt the existing time-ordering of blocks in the journal playback, care
// is taken to catch any overlaps and keep the array consistent. 
static int
add_block(journal *jnl, struct bucket **buf_ptr, off_t block_num, size_t size, __unused size_t offset, int32_t cksum, int *num_buckets_ptr, int *num_full_ptr)
{
        int     blk_index, overwriting;
    
        // on return from lookup_bucket(), blk_index is the index into the table where block_num should be
        // inserted (or the index of the elem to overwrite). 
        blk_index = lookup_bucket( buf_ptr, block_num, *num_full_ptr);
    
        // check if the index is within bounds (if we're adding this block to the end of
        // the table, blk_index will be equal to num_full)
        if (blk_index < 0 || blk_index > *num_full_ptr) {
                //printf("jnl: add_block: trouble adding block to co_buf\n");
                return -1;
        } // else printf("jnl: add_block: adding block 0x%llx at i=%d\n", block_num, blk_index);
    
        // Determine whether we're overwriting an existing entry by checking for overlap
        overwriting = do_overlap(jnl, buf_ptr, blk_index, block_num, size, offset, cksum, num_buckets_ptr, num_full_ptr);
        if (overwriting < 0) {
                return -1; // if we got an error, pass it along
        }
        
        // returns the index, or -1 on error
        blk_index = insert_block(jnl, buf_ptr, blk_index, block_num, size, offset, cksum, num_buckets_ptr, num_full_ptr, overwriting);
    
        return blk_index;
}

static int
replay_journal(journal *jnl)
{
        int             i, bad_blocks=0;
        unsigned int    orig_checksum, checksum, check_block_checksums = 0;
        size_t          ret;
        size_t          max_bsize = 0;          /* protected by block_ptr */
        block_list_header *blhdr;
        off_t           offset, txn_start_offset=0, blhdr_offset, orig_jnl_start;
        char            *buff, *block_ptr=NULL;
        struct bucket   *co_buf;
        int             num_buckets = STARTING_BUCKETS, num_full, check_past_jnl_end = 1, in_uncharted_territory=0;
        uint32_t        last_sequence_num = 0;
        int             replay_retry_count = 0;
    
        // wrap the start ptr if it points to the very end of the journal
        if (jnl->jhdr->start == jnl->jhdr->size) {
                jnl->jhdr->start = jnl->jhdr->jhdr_size;
        }
        if (jnl->jhdr->end == jnl->jhdr->size) {
                jnl->jhdr->end = jnl->jhdr->jhdr_size;
        }

        if (jnl->jhdr->start == jnl->jhdr->end) {
                return 0;
        }

        orig_jnl_start = jnl->jhdr->start;

        // allocate memory for the header_block.  we'll read each blhdr into this
        if (kmem_alloc_kobject(kernel_map, (vm_offset_t *)&buff, jnl->jhdr->blhdr_size)) {
                printf("jnl: %s: replay_journal: no memory for block buffer! (%d bytes)\n",
                       jnl->jdev_name, jnl->jhdr->blhdr_size);
                return -1;
        }

        // allocate memory for the coalesce buffer
        if ((MALLOC(co_buf, struct bucket *, num_buckets*sizeof(struct bucket), M_TEMP, M_WAITOK)) == NULL) {
                printf("jnl: %s: replay_journal: no memory for coalesce buffer!\n", jnl->jdev_name);
                return -1;
        }

restart_replay:

        // initialize entries
        for(i = 0; i < num_buckets; i++) {
                co_buf[i].block_num = -1;
        }
        num_full = 0; // empty at first


        printf("jnl: %s: replay_journal: from: %lld to: %lld (joffset 0x%llx)\n",
               jnl->jdev_name, jnl->jhdr->start, jnl->jhdr->end, jnl->jdev_offset);

        while (check_past_jnl_end || jnl->jhdr->start != jnl->jhdr->end) {
                offset = blhdr_offset = jnl->jhdr->start;
                ret = read_journal_data(jnl, &offset, buff, jnl->jhdr->blhdr_size);
                if (ret != (size_t)jnl->jhdr->blhdr_size) {
                        printf("jnl: %s: replay_journal: Could not read block list header block @ 0x%llx!\n", jnl->jdev_name, offset);
                        bad_blocks = 1;
                        goto bad_txn_handling;
                }

                blhdr = (block_list_header *)buff;
                
                orig_checksum = blhdr->checksum;
                blhdr->checksum = 0;
                if (jnl->flags & JOURNAL_NEED_SWAP) {
                        // calculate the checksum based on the unswapped data
                        // because it is done byte-at-a-time.
                        orig_checksum = (unsigned int)SWAP32(orig_checksum);
                        checksum = calc_checksum((char *)blhdr, BLHDR_CHECKSUM_SIZE);
                        swap_block_list_header(jnl, blhdr);
                } else {
                        checksum = calc_checksum((char *)blhdr, BLHDR_CHECKSUM_SIZE);
                }


                //
                // XXXdbg - if these checks fail, we should replay as much
                //          we can in the hopes that it will still leave the
                //          drive in a better state than if we didn't replay
                //          anything
                //
                if (checksum != orig_checksum) {
                        if (check_past_jnl_end && in_uncharted_territory) {

                                if (blhdr_offset != jnl->jhdr->end) {
                                        printf("jnl: %s: Extra txn replay stopped @ %lld / 0x%llx\n", jnl->jdev_name, blhdr_offset, blhdr_offset);
                                }

                                check_past_jnl_end = 0;
                                jnl->jhdr->end = blhdr_offset;
                                continue;
                        }

                        printf("jnl: %s: replay_journal: bad block list header @ 0x%llx (checksum 0x%x != 0x%x)\n",
                        jnl->jdev_name, blhdr_offset, orig_checksum, checksum);

                        if (blhdr_offset == orig_jnl_start) {
                                // if there's nothing in the journal at all, just bail out altogether.
                                goto bad_replay;
                        }

                        bad_blocks = 1;
                        goto bad_txn_handling;
                }

                if (   (last_sequence_num != 0)
                       && (blhdr->binfo[0].u.bi.b.sequence_num != 0)
                       && (blhdr->binfo[0].u.bi.b.sequence_num != last_sequence_num)
                       && (blhdr->binfo[0].u.bi.b.sequence_num != last_sequence_num+1)) {

                        txn_start_offset = jnl->jhdr->end = blhdr_offset;

                        if (check_past_jnl_end) {
                                check_past_jnl_end = 0;
                                printf("jnl: %s: 2: extra replay stopped @ %lld / 0x%llx (seq %d < %d)\n",
                                       jnl->jdev_name, blhdr_offset, blhdr_offset, blhdr->binfo[0].u.bi.b.sequence_num, last_sequence_num);
                                continue;
                        }

                        printf("jnl: %s: txn sequence numbers out of order in txn @ %lld / %llx! (%d < %d)\n",
                               jnl->jdev_name, blhdr_offset, blhdr_offset, blhdr->binfo[0].u.bi.b.sequence_num, last_sequence_num);
                        bad_blocks = 1;
                        goto bad_txn_handling;
                }
                last_sequence_num = blhdr->binfo[0].u.bi.b.sequence_num;

                if (blhdr_offset >= jnl->jhdr->end && jnl->jhdr->start <= jnl->jhdr->end) {
                        if (last_sequence_num == 0) {
                                check_past_jnl_end = 0;
                                printf("jnl: %s: pre-sequence-num-enabled txn's - can not go further than end (%lld %lld).\n",
                                       jnl->jdev_name, jnl->jhdr->start, jnl->jhdr->end);
                                if (jnl->jhdr->start != jnl->jhdr->end) {
                                        jnl->jhdr->start = jnl->jhdr->end;
                                }
                                continue;
                        }
                        printf("jnl: %s: examining extra transactions starting @ %lld / 0x%llx\n", jnl->jdev_name, blhdr_offset, blhdr_offset);
                }

                if (   blhdr->max_blocks <= 0 || blhdr->max_blocks > (jnl->jhdr->size/jnl->jhdr->jhdr_size)
                       || blhdr->num_blocks <= 0 || blhdr->num_blocks > blhdr->max_blocks) {
                        printf("jnl: %s: replay_journal: bad looking journal entry: max: %d num: %d\n",
                               jnl->jdev_name, blhdr->max_blocks, blhdr->num_blocks);
                        bad_blocks = 1;
                        goto bad_txn_handling;
                }
        
                max_bsize = 0;
                for (i = 1; i < blhdr->num_blocks; i++) {
                        if (blhdr->binfo[i].bnum < 0 && blhdr->binfo[i].bnum != (off_t)-1) {
                                printf("jnl: %s: replay_journal: bogus block number 0x%llx\n", jnl->jdev_name, blhdr->binfo[i].bnum);
                                bad_blocks = 1;
                                goto bad_txn_handling;
                        }
                        
                        if ((size_t)blhdr->binfo[i].u.bi.bsize > max_bsize) {
                                max_bsize = blhdr->binfo[i].u.bi.bsize;
                        }
                }

                if (blhdr->flags & BLHDR_CHECK_CHECKSUMS) {
                        check_block_checksums = 1;
                        if (kmem_alloc(kernel_map, (vm_offset_t *)&block_ptr, max_bsize)) {
                                goto bad_replay;
                        }
                } else {
                        block_ptr = NULL;
                }

                if (blhdr->flags & BLHDR_FIRST_HEADER) {
                        txn_start_offset = blhdr_offset;
                }

                //printf("jnl: replay_journal: adding %d blocks in journal entry @ 0x%llx to co_buf\n", 
                //       blhdr->num_blocks-1, jnl->jhdr->start);
                bad_blocks = 0;
                for (i = 1; i < blhdr->num_blocks; i++) {
                        int size, ret_val;
                        off_t number;

                        size = blhdr->binfo[i].u.bi.bsize;
                        number = blhdr->binfo[i].bnum;
                        
                        // don't add "killed" blocks
                        if (number == (off_t)-1) {
                                //printf("jnl: replay_journal: skipping killed fs block (index %d)\n", i);
                        } else {

                                if (check_block_checksums) {
                                        int32_t disk_cksum;
                                        off_t block_offset;

                                        block_offset = offset;

                                        // read the block so we can check the checksum
                                        ret = read_journal_data(jnl, &block_offset, block_ptr, size);
                                        if (ret != (size_t)size) {
                                                printf("jnl: %s: replay_journal: Could not read journal entry data @ offset 0x%llx!\n", jnl->jdev_name, offset);
                                                bad_blocks = 1;
                                                goto bad_txn_handling;
                                        }
                                
                                        disk_cksum = calc_checksum(block_ptr, size);

                                        // there is no need to swap the checksum from disk because
                                        // it got swapped when the blhdr was read in.
                                        if (blhdr->binfo[i].u.bi.b.cksum != 0 && disk_cksum != blhdr->binfo[i].u.bi.b.cksum) {
                                                printf("jnl: %s: txn starting at %lld (%lld) @ index %3d bnum %lld (%d) with disk cksum != blhdr cksum (0x%.8x 0x%.8x)\n",
                                                       jnl->jdev_name, txn_start_offset, blhdr_offset, i, number, size, disk_cksum, blhdr->binfo[i].u.bi.b.cksum);
                                                printf("jnl: 0x%.8x 0x%.8x 0x%.8x 0x%.8x  0x%.8x 0x%.8x 0x%.8x 0x%.8x\n",
                                                       *(int *)&block_ptr[0*sizeof(int)], *(int *)&block_ptr[1*sizeof(int)], *(int *)&block_ptr[2*sizeof(int)], *(int *)&block_ptr[3*sizeof(int)],
                                                       *(int *)&block_ptr[4*sizeof(int)], *(int *)&block_ptr[5*sizeof(int)], *(int *)&block_ptr[6*sizeof(int)], *(int *)&block_ptr[7*sizeof(int)]);

                                                bad_blocks = 1;
                                                goto bad_txn_handling;
                                        }
                                }


                                // add this bucket to co_buf, coalescing where possible
                                // printf("jnl: replay_journal: adding block 0x%llx\n", number);
                                ret_val = add_block(jnl, &co_buf, number, size, (size_t) offset, blhdr->binfo[i].u.bi.b.cksum, &num_buckets, &num_full);
                            
                                if (ret_val == -1) {
                                        printf("jnl: %s: replay_journal: trouble adding block to co_buf\n", jnl->jdev_name);
                                        goto bad_replay;
                                } // else printf("jnl: replay_journal: added block 0x%llx at i=%d\n", number);
                        }
                        
                        // increment offset
                        offset += size;
                        
                        // check if the last block added puts us off the end of the jnl.
                        // if so, we need to wrap to the beginning and take any remainder
                        // into account
                        //
                        if (offset >= jnl->jhdr->size) {
                                offset = jnl->jhdr->jhdr_size + (offset - jnl->jhdr->size);
                        }
                }

                if (block_ptr) {
                        kmem_free(kernel_map, (vm_offset_t)block_ptr, max_bsize);
                        block_ptr = NULL;
                }
                
bad_txn_handling:
                if (bad_blocks) {
                        /* Journal replay got error before it found any valid 
                         *  transations, abort replay */
                        if (txn_start_offset == 0) {
                                printf("jnl: %s: no known good txn start offset! aborting journal replay.\n", jnl->jdev_name);
                                goto bad_replay;
                        }

                        /* Repeated error during journal replay, abort replay */
                        if (replay_retry_count == 3) {
                                printf("jnl: %s: repeated errors replaying journal! aborting journal replay.\n", jnl->jdev_name);
                                goto bad_replay;
                        }
                        replay_retry_count++;

                        /* There was an error replaying the journal (possibly 
                         * EIO/ENXIO from the device).  So retry replaying all 
                         * the good transactions that we found before getting 
                         * the error.  
                         */
                        jnl->jhdr->start = orig_jnl_start;
                        jnl->jhdr->end = txn_start_offset;
                        check_past_jnl_end = 0;
                        last_sequence_num = 0;
                        printf("jnl: %s: restarting journal replay (%lld - %lld)!\n", jnl->jdev_name, jnl->jhdr->start, jnl->jhdr->end);
                        goto restart_replay;
                }

                jnl->jhdr->start += blhdr->bytes_used;
                if (jnl->jhdr->start >= jnl->jhdr->size) {
                        // wrap around and skip the journal header block
                        jnl->jhdr->start = (jnl->jhdr->start % jnl->jhdr->size) + jnl->jhdr->jhdr_size;
                }

                if (jnl->jhdr->start == jnl->jhdr->end) {
                        in_uncharted_territory = 1;
                }
        }

        if (jnl->jhdr->start != jnl->jhdr->end) {
                printf("jnl: %s: start %lld != end %lld.  resetting end.\n", jnl->jdev_name, jnl->jhdr->start, jnl->jhdr->end);
                jnl->jhdr->end = jnl->jhdr->start;
        }

        //printf("jnl: replay_journal: replaying %d blocks\n", num_full);
    
        /*
         * make sure it's at least one page in size, so
         * start max_bsize at PAGE_SIZE
         */
        for (i = 0, max_bsize = PAGE_SIZE; i < num_full; i++) {

                if (co_buf[i].block_num == (off_t)-1)
                        continue;

                if (co_buf[i].block_size > max_bsize)
                        max_bsize = co_buf[i].block_size;
        }
        /*
         * round max_bsize up to the nearest PAGE_SIZE multiple
         */
        if (max_bsize & (PAGE_SIZE - 1)) {
                max_bsize = (max_bsize + PAGE_SIZE) & ~(PAGE_SIZE - 1);
        }

        if (kmem_alloc(kernel_map, (vm_offset_t *)&block_ptr, max_bsize)) {
                goto bad_replay;
        }
    
        // Replay the coalesced entries in the co-buf
        for(i = 0; i < num_full; i++) {
                size_t size = co_buf[i].block_size;
                off_t jnl_offset = (off_t) co_buf[i].jnl_offset;
                off_t number = co_buf[i].block_num;
        
        
                // printf("replaying co_buf[%d]: block 0x%llx, size 0x%x, jnl_offset 0x%llx\n", i, co_buf[i].block_num,
                //      co_buf[i].block_size, co_buf[i].jnl_offset);
        
                if (number == (off_t)-1) {
                        // printf("jnl: replay_journal: skipping killed fs block\n");
                } else {
            
                        // do journal read, and set the phys. block 
                        ret = read_journal_data(jnl, &jnl_offset, block_ptr, size);
                        if (ret != size) {
                                printf("jnl: %s: replay_journal: Could not read journal entry data @ offset 0x%llx!\n", jnl->jdev_name, offset);
                                goto bad_replay;
                        }
                    
                        if (update_fs_block(jnl, block_ptr, number, size) != 0) {
                                goto bad_replay;
                        }
                }
        }
    
        
        // done replaying; update jnl header
        if (write_journal_header(jnl, 1, jnl->jhdr->sequence_num) != 0) {
                goto bad_replay;
        }

        printf("jnl: %s: journal replay done.\n", jnl->jdev_name);
    
        // free block_ptr
        if (block_ptr) {
                kmem_free(kernel_map, (vm_offset_t)block_ptr, max_bsize);
                block_ptr = NULL;
        }
    
        // free the coalesce buffer
        FREE(co_buf, M_TEMP);
        co_buf = NULL;
  
        kmem_free(kernel_map, (vm_offset_t)buff, jnl->jhdr->blhdr_size);
        return 0;

bad_replay:
        if (block_ptr) {
                kmem_free(kernel_map, (vm_offset_t)block_ptr, max_bsize);
        }
        if (co_buf) {
                FREE(co_buf, M_TEMP);
        }
        kmem_free(kernel_map, (vm_offset_t)buff, jnl->jhdr->blhdr_size);

        return -1;
}


#define DEFAULT_TRANSACTION_BUFFER_SIZE  (128*1024)
#define MAX_TRANSACTION_BUFFER_SIZE      (2048*1024)

// XXXdbg - so I can change it in the debugger
int def_tbuffer_size = 0;


//
// This function sets the size of the tbuffer and the
// size of the blhdr.  It assumes that jnl->jhdr->size
// and jnl->jhdr->jhdr_size are already valid.
//
static void
size_up_tbuffer(journal *jnl, int tbuffer_size, int phys_blksz)
{
        //
        // one-time initialization based on how much memory 
        // there is in the machine.
        //
        if (def_tbuffer_size == 0) {
                if (mem_size < (256*1024*1024)) {
                        def_tbuffer_size = DEFAULT_TRANSACTION_BUFFER_SIZE;
                } else if (mem_size < (512*1024*1024)) {
                        def_tbuffer_size = DEFAULT_TRANSACTION_BUFFER_SIZE * 2;
                } else if (mem_size < (1024*1024*1024)) {
                        def_tbuffer_size = DEFAULT_TRANSACTION_BUFFER_SIZE * 3;
                } else {
                        def_tbuffer_size = DEFAULT_TRANSACTION_BUFFER_SIZE * (mem_size / (256*1024*1024));
                }
        }

        // size up the transaction buffer... can't be larger than the number
        // of blocks that can fit in a block_list_header block.
        if (tbuffer_size == 0) {
                jnl->tbuffer_size = def_tbuffer_size;
        } else {
                // make sure that the specified tbuffer_size isn't too small
                if (tbuffer_size < jnl->jhdr->blhdr_size * 2) {
                        tbuffer_size = jnl->jhdr->blhdr_size * 2;
                }
                // and make sure it's an even multiple of the block size
                if ((tbuffer_size % jnl->jhdr->jhdr_size) != 0) {
                        tbuffer_size -= (tbuffer_size % jnl->jhdr->jhdr_size);
                }

                jnl->tbuffer_size = tbuffer_size;
        }

        if (jnl->tbuffer_size > (jnl->jhdr->size / 2)) {
                jnl->tbuffer_size = (jnl->jhdr->size / 2);
        }
    
        if (jnl->tbuffer_size > MAX_TRANSACTION_BUFFER_SIZE) {
                jnl->tbuffer_size = MAX_TRANSACTION_BUFFER_SIZE;
        }

        jnl->jhdr->blhdr_size = (jnl->tbuffer_size / jnl->jhdr->jhdr_size) * sizeof(block_info);
        if (jnl->jhdr->blhdr_size < phys_blksz) {
                jnl->jhdr->blhdr_size = phys_blksz;
        } else if ((jnl->jhdr->blhdr_size % phys_blksz) != 0) {
                // have to round up so we're an even multiple of the physical block size
                jnl->jhdr->blhdr_size = (jnl->jhdr->blhdr_size + (phys_blksz - 1)) & ~(phys_blksz - 1);
        }
}



static void
get_io_info(struct vnode *devvp, size_t phys_blksz, journal *jnl, struct vfs_context *context)
{
        off_t   readblockcnt;
        off_t   writeblockcnt;
        off_t   readmaxcnt=0, tmp_readmaxcnt;
        off_t   writemaxcnt=0, tmp_writemaxcnt;
        off_t   readsegcnt, writesegcnt;
        int32_t features;

        if (VNOP_IOCTL(devvp, DKIOCGETFEATURES, (caddr_t)&features, 0, context) == 0) {
                if (features & DK_FEATURE_FORCE_UNIT_ACCESS) {
                        const char *name = vnode_getname_printable(devvp);
                        jnl->flags |= JOURNAL_DO_FUA_WRITES;
                        printf("jnl: %s: enabling FUA writes (features 0x%x)\n", name, features);
                        vnode_putname_printable(name);
                }
                if (features & DK_FEATURE_UNMAP) {
                        jnl->flags |= JOURNAL_USE_UNMAP;
                }
        }

        //
        // First check the max read size via several different mechanisms...
        //
        VNOP_IOCTL(devvp, DKIOCGETMAXBYTECOUNTREAD, (caddr_t)&readmaxcnt, 0, context);

        if (VNOP_IOCTL(devvp, DKIOCGETMAXBLOCKCOUNTREAD, (caddr_t)&readblockcnt, 0, context) == 0) {
                tmp_readmaxcnt = readblockcnt * phys_blksz;
                if (readmaxcnt == 0 || (readblockcnt > 0 && tmp_readmaxcnt < readmaxcnt)) {
                        readmaxcnt = tmp_readmaxcnt;
                }
        }

        if (VNOP_IOCTL(devvp, DKIOCGETMAXSEGMENTCOUNTREAD, (caddr_t)&readsegcnt, 0, context)) {
                readsegcnt = 0;
        }

        if (readsegcnt > 0 && (readsegcnt * PAGE_SIZE) < readmaxcnt) {
                readmaxcnt = readsegcnt * PAGE_SIZE;
        }
            
        if (readmaxcnt == 0) {
                readmaxcnt = 128 * 1024;
        } else if (readmaxcnt > UINT32_MAX) {
                readmaxcnt = UINT32_MAX;
        }


        //
        // Now check the max writes size via several different mechanisms...
        //
        VNOP_IOCTL(devvp, DKIOCGETMAXBYTECOUNTWRITE, (caddr_t)&writemaxcnt, 0, context);

        if (VNOP_IOCTL(devvp, DKIOCGETMAXBLOCKCOUNTWRITE, (caddr_t)&writeblockcnt, 0, context) == 0) {
                tmp_writemaxcnt = writeblockcnt * phys_blksz;
                if (writemaxcnt == 0 || (writeblockcnt > 0 && tmp_writemaxcnt < writemaxcnt)) {
                        writemaxcnt = tmp_writemaxcnt;
                }
        }

        if (VNOP_IOCTL(devvp, DKIOCGETMAXSEGMENTCOUNTWRITE,     (caddr_t)&writesegcnt, 0, context)) {
                writesegcnt = 0;
        }

        if (writesegcnt > 0 && (writesegcnt * PAGE_SIZE) < writemaxcnt) {
                writemaxcnt = writesegcnt * PAGE_SIZE;
        }

        if (writemaxcnt == 0) {
                writemaxcnt = 128 * 1024;
        } else if (writemaxcnt > UINT32_MAX) {
                writemaxcnt = UINT32_MAX;
        }

        jnl->max_read_size  = readmaxcnt;
        jnl->max_write_size = writemaxcnt;
        // printf("jnl: %s: max read/write: %lld k / %lld k\n",
        //     jnl->jdev_name ? jnl->jdev_name : "unknown",
        //     jnl->max_read_size/1024, jnl->max_write_size/1024);
}


journal *
journal_create(struct vnode *jvp,
                           off_t         offset,
                           off_t         journal_size,
                           struct vnode *fsvp,
                           size_t        min_fs_blksz,
                           int32_t       flags,
                           int32_t       tbuffer_size,
                           void        (*flush)(void *arg),
                           void         *arg,
                           struct mount *fsmount)
{
        journal         *jnl;
        uint32_t        phys_blksz, new_txn_base;
        u_int32_t       min_size;
        struct vfs_context context;
        const char      *jdev_name;
        /* 
         * Cap the journal max size to 2GB.  On HFS, it will attempt to occupy
         * a full allocation block if the current size is smaller than the allocation
         * block on which it resides.  Once we hit the exabyte filesystem range, then
         * it will use 2GB allocation blocks.  As a result, make the cap 2GB.
         */
        context.vc_thread = current_thread();
        context.vc_ucred = FSCRED;

        jdev_name = vnode_getname_printable(jvp);

        /* Get the real physical block size. */
        if (VNOP_IOCTL(jvp, DKIOCGETBLOCKSIZE, (caddr_t)&phys_blksz, 0, &context)) {
                goto cleanup_jdev_name;
        }

        if (journal_size < (256*1024) || journal_size > (MAX_JOURNAL_SIZE)) {
                printf("jnl: %s: create: journal size %lld looks bogus.\n", jdev_name, journal_size);
                goto cleanup_jdev_name;
        }

        min_size = phys_blksz * (phys_blksz / sizeof(block_info));
        /* Reject journals that are too small given the sector size of the device */
        if (journal_size < min_size) {
                printf("jnl: %s: create: journal size (%lld) too small given sector size of (%u)\n", 
                                jdev_name, journal_size, phys_blksz);
                goto cleanup_jdev_name;
        }

        if (phys_blksz > min_fs_blksz) {
                printf("jnl: %s: create: error: phys blksize %u bigger than min fs blksize %zd\n",
                       jdev_name, phys_blksz, min_fs_blksz);
                goto cleanup_jdev_name;
        }

        if ((journal_size % phys_blksz) != 0) {
                printf("jnl: %s: create: journal size 0x%llx is not an even multiple of block size 0x%ux\n",
                       jdev_name, journal_size, phys_blksz);
                goto cleanup_jdev_name;
        }


        MALLOC_ZONE(jnl, struct journal *, sizeof(struct journal), M_JNL_JNL, M_WAITOK);
        memset(jnl, 0, sizeof(*jnl));

        jnl->jdev         = jvp;
        jnl->jdev_offset  = offset;
        jnl->fsdev        = fsvp;
        jnl->flush        = flush;
        jnl->flush_arg    = arg;
        jnl->flags        = (flags & JOURNAL_OPTION_FLAGS_MASK);
        jnl->jdev_name    = jdev_name;
        lck_mtx_init(&jnl->old_start_lock, jnl_mutex_group, jnl_lock_attr);

        // Keep a point to the mount around for use in IO throttling.
        jnl->fsmount      = fsmount;
        // XXX: This lock discipline looks correct based on dounmount(), but it
        // doesn't seem to be documented anywhere.
        mount_ref(fsmount, 0);

        get_io_info(jvp, phys_blksz, jnl, &context);
        
        if (kmem_alloc_kobject(kernel_map, (vm_offset_t *)&jnl->header_buf, phys_blksz)) {
                printf("jnl: %s: create: could not allocate space for header buffer (%u bytes)\n", jdev_name, phys_blksz);
                goto bad_kmem_alloc;
        }
        jnl->header_buf_size = phys_blksz;

        jnl->jhdr = (journal_header *)jnl->header_buf;
        memset(jnl->jhdr, 0, sizeof(journal_header));

        // we have to set this up here so that do_journal_io() will work
        jnl->jhdr->jhdr_size = phys_blksz;

        //
        // We try and read the journal header to see if there is already one
        // out there.  If there is, it's possible that it has transactions
        // in it that we might replay if we happen to pick a sequence number
        // that is a little less than the old one, there is a crash and the 
        // last txn written ends right at the start of a txn from the previous
        // incarnation of this file system.  If all that happens we would
        // replay the transactions from the old file system and that would
        // destroy your disk.  Although it is extremely unlikely for all those
        // conditions to happen, the probability is non-zero and the result is
        // severe - you lose your file system.  Therefore if we find a valid
        // journal header and the sequence number is non-zero we write junk
        // over the entire journal so that there is no way we will encounter
        // any old transactions.  This is slow but should be a rare event
        // since most tools erase the journal.
        //
        if (   read_journal_header(jnl, jnl->jhdr, phys_blksz) == phys_blksz
               && jnl->jhdr->magic == JOURNAL_HEADER_MAGIC
               && jnl->jhdr->sequence_num != 0) {

                new_txn_base = (jnl->jhdr->sequence_num + (journal_size / phys_blksz) + (random() % 16384)) & 0x00ffffff;
                printf("jnl: %s: create: avoiding old sequence number 0x%x (0x%x)\n", jdev_name, jnl->jhdr->sequence_num, new_txn_base);

#if 0
                int i;
                off_t pos=0;

                for(i = 1; i < journal_size / phys_blksz; i++) {
                        pos = i*phys_blksz;

                        // we don't really care what data we write just so long
                        // as it's not a valid transaction header.  since we have
                        // the header_buf sitting around we'll use that.
                        write_journal_data(jnl, &pos, jnl->header_buf, phys_blksz);
                }
                printf("jnl: create: done clearing journal (i=%d)\n", i);
#endif
        } else {
                new_txn_base = random() & 0x00ffffff;
        }

        memset(jnl->header_buf, 0, phys_blksz);
    
        jnl->jhdr->magic      = JOURNAL_HEADER_MAGIC;
        jnl->jhdr->endian     = ENDIAN_MAGIC;
        jnl->jhdr->start      = phys_blksz;    // start at block #1, block #0 is for the jhdr itself
        jnl->jhdr->end        = phys_blksz;
        jnl->jhdr->size       = journal_size;
        jnl->jhdr->jhdr_size  = phys_blksz;
        size_up_tbuffer(jnl, tbuffer_size, phys_blksz);

        jnl->active_start     = jnl->jhdr->start;

        // XXXdbg  - for testing you can force the journal to wrap around
        // jnl->jhdr->start = jnl->jhdr->size - (phys_blksz*3);
        // jnl->jhdr->end   = jnl->jhdr->size - (phys_blksz*3);
    
        jnl->jhdr->sequence_num = new_txn_base;

        lck_mtx_init(&jnl->jlock, jnl_mutex_group, jnl_lock_attr);
        lck_mtx_init(&jnl->flock, jnl_mutex_group, jnl_lock_attr);
        lck_rw_init(&jnl->trim_lock, jnl_mutex_group, jnl_lock_attr);


        jnl->flushing = FALSE;
        jnl->asyncIO = FALSE;
        jnl->flush_aborted = FALSE;
        jnl->writing_header = FALSE;
        jnl->async_trim = NULL;
        jnl->sequence_num = jnl->jhdr->sequence_num;
        
        if (write_journal_header(jnl, 1, jnl->jhdr->sequence_num) != 0) {
                printf("jnl: %s: journal_create: failed to write journal header.\n", jdev_name);
                goto bad_write;
        }

        goto journal_create_complete;


bad_write:
        kmem_free(kernel_map, (vm_offset_t)jnl->header_buf, phys_blksz);
bad_kmem_alloc:
        jnl->jhdr = NULL;
        FREE_ZONE(jnl, sizeof(struct journal), M_JNL_JNL);
        mount_drop(fsmount, 0);
cleanup_jdev_name:
        vnode_putname_printable(jdev_name);
        jnl = NULL;
journal_create_complete:
        return jnl;
}


journal *
journal_open(struct vnode *jvp,
                         off_t         offset,
                         off_t         journal_size,
                         struct vnode *fsvp,
                         size_t        min_fs_blksz,
                         int32_t       flags,
                         int32_t       tbuffer_size,
                         void        (*flush)(void *arg),
                         void         *arg,
                         struct mount *fsmount)
{
        journal         *jnl;
        uint32_t        orig_blksz=0;
        uint32_t        phys_blksz;
        u_int32_t       min_size = 0;
        int             orig_checksum, checksum;
        struct vfs_context context;
        const char      *jdev_name = vnode_getname_printable(jvp);

        context.vc_thread = current_thread();
        context.vc_ucred = FSCRED;

        /* Get the real physical block size. */
        if (VNOP_IOCTL(jvp, DKIOCGETBLOCKSIZE, (caddr_t)&phys_blksz, 0, &context)) {
                goto cleanup_jdev_name;
        }

        if (phys_blksz > min_fs_blksz) {
                printf("jnl: %s: open: error: phys blksize %u bigger than min fs blksize %zd\n",
                       jdev_name, phys_blksz, min_fs_blksz);
                goto cleanup_jdev_name;
        }

        if (journal_size < (256*1024) || journal_size > (1024*1024*1024)) {
                printf("jnl: %s: open: journal size %lld looks bogus.\n", jdev_name, journal_size);
                goto cleanup_jdev_name;
        }

        min_size = phys_blksz * (phys_blksz / sizeof(block_info));
        /* Reject journals that are too small given the sector size of the device */
        if (journal_size < min_size) {
                printf("jnl: %s: open: journal size (%lld) too small given sector size of (%u)\n", 
                                jdev_name, journal_size, phys_blksz);
                goto cleanup_jdev_name;
        }
    
        if ((journal_size % phys_blksz) != 0) {
                printf("jnl: %s: open: journal size 0x%llx is not an even multiple of block size 0x%x\n",
                       jdev_name, journal_size, phys_blksz);
                goto cleanup_jdev_name;
        }

        MALLOC_ZONE(jnl, struct journal *, sizeof(struct journal), M_JNL_JNL, M_WAITOK);
        memset(jnl, 0, sizeof(*jnl));

        jnl->jdev         = jvp;
        jnl->jdev_offset  = offset;
        jnl->fsdev        = fsvp;
        jnl->flush        = flush;
        jnl->flush_arg    = arg;
        jnl->flags        = (flags & JOURNAL_OPTION_FLAGS_MASK);
        jnl->jdev_name    = jdev_name;
        lck_mtx_init(&jnl->old_start_lock, jnl_mutex_group, jnl_lock_attr);

        /* We need a reference to the mount to later pass to the throttling code for
         * IO accounting.
         */
        jnl->fsmount      = fsmount;
        mount_ref(fsmount, 0);

        get_io_info(jvp, phys_blksz, jnl, &context);

        if (kmem_alloc_kobject(kernel_map, (vm_offset_t *)&jnl->header_buf, phys_blksz)) {
                printf("jnl: %s: create: could not allocate space for header buffer (%u bytes)\n", jdev_name, phys_blksz);
                goto bad_kmem_alloc;
        }
        jnl->header_buf_size = phys_blksz;

        jnl->jhdr = (journal_header *)jnl->header_buf;
        memset(jnl->jhdr, 0, sizeof(journal_header));

        // we have to set this up here so that do_journal_io() will work
        jnl->jhdr->jhdr_size = phys_blksz;

        if (read_journal_header(jnl, jnl->jhdr, phys_blksz) != phys_blksz) {
                printf("jnl: %s: open: could not read %u bytes for the journal header.\n",
                       jdev_name, phys_blksz);
                goto bad_journal;
        }

        orig_checksum = jnl->jhdr->checksum;
        jnl->jhdr->checksum = 0;

        if (jnl->jhdr->magic == SWAP32(JOURNAL_HEADER_MAGIC)) {
                // do this before the swap since it's done byte-at-a-time
                orig_checksum = SWAP32(orig_checksum);
                checksum = calc_checksum((char *)jnl->jhdr, JOURNAL_HEADER_CKSUM_SIZE);
                swap_journal_header(jnl);
                jnl->flags |= JOURNAL_NEED_SWAP;
        } else {
                checksum = calc_checksum((char *)jnl->jhdr, JOURNAL_HEADER_CKSUM_SIZE);
        }

        if (jnl->jhdr->magic != JOURNAL_HEADER_MAGIC && jnl->jhdr->magic != OLD_JOURNAL_HEADER_MAGIC) {
                printf("jnl: %s: open: journal magic is bad (0x%x != 0x%x)\n",
                       jnl->jdev_name, jnl->jhdr->magic, JOURNAL_HEADER_MAGIC);
                goto bad_journal;
        }

        // only check if we're the current journal header magic value
        if (jnl->jhdr->magic == JOURNAL_HEADER_MAGIC) {

                if (orig_checksum != checksum) {
                        printf("jnl: %s: open: journal checksum is bad (0x%x != 0x%x)\n",
                               jdev_name, orig_checksum, checksum);
                                   
                        //goto bad_journal;
                }
        }

        // XXXdbg - convert old style magic numbers to the new one
        if (jnl->jhdr->magic == OLD_JOURNAL_HEADER_MAGIC) {
                jnl->jhdr->magic = JOURNAL_HEADER_MAGIC;
        }

        if (phys_blksz != (size_t)jnl->jhdr->jhdr_size && jnl->jhdr->jhdr_size != 0) {
                /*
                 * The volume has probably been resized (such that we had to adjust the
                 * logical sector size), or copied to media with a different logical
                 * sector size.
                 * 
                 * Temporarily change the device's logical block size to match the
                 * journal's header size.  This will allow us to replay the journal
                 * safely.  If the replay succeeds, we will update the journal's header
                 * size (later in this function).
                 */
                orig_blksz = phys_blksz;
                phys_blksz = jnl->jhdr->jhdr_size;
                VNOP_IOCTL(jvp, DKIOCSETBLOCKSIZE, (caddr_t)&phys_blksz, FWRITE, &context);
                printf("jnl: %s: open: temporarily switched block size from %u to %u\n",
                           jdev_name, orig_blksz, phys_blksz);
        }

        if (   jnl->jhdr->start <= 0
               || jnl->jhdr->start > jnl->jhdr->size
               || jnl->jhdr->start > 1024*1024*1024) {
                printf("jnl: %s: open: jhdr start looks bad (0x%llx max size 0x%llx)\n",
                       jdev_name, jnl->jhdr->start, jnl->jhdr->size);
                goto bad_journal;
        }

        if (   jnl->jhdr->end <= 0
               || jnl->jhdr->end > jnl->jhdr->size
               || jnl->jhdr->end > 1024*1024*1024) {
                printf("jnl: %s: open: jhdr end looks bad (0x%llx max size 0x%llx)\n",
                       jdev_name, jnl->jhdr->end, jnl->jhdr->size);
                goto bad_journal;
        }

        if (jnl->jhdr->size < (256*1024) || jnl->jhdr->size > 1024*1024*1024) {
                printf("jnl: %s: open: jhdr size looks bad (0x%llx)\n", jdev_name, jnl->jhdr->size);
                goto bad_journal;
        }

// XXXdbg - can't do these checks because hfs writes all kinds of
//          non-uniform sized blocks even on devices that have a block size
//          that is larger than 512 bytes (i.e. optical media w/2k blocks).
//          therefore these checks will fail and so we just have to punt and
//          do more relaxed checking...
// XXXdbg    if ((jnl->jhdr->start % jnl->jhdr->jhdr_size) != 0) {
        if ((jnl->jhdr->start % 512) != 0) {
                printf("jnl: %s: open: journal start (0x%llx) not a multiple of 512?\n",
                       jdev_name, jnl->jhdr->start);
                goto bad_journal;
        }

//XXXdbg    if ((jnl->jhdr->end % jnl->jhdr->jhdr_size) != 0) {
        if ((jnl->jhdr->end % 512) != 0) {
                printf("jnl: %s: open: journal end (0x%llx) not a multiple of block size (0x%x)?\n",
                       jdev_name, jnl->jhdr->end, jnl->jhdr->jhdr_size);
                goto bad_journal;
        }

        // take care of replaying the journal if necessary
        if (flags & JOURNAL_RESET) {
                printf("jnl: %s: journal start/end pointers reset! (jnl %p; s 0x%llx e 0x%llx)\n",
                       jdev_name, jnl, jnl->jhdr->start, jnl->jhdr->end);
                jnl->jhdr->start = jnl->jhdr->end;
        } else if (replay_journal(jnl) != 0) {
                printf("jnl: %s: journal_open: Error replaying the journal!\n", jdev_name);
                goto bad_journal;
        }
        
        /*
         * When we get here, we know that the journal is empty (jnl->jhdr->start ==
         * jnl->jhdr->end).  If the device's logical block size was different from
         * the journal's header size, then we can now restore the device's logical
         * block size and update the journal's header size to match.
         *
         * Note that we also adjust the journal's start and end so that they will
         * be aligned on the new block size.  We pick a new sequence number to
         * avoid any problems if a replay found previous transactions using the old
         * journal header size.  (See the comments in journal_create(), above.)
         */
        
        if (orig_blksz != 0) {
                VNOP_IOCTL(jvp, DKIOCSETBLOCKSIZE, (caddr_t)&orig_blksz, FWRITE, &context);
                phys_blksz = orig_blksz;
                
                orig_blksz = 0;
                
                jnl->jhdr->jhdr_size = phys_blksz;
                jnl->jhdr->start = phys_blksz;
                jnl->jhdr->end = phys_blksz;
                jnl->jhdr->sequence_num = (jnl->jhdr->sequence_num +
                                                                   (journal_size / phys_blksz) +
                                                                   (random() % 16384)) & 0x00ffffff;
                
                if (write_journal_header(jnl, 1, jnl->jhdr->sequence_num)) {
                        printf("jnl: %s: open: failed to update journal header size\n", jdev_name);
                        goto bad_journal;
                }
        }

        // make sure this is in sync!
        jnl->active_start = jnl->jhdr->start;
        jnl->sequence_num = jnl->jhdr->sequence_num;

        // set this now, after we've replayed the journal
        size_up_tbuffer(jnl, tbuffer_size, phys_blksz);

        // TODO: Does this need to change if the device's logical block size changed?
        if ((off_t)(jnl->jhdr->blhdr_size/sizeof(block_info)-1) > (jnl->jhdr->size/jnl->jhdr->jhdr_size)) {
                printf("jnl: %s: open: jhdr size and blhdr size are not compatible (0x%llx, %d, %d)\n", jdev_name, jnl->jhdr->size,
                       jnl->jhdr->blhdr_size, jnl->jhdr->jhdr_size);
                goto bad_journal;
        }

        lck_mtx_init(&jnl->jlock, jnl_mutex_group, jnl_lock_attr);
        lck_mtx_init(&jnl->flock, jnl_mutex_group, jnl_lock_attr);
        lck_rw_init(&jnl->trim_lock, jnl_mutex_group, jnl_lock_attr);

        goto journal_open_complete;

bad_journal:
        if (orig_blksz != 0) {
                phys_blksz = orig_blksz;
                VNOP_IOCTL(jvp, DKIOCSETBLOCKSIZE, (caddr_t)&orig_blksz, FWRITE, &context);
                printf("jnl: %s: open: restored block size after error\n", jdev_name);
        }
        kmem_free(kernel_map, (vm_offset_t)jnl->header_buf, phys_blksz);
bad_kmem_alloc:
        FREE_ZONE(jnl, sizeof(struct journal), M_JNL_JNL);
        mount_drop(fsmount, 0);
cleanup_jdev_name:
        vnode_putname_printable(jdev_name);
        jnl = NULL;
journal_open_complete:
        return jnl;    
}


int
journal_is_clean(struct vnode *jvp,
                 off_t         offset,
                 off_t         journal_size,
                 struct vnode *fsvp,
                 size_t        min_fs_block_size)
{
        journal         jnl;
        uint32_t        phys_blksz;
        int             ret;
        int             orig_checksum, checksum;
        struct vfs_context context;
        const           char *jdev_name = vnode_getname_printable(jvp);

        context.vc_thread = current_thread();
        context.vc_ucred = FSCRED;

        /* Get the real physical block size. */
        if (VNOP_IOCTL(jvp, DKIOCGETBLOCKSIZE, (caddr_t)&phys_blksz, 0, &context)) {
                printf("jnl: %s: is_clean: failed to get device block size.\n", jdev_name);
                ret = EINVAL;
                goto cleanup_jdev_name;
        }

        if (phys_blksz > (uint32_t)min_fs_block_size) {
                printf("jnl: %s: is_clean: error: phys blksize %d bigger than min fs blksize %zd\n",
                       jdev_name, phys_blksz, min_fs_block_size);
                ret = EINVAL;
                goto cleanup_jdev_name;
        }

        if (journal_size < (256*1024) || journal_size > (MAX_JOURNAL_SIZE)) {
                printf("jnl: %s: is_clean: journal size %lld looks bogus.\n", jdev_name, journal_size);
                ret = EINVAL;
                goto cleanup_jdev_name;
        }
    
        if ((journal_size % phys_blksz) != 0) {
                printf("jnl: %s: is_clean: journal size 0x%llx is not an even multiple of block size 0x%x\n",
                       jdev_name, journal_size, phys_blksz);
                ret = EINVAL;
                goto cleanup_jdev_name;
        }

        memset(&jnl, 0, sizeof(jnl));

        if (kmem_alloc_kobject(kernel_map, (vm_offset_t *)&jnl.header_buf, phys_blksz)) {
                printf("jnl: %s: is_clean: could not allocate space for header buffer (%d bytes)\n", jdev_name, phys_blksz);
                ret = ENOMEM;
                goto cleanup_jdev_name;
        }
        jnl.header_buf_size = phys_blksz;

        get_io_info(jvp, phys_blksz, &jnl, &context);
    
        jnl.jhdr = (journal_header *)jnl.header_buf;
        memset(jnl.jhdr, 0, sizeof(journal_header));

        jnl.jdev        = jvp;
        jnl.jdev_offset = offset;
        jnl.fsdev       = fsvp;

        // we have to set this up here so that do_journal_io() will work
        jnl.jhdr->jhdr_size = phys_blksz;

        if (read_journal_header(&jnl, jnl.jhdr, phys_blksz) != (unsigned)phys_blksz) {
                printf("jnl: %s: is_clean: could not read %d bytes for the journal header.\n",
                       jdev_name, phys_blksz);
                ret = EINVAL;
                goto get_out;
        }

        orig_checksum = jnl.jhdr->checksum;
        jnl.jhdr->checksum = 0;

        if (jnl.jhdr->magic == SWAP32(JOURNAL_HEADER_MAGIC)) {
                // do this before the swap since it's done byte-at-a-time
                orig_checksum = SWAP32(orig_checksum);
                checksum = calc_checksum((char *)jnl.jhdr, JOURNAL_HEADER_CKSUM_SIZE);
                swap_journal_header(&jnl);
                jnl.flags |= JOURNAL_NEED_SWAP;
        } else {
                checksum = calc_checksum((char *)jnl.jhdr, JOURNAL_HEADER_CKSUM_SIZE);
        }

        if (jnl.jhdr->magic != JOURNAL_HEADER_MAGIC && jnl.jhdr->magic != OLD_JOURNAL_HEADER_MAGIC) {
                printf("jnl: %s: is_clean: journal magic is bad (0x%x != 0x%x)\n",
                       jdev_name, jnl.jhdr->magic, JOURNAL_HEADER_MAGIC);
                ret = EINVAL;
                goto get_out;
        }

        if (orig_checksum != checksum) {
                printf("jnl: %s: is_clean: journal checksum is bad (0x%x != 0x%x)\n", jdev_name, orig_checksum, checksum);
                ret = EINVAL;
                goto get_out;
        }

        //
        // if the start and end are equal then the journal is clean.
        // otherwise it's not clean and therefore an error.
        //
        if (jnl.jhdr->start == jnl.jhdr->end) {
                ret = 0;
        } else {
                ret = EBUSY;    // so the caller can differentiate an invalid journal from a "busy" one
        }

get_out:
        kmem_free(kernel_map, (vm_offset_t)jnl.header_buf, phys_blksz);
cleanup_jdev_name:
        vnode_putname_printable(jdev_name);
        return ret;
}


void
journal_close(journal *jnl)
{
        volatile off_t *start, *end;
        int             counter=0;

        CHECK_JOURNAL(jnl);

        // set this before doing anything that would block so that
        // we start tearing things down properly.
        //
        jnl->flags |= JOURNAL_CLOSE_PENDING;

        if (jnl->owner != current_thread()) {
                lock_journal(jnl);
        }

        wait_condition(jnl, &jnl->flushing, "journal_close");

        //
        // only write stuff to disk if the journal is still valid
        //
        if ((jnl->flags & JOURNAL_INVALID) == 0) {

                if (jnl->active_tr) {
                        /*
                         * "journal_end_transaction" will fire the flush asynchronously
                         */
                        journal_end_transaction(jnl);
                }
                
                // flush any buffered transactions
                if (jnl->cur_tr) {
                        transaction *tr = jnl->cur_tr;

                        jnl->cur_tr = NULL;
                        /*
                         * "end_transaction" will wait for any in-progress flush to complete
                         * before flushing "cur_tr" synchronously("must_wait" == TRUE)
                         */
                        end_transaction(tr, 1, NULL, NULL, FALSE, TRUE);
                }
                /*
                 * if there was an "active_tr", make sure we wait for
                 * it to flush if there was no "cur_tr" to process
                 */
                wait_condition(jnl, &jnl->flushing, "journal_close");
    
                //start = &jnl->jhdr->start;
                start = &jnl->active_start;
                end   = &jnl->jhdr->end;
    
                while (*start != *end && counter++ < 5000) {
                        //printf("jnl: close: flushing the buffer cache (start 0x%llx end 0x%llx)\n", *start, *end);
                        if (jnl->flush) {
                                jnl->flush(jnl->flush_arg);
                        }
                        tsleep((caddr_t)jnl, PRIBIO, "jnl_close", 2);
                }

                if (*start != *end) {
                        printf("jnl: %s: close: buffer flushing didn't seem to flush out all the transactions! (0x%llx - 0x%llx)\n",
                               jnl->jdev_name, *start, *end);
                }

                // make sure this is in sync when we close the journal
                jnl->jhdr->start = jnl->active_start;

                // if this fails there's not much we can do at this point...
                write_journal_header(jnl, 1, jnl->sequence_num);
        } else {
                // if we're here the journal isn't valid any more.
                // so make sure we don't leave any locked blocks lying around
                printf("jnl: %s: close: journal %p, is invalid.  aborting outstanding transactions\n", jnl->jdev_name, jnl);

                if (jnl->active_tr || jnl->cur_tr) {
                        transaction *tr;

                        if (jnl->active_tr) {
                                tr = jnl->active_tr;
                                jnl->active_tr = NULL;
                        } else {
                                tr = jnl->cur_tr;
                                jnl->cur_tr = NULL;
                        }
                        abort_transaction(jnl, tr);

                        if (jnl->active_tr || jnl->cur_tr) {
                                panic("jnl: %s: close: jnl @ %p had both an active and cur tr\n", jnl->jdev_name, jnl);
                        }
                }
        }

        free_old_stuff(jnl);

        kmem_free(kernel_map, (vm_offset_t)jnl->header_buf, jnl->header_buf_size);
        jnl->jhdr = (void *)0xbeefbabe;

        // Release reference on the mount
        if (jnl->fsmount)
                 mount_drop(jnl->fsmount, 0);

        vnode_putname_printable(jnl->jdev_name);

        unlock_journal(jnl);
        lck_mtx_destroy(&jnl->old_start_lock, jnl_mutex_group);
        lck_mtx_destroy(&jnl->jlock, jnl_mutex_group);
        lck_mtx_destroy(&jnl->flock, jnl_mutex_group);
        FREE_ZONE(jnl, sizeof(struct journal), M_JNL_JNL);
}

static void
dump_journal(journal *jnl)
{
        transaction *ctr;

        printf("journal for dev %s:", jnl->jdev_name);
        printf("  jdev_offset %.8llx\n", jnl->jdev_offset);
        printf("  magic: 0x%.8x\n", jnl->jhdr->magic);
        printf("  start: 0x%.8llx\n", jnl->jhdr->start);
        printf("  end:   0x%.8llx\n", jnl->jhdr->end);
        printf("  size:  0x%.8llx\n", jnl->jhdr->size);
        printf("  blhdr size: %d\n", jnl->jhdr->blhdr_size);
        printf("  jhdr size: %d\n", jnl->jhdr->jhdr_size);
        printf("  chksum: 0x%.8x\n", jnl->jhdr->checksum);
    
        printf("  completed transactions:\n");
        for (ctr = jnl->completed_trs; ctr; ctr = ctr->next) {
                printf("    0x%.8llx - 0x%.8llx\n", ctr->journal_start, ctr->journal_end);
        }
}



static off_t
free_space(journal *jnl)
{
        off_t free_space_offset;
        
        if (jnl->jhdr->start < jnl->jhdr->end) {
                free_space_offset = jnl->jhdr->size - (jnl->jhdr->end - jnl->jhdr->start) - jnl->jhdr->jhdr_size;
        } else if (jnl->jhdr->start > jnl->jhdr->end) {
                free_space_offset = jnl->jhdr->start - jnl->jhdr->end;
        } else {
                // journal is completely empty
                free_space_offset = jnl->jhdr->size - jnl->jhdr->jhdr_size;
        }

        return free_space_offset;
}


//
// The journal must be locked on entry to this function.
// The "desired_size" is in bytes.
//
static int
check_free_space(journal *jnl, int desired_size, boolean_t *delayed_header_write, uint32_t sequence_num)
{
        size_t  i;
        int     counter=0;

        //printf("jnl: check free space (desired 0x%x, avail 0x%Lx)\n",
        //         desired_size, free_space(jnl));

        if (delayed_header_write)
                *delayed_header_write = FALSE;
    
        while (1) {
                int old_start_empty;
                
                // make sure there's space in the journal to hold this transaction
                if (free_space(jnl) > desired_size && jnl->old_start[0] == 0) {
                        break;
                }
                if (counter++ == 5000) {
                        dump_journal(jnl);
                        panic("jnl: check_free_space: buffer flushing isn't working "
                              "(jnl @ %p s %lld e %lld f %lld [active start %lld]).\n", jnl,
                              jnl->jhdr->start, jnl->jhdr->end, free_space(jnl), jnl->active_start);
                }
                if (counter > 7500) {
                        printf("jnl: %s: check_free_space: giving up waiting for free space.\n", jnl->jdev_name);
                        return ENOSPC;
                }

                //
                // here's where we lazily bump up jnl->jhdr->start.  we'll consume
                // entries until there is enough space for the next transaction.
                //
                old_start_empty = 1;
                lock_oldstart(jnl);

                for (i = 0; i < sizeof(jnl->old_start)/sizeof(jnl->old_start[0]); i++) {
                        int   lcl_counter;

                        lcl_counter = 0;
                        while (jnl->old_start[i] & 0x8000000000000000LL) {
                                if (lcl_counter++ > 10000) {
                                        panic("jnl: check_free_space: tr starting @ 0x%llx not flushing (jnl %p).\n",
                                              jnl->old_start[i], jnl);
                                }
                                
                                unlock_oldstart(jnl);
                                if (jnl->flush) {
                                        jnl->flush(jnl->flush_arg);
                                }
                                tsleep((caddr_t)jnl, PRIBIO, "check_free_space1", 1);
                                lock_oldstart(jnl);
                        }

                        if (jnl->old_start[i] == 0) {
                                continue;
                        }

                        old_start_empty   = 0;
                        jnl->jhdr->start  = jnl->old_start[i];
                        jnl->old_start[i] = 0;

                        if (free_space(jnl) > desired_size) {
                                
                                if (delayed_header_write)
                                        *delayed_header_write = TRUE;
                                else {
                                        unlock_oldstart(jnl);
                                        write_journal_header(jnl, 1, sequence_num);
                                        lock_oldstart(jnl);
                                }
                                break;
                        }
                }
                unlock_oldstart(jnl);
                
                // if we bumped the start, loop and try again
                if (i < sizeof(jnl->old_start)/sizeof(jnl->old_start[0])) {
                        continue;
                } else if (old_start_empty) {
                        //
                        // if there is nothing in old_start anymore then we can
                        // bump the jhdr->start to be the same as active_start
                        // since it is possible there was only one very large
                        // transaction in the old_start array.  if we didn't do
                        // this then jhdr->start would never get updated and we
                        // would wind up looping until we hit the panic at the
                        // start of the loop.
                        //
                        jnl->jhdr->start = jnl->active_start;
                        
                        if (delayed_header_write)
                                *delayed_header_write = TRUE;
                        else
                                write_journal_header(jnl, 1, sequence_num);
                        continue;
                }


                // if the file system gave us a flush function, call it to so that
                // it can flush some blocks which hopefully will cause some transactions
                // to complete and thus free up space in the journal.
                if (jnl->flush) {
                        jnl->flush(jnl->flush_arg);
                }
        
                // wait for a while to avoid being cpu-bound (this will
                // put us to sleep for 10 milliseconds)
                tsleep((caddr_t)jnl, PRIBIO, "check_free_space2", 1);
        }

        return 0;
}

/*
 * Allocate a new active transaction.
 */
static errno_t
journal_allocate_transaction(journal *jnl)
{
        transaction *tr;
        
        MALLOC_ZONE(tr, transaction *, sizeof(transaction), M_JNL_TR, M_WAITOK);
        memset(tr, 0, sizeof(transaction));

        tr->tbuffer_size = jnl->tbuffer_size;

        if (kmem_alloc_kobject(kernel_map, (vm_offset_t *)&tr->tbuffer, tr->tbuffer_size)) {
                FREE_ZONE(tr, sizeof(transaction), M_JNL_TR);
                jnl->active_tr = NULL;
                return ENOMEM;
        }

        // journal replay code checksum check depends on this.
        memset(tr->tbuffer, 0, BLHDR_CHECKSUM_SIZE);
        // Fill up the rest of the block with unimportant bytes (0x5a 'Z' chosen for visibility)
        memset(tr->tbuffer + BLHDR_CHECKSUM_SIZE, 0x5a, jnl->jhdr->blhdr_size - BLHDR_CHECKSUM_SIZE);

        tr->blhdr = (block_list_header *)tr->tbuffer;
        tr->blhdr->max_blocks = (jnl->jhdr->blhdr_size / sizeof(block_info)) - 1;
        tr->blhdr->num_blocks = 1;      // accounts for this header block
        tr->blhdr->bytes_used = jnl->jhdr->blhdr_size;
        tr->blhdr->flags = BLHDR_CHECK_CHECKSUMS | BLHDR_FIRST_HEADER;

        tr->sequence_num = ++jnl->sequence_num;
        tr->num_blhdrs  = 1;
        tr->total_bytes = jnl->jhdr->blhdr_size;
        tr->jnl         = jnl;

        jnl->active_tr  = tr;
        
        return 0;
}

int
journal_start_transaction(journal *jnl)
{
        int ret;

        CHECK_JOURNAL(jnl);
    
        free_old_stuff(jnl);

        if (jnl->flags & JOURNAL_INVALID) {
                return EINVAL;
        }
        if (jnl->owner == current_thread()) {
                if (jnl->active_tr == NULL) {
                        panic("jnl: start_tr: active_tr is NULL (jnl @ %p, owner %p, current_thread %p\n",
                              jnl, jnl->owner, current_thread());
                }
                jnl->nested_count++;
                return 0;
        }
        lock_journal(jnl);

        if (jnl->owner != NULL || jnl->nested_count != 0 || jnl->active_tr != NULL) {
                panic("jnl: start_tr: owner %p, nested count %d, active_tr %p jnl @ %p\n",
                      jnl->owner, jnl->nested_count, jnl->active_tr, jnl);
        }

        jnl->owner = current_thread();
        jnl->nested_count = 1;

#if JOE
        // make sure there's room in the journal
        if (free_space(jnl) < jnl->tbuffer_size) {

                KERNEL_DEBUG(0xbbbbc030 | DBG_FUNC_START, jnl, 0, 0, 0, 0);

                // this is the call that really waits for space to free up
                // as well as updating jnl->jhdr->start
                if (check_free_space(jnl, jnl->tbuffer_size, NULL, jnl->sequence_num) != 0) {
                        printf("jnl: %s: start transaction failed: no space\n", jnl->jdev_name);
                        ret = ENOSPC;
                        goto bad_start;
                }
                KERNEL_DEBUG(0xbbbbc030 | DBG_FUNC_END, jnl, 0, 0, 0, 0);
        }
#endif

        // if there's a buffered transaction, use it.
        if (jnl->cur_tr) {
                jnl->active_tr = jnl->cur_tr;
                jnl->cur_tr    = NULL;

                return 0;
        }

        ret = journal_allocate_transaction(jnl);
        if (ret) {
                goto bad_start;
        }

        // printf("jnl: start_tr: owner 0x%x new tr @ 0x%x\n", jnl->owner, jnl->active_tr);

        return 0;

bad_start:
        jnl->owner        = NULL;
        jnl->nested_count = 0;
        unlock_journal(jnl);

        return ret;
}


int
journal_modify_block_start(journal *jnl, struct buf *bp)
{
        transaction *tr;
    
        CHECK_JOURNAL(jnl);


        free_old_stuff(jnl);

        if (jnl->flags & JOURNAL_INVALID) {
                return EINVAL;
        }

        // XXXdbg - for debugging I want this to be true.  later it may
        //          not be necessary.
        if ((buf_flags(bp) & B_META) == 0) {
                panic("jnl: modify_block_start: bp @ %p is not a meta-data block! (jnl %p)\n", bp, jnl);
        }

        tr = jnl->active_tr;
        CHECK_TRANSACTION(tr);

        if (jnl->owner != current_thread()) {
                panic("jnl: modify_block_start: called w/out a transaction! jnl %p, owner %p, curact %p\n",
                      jnl, jnl->owner, current_thread());
        }

        //printf("jnl: mod block start (bp 0x%x vp 0x%x l/blkno %qd/%qd bsz %d; total bytes %d)\n",
        //   bp, buf_vnode(bp), buf_lblkno(bp), buf_blkno(bp), buf_size(bp), tr->total_bytes);

        // can't allow blocks that aren't an even multiple of the
        // underlying block size.
        if ((buf_size(bp) % jnl->jhdr->jhdr_size) != 0) {
                uint32_t phys_blksz, bad=0;
            
                if (VNOP_IOCTL(jnl->jdev, DKIOCGETBLOCKSIZE, (caddr_t)&phys_blksz, 0, vfs_context_kernel())) {
                        bad = 1;
                } else if (phys_blksz != (uint32_t)jnl->jhdr->jhdr_size) {
                        if (phys_blksz < 512) {
                                panic("jnl: mod block start: phys blksz %d is too small (%d, %d)\n",
                                      phys_blksz, buf_size(bp), jnl->jhdr->jhdr_size);
                        }

                        if ((buf_size(bp) % phys_blksz) != 0) {
                                bad = 1;
                        } else if (phys_blksz < (uint32_t)jnl->jhdr->jhdr_size) {
                                jnl->jhdr->jhdr_size = phys_blksz;
                        } else {
                                // the phys_blksz is now larger... need to realloc the jhdr
                                char *new_header_buf;

                                printf("jnl: %s: phys blksz got bigger (was: %d/%d now %d)\n",
                                       jnl->jdev_name, jnl->header_buf_size, jnl->jhdr->jhdr_size, phys_blksz);
                                if (kmem_alloc_kobject(kernel_map, (vm_offset_t *)&new_header_buf, phys_blksz)) {
                                        printf("jnl: modify_block_start: %s: create: phys blksz change (was %d, now %d) but could not allocate space for new header\n",
                                               jnl->jdev_name, jnl->jhdr->jhdr_size, phys_blksz);
                                        bad = 1;
                                } else {
                                        memcpy(new_header_buf, jnl->header_buf, jnl->header_buf_size);
                                        memset(&new_header_buf[jnl->header_buf_size], 0x18, (phys_blksz - jnl->header_buf_size));
                                        kmem_free(kernel_map, (vm_offset_t)jnl->header_buf, jnl->header_buf_size);
                                        jnl->header_buf = new_header_buf;
                                        jnl->header_buf_size = phys_blksz;
                                        
                                        jnl->jhdr = (journal_header *)jnl->header_buf;
                                        jnl->jhdr->jhdr_size = phys_blksz;
                                }
                        }
                } else {
                        bad = 1;
                }
            
                if (bad) {
                        panic("jnl: mod block start: bufsize %d not a multiple of block size %d\n",
                              buf_size(bp), jnl->jhdr->jhdr_size);
                        return -1;
                }
        }

        // make sure that this transaction isn't bigger than the whole journal
        if (tr->total_bytes+buf_size(bp) >= (jnl->jhdr->size - jnl->jhdr->jhdr_size)) {
                panic("jnl: transaction too big (%d >= %lld bytes, bufsize %d, tr %p bp %p)\n",
                      tr->total_bytes, (tr->jnl->jhdr->size - jnl->jhdr->jhdr_size), buf_size(bp), tr, bp);
                return -1;
        }

        // if the block is dirty and not already locked we have to write
        // it out before we muck with it because it has data that belongs
        // (presumably) to another transaction.
        //
        if ((buf_flags(bp) & (B_DELWRI | B_LOCKED)) == B_DELWRI) {

                if (buf_flags(bp) & B_ASYNC) {
                        panic("modify_block_start: bp @ %p has async flag set!\n", bp);
                }
                if (bp->b_shadow_ref)
                        panic("modify_block_start: dirty bp @ %p has shadows!\n", bp);

                // this will cause it to not be buf_brelse()'d
                buf_setflags(bp, B_NORELSE);
                VNOP_BWRITE(bp);
        }
        buf_setflags(bp, B_LOCKED);

        return 0;
}

int
journal_modify_block_abort(journal *jnl, struct buf *bp)
{
        transaction     *tr;
        block_list_header *blhdr;
        int             i;
    
        CHECK_JOURNAL(jnl);

        free_old_stuff(jnl);

        tr = jnl->active_tr;
        
        //
        // if there's no active transaction then we just want to
        // call buf_brelse() and return since this is just a block
        // that happened to be modified as part of another tr.
        //
        if (tr == NULL) {
                buf_brelse(bp);
                return 0;
        }

        if (jnl->flags & JOURNAL_INVALID) {
        /* Still need to buf_brelse(). Callers assume we consume the bp. */
        buf_brelse(bp);
                return EINVAL;
        }

        CHECK_TRANSACTION(tr);
    
        if (jnl->owner != current_thread()) {
                panic("jnl: modify_block_abort: called w/out a transaction! jnl %p, owner %p, curact %p\n",
                      jnl, jnl->owner, current_thread());
        }

        // printf("jnl: modify_block_abort: tr 0x%x bp 0x%x\n", jnl->active_tr, bp);

        // first check if it's already part of this transaction
        for (blhdr = tr->blhdr; blhdr; blhdr = (block_list_header *)((long)blhdr->binfo[0].bnum)) {
                for (i = 1; i < blhdr->num_blocks; i++) {
                        if (bp == blhdr->binfo[i].u.bp) {
                                break;
                        }
                }

                if (i < blhdr->num_blocks) {
                        break;
                }
        }

        //
        // if blhdr is null, then this block has only had modify_block_start
        // called on it as part of the current transaction.  that means that
        // it is ok to clear the LOCKED bit since it hasn't actually been
        // modified.  if blhdr is non-null then modify_block_end was called
        // on it and so we need to keep it locked in memory.
        //
        if (blhdr == NULL) { 
                buf_clearflags(bp, B_LOCKED);
        }

        buf_brelse(bp);
        return 0;
}


int
journal_modify_block_end(journal *jnl, struct buf *bp, void (*func)(buf_t bp, void *arg), void *arg)
{
        int             i = 1;
        int             tbuffer_offset=0;
        block_list_header *blhdr, *prev=NULL;
        transaction     *tr;

        CHECK_JOURNAL(jnl);

        free_old_stuff(jnl);

        if (jnl->flags & JOURNAL_INVALID) {
        /* Still need to buf_brelse(). Callers assume we consume the bp. */
        buf_brelse(bp);
                return EINVAL;
        }

        tr = jnl->active_tr;
        CHECK_TRANSACTION(tr);

        if (jnl->owner != current_thread()) {
                panic("jnl: modify_block_end: called w/out a transaction! jnl %p, owner %p, curact %p\n",
                      jnl, jnl->owner, current_thread());
        }

        //printf("jnl: mod block end:  (bp 0x%x vp 0x%x l/blkno %qd/%qd bsz %d, total bytes %d)\n", 
        //   bp, buf_vnode(bp), buf_lblkno(bp), buf_blkno(bp), buf_size(bp), tr->total_bytes);

        if ((buf_flags(bp) & B_LOCKED) == 0) {
                panic("jnl: modify_block_end: bp %p not locked! jnl @ %p\n", bp, jnl);
        }
         
        // first check if it's already part of this transaction
        for (blhdr = tr->blhdr; blhdr; prev = blhdr, blhdr = (block_list_header *)((long)blhdr->binfo[0].bnum)) {
                tbuffer_offset = jnl->jhdr->blhdr_size;

                for (i = 1; i < blhdr->num_blocks; i++) {
                        if (bp == blhdr->binfo[i].u.bp) {
                                break;
                        }
                        if (blhdr->binfo[i].bnum != (off_t)-1) {
                                tbuffer_offset += buf_size(blhdr->binfo[i].u.bp);
                        } else {
                                tbuffer_offset += blhdr->binfo[i].u.bi.bsize;
                        }
                }

                if (i < blhdr->num_blocks) {
                        break;
                }
        }

        if (blhdr == NULL
            && prev
            && (prev->num_blocks+1) <= prev->max_blocks
            && (prev->bytes_used+buf_size(bp)) <= (uint32_t)tr->tbuffer_size) {
                blhdr = prev;

        } else if (blhdr == NULL) {
                block_list_header *nblhdr;
                if (prev == NULL) {
                        panic("jnl: modify block end: no way man, prev == NULL?!?, jnl %p, bp %p\n", jnl, bp);
                }

                // we got to the end of the list, didn't find the block and there's
                // no room in the block_list_header pointed to by prev
        
                // we allocate another tbuffer and link it in at the end of the list
                // through prev->binfo[0].bnum.  that's a skanky way to do things but
                // avoids having yet another linked list of small data structures to manage.

                if (kmem_alloc_kobject(kernel_map, (vm_offset_t *)&nblhdr, tr->tbuffer_size)) {
                        panic("jnl: end_tr: no space for new block tr @ %p (total bytes: %d)!\n",
                              tr, tr->total_bytes);
                }

                // journal replay code checksum check depends on this.
                memset(nblhdr, 0, BLHDR_CHECKSUM_SIZE);
                // Fill up the rest of the block with unimportant bytes
                memset(nblhdr + BLHDR_CHECKSUM_SIZE, 0x5a, jnl->jhdr->blhdr_size - BLHDR_CHECKSUM_SIZE);

                // initialize the new guy
                nblhdr->max_blocks = (jnl->jhdr->blhdr_size / sizeof(block_info)) - 1;
                nblhdr->num_blocks = 1;      // accounts for this header block
                nblhdr->bytes_used = jnl->jhdr->blhdr_size;
                nblhdr->flags = BLHDR_CHECK_CHECKSUMS;
            
                tr->num_blhdrs++;
                tr->total_bytes += jnl->jhdr->blhdr_size;

                // then link him in at the end
                prev->binfo[0].bnum = (off_t)((long)nblhdr);

                // and finally switch to using the new guy
                blhdr          = nblhdr;
                tbuffer_offset = jnl->jhdr->blhdr_size;
                i              = 1;
        }


        if ((i+1) > blhdr->max_blocks) {
                panic("jnl: modify_block_end: i = %d, max_blocks %d\n", i, blhdr->max_blocks);
        }

        // if this is true then this is a new block we haven't seen
        if (i >= blhdr->num_blocks) {
                int     bsize;
                vnode_t vp;

                vp = buf_vnode(bp);
                vnode_ref(vp);
                bsize = buf_size(bp);

                blhdr->binfo[i].bnum = (off_t)(buf_blkno(bp));
                blhdr->binfo[i].u.bp = bp;

                KERNEL_DEBUG_CONSTANT(0x3018004, vp, blhdr->binfo[i].bnum, bsize, 0, 0);

                if (func) {
                        void (*old_func)(buf_t, void *)=NULL, *old_arg=NULL;
                        
                        buf_setfilter(bp, func, arg, &old_func, &old_arg);
                        if (old_func != NULL && old_func != func) {
                            panic("jnl: modify_block_end: old func %p / arg %p (func %p)", old_func, old_arg, func);
                        }
                }
                
                blhdr->bytes_used += bsize;
                tr->total_bytes   += bsize;

                blhdr->num_blocks++;
        }
        buf_bdwrite(bp);

        return 0;
}

int
journal_kill_block(journal *jnl, struct buf *bp)
{
        int             i;
        int             bflags;
        block_list_header *blhdr;
        transaction     *tr;

        CHECK_JOURNAL(jnl);

        free_old_stuff(jnl);

        if (jnl->flags & JOURNAL_INVALID) {
                return EINVAL;
        }

        tr = jnl->active_tr;
        CHECK_TRANSACTION(tr);

        if (jnl->owner != current_thread()) {
                panic("jnl: modify_block_end: called w/out a transaction! jnl %p, owner %p, curact %p\n",
                      jnl, jnl->owner, current_thread());
        }

        bflags = buf_flags(bp);

        if ( !(bflags & B_LOCKED))
                panic("jnl: modify_block_end: called with bp not B_LOCKED");

        /*
         * bp must be BL_BUSY and B_LOCKED
         * first check if it's already part of this transaction
         */
        for (blhdr = tr->blhdr; blhdr; blhdr = (block_list_header *)((long)blhdr->binfo[0].bnum)) {

                for (i = 1; i < blhdr->num_blocks; i++) {
                        if (bp == blhdr->binfo[i].u.bp) {
                                vnode_t vp;

                                buf_clearflags(bp, B_LOCKED);

                                // this undoes the vnode_ref() in journal_modify_block_end()
                                vp = buf_vnode(bp);
                                vnode_rele_ext(vp, 0, 1);

                                // if the block has the DELWRI and FILTER bits sets, then
                                // things are seriously weird.  if it was part of another
                                // transaction then journal_modify_block_start() should
                                // have force it to be written.
                                //
                                //if ((bflags & B_DELWRI) && (bflags & B_FILTER)) {
                                //      panic("jnl: kill block: this defies all logic! bp 0x%x\n", bp);
                                //} else {
                                        tr->num_killed += buf_size(bp);
                                //}
                                blhdr->binfo[i].bnum = (off_t)-1;
                                blhdr->binfo[i].u.bp = NULL;
                                blhdr->binfo[i].u.bi.bsize = buf_size(bp);

                                buf_markinvalid(bp);
                                buf_brelse(bp);

                                break;
                        }
                }

                if (i < blhdr->num_blocks) {
                        break;
                }
        }

        return 0;
}

/*
;________________________________________________________________________________
;
; Routine:              journal_trim_set_callback
;
; Function:             Provide the journal with a routine to be called back when a
;                               TRIM has (or would have) been issued to the device.  That
;                               is, the transaction has been flushed to the device, and the
;                               blocks freed by the transaction are now safe for reuse.
;
;                               CAUTION: If the journal becomes invalid (eg., due to an I/O
;                               error when trying to write to the journal), this callback
;                               will stop getting called, even if extents got freed before
;                               the journal became invalid!
;
; Input Arguments:
;       jnl                     - The journal structure for the filesystem.
;       callback        - The function to call when the TRIM is complete.
;       arg                     - An argument to be passed to callback.
;________________________________________________________________________________
*/
__private_extern__ void
journal_trim_set_callback(journal *jnl, jnl_trim_callback_t callback, void *arg)
{
        jnl->trim_callback = callback;
        jnl->trim_callback_arg = arg;
}


/*
;________________________________________________________________________________
;
; Routine:              journal_trim_realloc
;
; Function:             Increase the amount of memory allocated for the list of extents
;                               to be unmapped (trimmed).  This routine will be called when
;                               adding an extent to the list, and the list already occupies
;                               all of the space allocated to it.  This routine returns ENOMEM
;                               if unable to allocate more space, or 0 if the extent list was
;                               grown successfully.
;
; Input Arguments:
;       trim            - The trim list to be resized.
;
; Output:
;       (result)        - ENOMEM or 0.
;
; Side effects:
;        The allocated_count and extents fields of tr->trim are updated
;        if the function returned 0.
;________________________________________________________________________________
*/
static int
trim_realloc(struct jnl_trim_list *trim)
{
        void *new_extents;
        uint32_t new_allocated_count;
        
        if (jnl_kdebug)
                KERNEL_DEBUG_CONSTANT(DBG_JOURNAL_TRIM_REALLOC | DBG_FUNC_START, trim, 0, trim->allocated_count, trim->extent_count, 0);
        
        new_allocated_count = trim->allocated_count + JOURNAL_DEFAULT_TRIM_EXTENTS;
        new_extents = kalloc(new_allocated_count * sizeof(dk_extent_t));
        if (new_extents == NULL) {
                printf("jnl: trim_realloc: unable to grow extent list!\n");
                /*
                 * Since we could be called when allocating space previously marked
                 * to be trimmed, we need to empty out the list to be safe.
                 */
                trim->extent_count = 0;
                if (jnl_kdebug)
                        KERNEL_DEBUG_CONSTANT(DBG_JOURNAL_TRIM_REALLOC | DBG_FUNC_END, ENOMEM, 0, trim->allocated_count, 0, 0);
                return ENOMEM;
        }
        
        /* Copy the old extent list to the newly allocated list. */
        if (trim->extents != NULL) {
                memmove(new_extents,
                                trim->extents,
                                trim->allocated_count * sizeof(dk_extent_t));
                kfree(trim->extents,
                          trim->allocated_count * sizeof(dk_extent_t));
        }
        
        trim->allocated_count = new_allocated_count;
        trim->extents = new_extents;

        if (jnl_kdebug)
                KERNEL_DEBUG_CONSTANT(DBG_JOURNAL_TRIM_REALLOC | DBG_FUNC_END, 0, 0, new_allocated_count, trim->extent_count, 0);
        
        return 0;
}

/*
 ;________________________________________________________________________________
 ;
 ; Routine:             trim_search_extent
 ;
 ; Function:            Search the given extent list to see if any of its extents
 ;                              overlap the given extent.
 ;
 ; Input Arguments:
 ;      trim            - The trim list to be searched.
 ;      offset          - The first byte of the range to be searched for.
 ;      length          - The number of bytes of the extent being searched for.
 ;  overlap_start - start of the overlapping extent
 ;  overlap_len   - length of the overlapping extent
 ;
 ; Output:
 ;      (result)        - TRUE if one or more extents overlap, FALSE otherwise.
 ;________________________________________________________________________________
 */
static int
trim_search_extent(struct jnl_trim_list *trim, uint64_t offset,
                uint64_t length, uint64_t *overlap_start, uint64_t *overlap_len)
{
        uint64_t end = offset + length;
        uint32_t lower = 0;                                             /* Lowest index to search */
        uint32_t upper = trim->extent_count;    /* Highest index to search + 1 */
        uint32_t middle;

        /* A binary search over the extent list. */
        while (lower < upper) {
                middle = (lower + upper) / 2;

                if (trim->extents[middle].offset >= end)
                        upper = middle;
                else if (trim->extents[middle].offset + trim->extents[middle].length <= offset)
                        lower = middle + 1;
                else {
                        if (overlap_start) {
                                *overlap_start = trim->extents[middle].offset;
                        }
                        if (overlap_len) {
                                *overlap_len = trim->extents[middle].length;
                        }
                        return TRUE;
                }
        }

        return FALSE;
}


/*
;________________________________________________________________________________
;
; Routine:              journal_trim_add_extent
;
; Function:             Keep track of extents that have been freed as part of this
;                               transaction.  If the underlying device supports TRIM (UNMAP),
;                               then those extents will be trimmed/unmapped once the
;                               transaction has been written to the journal.  (For example,
;                               SSDs can support trim/unmap and avoid having to recopy those
;                               blocks when doing wear leveling, and may reuse the same
;                               phsyical blocks for different logical blocks.)
;
;                               HFS also uses this, in combination with journal_trim_set_callback,
;                               to add recently freed extents to its free extent cache, but
;                               only after the transaction that freed them is committed to
;                               disk.  (This reduces the chance of overwriting live data in
;                               a way that causes data loss if a transaction never gets
;                               written to the journal.)
;
; Input Arguments:
;       jnl                     - The journal for the volume containing the byte range.
;       offset          - The first byte of the range to be trimmed.
;       length          - The number of bytes of the extent being trimmed.
;________________________________________________________________________________
*/
__private_extern__ int
journal_trim_add_extent(journal *jnl, uint64_t offset, uint64_t length)
{
        uint64_t end;
        transaction *tr;
        dk_extent_t *extent;
        uint32_t insert_index;
        uint32_t replace_count;
                
        CHECK_JOURNAL(jnl);

        /* TODO: Is it OK to manipulate the trim list even if JOURNAL_INVALID is set?  I think so... */
        if (jnl->flags & JOURNAL_INVALID) {
                return EINVAL;
        }

        tr = jnl->active_tr;
        CHECK_TRANSACTION(tr);

        if (jnl_kdebug)
                KERNEL_DEBUG_CONSTANT(DBG_JOURNAL_TRIM_ADD | DBG_FUNC_START, jnl, offset, length, tr->trim.extent_count, 0);

        if (jnl->owner != current_thread()) {
                panic("jnl: trim_add_extent: called w/out a transaction! jnl %p, owner %p, curact %p\n",
                          jnl, jnl->owner, current_thread());
        }

        free_old_stuff(jnl);
                
        end = offset + length;
                
        /*
         * Find the range of existing extents that can be combined with the
         * input extent.  We start by counting the number of extents that end
         * strictly before the input extent, then count the number of extents
         * that overlap or are contiguous with the input extent.
         */
        extent = tr->trim.extents;
        insert_index = 0;
        while (insert_index < tr->trim.extent_count && extent->offset + extent->length < offset) {
                ++insert_index;
                ++extent;
        }
        replace_count = 0;
        while (insert_index + replace_count < tr->trim.extent_count && extent->offset <= end) {
                ++replace_count;
                ++extent;
        }
                
        /*
         * If none of the existing extents can be combined with the input extent,
         * then just insert it in the list (before item number insert_index).
         */
        if (replace_count == 0) {
                /* If the list was already full, we need to grow it. */
                if (tr->trim.extent_count == tr->trim.allocated_count) {
                        if (trim_realloc(&tr->trim) != 0) {
                                printf("jnl: trim_add_extent: out of memory!");
                                if (jnl_kdebug)
                                        KERNEL_DEBUG_CONSTANT(DBG_JOURNAL_TRIM_ADD | DBG_FUNC_END, ENOMEM, 0, 0, tr->trim.extent_count, 0);
                                return ENOMEM;
                        }
                }
                
                /* Shift any existing extents with larger offsets. */
                if (insert_index < tr->trim.extent_count) {
                        memmove(&tr->trim.extents[insert_index+1],
                                        &tr->trim.extents[insert_index],
                                        (tr->trim.extent_count - insert_index) * sizeof(dk_extent_t));
                }
                tr->trim.extent_count++;
                
                /* Store the new extent in the list. */
                tr->trim.extents[insert_index].offset = offset;
                tr->trim.extents[insert_index].length = length;
                
                /* We're done. */
                if (jnl_kdebug)
                        KERNEL_DEBUG_CONSTANT(DBG_JOURNAL_TRIM_ADD | DBG_FUNC_END, 0, 0, 0, tr->trim.extent_count, 0);
                return 0;
        }
        
        /*
         * Update extent number insert_index to be the union of the input extent
         * and all of the replaced extents.
         */
        if (tr->trim.extents[insert_index].offset < offset)
                offset = tr->trim.extents[insert_index].offset;
        extent = &tr->trim.extents[insert_index + replace_count - 1];
        if (extent->offset + extent->length > end)
                end = extent->offset + extent->length;
        tr->trim.extents[insert_index].offset = offset;
        tr->trim.extents[insert_index].length = end - offset;
        
        /*
         * If we were replacing more than one existing extent, then shift any
         * extents with larger offsets, and update the count of extents.
         *
         * We're going to leave extent #insert_index alone since it was just updated, above.
         * We need to move extents from index (insert_index + replace_count) through the end of
         * the list by (replace_count - 1) positions so that they overwrite extent #(insert_index + 1).
         */
        if (replace_count > 1 && (insert_index + replace_count) < tr->trim.extent_count) {
                memmove(&tr->trim.extents[insert_index + 1],
                                &tr->trim.extents[insert_index + replace_count],
                                (tr->trim.extent_count - insert_index - replace_count) * sizeof(dk_extent_t));
        }
        tr->trim.extent_count -= replace_count - 1;

        if (jnl_kdebug)
                KERNEL_DEBUG_CONSTANT(DBG_JOURNAL_TRIM_ADD | DBG_FUNC_END, 0, 0, 0, tr->trim.extent_count, 0);
    return 0;
}

/*
 * journal_trim_extent_overlap
 *
 * Return 1 if there are any pending TRIMs that overlap with the given offset and length
 * Return 0 otherwise.
 */

int journal_trim_extent_overlap (journal *jnl, uint64_t offset, uint64_t length, uint64_t *end) {
        transaction *tr = NULL;
        int overlap = 0;

        uint64_t overlap_start;
        uint64_t overlap_len;
        tr = jnl->active_tr;
        CHECK_TRANSACTION(tr);

        /*
         * There are two lists that need to be examined for potential overlaps:
         *
         * The first is the current transaction. Since this function requires that
         * a transaction be active when this is called, this is the "active_tr"
         * pointer in the journal struct.  This has a trimlist pointer which needs
         * to be searched.
         */
        overlap = trim_search_extent (&tr->trim, offset, length, &overlap_start, &overlap_len);
        if (overlap == 0) {
                /*
                 * The second is the async trim list, which is only done if the current
                 * transaction group (active transaction) did not overlap with our target
                 * extent. This async trim list is the set of all previously
                 * committed transaction groups whose I/Os are now in-flight. We need to hold the
                 * trim lock in order to search this list.  If we grab the list before the
                 * TRIM has completed, then we will compare it. If it is grabbed AFTER the
                 * TRIM has completed, then the pointer will be zeroed out and we won't have
                 * to check anything.
                 */
                lck_rw_lock_shared (&jnl->trim_lock);
                if (jnl->async_trim != NULL) {
                        overlap = trim_search_extent(jnl->async_trim, offset, length, &overlap_start, &overlap_len);
                }
                lck_rw_unlock_shared (&jnl->trim_lock);
        }

        if (overlap) {
                /* compute the end (min) of the overlapping range */
                if ( (overlap_start + overlap_len) < (offset + length)) {
                        *end = (overlap_start + overlap_len);
                }
                else {
                        *end = (offset + length);
                }
        }


        return overlap;
}

/*
 * journal_request_immediate_flush
 *
 * FS requests that the journal flush immediately upon the
 * active transaction's completion.
 *
 * Returns 0 if operation succeeds
 * Returns EPERM if we failed to leave hint
 */
int
journal_request_immediate_flush (journal *jnl) {

        transaction *tr = NULL;
        /*
         * Is a transaction still in process? You must do
         * this while there are txns open
         */
        tr = jnl->active_tr;
        if (tr != NULL) {
                CHECK_TRANSACTION(tr);
                tr->flush_on_completion = TRUE;
        }
        else {
                return EPERM;
        }
        return 0;
}



/*
;________________________________________________________________________________
;
; Routine:              trim_remove_extent
;
; Function:             Indicate that a range of bytes, some of which may have previously
;                               been passed to journal_trim_add_extent, is now allocated.
;                               Any overlapping ranges currently in the journal's trim list will
;                               be removed.  If the underlying device supports TRIM (UNMAP), then
;                               these extents will not be trimmed/unmapped when the transaction
;                               is written to the journal.
;
;                               HFS also uses this to prevent newly allocated space from being
;                               added to its free extent cache (if some portion of the newly
;                               allocated space was recently freed).
;
; Input Arguments:
;       trim            - The trim list to update.
;       offset          - The first byte of the range to be trimmed.
;       length          - The number of bytes of the extent being trimmed.
;________________________________________________________________________________
*/
static int
trim_remove_extent(struct jnl_trim_list *trim, uint64_t offset, uint64_t length)
{
        u_int64_t end;
        dk_extent_t *extent;
        u_int32_t keep_before;
        u_int32_t keep_after;
        
        end = offset + length;
        
        /*
         * Find any existing extents that start before or end after the input
         * extent.  These extents will be modified if they overlap the input
         * extent.  Other extents between them will be deleted.
         */
        extent = trim->extents;
        keep_before = 0;
        while (keep_before < trim->extent_count && extent->offset < offset) {
                ++keep_before;
                ++extent;
        }
        keep_after = keep_before;
        if (keep_after > 0) {
                /* See if previous extent extends beyond both ends of input extent. */
                --keep_after;
                --extent;
        }
        while (keep_after < trim->extent_count && (extent->offset + extent->length) <= end) {
                ++keep_after;
                ++extent;
        }
        
        /*
         * When we get here, the first keep_before extents (0 .. keep_before-1)
         * start before the input extent, and extents (keep_after .. extent_count-1)
         * end after the input extent.  We'll need to keep, all of those extents,
         * but possibly modify #(keep_before-1) and #keep_after to remove the portion
         * that overlaps with the input extent.
         */
        
        /*
         * Does the input extent start after and end before the same existing
         * extent?  If so, we have to "punch a hole" in that extent and convert
         * it to two separate extents.
         */
        if (keep_before >  keep_after) {
                /* If the list was already full, we need to grow it. */
                if (trim->extent_count == trim->allocated_count) {
                        if (trim_realloc(trim) != 0) {
                                printf("jnl: trim_remove_extent: out of memory!");
                                return ENOMEM;
                        }
                }
                
                /*
                 * Make room for a new extent by shifting extents #keep_after and later
                 * down by one extent.  When we're done, extents #keep_before and
                 * #keep_after will be identical, and we can fall through to removing
                 * the portion that overlaps the input extent.
                 */
                memmove(&trim->extents[keep_before],
                                &trim->extents[keep_after],
                                (trim->extent_count - keep_after) * sizeof(dk_extent_t));
                ++trim->extent_count;
                ++keep_after;
                
                /*
                 * Fall through.  We now have the case where the length of extent
                 * #(keep_before - 1) needs to be updated, and the start of extent
                 * #(keep_after) needs to be updated.
                 */
        }
        
        /*
         * May need to truncate the end of extent #(keep_before - 1) if it overlaps
         * the input extent.
         */
        if (keep_before > 0) {
                extent = &trim->extents[keep_before - 1];
                if (extent->offset + extent->length > offset) {
                        extent->length = offset - extent->offset;
                }
        }
        
        /*
         * May need to update the start of extent #(keep_after) if it overlaps the
         * input extent.
         */
        if (keep_after < trim->extent_count) {
                extent = &trim->extents[keep_after];
                if (extent->offset < end) {
                        extent->length = extent->offset + extent->length - end;
                        extent->offset = end;
                }
        }
        
        /*
         * If there were whole extents that overlapped the input extent, get rid
         * of them by shifting any following extents, and updating the count.
         */
        if (keep_after > keep_before && keep_after < trim->extent_count) {
                memmove(&trim->extents[keep_before],
                                &trim->extents[keep_after],
                                (trim->extent_count - keep_after) * sizeof(dk_extent_t));
        }
        trim->extent_count -= keep_after - keep_before;

        return 0;
}

/*
 ;________________________________________________________________________________
 ;
 ; Routine:             journal_trim_remove_extent
 ;
 ; Function:            Make note of a range of bytes, some of which may have previously
 ;                              been passed to journal_trim_add_extent, is now in use on the
 ;                              volume.  The given bytes will be not be trimmed as part of
 ;                              this transaction, or a pending trim of a transaction being
 ;                              asynchronously flushed.
 ;
 ; Input Arguments:
 ;      jnl                     - The journal for the volume containing the byte range.
 ;      offset          - The first byte of the range to be trimmed.
 ;      length          - The number of bytes of the extent being trimmed.
 ;________________________________________________________________________________
 */
__private_extern__ int
journal_trim_remove_extent(journal *jnl, uint64_t offset, uint64_t length)
{
        int error = 0;
        transaction *tr;
        
        CHECK_JOURNAL(jnl);

        /* TODO: Is it OK to manipulate the trim list even if JOURNAL_INVALID is set?  I think so... */
        if (jnl->flags & JOURNAL_INVALID) {
                return EINVAL;
        }

        tr = jnl->active_tr;
        CHECK_TRANSACTION(tr);

        if (jnl_kdebug)
                KERNEL_DEBUG_CONSTANT(DBG_JOURNAL_TRIM_REMOVE | DBG_FUNC_START, jnl, offset, length, tr->trim.extent_count, 0);

        if (jnl->owner != current_thread()) {
                panic("jnl: trim_remove_extent: called w/out a transaction! jnl %p, owner %p, curact %p\n",
                          jnl, jnl->owner, current_thread());
        }

        free_old_stuff(jnl);
                
        error = trim_remove_extent(&tr->trim, offset, length);
        if (error == 0) {
                int found = FALSE;
                
                /*
                 * See if a pending trim has any extents that overlap with the
                 * one we were given.
                 */
                lck_rw_lock_shared(&jnl->trim_lock);
                if (jnl->async_trim != NULL)
                        found = trim_search_extent(jnl->async_trim, offset, length, NULL, NULL);
                lck_rw_unlock_shared(&jnl->trim_lock);
                
                if (found) {
                        /*
                         * There was an overlap, so avoid trimming the extent we
                         * just allocated.  (Otherwise, it might get trimmed after
                         * we've written to it, which will cause that data to be
                         * corrupted.)
                         */
                        uint32_t async_extent_count = 0;
                        
                        if (jnl_kdebug)
                                KERNEL_DEBUG_CONSTANT(DBG_JOURNAL_TRIM_REMOVE_PENDING | DBG_FUNC_START, jnl, offset, length, 0, 0);
                        lck_rw_lock_exclusive(&jnl->trim_lock);
                        if (jnl->async_trim != NULL) {
                                error = trim_remove_extent(jnl->async_trim, offset, length);
                                async_extent_count = jnl->async_trim->extent_count;
                        }
                        lck_rw_unlock_exclusive(&jnl->trim_lock);
                        if (jnl_kdebug)
                                KERNEL_DEBUG_CONSTANT(DBG_JOURNAL_TRIM_REMOVE_PENDING | DBG_FUNC_END, error, 0, 0, async_extent_count, 0);
                }
        }

        if (jnl_kdebug)
                KERNEL_DEBUG_CONSTANT(DBG_JOURNAL_TRIM_REMOVE | DBG_FUNC_END, error, 0, 0, tr->trim.extent_count, 0);
        return error;
}


static int
journal_trim_flush(journal *jnl, transaction *tr)
{
        int errno = 0;
        
        if (jnl_kdebug)
                KERNEL_DEBUG_CONSTANT(DBG_JOURNAL_TRIM_FLUSH | DBG_FUNC_START, jnl, tr, 0, tr->trim.extent_count, 0);

        lck_rw_lock_shared(&jnl->trim_lock);
        if (tr->trim.extent_count > 0) {
                dk_unmap_t unmap;
                                
                bzero(&unmap, sizeof(unmap));
                if (CONFIG_HFS_TRIM && (jnl->flags & JOURNAL_USE_UNMAP)) {
                        unmap.extents = tr->trim.extents;
                        unmap.extentsCount = tr->trim.extent_count;
                        if (jnl_kdebug)
                                KERNEL_DEBUG_CONSTANT(DBG_JOURNAL_TRIM_UNMAP | DBG_FUNC_START, jnl, tr, 0, tr->trim.extent_count, 0);
                        errno = VNOP_IOCTL(jnl->fsdev, DKIOCUNMAP, (caddr_t)&unmap, FWRITE, vfs_context_kernel());
                        if (jnl_kdebug)
                                KERNEL_DEBUG_CONSTANT(DBG_JOURNAL_TRIM_UNMAP | DBG_FUNC_END, errno, 0, 0, 0, 0);
                }
                
                /*
                 * Call back into the file system to tell them that we have
                 * trimmed some extents and that they can now be reused.
                 *
                 * CAUTION: If the journal becomes invalid (eg., due to an I/O
                 * error when trying to write to the journal), this callback
                 * will stop getting called, even if extents got freed before
                 * the journal became invalid!
                 */
                if (jnl->trim_callback)
                        jnl->trim_callback(jnl->trim_callback_arg, tr->trim.extent_count, tr->trim.extents);
        }
        lck_rw_unlock_shared(&jnl->trim_lock);

        /*
         * If the transaction we're flushing was the async transaction, then
         * tell the current transaction that there is no pending trim
         * any more.
         *
         * NOTE: Since we released the lock, another thread could have
         * removed one or more extents from our list.  That's not a
         * problem since any writes to the re-allocated blocks
         * would get sent to the device after the DKIOCUNMAP.
         */
        lck_rw_lock_exclusive(&jnl->trim_lock);
        if (jnl->async_trim == &tr->trim)
                jnl->async_trim = NULL;
        lck_rw_unlock_exclusive(&jnl->trim_lock);

        /*
         * By the time we get here, no other thread can discover the address
         * of "tr", so it is safe for us to manipulate tr->trim without
         * holding any locks.
         */
        if (tr->trim.extents) {                 
                kfree(tr->trim.extents, tr->trim.allocated_count * sizeof(dk_extent_t));
                tr->trim.allocated_count = 0;
                tr->trim.extent_count = 0;
                tr->trim.extents = NULL;
        }
        
        if (jnl_kdebug)
                KERNEL_DEBUG_CONSTANT(DBG_JOURNAL_TRIM_FLUSH | DBG_FUNC_END, errno, 0, 0, 0, 0);

        return errno;
}

static int
journal_binfo_cmp(const void *a, const void *b)
{
        const block_info *bi_a = (const struct block_info *)a;
        const block_info *bi_b = (const struct block_info *)b;
        daddr64_t res;

        if (bi_a->bnum == (off_t)-1) {
                return 1;
        }
        if (bi_b->bnum == (off_t)-1) {
                return -1;
        }

        // don't have to worry about negative block
        // numbers so this is ok to do.
        //
        res = (buf_blkno(bi_a->u.bp) - buf_blkno(bi_b->u.bp));

        return (int)res;
}


/*
 * End a transaction.  If the transaction is small enough, and we're not forcing
 * a write to disk, the "active" transaction becomes the "current" transaction,
 * and will be reused for the next transaction that is started (group commit).
 *
 * If the transaction gets written to disk (because force_it is true, or no
 * group commit, or the transaction is sufficiently full), the blocks get
 * written into the journal first, then the are written asynchronously.  When
 * those async writes complete, the transaction can be freed and removed from
 * the journal.
 *
 * An optional callback can be supplied.  If given, it is called after the
 * the blocks have been written to the journal, but before the async writes
 * of those blocks to their normal on-disk locations.  This is used by
 * journal_relocate so that the location of the journal can be changed and
 * flushed to disk before the blocks get written to their normal locations.
 * Note that the callback is only called if the transaction gets written to
 * the journal during this end_transaction call; you probably want to set the
 * force_it flag.
 *
 * Inputs:
 *      tr                       Transaction to add to the journal
 *      force_it         If true, force this transaction to the on-disk journal immediately.
 *      callback         See description above.  Pass NULL for no callback.
 *      callback_arg Argument passed to callback routine.
 *
 * Result
 *               0              No errors
 *              -1              An error occurred.  The journal is marked invalid.
 */
static int
end_transaction(transaction *tr, int force_it, errno_t (*callback)(void*), void *callback_arg, boolean_t drop_lock, boolean_t must_wait)
{
        block_list_header  *blhdr=NULL, *next=NULL;
        int             i, ret_val = 0;
        errno_t         errno;
        journal         *jnl = tr->jnl;
        struct buf      *bp;
        size_t          tbuffer_offset;
        boolean_t       drop_lock_early;

        if (jnl->cur_tr) {
                panic("jnl: jnl @ %p already has cur_tr %p, new tr: %p\n",
                          jnl, jnl->cur_tr, tr);
        }

        // if there weren't any modified blocks in the transaction
        // just save off the transaction pointer and return.
        if (tr->total_bytes == jnl->jhdr->blhdr_size) {
                jnl->cur_tr = tr;
                goto done;
        }
        
    // if our transaction buffer isn't very full, just hang
    // on to it and don't actually flush anything.  this is
    // what is known as "group commit".  we will flush the
    // transaction buffer if it's full or if we have more than
    // one of them so we don't start hogging too much memory.
    //
    // We also check the device supports UNMAP/TRIM, and if so,
    // the number of extents waiting to be trimmed.  If it is
    // small enough, then keep accumulating more (so we can
    // reduce the overhead of trimming).  If there was a prior
    // trim error, then we stop issuing trims for this
    // volume, so we can also coalesce transactions.
        //
    if (   force_it == 0
                   && (jnl->flags & JOURNAL_NO_GROUP_COMMIT) == 0 
                   && tr->num_blhdrs < 3
                   && (tr->total_bytes <= ((tr->tbuffer_size*tr->num_blhdrs) - tr->tbuffer_size/8))
                   && (!(jnl->flags & JOURNAL_USE_UNMAP) || (tr->trim.extent_count < jnl_trim_flush_limit))) {

                jnl->cur_tr = tr;
                goto done;
        }

        KERNEL_DEBUG(0xbbbbc018|DBG_FUNC_START, jnl, tr, drop_lock, must_wait, 0);

        lock_condition(jnl, &jnl->flushing, "end_transaction");

        /*
         * if the previous 'finish_end_transaction' was being run
         * asynchronously, it could have encountered a condition
         * that caused it to mark the journal invalid... if that
         * occurred while we were waiting for it to finish, we
         * need to notice and abort the current transaction
         */
        if ((jnl->flags & JOURNAL_INVALID) || jnl->flush_aborted == TRUE) {
                unlock_condition(jnl, &jnl->flushing);

                abort_transaction(jnl, tr);
                ret_val = -1;
                KERNEL_DEBUG(0xbbbbc018|DBG_FUNC_END, jnl, tr, ret_val, 0, 0);
                goto done;
        }
        
        /*
         * Store a pointer to this transaction's trim list so that
         * future transactions can find it.
         *
         * Note: if there are no extents in the trim list, then don't
         * bother saving the pointer since nothing can add new extents
         * to the list (and other threads/transactions only care if
         * there is a trim pending).
         */
        lck_rw_lock_exclusive(&jnl->trim_lock);
        if (jnl->async_trim != NULL)
                panic("jnl: end_transaction: async_trim already non-NULL!");
        if (tr->trim.extent_count > 0)
                jnl->async_trim = &tr->trim;
        lck_rw_unlock_exclusive(&jnl->trim_lock);

        /*
         * snapshot the transaction sequence number while we are still behind
         * the journal lock since it will be bumped upon the start of the
         * next transaction group which may overlap the current journal flush...
         * we pass the snapshot into write_journal_header during the journal
         * flush so that it can write the correct version in the header...
         * because we hold the 'flushing' condition variable for the duration
         * of the journal flush, 'saved_sequence_num' remains stable
         */
        jnl->saved_sequence_num = jnl->sequence_num;
        
        /*
         * if we're here we're going to flush the transaction buffer to disk.
         * 'check_free_space' will not return untl there is enough free
         * space for this transaction in the journal and jnl->old_start[0]
         * is avaiable for use
         */
        KERNEL_DEBUG(0xbbbbc030 | DBG_FUNC_START, jnl, 0, 0, 0, 0);

        check_free_space(jnl, tr->total_bytes, &tr->delayed_header_write, jnl->saved_sequence_num);

        KERNEL_DEBUG(0xbbbbc030 | DBG_FUNC_END, jnl, tr->delayed_header_write, 0, 0, 0);

        // range check the end index
        if (jnl->jhdr->end <= 0 || jnl->jhdr->end > jnl->jhdr->size) {
                panic("jnl: end_transaction: end is bogus 0x%llx (sz 0x%llx)\n",
                          jnl->jhdr->end, jnl->jhdr->size);
        }
        if (tr->delayed_header_write == TRUE) {
                thread_t        thread = THREAD_NULL;

                lock_condition(jnl, &jnl->writing_header, "end_transaction");
                /*
                 * fire up a thread to write the journal header
                 * asynchronously... when it finishes, it will call
                 * unlock_condition... we can overlap the preparation of
                 * the log and buffers during this time
                 */
                kernel_thread_start((thread_continue_t)write_header_thread, jnl, &thread);
        } else
                jnl->write_header_failed = FALSE;


        // this transaction starts where the current journal ends
        tr->journal_start = jnl->jhdr->end;

        lock_oldstart(jnl);
        /*
         * Because old_start is locked above, we can cast away the volatile qualifier before passing it to memcpy.
         * slide everyone else down and put our latest guy in the last
         * entry in the old_start array
         */
        memcpy(__CAST_AWAY_QUALIFIER(&jnl->old_start[0], volatile, void *), __CAST_AWAY_QUALIFIER(&jnl->old_start[1], volatile, void *), sizeof(jnl->old_start)-sizeof(jnl->old_start[0]));
        jnl->old_start[sizeof(jnl->old_start)/sizeof(jnl->old_start[0]) - 1] = tr->journal_start | 0x8000000000000000LL;

        unlock_oldstart(jnl);


        for (blhdr = tr->blhdr; blhdr; blhdr = next) {
                char    *blkptr;
                buf_t   sbp;
                int32_t bsize;

                tbuffer_offset = jnl->jhdr->blhdr_size;

                for (i = 1; i < blhdr->num_blocks; i++) {

                        if (blhdr->binfo[i].bnum != (off_t)-1) {
                                void (*func)(buf_t, void *);
                                void  *arg;

                                bp = blhdr->binfo[i].u.bp;

                                if (bp == NULL) {
                                        panic("jnl: inconsistent binfo (NULL bp w/bnum %lld; jnl @ %p, tr %p)\n",
                                                blhdr->binfo[i].bnum, jnl, tr);
                                }
                                /*
                                 * acquire the bp here so that we can safely
                                 * mess around with its data.  buf_acquire()
                                 * will return EAGAIN if the buffer was busy,
                                 * so loop trying again.
                                 */
                                do {
                                        errno = buf_acquire(bp, BAC_REMOVE, 0, 0);
                                } while (errno == EAGAIN);
                                        
                                if (errno)
                                        panic("could not acquire bp %p (err %d)\n", bp, errno);

                                if ((buf_flags(bp) & (B_LOCKED|B_DELWRI)) != (B_LOCKED|B_DELWRI)) {
                                        if (jnl->flags & JOURNAL_CLOSE_PENDING) {
                                                buf_clearflags(bp, B_LOCKED);
                                                buf_brelse(bp);
                                                
                                                /*
                                                 * this is an odd case that appears to happen occasionally
                                                 * make sure we mark this block as no longer valid
                                                 * so that we don't process it in "finish_end_transaction" since
                                                 * the bp that is recorded in our array no longer belongs
                                                 * to us (normally we substitute a shadow bp to be processed
                                                 * issuing a 'buf_bawrite' on a stale buf_t pointer leads
                                                 * to all kinds of problems.
                                                 */
                                                blhdr->binfo[i].bnum = (off_t)-1;
                                                continue;
                                        } else {
                                                panic("jnl: end_tr: !!!DANGER!!! bp %p flags (0x%x) not LOCKED & DELWRI\n", bp, buf_flags(bp));
                                        }
                                }
                                bsize = buf_size(bp);

                                buf_setfilter(bp, NULL, NULL, &func, &arg);
                                
                                blkptr = (char *)&((char *)blhdr)[tbuffer_offset];

                                sbp = buf_create_shadow_priv(bp, FALSE, (uintptr_t)blkptr, 0, 0);

                                if (sbp == NULL)
                                        panic("jnl: buf_create_shadow returned NULL");

                                /*
                                 * copy the data into the transaction buffer...
                                 */
                                memcpy(blkptr, (char *)buf_dataptr(bp), bsize);

                                buf_clearflags(bp, B_LOCKED);
                                buf_markclean(bp);
                                buf_drop(bp);

                                /*
                                 * adopt the shadow buffer for this block
                                 */
                                if (func) {
                                        /*
                                         * transfer FS hook function to the
                                         * shadow buffer... it will get called
                                         * in finish_end_transaction
                                         */
                                        buf_setfilter(sbp, func, arg, NULL, NULL);
                                }
                                blhdr->binfo[i].u.bp = sbp;

                        } else {
                                // bnum == -1, only true if a block was "killed" 
                                bsize = blhdr->binfo[i].u.bi.bsize;
                        }
                        tbuffer_offset += bsize;
                }
                next = (block_list_header *)((long)blhdr->binfo[0].bnum);
        }
        /*
         * if callback != NULL, we don't want to drop the journal
         * lock, or complete end_transaction asynchronously, since
         * the caller is expecting the callback to run in the calling
         * context
         *
         * if drop_lock == FALSE, we can't complete end_transaction
         * asynchronously
         */
        if (callback)
                drop_lock_early = FALSE;
        else
                drop_lock_early = drop_lock;

        if (drop_lock_early == FALSE)
                must_wait = TRUE;

        if (drop_lock_early == TRUE) {
                jnl->owner = NULL;
                unlock_journal(jnl);
                drop_lock = FALSE;
        }
        if (must_wait == TRUE)
                ret_val = finish_end_transaction(tr, callback, callback_arg);
        else {
                thread_t        thread = THREAD_NULL;

                /*
                 * fire up a thread to complete processing this transaction
                 * asynchronously... when it finishes, it will call
                 * unlock_condition
                 */
                kernel_thread_start((thread_continue_t)finish_end_thread, tr, &thread);
        }
        KERNEL_DEBUG(0xbbbbc018|DBG_FUNC_END, jnl, tr, ret_val, 0, 0);
done:
        if (drop_lock == TRUE) {
                jnl->owner = NULL;
                unlock_journal(jnl);
        }
        return (ret_val);
}


static void
finish_end_thread(transaction *tr)
{
        proc_set_task_policy(current_task(), current_thread(),
                             TASK_POLICY_INTERNAL, TASK_POLICY_IOPOL, IOPOL_PASSIVE);

        finish_end_transaction(tr, NULL, NULL);

        thread_deallocate(current_thread());
        thread_terminate(current_thread());
}

static void
write_header_thread(journal *jnl)
{
        proc_set_task_policy(current_task(), current_thread(),
                             TASK_POLICY_INTERNAL, TASK_POLICY_IOPOL, IOPOL_PASSIVE);

        if (write_journal_header(jnl, 1, jnl->saved_sequence_num))
                jnl->write_header_failed = TRUE;
        else
                jnl->write_header_failed = FALSE;
        unlock_condition(jnl, &jnl->writing_header);

        thread_deallocate(current_thread());
        thread_terminate(current_thread());
}

static int
finish_end_transaction(transaction *tr, errno_t (*callback)(void*), void *callback_arg)
{
        int             i, amt;
        int             ret = 0;
        off_t           end;
        journal         *jnl = tr->jnl;
        buf_t           bp, *bparray;
        vnode_t         vp;
        block_list_header  *blhdr=NULL, *next=NULL;
        size_t          tbuffer_offset;
        int             bufs_written = 0;
        int             ret_val = 0;

        KERNEL_DEBUG(0xbbbbc028|DBG_FUNC_START, jnl, tr, 0, 0, 0);

        end  = jnl->jhdr->end;

        for (blhdr = tr->blhdr; blhdr; blhdr = (block_list_header *)((long)blhdr->binfo[0].bnum)) {

                amt = blhdr->bytes_used;

                blhdr->binfo[0].u.bi.b.sequence_num = tr->sequence_num;

                blhdr->checksum = 0;
                blhdr->checksum = calc_checksum((char *)blhdr, BLHDR_CHECKSUM_SIZE);

                if (kmem_alloc(kernel_map, (vm_offset_t *)&bparray, blhdr->num_blocks * sizeof(struct buf *))) {
                        panic("can't allocate %zd bytes for bparray\n", blhdr->num_blocks * sizeof(struct buf *));
                }
                tbuffer_offset = jnl->jhdr->blhdr_size;

                for (i = 1; i < blhdr->num_blocks; i++) {
                        void (*func)(buf_t, void *);
                        void    *arg;
                        int32_t bsize;
                    
                        /*
                         * finish preparing the shadow buf_t before 
                         * calculating the individual block checksums
                         */
                        if (blhdr->binfo[i].bnum != (off_t)-1) {
                                daddr64_t blkno;
                                daddr64_t lblkno;

                                bp = blhdr->binfo[i].u.bp;
                                
                                vp = buf_vnode(bp);
                                blkno = buf_blkno(bp);
                                lblkno = buf_lblkno(bp);

                                if (vp == NULL && lblkno == blkno) {
                                        printf("jnl: %s: end_tr: bad news! bp @ %p w/null vp and l/blkno = %qd/%qd.  aborting the transaction (tr %p jnl %p).\n",
                                               jnl->jdev_name, bp, lblkno, blkno, tr, jnl);
                                        ret_val = -1;
                                        goto bad_journal;
                                }
            
                                // if the lblkno is the same as blkno and this bp isn't
                                // associated with the underlying file system device then
                                // we need to call bmap() to get the actual physical block.
                                //
                                if ((lblkno == blkno) && (vp != jnl->fsdev)) {
                                        off_t   f_offset;
                                        size_t  contig_bytes;

                                        if (VNOP_BLKTOOFF(vp, lblkno, &f_offset)) {
                                                printf("jnl: %s: end_tr: vnop_blktooff failed @ %p, jnl %p\n", jnl->jdev_name, bp, jnl);
                                                ret_val = -1;
                                                goto bad_journal;
                                        }
                                        if (VNOP_BLOCKMAP(vp, f_offset, buf_count(bp), &blkno, &contig_bytes, NULL, 0, NULL)) {
                                                printf("jnl: %s: end_tr: can't blockmap the bp @ %p, jnl %p\n", jnl->jdev_name, bp, jnl);
                                                ret_val = -1;
                                                goto bad_journal;
                                        }
                                        if ((uint32_t)contig_bytes < buf_count(bp)) {
                                                printf("jnl: %s: end_tr: blk not physically contiguous on disk@ %p, jnl %p\n", jnl->jdev_name, bp, jnl);
                                                ret_val = -1;
                                                goto bad_journal;
                                        }
                                        buf_setblkno(bp, blkno);
                                }
                                // update this so we write out the correct physical block number!
                                blhdr->binfo[i].bnum = (off_t)(blkno);

                                /*
                                 * pick up the FS hook function (if any) and prepare
                                 * to fire this buffer off in the next pass
                                 */
                                buf_setfilter(bp, buffer_flushed_callback, tr, &func, &arg);

                                if (func) {
                                        /*
                                         * call the hook function supplied by the filesystem...
                                         * this needs to happen BEFORE cacl_checksum in case
                                         * the FS morphs the data in the buffer
                                         */
                                        func(bp, arg);
                                }
                                bparray[i] = bp;
                                bsize = buf_size(bp);
                                blhdr->binfo[i].u.bi.bsize = bsize;
                                blhdr->binfo[i].u.bi.b.cksum = calc_checksum(&((char *)blhdr)[tbuffer_offset], bsize);
                        } else {
                                bparray[i] = NULL;
                                bsize = blhdr->binfo[i].u.bi.bsize;
                                blhdr->binfo[i].u.bi.b.cksum = 0;
                        }
                        tbuffer_offset += bsize;
                }
                /*
                 * if we fired off the journal_write_header asynchronously in
                 * 'end_transaction', we need to wait for its completion
                 * before writing the actual journal data
                 */
                wait_condition(jnl, &jnl->writing_header, "finish_end_transaction");

                if (jnl->write_header_failed == FALSE)
                        ret = write_journal_data(jnl, &end, blhdr, amt);
                else 
                        ret_val = -1;
                /*
                 * put the bp pointers back so that we can 
                 * make the final pass on them
                 */
                for (i = 1; i < blhdr->num_blocks; i++)
                        blhdr->binfo[i].u.bp = bparray[i];

                kmem_free(kernel_map, (vm_offset_t)bparray, blhdr->num_blocks * sizeof(struct buf *));

                if (ret_val == -1)
                        goto bad_journal;

                if (ret != amt) {
                        printf("jnl: %s: end_transaction: only wrote %d of %d bytes to the journal!\n",
                               jnl->jdev_name, ret, amt);

                        ret_val = -1;
                        goto bad_journal;
                }
        }
        jnl->jhdr->end  = end;    // update where the journal now ends
        tr->journal_end = end;    // the transaction ends here too

        if (tr->journal_start == 0 || tr->journal_end == 0) {
                panic("jnl: end_transaction: bad tr journal start/end: 0x%llx 0x%llx\n",
                      tr->journal_start, tr->journal_end);
        }

        if (write_journal_header(jnl, 0, jnl->saved_sequence_num) != 0) {
                ret_val = -1;
                goto bad_journal;
        }
        /*
         * If the caller supplied a callback, call it now that the blocks have been
         * written to the journal.  This is used by journal_relocate so, for example,
         * the file system can change its pointer to the new journal.
         */
        if (callback != NULL && callback(callback_arg) != 0) {
                ret_val = -1;
                goto bad_journal;
        }
        
        //
        // Send a DKIOCUNMAP for the extents trimmed by this transaction, and
        // free up the extent list.
        //
        journal_trim_flush(jnl, tr);
        
        // the buffer_flushed_callback will only be called for the 
        // real blocks that get flushed so we have to account for 
        // the block_list_headers here.
        //
        tr->num_flushed = tr->num_blhdrs * jnl->jhdr->blhdr_size;

        lock_condition(jnl, &jnl->asyncIO, "finish_end_transaction");

        //
        // setup for looping through all the blhdr's.
        //
        for (blhdr = tr->blhdr; blhdr; blhdr = next) {
                uint16_t        num_blocks;

                /*
                 * grab this info ahead of issuing the buf_bawrites...
                 * once the last one goes out, its possible for blhdr
                 * to be freed (especially if we get preempted) before
                 * we do the last check of num_blocks or
                 * grab the next blhdr pointer...
                 */
                next = (block_list_header *)((long)blhdr->binfo[0].bnum);
                num_blocks = blhdr->num_blocks;

                /*
                 * we can re-order the buf ptrs because everything is written out already
                 */
                qsort(&blhdr->binfo[1], num_blocks-1, sizeof(block_info), journal_binfo_cmp);

                /*
                 * need to make sure that the loop issuing the buf_bawrite's
                 * does not touch blhdr once the last buf_bawrite has been
                 * issued... at that point, we no longer have a legitmate
                 * reference on the associated storage since it will be
                 * released upon the completion of that last buf_bawrite
                 */
                for (i = num_blocks-1; i >= 1; i--) {
                        if (blhdr->binfo[i].bnum != (off_t)-1)
                                break;
                        num_blocks--;
                }
                for (i = 1; i < num_blocks; i++) {

                        if ((bp = blhdr->binfo[i].u.bp)) {
                                vp = buf_vnode(bp);
                    
                                buf_bawrite(bp);
                                
                                // this undoes the vnode_ref() in journal_modify_block_end()
                                vnode_rele_ext(vp, 0, 1);

                                bufs_written++;
                        }
                }
        }
        if (bufs_written == 0) {
                /*
                 * since we didn't issue any buf_bawrite's, there is no
                 * async trigger to cause the memory associated with this
                 * transaction to be freed... so, move it to the garbage
                 * list now
                 */
                lock_oldstart(jnl);

                tr->next       = jnl->tr_freeme;
                jnl->tr_freeme = tr;

                unlock_oldstart(jnl);

                unlock_condition(jnl, &jnl->asyncIO);
        }

        //printf("jnl: end_tr: tr @ 0x%x, jnl-blocks: 0x%llx - 0x%llx. exit!\n",
        //   tr, tr->journal_start, tr->journal_end);

bad_journal:
        if (ret_val == -1) {
                /*
                 * 'flush_aborted' is protected by the flushing condition... we need to
                 * set it before dropping the condition so that it will be
                 * noticed in 'end_transaction'... we add this additional
                 * aborted condition so that we can drop the 'flushing' condition
                 * before grabbing the journal lock... this avoids a deadlock
                 * in 'end_transaction' which is holding the journal lock while
                 * waiting for the 'flushing' condition to clear...
                 * everyone else will notice the JOURNAL_INVALID flag
                 */
                jnl->flush_aborted = TRUE;

                unlock_condition(jnl, &jnl->flushing);
                lock_journal(jnl);

                jnl->flags |= JOURNAL_INVALID;
                jnl->old_start[sizeof(jnl->old_start)/sizeof(jnl->old_start[0]) - 1] &= ~0x8000000000000000LL;
                abort_transaction(jnl, tr);             // cleans up list of extents to be trimmed

                unlock_journal(jnl);
        } else
                unlock_condition(jnl, &jnl->flushing);

        KERNEL_DEBUG(0xbbbbc028|DBG_FUNC_END, jnl, tr, bufs_written, ret_val, 0);

        return (ret_val);
}


static void
lock_condition(journal *jnl, boolean_t *condition, const char *condition_name)
{

        KERNEL_DEBUG(0xbbbbc020|DBG_FUNC_START, jnl, condition, 0, 0, 0);

        lock_flush(jnl);

        while (*condition == TRUE)
                msleep(condition, &jnl->flock, PRIBIO, condition_name, NULL);

        *condition = TRUE;
        unlock_flush(jnl);

        KERNEL_DEBUG(0xbbbbc020|DBG_FUNC_END, jnl, condition, 0, 0, 0);
}

static void
wait_condition(journal *jnl, boolean_t *condition, const char *condition_name)
{

        if (*condition == FALSE)
                return;

        KERNEL_DEBUG(0xbbbbc02c|DBG_FUNC_START, jnl, condition, 0, 0, 0);

        lock_flush(jnl);

        while (*condition == TRUE)
                msleep(condition, &jnl->flock, PRIBIO, condition_name, NULL);

        unlock_flush(jnl);

        KERNEL_DEBUG(0xbbbbc02c|DBG_FUNC_END, jnl, condition, 0, 0, 0);
}

static void
unlock_condition(journal *jnl, boolean_t *condition)
{
        lock_flush(jnl);

        *condition = FALSE;
        wakeup(condition);

        unlock_flush(jnl);
}

static void
abort_transaction(journal *jnl, transaction *tr)
{
        block_list_header *blhdr, *next;

        // for each block list header, iterate over the blocks then
        // free up the memory associated with the block list.
        //
        // find each of the primary blocks (i.e. the list could
        // contain a mix of shadowed and real buf_t's depending
        // on when the abort condition was detected) and mark them
        // clean and locked in the cache... this at least allows 
        // the FS a consistent view between it's incore data structures
        // and the meta-data held in the cache
        //
        KERNEL_DEBUG(0xbbbbc034|DBG_FUNC_START, jnl, tr, 0, 0, 0);

        for (blhdr = tr->blhdr; blhdr; blhdr = next) {
                int     i;
                
                for (i = 1; i < blhdr->num_blocks; i++) {
                        buf_t           bp, tbp, sbp;
                        vnode_t         bp_vp;
                        errno_t         errno;

                        if (blhdr->binfo[i].bnum == (off_t)-1)
                                continue;

                        tbp = blhdr->binfo[i].u.bp;

                        bp_vp = buf_vnode(tbp);

                        buf_setfilter(tbp, NULL, NULL, NULL, NULL);

                        if (buf_shadow(tbp))
                                sbp = tbp;
                        else
                                sbp = NULL;

                        if (bp_vp) {
                                errno = buf_meta_bread(bp_vp,
                                                       buf_lblkno(tbp),
                                                       buf_size(tbp),
                                                       NOCRED,
                                                       &bp);
                                if (errno == 0) {
                                        if (sbp == NULL && bp != tbp && (buf_flags(tbp) & B_LOCKED)) {
                                                panic("jnl: abort_tr: got back a different bp! (bp %p should be %p, jnl %p\n",
                                                      bp, tbp, jnl);
                                        }
                                        /*
                                         * once the journal has been marked INVALID and aborted,
                                         * NO meta data can be written back to the disk, so 
                                         * mark the buf_t clean and make sure it's locked in the cache
                                         * note: if we found a shadow, the real buf_t needs to be relocked
                                         */
                                        buf_setflags(bp, B_LOCKED);
                                        buf_markclean(bp);
                                        buf_brelse(bp);

                                        KERNEL_DEBUG(0xbbbbc034|DBG_FUNC_NONE, jnl, tr, bp, 0, 0);

                                        /*
                                         * this undoes the vnode_ref() in journal_modify_block_end()
                                         */
                                        vnode_rele_ext(bp_vp, 0, 1);
                                } else {
                                        printf("jnl: %s: abort_tr: could not find block %lld vp %p!\n",
                                               jnl->jdev_name, blhdr->binfo[i].bnum, tbp);
                                        if (bp) {
                                                buf_brelse(bp);
                                        }
                                }
                        }
                        if (sbp)
                                buf_brelse(sbp);
                }
                next = (block_list_header *)((long)blhdr->binfo[0].bnum);

                // we can free blhdr here since we won't need it any more
                blhdr->binfo[0].bnum = 0xdeadc0de;
                kmem_free(kernel_map, (vm_offset_t)blhdr, tr->tbuffer_size);
        }

        /*
         * If the transaction we're aborting was the async transaction, then
         * tell the current transaction that there is no pending trim
         * any more.
         */
        lck_rw_lock_exclusive(&jnl->trim_lock);
        if (jnl->async_trim == &tr->trim)
                jnl->async_trim = NULL;
        lck_rw_unlock_exclusive(&jnl->trim_lock);
        
        
        if (tr->trim.extents) {
                kfree(tr->trim.extents, tr->trim.allocated_count * sizeof(dk_extent_t));
        }
        tr->trim.allocated_count = 0;
        tr->trim.extent_count = 0;
        tr->trim.extents = NULL;
        tr->tbuffer     = NULL;
        tr->blhdr       = NULL;
        tr->total_bytes = 0xdbadc0de;
        FREE_ZONE(tr, sizeof(transaction), M_JNL_TR);

        KERNEL_DEBUG(0xbbbbc034|DBG_FUNC_END, jnl, tr, 0, 0, 0);
}


int
journal_end_transaction(journal *jnl)
{
        int ret;
        transaction *tr;
    
        CHECK_JOURNAL(jnl);

        free_old_stuff(jnl);

        if ((jnl->flags & JOURNAL_INVALID) && jnl->owner == NULL) {
                return 0;
        }

        if (jnl->owner != current_thread()) {
                panic("jnl: end_tr: I'm not the owner! jnl %p, owner %p, curact %p\n",
                      jnl, jnl->owner, current_thread());
        }
        jnl->nested_count--;

        if (jnl->nested_count > 0) {
                return 0;
        } else if (jnl->nested_count < 0) {
                panic("jnl: jnl @ %p has negative nested count (%d). bad boy.\n", jnl, jnl->nested_count);
        }
    
        if (jnl->flags & JOURNAL_INVALID) {
                if (jnl->active_tr) {
                        if (jnl->cur_tr != NULL) {
                                panic("jnl: journal @ %p has active tr (%p) and cur tr (%p)\n",
                                      jnl, jnl->active_tr, jnl->cur_tr);
                        }
                        tr             = jnl->active_tr;
                        jnl->active_tr = NULL;

                        abort_transaction(jnl, tr);
                }
                jnl->owner = NULL;
                unlock_journal(jnl);

                return EINVAL;
        }

        tr = jnl->active_tr;
        CHECK_TRANSACTION(tr);

        // clear this out here so that when check_free_space() calls
        // the FS flush function, we don't panic in journal_flush()
        // if the FS were to call that.  note: check_free_space() is
        // called from end_transaction().
        // 
        jnl->active_tr = NULL;
        
        /* Examine the force-journal-flush state in the active txn */
        if (tr->flush_on_completion == TRUE) {
                /*
                 * If the FS requested it, disallow group commit and force the
                 * transaction out to disk immediately.
                 */
                ret = end_transaction(tr, 1, NULL, NULL, TRUE, TRUE);
        }
        else {
                /* in the common path we can simply use the double-buffered journal */
                ret = end_transaction(tr, 0, NULL, NULL, TRUE, FALSE);
        }

        return ret;
}


/* 
 * Flush the contents of the journal to the disk. 
 *
 *  Input: 
 *      wait_for_IO - 
 *      If TRUE, wait to write in-memory journal to the disk 
 *      consistently, and also wait to write all asynchronous 
 *      metadata blocks to its corresponding locations
 *      consistently on the disk.  This means that the journal 
 *      is empty at this point and does not contain any 
 *      transactions.  This is overkill in normal scenarios  
 *      but is useful whenever the metadata blocks are required 
 *      to be consistent on-disk instead of just the journal 
 *      being consistent; like before live verification 
 *      and live volume resizing.  
 *
 *      If FALSE, only wait to write in-memory journal to the 
 *      disk consistently.  This means that the journal still 
 *      contains uncommitted transactions and the file system 
 *      metadata blocks in the journal transactions might be 
 *      written asynchronously to the disk.  But there is no 
 *      guarantee that they are written to the disk before 
 *      returning to the caller.  Note that this option is 
 *      sufficient for file system data integrity as it 
 *      guarantees consistent journal content on the disk.
 */
int
journal_flush(journal *jnl, boolean_t wait_for_IO)
{
        boolean_t drop_lock = FALSE;
    
        CHECK_JOURNAL(jnl);
    
        free_old_stuff(jnl);

        if (jnl->flags & JOURNAL_INVALID) {
                return -1;
        }

        KERNEL_DEBUG(DBG_JOURNAL_FLUSH | DBG_FUNC_START, jnl, 0, 0, 0, 0);

        if (jnl->owner != current_thread()) {
                lock_journal(jnl);
                drop_lock = TRUE;
        }

        // if we're not active, flush any buffered transactions
        if (jnl->active_tr == NULL && jnl->cur_tr) {
                transaction *tr = jnl->cur_tr;

                jnl->cur_tr = NULL;

                if (wait_for_IO) {
                        wait_condition(jnl, &jnl->flushing, "journal_flush");
                        wait_condition(jnl, &jnl->asyncIO, "journal_flush");
                }
                /*
                 * "end_transction" will wait for any current async flush
                 * to complete, before flushing "cur_tr"... because we've
                 * specified the 'must_wait' arg as TRUE, it will then
                 * synchronously flush the "cur_tr"
                 */
                end_transaction(tr, 1, NULL, NULL, drop_lock, TRUE);   // force it to get flushed

        } else  { 
                if (drop_lock == TRUE) {
                        unlock_journal(jnl);
                }

                /* Because of pipelined journal, the journal transactions 
                 * might be in process of being flushed on another thread.  
                 * If there is nothing to flush currently, we should 
                 * synchronize ourselves with the pipelined journal thread 
                 * to ensure that all inflight transactions, if any, are 
                 * flushed before we return success to caller.
                 */
                wait_condition(jnl, &jnl->flushing, "journal_flush");
        }
        if (wait_for_IO) {
                wait_condition(jnl, &jnl->asyncIO, "journal_flush");
        }

        KERNEL_DEBUG(DBG_JOURNAL_FLUSH | DBG_FUNC_END, jnl, 0, 0, 0, 0);

        return 0;
}

int
journal_active(journal *jnl)
{
        if (jnl->flags & JOURNAL_INVALID) {
                return -1;
        }
    
        return (jnl->active_tr == NULL) ? 0 : 1;
}

void *
journal_owner(journal *jnl)
{
        return jnl->owner;
}

int journal_uses_fua(journal *jnl)
{
        if (jnl->flags & JOURNAL_DO_FUA_WRITES)
                return 1;
        return 0;
}

/*
 * Relocate the journal.
 * 
 * You provide the new starting offset and size for the journal. You may
 * optionally provide a new tbuffer_size; passing zero defaults to not
 * changing the tbuffer size except as needed to fit within the new journal
 * size.
 * 
 * You must have already started a transaction. The transaction may contain
 * modified blocks (such as those needed to deallocate the old journal,
 * allocate the new journal, and update the location and size of the journal
 * in filesystem-private structures). Any transactions prior to the active
 * transaction will be flushed to the old journal. The new journal will be
 * initialized, and the blocks from the active transaction will be written to
 * the new journal.
 *
 * The caller will need to update the structures that identify the location
 * and size of the journal.  These updates should be made in the supplied
 * callback routine.  These updates must NOT go into a transaction.  You should
 * force these updates to the media before returning from the callback.  In the
 * even of a crash, either the old journal will be found, with an empty journal,
 * or the new journal will be found with the contents of the active transaction.
 *
 * Upon return from the callback, the blocks from the active transaction are
 * written to their normal locations on disk.
 *
 * (Remember that we have to ensure that blocks get committed to the journal
 * before being committed to their normal locations.  But the blocks don't count
 * as committed until the new journal is pointed at.)
 *
 * Upon return, there is still an active transaction: newly allocated, and
 * with no modified blocks.  Call journal_end_transaction as normal.  You may
 * modifiy additional blocks before calling journal_end_transaction, and those
 * blocks will (eventually) go to the relocated journal.
 *
 * Inputs:
 *      jnl                             The (opened) journal to relocate.
 *      offset                  The new journal byte offset (from start of the journal device).
 *      journal_size    The size, in bytes, of the new journal.
 *      tbuffer_size    The new desired transaction buffer size.  Pass zero to keep
 *                                      the same size as the current journal.  The size will be
 *                                      modified as needed to fit the new journal.
 *      callback                Routine called after the new journal has been initialized,
 *                                      and the active transaction written to the new journal, but
 *                                      before the blocks are written to their normal locations.
 *                                      Pass NULL for no callback.
 *      callback_arg    An argument passed to the callback routine.
 *
 * Result:
 *      0                               No errors
 *      EINVAL                  The offset is not block aligned
 *      EINVAL                  The journal_size is not a multiple of the block size
 *      EINVAL                  The journal is invalid
 *      (any)                   An error returned by journal_flush.
 *
 */
int journal_relocate(journal *jnl, off_t offset, off_t journal_size, int32_t tbuffer_size,
        errno_t (*callback)(void *), void *callback_arg)
{
        int             ret;
        transaction     *tr;
        size_t i = 0;

        /*
         * Sanity check inputs, and adjust the size of the transaction buffer.
         */
        if ((offset % jnl->jhdr->jhdr_size) != 0) {
                printf("jnl: %s: relocate: offset 0x%llx is not an even multiple of block size 0x%x\n",
                       jnl->jdev_name, offset, jnl->jhdr->jhdr_size);
                return EINVAL;
        }
        if ((journal_size % jnl->jhdr->jhdr_size) != 0) {
                printf("jnl: %s: relocate: journal size 0x%llx is not an even multiple of block size 0x%x\n",
                       jnl->jdev_name, journal_size, jnl->jhdr->jhdr_size);
                return EINVAL;
        }

        CHECK_JOURNAL(jnl);

        /* Guarantee we own the active transaction. */
        if (jnl->flags & JOURNAL_INVALID) {
                return EINVAL;
        }
        if (jnl->owner != current_thread()) {
                panic("jnl: relocate: Not the owner! jnl %p, owner %p, curact %p\n",
                      jnl, jnl->owner, current_thread());
        }
        
        if (tbuffer_size == 0)
                tbuffer_size = jnl->tbuffer_size;
        size_up_tbuffer(jnl, tbuffer_size, jnl->jhdr->jhdr_size);
        
        /*
         * Flush any non-active transactions.  We have to temporarily hide the
         * active transaction to make journal_flush flush out non-active but
         * current (unwritten) transactions.
         */
        tr = jnl->active_tr;
        CHECK_TRANSACTION(tr);
        jnl->active_tr = NULL;
        ret = journal_flush(jnl, TRUE);
        jnl->active_tr = tr;

        if (ret) {
                return ret;
        }
        wait_condition(jnl, &jnl->flushing, "end_transaction");

        /*
         * At this point, we have completely flushed the contents of the current
         * journal to disk (and have asynchronously written all of the txns to 
         * their actual desired locations).  As a result, we can (and must) clear 
         * out the old_start array.  If we do not, then if the last written transaction
         * started at the beginning of the journal (starting 1 block into the 
         * journal file) it could confuse the buffer_flushed callback. This is
         * because we're about to reset the start/end pointers of the journal header
         * below. 
         */
        lock_oldstart(jnl); 
        for (i = 0; i < sizeof (jnl->old_start) / sizeof(jnl->old_start[0]); i++) { 
                jnl->old_start[i] = 0; 
        }
        unlock_oldstart(jnl);

        /* Update the journal's offset and size in memory. */
        jnl->jdev_offset = offset;
        jnl->jhdr->start = jnl->jhdr->end = jnl->jhdr->jhdr_size;
        jnl->jhdr->size = journal_size;
        jnl->active_start = jnl->jhdr->start;
        
        /*
         * Force the active transaction to be written to the new journal.  Call the
         * supplied callback after the blocks have been written to the journal, but
         * before they get written to their normal on-disk locations.
         */
        jnl->active_tr = NULL;
        ret = end_transaction(tr, 1, callback, callback_arg, FALSE, TRUE);
        if (ret) {
                printf("jnl: %s: relocate: end_transaction failed (%d)\n", jnl->jdev_name, ret);
                goto bad_journal;
        }
        
        /*
         * Create a new, empty transaction to be the active transaction.  This way
         * our caller can use journal_end_transaction as usual.
         */
        ret = journal_allocate_transaction(jnl);
        if (ret) {
                printf("jnl: %s: relocate: could not allocate new transaction (%d)\n", jnl->jdev_name, ret);
                goto bad_journal;
        }
        
        return 0;

bad_journal:
        jnl->flags |= JOURNAL_INVALID;
        abort_transaction(jnl, tr);
        return ret;
}


#else   // !JOURNALING - so provide stub functions

int journal_uses_fua(__unused journal *jnl)
{
        return 0;
}

journal *
journal_create(__unused struct vnode *jvp,
               __unused off_t         offset,
               __unused off_t         journal_size,
               __unused struct vnode *fsvp,
               __unused size_t        min_fs_blksz,
               __unused int32_t       flags,
               __unused int32_t       tbuffer_size,
               __unused void        (*flush)(void *arg),
               __unused void         *arg,
               __unused struct mount *fsmount)
{
    return NULL;
}

journal *
journal_open(__unused struct vnode *jvp,
             __unused off_t         offset,
             __unused off_t         journal_size,
             __unused struct vnode *fsvp,
             __unused size_t        min_fs_blksz,
             __unused int32_t       flags,
             __unused int32_t       tbuffer_size,
             __unused void        (*flush)(void *arg),
             __unused void         *arg,
             __unused struct mount *fsmount)
{
        return NULL;
}


int
journal_modify_block_start(__unused journal *jnl, __unused struct buf *bp)
{
        return EINVAL;
}

int
journal_modify_block_end(__unused journal *jnl,
                         __unused struct buf *bp,
                         __unused void (*func)(struct buf *bp, void *arg),
                         __unused void *arg)
{
        return EINVAL;
}

int
journal_kill_block(__unused journal *jnl, __unused struct buf *bp)
{
        return EINVAL;
}

int journal_relocate(__unused journal *jnl,
                     __unused off_t offset,
                     __unused off_t journal_size,
                     __unused int32_t tbuffer_size,
                     __unused errno_t (*callback)(void *),
                     __unused void *callback_arg)
{
        return EINVAL;
}

void
journal_close(__unused journal *jnl)
{
}

int
journal_start_transaction(__unused journal *jnl)
{
        return EINVAL;
}

int
journal_end_transaction(__unused journal *jnl)
{
        return EINVAL;
}

int
journal_flush(__unused journal *jnl, __unused boolean_t wait_for_IO)
{
        return EINVAL;
}

int
journal_is_clean(__unused struct vnode *jvp,
                 __unused off_t         offset,
                 __unused off_t         journal_size,
                 __unused struct vnode *fsvp,
                 __unused size_t        min_fs_block_size)
{
        return 0;
}


void *
journal_owner(__unused journal *jnl)
{
        return NULL;
}
#endif  // !JOURNALING