xnu-1228.3.13.tar.gz

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

/*
 * Copyright (c) 1995-2007 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/thread.h>
#include <sys/disk.h>
#include <sys/kdebug.h>
#include <miscfs/specfs/specdev.h>
#include <libkern/OSAtomic.h>   /* OSAddAtomic */

extern task_t kernel_task;

#define DBG_JOURNAL_FLUSH 1

#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"

/* XXX next prototytype 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 int end_transaction(transaction *tr, int force_it, errno_t (*callback)(void*), void *callback_arg);
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);




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

typedef struct bucket {
    off_t   block_num;
    size_t  jnl_offset;
    size_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\
        || jnl->jhdr->start > 1024*1024*1024) {\
        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\
        || jnl->jhdr->end > 1024*1024*1024) {\
        panic("%s:%d: jhdr end looks bad (0x%llx max size 0x%llx)\n", \
        __FILE__, __LINE__, jnl->jhdr->end, jnl->jhdr->size);\
    }\
    if (jnl->jhdr->size > 1024*1024*1024) {\
        panic("%s:%d: jhdr size looks bad (0x%llx)\n",\
        __FILE__, __LINE__, 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 || tr->journal_start > 1024*1024*1024) {\
        panic("%s:%d: tr journal start looks bad: 0x%llx\n", __FILE__, __LINE__, tr->journal_start);\
    }\
    if (tr->journal_end < 0 || tr->journal_end > 1024*1024*1024) {\
        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 int
calc_checksum(char *ptr, int len)
{
    int i, 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_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 %lu\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);
    }

    err = VNOP_STRATEGY(bp);
    if (!err) {
                err = (int)buf_biowait(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)
{
    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 ((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->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 ((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;

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

    for(; tr; tr=next) {
        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, (SInt32 *)&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);
}


#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].bsize   = SWAP32(blhdr->binfo[i].bsize);
                blhdr->binfo[i].b.cksum = SWAP32(blhdr->binfo[i].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 *)0 + 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 (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 (%lu)\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 %lu\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 <= (*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 <= (*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 > (*buf_ptr)[index].block_num*jhdr_size) {
        if (block_end >= ((*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 %lu\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 (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 (%lu)\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, orig_checksum, checksum, check_block_checksums=0, bad_blocks=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;
    
    // 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(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 = 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].b.sequence_num != 0)
                    && (blhdr->binfo[0].b.sequence_num != last_sequence_num)
                    && (blhdr->binfo[0].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].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].b.sequence_num, last_sequence_num);
                    bad_blocks = 1;
                    goto bad_txn_handling;
                }
                last_sequence_num = blhdr->binfo[0].b.sequence_num;

                if (blhdr_offset >= jnl->jhdr->end && jnl->jhdr->start <= jnl->jhdr->end) {
                    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 > 2048
                           || 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 (blhdr->binfo[i].bsize > max_bsize) {
                            max_bsize = blhdr->binfo[i].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].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].b.cksum != 0 && disk_cksum != blhdr->binfo[i].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].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].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) {
                    if (txn_start_offset == 0) {
                        printf("jnl: %s: no known good txn start offset! aborting journal replay.\n", jnl->jdev_name);
                        goto bad_replay;
                    }

                    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) != 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 DEFAULT_TRANSACTION_BUFFER_SIZE  (256*1024)  // better performance but uses more mem
#define MAX_TRANSACTION_BUFFER_SIZE      (512*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 if (mem_size >= (1024*1024*1024)) {
                        def_tbuffer_size = DEFAULT_TRANSACTION_BUFFER_SIZE * 4;
                }
        }

    // 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;
    off_t       writemaxcnt;
    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_name(devvp);
            jnl->flags |= JOURNAL_DO_FUA_WRITES;
            printf("jnl: %s: enabling FUA writes (features 0x%x)\n", name ? name : "no-name-dev", features);
        }
    }

    if (VNOP_IOCTL(devvp, DKIOCGETMAXBYTECOUNTREAD, (caddr_t)&readmaxcnt, 0, context)) {
        readmaxcnt = 0;
    } 

    if (readmaxcnt == 0) {
        if (VNOP_IOCTL(devvp, DKIOCGETMAXBLOCKCOUNTREAD, (caddr_t)&readblockcnt, 0, context)) {
            readmaxcnt = 128 * 1024;
        } else {
            readmaxcnt = readblockcnt * phys_blksz;
        }
    }


    if (VNOP_IOCTL(devvp, DKIOCGETMAXBYTECOUNTWRITE, (caddr_t)&writemaxcnt, 0, context)) {
        writemaxcnt = 0;
    }

    if (writemaxcnt == 0) {
        if (VNOP_IOCTL(devvp, DKIOCGETMAXBLOCKCOUNTWRITE, (caddr_t)&writeblockcnt, 0, context)) {
            writemaxcnt = 128 * 1024;
        } else {
            writemaxcnt = writeblockcnt * phys_blksz;
        }
    }

    jnl->max_read_size  = readmaxcnt;
    jnl->max_write_size = writemaxcnt;

    // just in case it's still zero...
    if (jnl->max_read_size == 0) {
        jnl->max_read_size = 128 * 1024;
        jnl->max_write_size = 128 * 1024;
    }
}


static const char *
get_jdev_name(struct vnode *jvp)
{
    const char *jdev_name;
    
    jdev_name = vnode_name(jvp);
    if (jdev_name == NULL) {
        jdev_name = vfs_addname("unknown-dev", strlen("unknown-dev"), 0, 0);
    } else {
        // this just bumps the refcount on the name so we have our own copy
        jdev_name = vfs_addname(jdev_name, strlen(jdev_name), 0, 0);
    }

    return jdev_name;
}


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)
{
    journal *jnl;
    size_t      phys_blksz;
    struct vfs_context context;
    const char *jdev_name;

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

    jdev_name = get_jdev_name(jvp);

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

    if (phys_blksz > min_fs_blksz) {
                printf("jnl: %s: create: error: phys blksize %lu bigger than min fs blksize %lu\n",
                    jdev_name, phys_blksz, min_fs_blksz);
                return NULL;
    }

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


    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);

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

    memset(jnl->header_buf, 0, phys_blksz);
    
    jnl->jhdr             = (journal_header *)jnl->header_buf;
    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 = random() & 0x00ffffff;

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

    if (write_journal_header(jnl) != 0) {
        printf("jnl: %s: journal_create: failed to write journal header.\n", jdev_name);
        goto bad_write;
    }

    return jnl;


  bad_write:
    kmem_free(kernel_map, (vm_offset_t)jnl->header_buf, phys_blksz);
  bad_kmem_alloc:
    if (jdev_name) {
        vfs_removename(jdev_name);
    }
    jnl->jhdr = NULL;
    FREE_ZONE(jnl, sizeof(struct journal), M_JNL_JNL);
    return NULL;
}


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)
{
    journal *jnl;
    int      orig_blksz=0;
    size_t   phys_blksz;
    int      orig_checksum, checksum;
    struct vfs_context context;
    const char *jdev_name = get_jdev_name(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)) {
                return NULL;
    }

    if (phys_blksz > min_fs_blksz) {
                printf("jnl: %s: open: error: phys blksize %lu bigger than min fs blksize %lu\n",
                    jdev_name, phys_blksz, min_fs_blksz);
                return NULL;
    }

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

    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);

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

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

    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 %lu 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) {
                printf("jnl: %s: open: phys_blksz %lu does not match journal header size %d\n",
                    jdev_name, phys_blksz, jnl->jhdr->jhdr_size);

                orig_blksz = phys_blksz;
                phys_blksz = jnl->jhdr->jhdr_size;
                if (VNOP_IOCTL(jvp, DKIOCSETBLOCKSIZE, (caddr_t)&phys_blksz, FWRITE, &context)) {
                    printf("jnl: %s: could not set block size to %lu bytes.\n", jdev_name, phys_blksz);
                    goto bad_journal;
                }
//              goto bad_journal;
    }

    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 > 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;
    }

    if (orig_blksz != 0) {
        VNOP_IOCTL(jvp, DKIOCSETBLOCKSIZE, (caddr_t)&orig_blksz, FWRITE, &context);
        phys_blksz = orig_blksz;
        if (orig_blksz < jnl->jhdr->jhdr_size) {
            printf("jnl: %s: open: jhdr_size is %d but orig phys blk size is %d.  switching.\n",
                jdev_name, jnl->jhdr->jhdr_size, orig_blksz);
                                   
            jnl->jhdr->jhdr_size = orig_blksz;
        }
    }

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

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

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

    return jnl;

  bad_journal:
    if (orig_blksz != 0) {
        phys_blksz = orig_blksz;
        VNOP_IOCTL(jvp, DKIOCSETBLOCKSIZE, (caddr_t)&orig_blksz, FWRITE, &context);
    }
    kmem_free(kernel_map, (vm_offset_t)jnl->header_buf, phys_blksz);
  bad_kmem_alloc:
    if (jdev_name) {
        vfs_removename(jdev_name);
    }
    FREE_ZONE(jnl, sizeof(struct journal), M_JNL_JNL);
    return NULL;    
}


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;
    int     phys_blksz, ret;
    int     orig_checksum, checksum;
    struct vfs_context context;
    const char *jdev_name = get_jdev_name(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);
        return EINVAL;
    }

    if (phys_blksz > (int)min_fs_block_size) {
        printf("jnl: %s: is_clean: error: phys blksize %d bigger than min fs blksize %lu\n",
            jdev_name, phys_blksz, min_fs_block_size);
        return EINVAL;
    }

    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);
        return EINVAL;
    }

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

    if (kmem_alloc(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);
        return ENOMEM;
    }

    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 = EINVAL;
    }

  get_out:
    kmem_free(kernel_map, (vm_offset_t)jnl.header_buf, phys_blksz);
    if (jdev_name) {
        vfs_removename(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);
    }

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

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

                        jnl->cur_tr = NULL;
                        end_transaction(tr, 1, NULL, NULL);   // force it to get flushed
                }
    
                //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);
    } 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->jhdr->jhdr_size);
    jnl->jhdr = (void *)0xbeefbabe;

    if (jnl->jdev_name) {
        vfs_removename(jnl->jdev_name);
    }

    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)
{
    size_t i;
    int    counter=0;

    //printf("jnl: check free space (desired 0x%x, avail 0x%Lx)\n",
//         desired_size, free_space(jnl));
    
    while (1) {
                int old_start_empty;
                
                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;
                }

                // make sure there's space in the journal to hold this transaction
                if (free_space(jnl) > desired_size && jnl->old_start[0] == 0) {
                        break;
                }
                //
                // 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++ > 100) {
                                        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) {
                                unlock_oldstart(jnl);
                                write_journal_header(jnl);
                                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;
                        write_journal_header(jnl);
                        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(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->jhdr->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);
    
    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;

    free_old_stuff(jnl);

    // make sure there's room in the journal
    if (free_space(jnl) < jnl->tbuffer_size) {
        // 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) != 0) {
                printf("jnl: %s: start transaction failed: no space\n", jnl->jdev_name);
                ret = ENOSPC;
                goto bad_start;
        }
    }

    // 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);

    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());
    }

    free_old_stuff(jnl);

    //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) {
                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);
                }

                // 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);

    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) {
                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());
    }

    free_old_stuff(jnl);

    // 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].b.bp) {
                                if (buf_size(bp) != blhdr->binfo[i].bsize) {
                                        panic("jnl: bp @ %p changed size on me! (%d vs. %lu, jnl %p)\n",
                                                  bp, buf_size(bp), blhdr->binfo[i].bsize, jnl);
                                }
                                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)(struct buf *bp, void *arg), void *arg)
{
    int                i = 1;
    int                tbuffer_offset=0;
    char              *blkptr;
    block_list_header *blhdr, *prev=NULL;
    transaction       *tr;

    CHECK_JOURNAL(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());
    }

    free_old_stuff(jnl);

    //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].b.bp) {
                                if (buf_size(bp) != blhdr->binfo[i].bsize) {
                                        panic("jnl: bp @ %p changed size on me! (%d vs. %lu, jnl %p)\n",
                                                  bp, buf_size(bp), blhdr->binfo[i].bsize, jnl);
                                }
                                break;
                        }
                        tbuffer_offset += blhdr->binfo[i].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(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 the function pointer is not set then copy the
        // block of data now.  if the function pointer is set 
        // the copy will happen after calling the callback in
        // end_transaction() just before it goes to disk.
        //
        if (func == NULL) {
                blkptr = (char *)&((char *)blhdr)[tbuffer_offset];
                memcpy(blkptr, (char *)0 + buf_dataptr(bp), buf_size(bp));
        }

    // 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].bsize = bsize;
                blhdr->binfo[i].b.bp    = bp;
                if (func) {
                        void *old_func=NULL, *old_arg=NULL;
                        
                        buf_setfilter(bp, func, arg, &old_func, &old_arg);
                        if (old_func != NULL) {
                                panic("jnl: modify_block_end: old func %p / arg %p", old_func, old_arg);
                        }
                }
                
                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);

    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());
    }

    free_old_stuff(jnl);

    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].b.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].b.bp   = NULL;
                                blhdr->binfo[i].bnum = (off_t)-1;

                                buf_markinvalid(bp);
                                buf_brelse(bp);

                                break;
                        }
                }

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

    return 0;
}


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->b.bp == NULL) {
                return 1;
    }
    if (bi_b->b.bp == NULL) {
                return -1;
    }

    // don't have to worry about negative block
    // numbers so this is ok to do.
    //
    res = (buf_blkno(bi_a->b.bp) - buf_blkno(bi_b->b.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)
{
    int                 i, ret, amt;
    errno_t             errno;
    off_t               end;
    journal            *jnl = tr->jnl;
    struct buf         *bp, **bparray;
    block_list_header  *blhdr=NULL, *next=NULL;
    size_t              tbuffer_offset;

        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;
                return 0;
    }

    // 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.
    //
    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->cur_tr = tr;
                return 0;
    }


    // if we're here we're going to flush the transaction buffer to disk.
    // make sure there is room in the journal first.
    check_free_space(jnl, tr->total_bytes);

    // 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);
    }

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

        //
        // if the first entry in old_start[] isn't free yet, loop calling the
        // file system flush routine until it is (or we panic).
        //
        i = 0;
        lock_oldstart(jnl);
        while ((jnl->old_start[0] & 0x8000000000000000LL) != 0) {
                if (jnl->flush) {
                        unlock_oldstart(jnl);

                        if (jnl->flush) {
                                jnl->flush(jnl->flush_arg);
                        }

                        // yield the cpu so others can get in to clear the lock bit
                        (void)tsleep((void *)jnl, PRIBIO, "jnl-old-start-sleep", 1);

                        lock_oldstart(jnl);
                }
                if (i++ >= 500) {
                        panic("jnl: transaction that started at 0x%llx is not completing! jnl %p\n",
                                  jnl->old_start[0] & (~0x8000000000000000LL), jnl);
                }
        }

        //
        // slide everyone else down and put our latest guy in the last
        // entry in the old_start array
        //
        memcpy(&jnl->old_start[0], &jnl->old_start[1], 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 each block, make sure that the physical block # is set
    for(blhdr=tr->blhdr; blhdr; blhdr=next) {
                char *blkptr;
                
                tbuffer_offset = jnl->jhdr->blhdr_size;
                for(i=1; i < blhdr->num_blocks; i++) {
                        daddr64_t blkno;
                        daddr64_t lblkno;
                        struct vnode *vp;

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

                        // if this block has a callback function set, call
                        // it now and then copy the data from the bp into
                        // the journal. 
                        if (bp) {
                                void (*func)(struct buf *, void *);
                                void  *arg;

                                buf_setfilter(bp, NULL, NULL, (void **)&func, &arg);

                                if (func) {
                                        // 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, 0, 0, 0);
                                        } while (errno == EAGAIN);
                                        
                                        if (errno == 0) {
                                        
                                                // call the hook function and then copy the
                                                // data into the transaction buffer...
                                                func(bp, arg);

                                                blkptr = (char *)&((char *)blhdr)[tbuffer_offset];
                                                memcpy(blkptr, (char *)buf_dataptr(bp), buf_size(bp));

                                                buf_drop(bp);
                                        } else {
                                                panic("could not acquire bp %p (err %d)\n", bp, errno);
                                        }
                                }

                        } else {   // bp == NULL, only true if a block was "killed" 
                                if (blhdr->binfo[i].bnum != (off_t)-1) {
                                        panic("jnl: inconsistent binfo (NULL bp w/bnum %lld; jnl @ %p, tr %p)\n",
                                                blhdr->binfo[i].bnum, jnl, tr);
                                }

                                tbuffer_offset += blhdr->binfo[i].bsize;
                                continue;
                        }

                        tbuffer_offset += blhdr->binfo[i].bsize;

                        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);
                            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);
                                        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);
                                        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);
                                        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);
                }

                next = (block_list_header *)((long)blhdr->binfo[0].bnum);
    }
    


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

                blhdr->binfo[0].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 %lu bytes for bparray\n", blhdr->num_blocks * sizeof(struct buf *));
                }

                // calculate individual block checksums
                tbuffer_offset = jnl->jhdr->blhdr_size;
                for(i=1; i < blhdr->num_blocks; i++) {
                    bparray[i] = blhdr->binfo[i].b.bp;
                    if (bparray[i]) {
                        blhdr->binfo[i].b.cksum = calc_checksum(&((char *)blhdr)[tbuffer_offset], blhdr->binfo[i].bsize);
                    } else {
                        blhdr->binfo[i].b.cksum = 0;
                    }

                    tbuffer_offset += blhdr->binfo[i].bsize;
                }

                ret = write_journal_data(jnl, &end, blhdr, amt);

                // always put the bp pointers back
                for(i=1; i < blhdr->num_blocks; i++) {
                    blhdr->binfo[i].b.bp = bparray[i];
                }

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

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

                        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) {
                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) {
                goto bad_journal;
        }
        
    //
    // setup for looping through all the blhdr's.  we null out the
    // tbuffer and blhdr fields so that they're not used any more.
    //
    blhdr       = tr->blhdr;
    tr->tbuffer = NULL;
    tr->blhdr   = NULL;

    // 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;

    // for each block, set the iodone callback and unlock it
    for(; blhdr; blhdr=next) {

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

                for(i=1; i < blhdr->num_blocks; i++) {
                        if (blhdr->binfo[i].b.bp == NULL) {
                                continue;
                        }

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

                        // have to pass BAC_REMOVE here because we're going to bawrite()
                        // the buffer when we're done
                        do {
                                errno = buf_acquire(bp, BAC_REMOVE, 0, 0);
                        } while (errno == EAGAIN);
                        
                        if (errno == 0) {
                                struct vnode *save_vp;
                                void *cur_filter;

                                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);
                                                continue;
                                        } else {
                                                panic("jnl: end_tr: !!!DANGER!!! bp %p flags (0x%x) not LOCKED & DELWRI\n", bp, buf_flags(bp));
                                        }
                                }
                                save_vp = buf_vnode(bp);

                                buf_setfilter(bp, buffer_flushed_callback, tr, &cur_filter, NULL);

                                if (cur_filter) {
                                        panic("jnl: bp @ %p (blkno %qd, vp %p) has non-null iodone (%p) buffflushcb %p\n",
                                                  bp, buf_blkno(bp), save_vp, cur_filter, buffer_flushed_callback);
                                }
                                buf_clearflags(bp, B_LOCKED);

                                // kicking off the write here helps performance
                                buf_bawrite(bp);
                                // XXXdbg this is good for testing: buf_bdwrite(bp);
                                //buf_bdwrite(bp);
                                
                                // this undoes the vnode_ref() in journal_modify_block_end()
                                vnode_rele_ext(save_vp, 0, 1);
                        } else {
                                printf("jnl: %s: end_transaction: could not acquire block %p (errno %d)!\n",
                                    jnl->jdev_name,bp, errno);
                        }
                }

                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);
    }

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


  bad_journal:
    jnl->flags |= JOURNAL_INVALID;
    jnl->old_start[sizeof(jnl->old_start)/sizeof(jnl->old_start[0]) - 1] &= ~0x8000000000000000LL;
    abort_transaction(jnl, tr);
    return -1;
}

static void
abort_transaction(journal *jnl, transaction *tr)
{
    int                i;
    errno_t             errno;
    block_list_header *blhdr, *next;
    struct buf        *bp;
    struct vnode      *save_vp;

    // for each block list header, iterate over the blocks then
    // free up the memory associated with the block list.
    //
    // for each block, clear the lock bit and release it.
    //
    for(blhdr=tr->blhdr; blhdr; blhdr=next) {

                for(i=1; i < blhdr->num_blocks; i++) {
                        if (blhdr->binfo[i].b.bp == NULL) {
                                continue;
                        }
                        if ( (buf_vnode(blhdr->binfo[i].b.bp) == NULL) ||
                             !(buf_flags(blhdr->binfo[i].b.bp) & B_LOCKED) ) {
                                continue;
                        }

                        errno = buf_meta_bread(buf_vnode(blhdr->binfo[i].b.bp),
                                                         buf_lblkno(blhdr->binfo[i].b.bp),
                                                         buf_size(blhdr->binfo[i].b.bp),
                                                         NOCRED,
                                                         &bp);
                        if (errno == 0) {
                                if (bp != blhdr->binfo[i].b.bp) {
                                        panic("jnl: abort_tr: got back a different bp! (bp %p should be %p, jnl %p\n",
                                                  bp, blhdr->binfo[i].b.bp, jnl);
                                }

                                // releasing a bp marked invalid
                                // also clears the locked and delayed state
                                buf_markinvalid(bp);
                                save_vp = buf_vnode(bp);

                                buf_brelse(bp);

                                vnode_rele_ext(save_vp, 0, 1);
                        } else {
                                printf("jnl: %s: abort_tr: could not find block %Ld vp %p!\n",
                                    jnl->jdev_name, blhdr->binfo[i].bnum, blhdr->binfo[i].b.bp);
                                if (bp) {
                                        buf_brelse(bp);
                                }
                        }
                }

                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);
    }

    tr->tbuffer     = NULL;
    tr->blhdr       = NULL;
    tr->total_bytes = 0xdbadc0de;
        FREE_ZONE(tr, sizeof(transaction), M_JNL_TR);
}


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

    free_old_stuff(jnl);

    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;
    ret = end_transaction(tr, 0, NULL, NULL);

    jnl->owner = NULL;
    unlock_journal(jnl);

    return ret;
}


int
journal_flush(journal *jnl)
{
    int need_signal = 0;
    
    CHECK_JOURNAL(jnl);
    
    if (jnl->flags & JOURNAL_INVALID) {
                return -1;
    }

    KERNEL_DEBUG_CONSTANT((FSDBG_CODE(DBG_JOURNAL, DBG_JOURNAL_FLUSH)) 
        | DBG_FUNC_START, 0, 0, 0, 0, 0);

    if (jnl->owner != current_thread()) {
                lock_journal(jnl);
                need_signal = 1;
    }

    free_old_stuff(jnl);

    // 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;
                end_transaction(tr, 1, NULL, NULL);   // force it to get flushed
    }

    if (need_signal) {
                unlock_journal(jnl);
    }

    KERNEL_DEBUG_CONSTANT((FSDBG_CODE(DBG_JOURNAL, DBG_JOURNAL_FLUSH)) 
        | DBG_FUNC_END, 0, 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;
        
        /*
         * 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);
        jnl->active_tr = tr;
        if (ret) {
                return ret;
        }
        
        /* 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);
        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;
}