xnu-792.2.4.tar.gz

[apple/xnu.git] / bsd / hfs / hfs_btreeio.c

/*
 * Copyright (c) 2000-2004 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This 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 OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/buf.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/vnode.h>


#include "hfs.h"
#include "hfs_cnode.h"
#include "hfs_dbg.h"
#include "hfs_endian.h"

#include "hfscommon/headers/FileMgrInternal.h"
#include "hfscommon/headers/BTreesPrivate.h"

#define FORCESYNCBTREEWRITES 0


static int ClearBTNodes(struct vnode *vp, long blksize, off_t offset, off_t amount);


__private_extern__
OSStatus SetBTreeBlockSize(FileReference vp, ByteCount blockSize, ItemCount minBlockCount)
{
        BTreeControlBlockPtr    bTreePtr;
        
        DBG_ASSERT(vp != NULL);
        DBG_ASSERT(blockSize >= kMinNodeSize);
    if (blockSize > MAXBSIZE )
        return (fsBTBadNodeSize);

        bTreePtr = (BTreeControlBlockPtr)VTOF(vp)->fcbBTCBPtr;
        bTreePtr->nodeSize = blockSize;
        
    return (E_NONE);
}


__private_extern__
OSStatus GetBTreeBlock(FileReference vp, UInt32 blockNum, GetBlockOptions options, BlockDescriptor *block)
{
    OSStatus     retval = E_NONE;
    struct buf   *bp = NULL;

    if (options & kGetEmptyBlock) {
        daddr64_t blkno;
        off_t offset;

        offset = (daddr64_t)blockNum * (daddr64_t)block->blockSize;
        bp = buf_getblk(vp, (daddr64_t)blockNum, block->blockSize, 0, 0, BLK_META);
        if (bp &&
            VNOP_BLOCKMAP(vp, offset, block->blockSize, &blkno, NULL, NULL, 0, NULL) == 0) {
            buf_setblkno(bp, blkno);
        }
    } else {
        retval = buf_meta_bread(vp, (daddr64_t)blockNum, block->blockSize, NOCRED, &bp);
    }
    if (bp == NULL)
        retval = -1;    //XXX need better error

    if (retval == E_NONE) {
        block->blockHeader = bp;
        block->buffer = (char *)buf_dataptr(bp);
        block->blockReadFromDisk = (buf_fromcache(bp) == 0);    /* not found in cache ==> came from disk */

                // XXXdbg 
                block->isModified = 0;

#if BYTE_ORDER == LITTLE_ENDIAN
        /* Endian swap B-Tree node (only if it's a valid block) */
        if (!(options & kGetEmptyBlock)) {
            /* This happens when we first open the b-tree, we might not have all the node data on hand */
            if ((((BTNodeDescriptor *)block->buffer)->kind == kBTHeaderNode) &&
                (((BTHeaderRec *)((char *)block->buffer + 14))->nodeSize != buf_count(bp)) &&
                (SWAP_BE16 (((BTHeaderRec *)((char *)block->buffer + 14))->nodeSize) != buf_count(bp))) {

                /* Don't swap the descriptors at all, we don't care (this block will be invalidated) */
                SWAP_BT_NODE (block, ISHFSPLUS(VTOVCB(vp)), VTOC(vp)->c_fileid, 3);

            /* The node needs swapping */
            } else if (*((UInt16 *)((char *)block->buffer + (block->blockSize - sizeof (UInt16)))) == 0x0e00) {
                SWAP_BT_NODE (block, ISHFSPLUS(VTOVCB(vp)), VTOC(vp)->c_fileid, 0);
#if 0
            /* The node is not already in native byte order, hence corrupt */
            } else if (*((UInt16 *)((char *)block->buffer + (block->blockSize - sizeof (UInt16)))) != 0x000e) {
                panic ("%s Corrupt B-Tree node detected!\n", "GetBTreeBlock:");
#endif
            }
        }
#endif
    } else {
        if (bp)
                buf_brelse(bp);
        block->blockHeader = NULL;
        block->buffer = NULL;
    }

    return (retval);
}


__private_extern__
void ModifyBlockStart(FileReference vp, BlockDescPtr blockPtr)
{
        struct hfsmount *hfsmp = VTOHFS(vp);
    struct buf *bp = NULL;

        if (hfsmp->jnl == NULL) {
                return;
        }
        
    bp = (struct buf *) blockPtr->blockHeader;
    if (bp == NULL) {
                panic("ModifyBlockStart: null bp  for blockdescptr 0x%x?!?\n", blockPtr);
                return;
    }

        journal_modify_block_start(hfsmp->jnl, bp);
        blockPtr->isModified = 1;
}

static int
btree_journal_modify_block_end(struct hfsmount *hfsmp, struct buf *bp)
{
#if BYTE_ORDER == LITTLE_ENDIAN
    struct vnode *vp = buf_vnode(bp);
    BlockDescriptor block;
                                    
    /* Prepare the block pointer */
    block.blockHeader = bp;
    block.buffer = (char *)buf_dataptr(bp);
    /* not found in cache ==> came from disk */
    block.blockReadFromDisk = (buf_fromcache(bp) == 0);
    block.blockSize = buf_count(bp);

    // XXXdbg have to swap the data before it goes in the journal
    SWAP_BT_NODE (&block, ISHFSPLUS (VTOVCB(vp)), VTOC(vp)->c_fileid, 1);
#endif

    return journal_modify_block_end(hfsmp->jnl, bp);
}


__private_extern__
OSStatus ReleaseBTreeBlock(FileReference vp, BlockDescPtr blockPtr, ReleaseBlockOptions options)
{
    struct hfsmount     *hfsmp = VTOHFS(vp);
    extern int bdwrite_internal(struct buf *, int);
    OSStatus    retval = E_NONE;
    struct buf *bp = NULL;

    bp = (struct buf *) blockPtr->blockHeader;

    if (bp == NULL) {
        retval = -1;
        goto exit;
    }

    if (options & kTrashBlock) {
                buf_markinvalid(bp);

                if (hfsmp->jnl && (buf_flags(bp) & B_LOCKED)) {
                        journal_kill_block(hfsmp->jnl, bp);
                } else {
                        buf_brelse(bp); /* note: B-tree code will clear blockPtr->blockHeader and blockPtr->buffer */
                }
    } else {
        if (options & kForceWriteBlock) {
                        if (hfsmp->jnl) {
                                if (blockPtr->isModified == 0) {
                                        panic("hfs: releaseblock: modified is 0 but forcewrite set! bp 0x%x\n", bp);
                                }

                                retval = btree_journal_modify_block_end(hfsmp, bp);
                                blockPtr->isModified = 0;
                        } else {
                                retval = VNOP_BWRITE(bp);
                        }
        } else if (options & kMarkBlockDirty) {
                        struct timeval tv;
                        microuptime(&tv);
            if ((options & kLockTransaction) && hfsmp->jnl == NULL) {
                /*
                 *
                 * Set the B_LOCKED flag and unlock the buffer, causing buf_brelse to move
                 * the buffer onto the LOCKED free list.  This is necessary, otherwise
                 * getnewbuf() would try to reclaim the buffers using buf_bawrite, which
                 * isn't going to work.
                 *
                 */
                extern int count_lock_queue(void);

                /* Don't hog all the buffers... */
                if (count_lock_queue() > kMaxLockedMetaBuffers) {
                     hfs_btsync(vp, HFS_SYNCTRANS);
                     /* Rollback sync time to cause a sync on lock release... */
                     (void) BTSetLastSync(VTOF(vp), tv.tv_sec - (kMaxSecsForFsync + 1));
                }
                buf_setflags(bp, B_LOCKED);
            }

            /* 
             * Delay-write this block.
             * If the maximum delayed buffers has been exceeded then
             * free up some buffers and fall back to an asynchronous write.
             */
                        if (hfsmp->jnl) {
                                if (blockPtr->isModified == 0) {
                                        panic("hfs: releaseblock: modified is 0 but markdirty set! bp 0x%x\n", bp);
                                }
                                retval = btree_journal_modify_block_end(hfsmp, bp);
                                blockPtr->isModified = 0;
                        } else if (bdwrite_internal(bp, 1) != 0) {
                hfs_btsync(vp, 0);
                /* Rollback sync time to cause a sync on lock release... */
                (void) BTSetLastSync(VTOF(vp), tv.tv_sec - (kMaxSecsForFsync + 1));

                buf_clearflags(bp, B_LOCKED);
                buf_bawrite(bp);
            }
        } else {
                        // check if we had previously called journal_modify_block_start() 
                        // on this block and if so, abort it (which will call buf_brelse()).
                        if (hfsmp->jnl && blockPtr->isModified) {
                                // XXXdbg - I don't want to call modify_block_abort()
                                //          because I think it may be screwing up the
                                //          journal and blowing away a block that has
                                //          valid data in it.
                                //   
                                //    journal_modify_block_abort(hfsmp->jnl, bp);
                                //panic("hfs: releaseblock called for 0x%x but mod_block_start previously called.\n", bp);
                                btree_journal_modify_block_end(hfsmp, bp);
                                blockPtr->isModified = 0;
                        } else {
                                buf_brelse(bp); /* note: B-tree code will clear blockPtr->blockHeader and blockPtr->buffer */
                        }
        };
    };

exit:
    return (retval);
}


__private_extern__
OSStatus ExtendBTreeFile(FileReference vp, FSSize minEOF, FSSize maxEOF)
{
#pragma unused (maxEOF)

        OSStatus        retval = 0, ret = 0;
        UInt64          actualBytesAdded, origSize;
        UInt64          bytesToAdd;
        u_int32_t       startAllocation;
        u_int32_t       fileblocks;
        BTreeInfoRec btInfo;
        ExtendedVCB     *vcb;
        FCB                     *filePtr;
    struct proc *p = NULL;
        UInt64          trim = 0;
        int  lockflags = 0;

        filePtr = GetFileControlBlock(vp);

        if ( minEOF > filePtr->fcbEOF )
        {
                bytesToAdd = minEOF - filePtr->fcbEOF;

                if (bytesToAdd < filePtr->ff_clumpsize)
                        bytesToAdd = filePtr->ff_clumpsize;             //XXX why not always be a mutiple of clump size?
        }
        else
        {
                return -1;
        }

        vcb = VTOVCB(vp);
        
        /*
         * The Extents B-tree can't have overflow extents. ExtendFileC will
         * return an error if an attempt is made to extend the Extents B-tree
         * when the resident extents are exhausted.
         */

        /* Protect allocation bitmap and extents overflow file. */
        lockflags = SFL_BITMAP;
        if (VTOC(vp)->c_fileid != kHFSExtentsFileID)
                lockflags |= SFL_EXTENTS;
        lockflags = hfs_systemfile_lock(vcb, lockflags, HFS_EXCLUSIVE_LOCK);

        (void) BTGetInformation(filePtr, 0, &btInfo);

#if 0  // XXXdbg
        /*
         * The b-tree code expects nodes to be contiguous. So when
         * the allocation block size is less than the b-tree node
         * size, we need to force disk allocations to be contiguous.
         */
        if (vcb->blockSize >= btInfo.nodeSize) {
                extendFlags = 0;
        } else {
                /* Ensure that all b-tree nodes are contiguous on disk */
                extendFlags = kEFContigMask;
        }
#endif

        origSize = filePtr->fcbEOF;
        fileblocks = filePtr->ff_blocks;
        startAllocation = vcb->nextAllocation;

        // loop trying to get a contiguous chunk that's an integer multiple
        // of the btree node size.  if we can't get a contiguous chunk that
        // is at least the node size then we break out of the loop and let
        // the error propagate back up.
        do {
                retval = ExtendFileC(vcb, filePtr, bytesToAdd, 0,
                                     kEFContigMask | kEFMetadataMask,
                                     &actualBytesAdded);
                if (retval == dskFulErr && actualBytesAdded == 0) {

                        if (bytesToAdd == btInfo.nodeSize || bytesToAdd < (minEOF - origSize)) {
                                // if we're here there's nothing else to try, we're out
                                // of space so we break and bail out.
                                break;
                        } else {
                                bytesToAdd >>= 1;
                                if (bytesToAdd < btInfo.nodeSize) {
                                        bytesToAdd = btInfo.nodeSize;
                                } else if ((bytesToAdd % btInfo.nodeSize) != 0) {
                                        // make sure it's an integer multiple of the nodeSize
                                        bytesToAdd -= (bytesToAdd % btInfo.nodeSize);
                                }
                        }
                }
        } while (retval == dskFulErr && actualBytesAdded == 0);

        /*
         * If a new extent was added then move the roving allocator
         * reference forward by the current b-tree file size so 
         * there's plenty of room to grow.
         */
        if ((retval == 0) &&
            ((VCBTOHFS(vcb)->hfs_flags & HFS_METADATA_ZONE) == 0) &&
            (vcb->nextAllocation > startAllocation) &&
            ((vcb->nextAllocation + fileblocks) < vcb->totalBlocks)) {
                vcb->nextAllocation += fileblocks;
        }
                
        filePtr->fcbEOF = (u_int64_t)filePtr->ff_blocks * (u_int64_t)vcb->blockSize;

        // XXXdbg ExtendFileC() could have returned an error even though
        // it grew the file to be big enough for our needs.  If this is
        // the case, we don't care about retval so we blow it away.
        //
        if (filePtr->fcbEOF >= minEOF && retval != 0) {
                retval = 0;
        }

        // XXXdbg if the file grew but isn't large enough or isn't an
        // even multiple of the nodeSize then trim things back.  if
        // the file isn't large enough we trim back to the original
        // size.  otherwise we trim back to be an even multiple of the
        // btree node size.
        //
        if ((filePtr->fcbEOF < minEOF) || (actualBytesAdded % btInfo.nodeSize) != 0) {

                if (filePtr->fcbEOF < minEOF) {
                        retval = dskFulErr;
                        
                        if (filePtr->fcbEOF < origSize) {
                                panic("hfs: btree file eof %lld less than orig size %lld!\n",
                                          filePtr->fcbEOF, origSize);
                        }
                        
                        trim = filePtr->fcbEOF - origSize;
                        if (trim != actualBytesAdded) {
                                panic("hfs: trim == %lld but actualBytesAdded == %lld\n",
                                          trim, actualBytesAdded);
                        }
                } else {
                        trim = (actualBytesAdded % btInfo.nodeSize);
                }

                ret = TruncateFileC(vcb, filePtr, filePtr->fcbEOF - trim, 0);
                filePtr->fcbEOF = (u_int64_t)filePtr->ff_blocks * (u_int64_t)vcb->blockSize;

                // XXXdbg - panic if the file didn't get trimmed back properly
                if ((filePtr->fcbEOF % btInfo.nodeSize) != 0) {
                        panic("hfs: truncate file didn't! fcbEOF %lld nsize %d fcb 0x%x\n",
                                  filePtr->fcbEOF, btInfo.nodeSize, filePtr);
                }

                if (ret) {
                        // XXXdbg - this probably doesn't need to be a panic()
                        panic("hfs: error truncating btree files (sz 0x%llx, trim %lld, ret %d)\n",
                                  filePtr->fcbEOF, trim, ret);
                        goto out;
                }
                actualBytesAdded -= trim;
        }

        if(VTOC(vp)->c_fileid != kHFSExtentsFileID) {
                /*
                 * Get any extents overflow b-tree changes to disk ASAP!
                 */
                (void) BTFlushPath(VTOF(vcb->extentsRefNum));
                (void) hfs_fsync(vcb->extentsRefNum, MNT_WAIT, 0, p);
        }
        hfs_systemfile_unlock(vcb, lockflags);
        lockflags = 0;

        if ((filePtr->fcbEOF % btInfo.nodeSize) != 0) {
                panic("hfs: extendbtree: fcb 0x%x has eof 0x%llx not a multiple of 0x%x (trim %llx)\n",
                          filePtr, filePtr->fcbEOF, btInfo.nodeSize, trim);
        }

        /*
         * Update the Alternate MDB or Alternate VolumeHeader
         */
        if ((VTOC(vp)->c_fileid == kHFSExtentsFileID)   ||
            (VTOC(vp)->c_fileid == kHFSCatalogFileID)   ||
            (VTOC(vp)->c_fileid == kHFSAttributesFileID)
           ) {
                VTOC(vp)->c_flag |= C_MODIFIED;
                MarkVCBDirty( vcb );
                ret = hfs_flushvolumeheader(VCBTOHFS(vcb), MNT_WAIT, HFS_ALTFLUSH);
        } else {
                VTOC(vp)->c_touch_chgtime = TRUE;
                VTOC(vp)->c_touch_modtime = TRUE;
                (void) hfs_update(vp, TRUE);
        }

        ret = ClearBTNodes(vp, btInfo.nodeSize, filePtr->fcbEOF - actualBytesAdded, actualBytesAdded);
out:
        if (retval == 0)
                retval = ret;
        
        if (lockflags)
                hfs_systemfile_unlock(vcb, lockflags);
        
        return retval;
}


/*
 * Clear out (zero) new b-tree nodes on disk.
 */
static int
ClearBTNodes(struct vnode *vp, long blksize, off_t offset, off_t amount)
{
        struct hfsmount *hfsmp = VTOHFS(vp);
        struct buf *bp = NULL;
        daddr64_t blk;
        daddr64_t blkcnt;
    
        blk = offset / blksize;
        blkcnt = amount / blksize;
        
        while (blkcnt > 0) {
                bp = buf_getblk(vp, blk, blksize, 0, 0, BLK_META);
                if (bp == NULL)
                        continue;

        // XXXdbg
                if (hfsmp->jnl) {
                        // XXXdbg -- skipping this for now since it makes a transaction
                        //           become *way* too large
                    //journal_modify_block_start(hfsmp->jnl, bp);
                }
                bzero((char *)buf_dataptr(bp), blksize);

                buf_markaged(bp);

        // XXXdbg
                if (hfsmp->jnl) {
                        // XXXdbg -- skipping this for now since it makes a transaction
                        //           become *way* too large
                        //journal_modify_block_end(hfsmp->jnl, bp);

                        // XXXdbg - remove this once we decide what to do with the
                        //          writes to the journal
                        if ((blk % 32) == 0)
                            VNOP_BWRITE(bp);
                        else
                            buf_bawrite(bp);
                } else {
                        /* wait/yield every 32 blocks so we don't hog all the buffers */
                        if ((blk % 32) == 0)
                                VNOP_BWRITE(bp);
                        else
                                buf_bawrite(bp);
                }
                --blkcnt;
                ++blk;
        }

        return (0);
}


extern char  hfs_attrname[];

extern int  hfs_attrkeycompare(HFSPlusAttrKey *searchKey, HFSPlusAttrKey *trialKey);

int  hfs_create_attr_btree(struct hfsmount *hfsmp, uint32_t nodesize, uint32_t nodecnt);

/*
 * Create an HFS+ Attribute B-tree File.
 *
 * A journal transaction must be already started.
 */
int
hfs_create_attr_btree(struct hfsmount *hfsmp, uint32_t nodesize, uint32_t nodecnt)
{
        struct vnode* vp = NULL;
        struct cat_desc cndesc;
        struct cat_attr cnattr;
        struct cat_fork cfork;
        BlockDescriptor blkdesc;
        BTNodeDescriptor  *ndp;
        BTHeaderRec  *bthp;
        BTreeControlBlockPtr btcb = NULL;
        struct buf *bp = NULL;
        void * buffer;
        u_int16_t *index;
        u_int16_t  offset;
        int result;

        printf("Creating HFS+ Attribute B-tree File (%d nodes) on %s\n", nodecnt, hfsmp->vcbVN);

        /*
         * Set up Attribute B-tree vnode
         */
        bzero(&cndesc, sizeof(cndesc));
        cndesc.cd_parentcnid = kHFSRootParentID;
        cndesc.cd_flags |= CD_ISMETA;
        cndesc.cd_nameptr = hfs_attrname;
        cndesc.cd_namelen = strlen(hfs_attrname);
        cndesc.cd_cnid = kHFSAttributesFileID;

        bzero(&cnattr, sizeof(cnattr));
        cnattr.ca_nlink = 1;
        cnattr.ca_mode = S_IFREG;
        cnattr.ca_fileid = cndesc.cd_cnid;

        bzero(&cfork, sizeof(cfork));
        cfork.cf_clump = nodesize * nodecnt;

        result = hfs_getnewvnode(hfsmp, NULL, NULL, &cndesc, 0, &cnattr, &cfork, &vp);
        if (result)
                return (result);

        /*
         * Set up Attribute B-tree control block
         */
        MALLOC(btcb, BTreeControlBlock *, sizeof(BTreeControlBlock), M_TEMP, M_WAITOK);
        bzero(btcb, sizeof(BTreeControlBlock));

        btcb->nodeSize          = nodesize;
        btcb->maxKeyLength      = kHFSPlusAttrKeyMaximumLength;
        btcb->btreeType         = 0xFF;
        btcb->attributes        = kBTVariableIndexKeysMask | kBTBigKeysMask;
        btcb->version           = kBTreeVersion;
        btcb->writeCount        = 1;
        btcb->flags             = 0;  /* kBTHeaderDirty */
        btcb->fileRefNum        = vp;
        btcb->getBlockProc      = GetBTreeBlock;
        btcb->releaseBlockProc  = ReleaseBTreeBlock;
        btcb->setEndOfForkProc  = ExtendBTreeFile;
        btcb->keyCompareProc    = (KeyCompareProcPtr)hfs_attrkeycompare;
        VTOF(vp)->fcbBTCBPtr    = btcb;

        /*
         * Allocate some space
         */
        result = ExtendBTreeFile(vp, nodesize, cfork.cf_clump);
        if (result)
                goto exit;

        btcb->totalNodes = VTOF(vp)->ff_size / nodesize;
        btcb->freeNodes = btcb->totalNodes - 1;

        /*
         * Initialize the b-tree header on disk
         */
        bp = buf_getblk(vp, 0, nodesize, 0, 0, BLK_META);
        if (bp == NULL) {
                result = EIO;
                goto exit;
        }

        buffer = (void *)buf_dataptr(bp);
        blkdesc.buffer = buffer;
        blkdesc.blockHeader = (void *)bp;
        blkdesc.blockReadFromDisk = 0;
        blkdesc.isModified = 0;

        ModifyBlockStart(vp, &blkdesc);

        if (buf_size(bp) != nodesize)
                panic("hfs_create_attr_btree: bad buffer size (%d)\n", buf_size(bp));

        bzero(buffer, nodesize);
        index = (int16_t *)buffer;

        /* FILL IN THE NODE DESCRIPTOR:  */
        ndp = (BTNodeDescriptor *)buffer;
        ndp->kind = kBTHeaderNode;
        ndp->numRecords = 3;
        offset = sizeof(BTNodeDescriptor);
        index[(nodesize / 2) - 1] = offset;

        /* FILL IN THE HEADER RECORD:  */
        bthp = (BTHeaderRec *)((UInt8 *)buffer + offset);
        bthp->nodeSize     = nodesize;
        bthp->totalNodes   = btcb->totalNodes;
        bthp->freeNodes    = btcb->freeNodes;
        bthp->clumpSize    = cfork.cf_clump;
        bthp->btreeType    = 0xFF;
        bthp->attributes   = kBTVariableIndexKeysMask | kBTBigKeysMask;
        bthp->maxKeyLength = kHFSPlusAttrKeyMaximumLength;
        bthp->keyCompareType = kHFSBinaryCompare;
        offset += sizeof(BTHeaderRec);
        index[(nodesize / 2) - 2] = offset;

        /* FILL IN THE USER RECORD:  */
        offset += kBTreeHeaderUserBytes;
        index[(nodesize / 2) - 3] = offset;

        /* FILL IN THE MAP RECORD (only one node in use). */
        *((u_int8_t *)buffer + offset) = 0x80;
        offset += nodesize - sizeof(BTNodeDescriptor) - sizeof(BTHeaderRec)
                           - kBTreeHeaderUserBytes - (4 * sizeof(int16_t));
        index[(nodesize / 2) - 4] = offset;

        if (hfsmp->jnl) {
                result = btree_journal_modify_block_end(hfsmp, bp);
        } else {
                result = VNOP_BWRITE(bp);
        }
        if (result)
                goto exit;

        /* Publish new btree file */
        hfsmp->hfs_attribute_vp = vp;
        (void) hfs_flushvolumeheader(hfsmp, MNT_WAIT, HFS_ALTFLUSH);

exit:
        hfs_unlock(VTOC(vp));
        if (result) {
                if (btcb) {
                        FREE (btcb, M_TEMP);
                }
                vnode_put(vp);
        //      hfs_truncate();  /* XXX need to give back blocks */
        }
        return (result);
}