User:Finxx/HFS+

Filesystems
Virtual Filesystems
VFS
Disk Filesystems
FAT 12/16/32, VFAT, ExFAT Ext 2/3/4 LEAN HPFS NTFS HFS HFS+ MFS ReiserFS FFS (Amiga) FFS (BSD)/UFS BeFS BFS XFS SFS ZDSFS ZFS USTAR
CD/DVD Filesystems
ISO 9660 Joliet UDF
Network Filesystems
NFS RFS AFS
Flash Filesystems
JFFS2 YAFFS

HFS+ is the successor to HFS, and was introduced by Apple in Mac OS 8.1. It has support for larger disks and allows for more than 65,000 files. It also has support for journaling. The format is described in Apple's "legacy" documentation, as TN1150.

Concepts

Files in HFS+ as stored in what are called "forks". Data is stored in "allocation blocks".

struct HFSPlusExtentDescriptor {
    UInt32                  startBlock;
    UInt32                  blockCount;
};
typedef struct HFSPlusExtentDescriptor HFSPlusExtentDescriptor;

struct HFSPlusForkData {
    UInt64                  logicalSize;
    UInt32                  clumpSize;
    UInt32                  totalBlocks;
    HFSPlusExtentRecord     extents; // additional extents are in extent overflow
};
typedef struct HFSPlusForkData HFSPlusForkData;
 
typedef HFSPlusExtentDescriptor HFSPlusExtentRecord[8];

Structure

Offset	Size	Description
0	2	Reserved
2	1	Volume Header
3	...	Files
Last - 1	1	Volume Header backup
Last	1	Reserved

struct HFSPlusVolumeHeader {
    UInt16              signature;
    UInt16              version;
    UInt32              attributes;
    UInt32              lastMountedVersion;
    UInt32              journalInfoBlock;
 
    UInt32              createDate;
    UInt32              modifyDate;
    UInt32              backupDate;
    UInt32              checkedDate;
 
    UInt32              fileCount;
    UInt32              folderCount;
 
    UInt32              blockSize;
    UInt32              totalBlocks;
    UInt32              freeBlocks;
 
    UInt32              nextAllocation;
    UInt32              rsrcClumpSize;
    UInt32              dataClumpSize;
    HFSCatalogNodeID    nextCatalogID;
 
    UInt32              writeCount;
    UInt64              encodingsBitmap;
 
    UInt32              finderInfo[8];
 
    HFSPlusForkData     allocationFile;
    HFSPlusForkData     extentsFile;
    HFSPlusForkData     catalogFile;
    HFSPlusForkData     attributesFile;
    HFSPlusForkData     startupFile;
};
typedef struct HFSPlusVolumeHeader HFSPlusVolumeHeader;

External Links

• TN1150 - HFS Plus Volume Format