Defines a single extent for HFS volumes.

struct HFSExtentDescriptor {
    UInt16 startBlock; 
    UInt16 blockCount;
};
typedef HFSExtentDescriptor HFSExtentRecord;

Field descriptions

startBlock

The first allocation block of the extent.

blockCount

The number of allocation blocks in the extent.

Discussion

The extent descriptor is used to describe a single continguous range of allocation blocks (an extent) belonging to a file. An array of three extent descriptors makes an extent record, defined by the HFSExtentRecord data type.

If a fork does not use all of the extent descriptors in an extent record, the unused extent descriptors will have their startBlock and blockCount fields set to 0.

© 2001 Apple Computer, Inc. (Last Updated July 17, 2001)