here - OSTA - Optical Storage Technology Association

2.2.13.6 Recommended procedure for reclaiming space from the Metadata
Partition
Blocks allocated to the Metadata File, and its mirror, shall only be returned to the volume
in one of the following two ways:
• Truncation of the Metadata File and its mirror.
• Marking the AD(s) for a region of the Metadata file, and it’s mirror, as sparse (not
allocated) and setting the corresponding bits in the Metadata Bitmap file to zero,
indicating these blocks are not available for use.
Any region to be removed shall:
• Currently contain no referenced metadata (i.e. all corresponding bits in the
Metadata Bitmap file shall already be set (one)).
• Match the size/alignment restrictions laid down in section 2.2.13.1.
In the truncation case (metadata partition being truncated):
1. Update the SBD in the Metadata Bitmap File to reduce the bitmap size.
2. Update the Metadata Bitmap File Entry Information Length to reflect the
decreased bitmap size.
3. Update the Metadata File, and mirror, file entry Information Length fields to
‘remove’ the region.
4. Mark the de-allocated blocks as available in the partition unallocated space
bitmap.
In the mark sparse case (region in middle of metadata partition being removed):
1. Clear the corresponding bits in the Metadata Bitmap file to zero.
2. Generate sparse (not allocated) Allocation Descriptor(s) in the Metadata File (and
its mirror) for the region being de-allocated.
3. Mark the de-allocated blocks as available in the partition Unallocated Space
Bitmap.
2.2.122.2.14 Partition Descriptor
struct PartitionDescriptor { /* ECMA 167 3/10.5 */
struct tag
DescriptorTag;
Uint32
VolumeDescriptorSequenceNumber;
Uint16
PartitionFlags;
Uint16
PartitionNumber;
struct EntityID PartitionContents;
byte
PartitionContentsUse[128];
Uint32
AccessType;
Uint32
PartitionStartingLocation;
Uint32
PartitionLength;
UDF 2.01
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