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91 lines
2.8 KiB
Plaintext
91 lines
2.8 KiB
Plaintext
=== Tape Partition Block (`TPBT`)
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This block lists all tape partitions.
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Tape partitions are separations written to media.
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They are used to distinguish two sets of related data that are distant enough to warrant separation but still belong on the same tape.
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A well-known example is the LTFS filesystem.
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==== Structure Definition
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[source,c]
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#define TAPE_PARTITION_MAGIC 0x54504254
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typedef struct TapePartitionHeader
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{
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uint32_t identifier; ///< Block type identifier. Must be set to BlockType::TapePartitionBlock. This magic value
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///< allows parsers to identify the block type.
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uint8_t entries; ///< Number of partition entries following this header. Specifies how many TapePartitionEntry
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///< structures are in this block. Valid range: 0-255. Most tapes have 1-4 partitions.
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uint64_t length; ///< Size of entry data in bytes (excluding this header). Calculated as: entries ×
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///< sizeof(TapePartitionEntry). This is the number of bytes following the header.
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uint64_t crc64; ///< CRC64-ECMA checksum of the entry data. Computed over the array of TapePartitionEntry
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///< structures only. Does NOT include this header. Used for integrity verification.
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} TapePartitionHeader;
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==== Field Descriptions
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[cols="2,2,2,6",options="header"]
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|===
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|Type
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|Size
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|Name
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|Description
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|uint32_t
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|4 bytes
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|identifier
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|The tape partition block identifier, always `TPBT`
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|uint16_t
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|2 bytes
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|entries
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|The number of entries following this header
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|uint32_t
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|4 bytes
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|length
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|The length in bytes of the data following this header.
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|uint64_t
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|8 bytes
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|crc64
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|The CRC64-ECMA checksum of the data following this header
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|===
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==== Tape partition entries
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[source,c]
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typedef struct TapePartitionEntry
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{
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uint8_t Number; ///< Partition number (unique identifier for this partition). Identifies this partition among all
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///< partitions on the tape. Valid range: 0-255, though most tapes use 0-3.
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uint64_t FirstBlock; ///< First block in the partition (inclusive). Starting block address for this partition's
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///< address space. Often 0, but format-dependent.
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uint64_t LastBlock; ///< Last block in the partition (inclusive). Ending block address for this partition's address
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///< space. Must be ≥ FirstBlock. The partition contains all blocks from FirstBlock through
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///< LastBlock inclusive.
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} TapePartitionEntry;
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==== Field Descriptions
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[cols="2,2,2,6",options="header"]
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|===
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|Type
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|Size
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|Name
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|Description
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|uint8_t
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|1 byte
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|number
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|Partition number.
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|uint64_t
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|8 bytes
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|firstBlock
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|First block number, inclusive, of the partition.
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|uint64_t
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|8 bytes
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|lastBlock
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|Last block number, inclusive, of the partition.
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|=== |