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block: vhdx header for the QEMU support of VHDX images
This is based on Microsoft's VHDX specification:
"VHDX Format Specification v0.95", published 4/12/2012
https://www.microsoft.com/en-us/download/details.aspx?id=29681
These structures define the various header, metadata, and other
block structures defined in the VHDX specification.
Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Jeff Cody
Stefan Hajnoczi
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1 changed files with 311 additions and 0 deletions
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block/vhdx.h
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block/vhdx.h
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/*
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* Block driver for Hyper-V VHDX Images
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*
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* Copyright (c) 2013 Red Hat, Inc.,
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*
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* Authors:
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* Jeff Cody <jcody@redhat.com>
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*
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* This is based on the "VHDX Format Specification v0.95", published 4/12/2012
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* by Microsoft:
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* https://www.microsoft.com/en-us/download/details.aspx?id=29681
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*
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* This work is licensed under the terms of the GNU LGPL, version 2 or later.
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* See the COPYING.LIB file in the top-level directory.
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*
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*/
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#ifndef BLOCK_VHDX_H
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#define BLOCK_VHDX_H
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/* Structures and fields present in the VHDX file */
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/* The header section has the following blocks,
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* each block is 64KB:
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*
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* _____________________________________________________________________________
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* | File Id. | Header 1 | Header 2 | Region Table | Reserved (768KB) |
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* |----------|---------------|------------|--------------|--------------------|
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* | | | | | |
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* 0.........64KB...........128KB........192KB..........256KB................1MB
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*/
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#define VHDX_HEADER_BLOCK_SIZE (64*1024)
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#define VHDX_FILE_ID_OFFSET 0
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#define VHDX_HEADER1_OFFSET (VHDX_HEADER_BLOCK_SIZE*1)
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#define VHDX_HEADER2_OFFSET (VHDX_HEADER_BLOCK_SIZE*2)
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#define VHDX_REGION_TABLE_OFFSET (VHDX_HEADER_BLOCK_SIZE*3)
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/*
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* A note on the use of MS-GUID fields. For more details on the GUID,
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* please see: https://en.wikipedia.org/wiki/Globally_unique_identifier.
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*
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* The VHDX specification only states that these are MS GUIDs, and which
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* bytes are data1-data4. It makes no mention of what algorithm should be used
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* to generate the GUID, nor what standard. However, looking at the specified
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* known GUID fields, it appears the GUIDs are:
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* Standard/DCE GUID type (noted by 10b in the MSB of byte 0 of .data4)
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* Random algorithm (noted by 0x4XXX for .data3)
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*/
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/* ---- HEADER SECTION STRUCTURES ---- */
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/* These structures are ones that are defined in the VHDX specification
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* document */
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typedef struct VHDXFileIdentifier {
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uint64_t signature; /* "vhdxfile" in ASCII */
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uint16_t creator[256]; /* optional; utf-16 string to identify
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the vhdx file creator. Diagnotistic
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only */
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} VHDXFileIdentifier;
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/* the guid is a 16 byte unique ID - the definition for this used by
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* Microsoft is not just 16 bytes though - it is a structure that is defined,
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* so we need to follow it here so that endianness does not trip us up */
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typedef struct MSGUID {
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uint32_t data1;
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uint16_t data2;
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uint16_t data3;
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uint8_t data4[8];
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} MSGUID;
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#define guid_eq(a, b) \
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(memcmp(&(a), &(b), sizeof(MSGUID)) == 0)
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#define VHDX_HEADER_SIZE (4*1024) /* although the vhdx_header struct in disk
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is only 582 bytes, for purposes of crc
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the header is the first 4KB of the 64KB
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block */
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/* The full header is 4KB, although the actual header data is much smaller.
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* But for the checksum calculation, it is over the entire 4KB structure,
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* not just the defined portion of it */
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typedef struct QEMU_PACKED VHDXHeader {
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uint32_t signature; /* "head" in ASCII */
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uint32_t checksum; /* CRC-32C hash of the whole header */
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uint64_t sequence_number; /* Seq number of this header. Each
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VHDX file has 2 of these headers,
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and only the header with the highest
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sequence number is valid */
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MSGUID file_write_guid; /* 128 bit unique identifier. Must be
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updated to new, unique value before
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the first modification is made to
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file */
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MSGUID data_write_guid; /* 128 bit unique identifier. Must be
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updated to new, unique value before
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the first modification is made to
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visible data. Visbile data is
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defined as:
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- system & user metadata
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- raw block data
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- disk size
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- any change that will
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cause the virtual disk
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sector read to differ
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This does not need to change if
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blocks are re-arranged */
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MSGUID log_guid; /* 128 bit unique identifier. If zero,
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there is no valid log. If non-zero,
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log entries with this guid are
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valid. */
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uint16_t log_version; /* version of the log format. Mustn't be
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zero, unless log_guid is also zero */
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uint16_t version; /* version of th evhdx file. Currently,
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only supported version is "1" */
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uint32_t log_length; /* length of the log. Must be multiple
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of 1MB */
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uint64_t log_offset; /* byte offset in the file of the log.
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Must also be a multiple of 1MB */
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} VHDXHeader;
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/* Header for the region table block */
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typedef struct QEMU_PACKED VHDXRegionTableHeader {
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uint32_t signature; /* "regi" in ASCII */
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uint32_t checksum; /* CRC-32C hash of the 64KB table */
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uint32_t entry_count; /* number of valid entries */
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uint32_t reserved;
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} VHDXRegionTableHeader;
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/* Individual region table entry. There may be a maximum of 2047 of these
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*
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* There are two known region table properties. Both are required.
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* BAT (block allocation table): 2DC27766F62342009D64115E9BFD4A08
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* Metadata: 8B7CA20647904B9AB8FE575F050F886E
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*/
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#define VHDX_REGION_ENTRY_REQUIRED 0x01 /* if set, parser must understand
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this entry in order to open
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file */
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typedef struct QEMU_PACKED VHDXRegionTableEntry {
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MSGUID guid; /* 128-bit unique identifier */
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uint64_t file_offset; /* offset of the object in the file.
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Must be multiple of 1MB */
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uint32_t length; /* length, in bytes, of the object */
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uint32_t data_bits;
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} VHDXRegionTableEntry;
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/* ---- LOG ENTRY STRUCTURES ---- */
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#define VHDX_LOG_HDR_SIZE 64
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typedef struct QEMU_PACKED VHDXLogEntryHeader {
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uint32_t signature; /* "loge" in ASCII */
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uint32_t checksum; /* CRC-32C hash of the 64KB table */
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uint32_t entry_length; /* length in bytes, multiple of 1MB */
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uint32_t tail; /* byte offset of first log entry of a
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seq, where this entry is the last
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entry */
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uint64_t sequence_number; /* incremented with each log entry.
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May not be zero. */
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uint32_t descriptor_count; /* number of descriptors in this log
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entry, must be >= 0 */
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uint32_t reserved;
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MSGUID log_guid; /* value of the log_guid from
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vhdx_header. If not found in
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vhdx_header, it is invalid */
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uint64_t flushed_file_offset; /* see spec for full details - this
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sould be vhdx file size in bytes */
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uint64_t last_file_offset; /* size in bytes that all allocated
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file structures fit into */
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} VHDXLogEntryHeader;
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#define VHDX_LOG_DESC_SIZE 32
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typedef struct QEMU_PACKED VHDXLogDescriptor {
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uint32_t signature; /* "zero" or "desc" in ASCII */
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union {
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uint32_t reserved; /* zero desc */
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uint32_t trailing_bytes; /* data desc: bytes 4092-4096 of the
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data sector */
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};
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union {
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uint64_t zero_length; /* zero desc: length of the section to
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zero */
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uint64_t leading_bytes; /* data desc: bytes 0-7 of the data
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sector */
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};
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uint64_t file_offset; /* file offset to write zeros - multiple
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of 4kB */
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uint64_t sequence_number; /* must match same field in
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vhdx_log_entry_header */
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} VHDXLogDescriptor;
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typedef struct QEMU_PACKED VHDXLogDataSector {
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uint32_t data_signature; /* "data" in ASCII */
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uint32_t sequence_high; /* 4 MSB of 8 byte sequence_number */
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uint8_t data[4084]; /* raw data, bytes 8-4091 (inclusive).
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see the data descriptor field for the
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other mising bytes */
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uint32_t sequence_low; /* 4 LSB of 8 byte sequence_number */
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} VHDXLogDataSector;
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/* block states - different state values depending on whether it is a
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* payload block, or a sector block. */
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#define PAYLOAD_BLOCK_NOT_PRESENT 0
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#define PAYLOAD_BLOCK_UNDEFINED 1
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#define PAYLOAD_BLOCK_ZERO 2
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#define PAYLOAD_BLOCK_UNMAPPED 5
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#define PAYLOAD_BLOCK_FULL_PRESENT 6
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#define PAYLOAD_BLOCK_PARTIALLY_PRESENT 7
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#define SB_BLOCK_NOT_PRESENT 0
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#define SB_BLOCK_PRESENT 6
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/* per the spec */
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#define VHDX_MAX_SECTORS_PER_BLOCK (1<<23)
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/* upper 44 bits are the file offset in 1MB units lower 3 bits are the state
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other bits are reserved */
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#define VHDX_BAT_STATE_BIT_MASK 0x07
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#define VHDX_BAT_FILE_OFF_BITS (64-44)
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typedef uint64_t VHDXBatEntry;
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/* ---- METADATA REGION STRUCTURES ---- */
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#define VHDX_METADATA_ENTRY_SIZE 32
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#define VHDX_METADATA_MAX_ENTRIES 2047 /* not including the header */
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#define VHDX_METADATA_TABLE_MAX_SIZE \
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(VHDX_METADATA_ENTRY_SIZE * (VHDX_METADATA_MAX_ENTRIES+1))
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typedef struct QEMU_PACKED VHDXMetadataTableHeader {
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uint64_t signature; /* "metadata" in ASCII */
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uint16_t reserved;
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uint16_t entry_count; /* number table entries. <= 2047 */
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uint32_t reserved2[5];
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} VHDXMetadataTableHeader;
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#define VHDX_META_FLAGS_IS_USER 0x01 /* max 1024 entries */
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#define VHDX_META_FLAGS_IS_VIRTUAL_DISK 0x02 /* virtual disk metadata if set,
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otherwise file metdata */
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#define VHDX_META_FLAGS_IS_REQUIRED 0x04 /* parse must understand this
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entry to open the file */
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typedef struct QEMU_PACKED VHDXMetadataTableEntry {
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MSGUID item_id; /* 128-bit identifier for metadata */
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uint32_t offset; /* byte offset of the metadata. At
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least 64kB. Relative to start of
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metadata region */
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/* note: if length = 0, so is offset */
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uint32_t length; /* length of metadata. <= 1MB. */
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uint32_t data_bits; /* least-significant 3 bits are flags, the
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rest are reserved (see above) */
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uint32_t reserved2;
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} VHDXMetadataTableEntry;
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#define VHDX_PARAMS_LEAVE_BLOCKS_ALLOCED 0x01 /* Do not change any blocks to
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be BLOCK_NOT_PRESENT.
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If set indicates a fixed
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size VHDX file */
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#define VHDX_PARAMS_HAS_PARENT 0x02 /* has parent / backing file */
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typedef struct QEMU_PACKED VHDXFileParameters {
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uint32_t block_size; /* size of each payload block, always
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power of 2, <= 256MB and >= 1MB. */
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uint32_t data_bits; /* least-significant 2 bits are flags, the rest
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are reserved (see above) */
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} VHDXFileParameters;
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typedef struct QEMU_PACKED VHDXVirtualDiskSize {
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uint64_t virtual_disk_size; /* Size of the virtual disk, in bytes.
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Must be multiple of the sector size,
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max of 64TB */
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} VHDXVirtualDiskSize;
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typedef struct QEMU_PACKED VHDXPage83Data {
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MSGUID page_83_data[16]; /* unique id for scsi devices that
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support page 0x83 */
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} VHDXPage83Data;
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typedef struct QEMU_PACKED VHDXVirtualDiskLogicalSectorSize {
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uint32_t logical_sector_size; /* virtual disk sector size (in bytes).
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Can only be 512 or 4096 bytes */
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} VHDXVirtualDiskLogicalSectorSize;
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typedef struct QEMU_PACKED VHDXVirtualDiskPhysicalSectorSize {
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uint32_t physical_sector_size; /* physical sector size (in bytes).
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Can only be 512 or 4096 bytes */
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} VHDXVirtualDiskPhysicalSectorSize;
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typedef struct QEMU_PACKED VHDXParentLocatorHeader {
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MSGUID locator_type[16]; /* type of the parent virtual disk. */
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uint16_t reserved;
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uint16_t key_value_count; /* number of key/value pairs for this
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locator */
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} VHDXParentLocatorHeader;
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/* key and value strings are UNICODE strings, UTF-16 LE encoding, no NULs */
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typedef struct QEMU_PACKED VHDXParentLocatorEntry {
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uint32_t key_offset; /* offset in metadata for key, > 0 */
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uint32_t value_offset; /* offset in metadata for value, >0 */
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uint16_t key_length; /* length of entry key, > 0 */
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uint16_t value_length; /* length of entry value, > 0 */
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} VHDXParentLocatorEntry;
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/* ----- END VHDX SPECIFICATION STRUCTURES ---- */
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#endif
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