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Re: [Qemu-devel] [PATCH v2 2/5] block: vhdx header for the QEMU support
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From: |
Kevin Wolf |
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Subject: |
Re: [Qemu-devel] [PATCH v2 2/5] block: vhdx header for the QEMU support of VHDX images |
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Date: |
Tue, 23 Apr 2013 17:10:18 +0200 |
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User-agent: |
Mutt/1.5.21 (2010-09-15) |
Am 23.04.2013 um 16:24 hat Jeff Cody geschrieben:
> 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 <address@hidden>
> ---
> block/vhdx.h | 327
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 327 insertions(+)
> create mode 100644 block/vhdx.h
>
> diff --git a/block/vhdx.h b/block/vhdx.h
> new file mode 100644
> index 0000000..f5cf1ed
> --- /dev/null
> +++ b/block/vhdx.h
> @@ -0,0 +1,327 @@
> +/*
> + * Block driver for Hyper-V VHDX Images
> + *
> + * Copyright (c) 2013 Red Hat, Inc.,
> + *
> + * Authors:
> + * Jeff Cody <address@hidden>
> + *
> + * This is based on the "VHDX Format Specification v0.95", published
> 4/12/2012
> + * by Microsoft:
> + * https://www.microsoft.com/en-us/download/details.aspx?id=29681
> + *
> + * This work is licensed under the terms of the GNU LGPL, version 2 or later.
> + * See the COPYING.LIB file in the top-level directory.
> + *
> + */
> +
> +#ifndef BLOCK_VHDX_H
> +#define BLOCK_VHDX_H
> +
> +/* Structures and fields present in the VHDX file */
> +
> +/* The header section has the following blocks,
> + * each block is 64KB:
> + *
> + *
> _____________________________________________________________________________
> + * | File Id. | Header 1 | Header 2 | Region Table | Reserved
> (768KB) |
> + *
> |----------|---------------|------------|--------------|--------------------|
> + * | | | | |
> |
> + *
> 0.........64KB...........128KB........192KB..........256KB................1MB
> + */
> +
> +#define VHDX_HEADER_BLOCK_SIZE (64*1024)
> +
> +#define VHDX_FILE_ID_OFFSET 0
> +#define VHDX_HEADER1_OFFSET (VHDX_HEADER_BLOCK_SIZE*1)
> +#define VHDX_HEADER2_OFFSET (VHDX_HEADER_BLOCK_SIZE*2)
> +#define VHDX_REGION_TABLE_OFFSET (VHDX_HEADER_BLOCK_SIZE*3)
> +
> +
> +/*
> + * A note on the use of MS-GUID fields. For more details on the GUID,
> + * please see: https://en.wikipedia.org/wiki/Globally_unique_identifier.
> + *
> + * The VHDX specification only states that these are MS GUIDs, and which
> + * bytes are data1-data4. It makes no mention of what algorithm should be
> used
> + * to generate the GUID, nor what standard. However, looking at the
> specified
> + * known GUID fields, it appears the GUIDs are:
> + * Standard/DCE GUID type (noted by 10b in the MSB of byte 0 of .data4)
> + * Random algorithm (noted by 0x4XXX for .data3)
> + */
> +
> +/* ---- HEADER SECTION STRUCTURES ---- */
> +
> +/* Important note: these structures are as defined in the VHDX specification,
> + * including byte order and size. However, without being packed structures,
> + * they will not match 1:1 data read from disk. Rather than use potentially
> + * non-portable packed structures, data is copied from read buffers into
> + * the structures below. However, for reference, please refrain from
> + * modifying these structures to something that does not represent the spec
> */
> +
> +#define VHDX_FILE_ID_MAGIC 0x656C696678646876 /* 'vhdxfile' */
> +typedef struct vhdx_file_identifier {
According to the qemu coding style, this is not a valid name for a
struct. I think you can choose between VHDXFileIdentifier and
VhdxFileIdentifier, where existing code tends towards the former.
More instances of this follow, but I won't comment on each.
> + uint64_t signature; /* "vhdxfile" in ASCII */
> + uint16_t creator[256]; /* optional; utf-16 string to
> identify
> + the vhdx file creator.
> Diagnotistic
> + only */
> +} vhdx_file_identifier;
> +
> +
> +/* the guid is a 16 byte unique ID - the definition for this used by
> + * Microsoft is not just 16 bytes though - it is a structure that is defined,
> + * so we need to follow it here so that endianness does not trip us up */
> +
> +typedef struct ms_guid {
> + uint32_t data1;
> + uint16_t data2;
> + uint16_t data3;
> + uint8_t data4[8];
> +} ms_guid;
> +
> +#define guid_eq(a, b) \
> + (memcmp(&(a), &(b), sizeof(ms_guid)) == 0)
> +
> +#define VHDX_HEADER_SIZE (4*1024) /* although the vhdx_header struct in
> disk
> + is only 582 bytes, for purposes of crc
> + the header is the first 4KB of the
> 64KB
> + block */
> +
> +#define VHDX_HDR_MAGIC 0x64616568 /* 'head' */
> +typedef struct QEMU_PACKED vhdx_header {
> + uint32_t signature; /* "head" in ASCII */
> + uint32_t checksum; /* CRC-32C hash of the whole header
> */
> + uint64_t sequence_number; /* Seq number of this header. Each
> + VHDX file has 2 of these headers,
> + and only the header with the
> highest
> + sequence number is valid */
> + ms_guid file_write_guid; /* 128 bit unique identifier. Must be
> + updated to new, unique value
> before
> + the first modification is made to
> + file */
> + ms_guid data_write_guid; /* 128 bit unique identifier. Must be
> + updated to new, unique value
> before
> + the first modification is made to
> + visible data. Visbile data is
> + defined as:
> + - system & user metadata
> + - raw block data
> + - disk size
> + - any change that will
> + cause the virtual disk
> + sector read to differ
> +
> + This does not need to change if
> + blocks are re-arranged */
> + ms_guid log_guid; /* 128 bit unique identifier. If
> zero,
> + there is no valid log. If
> non-zero,
> + log entries with this guid are
> + valid. */
> + uint16_t log_version; /* version of the log format.
> Mustn't be
> + zero, unless log_guid is also
> zero */
> + uint16_t version; /* version of th evhdx file.
> Currently,
> + only supported version is "1" */
> + uint32_t log_length; /* length of the log. Must be
> multiple
> + of 1MB */
> + uint64_t log_offset; /* byte offset in the file of the
> log.
> + Must also be a multiple of 1MB */
> +} vhdx_header;
> +
> +/* 4KB in packed data size, not to be used except for initial data read */
> +typedef struct QEMU_PACKED vhdx_header_padded {
> + vhdx_header header;
> + uint8_t reserved[502]; /* per the VHDX spec */
> + uint8_t reserved_[3514]; /* for the initial packed struct
> read */
> +} vhdx_header_padded;
> +
> +/* Header for the region table block */
> +#define VHDX_RT_MAGIC 0x69676572 /* 'regi ' */
> +typedef struct QEMU_PACKED vhdx_region_table_header {
> + uint32_t signature; /* "regi" in ASCII */
> + uint32_t checksum; /* CRC-32C hash of the 64KB table */
> + uint32_t entry_count; /* number of valid entries */
> + uint32_t reserved;
> +} vhdx_region_table_header;
> +
> +/* Individual region table entry. There may be a maximum of 2047 of these
> + *
> + * There are two known region table properties. Both are required.
> + * BAT (block allocation table): 2DC27766F62342009D64115E9BFD4A08
> + * Metadata: 8B7CA20647904B9AB8FE575F050F886E
> + */
> +#define VHDX_REGION_ENTRY_REQUIRED 0x01 /* if set, parser must understand
> + this entry in order to open
> + file */
> +typedef struct QEMU_PACKED vhdx_region_table_entry {
> + ms_guid guid; /* 128-bit unique identifier */
> + uint64_t file_offset; /* offset of the object in the file.
> + Must be multiple of 1MB */
> + uint32_t length; /* length, in bytes, of the object */
> + uint32_t data_bits;
> +} vhdx_region_table_entry;
> +
> +
> +/* ---- LOG ENTRY STRUCTURES ---- */
> +#define VHDX_LOG_HDR_SIZE 64
> +#define VHDX_LOGE_MAGIC 0x65676F6C /* 'loge' */
> +typedef struct QEMU_PACKED vhdx_log_entry_header {
> + uint32_t signature; /* "loge" in ASCII */
> + uint32_t checksum; /* CRC-32C hash of the 64KB table */
> + uint32_t entry_length; /* length in bytes, multiple of 1MB
> */
> + uint32_t tail; /* byte offset of first log entry of
> a
> + seq, where this entry is the last
> + entry */
> + uint64_t sequence_number; /* incremented with each log entry.
> + May not be zero. */
> + uint32_t descriptor_count; /* number of descriptors in this log
> + entry, must be >= 0 */
> + uint32_t reserved;
> + ms_guid log_guid; /* value of the log_guid from
> + vhdx_header. If not found in
> + vhdx_header, it is invalid */
> + uint64_t flushed_file_offset; /* see spec for full details - this
> + sould be vhdx file size in bytes
> */
> + uint64_t last_file_offset; /* size in bytes that all allocated
> + file structures fit into */
> +} vhdx_log_entry_header;
> +
> +#define VHDX_LOG_DESC_SIZE 32
> +
> +#define VHDX_ZERO_MAGIC 0x6F72657A /* 'zero' */
> +#define VHDX_DATA_MAGIC 0x63736564 /* 'desc' */
> +typedef struct QEMU_PACKED vhdx_log_descriptor {
> + uint32_t signature; /* "zero" or "desc" in ASCII */
> + union {
> + uint32_t reserved; /* zero desc */
> + uint32_t trailing_bytes; /* data desc: bytes 4092-4096 of the
> + data sector */
> + };
Indentation inside the union is off.
> + union {
> + uint64_t zero_length; /* zero desc: length of the section
> to
> + zero */
> + uint64_t leading_bytes; /* data desc: bytes 0-7 of the data
> + sector */
> + };
Here as well.
> + uint64_t file_offset; /* file offset to write zeros -
> multiple
> + of 4kB */
> + uint64_t sequence_number; /* must match same field in
> + vhdx_log_entry_header */
> +} vhdx_log_descriptor;
> +
> +#define VHDX_DATAS_MAGIC 0x61746164 /* 'data' */
> +typedef struct QEMU_PACKED vhdx_log_data_sector {
> + uint32_t data_signature; /* "data" in ASCII */
> + uint32_t sequence_high; /* 4 MSB of 8 byte sequence_number */
> + uint8_t data[4084]; /* raw data, bytes 8-4091
> (inclusive).
> + see the data descriptor field for
> the
> + other mising bytes */
> + uint32_t sequence_low; /* 4 LSB of 8 byte sequence_number */
> +} vhdx_log_data_sector;
> +
> +
> +
> +/* block states - different state values depending on whether it is a
> + * payload block, or a sector block. */
> +
> +#define PAYLOAD_BLOCK_NOT_PRESENT 0
> +#define PAYLOAD_BLOCK_UNDEFINED 1
> +#define PAYLOAD_BLOCK_ZERO 2
> +#define PAYLOAD_BLOCK_UNMAPPED 5
> +#define PAYLOAD_BLOCK_FULL_PRESENT 6
> +#define PAYLOAD_BLOCK_PARTIALLY_PRESENT 7
Looks like an enum?
> +#define SB_BLOCK_NOT_PRESENT 0
> +#define SB_BLOCK_PRESENT 6
> +
> +/* per the spec */
> +#define VHDX_MAX_SECTORS_PER_BLOCK (1<<23)
> +
> +/* upper 44 bits are the file offset in 1MB units lower 3 bits are the state
> + other bits are reserved */
> +#define VHDX_BAT_STATE_BIT_MASK 0x07
> +#define VHDX_BAT_FILE_OFF_BITS (64-44)
> +typedef uint64_t vhdx_bat_entry;
> +
> +/* ---- METADATA REGION STRUCTURES ---- */
> +
> +#define VHDX_METADATA_ENTRY_SIZE 32
> +#define VHDX_METADATA_MAX_ENTRIES 2047 /* not including the header */
> +#define VHDX_METADATA_TABLE_MAX_SIZE \
> + (VHDX_METADATA_ENTRY_SIZE * (VHDX_METADATA_MAX_ENTRIES+1))
> +#define VHDX_METADATA_MAGIC 0x617461646174656D /* 'metadata' */
> +typedef struct QEMU_PACKED vhdx_metadata_table_header {
> + uint64_t signature; /* "metadata" in ASCII */
> + uint16_t reserved;
> + uint16_t entry_count; /* number table entries. <= 2047 */
> + uint32_t reserved2[5];
> +} vhdx_metadata_table_header;
> +
> +#define VHDX_META_FLAGS_IS_USER 0x01 /* max 1024 entries */
> +#define VHDX_META_FLAGS_IS_VIRTUAL_DISK 0x02 /* virtual disk metadata if
> set,
> + otherwise file metdata */
> +#define VHDX_META_FLAGS_IS_REQUIRED 0x04 /* parse must understand this
> + entry to open the file */
> +typedef struct QEMU_PACKED vhdx_metadata_table_entry {
> + ms_guid item_id; /* 128-bit identifier for metadata */
> + uint32_t offset; /* byte offset of the metadata. At
> + least 64kB. Relative to start of
> + metadata region */
> + /* note: if length = 0, so is offset
> */
> + uint32_t length; /* length of metadata. <= 1MB. */
> + uint32_t data_bits; /* least-significant 3 bits are flags, the
> + rest are reserved (see above) */
> + uint32_t reserved2;
> +} vhdx_metadata_table_entry;
> +
> +#define VHDX_PARAMS_LEAVE_BLOCKS_ALLOCED 0x01 /* Do not change any blocks
> to
> + be BLOCK_NOT_PRESENT.
> + If set indicates a fixed
> + size VHDX file */
> +#define VHDX_PARAMS_HAS_PARENT 0x02 /* has parent / backing
> file */
> +typedef struct QEMU_PACKED vhdx_file_parameters {
> + uint32_t block_size; /* size of each payload block, always
> + power of 2, <= 256MB and >= 1MB.
> */
> + uint32_t data_bits; /* least-significant 2 bits are flags, the rest
> + are reserved (see above) */
> +} vhdx_file_parameters;
> +
> +typedef struct QEMU_PACKED vhdx_virtual_disk_size {
> + uint64_t virtual_disk_size; /* Size of the virtual disk, in
> bytes.
> + Must be multiple of the sector
> size,
> + max of 64TB */
> +} vhdx_virtual_disk_size;
> +
> +typedef struct QEMU_PACKED vhdx_page83_data {
> + uint8_t page_83_data[16]; /* unique id for scsi devices that
> + support page 0x83 */
> +} vhdx_page83_data;
> +
> +typedef struct QEMU_PACKED vhdx_virtual_disk_logical_sector_size {
> + uint32_t logical_sector_size; /* virtual disk sector size (in
> bytes).
> + Can only be 512 or 4096 bytes */
> +} vhdx_virtual_disk_logical_sector_size;
> +
> +typedef struct QEMU_PACKED vhdx_virtual_disk_physical_sector_size {
> + uint32_t physical_sector_size; /* physical sector size (in bytes).
> + Can only be 512 or 4096 bytes */
> +} vhdx_virtual_disk_physical_sector_size;
What's the point with all the single-field structs?
> +typedef struct QEMU_PACKED vhdx_parent_locator_header {
> + uint8_t locator_type[16]; /* type of the parent virtual disk.
> */
> + uint16_t reserved;
> + uint16_t key_value_count; /* number of key/value pairs for this
> + locator */
> +} vhdx_parent_locator_header;
> +
> +/* key and value strings are UNICODE strings, UTF-16 LE encoding, no NULs */
> +typedef struct QEMU_PACKED vhdx_parent_locator_entry {
> + uint32_t key_offset; /* offset in metadata for key, > 0 */
> + uint32_t value_offset; /* offset in metadata for value, >0
> */
> + uint16_t key_length; /* length of entry key, > 0 */
> + uint16_t value_length; /* length of entry value, > 0 */
> +} vhdx_parent_locator_entry;
> +
> +
> +/* ----- END VHDX SPECIFICATION STRUCTURES ---- */
> +
> +#endif
Kevin