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[Qemu-devel] [PATCH v2 2/5] block: vhdx header for the QEMU support of V
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From: |
Jeff Cody |
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Subject: |
[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 10:24:21 -0400 |
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 {
+ 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 */
+ };
+ 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 */
+ };
+ 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
+
+#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;
+
+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
--
1.8.1.4