Patchwork [02/15] block: vhdx header for the QEMU support of VHDX images

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Submitter Stefan Hajnoczi
Date May 3, 2013, 11:52 a.m.
Message ID <1367581972-4208-3-git-send-email-stefanha@redhat.com>
Download mbox | patch
Permalink /patch/241279/
State New
Headers show

Comments

Stefan Hajnoczi - May 3, 2013, 11:52 a.m.
From: Jeff Cody <jcody@redhat.com>

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>
---
 block/vhdx.h | 311 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 311 insertions(+)
 create mode 100644 block/vhdx.h

Patch

diff --git a/block/vhdx.h b/block/vhdx.h
new file mode 100644
index 0000000..fcddd37
--- /dev/null
+++ b/block/vhdx.h
@@ -0,0 +1,311 @@ 
+/*
+ * Block driver for Hyper-V VHDX Images
+ *
+ * Copyright (c) 2013 Red Hat, Inc.,
+ *
+ * Authors:
+ *  Jeff Cody <jcody@redhat.com>
+ *
+ *  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 ---- */
+
+/* These structures are ones that are defined in the VHDX specification
+ * document */
+
+typedef struct VHDXFileIdentifier {
+    uint64_t    signature;              /* "vhdxfile" in ASCII */
+    uint16_t    creator[256];           /* optional; utf-16 string to identify
+                                           the vhdx file creator.  Diagnotistic
+                                           only */
+} VHDXFileIdentifier;
+
+
+/* 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 MSGUID {
+    uint32_t  data1;
+    uint16_t  data2;
+    uint16_t  data3;
+    uint8_t   data4[8];
+} MSGUID;
+
+#define guid_eq(a, b) \
+    (memcmp(&(a), &(b), sizeof(MSGUID)) == 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 */
+
+/* The full header is 4KB, although the actual header data is much smaller.
+ * But for the checksum calculation, it is over the entire 4KB structure,
+ * not just the defined portion of it */
+typedef struct QEMU_PACKED VHDXHeader {
+    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 */
+    MSGUID      file_write_guid;       /* 128 bit unique identifier. Must be
+                                           updated to new, unique value before
+                                           the first modification is made to
+                                           file */
+    MSGUID      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 */
+    MSGUID      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 */
+} VHDXHeader;
+
+/* Header for the region table block */
+typedef struct QEMU_PACKED VHDXRegionTableHeader {
+    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;
+} VHDXRegionTableHeader;
+
+/* 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 VHDXRegionTableEntry {
+    MSGUID      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;
+} VHDXRegionTableEntry;
+
+
+/* ---- LOG ENTRY STRUCTURES ---- */
+#define VHDX_LOG_HDR_SIZE 64
+typedef struct QEMU_PACKED VHDXLogEntryHeader {
+    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;
+    MSGUID      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 */
+} VHDXLogEntryHeader;
+
+#define VHDX_LOG_DESC_SIZE 32
+
+typedef struct QEMU_PACKED VHDXLogDescriptor {
+    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 */
+} VHDXLogDescriptor;
+
+typedef struct QEMU_PACKED VHDXLogDataSector {
+    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 */
+} VHDXLogDataSector;
+
+
+
+/* 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 VHDXBatEntry;
+
+/* ---- 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))
+typedef struct QEMU_PACKED VHDXMetadataTableHeader {
+    uint64_t    signature;              /* "metadata" in ASCII */
+    uint16_t    reserved;
+    uint16_t    entry_count;            /* number table entries. <= 2047 */
+    uint32_t    reserved2[5];
+} VHDXMetadataTableHeader;
+
+#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 VHDXMetadataTableEntry {
+    MSGUID      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;
+} VHDXMetadataTableEntry;
+
+#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 VHDXFileParameters {
+    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) */
+} VHDXFileParameters;
+
+typedef struct QEMU_PACKED VHDXVirtualDiskSize {
+    uint64_t    virtual_disk_size;      /* Size of the virtual disk, in bytes.
+                                           Must be multiple of the sector size,
+                                           max of 64TB */
+} VHDXVirtualDiskSize;
+
+typedef struct QEMU_PACKED VHDXPage83Data {
+    MSGUID      page_83_data[16];       /* unique id for scsi devices that
+                                           support page 0x83 */
+} VHDXPage83Data;
+
+typedef struct QEMU_PACKED VHDXVirtualDiskLogicalSectorSize {
+    uint32_t    logical_sector_size;    /* virtual disk sector size (in bytes).
+                                           Can only be 512 or 4096 bytes */
+} VHDXVirtualDiskLogicalSectorSize;
+
+typedef struct QEMU_PACKED VHDXVirtualDiskPhysicalSectorSize {
+    uint32_t    physical_sector_size;   /* physical sector size (in bytes).
+                                           Can only be 512 or 4096 bytes */
+} VHDXVirtualDiskPhysicalSectorSize;
+
+typedef struct QEMU_PACKED VHDXParentLocatorHeader {
+    MSGUID      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 */
+} VHDXParentLocatorHeader;
+
+/* key and value strings are UNICODE strings, UTF-16 LE encoding, no NULs */
+typedef struct QEMU_PACKED VHDXParentLocatorEntry {
+    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 */
+} VHDXParentLocatorEntry;
+
+
+/* ----- END VHDX SPECIFICATION STRUCTURES ---- */
+
+#endif