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Re: [Qemu-devel] [PATCH v2 2/5] block: vhdx header for the QEMU support
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From: |
Jeff Cody |
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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 12:32:41 -0400 |
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User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Tue, Apr 23, 2013 at 05:10:18PM +0200, Kevin Wolf wrote:
> 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.
>
OK. I'll go through and change them all; almost all of them will need
to be changed.
> > + 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.
>
OK, thanks.
> > + 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?
>
The spec lays them out as #define's, so this is a case where I figured
it helped with a reader comparing against the spec. But I can make
this (and the corresponding ones below) into enums, if you are
worried about namespace pollution.
> > +#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?
>
Another case of laying out as it was in the spec, for readability. I
tried to keep the header as faithful to the spec as possible; if you
have a strong preference, I can drop these and just use the single
field types inside vhdx.c.
> > +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