133 lines
3.6 KiB
Plaintext
133 lines
3.6 KiB
Plaintext
|
= Virtual Machine Archive format (VMA) =
|
||
|
|
|
||
|
|
This format contains a header which includes the VM configuration as
|
||
|
|
binary blobs, and a list of devices (dev_id, name).
|
||
|
|
|
||
|
|
The actual VM image data is stored inside extents. An extent contains
|
||
|
|
up to 64 clusters, and start with a 512 byte header containing
|
||
|
|
additional information for those clusters.
|
||
|
|
|
||
|
|
We use a cluster size of 65536, and use 8 bytes for each
|
||
|
|
cluster in the header to store the following information:
|
||
|
|
|
||
|
|
* 1 byte dev_id (to identity the drive)
|
||
|
|
* 1 byte not used (reserved)
|
||
|
|
* 2 bytes zero indicator (mark zero regions (16x4096))
|
||
|
|
* 4 bytes cluster number
|
||
|
|
|
||
|
|
We only store non-zero blocks (such block is 4096 bytes).
|
||
|
|
|
||
|
|
Each archive is marked with a uuid. The archive header and all
|
||
|
|
extent headers includes that uuid and a MD5 checksum (over header
|
||
|
|
data).
|
||
|
|
|
||
|
|
All numbers in VMA archive are stored in Big Endian byte order.
|
||
|
|
|
||
|
|
== VMA Header ==
|
||
|
|
|
||
|
|
Byte 0 - 3: magic
|
||
|
|
VMA magic string ("VMA\x00")
|
||
|
|
|
||
|
|
4 - 7: version
|
||
|
|
Version number (valid value is 1)
|
||
|
|
|
||
|
|
8 - 23: uuid
|
||
|
|
Unique ID, Same uuid is used to mark extents.
|
||
|
|
|
||
|
|
24 - 31: ctime
|
||
|
|
Backup time stamp (seconds since epoch)
|
||
|
|
|
||
|
|
32 - 47: md5sum
|
||
|
|
Header checksum (from byte 0 to header_size). This field
|
||
|
|
is filled with zero to generate the checksum.
|
||
|
|
|
||
|
|
48 - 51: blob_buffer_offset
|
||
|
|
Start of blob buffer (multiple of 512)
|
||
|
|
|
||
|
|
52 - 55: blob_buffer_size
|
||
|
|
Size of blob buffer (multiple of 512)
|
||
|
|
|
||
|
|
56 - 59: header_size
|
||
|
|
Overall size of this header (multiple of 512)
|
||
|
|
|
||
|
|
60 - 2043: reserved
|
||
|
|
|
||
|
|
2044 - 3067: uint32_t config_names[256]
|
||
|
|
Offsets into blob_buffer table
|
||
|
|
|
||
|
|
3068 - 4091: uint32_t config_data[256]
|
||
|
|
Offsets into blob_buffer table
|
||
|
|
|
||
|
|
4092 - 4095: reserved
|
||
|
|
|
||
|
|
4096 - 12287: VmaDeviceInfoHeader dev_info[256]
|
||
|
|
The offset in this table is used as 'dev_id' inside
|
||
|
|
the data streams.
|
||
|
|
|
||
|
|
12288 - header_size: Blob buffer
|
||
|
|
|
||
|
|
|
||
|
|
=== Devive Info Header (VmaDeviceInfoHeader) ===
|
||
|
|
|
||
|
|
This is use to store details about the contained disk images.
|
||
|
|
|
||
|
|
Byte 0 - 3: devive name (offsets into blob_buffer table)
|
||
|
|
|
||
|
|
4 - 7: reserved
|
||
|
|
|
||
|
|
8 - 15: device size in bytes
|
||
|
|
|
||
|
|
16 - 31: reserved
|
||
|
|
|
||
|
|
Note: Devive name 'vmstate' is reserved to store VM RAM state.
|
||
|
|
|
||
|
|
=== Blob buffer ===
|
||
|
|
|
||
|
|
The blob buffer is used to store both configuration file names and
|
||
|
|
configuration data.
|
||
|
|
|
||
|
|
This region contain a list of binary data blobs. Each blob starts with
|
||
|
|
a 2 byte size field, followed by the actual data.
|
||
|
|
|
||
|
|
== Image Data Streams ==
|
||
|
|
|
||
|
|
The VMA header is followed by the image data stream. Image data is grouped
|
||
|
|
with extents, which contains up to 59 clusters from different images.
|
||
|
|
|
||
|
|
=== VMA Extent Header ===
|
||
|
|
|
||
|
|
Byte 0 - 3: magic
|
||
|
|
VMA extent magic string ("VMAE")
|
||
|
|
|
||
|
|
4 - 5: reserved
|
||
|
|
|
||
|
|
6 - 7: block_count
|
||
|
|
Overall number of contained 4K block
|
||
|
|
|
||
|
|
8 - 23: uuid
|
||
|
|
Unique ID, Same uuid as used in the VMA header.
|
||
|
|
|
||
|
|
24 - 39: md5sum
|
||
|
|
Header checksum (from byte 0 to header_size). This field
|
||
|
|
is filled with zero to generate the checksum.
|
||
|
|
|
||
|
|
40 - 511: blockinfo[59]
|
||
|
|
|
||
|
|
|
||
|
|
Each 'blockinfo' (8 bytes) give further details about contained clusters:
|
||
|
|
|
||
|
|
Byte 0 - 1: mask
|
||
|
|
Bitmap used to indicate non-zero 4K blocks inside the
|
||
|
|
cluster.
|
||
|
|
|
||
|
|
2: reserved
|
||
|
|
|
||
|
|
3: dev_id
|
||
|
|
Device ID (offset into dev_info table)
|
||
|
|
|
||
|
|
4 - 7: cluster_num
|
||
|
|
|
||
|
|
The extend header if followed by the actual cluster data, where we only
|
||
|
|
store non-zero 4K blocks.
|
||
|
|
|