diff options
Diffstat (limited to 'docs/interop')
| -rw-r--r-- | docs/interop/prl-xml.txt | 158 |
1 files changed, 158 insertions, 0 deletions
diff --git a/docs/interop/prl-xml.txt b/docs/interop/prl-xml.txt new file mode 100644 index 0000000000..7031f8752c --- /dev/null +++ b/docs/interop/prl-xml.txt @@ -0,0 +1,158 @@ += License = + +Copyright (c) 2015-2017, Virtuozzo, Inc. +Authors: + 2015 Denis Lunev <den@openvz.org> + 2015 Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> + 2016-2017 Klim Kireev <klim.kireev@virtuozzo.com> + 2016-2017 Edgar Kaziakhmedov <edgar.kaziakhmedov@virtuozzo.com> + +This work is licensed under the terms of the GNU GPL, version 2 or later. +See the COPYING file in the top-level directory. + +This specification contains minimal information about Parallels Disk Format, +which is enough to proper work with QEMU. Nevertheless, Parallels Cloud Server +and Parallels Desktop are able to add some unspecified nodes to xml and use +them, but they are for internal work and don't affect functionality. Also it +uses auxiliary xml "Snapshot.xml", which allows to store optional snapshot +information, but it doesn't influence open/read/write functionality. QEMU and +other software should not use fields not covered in this document and +Snapshot.xml file and must leave them as is. + += Parallels Disk Format = + +Parallels disk consists of two parts: the set of snapshots and the disk +descriptor file, which stores information about all files and snapshots. + +== Definitions == + Snapshot a record of the contents captured at a particular time, + capable of storing current state. A snapshot has UUID and + parent UUID. + + Snapshot image an overlay representing the difference between this + snapshot and some earlier snapshot. + + Overlay an image storing the different sectors between two captured + states. + + Root image snapshot image with no parent, the root of snapshot tree. + + Storage the backing storage for a subset of the virtual disk. When + there is more than one storage in a Parallels disk then that + is referred to as a split image. In this case every storage + covers specific address space area of the disk and has its + particular root image. Split images are not considered here + and are not supported. Each storage consists of disk + parameters and a list of images. The list of images always + contains a root image and may also contain overlays. The + root image can be an expandable Parallels image file or + plain. Overlays must be expandable. + + Description DiskDescriptor.xml stores information about disk parameters, + file snapshots, storages. + + Top The overlay between actual state and some previous snapshot. + Snapshot It is not a snapshot in the classical sense because it + serves as the active image that the guest writes to. + + Sector a 512-byte data chunk. + +== Description file == +All information is placed in a single XML element Parallels_disk_image. +The element has only one attribute "Version", that must be 1.0. +Schema of DiskDescriptor.xml: + +<Parallels_disk_image Version="1.0"> + <Disk_Parameters> + ... + </Disk_Parameters> + <StorageData> + ... + </StorageData> + <Snapshots> + ... + </Snapshots> +</Parallels_disk_image> + +== Disk_Parameters element == +The Disk_Parameters element describes the physical layout of the virtual disk +and some general settings. + +The Disk_Parameters element MUST contain the following child elements: + * Disk_size - number of sectors in the disk, + desired size of the disk. + * Cylinders - number of the disk cylinders. + * Heads - number of the disk heads. + * Sectors - number of the disk sectors per cylinder + (sector size is 512 bytes) + Limitation: Product of the Heads, Sectors and Cylinders + values MUST be equal to the value of the Disk_size parameter. + * Padding - must be 0. Parallels Cloud Server and Parallels Desktop may + use padding set to 1, however this case is not covered + by this spec, QEMU and other software should not open + such disks and should not create them. + +== StorageData element == +This element of the file describes the root image and all snapshot images. + +The StorageData element consists of the Storage child element, as shown below: +<StorageData> + <Storage> + ... + </Storage> +</StorageData> + +A Storage element has following child elements: + * Start - start sector of the storage, in case of non split storage + equals to 0. + * End - number of sector following the last sector, in case of non + split storage equals to Disk_size. + * Blocksize - storage cluster size, number of sectors per one cluster. + Cluster size for each "Compressed" (see below) image in + parallels disk must be equal to this field. Note: cluster + size for Parallels Expandable Image is in 'tracks' field of + its header (see docs/interop/parallels.txt). + * Several Image child elements. + +Each Image element has following child elements: + * GUID - image identifier, UUID in curly brackets. + For instance, {12345678-9abc-def1-2345-6789abcdef12}. + The GUID is used by the Snapshots element to reference images + (see below) + * Type - image type of the element. It can be: + "Plain" for raw files. + "Compressed" for expanding disks. + * File - path to image file. Path can be relative to DiskDecriptor.xml or + absolute. + +== Snapshots element == +The Snapshots element describes the snapshot relations with the snapshot tree. + +The element contains the set of Shot child elements, as shown below: +<Snapshots> + <TopGUID> ... </TopGUID> /* Optional child element */ + <Shot> + ... + </Shot> + <Shot> + ... + </Shot> + ... +</Snapshots> + +Each Shot element contains the following child elements: + * GUID - an image GUID. + * ParentGUID - GUID of the image of the parent snapshot. + +The software may traverse snapshots from child to parent using <ParentGUID> +field as reference. ParentGUID of root snapshot is +{00000000-0000-0000-0000-000000000000}. There should be only one root +snapshot. Top snapshot could be described via two ways: via TopGUID child +element of the Snapshots element or via predefined GUID +{5fbaabe3-6958-40ff-92a7-860e329aab41}. If TopGUID is defined, predefined GUID is +interpreted as usual GUID. All snapshot images (except Top Snapshot) should be +opened read-only. There is another predefined GUID, +BackupID = {704718e1-2314-44c8-9087-d78ed36b0f4e}, which is used by original and +some third-party software for backup, QEMU and other software may operate with +images with GUID = BackupID as usual, however, it is not recommended to use this +GUID for new disks. Top snapshot cannot have this GUID. |