From: Klim Kireev <klim.kir...@virtuozzo.com> This patch adds main information about Parallels Disk format, which consists of DiskDescriptor.xml and other files.
Signed-off-by: Edgar Kaziakhmedov <edgar.kaziakhme...@virtuozzo.com> Signed-off-by: Klim Kireev <klim.kir...@virtuozzo.com> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> Signed-off-by: Denis V. Lunev <d...@openvz.org> CC: Stefan Hajnoczi <stefa...@redhat.com> --- docs/interop/prl-xml.txt | 155 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 155 insertions(+) create mode 100644 docs/interop/prl-xml.txt diff --git a/docs/interop/prl-xml.txt b/docs/interop/prl-xml.txt new file mode 100644 index 0000000..8ccb91a --- /dev/null +++ b/docs/interop/prl-xml.txt @@ -0,0 +1,155 @@ += License = + +Copyright (c) 2015 Denis Lunev +Copyright (c) 2015 Vladimir Sementsov-Ogievskiy +Copyright (c) 2016-2017 Klim Kireev +Copyright (c) 2016-2017 Edgar Kaziakhmedov + +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 unspecified here fields 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 without parent, the root of snapshot tree. + + Storage a special conception of data, which consists of disk + parameters and a list of images. One of this image is root, + others are overlays. Images must be expandable (parallels + image file), however root image could be expandable or + plain. There may be more then one storage in the Parallels + disk and it is defined 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 isn't supported + in QEMU. + + 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 classical meaning. + + Sector a 512-byte data chunk. + +== Description file == +All information is placed in single XML section Parallels_disk_image. +The section has only one attribute "Version", that must be 1.0. +General structure of DiskDescriptor.xml: + +<Parallels_disk_image Version="1.0"> + <Disk_Parameters> + ... + </Disk_Parameters> + <StorageData> + ... + </StorageData> + <Snapshots> + ... + </Snapshots> +</Parallels_disk_image> + +== Disk_Parameters section == +The Disk_Parameters section describes the physical layout of the virtual disk +and some general settings. + +The Disk_Parameters section MUST contain the following subsections: + * 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. + Attention: this field affects the read/write functionality. + +== StorageData section == +This section of the file describes root image and all snapshot images. + +The StorageData section consists of the Storage subsection, as shown below: +<StorageData> + <Storage> + ... + </Storage> +</StorageData> + +A Storage descriptor consists of the following subsections: + * Start - start sector of the storage, equals to 0. + * End - number of sectors in 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 subsections. + +Each Image section consists of the following subsections: + * GUID - image identifier, UUID in curly brackets. + For instance, {12345678-9abc-def1-2345-6789abcdef12}. + * Type - image type of the element. It can be: + "Plain" for plain disks. + "Compressed" for expanding disks. + * File - path to image file. Path can be relative to DiskDecriptor.xml or + absolute. + +== Snapshots section == +The Snapshots section describes the snapshot relations with the snapshot tree. + +The section contains the set of Shot subsections, as shown below: +<Snapshots> + <TopGUID> ... </TopGUID> //Optional subsection + <Shot> + ... + </Shot> + <Shot> + ... + </Shot> + ... +</Snapshots> + +Each Shot section contains the following subsections: + * 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 one root +snapshot. Top snapshot could be described via two ways: via TopGUID subsection +in the Snapshots section 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) sould be +opened read-only. +There is another predefined GIUD, +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. + +NOTE: To address top snapshot QEMU supports only predefined GUID mode. -- 2.7.4