On Mon, Dec 18, 2017 at 02:09:07PM +0300, Denis V. Lunev wrote:
From: Klim Kireev <address@hidden>
This patch adds main information about Parallels Disk
format, which consists of DiskDescriptor.xml and other files.
Signed-off-by: Edgar Kaziakhmedov <address@hidden>
Signed-off-by: Klim Kireev <address@hidden>
Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
Signed-off-by: Denis V. Lunev <address@hidden>
CC: Stefan Hajnoczi <address@hidden>
---
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
s/unspecified here fields/fields not covered in this document/
+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.
s/without parent/with no parent/
+
+ 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
s/then/than/
+ disk and it is defined as a split image.
I was having trouble understanding this paragraph. At this point I can
begin to see that split images consist of multiple storages. That makes
the concept of storage clearer.
Perhaps rephrase this paragraph as:
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. 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.
+ 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
s/isn't/aren't/
+ 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.
To make this clearer the last line could be:
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 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.
What does "Attention: this field affects the read/write functionality" mean?
+
+== StorageData section ==
+This section of the file describes root image and all snapshot images.
s/root image/the root image/
+
+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.
Just to be clear, if Start > 0 then End is still Disk_size and not Start
+ Disk_size? Please tweak the wording to make this clear.
+ * 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).
What is the purpose of this field if the Parallels Expandable Image
header also has the same value?
+ * Several Image subsections.
+
+Each Image section consists of the following subsections:
I'm confused by the use of "section" and "subsections" here. This spec
is ambiguous and does not describe the XML clearly. Is a "section"
always an XML tag and a "subsection" is a child XML tag?
In other words, are we talking about:
<Image>
<GUID>{12345678-9abc-def1-2345-6789abcdef12}</GUID>
<Type>Plain</Type>
<File>my_file</File>
</Image>
Or could it be:
<Image GUID="{12345678-9abc-def1-2345-6789abcdef12}"
Type="Plain"
File="my_file" />
?
Please use XML terminology ("tag", "attribute", etc) instead of
"section"/"subsection".
+ * GUID - image identifier, UUID in curly brackets.
+ For instance, {12345678-9abc-def1-2345-6789abcdef12}.
How is the GUID used? Does it need to be validated against the GUID in
the image file?
+ * Type - image type of the element. It can be:
+ "Plain" for plain disks.
What is a plain disk? Is this a raw file or a Parallels Expandable
Image file?
+ "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
s/sould/should/
+opened read-only.
+There is another predefined GIUD,
s/GIUD/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.
+NOTE: To address top snapshot QEMU supports only predefined GUID mode.
This sounds like an implementation limitation and a spec violation
(since the spec says <TopGUID> may be used). Please implement <TopGUID>
support unless it's really hard to do, or drop <TopGUID> from this spec
so that it's clear this feature doesn't need to be supported by QEMU and
other open source software.