75 lines
2.1 KiB
ReStructuredText
75 lines
2.1 KiB
ReStructuredText
|
=============
|
||
|
|
D-Bus VMState
|
||
|
|
=============
|
||
|
|
|
||
|
|
Introduction
|
||
|
|
============
|
||
|
|
|
||
|
|
The QEMU dbus-vmstate object's aim is to migrate helpers' data running
|
||
|
|
on a QEMU D-Bus bus. (refer to the :doc:`dbus` document for
|
||
|
|
some recommendations on D-Bus usage)
|
||
|
|
|
||
|
|
Upon migration, QEMU will go through the queue of
|
||
|
|
``org.qemu.VMState1`` D-Bus name owners and query their ``Id``. It
|
||
|
|
must be unique among the helpers.
|
||
|
|
|
||
|
|
It will then save arbitrary data of each Id to be transferred in the
|
||
|
|
migration stream and restored/loaded at the corresponding destination
|
||
|
|
helper.
|
||
|
|
|
||
|
|
For now, the data amount to be transferred is arbitrarily limited to
|
||
|
|
1Mb. The state must be saved quickly (a fraction of a second). (D-Bus
|
||
|
|
imposes a time limit on reply anyway, and migration would fail if data
|
||
|
|
isn't given quickly enough.)
|
||
|
|
|
||
|
|
dbus-vmstate object can be configured with the expected list of
|
||
|
|
helpers by setting its ``id-list`` property, with a comma-separated
|
||
|
|
``Id`` list.
|
||
|
|
|
||
|
|
Interface
|
||
|
|
=========
|
||
|
|
|
||
|
|
On object path ``/org/qemu/VMState1``, the following
|
||
|
|
``org.qemu.VMState1`` interface should be implemented:
|
||
|
|
|
||
|
|
.. code:: xml
|
||
|
|
|
||
|
|
<interface name="org.qemu.VMState1">
|
||
|
|
<property name="Id" type="s" access="read"/>
|
||
|
|
<method name="Load">
|
||
|
|
<arg type="ay" name="data" direction="in"/>
|
||
|
|
</method>
|
||
|
|
<method name="Save">
|
||
|
|
<arg type="ay" name="data" direction="out"/>
|
||
|
|
</method>
|
||
|
|
</interface>
|
||
|
|
|
||
|
|
"Id" property
|
||
|
|
-------------
|
||
|
|
|
||
|
|
A string that identifies the helper uniquely. (maximum 256 bytes
|
||
|
|
including terminating NUL byte)
|
||
|
|
|
||
|
|
.. note::
|
||
|
|
|
||
|
|
The helper ID namespace is a separate namespace. In particular, it is not
|
||
|
|
related to QEMU "id" used in -object/-device objects.
|
||
|
|
|
||
|
|
Load(in u8[] bytes) method
|
||
|
|
--------------------------
|
||
|
|
|
||
|
|
The method called on destination with the state to restore.
|
||
|
|
|
||
|
|
The helper may be initially started in a waiting state (with
|
||
|
|
an --incoming argument for example), and it may resume on success.
|
||
|
|
|
||
|
|
An error may be returned to the caller.
|
||
|
|
|
||
|
|
Save(out u8[] bytes) method
|
||
|
|
---------------------------
|
||
|
|
|
||
|
|
The method called on the source to get the current state to be
|
||
|
|
migrated. The helper should continue to run normally.
|
||
|
|
|
||
|
|
An error may be returned to the caller.
|