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