Merge "Support libvirt/KVM on System z (S/390) as a hypervisor platform"
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specs/kilo/approved/libvirt-kvm-systemz.rst
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specs/kilo/approved/libvirt-kvm-systemz.rst
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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================================================================
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Support KVM/libvirt on System z (S/390) as a hypervisor platform
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================================================================
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https://blueprints.launchpad.net/nova/+spec/libvirt-kvm-systemz
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Add support for KVM/libvirt in Linux on System z as a Nova hypervisor
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platform. The existing Nova driver for KVM/libvirt will be used. There are
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some platform-specific changes needed in the Nova driver to get the platform
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going.
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Additional OpenStack functionality beyond initial Nova support is not part of
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this blueprint; we will have specific additional blueprints for that, as
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needed.
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A 3rd party Continuous Integration environment for OpenStack for KVM/libvirt
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on System z will be established and maintained.
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Problem description
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===================
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The existing Nova driver for KVM/libvirt does not work unchanged for KVM on
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System z.
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The issues currently known, are:
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1. The System z machine type (``'s390-ccw-virtio'``) needs to be returned by
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``LibvirtDriver._get_machine_type()``, if the host architecture is System z.
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This then causes the ``os/type/@machine`` attribute in the libvirt
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domain.xml to be set up accordingly.
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2. The CPU capabilities returned by libvirt on System z do not include the
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``model`` element. This is intended to be added to libvirt, but until then
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we need a temporary circumvention in the Nova driver (adding the model
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information from /proc/cpuinfo if not present and if on S390x).
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3. For the interactive console and the log of OpenStack instances, console
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devices need to be generated (instead of serial devices), if the host
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architecture is System z (see `[2]`_). These console devices need to have a
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target type ``"sclp"`` for the interactive console of OpenStack, and
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``"sclplm"`` for the log of OpenStack.
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Background: Linux on System z writes its messages during its early boot
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phases to an interface called "SCLP". SCLP is available in QEMU as a
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console device. As a result, it is also a console device in libvirt, with
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type="pty" and target type="sclp" for the interactive console of OpenStack,
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and with type="file" and target type="sclplm" ("lm" for "line mode") for the
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log of OpenStack. If we use the default target type ("virtio"), we will not
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capture the messages written by Linux in its early boot phases, and we do
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want to provide them.
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Changing the default target type for console devices in libvirt to "sclp" or
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"sclplm" (e.g. dependent on the ``console/@type`` attribute) would be a
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backwards incompatible change of libvirt.
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If commonality in the Nova driver across the libvirt platforms is important:
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A console device could also be used for other platforms including x86, and
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is already used in one of the code paths in the current Nova driver. Serial
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devices in libvirt are meant to represent serial ports (aka RS-232), so they
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are not an ideal choice anyway, for interactive console and log.
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4. The FCP support in the libvirt volume driver needs to be adjusted to
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the System z specific format of the device file paths.
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In the hypervisor support matrix
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(https://wiki.openstack.org/wiki/HypervisorSupportMatrix),
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the (new) column for KVM/libvirt on System z is intended to look like the
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column for KVM/libvirt on x86, except that the following functions will not be
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supported (in addition to those marked as not supported for KVM/libvirt on
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x86):
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* VNC Console
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* SPICE Console
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* Inject Networking
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For block storage, Cinder will be supported.
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For networking, Neutron will be supported. Nova networking should work but will
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not be a focus.
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As a result, all features marked as required on
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https://wiki.openstack.org/wiki/HypervisorSupportMatrix/Requirements
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will be supported for KVM/libvirt on System z.
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Use Cases
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---------
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Use OpenStack with KVM on System z
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Project Priority
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----------------
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None
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Proposed change
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===============
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Change code in the libvirt Nova driver to address these issues, dependent on
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the host capabilities indicating a CPU architecture of ``arch.S390X``.
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For details, see section `Work Items`_.
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Alternatives
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------------
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None
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Data model impact
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-----------------
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None
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REST API impact
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---------------
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None
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Security impact
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---------------
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None
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Notifications impact
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--------------------
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None
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Other end user impact
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---------------------
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None
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Performance Impact
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------------------
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None
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Other deployer impact
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---------------------
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None (no need for platform-specific parameters in nova.conf as part of this
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blueprint)
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Developer impact
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----------------
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None (changes should not affect other libvirt platforms)
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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mzoeller
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Other contributors:
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maiera
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Work Items
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----------
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In ``nova/virt/libvirt/driver.py``:
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* For issue 1:
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In ``LibvirtDriver._get_machine_type()``, return the System z machine type
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(``'s390-ccw-virtio'``), if the host architecture is System z.
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* For issue 2:
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In `` LibvirtDriver._get_host_capabilities()``, add the ``model`` variable
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to the capabilities, if not present and if the host architecture is System z;
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the model is based on the machine type from /proc/cpuinfo.
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* For issue 3:
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In ``LibvirtDriver._get_guest_config()``, create console devices instead of
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serial devices for the interactive console and for the log, with target type
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"sclplm" (for the log) and "sclp" (for the interactive console), if the host
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architecture is System z.
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In ``nova/virt/libvirt/config.py``:
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* For issue 3:
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In ``LibvirtConfigGuestChar.__init__()`` and ``format_dom()``, add support
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for specifying a target type.
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In ``nova/virt/libvirt/volume.py``:
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* For issue 4:
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The FCP support in the libvirt volume driver needs to be adjusted to
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the System z specific format of the device file paths.
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In ``nova/virt/libvirt/utils.py``:
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* For issue 4:
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Possibly, supporting utility functions for the FCP support issue are needed.
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Doc changes (see section `Documentation Impact`_).
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Dependencies
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============
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* Software versions:
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- Linux kernel: 3.10 or higher
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- libvirt: 1.0.4 or higher
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- qemu: 1.4.0 or higher
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* 3rd party CI environment for KVM/libvirt on System z set up
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* Future replacements for temporary circumventions:
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- libvirt patch to add model information to CPU capabilities.
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Testing
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=======
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Unit test:
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* Existing Nova unit tests should suffice for the generic bits of Nova.
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* Additional Nova unit tests for any s390-specific behaviors will be written.
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3rd party CI:
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* A 3rd party CI environment for KVM/libvirt on Systemz will be set up and run
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by by IBM, to run full tempest tests.
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Documentation Impact
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====================
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* No changes needed in config docs.
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* Doc changes for the platform will be made as needed (details are to be
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determined).
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References
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==========
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* _`[1]` libvirt: Domain XML format, Device Addresses,
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http://libvirt.org/formatdomain.html#elementsAddress
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* _`[2]` libvirt: Domain XML format, Console,
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http://libvirt.org/formatdomain.html#elementCharConsole
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* _`[3]` Linux on System z Device Driver book,
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http://public.dhe.ibm.com/software/dw/linux390/docu/l316dd25.pdf
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* _`[4]` Linux on System z,
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http://www.ibm.com/developerworks/linux/linux390/
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