Add blueprint for vHost connector support

Change-Id: Ia0c6488c7867bf1dbb92d0ba76b2a99da186619c

specs/juno/vhost-support.rst

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+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+==========================================
+
+Add vHost Executor
+
+==========================================
+
+https://blueprints.launchpad.net/cinder/+spec/vhost-support
+
+The vHost driver was added in the 3.6 Linux kernel. The Linux-IO Target vHost
+fabric module implements I/O processing based on the Linux virtio mechanism. It
+provides virtually bare-metal local storage performance for KVM guests.
+Currently Linux guest VMs are supported.
+
+Problem description
+===================
+
+The vHost driver is not a self-contained virtio device, as it depends on
+userspace to handle the control plane while the data plane is done in kernel.
+This means the data plane does not go through emulations, which can slow down
+I/O performance. Cinder today does not provide an option for taking advantage
+of the Linux vHost driver.
+
+Proposed change
+===============
+
+Add an additional brick executor that knows how to work with vHost.  The
+executor will have a first pass implementation of creating, deleting, listing
+vHost endpoints through LIO.
+
+Creating the endpoint requires a block device to be available on the machine
+that is creating the vHost target. The vHost executor would pass the block
+device path to to rtstools, and rtstools will create vHost endpoint with a lun
+to the block device.
+
+Alternatives
+------------
+
+n/a
+
+Data model impact
+-----------------
+
+n/a
+
+REST API impact
+---------------
+
+n/a
+
+Security impact
+---------------
+
+n/a
+
+Notifications impact
+--------------------
+
+n/a
+
+Other end user impact
+---------------------
+
+n/a
+
+Performance Impact
+------------------
+
+Cinder itself being the control plane will not experience any different
+performance. The data plane should experience a greater deal of performance [1].
+
+Other deployer impact
+---------------------
+
+n/a
+
+Developer impact
+----------------
+
+n/a
+
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+    thingee
+
+Work Items
+----------
+
+* Add vHost executor to brick
+
+Dependencies
+============
+
+n/a
+
+Testing
+=======
+
+There will be appropriate unit tests available making sure target creation,
+deletion, listing works.
+
+Documentation Impact
+====================
+
+n/a
+
+References
+==========
+
+[1] - http://linux-iscsi.org/wiki/VHost#Linux_performance