Untyped vol to default vol type

This spec proposes to use default volume type instead of
allowing users to create untyped volumes.

Change-Id: Ib5050f5b23300414a7903b48917460639e12aab7
Partial-Implements: blueprint untyped-volumes-default-volume-type

specs/train/untyped-volumes-to-default-volume-type.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
+
+======================================
+Untyped volumes to default volume type
+======================================
+
+https://blueprints.launchpad.net/cinder/+spec/untyped-volumes-default-volume-type
+
+This blueprint proposes to use a default volume type instead of allowing users
+to create untyped volumes.
+
+Problem description
+===================
+
+Currently a user is able to create a volume without any volume type, since
+a volume's characteristics are defined by a volume type, creating untyped
+volumes shouldn't be allowed.
+
+Use Cases
+=========
+
+Most users use volume types, and our code is simpler and less buggy if we
+just always attach volume types to volumes, so we should just force all
+deployments to use volume types.
+
+Proposed change
+===============
+
+This spec proposes the following changes :
+
+* Create a default volume type during cinder database migration or on cinder
+  services start time. The default volume type will have no extra specs
+  assigned to it and will be named ``__DEFAULT__``
+* If a volume type named ``__DEFAULT__`` already exists, the deployer
+  needs to rename or remove it before upgrading
+* Add an online migration to convert all untyped volumes and snapshots to
+  ``__DEFAULT__`` volume type
+* Set a default value ``__DEFAULT__`` for ``default_volume_type`` config
+  option so the default value is picked when it is unset in cinder.conf
+* Don't allow deletion of the ``__DEFAULT__`` volume type via type-delete
+* Updating of volume type (``__DEFAULT__``) will be handled by MANAGE_POLICY
+  which defaults to admin-only
+
+Alternatives
+------------
+
+1. Mandate specifying volume type while creating volumes.
+2. Do this as a behind-the-scenes DB migration rather than relying on manual
+   intervention with upgrade checkers.
+3. Do this as a best-effort-if-it's-safe operation in the volume manager,
+   which would migrate most deployments, and skip those that are ruled out for whatever reason.
+
+REST API impact
+---------------
+
+None
+
+Data model impact
+-----------------
+
+None
+
+Security impact
+---------------
+
+None
+
+Notifications impact
+--------------------
+
+None
+
+Other end user impact
+---------------------
+
+* All volumes created without specifying the volume-type parameter
+  will be associated with the default volume type.
+* Untyped Volumes and Snapshots will be assigned ``__DEFAULT__``
+  volume type
+* Users will no longer be able to create a volume with None volume type.
+
+Performance Impact
+------------------
+
+None
+
+Other deployer impact
+---------------------
+
+None
+
+Developer impact
+----------------
+
+None
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  Rajat Dhasmana <rajatdhasmana@gmail.com>
+
+Other assignee:
+  Eric Harney <eharney@redhat.com>
+
+Work Items
+----------
+By restricting untyped volumes, we need to do the following changes:
+
+* Add an upgrade check to verify that current deployment doesn't contain
+  any volume type named ``__DEFAULT__`` else the upgrade will fail
+
+* Create ``__DEFAULT__`` volume type at the time of cinder db migration or
+  service start time
+
+* Add upgrade check to verify no type named ``__DEFAULT__`` exists before
+  upgrading
+
+* Add an online migration to convert all untyped volumes and snapshots to
+  ``__DEFAULT__`` volume type
+
+* Related code changes to associate default_volume_type to volumes if no
+  volume type is specified by user
+
+Dependencies
+============
+
+None
+
+Testing
+=======
+
+Unit-tests, tempest and other related tests will be implemented.
+
+Documentation Impact
+====================
+
+Need to update volume type related docs.
+
+References
+==========
+
+None