Document more review processes

The Cinder team has some code review policies that are
generally known but not documented anywhere.  This patch
provides a place for us to document those reiview
practices that may not be known to everyone.

I have started by documenting the new process proposed at
the Dublin PTG for targeting milestones.  I also add
documentation to formalize the fact that we should not
merge vendor patches without their CI passing on the
patch.

Change-Id: Ie3bb23dcb6299f15ae69e12095c1aa9640565c33

doc/source/contributor/gerrit.rst

@@ -1,8 +1,15 @@
-Code Reviews with Gerrit
-========================
+Code Reviews
+============
 
-Cinder uses the `Gerrit`_ tool to review proposed code changes. The review site
-is https://review.openstack.org
+Cinder follows the same `Review guidelines`_ outlined by the OpenStack community.
+This page provides additional information that is helpful for reviewers of
+patches to Cinder.
+
+Gerrit
+------
+
+Cinder uses the `Gerrit`_ tool to review proposed code changes. The review
+site is https://review.openstack.org
 
 Gerrit is a complete replacement for Github pull requests. `All Github pull
 requests to the Cinder repository will be ignored`.
@@ -11,6 +18,75 @@ See `Gerrit Workflow Quick Reference`_ for information about how to get
 started using Gerrit. See `Development Workflow`_ for more detailed
 documentation on how to work with Gerrit.
 
-.. _Gerrit: https://bugs.chromium.org/p/gerrit/
+Targeting Milestones
+--------------------
+
+In an effort to guide team review priorities the Cinder team has
+adopted the process of adding comments to reviews to target a
+milestone for a particular patch.  This process is not required
+for all patches but is beneficial for patches that may be time sensitive.
+For example patches that need to land earlier in the release cycle so as to
+get additional test time or because later development activities are dependent
+upon that functionality merging.
+
+To target a patch to a milestone a reviewer should add a comment using the
+following format:
+
+  ``target-<release>-<milestone>``
+
+Release should be used to indicate the release to which the patch should be
+targeted, all lower case.  The milestone is a single number, 1 to 3,
+indicating the milestone number. So, to target a patch to land in
+Milestone 2 of the Rocky release a comment like the following
+would be added:
+
+  ``target-rocky-2``
+
+Adding this tag allows reviewers to search for these tags and use them as a
+guide in review priorities.
+
+Targeting patches should be done by Cinder Core Review Team members.
+If a patch developer feels that a patch should be targeted to a
+milestone the developer should bring the request up to the Cinder
+team in a weekly meeting or on the #openstack-cinder Freenode IRC
+channel.
+
+Reviewing Vendor Patches
+------------------------
+
+It is important to consider, when reviewing patches to a vendor's Cinder
+driver, whether the patch passes the vendor's CI process.  CI reports
+are the only tool we have to ensure that a patch works with the Vendor's
+driver.  A patch to a vendor's driver that does not pass that
+vendor's CI should not be merged.  If a patch is submitted by a person
+that does not work with the vendor that owns the driver, a +1 review
+from someone at that vendor is also required.  Finally, a patch should
+not be merged before the Vendor's CI has run against the patch.
+
+.. note::
+
+    Patches which have passed vendor CI and have merged in master
+    are exempt from this requirement upon backport to stable and/or
+    driverfixes branches as vendors are not required to run CI on those
+    branches.  If the vendor, however, is running CI on stable and/or
+    driverfix branches failures should not be ignored unless otherwise
+    verified by a developer from the vendor.
+
+Unit Tests
+----------
+
+Cinder requires unit tests with all patches that introduce a new
+branch or function in the code.  Changes that do not come with a
+unit test change should be considered closely and usually returned
+to the submitter with a request for the addition of unit test.
+
+.. note::
+
+   Unit test changes are not validated in any way by vendor's CI.
+   Vendor CI's run the tempest volume tests against a change which
+   does not include a unit test execution.
+
+.. _Review guidelines: https://docs.openstack.org/doc-contrib-guide/docs-review-guidelines.html
+.. _Gerrit: https://review.openstack.org/#/q/project:openstack/cinder+status:open 
 .. _Development Workflow: https://docs.openstack.org/infra/manual/developers.html#development-workflow
 .. _Gerrit Workflow Quick Reference: https://docs.openstack.org/infra/manual/developers.html#development-workflow