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Cinder/how-to-contribute-a-driver

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How To Contribute a driver to Cinder

Deadline for the Current Development Cycle

The deadline for new backend drivers is Milestone 2 of the current development cycle. By this deadline, your driver should have working third party CI and no code review issues. You can find the date of Milestone 2 on the current release schedule. (Take the link for the "Series" name, and a link to the release schedule will be at the top of the page.) If you are working toward the next cycle, and the schedule has not yet been posted, you can get a rough idea by looking at previous release schedules.

For clarification, a patch is also considered a new driver when it's introducing a new protocol into the driver. For example, if your driver supports iSCSI, but your patch proposes support for FibreChannel, that's a new driver patch.

All About Cinder Drivers

See All About Cinder Drivers for general information about drivers, including a discussion of "supported" vs. "unsupported" drivers and driver compliance.

Third Party CI Requirement Policy

See third party CI wiki.

For people working on getting their CI to handle Python 3, see Cinder Third Party CI update to Python 3.7

Before you write any code

  • Understand how Cinder works, what it's used for, why the other projects in OpenStack may or may not use it. Fully understand the difference between ephemeral storage on the Nova side versus the persistent storage offered by Cinder
  • Cinder offers a reference implementation that should be used as a model. The reference implementation driver file is cinder/volume/drivers/lvm.py, not to be mistaken for cinder/volume/driver.py which is the base class that all of the drivers inherit from. Note that there are a lot of options that show up there regarding iSCSI targets etc, but this gives you an idea of the expectations in terms of features that are implemented and some of the behaviors. I strongly recommend loading up devstack (you're going to need it to test your driver anyway) and play around with the default LVM. It's really important that you get a feel for how Cinder works and interacts with the other OpenStack projects before you get too far along.
  • You must submit a blueprint in Launchpad introducing your driver, so that it can be targeted for a release, and prioritized to receive code reviews. This will also get your effort to contribute a driver some visibility within the Cinder community. Do this right away so that you don't get any surprises later. You don't need a cinder spec for most drivers. (If a spec is required for some reason, we will let you know.)
  • We have a development channel on freenode: #openstack-cinder. There are developers here round the clock, it's a great resource for you get started. Log in, ask questions, don't stare at code in isolation for a week... if you're stuck on something just ask. There's also no need to start off with "Can I ask a question"... you likely won't get a response. Just type in your question, that way anybody monitoring the channel that might know the answer can step in and answer.

Writing Code

  • You must implement all of the methods that exist as core features.
  • Your driver should not make any state changes. (e.g. make Cinder database calls). The volume manager is responsible for making state changes after the driver is done talking to the storage backend. Your driver should try not to read from database if possible.
  • Unit tests for new code are required.
  • Make sure you're not duplicating a configuration option that already exists. To verify this, you'll need to need look at the cinder/etc/cinder.conf.sample file.
    • Every effort should be made to reuse common config options before introducing driver-specific ones.
    • If options are added, you will need to run "tox -e genopts" to update the opts.py file that is used to generate our configuration references.
  • Make sure to follow the OpenStack Style Guide. Very likely you'll get nit pick reviews otherwise, which is not productive either way.
  • Cinder's manager layer will log useful information like failures from the driver that are raised. However, you're more than welcome to add additional logging, but please follow our logging guideline. (NOTE: In order to assist operators using public internet search engines to troubleshoot problems, log messages are no longer translated.)

Submitting Driver For Review

When submitting your driver, please include a release note along with your patch. See the Reno Documentation for details on how to generate new release notes.

The release note should be something along the lines of:

---
features:
 - Added backend driver for vendor storage.
  • All new code must be Python 3.7 compatible. Unit tests will be run with all of the current cycle's supported runtimes, but additional runtime testing should be performed. Check the supported runtimes for the current cycle.
    • for the Victoria cycle: python 3.6, python 3.7, and python 3.8
    • for the Wallaby cycle: python 3.6 and python 3.8
  • Do NOT bother the Cinder team for reviews. We are aware of your patch being posted.

After Your Driver Is Added

Congratulations! You're not done yet though. After your driver has been merged there are still some things that need to be done.

  • Make sure there is documentation for your driver so that operators know how to configure it
    • documentation is stored in the same repository where you committed your driver code
    • files go in cinder/doc/source/configuration/block-storage/drivers
    • look at the other files in that directory to get an idea of what's expected
      • note: for a backup driver, your doc goes in cinder/doc/source/configuration/block-storage/backup
  • Update cinder/doc/source/reference/support-matrix.ini with the appropriate information for your driver
  • Continue to be available on IRC and attend the weekly meetings in case questions come up.
  • Subscribe to receive bugs for your driver! The Cinder team will be triaging bugs and will tag bugs with the name of your company that are related to your driver. To subscribe:
    • Go to https://bugs.launchpad.net/openstack/cinder/+bug
    • Click 'Subscribe to bug mail'
    • Click the radio button "are added and changed in any way"
    • Click checkbox 'Bugs must match this filter (...)"
    • Click tags
    • With "match all tags" selected type in the field the name of your company.