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Development Work Flow

From GlusterDocumentation

Contents

Development work flow of Gluster

This document provides a detailed overview of the development model followed by the GlusterFS project.

For a simpler overview visit Simplified_dev_workflow.

Basics

The GlusterFS development model largely revolves around the features and functionality provided by Git version control system, Gerrit code review system and Jenkins continuous integration system. It is a primer for a contributor to the project.

Git

Git is a extremely flexible, distributed version control system. GlusterFS' main git repository is at http://git.gluster.org and public mirrors are at GlusterForge (https://forge.gluster.org/glusterfs-core/glusterfs) and at GitHub (https://github.com/gluster/glusterfs). The development repo is hosted inside Gerrit and every code merge is instantly replicated to the public mirrors.

A good introduction to Git can be found at http://www-cs-students.stanford.edu/~blynn/gitmagic/.

Gerrit

Gerrit is an excellent code review system which is developed with a git based workflow in mind. The GlusterFS project code review system is hosted at review.gluster.org. Gerrit works on "Change"s. A change is a set of modifications to various files in your repository to accomplish a task. It is essentially one large git commit with all the necessary changes which can be both built and tested.

Gerrit usage is described later in 'Review Process' section.

Jenkins

Jenkins is a Continuous Integration build system. Jenkins is hosted at http://build.gluster.org. Jenkins is configured to work with Gerrit by setting up hooks. Every "Change" which is pushed to Gerrit is automatically picked up by Jenkins, built and smoke tested. Output of all builds and tests can be viewed at http://build.gluster.org/job/smoke/. Jenkins is also setup with a 'regression' job which is designed to execute test scripts provided as part of the code change.

Preparatory Setup

Here is a list of initial one-time steps before you can start hacking on code.

Register

Sign up for an account at http://review.gluster.org by clicking 'Register' on the right-hand top. You can use your gmail login as the openID identity.

Preferred email

On first login, add your git/work email to your identity. You will have to click on the URL which is sent to your email and set up a proper Full Name. Make sure you set your git/work email as your preferred email. This should be the email address from which all your code commits are associated.

Set Username

Select yourself a username.

Watch glusterfs

In Gerrit settings, watch the 'glusterfs' project. Tick on all the three (New Changes, All Comments, Submitted Changes) types of notifications.

Email filters

Set up a filter rule in your mail client to tag or classify mails with the header

 List-Id: <gerrit-glusterfs.review.gluster.org>

as mails originating from the review system.

SSH keys

Provide your SSH public key into Gerrit so that you can successfully access the development git repo as well as push changes for review/merge.

Clone a working tree

Get yourself a working tree by cloning the development repository from Gerrit

 sh$ git clone ssh://[username@]git.gluster.org/glusterfs.git glusterfs

Branching policy

This section describes both, the branching policies on the public repo as well as the suggested best-practice for local branching

Master/release branches

In glusterfs.git, the master branch is the forward development branch. This is where new features come in first. In fact this is where almost every change (commit) comes in first. The master branch is always kept in a buildable state and smoke tests pass.

Release trains (3.1.z, 3.2.z, 3.2.z) each have a branch originating from master. Code freeze of each new release train is marked by the creation of the release-3.y branch. At this point no new features are added to the release-3.y branch. All fixes and commits first get into master. From there, only bug fixes get backported to the relevant release branches. From the release-3.y branch, actual release code snapshots (e.g. glusterfs-3.2.2 etc.) are tagged (git annotated tag with 'git tag -a') shipped as a tarball.

Personal per-task branches

As a best practice, it is recommended you perform all code changes for a task in a local branch in your working tree. The local branch should be created from the upstream branch to which you intend to submit the change. If you are submitting changes to master branch, first create a local task branch like this -

 sh$ git checkout master
 sh$ git branch bug-XYZ && git checkout bug-XYZ
 ... <hack, commit>

If you are backporting a fix to a release branch, or making a new change to a release branch, your commands would be slightly different. If you are checking out a release branch in your local working tree for the first time, make sure to set it up as a remote tracking branch like this -

 sh$ git checkout -b release-3.2 origin/release-3.2

The above step is not necessary to be repeated. In the future if you want to work to the release branch -

 sh$ git checkout release-3.2
 sh$ git branch bug-XYZ-release-3.2 && git checkout bug-XYZ-release-3.2
 ... <cherry-pick, hack, commit>

Building

Environment Setup

Ubuntu

To setup the build environment on an Ubuntu system, type the following command to install the required packages:

sudo apt-get -y install python-pyxattr libreadline-dev systemtap-sdt-dev tar python-pastedeploy python-simplejson python-sphinx python-webob libssl-dev pkg-config python-dev python-eventlet python-netifaces libaio-dev libibverbs-dev libtool libxml2-dev liblvm2-dev make autoconf automake bison dos2unix flex libfuse-dev
CentOS/RHEL/Fedora

On Fedora systems, install the required packages by following the instructions in CompilingRPMS.

Creating build environment

Once the required packages are installed for your appropiate system, generate the build configuration:

sh$ ./autogen.sh
sh$ ./configure --enable-fusermount

Build and install

GlusterFS

Ubuntu

Type the following to build and install GlusterFS on the system:

sh$ make
sh$ make install
CentOS/RHEL/Fedora

In an rpm based system, there are two methods to build GlusterFS. One is to use the method describe above for Ubuntu. The other is to build and install RPMS as described in CompilingRPMS.

GlusterFS UFO/SWIFT

To build and run Gluster UFO you can do the following:

  1. Build, create, and install the RPMS as described in CompilingRPMS.
  2. Configure UFO/SWIFT as described in Howto Using UFO SWIFT - A quick and dirty setup guide

Commit policy

For a Gerrit based work flow, each commit should be an independent, buildable and testable change. Typically you would have a local branch per task, and most of the times that branch will have one commit.

If you have a second task at hand which depends on the changes of the first one, then technically you can have it as a separate commit on top of the first commit. But it is important that the first commit should be a testable change by itself (if not, it is an indication that the two commits are essentially part of a single change). Gerrit accommodates these situations by marking Change 1 as a "dependency" of Change 2 (there is a 'Dependencies' tab in the Change page in Gerrit) automatically when you push the changes for review from the same local branch.

You will need to sign-off your commit (git commit -s) before sending the patch for review. By signing off your patch, you agree to the terms listed under "Developer's Certificate of Origin" section in the CONTRIBUTING file available in the repository root.

Provide a meaningful commit message. Your commit message should be in the following format

  • A short one line subject describing what the patch accomplishes
  • An empty line following the subject
  • Situation necessitating the patch
  • Description of the code changes
  • Reason for doing it this way (compared to others)
  • Description of test cases

Test cases

Part of the workflow is to aggregate and execute pre-commit test cases which accompany patches, cumulatively for every new patch. This guarantees that tests which are working till the present are not broken with the new patch. Every change submitted to Gerrit much include test cases in

   tests/group/script.t

as part of the patch. This is so that code changes and accompanying test cases are reviewed together. All new commits now come under the following categories w.r.t test cases:

New 'group' directory and/or 'script.t'

This is typically when code is adding a new module and/or feature

Extend/Modify old test cases in existing scripts

This is typically when present behavior (default values etc.) of code is changed

No test cases

This is typically when code change is trivial (e.g. fixing typos in output strings, code comments)

Only test case and no code change

This is typically when we are adding test cases to old code (already existing before this regression test policy was enforced)

More details on how to work with test case scripts can be found in

   tests/README


Review process

rfc.sh

After doing the local commit, it is time to submit the code for review. There is a script available inside glusterfs.git called rfc.sh. You can submit your changes for review by simply executing

 sh$ ./rfc.sh

This script does the following:

  • The first time it is executed, it downloads a git hook from http://review.gluster.org/tools/hooks/commit-msg and sets it up locally to generate a Change-Id: tag in your commit message (if it was not already generated.)
  • Rebase your commit against the latest upstream HEAD. This rebase also causes your commits to undergo massaging from the just downloaded commit-msg hook.
  • Prompt for a Bug Id for each commit (if it was not already provded) and include it as a "BUG:" tag in the commit log. You can just hit <enter> at this prompt if your submission is purely for review purposes.
  • Push the changes to review.gluster.org for review. If you had provided a bug id, it assigns the topic of the change as "bug-XYZ". If not it sets the topic as "rfc".

On a successful push, you will see a URL pointing to the change in review.gluster.org

Auto verification

The integration between Jenkins and Gerrit triggers an event in Jenkins on every push of changes, to pick up the change and run build and smoke test on it.

If the build and smoke tests execute successfuly, Jenkins marks the change as '+0 Verified'. If they fail, '-1 Verified' is marked on the change. This means passing the automated smoke test is a necessary condition but not sufficient.

It is important to note that Jenkins verification is only a generic verification of high level tests. More concentrated testing effort for the patch is necessary with manual verification.

If auto verification fails, it is a good reason to skip code review till a fixed change is pushed later. You can click on the build URL automatically put as a comment to inspect the reason for auto verification failure. In the Jenkins job page, you can click on the 'Console Output' link to see the exact point of failure.

Reviewing / Commenting

Code review with Gerrit is relatively easy compared to other available tools. Each change is presented as multiple files and each file can be reviewed in Side-by-Side mode. While reviewing it is possible to comment on each line by double-clicking on it and writing in your comments in the text box. Such in-line comments are saved as drafts, till you finally publish them as a Review from the 'Change page'.

There are many small and handy features in Gerrit, like 'starring' changes you are interested to follow, setting the amount of context to view in the side-by-side view page etc.

Incorporate, Amend, rfc.sh, Reverify

Code review comments are notified via email. After incorporating the changes in code, you can mark each of the inline comment as 'done' (optional). After all the changes to your local files, amend the previous commit with these changes with -

 sh$ git commit -a --amend

Push the amended commit by executing rfc.sh. If your previous push was an "rfc" push (i.e, without a Bug Id) you will be prompted for a Bug Id again. You can re-push an rfc change without any other code change too by giving a Bug Id.

On the new push, Jenkins will re-verify the new change (independent of what the verification result was for the previous push).

It is the Change-Id line in the commit log (which does not change) that associates the new push as an update for the old push (even though they had different commit ids) under the same Change. In the side-by-side view page, it is possible to set knobs in the 'Patch History' tab to view changes between patches as well. This is handy to inspect how review comments were incorporated.

If further changes are found necessary, comments can be made on the new patch as well, and the same cycle repeats.

If no further changes are necessary, the reviewer can mark the patch as reviewed with a certain score depending on the depth of review and confidence (+1 or +2). A -1 review indicates non-agreement for the change to get merged upstream.

Regression tests and test cases

All code changes which are not trivial (typo fixes, code comment changes) must be accompanied with either a new test case script or extend/modify an existing test case script. It is important to review the test case in conjunction with the code change to analyse whether the code change is actually verified by the test case.


Regression tests (i.e, execution of all test cases accumulated with every commit) is not automatically triggered as the test cases can be extensive and is quite expensive to execute for every change submission in the review/resubmit cycle. Instead it is triggered by the maintainers, after code review. Passing the regression test is a necessary condition for merge along with code review points.

Submission Qualifiers

For a change to get merged, there are two qualifiers which are enforced by the Gerrit system. They are - A change should have at least one '+2 Reviewed', and a change should have at least one '+1 Verified' (regression test). The project maintainer will merge the changes once a patch meets these qualifiers.

Submission Disqualifiers

There are three types of "negative votes".

 -1 Verified
 -1 Code-Review ("I would prefer that you didn't submit this")
 -2 Code-Review ("Do not submit")

The implication and scope of each of the three are different. They behave differently as changes are resubmitted as new patchsets.

-1 Verified

Anybody voting -1 Verified will prevent *that patchset only* from getting merged. The flag is automatically cleared on the next patchset post. The intention is that this vote is based on the result of some kind of testing. A voter is expected to explain the test case which failed. Jenkins jobs (smoke, regression, ufounit) use this field for voting -1/0/+1. When voting -1, Jenkins posts the link to the URL which has the console output of the failed job.

-1 Code-Review ("I would prefer that you didn't submit this")

This is an advisory vote based on the content of the patch. Typically issues in source code (both design and implementation), source code comments, log messages, license headers etc. found by human inspection. The reviewer explains the specific issues by commenting against the most relevant lines of source code in the patch. On a resubmission, -1 votes are cleared automatically. It is the responsibility of the maintainers to honor -1 Code-Review votes from reviewers (by not merging the patches), and inspecting that -1 comments on previous submissions are addressed in the new patchset. Generally this is the recommended "negative" vote.

-2 Code-Review ("Do not submit")

This is a stronger vote which actually prevents Gerrit from merging the patch. The -2 vote persists even after resubmission and continues to prevent the patch from getting merged, until the voter revokes the -2 vote (and then is further subjected to Submission Qualifiers). Typically one would vote -2 if they are *against the goal* of what the patch is trying to achieve (and not an issue with the patch, which can change on resubmission). A reviewer would also vote -2 on a patch even if there is agreement with the goal, but the issue in the code is of such a critical nature that the reviewer personally wants to inspect the next patchset and only then revoke the vote after finding the new patch satisfactory. This prevents the merge of the patch in the mean time. Every registered user has the right to exercise the -2 Code review vote, and cannot be overridden by the maintainers.

 

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