This section provides some overview on workflows using Git. In particular, the information covers basic practices that describe roles and actions in a collaborative development environment. Again, if you are familiar with this type of development environment, you might want to just skip this section.
The Yocto Project files are maintained using Git in a "master" branch whose Git history tracks every change and whose structure provides branches for all diverging functionality. Although there is no need to use Git, many open source projects do so. For the Yocto Project, a key individual called the "maintainer" is responsible for the "master" branch of a given Git repository. The "master" branch is the “upstream” repository where the final builds of the project occur. The maintainer is responsible for allowing changes in from other developers and for organizing the underlying branch structure to reflect release strategies and so forth.
The project also has contribution repositories known as "contrib" areas. These areas temporarily hold changes to the project that have been submitted or committed by the Yocto Project development team and by community members that contribute to the project. The maintainer determines if the changes are qualified to be moved from the "contrib" areas into the "master" branch of the Git repository.
Developers (including contributing community members) create and maintain cloned repositories of the upstream "master" branch. These repositories are local to their development platforms and are used to develop changes. When a developer is satisfied with a particular feature or change, they "push" the changes to the appropriate "contrib" repository.
Developers are responsible for keeping their local repository up-to-date with "master". They are also responsible for straightening out any conflicts that might arise within files that are being worked on simultaneously by more than one person. All this work is done locally on the developer’s machines before anything is pushed to a "contrib" area and examined at the maintainer’s level.
A somewhat formal method exists by which developers commit changes and push them into the "contrib" area and subsequently request that the maintainer include them into "master" This process is called “submitting a patch” or "submitting a change." For information on submitting patches and changes, see the "How to Submit a Change" section.
To summarize the environment: we have a single point of entry for changes into the project’s "master" branch of the Git repository, which is controlled by the project’s maintainer. And, we have a set of developers who independently develop, test, and submit changes to "contrib" areas for the maintainer to examine. The maintainer then chooses which changes are going to become a permanent part of the project.
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While each development environment is unique, there are some best practices or methods that help development run smoothly. The following list describes some of these practices. For more information about Git workflows, see the workflow topics in the Git Community Book.
Make Small Changes: It is best to keep the changes you commit small as compared to bundling many disparate changes into a single commit. This practice not only keeps things manageable but also allows the maintainer to more easily include or refuse changes.
It is also good practice to leave the repository in a state that allows you to still successfully build your project. In other words, do not commit half of a feature, then add the other half as a separate, later commit. Each commit should take you from one buildable project state to another buildable state.
Use Branches Liberally: It is very easy to create, use, and delete local branches in your working Git repository. You can name these branches anything you like. It is helpful to give them names associated with the particular feature or change on which you are working. Once you are done with a feature or change and have merged it into your local master branch, simply discard the temporary branch.
Merge Changes: The git merge
command allows you to take the
changes from one branch and fold them into another branch.
This process is especially helpful when more than a single developer might be working
on different parts of the same feature.
Merging changes also automatically identifies any collisions or "conflicts"
that might happen as a result of the same lines of code being altered by two different
developers.
Manage Branches: Because branches are easy to use, you should use a system where branches indicate varying levels of code readiness. For example, you can have a "work" branch to develop in, a "test" branch where the code or change is tested, a "stage" branch where changes are ready to be committed, and so forth. As your project develops, you can merge code across the branches to reflect ever-increasing stable states of the development.
Use Push and Pull: The push-pull workflow is based on the
concept of developers "pushing" local commits to a remote repository, which is
usually a contribution repository.
This workflow is also based on developers "pulling" known states of the project down into their
local development repositories.
The workflow easily allows you to pull changes submitted by other developers from the
upstream repository into your work area ensuring that you have the most recent software
on which to develop.
The Yocto Project has two scripts named create-pull-request
and
send-pull-request
that ship with the release to facilitate this
workflow.
You can find these scripts in the scripts
folder of the
Source Directory.
For information on how to use these scripts, see the
"Using Scripts to Push a Change Upstream and Request a Pull" section.
Patch Workflow: This workflow allows you to notify the
maintainer through an email that you have a change (or patch) you would like considered
for the "master" branch of the Git repository.
To send this type of change, you format the patch and then send the email using the Git commands
git format-patch
and git send-email
.
For information on how to use these scripts, see the
"How to Submit a Change"
section.