Difference between revisions of "Git For Developers"

Revision as of 07:07, 29 August 2011

Git is a distributed version control system. This page provides information for developers on how we manage our sources within git.

Public Repo

This page is mean for the Net-SNMP development team. If you're looking for the page on the read-only git repo available to the general public, see the Git page.

Setup

 git clone ssh://USERNAME@net-snmp.git.sourceforge.net/gitroot/net-snmp/MODULE

where MODULE is either 'net-snmp' (for code) or 'htdocs' (for web documentation)

A variation of this is to use ssh only to push changes and the git protocol to pull, this is achived by

 git clone git://net-snmp.git.sourceforge.net/gitroot/net-snmp/MODULE
 cd MODULE
 git config remote.origin.pushurl ssh://USERNAME@net-snmp.git.sourceforge.net/gitroot/net-snmp/MODULE

Make sure your email address and name are correct:

 git config user.email "YOURSFACCOUNTNAME@users.sourceforge.net"
 git config user.name "YOUR NAME"

Git workflows

The first link below should be read before any code is checked in. Specifically, it describes the one important aspect: always commit to the lowest branch you want the patch to apply to!

• First and foremost, read Net-SNMP's Git Workflow
• Then, consider using the Git Branch Management macros for performing the routine tasks (branch merging, etc).
• The gitworkflows manual page is similar to ours
• A good diagram showing another similar workflow pattern.

Making changes

This is where you type vi or emacs or if you're a real developer who likes to get dirty perl -i -p -e ...

Checking out the right branch

git maintains all the code in a single directory, and lets you switch between the branches in the same directory. This is very very different than SVN and other repository systems, but most people find once they let go of the idea that they need separate directories, they're happier in the long run.

The branch may not exist yet in your local repository (run git branch -a to list all the branches known, including the remote ones). To start, simply check it out:

 # git checkout V5-4-patches
 Branch V5-5-patches set up to track remote branch V5-5-patches from origin.
 Switched to a new branch 'V5-5-patches'

(and now 'git branch' without the '-a' will list it as a known local branch).

Moving changes to a different branch

If you have changes in the local repository already and want to apply them (or test them) against a different branch, the easiest way to do this is with stash and pop:

 # git checkout V5-6-patches
 error: Your local changes to the following files would be overwritten by checkout:
         NEWS
 Please, commit your changes or stash them before you can switch branches.
 Aborting
 
 # git stash
 Saved working directory and index state WIP on V5-5-patches: 6a5e5a6 Merge branch 'V5-4-patches' into V5-5-patches
 HEAD is now at 6a5e5a6 Merge branch 'V5-4-patches' into V5-5-patches
 
 # git checkout V5-6-patches
 Branch V5-6-patches set up to track remote branch V5-6-patches from origin.
 Switched to a new branch 'V5-6-patches'
 
 # git stash pop
 Auto-merging NEWS
 # On branch V5-6-patches
 # Changes not staged for commit:
 #   (use "git add <file>..." to update what will be committed)
 #   (use "git checkout -- <file>..." to discard changes in working directory)
 #
 #       modified:   NEWS
 #
 no changes added to commit (use "git add" and/or "git commit -a")
 Dropped refs/stash@{0} (102700302cd0a9db42b1669105291bb92fe807e9)

Committing the changes

 # git commit -m "commit message" FILES

Or if you want to commit everything in a directory and down, use a directory name instead of FILES.

Or if you want to commit everything anywhere in the repo, use the -a switch.

NOTE: this only commits them to your local copy of the repository. This is different than SVN, if you're more familiar with SVN. Next you need to push them to the master repository:

Pulling the latest changes from the upstream

Whether or not you've modified files locally and checked in the changes to your local repository, you'll need to occasionally pull down any changes that others have made upstream. You do this with a pull. The --rebase option means rather than treat your development as a parallel set, try and apply your resulting patches to the end of the pulled branch instead of merging them. This tends to keep a cleaner history tree.

 # git pull --rebase origin master

Assuming you followed the instructions above, and didn't cloning from somewhere else first, you should be able to shorten this to:

 # git pull --rebase

This will merge any changes you've made with any that others have made. If something goes wrong, git will complain about conflicts and you'll need to resolve those either manually or using git mergetool. That's a longer subject for another lesson: Git Merging.

You may also wish to pull all the remote branches:

 # git pull --all

Reviewing local commits

The most effective way to use git is to commit changes to the local tree as multiple small changes. That makes it easy to edit or revert any local changes if necessary. Once the local changes have been tested and before pushing these upstream, review the local changes and rearrange these if necessary. Try to make sure that any contributed change at least compiles such that the tree remains bisectable. One way to edit local commits is via the git rebase command. That command does not only allow to change the description of each commit, to change the order of commits, to squash multiple commits together but also to leave out some commits. Of course, if any changes have been made these have to be retested. The rebase command can be invoked as follows when working on the master branch:

  # git rebase --interactive origin/master

Pushing the changes upstream

Once you're sure your commits are safe themselves and you've updated your repo with the latest upstream you can push your changes upstream to the master repository on sourceforge:

 # git push origin master

Assuming you followed the instructions above, and didn't cloning from somewhere else first, you should be able to shorten this to:

 # git push

And you're done!

Notes on the htdocs repository

The htdocs module, which contains the Net-SNMP website, is only synchronized from the git repository once an hour. It may take up to an hour before the changes take effect on the website.

Creating tags and branches

Tagging

Tags are simply a symbolic way of remembering "a point in time" that is easier than the sha1 hash that is more frequently seen.

 git tag my-really-super-feature-works

for example will create the above tag.

XXX: discuss annotated/signed/etc tags

Pushing tags

By default, git push doesn't push tags. IE, it *only* pushes code. If you've created a tag and you want it pushed upstream, you'll need to push it manually:

 git push origin TAGNAME

Or you can push all your tags:

 git push --tags

Note: Please don't push personal tags... Use the individual push instead if you're creating helpful personal tags.