diff options
Diffstat (limited to 'GIT')
| -rw-r--r-- | GIT | 162 |
1 files changed, 162 insertions, 0 deletions
@@ -0,0 +1,162 @@ +=========================== WHY USE GIT+TOPGIT? ========================== + +Three major concerns were on our mind when setting up this project. + + o First we needed to structure the project in such a way that it would be + easy to rebase all of our changes on the latest official ZFS release + from Sun. We absolutely need to be able to benefit from the upstream + improvements and not get locked in to an old version of the code base. + + o Secondly, we wanted to be able to easily manage our changes in terms + of a patch stack. This allows us to easily isolate specific changes + and push them upstream for inclusion. It also allows us to easily + update or drop specific changes based on what occurs upstream. + + o Thirdly we needed our DVCS to be integrated with the management of this + patch stack. We have tried other methods in the past such as SVN+Quilt + but have found managing the patch stack becomes cumbersome. By using + Git+TopGit to more tightly integrate our patch stack in to the repo + we expect several benefits. One of the most important will be the + ability to easily work on the patch stack with a distributed developer + team, additionally the repo can track patch history, and we can utilize + Git to merge patches and resolve conflicts. + +TopGit is designed to specifically address these concerns by providing +tools to simplify the handling of large numbers of interdependent topic +branches. When using a TopGit aware repo every topic branch represents +a 'patch' and that branch references its dependent branches. The union +of all these branches is your final source base. + +========================= SETTING UP GIT+TOPGIT ========================== + +First off you need to install a Git package on your system. For my +purposes I have been working on a RHEL5 system with git version 1.5.4.5 +installed and it has been working well. You will also need to go get +the latest version of TopGit which likely is not packaged nicely so you +will need to build it from source. You can use Git to clone TopGit +from the official site here and your all set: + + > git clone http://repo.or.cz/w/topgit.git + > make + > make install # Default installs to $(HOME) + +========================== TOPGIT AND ZFS ================================ + +One you have Git and TopGit installed you will want to clone a copy of +the Linux ZFS repo. While this project does not yet have a public home +it hopefully will some day. In the meanwhile if you have VPN access to +LLNL you can clone the latest official repo here. Cloning a TopGit +controlled repo is very similar to cloning a normal Git repo, but you +need to remember to use 'tg remote' to populate all topic branches. + + > git clone http://eris.llnl.gov/git/zfs.git zfs + > cd zfs + > tg remote --populate origin + +Now that you have the Linux ZFS repo the first thing you will probably +want to do is have a look at all the topic branches. TopGit provides +a summary command which shows all the branches and a brief summary for +each branch obtained from the .topmsg files. + + > tg summary + 0 t/LAST [PATCH] LAST + t/feature-commit-cb [PATCH] zfs commit callbacks + t/fix-clock-wrap [PATCH] fix clock wrap + t/fix-dnode-cons [PATCH] fix dnode constructor + ... + +By convention all TopGit branches are prefixed with 't/', and the Linux +ZFS repo also introduces the convention that the top most development +branch be called 't/LAST". This provides a consistent label to be used +when you need to reference the branch which contains the union of all +topic branches. + +One thing you may also notice about the 'tg summary' command is it does +not show the branches in dependent order. While this project only expresses +a single dependency per branch TopGit implements dependencies as a DAC just +like Git. To see the dependencies you will need to use the --graphviz +option and pipe the result to dot for display. The following command while +long works fairly well for me. Longer term it would be nice to update this +option to use a preferred config options stored in the repo if they exist. + + > tg summary --graphviz | dot -Txlib -Nfontsize=8 -Eminlen=0.01 \ + -Grankdir=LR -Nheight=0.3 -Nwidth=2 -Nfixedsize=true + +========================= UPDATING A TOPIC BRANCH ======================== + +Updating a topic branch in TopGit is a pretty straight forward but there +are a few rules you need to be aware of. The basic process involves +checking out the relevant topic branch where the changes need to be made, +making the changes, committing the changes to the branch and then merging +those changes in to dependent branches. TopGit provides some tools to make +this pretty easy, although it may be a little sluggish. Here is an example: + + > git checkout t/feature-commit-cb # Checkout the proper branch + > ...update branch... # Update the branch + > git commit -a # Commit your changes + > git checkout t/LAST # Checkout the LAST branch + > tg update # Recursively merge in new branch + +Assuming you change does not introduce any conflicts your done. All branches +were dependent on your change will have had the changed merged in. If your +change introduced a conflict you will need to resolve the conflict and then +continue on with the update. + +========================== ADDING A TOPIC BRANCH ========================= + +Adding a topic branch in TopGit is a little more complicated. When adding +a new branch to the end of the patch graph things are pretty easy and TopGit +does all the work. However, I expect out common case to be adding patches +to the middle of the graph. TopGit will allow you to do this but you must +be careful to manually update the dependency information in the .topdeps +file. + + > git co t/existing-topic-branch # Checkout the branch to add after + > tg create t/new-topic-branch # Create a new topic branch + > ...update .topmsg... # Update the branch message + > ...create patch... # Update with your changes + > git commit -a # Commit your changes + > git co t/dependent-topic-branch # Checkout dependent branch + > ...update .topdeps... # Manually update dependencies + > git commit -a # Commit your changes + > tg update # TopGit update + > git checkout t/LAST # Checkout the LAST branch + > tg update # Recursively merge in new branch + +========================= REMOVING A TOPIC BRANCH ======================== + +Removing a topic branch in TopGit is also currently not very easy. To remove +a dependent branch the basic process is to commit a patch which reverts all +changes on the branch. Then that reversion must be merged in to all dependent +branches, the dependencies manually updated and finally the branch removed. +If the branch is not empty you will not be able to remove it. + + > git co t/del-topic-branch # Checkout the branch to delete + > tg patch | patch -R -p1 # Revert all branch changes + > git commit -a # Commit your changes + > git checkout t/LAST # Checkout the LAST branch + > tg update # Recursively merge revert + > git co t/dependent-topic-branch # Checkout dependent branch + > ...update .topdeps... # Manually update dependencies + > git commit -a # Commit your changes + > tg delete t/del-topic-branch # Delete empty topic branch + +============================ TOPGIT TODO ================================= + +TopGit is still a young package which seems to be under active development +by its author. It provides the minimum set of commands needed but there +are clearly areas which simply have not yet been implemented. My short +list of features includes: + + o 'tg summary --deps', option to display a text version of the topic + branch dependency DAC. + + o 'tg depend list', list all topic branch dependencies. + + o 'tg depend delete', cleanly remove a topic branch dependency. + + o 'tg create', cleanly insert a topic branch in the middle + of the graph and properly take care updating all dependencies. + + o 'tg delete', cleanly delete a topic branch in the middle + of the graph and properly take care updating all dependencies. |