--- /dev/null
+=========================== 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 or graph. 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 or graph. 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 patches in to the repo
+ we expect several benefits. One of the most important will be the
+ ability to easily work on the patch's with a distributed development
+ 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 git://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 git://eris.llnl.gov/zfs.git
+ > cd zfs
+ > tg remote --populate origin
+
+Alternately, if you don't want to worry about using TopGit on your system
+you can simply clone the repo and then checkout the origin/top branch. At
+this point you can simply create a new branch to track your changes. You
+can then feed your patch back to the official repo maintainers to be merged
+in to the proper topic branches.
+
+ > git clone git://eris.llnl.gov/zfs.git
+ > cd zfs
+ > git checkout origin/top
+ > git checkout -b <new_branch_name>
+
+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 feature-branch [PATCH] feature-branch
+ feature-commit-cb [PATCH] feature commit cb
+ feature-zap-cursor-to-key [PATCH] feature zap cursor to key
+ ...
+
+By convention all TopGit branches are usually prefixed with 't/', however
+I have chosen not to do this for simplicity. A different convention I have
+adopted is to tag the top most TopGit branch as 'top' for easy reference.
+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. This is done because TopGit allows
+each branch to express multiple dependencies as a DAC. Initially this seemed
+like an added complication which I planned to avoid by just implementing a
+stack using the graph. However, this ended up being problematic because
+with a stack when a change was made to a branch near the base, it was a
+very expensive operation to merge the change up to the top of the stack.
+By defining the dependencies as a graph it is possible to keep the depth
+much shallower thus minimizing the merging. It has also proved insightful
+as to each patches actual dependencies.
+
+To see the dependencies you will need to use the --graphviz option and pipe
+the result to dot for display. The following command 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.
+
+ > tg summary --graphviz | dot -Txlib -Nfontsize=8
+
+========================= 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 depending on how many
+dependent branches are impacted by the change. Here is an example:
+
+ > git checkout modify-topic-branch # Checkout the proper branch
+ > ...update branch... # Update the branch
+ > git commit -a # Commit your changes
+ > git checkout top # Checkout the top 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 can be pretty straight forward. If your
+adding a non-conflicting patch in parallel with other patches of the same
+type, then things are pretty easy and TopGit does all the work.
+
+ > git co existing-topic-branch # Checkout the branch to add after
+ > tg create 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 dependent-topic-branch # Checkout dependent branch
+ > tg depend add new-topic-branch # Update dependencies
+ > git checkout top # Checkout the top branch
+ > tg update # Recursively merge in new branch
+
+If you need to add your patch in series with another change things are
+a little more complicated. In this case TopGit does not yet support removing
+dependencies so you will need to do it by hand, as follows.
+
+ > git co existing-topic-branch # Checkout the branch to add after
+ > tg create 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 dependent-topic-branch # Checkout dependent branch
+ > ...update .topdeps... # Manually update dependencies
+ > git commit -a # Commit your changes
+ > tg update # TopGit update
+ > git checkout top # Checkout the top branch
+ > tg update # Recursively merge in new branch
+
+Once your done, I find it is a good idea view the repo using the
+'tg summary --graphviz' command and verify the updated dependency graph.
+
+========================= 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 delete-topic-branch # Checkout the branch to delete
+ > tg patch | patch -R -p1 # Revert all branch changes
+ > git commit -a # Commit your changes
+ > git checkout top # Checkout the top branch
+ > tg update # Recursively merge revert
+ > git co dependent-topic-branch # Checkout dependent branch
+ > ...update .topdeps... # Manually update dependencies
+ > git commit -a # Commit your changes
+ > tg delete delete-topic-branch # Delete empty topic branch
+
+Once your done, I find it is a good idea view the repo using the
+'tg summary --graphviz' command and verify the updated dependency graph.
+
+============================ 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.
git://git.camperquake.de / zfs.git / commitdiff