Building from source
--------------------
Install “git-buildpackage” and run the following steps:

  gbp clone git+ssh://git.debian.org/git/pkg-systemd/systemd.git
  cd systemd
  gbp buildpackage

We recommend you use pbuilder to make sure you build in a clean environment:

  gbp buildpackage --git-pbuilder

Patch handling
--------------
The official form of modifications to the upstream source are quilt patches in
debian/patches/, like most Debian packages do. You are welcome to use quilt to
add or modify patches, but you might prefer using a git commit based approach.
gbp-pq provides that by synthesizing a "patch-queue/<branch>" local branch
which represents each quilt patch as git commit. You create this with

  gbp pq import --force

Then you are in the patch-queue branch and can git log, commit, cherry-pick
upstream commits, rebase, etc. there. After you are done, run

  gbp pq export

which will put you back into master and update debian/patches/ (including
series). You need to git add etc. new patches, add a changelog and other
packaging changes, and then debcommit as usual.

Rebasing patches to a new upstream version
------------------------------------------
gbp pq's "rebase" command does not work very conveniently as it fails on merge
conflicts. First, ensure you are in the master branch:

  git checkout master  # in case you aren't already

Now, do one of

 (1) To import a new upstream release into the existing master branch for unstable,
do:

  gbp pq import --force
  gbp pq switch   # switch back to master from patch-queue/master
  gbp import-orig [...]
  gbp pq switch   # switch to patch-queue/master
  git rebase master

 (2) To import a new upstream release into a new branch for Debian experimental, do:

  git branch experimental
  git checkout experimental
  editor debian/gbp.conf  # set "debian-branch=experimental"
  gbp import-orig [...]
  git branch patch-queue/experimental patch-queue/master
  git checkout patch-queue/experimental
  git rebase experimental

Now resolve all the conflicts, skip obsolete patches, etc. When you are done, run

  gbp pq export

Note that our debian/gbp.conf disables patch numbers.

Cherry-picking upstream patches
-------------------------------
You can add the systemd upstream branch as an additional remote to the Debian
packaging branch. Call it "github" or similar to avoid confusing it with the
already existing "upstream" branch from git-buildpackage:

  git remote add github https://github.com/systemd/systemd.git
  git fetch github -n

Now you can look at the upstream log and cherry-pick patches into the
patch-queue branch:

  gbp pq import --force
  git log github/master
  git cherry-pick 123DEADBEEF
