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Overview

The build process is divided into two levels:

  1. Yocto
  2. ostbuild

Yocto is used as a reliable, well-maintained bootstrapping tool. It provides the basic filesystem layout as well as binaries for core build utilities like gcc and bash. This gets us out of circular dependency problems.

At the end, the Yocto build process generates two tarballs: one for a base "runtime", and one "devel" with all of the development tools like gcc. We then import that into an OSTree branch e.g. "bases/yocto/gnomeos-3.6-i686-devel".

At present, it's still (mostly) possible to put this data on an ext4 filesystem and boot into it.

We also have a Yocto recipe "ostree-native" which generates (as you might guess) a native binary of ostree. That binary is used to import into an "archive mode" OSTree repository. You can see it in $builddir/tmp/deploy/images/repo.

Now that we have an OSTree repository storing a base filesystem, we can use "ostbuild" which uses "linux-user-chroot" to chroot inside, run a build on a source tree, and outputs binaries, which we then add to the build tree for the next module, and so on.

The final result of all of this is that the OSTree repository gains new commits (which can be downloaded by clients), while still retaining old build history.

Yocto details

I have a branch of Yocto here:

https://github.com/cgwalters/poky

It has a collection of patches on top of the "Edison" release of Yocto, some of which are hacky, others upstreamable. The most important part though are the modifications to commit the generated root filesystem into OSTree.

For every GNOME OS release, there is a branch on which the needed patches have landed. By now, that branch is "gnomeos-3.6".

ostbuild details

The simple goal of ostbuild is that it only takes as input a "manifest" which is basically just a list of components to build. You can see an example of this here:

http://git.gnome.org/gnome-ostree/gnomeos-3.6.json

A component is a pure metadata file which includes the git repository URL and branch name, as well as ./configure flags (--enable-foo).

There is no support for building from "tarballs" - I want the ability to review all of the code that goes in, and to efficiently store source code updates. It's also just significantly easier from an implementation perspective, versus having to maintain a version control abstraction layer.

The result of a build of a component is an OSTree branch like "artifacts/gnomeos-3.6-i686-devel/libxslt/master". Then, a "compose" process merges together the individual filesystem trees into the final branches (e.g. gnomeos-3.6-i686-devel).

Doing local builds

This is where you want to modify one (or a few) components on top of what comes from the ostree.gnome.org server, and test the result locally. I'm working on this.

Doing a full build on your system

Following this process is equivalent to what we have set up on the ostree.gnome.org build server. It will generate a completely new repository.

$ srcdir=/src
$ builddir=/src/build


# First, you'll need "http://git.gnome.org/browse/linux-user-chroot/"
# installed as setuid root.

$ cd $srcdir

$ git clone gnome:linux-user-chroot
$ cd linux-user-chroot
$ NOCONFIGURE=1 ./autogen.sh
$ ./configure
$ make
$ sudo make install
$ sudo chown root:root /usr/local/bin/linux-user-chroot
$ sudo chmod u+s /usr/local/bin/linux-user-chroot


# We're going to be using Yocto.  You probably want to refer to:
# http://www.yoctoproject.org/docs/current/yocto-project-qs/yocto-project-qs.html
# Next, we're grabbing my Poky branch.

$ git clone git://github.com/cgwalters/poky.git
$ cd poky
$ git co gnomeos-3.6
$ cd $builddir


# This command enters the Poky environment, creating
# a directory named gnomeos-build.

$ . $srcdir/poky/oe-init-build-env gnomeos-build


# Now edit conf/bblayers.conf, and add
#   /src/poky/meta-gnomeos
# to BBLAYERS.
#
# Check the conf/local.conf file and make sure "tools-profile" and
# "tools-testapps" are not in EXTRA_IMAGE_FEATURES
#
# Also, you should choose useful values for BB_NUMBER_THREADS and
# PARALLEL_MAKE
#
# For the meaning of this variables you can check:
# http://www.yoctoproject.org/docs/current/poky-ref-manual/poky-ref-manual.html#var-EXTRA_IMAGE_FEATURES
# http://www.yoctoproject.org/docs/current/poky-ref-manual/poky-ref-manual.html#var-BB_NUMBER_THREADS
# http://www.yoctoproject.org/docs/current/poky-ref-manual/poky-ref-manual.html#var-PARALLEL_MAKE

$ bitbake ostree-native


# After this command, we will have a native compilation of OSTree
# e.g. tmp/work/x86_64-linux/ostree-native-1.0-r0/image/opt/gnome-os/tanty/build/gnomeos-build/tmp/sysroots/

$ bitbake gnomeos-contents-{runtime,devel}


# At the end, the Yocto build process generates two tarballs: one for
# a base "runtime", and one "devel" with all of the development tools
# like gcc.  We then import that into an OSTree branch
# e.g. "bases/yocto/gnomeos-3.6-i686-devel".


# This bit is just for shorthand convenience, you can skip it

$ cd $builddir
$ ln -s gnomeos-build/tmp/deploy/images/repo repo


# Now create a file ~/.config/ostbuild.cfg
# example contents:
# [global]
# repo=/src/build/repo
# mirrordir=/src/build/ostbuild/src
# workdir=/src/build/ostbuild/work


# And create the mirrordir and workdir directories

$ mkdir -p $builddir/ostbuild/src
$ mkdir -p $builddir/ostbuild/work


# Now we want to use the "ostbuild" binary that was created
# as part of "bitbake ostree-native".  You can do e.g.:

$ export PATH=$builddir/gnomeos-build/tmp/sysroots/x86_64-linux/usr/bin:$PATH


# This next command will download all of the source code to the
# modules specified in $gnome-ostree/gnomeos-3.6.json, and create a
# file $workdir/manifest.json that has the exact git commits we want
# to build.

$ ostbuild resolve --manifest /src/gnome-ostree/gnomeos-3.6.json


# By then, you should create your own prefix for the builds of the
# OSTree

$ ostbuild prefix my-prefix


# This command builds everything
$ ostbuild build-components --src-snapshot $builddir/ostbuild/work/snapshots/gnomeos-3.6-src-snapshot-<year>.<number>-<hash>.json
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