Hacking on rpm-ostree

1. Setting up a development environment
   1. Via toolbx/Installing natively
   2. Using the fcos-buildroot container
2. Building and testing
   1. Baseline build
   2. Unit tests
   3. Virtualized integration testing
      1. Iteration on kola external tests
      2. vmcheck
3. Testing with a custom libdnf
4. Testing with a custom ostree
5. Testing with a custom Rust crate (example: ostree-rs-ext)
6. Using GDB with the rpm-ostree daemon
   1. Server-side (composes)
   2. Client-side
      1. Attaching to the daemon
      2. Attaching to the CLI

Setting up a development environment

The majority of developers on rpm-ostree build and test it from a toolbox container, separate from the host system. The instructions below may also work when run in a traditional login on a virtual machine, but are less frequently tested.

Via toolbx/Installing natively

When developing either in a toolbx container or natively on your system, you must install all the required dependencies. In the ci/ subfolder, there are scripts that will do this for you:

• To install the build dependencies: ./ci/installdeps.sh and ci/install-cxx.sh
  • Note: This command must be rerun after the dependencies in Cargo.lock change. This will eventually be fixed.
• To install the test dependencies:
  • For make check: ./ci/install-test-deps.sh
  • For make vmcheck: Follow the instructions for installing cosa inside an existing container from the cosa GitHub repository

Today rpm-ostree uses cxx.rs, and as of https://github.com/coreos/rpm-ostree/pull/3864 we commit the generated code to git. If you want to regenerate it (particularly when changing it), use ci/install-cxx.sh. Most importantly, it currently must be reinstalled after you run make clean on the project.

Using the fcos-buildroot container

The fcos-buildroot container has all the dependencies needed for building and testing included. As a consequence, it is comparatively large (~ 2.5 GB). Since this is the same container used by the CI system, this is useful for reproducing CI failures.

You can either work from inside the container in an interactive manner:

# IMPORTANT: Run this command from the projects root directory!
$ podman run --rm -it -v "$PWD:$PWD:z" -w "$PWD" \
    quay.io/coreos-assembler/fcos-buildroot:testing-devel

Or you use the container in an ephemeral fashion with an alias like this:

# IMPORTANT: Run this command from the projects root directory!
$ alias buildroot="podman run --rm -it -v \"$PWD:$PWD:z\" -w \"$PWD\" \
    quay.io/coreos-assembler/fcos-buildroot:testing-devel"
# These commands run in the container now
$ buildroot make ...

The above commands will mount your current working directory into the container for your build artifacts etc. to persist.

Building and testing

Baseline build

rpm-ostree uses autotools to build both our C/C++ side as well as to invoke cargo to build the Rust code. After you’ve cloned the repository:

$ git submodule update --init
$ ./autogen.sh --prefix=/usr --libdir=/usr/lib64 --sysconfdir=/etc
$ make

Unit tests

$ make check

Virtualized integration testing

The unit tests today don’t cover much; rpm-ostree is very oriented to run as a privileged systemd unit managing a host system.

rpm-ostree has some tests that use the coreos-assembler/kola framework.

You will want to build a custom image, then run make install in the ${topsrcdir}/tests/kolainst/ directory, and finally kola run --qemu-image path/to/custom-rpm-ostree-qemu.qcow2 'ext.rpm-ostree.*'. See the kola external tests documentation for more information and also how to filter tests.

Iteration on kola external tests

make                                 # To build
cosa build-fast                      # Generate a local FCOS VM
sudo make -C tests/kolainst install  # Run this only when you change the test suite
kola run ext.rpm-ostree.destructive.container-image  # Or any other test you want

vmcheck

There’s also a vmcheck test suite, which predates Fedora CoreOS, coreos-assembler and the external test suite integration.

One approach for (somewhat) fast iteration is cosa build-fast, then run e.g. ./tests/vmcheck.sh.

To filter tests, use the TESTS= environment variable. For example, to run only tests/vmcheck/test-misc-2.sh, you can do:

TESTS='misc-2' ./tests/vmcheck.sh

For development, there is also a make vmsync which copies the built rpm-ostree into an unlocked VM. To use this, you must have an ssh-config file with a host defined in it called vmcheck. You can provision the VM however you want; libvirt directly, vagrant, a remote OpenStack/EC2 instance, etc. For QEMU, we have a helper script at tests/vm.sh which uses kola to spawn a CoreOS QEMU image. You can use it like this:

export COSA_DIR=/path/to/cosa/workdir
tests/vm.sh spawn
make vmsync

Note that by default, these commands will retrieve the latest version of ostree from the build environment and include those binaries when syncing to the VM. So make sure to have the latest ostree installed or built. This allows you to not have to worry about using libostree APIs that are not yet released.

For more details on how tests are structured, see tests/README.md.

Testing with a custom libdnf

rpm-ostree bundles libdnf since commit https://github.com/coreos/rpm-ostree/commit/125c482b1d16ce8376378f220fc2f93a5b157bc1 the rationale is:

• libdnf broke ABI several times silently in the past
• Today, dnf does not actually use libdnf much, which means for the most part any libdnf breakage is first taken by us
• libdnf is trying to rewrite more in C++, which is unlikely to help API/ABI stability
• dnf and rpm-ostree release on separate cycles (e.g. today rpm-ostree is used by OpenShift)

In general, until libdnf is defined 100% API/ABI stable, we will continue to bundle it.

However, because it’s a git submodule, it’s easy to test updates to it, and it also means we’re not forking it.

So just do e.g.:

cd libdnf
git fetch origin
git reset --hard origin/main
cd ..

The various make targets will pick up the changes and recompile.

Testing with a custom ostree

It is sometimes necessary to develop against a version of ostree which is not even yet in git main. In such situations, one can simply do:

$ # from the rpm-ostree build dir
$ INSTTREE=$PWD/insttree
$ rm -rf $INSTTREE
$ # from the ostree build dir
$ make
$ make install DESTDIR=$INSTTREE
$ # from the rpm-ostree build dir
$ make
$ make install DESTDIR=$INSTTREE

At this point, simply set SKIP_INSTALL=1 when running vmsync and vmoverlay to reuse the installation tree and sync the installed binaries there:

$ make vmsync SKIP_INSTALL=1
$ make vmoverlay SKIP_INSTALL=1

Of course, you can use this pattern for not just ostree but whatever else you’d like to install into the VM (e.g. bubblewrap, libsolv, etc…).

Testing with a custom Rust crate (example: ostree-rs-ext)

A common case is testing changes in the ostree-rs-ext crate. Once you have your changes ready in a clone of the ostree-rs-ext repository, you can edit rpm-ostree’s Cargo.toml to point to it.

...
[patch.crates-io]
ostree-ext = { path = "../ostree-rs-ext/lib/" }

See the example from the Overriding Dependencies section of the Cargo Book.

Using GDB with the rpm-ostree daemon

If you’re new to rpm-ostree, before using GDB, it may be helpful to review the daemon architecture doc for an architecture recap.

Server-side (composes)

Server-side composes do not use the daemon architecture and so one can naturally do e.g. gdb --args rpm-ostree compose tree .... If using coreos-assembler, you can set the COSA_RPMOSTREE_GDB environment variable like this:

$ COSA_RPMOSTREE_GDB="gdb --args" cosa build

When cosa gets to the point of invoking rpm-ostree for the compose, it will call GDB instead.

Client-side

On the client side, you need to use the make vmsync flow before using GDB because it also copies over the source files into /root/sync.

You can use GDB from a privileged container. Make sure to use the --pid=host flag when using e.g. podman run so that you can attach to processes running on the host. For example:

(host) podman run -ti --privileged --pid=host -v /:/host --name gdb \
        registry.fedoraproject.org/fedora:36 /bin/bash
(cnt) dnf install -y gdb procps-ng

If for whatever reason, you can’t use a container, you can also layer GDB with e.g. rpm-ostree install gdb-minimal -A, and then use it directly. (XXX: apply-live currently isn’t compatible with make vmsync, so you’ll want to reboot for now: https://github.com/ostreedev/ostree/issues/2369).

Attaching to the daemon

Run e.g. rpm-ostree status to ensure the daemon is started, and then:

(cnt) gdb -p $(pidof rpm-ostree) \
        -ex 'set sysroot /host' \
        -ex 'directory /host/var/roothome/sync' \
        -ex 'directory /host/var/roothome/sync/libdnf/libdnf'

Then in GDB, you can do e.g.:

(gdb) break deploy_transaction_execute
(gdb) continue

And in a separate terminal in the VM, run the CLI command which would trigger the breakpoint (e.g. rpm-ostree override replace foobar.rpm).

Attaching to the CLI

To attach to the CLI itself (or debug early daemon startup), you can use gdb --args rpm-ostree status if running GDB from the host directly.

If running GDB in a container, you can use the RPMOSTREE_GDB_HOOK env var to have rpm-ostree wait for you to attach GDB from the container:

(host) RPMOSTREE_GDB_HOOK=1 rpm-ostree status
RPMOSTREE_GDB_HOOK detected; stopping...
Attach via gdb using `gdb -p 2519`.

Then:

(cnt) gdb -p 2519 \
        -ex 'set sysroot /host' \
        -ex 'directory /host/var/roothome/sync' \
        -ex 'directory /host/var/roothome/sync/libdnf/libdnf' \
        -ex n -ex n