Insert generated image.json into the ostree commit

This is part of coreos/fedora-coreos-tracker#1151

Our generated disk images are largely just a "shell" around the egg
of an ostree commit.  There is almost nothing that lives
in the disk image that isn't in the commit.

(This is especially true now that a preparatory commit previous to
 this moved the *content* of our static `grub.cfg` into `image.json`)

In the original coreos-assembler design I'd tried to cleanly
separate builds of the ostree from disk image builds, but also
support linking them together (with matching version numbers, etc.)
The separate `image.yaml` was part of this.  This...mostly worked.

This change furthers that separation by having image builds input from
*just the ostree commit*.  Crucially we would no longer need the config
git repository to perform an image build.

And this in turn unlocks truly better separating ostree builds from
disk image builds in the pipeline *and* supporting
downstream tooling generating disk images from custom containers.

One neat thing here is we will finally fix a longstanding issue
where coreos-assembler fails when just the `image.yaml` changes:

Closes: coreos#972

src/cmd-buildextend-live

@@ -18,7 +18,7 @@ import time
 
 sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
 from cosalib.builds import Builds
-from cosalib.cmdlib import run_verbose, sha256sum_file, generate_image_json
+from cosalib.cmdlib import run_verbose, sha256sum_file, extract_image_json
 from cosalib.cmdlib import import_ostree_commit, get_basearch, ensure_glob
 from cosalib.meta import GenericBuildMeta
 
@@ -46,9 +46,6 @@ if not args.build:
     args.build = builds.get_latest()
 print(f"Targeting build: {args.build}")
 
-image_json = generate_image_json('src/config/image.yaml')
-squashfs_compression = 'lz4' if args.fast else image_json['squashfs-compression']
-
 srcdir_prefix = "src/config/live/"
 
 if not os.path.isdir(srcdir_prefix):
@@ -58,6 +55,13 @@ workdir = os.path.abspath(os.getcwd())
 builddir = builds.get_build_dir(args.build)
 buildmeta_path = os.path.join(builddir, 'meta.json')
 buildmeta = GenericBuildMeta(workdir=workdir, build=args.build)
+repo = os.path.join(workdir, 'tmp/repo')
+
+# Grab the commit hash for this build
+buildmeta_commit = buildmeta['ostree-commit']
+
+image_json = extract_image_json(repo, buildmeta_commit)
+squashfs_compression = 'lz4' if args.fast else image_json['squashfs-compression']
 
 base_name = buildmeta['name']
 if base_name == "rhcos" and args.fast:
@@ -71,12 +75,6 @@ if os.path.exists(build_semaphore):
     raise Exception(
         f"{build_semaphore} exists: another process is building live")
 
-
-# Grab the commit hash for this build
-buildmeta_commit = buildmeta['ostree-commit']
-
-repo = os.path.join(workdir, 'tmp/repo')
-
 # Don't run if it's already been done, unless forced
 if 'live-iso' in buildmeta['images'] and not args.force:
     print(f"'live' has already been built for {args.build}. Skipping.")

src/cmd-buildextend-metal

@@ -118,6 +118,9 @@ ostree_repo=${tmprepo}
 # Ensure that we have the cached unpacked commit
 import_ostree_commit_for_build "${build}"
 
+image_json=image.json
+extract_image_json "${tmprepo}" "${commit}" > "${image_json}"
+
 image_format=raw
 if [[ $image_type == qemu ]]; then
     image_format=qcow2

src/cmdlib.sh

@@ -394,6 +394,13 @@ EOF
         done
     fi
 
+    local imagejsondir="${tmp_overridesdir}/imagejson"
+    export ostree_image_json="/usr/share/coreos-assembler/image.json"
+    mkdir -p "${imagejsondir}/usr/share/coreos-assembler/"
+    cp "${image_json}" "${imagejsondir}${ostree_image_json}"
+    commit_overlay cosa-image-json "${imagejsondir}"
+    layers="${layers} cosa-image-json"
+
     local_overrides_lockfile="${tmp_overridesdir}/local-overrides.json"
     if [ -n "${with_cosa_overrides}" ] && [[ -n $(ls "${overridesdir}/rpm/"*.rpm 2> /dev/null) ]]; then
         (cd "${overridesdir}"/rpm && rm -rf .repodata && createrepo_c .)
@@ -874,6 +881,7 @@ builds.bump_timestamp()
 print('Build ${buildid} was inserted ${arch:+for $arch}')")
 }
 
+# Prepare the image.json as part of an ostree image build
 write_image_json() {
     local srcfile=$1; shift
     local outfile=$1; shift
@@ -884,6 +892,19 @@ from cosalib import cmdlib
 cmdlib.write_image_json('${srcfile}', '${outfile}')")
 }
 
+# Fetch the image.json from the ostree commit to stdout.
+# Should be used by disk image builds.
+extract_image_json() {
+    local repo=$1; shift
+    local commit=$1; shift
+    (python3 -c "
+import sys, json
+sys.path.insert(0, '${DIR}')
+from cosalib import cmdlib
+json.dump(sys.stdout, cmdlib.extract_image_json('${repo}', '${commit}'), sort_keys=True)
+")
+}
+
 # Shell wrapper for the Python import_ostree_commit
 import_ostree_commit_for_build() {
     local buildid=$1; shift

src/cosalib/cmdlib.py

@@ -350,6 +350,13 @@ def cmdlib_sh(script):
     '''])
 
 
+# Should be used by disk image builds to extract the image.json from the
+# ostree commit.
+def extract_image_json(repo, commit):
+    out = subprocess.check_output(['ostree', f'--repo={repo}', 'cat', commit, '/usr/share/coreos-assembler/image.json'])
+    return json.loads(out)
+
+
 def generate_image_json(srcfile):
     r = yaml.safe_load(open("/usr/lib/coreos-assembler/image-default.yaml"))
     for k, v in flatten_image_yaml(srcfile).items():

src/cosalib/ova.py

@@ -10,7 +10,7 @@
 sys.path.insert(0, f"{cosa_dir}/cosalib")
 sys.path.insert(0, cosa_dir)
 
-from cosalib.cmdlib import generate_image_json, image_info
+from cosalib.cmdlib import extract_image_json, image_info
 from cosalib.qemuvariants import QemuVariantImage
 
 
@@ -86,7 +86,7 @@ def generate_ovf_parameters(self, vmdk, cpu=2, memory=4096):
         Returns a dictionary with the parameters needed to create an OVF file
         based on the qemu, vmdk, image.yaml, and info from the build metadata
         """
-        image_json = generate_image_json('src/config/image.yaml')
+        image_json = extract_image_json(self._workdir, self.meta['ostree-commit'])
 
         system_type = 'vmx-{}'.format(image_json['vmware-hw-version'])
         os_type = image_json['vmware-os-type']