oscontainer: add com.coreos.rpm.* labels

These labels allow one to query the RPM version of a subset of packages
without having to download them. See also:

openshift/os#409 (comment)

src/oscontainer.py

@@ -26,6 +26,10 @@
 # https://access.redhat.com/documentation/en-us/openshift_container_platform/4.1/html/builds/custom-builds-buildah
 NESTED_BUILD_ARGS = ['--storage-driver', 'vfs']
 
+# These packages have their versions as labels
+IMPORTANT_PACKAGES = ['kernel', 'kernel-rt-core', 'systemd', 'ignition', 'ostree',
+                      'rpm-ostree', 'runc']
+
 
 def run_get_json(args):
     return json.loads(subprocess.check_output(args))
@@ -159,11 +163,16 @@ def oscontainer_build(containers_storage, tmpdir, src, ref, image_name_and_tag,
         if ostree_version is not None:
             config += ['-l', 'version=' + ostree_version]
 
+        base_pkgs = RpmOstree.db_query_all(r, rev, None)
+        for pkg in base_pkgs:
+            name = pkg.get_name()
+            if name in IMPORTANT_PACKAGES:
+                config += ['-l', f"com.coreos.rpm.{name}={pkg.get_evr()}.{pkg.get_arch()}"]
+
         # Generate pkglist.txt in to the oscontainer at /
         pkg_list_dest = os.path.join(mnt, 'pkglist.txt')
-        pkgs = RpmOstree.db_query_all(r, rev, None)
         # should already be sorted, but just re-sort to be sure
-        nevras = sorted([pkg.get_nevra() for pkg in pkgs])
+        nevras = sorted([pkg.get_nevra() for pkg in base_pkgs])
         with open(pkg_list_dest, 'w') as f:
             for nevra in nevras:
                 f.write(nevra)
@@ -200,6 +209,11 @@ def oscontainer_build(containers_storage, tmpdir, src, ref, image_name_and_tag,
                                          if obj.get('kind', 'os-extension') == 'os-extension'])
             config += ['-l', f"com.coreos.os-extensions={extensions_label}"]
 
+            for pkgname in meta['extensions']['manifest']:
+                if pkgname in IMPORTANT_PACKAGES:
+                    evra = meta['extensions']['manifest'][pkgname]
+                    config += ['-l', f"com.coreos.rpm.{pkgname}={evra}"]
+
         if display_name is not None:
             config += ['-l', 'io.openshift.build.version-display-names=machine-os=' + display_name,
                        '-l', 'io.openshift.build.versions=machine-os=' + ostree_version]