stages/ostree: add ref support

Add a new optional `ref` option. When set, a references for the
commit that was pulled with the value of `ref` will be created
in the system ostree repo. It will also be used when deploying
the commit and thus will be set as the origin for it. This is
necessary for updates to work.

stages/org.osbuild.ostree

@@ -42,6 +42,10 @@ STAGE_OPTS = """
     "description": "Additional kernel command line options",
     "type": "string"
   },
+  "ref": {
+    "description": "OStree ref to create and use for deployment",
+    "type": "string"
+  },
   "rootfs": {
     "description": "Identifier to locate the root file system",
     "type": "string"
@@ -104,18 +108,23 @@ def main(tree, sources, options):
     rootfs = options["rootfs"]
     mounts = options.get("mounts", [])
     kopts = options.get("kernel_opts", [])
-
-    print(f"Fetching ostree commit {commit}")
-    osbuild.sources.get("org.osbuild.ostree", [commit])
+    ref = options.get("ref", commit)
 
     ostree("admin", "init-fs", "--modern", tree,
            sysroot=tree)
 
-    ostree("pull-local",
-           f"{sources}/org.osbuild.ostree/repo",
-           commit,
+    print(f"Fetching ostree commit {commit}")
+    osbuild.sources.get("org.osbuild.ostree", [commit])
+
+    source_repo = f"{sources}/org.osbuild.ostree/repo"
+
+    ostree("pull-local", source_repo, commit,
            repo=f"{tree}/ostree/repo")
 
+    if ref != commit:
+        ostree("refs", "--create", ref, commit,
+               repo=f"{tree}/ostree/repo")
+
     ostree("admin", "os-init", osname, sysroot=tree)
 
     kargs = []
@@ -129,7 +138,7 @@ def main(tree, sources, options):
             os.makedirs(path, exist_ok=True)  # FIXME: SELinux
             mounter.mount(path, path)
 
-        ostree("admin", "deploy", commit,
+        ostree("admin", "deploy", ref,
                f"--karg=root={rootfs}",
                *kargs,
                sysroot=tree,