util/containers: read host config

Add utility function to read the host's container storage config.

.mypy.ini

@@ -5,3 +5,6 @@ ignore_missing_imports = True
 
 [mypy-mako.*]
 ignore_missing_imports = True
+
+[mypy-tomli.*]
+ignore_missing_imports = True

osbuild.spec

@@ -39,6 +39,12 @@ Requires:       util-linux
 Requires:       python3-%{pypi_name} = %{version}-%{release}
 Requires:       (%{name}-selinux if selinux-policy-%{selinuxtype})
 
+# This is required for `osbuild`, for RHEL-10 and above
+# the stdlib toml package can be used instead
+%if 0%{?rhel} < 10
+Requires:       python3-tomli
+%endif
+
 # Turn off dependency generators for runners. The reason is that runners are
 # tailored to the platform, e.g. on RHEL they are using platform-python. We
 # don't want to pick up those dependencies on other platform.

osbuild/util/containers.py

@@ -128,3 +128,20 @@ def container_source(image):
 
         image_source = f"{container_format}:{tmp_source}"
         yield image_name, image_source
+
+
+def get_host_storage(storage_conf=None):
+    """
+    Read the host storage configuration.
+    """
+    # pylint: disable=import-outside-toplevel
+    # importing this at the top level will break the buildroot
+    try:
+        import tomllib as toml
+    except ImportError:
+        import tomli as toml
+
+    if not storage_conf:
+        with open("/etc/containers/storage.conf", "rb") as conf_file:
+            storage_conf = toml.load(conf_file)
+    return storage_conf