util: Add bls module

- Add functions for appending kernel parameters to the
Boot Loader Specification (BLS) as needed.

Signed-off-by: Renata Ravanelli <rravanel@redhat.com>

osbuild/util/bls.py

@@ -0,0 +1,34 @@
+"""
+Function for appending parameters to
+Boot Loader Specification (BLS).
+"""
+import glob
+from typing import List
+
+
+def options_append(root_path: str, kernel_arguments: List[str]) -> None:
+    """
+    Add kernel arguments to the Boot Loader Specification (BLS) configuration files.
+    There is unlikely to be more than one BLS config, but just in case, we'll iterate over them.
+
+    Parameters
+    ----------
+
+    root_path (str): The root path for locating BLS configuration files.
+    kernel_arguments (list): A list of kernel arguments to be added.
+
+    """
+    bls_glob = f"{root_path}/loader/entries/*.conf"
+    bls_conf_files = glob.glob(bls_glob)
+    if len(bls_conf_files) == 0:
+        raise RuntimeError(f"no BLS configuration found in {bls_glob}")
+    for entry in bls_conf_files:
+        # Read in the file and then append to the options line.
+        with open(entry, encoding="utf8") as f:
+            lines = f.read().splitlines()
+        with open(entry, "w", encoding="utf8") as f:
+            for line in lines:
+                if line.startswith('options '):
+                    f.write(f"{line} {' '.join(kernel_arguments)}\n")
+                else:
+                    f.write(f"{line}\n")