mkosi-initrd: add some autodetection logic if output is not specified

Make use of installation layout (bls or other), `$BOOT_ROOT` partition and
entry token provided by `kernel-install`.

mkosi/initrd.py

@@ -1,12 +1,15 @@
 # SPDX-License-Identifier: LGPL-2.1-or-later
 
 import argparse
+import json
 import os
 import platform
 import shutil
+import subprocess
 import sys
 import tempfile
 from pathlib import Path
+from typing import Optional, cast
 
 import mkosi.resources
 from mkosi.config import DocFormat, OutputFormat
@@ -18,6 +21,30 @@
 from mkosi.util import resource_path
 
 
+def get_layout_output_dir() -> tuple[Optional[str], str]:
+ layout = ""
+ output_dir = ""
+
+ if find_binary("kernel-install"):
+ output = json.loads(
+ run(
+ ["kernel-install", "--json=short", "inspect"],
+ stdout=subprocess.PIPE,
+ stderr=subprocess.DEVNULL,
+ check=False,
+ ).stdout
+ )
+ layout = cast(str, output["Layout"])
+ if layout == "bls":
+ boot_root = cast(str, output["BootRoot"])
+ entry_token = cast(str, output["EntryToken"])
+ output_dir = f"{boot_root}/{entry_token}"
+ elif layout == "other":
+ output_dir = "/boot"
+
+ return (layout or None, output_dir)
+
+
 @uncaught_exception_handler()
 def main() -> None:
  log_setup()
@@ -88,6 +115,16 @@ def main() -> None:
  show_docs("mkosi-initrd", DocFormat.all(), resources=r)
  return
 
+ if not args.output_dir:
+ layout, args.output_dir = get_layout_output_dir()
+ if args.output_dir:
+ if layout == "bls":
+ args.output_dir += "/" + args.kernel_version
+ if not Path(args.output_dir).is_dir():
+ args.output_dir = ""
+ elif layout == "other" and args.output == "initrd":
+ args.output += "-" + args.kernel_version
+
  cmdline: list[PathString] = [
  "mkosi",
  "--force",