utils: add uefi.py

Add UEFI related utilities inside a new utility module: uefi.py

	_check_efibootmgr_json
	======================
Check if the system efibootmgr executable supports JSON output. This is
a private function used only by other functions from uefi.py.

	is_uefi_supported
	=================
Check if the system supports UEFI firmware.

	run_efibootmgr_json
	===================
Runs efibootmgr with json output support. Return the JSON output as a
Python dict.

	efibootmgr_create_bootentry
	===========================
Create nvram boot entry. This bootentry is usually later set to boot
next just once via "BootNext" nvram variable.

	efibootmgr_delete_bootentry
	===========================
Delete a nvram boot entry. Used to avoid duplicates when booting the
same disk and partition from a given client.

	efibootmgr_bootnext
	===================
Set nvram "BootNext" variable to a given boot entry so after client
reboot, PXE is not executed and the given boot entry takes precedence.

Add dependency with efibootmgr version >= 18, and efibootmgr JSON output
which is currently out of tree from util-linux repo.

src/utils/uefi.py

@@ -0,0 +1,97 @@
+#
+# Copyright (C) 2023 Soleta Networks <info@soleta.eu>
+#
+# This program is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Affero General Public License as published by the
+# Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+
+import json
+import logging
+import os
+import shlex
+import subprocess
+
+import fdisk
+
+def _find_bootentry(entries, label):
+    for entry in entries:
+        if entry['description'] == label:
+            return entry
+    else:
+        raise NameError('Boot entry {label} not found')
+
+
+def _strip_boot_prefix(entry):
+    try:
+        num = entry['name'][4:]
+    except:
+        raise KeyError('Unable to strip "Boot" prefix from boot entry')
+    return num
+
+
+def _check_efibootmgr_json():
+    """
+    Checks if efibootmgr --json option is supported.
+    Returns True if supported, False otherwise.
+    """
+    supported = True
+    try:
+        subprocess.run(['efibootmgr-json', '--json'], stdout=subprocess.DEVNULL,
+                       stderr=subprocess.DEVNULL, check=True)
+    except subprocess.CalledProcessError:
+        supported = False
+    return supported
+
+
+def is_uefi_supported():
+    return True if os.path.exists("/sys/firmware/efi") else False
+
+
+def run_efibootmgr_json():
+    if _check_efibootmgr_json() is False:
+        raise RuntimeError('efibootmgr-json not available')
+
+    proc = subprocess.run(['efibootmgr-json', '--json'], capture_output=True, text=True)
+    dict_json = json.loads(proc.stdout)
+
+    return dict_json
+
+
+def efibootmgr_bootnext(description):
+    logging.info(f'Setting BootNext to value from boot entry with label {description}')
+    bootnext_cmd = 'efibootmgr-json -n {bootnum}'
+    boot_entries = run_efibootmgr_json().get('vars', [])
+
+    entry = _find_bootentry(boot_entries, description)
+    num = _strip_boot_prefix(entry)  # efibootmgr output uses BootXXXX for each entry, remove the "Boot" prefix.
+    bootnext_cmd = bootnext_cmd.format(bootnum=num)
+    subprocess.run(shlex.split(bootnext_cmd), check=True,
+                   stdout=subprocess.DEVNULL)
+
+
+def efibootmgr_delete_bootentry(label):
+    dict_json = run_efibootmgr_json()
+    efibootmgr_cmd = 'efibootmgr-json -q -b {bootnum} -B'
+
+    for entry in dict_json.get('vars', []):
+        if entry['description'] == label:
+            num = entry['name'][4:]  # Remove "Boot" prefix to extract num
+            efibootmgr_cmd = efibootmgr_cmd.format(bootnum=num)
+            subprocess.run(shlex.split(efibootmgr_cmd), check=True)
+            break
+    else:
+        logging.info(f'Cannot delete boot entry {label} because it was not found.')
+
+
+def efibootmgr_create_bootentry(disk, part, loader, label, add_to_bootorder=True):
+    entries = run_efibootmgr_json().get('vars', [])
+    create_opt = '-c' if add_to_bootorder else '-C'
+    index_opt = f'-I {len(entries)}'  # Requires efibootmgr version 18
+    efibootmgr_cmd = f'efibootmgr-json {create_opt} {index_opt} -d {disk} -p {part} -L {label} -l {loader}'
+    logging.info(f'efibootmgr-json command creating boot entry: {efibootmgr_cmd}')
+    try:
+        proc = subprocess.run(shlex.split(efibootmgr_cmd), check=True, text=True)
+    except subprocess.CalledProcessError as e:
+        logging.error(f'Unexpected error adding boot entry to nvram. UEFI firmware might be buggy?.')
+        raise e