boot-next

#!/usr/bin/env python3
import contextlib, ctypes, os, pathlib, subprocess, sys

EFIVARSFS = pathlib.Path('/sys/firmware/efi/efivars')
LOADER_GUID = '4a67b082-0a4c-41cf-b6c7-440b29bb8c4f'
LOADER_ENTRY_ONE_SHOT = 'LoaderEntryOneShot'

FS_IMMUTABLE_FL = 0x00000010  # see <linux/fs.h>

try:
    libe2p = ctypes.CDLL('libe2p.so.2', use_errno=True)
    fgetflags = libe2p.fgetflags
    fgetflags.restype = ctypes.c_int
    fgetflags.argtypes = [ctypes.c_char_p, ctypes.c_void_p]
    fsetflags = libe2p.fsetflags
    fsetflags.restype = ctypes.c_int
    fsetflags.argtypes = [ctypes.c_char_p, ctypes.c_ulong]
    @contextlib.contextmanager
    def ensure_not_immutable(path):
        flags = (ctypes.c_ulong * 1)()
        rc = fgetflags(path, ctypes.byref(flags))
        if rc == 0 and (flags[0] & FS_IMMUTABLE_FL) != 0:
            rc = fsetflags(path, flags[0] & ~FS_IMMUTABLE_FL)
            did_chattr = rc == 0
        else:
            did_chattr = False
        yield
        if did_chattr:
            fsetflags(path, flags[0])
except OSError:
    @contextlib.contextmanager
    def ensure_not_immutable(path):
        yield

if len(sys.argv) > 1:
    var_value = b'\7\0\0\0' + sys.argv[1].encode('utf-16le') + b'\0\0'
    var_path = EFIVARSFS / '{1}-{0}'.format(LOADER_GUID, LOADER_ENTRY_ONE_SHOT)
    with ensure_not_immutable(bytes(var_path)), open(var_path, 'wb') as f:
        f.write(var_value)

var_name = '{0}-{1}'.format(LOADER_GUID, LOADER_ENTRY_ONE_SHOT)
sys.exit(subprocess.call(['efivar', '-p', '-n', var_name]))

boot-next.service

[Unit]
Description=Set bootloader configuration
After=sleep.target

[Service]
Type=oneshot
ExecStart=/bin/sh -c 'printf "\7\0\0\0\141\0\162\0\143\0\150\0\0\0" > /sys/firmware/efi/efivars/LoaderEntryOneShot-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f'

[Install]
WantedBy=basic.target sleep.target

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