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Filename : cc_grub_dpkg.py
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# Copyright (C) 2009-2010, 2020 Canonical Ltd.
# Copyright (C) 2012 Hewlett-Packard Development Company, L.P.
#
# Author: Scott Moser <scott.moser@canonical.com>
# Author: Juerg Haefliger <juerg.haefliger@hp.com>
# Author: Matthew Ruffell <matthew.ruffell@canonical.com>
#
# This file is part of cloud-init. See LICENSE file for license information.
"""Grub Dpkg: Configure grub debconf installation device"""

import logging
import os
from textwrap import dedent

from cloudinit import subp, util
from cloudinit.cloud import Cloud
from cloudinit.config import Config
from cloudinit.config.schema import MetaSchema, get_meta_doc
from cloudinit.settings import PER_INSTANCE
from cloudinit.subp import ProcessExecutionError

MODULE_DESCRIPTION = """\
Configure which device is used as the target for grub installation. This module
can be enabled/disabled using the ``enabled`` config key in the ``grub_dpkg``
config dict. This module automatically selects a disk using ``grub-probe`` if
no installation device is specified.

The value which is placed into the debconf database is in the format which the
grub postinstall script expects. Normally, this is a /dev/disk/by-id/ value,
but we do fallback to the plain disk name if a by-id name is not present.

If this module is executed inside a container, then the debconf database is
seeded with empty values, and install_devices_empty is set to true.
"""
distros = ["ubuntu", "debian"]
meta: MetaSchema = {
    "id": "cc_grub_dpkg",
    "name": "Grub Dpkg",
    "title": "Configure grub debconf installation device",
    "description": MODULE_DESCRIPTION,
    "distros": distros,
    "frequency": PER_INSTANCE,
    "examples": [
        dedent(
            """\
            grub_dpkg:
              enabled: true
              # BIOS mode (install_devices needs disk)
              grub-pc/install_devices: /dev/sda
              grub-pc/install_devices_empty: false
              # EFI mode (install_devices needs partition)
              grub-efi/install_devices: /dev/sda
            """
        )
    ],
    "activate_by_schema_keys": [],
}

__doc__ = get_meta_doc(meta)
LOG = logging.getLogger(__name__)


def fetch_idevs():
    """
    Fetches the /dev/disk/by-id device grub is installed to.
    Falls back to plain disk name if no by-id entry is present.
    """
    disk = ""
    devices = []

    # BIOS mode systems use /boot and the disk path,
    # EFI mode systems use /boot/efi and the partition path.
    probe_target = "disk"
    probe_mount = "/boot"
    if is_efi_booted():
        probe_target = "device"
        probe_mount = "/boot/efi"

    try:
        # get the root disk where the /boot directory resides.
        disk = subp.subp(
            ["grub-probe", "-t", probe_target, probe_mount], capture=True
        ).stdout.strip()
    except ProcessExecutionError as e:
        # grub-common may not be installed, especially on containers
        # FileNotFoundError is a nested exception of ProcessExecutionError
        if isinstance(e.reason, FileNotFoundError):
            LOG.debug("'grub-probe' not found in $PATH")
        # disks from the container host are present in /proc and /sys
        # which is where grub-probe determines where /boot is.
        # it then checks for existence in /dev, which fails as host disks
        # are not exposed to the container.
        elif "failed to get canonical path" in e.stderr:
            LOG.debug("grub-probe 'failed to get canonical path'")
        else:
            # something bad has happened, continue to log the error
            raise
    except Exception:
        util.logexc(LOG, "grub-probe failed to execute for grub_dpkg")

    if not disk or not os.path.exists(disk):
        # If we failed to detect a disk, we can return early
        return ""

    try:
        # check if disk exists and use udevadm to fetch symlinks
        devices = (
            subp.subp(
                ["udevadm", "info", "--root", "--query=symlink", disk],
                capture=True,
            )
            .stdout.strip()
            .split()
        )
    except Exception:
        util.logexc(
            LOG, "udevadm DEVLINKS symlink query failed for disk='%s'", disk
        )

    LOG.debug("considering these device symlinks: %s", ",".join(devices))
    # filter symlinks for /dev/disk/by-id entries
    devices = [dev for dev in devices if "disk/by-id" in dev]
    LOG.debug("filtered to these disk/by-id symlinks: %s", ",".join(devices))
    # select first device if there is one, else fall back to plain name
    idevs = sorted(devices)[0] if devices else disk
    LOG.debug("selected %s", idevs)

    return idevs


def is_efi_booted() -> bool:
    """
    Check if the system is booted in EFI mode.
    """
    try:
        return os.path.exists("/sys/firmware/efi")
    except OSError as e:
        LOG.error("Failed to determine if system is booted in EFI mode: %s", e)
        # If we can't determine if we're booted in EFI mode, assume we're not.
        return False


def handle(name: str, cfg: Config, cloud: Cloud, args: list) -> None:
    mycfg = cfg.get("grub_dpkg", cfg.get("grub-dpkg", {}))
    if not mycfg:
        mycfg = {}

    enabled = mycfg.get("enabled", True)
    if util.is_false(enabled):
        LOG.debug("%s disabled by config grub_dpkg/enabled=%s", name, enabled)
        return

    dconf_sel = get_debconf_config(mycfg)
    LOG.debug("Setting grub debconf-set-selections with '%s'", dconf_sel)

    try:
        subp.subp(["debconf-set-selections"], data=dconf_sel)
    except Exception as e:
        util.logexc(
            LOG, "Failed to run debconf-set-selections for grub_dpkg: %s", e
        )


def get_debconf_config(mycfg: Config) -> str:
    """
    Returns the debconf config for grub-pc or
    grub-efi depending on the systems boot mode.
    """
    if is_efi_booted():
        idevs = util.get_cfg_option_str(
            mycfg, "grub-efi/install_devices", None
        )

        if idevs is None:
            idevs = fetch_idevs()

        return "grub-pc grub-efi/install_devices string %s\n" % idevs
    else:
        idevs = util.get_cfg_option_str(mycfg, "grub-pc/install_devices", None)
        if idevs is None:
            idevs = fetch_idevs()

        idevs_empty = mycfg.get("grub-pc/install_devices_empty")
        if idevs_empty is None:
            idevs_empty = not idevs
        elif not isinstance(idevs_empty, bool):
            idevs_empty = util.translate_bool(idevs_empty)
        idevs_empty = str(idevs_empty).lower()

        # now idevs and idevs_empty are set to determined values
        # or, those set by user
        return (
            "grub-pc grub-pc/install_devices string %s\n"
            "grub-pc grub-pc/install_devices_empty boolean %s\n"
            % (idevs, idevs_empty)
        )