sound_card_init/sound_card_init.conf

# Copyright 2020 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

# Installed by sound_card_init package.
# sound_card_init upstart job.
# sound_card_init is started by /lib/udev/rules.d/99-sound_card_init.rules

description     "Chrome OS sound card initializer"
author          "chromium-os-dev@chromium.org"

# sound_card_init is a short-running process, but we don't start it as
# a task job, because sound_card_init needs the sound card to be ready in
# CRAS therefore we do not want to block the udev rule processing.

# Make the task killable, because if it has a leak it's better to
# restart it than to OOM-panic.
oom score 0

# SOUND_CARD_ID is provided by /lib/udev/rules.d/99-sound_card_init.rules.
import SOUND_CARD_ID

pre-start script
  if ! echo "${SOUND_CARD_ID}" | grep -Eq "^[a-zA-Z0-9]+$"; then
    logger -t "${UPSTART_JOB}" \
      "Invalid SOUND_CARD_ID supplied"
    exit 1
  else
    mkdir -m 0755 -p /var/lib/sound_card_init/"${SOUND_CARD_ID}"
    chown -R sound_card_init:sound_card_init /var/lib/sound_card_init
  fi
end script


script
  CONFIG="$(cros_config /audio/main sound-card-init-conf)"
  if [ -f /etc/sound_card_init/"${CONFIG}" ]; then
    # Here (in order) are a list of the args added:
    # --uts: Create and enter new UTS namespace (hostname/NIS domain name).
    # -e: doesn't need network access.
    # -l: process doesn't use SysV shared memory or IPC.
    # -N: doesn't need to modify control groups settings.
    # -v: run inside a new VFS namespace.
    # -p -r: process doesn't need to access other processes in the system.
    # -n: process doesn't need new privileges.
    # -P: set /mnt/empty as the root fs.
    # -b: bind /
    # -k: Get a writeable and empty /run tmpfs path.
    # -b: need /run/cras to connect cras.
    # -b: need /dev to send ioctls to the system's block devices.
    # -k: empty /sys tmpfs path.
    # -b: need /sys/firmware/vpd/ro/ access to read the default calibration
    #     value in vpd.
    # -k: get a writeable and empty /var tmpfs path.
    # -b: need /var/lib/sound_card_init/$SOUND_CARD_ID writable access for
    #     datastore update.
    # -b: need /var/lib/cras readable
    exec minijail0 \
        --uts \
        -e \
        -l \
        -N \
        -v \
        -p -r \
        -n \
        -P /mnt/empty \
        -b / \
        -k 'tmpfs,/run,tmpfs,MS_NODEV|MS_NOEXEC|MS_NOSUID,mode=755,size=10M' \
        -b /run/cras \
        -b /dev \
        -k 'tmpfs,/sys,tmpfs,MS_NODEV|MS_NOEXEC|MS_NOSUID,mode=755,size=10M' \
        -b /sys/firmware/vpd/ro/ \
        -k 'tmpfs,/var,tmpfs,MS_NODEV|MS_NOEXEC|MS_NOSUID,mode=755,size=10M' \
        -b /var/lib/sound_card_init/"${SOUND_CARD_ID}"/,,1 \
        -b /var/lib/cras/ \
        -u sound_card_init -g sound_card_init -G \
        -S /usr/share/policy/sound_card_init-seccomp.policy \
        /usr/bin/sound_card_init "--id=${SOUND_CARD_ID}" "--conf=${CONFIG}"
  fi
end script