util/vpd_get_value

#!/bin/sh
# Copyright 2016 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.
#
# Helper utility to read a single value from VPD.
#
# The script is optimized for reading one entry from VPD, first RO then RW.
# If the given key is not found, prints nothing.

# CACHE_FILE is defined from dump_vpd_log.
CACHE_FILE=/mnt/stateful_partition/unencrypted/cache/vpd/full-v2.txt
SYS_VPD=/sys/firmware/vpd
TMP_FILE=

: "${VPD_IGNORE_CACHE:=}"
: "${VPD_IGNORE_SYS_CACHE}"

main() {
  if [ "$#" != 1 ]; then
    echo "Usage: $0 key_name" >&2
    exit 1
  fi
  local key="$1"

  if [ -n "${VPD_IGNORE_CACHE}" ]; then
    exec vpd -g "${key}"
  fi

  # Reading from /sys (works on ARM 3.18+, x86 4.4+) is most efficient;
  # otherwise we have to parse from VPD cache (maintained by dump_vpd_log).
  local sys_vpd_present=0
  # VPD ro section may have no entries for reference boards; check for rw as
  # well to prefer the fast path when possible.
  if [ -d "${SYS_VPD}/ro" ] || [ -d "${SYS_VPD}/rw" ]; then
    sys_vpd_present=1
  fi
  if [ -z "${VPD_IGNORE_SYS_CACHE}" ] && [ "${sys_vpd_present}" = "1" ]; then
    for file in "${SYS_VPD}/ro/${key}" "${SYS_VPD}/rw/${key}"; do
      if [ -f "${file}" ]; then
        cat "${file}"
        return 0
      fi
    done
  else
    if [ ! -f "${CACHE_FILE}" ]; then
      # /etc/init/vpd-log.conf was not executed, or cache corrupted, or if
      # system stateful partition was not mounted yet.
      TMP_FILE="$(mktemp)"
      dump_vpd_log --full --stdout >"${TMP_FILE}"
      CACHE_FILE="${TMP_FILE}"
    fi
    # Use printf(1) to suppress the newline that head(1) adds to the value.
    printf '%s' "$(sed -n "s/^\"${key}\"=\"\(.*\)\"\$/\1/p" "${CACHE_FILE}" |
      head -1)"
    if [ -e "${TMP_FILE}" ]; then
      rm -f "${TMP_FILE}"
    fi
  fi
}
main "$@"