fs/skeleton/bin/update-gpio-links

#! /bin/sh

#
# load /etc/gpios, look for matching model name,
# create named symlinks in /dev/gpio/...
#

die() {
  local message="$1"
  echo "$0: fatal error: $message" >&2
  exit 1
}

warn() {
  local message="$1"
  echo "$0: warning: $message" >&2
}

# /sys tree for gpios
sys_dir()
{
  echo /sys/class/gpio
}

# path to a specific gpio dir
gpio_dir()
{
  local gpio="$1"
  local sys="$(sys_dir)"
  echo "$sys/gpio$gpio"
}

# unexport then export to allow possible reconfiguration
reexport_gpio()
{
  local gpio="$1"
  local sys="$(sys_dir)" gdir control

  gdir=$(gpio_dir "$gpio")

  if [ -d "$gdir" ]; then
    echo "$gpio" >"$sys/unexport" || return 1
  fi

  echo "$gpio" >"$sys/export" || return 1

  if [ ! -d "$gdir" ]; then
    warn "$gdir failed to appear"
    return 1
  fi

  return 0
}

set_gpio_prop()
{
  local gpio="$1" key="$2" value="$3"
  local gdir keyfile

  gdir=$(gpio_dir "$gpio")
  keyfile="$gdir/$key"

  # allow "" and "-" as noop values
  if [ -z "$value" ] || [ "$value" = "-" ]; then
    return 0
  fi

  if [ ! -f "$keyfile" ]; then
    echo "set_gpio_prop: '$keyfile' not found" >&2
    return 1
  fi

  echo "$value" >"$keyfile" || return 1

  return 0
}

# check whether the platform and optional hwver match a model.
# returns 0 on match.
model_matches()
{
  local model platform hwver
  model="$1"
  platform="$2"
  hwver="$3"

  if [ "$model" = "$platform" ] || \
      printf "%s\n" "$platform-$hwver" | grep -E -q "^$model$" ; then
    return 0
  fi

  return 1
}

# create links for all gpios in config file
create_gpio_links()
{
  local config="$1" linkdir="$2"
  local platform real_platform err="0" line="0" tmp="/tmp/gpios.$$"
  local m hwver real_hwver

  read real_platform </etc/platform
  read real_hwver </etc/hw_ver

  # allow override values for testing
  platform=${PLATFORM_FOR_TEST-$real_platform}
  hwver=${HWVER_FOR_TEST-$real_hwver}

  rm -rf "$linkdir.new" "$linkdir.old"
  mkdir "$linkdir.new" || return 1

  # remove comments
  sed -e 's/#.*//' "$config" >"$tmp" || return 1

  while read model gpio name active_low edge direction rest; do
    line=$(( $line + 1 ))
    m=$config:$line

    # ignore blank lines
    if [ -z "$model" ]; then
      continue
    fi

    # check for min and max args
    if [ -z "$direction" ] || [ -n "$rest" ]; then
      warn "wrong number of fields for '$m'"
      err=1
      continue
    fi

    # skip lines not for this platform
    if ! model_matches "$model" "$platform" "$hwver"; then
      continue
    fi

    # print the lines that would have been acted upon
    if [ "$dryrun" != "" ]; then
      printf "dryrun: %s %s\n" $gpio $name
      continue
    fi

    if ! reexport_gpio "$gpio"; then
      err=1
      continue
    fi

    gdir=$(gpio_dir $gpio)

    # set up link
    if ! ln -s "$gdir" "$linkdir.new/$name"; then
      err=1
      continue
    fi

    # set properties (may be noops)
    if ! set_gpio_prop "$gpio" active_low "$active_low" ||
       ! set_gpio_prop "$gpio" edge "$edge" ||
       ! set_gpio_prop "$gpio" direction "$direction"; then
      err=1
      continue
    fi

  done <"$tmp"

  rm -f "$tmp"

  if [ -e "$linkdir" ]; then
    mv "$linkdir" "$linkdir.old" || return 1
  fi

  mv "$linkdir.new" "$linkdir" || return 1

  rm -rf "$linkdir.old"
  return $err
}

#
# main
#

config=/etc/gpios
dir=/dev/gpio

# for testing
if [ -n "$1" ]; then
  config="$1"
fi

create_gpio_links "$config" "$dir" || die "create_gpio_links($config, $dir)"

exit 0