#!/usr/bin/env bash

# BeeGFS Client Mount Utility / External Mount Helper
# If placed in /sbin, this script is called automatically by `mount` whenever a filesystem with type
# `beegfs` is being mounted. It's main purpose is to do name resolution of the management hostname
# as the kernel module can't do that by itself. The hostname is taken from either the mount option
# string itself ('sysMgmtdHost=') or from the config file given by the mount options ('cfgFile=').

function usage() {
  echo "Usage: $(basename "$0") <fs_name> <directory> [-sfnv] [-o options]"
  exit 1
}

SPEC="$1"
shift
DIR="$1"
shift

[[ -n "$SPEC" && -n "$DIR" ]] || usage

FLAGS=
OPTIONS=

# Read in all possible flags (see `man mount 8`)
while getopts 'hsfnvo:t:' FLAG; do
  case "$FLAG" in
    s|f|n|v)
      FLAGS+=("-$FLAG")
      ;;
    o)
      OPTIONS="$OPTARG"
      ;;
    h|*)
      usage
      ;;
  esac
done
shift "$((OPTIND -1))"

# If there is a config file available and sysMgmtdHost is set, load the management hostname from the
# config file
CFG_FILE=$(echo "$OPTIONS" | grep -oP 'cfgFile=[^,]+' | cut -d= -f2)

if [[ -n "$CFG_FILE" ]]; then
  [[ -f "$CFG_FILE"  ]] || {
    echo "Can not open config file '$CFG_FILE'"
    exit 1
  }

  H=$(grep -oP '^\s*sysMgmtdHost\s*=\s*\S+\s*$' "$CFG_FILE" | tr -d ' ' | cut -d= -f2)
  if [[ $H == *$'\n'* ]]; then
    echo "Multiple definitions of 'sysMgmtdHost' found in '$CFG_FILE'."
    exit 1
  elif [[ -n "$H" ]]; then
    HOST_NAME="$H"
  fi
fi

# If it has explicitly been set as a mount option, use that (overrides config file).
HOST_NAME_OPTION=$(echo "$OPTIONS" | grep -oP 'sysMgmtdHost=[^,]+' | cut -d= -f2)
if [[ -n "$HOST_NAME_OPTION" ]]; then
  HOST_NAME="$HOST_NAME_OPTION"
fi

# A management host must be provided
[[ -n "$HOST_NAME" ]] || {
  echo "Can not determine management host - neither through a mount option ('sysMgmtdHost') nor through \
a client config file ('cfgFile')."
  exit 1
}

# Resolve management address
MGMTD_ADDR=$(getent ahostsv4 "$HOST_NAME" | cut -f1 -d' ' | head -n1)

# If resolve fails, error out
[[ -n "$MGMTD_ADDR" ]] || {
  echo "Can not resolve management host address using hostname '$HOST_NAME'"
  exit 1
}

# If the host argument was given, replace it with the resolved address, otherwise append
if [[ -n "$HOST_NAME_OPTION" ]]; then
  # shellcheck disable=SC2001
  OPTIONS=$(echo "$OPTIONS" | sed "s/sysMgmtdHost=[^,]\\+/sysMgmtdHost=$MGMTD_ADDR/g")
else
  OPTIONS="$OPTIONS,sysMgmtdHost=$MGMTD_ADDR"
fi

# Take the part behind the "." as fstype (typically "beegfs"). This allows multiple mount utilities
# and client modules being installed at the same time.
FS_TYPE=$(basename "$0" | sed 's/^.*\.//')

set -ex
mount --internal -t "$FS_TYPE" --source "$SPEC" --target "$DIR" ${FLAGS[*]} -o"$OPTIONS"