Check to see if deferred deletion is supported

check_for_deferred_deletion.sh

#!/bin/bash

PIPE1=/run/dss-$$-fifo1
PIPE2=/run/dss-$$-fifo2
TEMPDIR=$(mktemp --tmpdir -d)

platform_supports_deferred_deletion() {
  local deferred_deletion_supported=1
  trap cleanup_pipes EXIT
  if [ ! -x "./dss-child-read-write.sh" ];then
    return 1
  fi
  mkfifo $PIPE1
  mkfifo $PIPE2
  unshare -m ./dss-child-read-write.sh $PIPE1 $PIPE2 "$TEMPDIR" &
  read -t 10 n <>$PIPE1
  if [ "$n" != "start" ];then
    return 1
  fi
  rmdir $TEMPDIR > /dev/null 2>&1
  deferred_deletion_supported=$?
  echo "finish" > $PIPE2
  return $deferred_deletion_supported
}

cleanup_pipes(){
  rm -f $PIPE1
  rm -f $PIPE2
  rmdir $TEMPDIR 2>/dev/null
}

platform_supports_deferred_deletion

if [ "$?" -eq 1 ]
then
  echo "Deferred deletion is not supported"
else
  echo "Deferred deletion is supported"
fi

dss-child-read-write.sh

#!/bin/bash
# This is a helper script which is called by container-storage-setup.sh (d-s-s).
# This script helps in providing synchronization primitives to d-s-s so that
# d-s-s can determine whether deferred deletion is supported by the underlying
# kernel or not.

# $1 is named FIFO pipe.
# This helper script will write to $1 to signal d-s-s that unshare has been completed successfully.

# $2 is another named FIFO pipe.
# This helper script will read from $2. The write for this pipe would come from d-s-s to indicate
# that helper script can terminate now.

# $3 is absolute path to a temp dir which child will bind mount. Parent will
# later try to remove this dir.

if ! mount -o bind $3 $3; then
   echo "stop" > $1
   exit 1
fi
echo "start" > $1
read -t 10 n <>$2