#!/bin/sh
#
# Copyright 2021 Patrick Volkerding, Sebeka, MN, USA
#
# Redistribution and use of this script, with or without modification, is.
# permitted provided that the following conditions are met:
#
# 1. Redistributions of this script must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
#
#  THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
#  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF.
#  MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
#  EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,.
#  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
#  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
#  OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,.
#  WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR.
#  OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF.
#  ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#


SYSFILE=/sys/kernel/debug/sched/preempt

function show_preempt_mode()
{
  local PREEMPT_MODE=$(cat $SYSFILE | sed -r "s/^.*\((.*)\).*?$/\1/g")

  echo "Dynamic Preempt: ${PREEMPT_MODE}"
}

if [ ! -e $SYSFILE ]; then
  echo "${SYSFILE} not found?"
  exit 1
elif [ $# -ge 1 ]; then
  echo "Usage: $(basename $0) <method> ..."
  exit 1
elif [ $# -eq 0 ]; then
  show_preempt_mode
  exit 0
fi

PREEMPT_MODE="$1"

# Sanity check:
if ! echo $PREEMPT_MODE | grep -wq -e none -e voluntary -e full ; then
  echo "ERROR: Invalid mode for Dynamic Preempt: $PREEMPT_MODE"
  exit 1
fi

echo "$PREEMPT_MODE" > $SYSFILE

show_preempt_mode
exit 0

debugfs   /sys/kernel/debug       debugfs     defaults                 0   0

root@darkstar:~/works# preemptctl
Dynamic Preempt: voluntary
root@darkstar:~/works# preemptctl none
Dynamic Preempt: none
root@darkstar:~/works# preemptctl 
Dynamic Preempt: none
root@darkstar:~/works#