#!/usr/bin/python3

"""
Script for parsing cgroup information

This script will read some limits from the cgroup system and parse
them, printing out "VARIABLE=VALUE" on each line for every limit that is
successfully read. Output of this script can be directly fed into
bash's export command. Recommended usage from a bash script:

    set -o errexit
    export_vars=$(cgroup-limits) ; export $export_vars

Variables currently supported:
    MAX_MEMORY_LIMIT_IN_BYTES
        Maximum possible limit MEMORY_LIMIT_IN_BYTES can have. This is
        currently constant value of 9223372036854775807.
    MEMORY_LIMIT_IN_BYTES
        Maximum amount of user memory in bytes. If this value is set
        to the same value as MAX_MEMORY_LIMIT_IN_BYTES, it means that
        there is no limit set. The value is taken from
        /sys/fs/cgroup/memory/memory.limit_in_bytes
    NUMBER_OF_CORES
        Number of detected CPU cores that can be used. This value is
        calculated from /sys/fs/cgroup/cpuset/cpuset.cpus
    NO_MEMORY_LIMIT
        Set to "true" if MEMORY_LIMIT_IN_BYTES is so high that the caller
        can act as if no memory limit was set. Undefined otherwise.
"""

from __future__ import print_function
import sys


def _read_file(path):
    try:
        with open(path, 'r') as f:
            return f.read().strip()
    except IOError:
        return None


def get_memory_limit():
    """
    Read memory limit, in bytes.
    """

    limit = _read_file('/sys/fs/cgroup/memory/memory.limit_in_bytes')
    if limit is None or not limit.isdigit():
        print("Warning: Can't detect memory limit from cgroups",
              file=sys.stderr)
        return None
    return int(limit)


def get_number_of_cores():
    """
    Read number of CPU cores.
    """

    core_count = 0

    line = _read_file('/sys/fs/cgroup/cpuset/cpuset.cpus')
    if line is None:
        print("Warning: Can't detect number of CPU cores from cgroups",
              file=sys.stderr)
        return None

    for group in line.split(','):
        core_ids = list(map(int, group.split('-')))
        if len(core_ids) == 2:
            core_count += core_ids[1] - core_ids[0] + 1
        else:
            core_count += 1

    return core_count


if __name__ == "__main__":
    env_vars = {
        "MAX_MEMORY_LIMIT_IN_BYTES": 9223372036854775807,
        "MEMORY_LIMIT_IN_BYTES": get_memory_limit(),
        "NUMBER_OF_CORES": get_number_of_cores()
    }

    env_vars = {k: v for k, v in env_vars.items() if v is not None}

    if env_vars.get("MEMORY_LIMIT_IN_BYTES", 0) >= 92233720368547:
        env_vars["NO_MEMORY_LIMIT"] = "true"

    for key, value in env_vars.items():
        print("{0}={1}".format(key, value))