Inspired by https://poisonpacket.wordpress.com/2015/05/26/btrfs-snapshot-size-disk-usage/

btrfs-size.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# \Author: Like Ma <likemartinma@gmail.com>
# \brief: It shows btrfs subvolume info and supports Python 2/3
import sys
from re import compile as rcomp
from subprocess import Popen, PIPE, STDOUT

SUBVOL_CHECKER = rcomp(
    r'^ID\s+(?P<id>\d+)\s+gen\s+(?P<gen>\d+)\s+'
    r'top\s+level\s+(?P<ogen>\d+)\s+path\s+(?P<path>.+)')

QGROUP_HDR_CHECKER = rcomp(r'^qgroupid\s+rfer\s+excl\s*')
QGROUP_CHECKER = rcomp(r'\d+/(?P<id>\d+)\s+(?P<rfer>\d+)\s+(?P<excl>\d+)')
CTIME_CHECKER = rcomp(r'^\s*Creation time:\s*(\S+)\s*(\S+)\s*')


def each_stdout_stderr(*args):
    proc = Popen(args, stdout=PIPE, stderr=STDOUT)
    try:
        for i in proc.stdout:
            yield i.decode("utf-8")  # Decoding is for python3
    finally:
        proc.wait()


def btrfs_subvolume_list(mp):
    for i in each_stdout_stderr('btrfs', 'subvolume', 'list', mp):
        m = SUBVOL_CHECKER.match(i.strip())
        if m:
            yield m.groupdict()


def btrfs_subvolume_creation_time(path):
    result = None
    for i in each_stdout_stderr('btrfs', 'subvolume', 'show', path):
        m = CTIME_CHECKER.match(i)
        if m:
            result = '%s %s' % (m.group(1), m.group(2))
            break

    return result


def parse_btrfs_qgroup_show(fp):
    result = {}
    for i in fp:
        if 'unrecognized option' in i:
            return None

        if QGROUP_HDR_CHECKER.match(i) or i.startswith('^---'):
            continue

        m = QGROUP_CHECKER.match(i.strip())
        if m:
            d = m.groupdict()
            result[d['id']] = d

    return result


def btrfs_qgroup_show(mp):
    result = parse_btrfs_qgroup_show(
        each_stdout_stderr('btrfs', 'qgroup', 'show', mp, '--raw'))
    if result:
        return result

    return parse_btrfs_qgroup_show(
        each_stdout_stderr('btrfs', 'qgroup', 'show', mp))


def format_byte(size):
    units = ('T', 'G', 'M', 'K')
    q = 1 << 40
    for i in units:
        if size >= q:
            return '%d %s' % (int(size / q), i)
        q >>= 10


if len(sys.argv) < 2:
    sys.stderr.write('%s <mount point>\n' % sys.argv[0])
    sys.exit(1)

mp = sys.argv[1]
qgroup = btrfs_qgroup_show(mp)
subvolumes = []
for i in btrfs_subvolume_list(mp):
    rec = qgroup.get(i['id'])
    if rec:
        i.update(rec)
        subvolumes.append(i)

print('%6s %-32s %-20s %16s %16s' %
      ('ID', 'Subvolume', 'Creation Time', 'Total', 'Exclusive Data'))
for i in subvolumes:
    ctime = btrfs_subvolume_creation_time('%s/%s' % (mp, i['path']))
    print('%6s %-32s %-20s %16s %16s' % (i['id'],
                                         i['path'],
                                         ctime,
                                         format_byte(int(i['rfer'])),
                                         format_byte(int(i['excl']))))

# vim: ts=4 sw=4 sts=4 et: