Initial rewrite of bash script

This implements a faster version of https://github.com/agronick/btrfs-size in
python. The original was slow mainly due to looking up paths for qgroup ids
one at a time. This new implementation instead runs two shell commands and
indexes paths to qgroup ids.

btrfs-subvolumes.py

@@ -0,0 +1,115 @@
+#!/usr/bin/env python3
+
+# List BTFS subvolume space use information similar to `df -h`
+#
+# Note: this requires the "hurry.filesize" module. Install it with:
+#
+#     pip install hurry.filesize
+#
+# This is rewritten from a shell script that was too slow:
+# https://github.com/agronick/btrfs-size
+
+from __future__ import print_function
+
+from hurry.filesize import size
+
+import argparse
+import subprocess
+import sys
+import os
+import re
+
+parser = argparse.ArgumentParser(description="List subvolume and snapshot sizes on BTRFS volumes")
+parser.add_argument("path", help="Path or UUID of the BTRFS volume to inspect")
+parser.add_argument(
+    "-s",
+    dest="sort",
+    choices=[
+        "exclusive",
+        "total"
+    ],
+    help="Sort output instead of using the order from btrfs"
+)
+
+
+class BtrfsQuota:
+    def __init__(self, raw_id, total_bytes, exclusive_bytes):
+        self.id = raw_id.split("/")[1]
+        self.total_bytes = int(total_bytes)
+        self.exclusive_bytes = int(exclusive_bytes)
+
+def btrfs_subvols_get(path):
+    """Return a dictionary of subvolume names indexed by their subvolume ID"""
+    try:
+        raw = subprocess.check_output(["btrfs", "subvolume", "list", path])
+        volumes = re.findall(r'^ID (\d+) .* path (.*)$', raw.decode("utf8"), re.MULTILINE)
+
+        return dict(volumes)
+
+    except subprocess.CalledProcessError as e:
+        if e.returncode != 0:
+            print("\nFailed to list subvolumes")
+            print("Is '%s' really a BTRFS volume?" % path)
+            sys.exit(1)
+
+def btrfs_quotas_get(path):
+    """Return a list of BtrfsQuota objects for path"""
+    try:
+        # Get the lines of output, ignoring the two header lines
+        raw = subprocess.check_output(["btrfs", "qgroup", "show", "--raw", path])
+        lines = raw.decode("utf8").split("\n")[2:]
+
+        return [BtrfsQuota(*line.split()) for line in lines if line != '']
+
+    except subprocess.CalledProcessError as e:
+        if e.returncode != 0:
+            print("\nFailed to get subvolume quotas. Have you enabled quotas on this volume?")
+            print("(You can do so with: sudo btrfs quota enable '%s')" % path)
+            sys.exit(1)
+
+def print_table(subvols, quotas):
+    # Get the column size right for the path
+    max_path_length = 0
+    for path in subvols.values():
+        max_path_length = max(len(path), max_path_length)
+
+    template = "{path:<{path_len}}{bytes:>16}{exclusive:>16}"
+
+    # Print table header
+    header = template.format(
+        path="Subvolume",
+        bytes="Total size",
+        exclusive="Exclusive size",
+        path_len=max_path_length
+    )
+
+    print(header)
+    print("-" * len(header))
+
+    # Print table rows
+    for quota in quotas:
+        if quota.id in subvols:
+            print(template.format(
+                path_len=max_path_length,
+                path=subvols[quota.id],
+                bytes=size(quota.total_bytes),
+                exclusive=size(quota.exclusive_bytes)
+            ))
+
+
+# Re-run the script as root if started with a non-priveleged account
+if os.getuid() != 0:
+    cmd = 'sudo "' + '" "'.join(sys.argv) + '"'
+    sys.exit(subprocess.call(cmd, shell=True))
+
+args = parser.parse_args()
+
+subvols = btrfs_subvols_get(args.path)
+quotas = btrfs_quotas_get(args.path)
+
+if args.sort == "exclusive":
+    quotas.sort(key=lambda q: q.exclusive_bytes, reverse=True)
+elif args.sort == "bytes":
+    quotas.sort(key=lambda q: q.total_bytes, reverse=True)
+
+print_table(subvols, quotas)