scripts -> modules

modules/tile_gen/scripts/shrink_btrfs.py

@@ -0,0 +1,105 @@
+#!/usr/bin/env python3
+import os
+import subprocess
+import sys
+import tempfile
+from pathlib import Path
+
+import click
+
+
+# btrfs cannot shrink smaller than 256 MiB
+SMALLEST_SIZE = 256 * 1024 * 1024
+
+
+@click.command()
+@click.argument(
+    'btrfs_img',
+    type=click.Path(exists=True, dir_okay=False, file_okay=True, path_type=Path),
+)
+def cli(btrfs_img: Path):
+    """
+    Shrinks a Btrfs image
+    // I cannot believe that Btrfs is over 15 years old,
+    // yet there is no resize2fs tool which can shrink a disk image
+    // to minimum size.
+    // It cannot even tell you how much should be the right size,
+    // it just randomly fails after which you have to umount and mount again.
+    // So we have to make a loop which tries to shrink it until it fails.
+
+    // Also, WONTFIX bugs like how instead of telling you that
+    // minimum fs size is 256 MB, it says "ERROR: unable to resize - Invalid argument"
+    // https://bugzilla.kernel.org/show_bug.cgi?id=118111
+    """
+
+    if os.geteuid() != 0:
+        sys.exit('  needs sudo')
+
+    current_dir = Path.cwd()
+
+    mnt_dir = Path(tempfile.mkdtemp(dir=current_dir, prefix='tmp_shrink_'))
+    subprocess.run(['mount', '-t', 'btrfs', btrfs_img, mnt_dir], check=True)
+
+    # shink until max. 10 MB left or reached SMALLEST_SIZE or failure
+    while True:
+        # needs to start with a balancing
+        # https://btrfs.readthedocs.io/en/latest/Balance.html
+        # https://marc.merlins.org/perso/btrfs/post_2014-05-04_Fixing-Btrfs-Filesystem-Full-Problems.html
+        do_balancing(mnt_dir)
+
+        free_bytes = get_usage(mnt_dir, 'Device unallocated')
+        device_size = get_usage(mnt_dir, 'Device size')
+        shrink_idea = free_bytes * 0.7
+
+        # workaround for the SMALLEST_SIZE limit
+        if device_size - free_bytes < SMALLEST_SIZE:
+            shrink_idea = (device_size - SMALLEST_SIZE) * 0.7
+
+        # stop if 10 MB left
+        if shrink_idea < 10_000_000:
+            break
+
+        # stop if process error
+        if not do_shrink(mnt_dir, shrink_idea):
+            break
+
+    total_size = get_usage(mnt_dir, 'Device size')
+
+    subprocess.run(['umount', mnt_dir])
+    mnt_dir.rmdir()
+
+    subprocess.run(['truncate', '-s', str(total_size), btrfs_img])
+    print(f'Truncated {btrfs_img} to {total_size//1_000_000} MB size')
+    print('shrink_btrfs.py DONE')
+
+
+def get_usage(mnt: Path, key: str):
+    p = subprocess.run(
+        ['btrfs', 'filesystem', 'usage', '-b', mnt], text=True, capture_output=True, check=True
+    )
+    for line in p.stdout.splitlines():
+        if f'{key}:' not in line:
+            continue
+        free = int(line.split(':')[1])
+        return free
+
+
+def do_shrink(mnt: Path, delta_size: float):
+    delta_size = int(delta_size)
+    print(f'Trying to shrink by {delta_size//1_000_000} MB')
+    p = subprocess.run(['btrfs', 'filesystem', 'resize', str(-delta_size), mnt])
+    return p.returncode == 0
+
+
+def do_balancing(mnt: Path):
+    print('Starting btrfs balancing')
+    p = subprocess.run(
+        ['btrfs', 'balance', 'start', '-dusage=100', mnt], capture_output=True, text=True
+    )
+    if p.returncode:
+        print(f'Balance error: {p.stdout} {p.stderr}')
+    print('Balancing done')
+
+
+if __name__ == '__main__':
+    cli()