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storage: Reimplement btrfs polling with benefits
The subvolume polling is now done by a long-running monitor program that only reports changes back to Cockpit. This reduces traffic in general and allows us to do additional clever things. The monitor program can optionally keep all btrfs filesystems mounted in a "secret" location, so that we can list the subvolumes of all btrfs filesystems, even those that are not officially mounted otherwise. This mode is only enabled in Anaconda mode: It is important there since filesystems are normally not mounted when preparing storage for Anaconda, and outside of Anaconda mode, keeping long standing secret mounts is deemed to invasive. The program can also carry out btrfs operations (such as creating subvolumes) while temporarily mounting it. This allows Cockpit to always create and delete subvolumes. The UI still only does it when monitoring subvolumes works as well, however.
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| Original file line number | Diff line number | Diff line change |
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| #! /usr/bin/python3 | ||
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| # btrfs-tool -- Query and monitor btrfs filesystems | ||
| # | ||
| # This program monitors all btrfs filesystems and reports their | ||
| # subvolumes and other things. | ||
| # | ||
| # It can do that continously, or as a one shot operation. The tool | ||
| # mounts btrfs filesystems as necessary to retrieve the requested | ||
| # information, but does it in a polite way: they are mounted once and | ||
| # then left mounted until that is no longer needed. Typically, you | ||
| # might see some mounts when a Cockpit session starts, and the | ||
| # corresponding unmounts when it ends. | ||
| # | ||
| # This tool can be run multiple times concurrently with itself, and it | ||
| # wont get confused. | ||
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| import contextlib | ||
| import fcntl | ||
| import json | ||
| import os | ||
| import re | ||
| import signal | ||
| import subprocess | ||
| import sys | ||
| import time | ||
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| def debug(msg): | ||
| # subprocess.check_call(["logger", msg]) | ||
| pass | ||
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| TMP_MP_DIR = "/var/lib/cockpit/btrfs" | ||
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| def read_all(fd): | ||
| data = b"" | ||
| while True: | ||
| part = os.read(fd, 4096) | ||
| if len(part) == 0: | ||
| return data | ||
| data += part | ||
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| @contextlib.contextmanager | ||
| def mount_database(): | ||
| path = TMP_MP_DIR + "/db" | ||
| os.makedirs(TMP_MP_DIR, mode=0o700, exist_ok=True) | ||
| fd = os.open(path, os.O_RDWR | os.O_CREAT) | ||
| fcntl.flock(fd, fcntl.LOCK_EX) | ||
| data = read_all(fd) | ||
| blob = {} | ||
| try: | ||
| if len(data) > 0: | ||
| blob = json.loads(data) | ||
| except Exception as err: | ||
| sys.stderr.write(f"Failed to read {path} as JSON: {err}\n") | ||
| try: | ||
| yield blob | ||
| data = json.dumps(blob).encode() + b"\n" | ||
| os.lseek(fd, 0, os.SEEK_SET) | ||
| os.truncate(fd, 0) | ||
| os.write(fd, data) | ||
| finally: | ||
| os.close(fd) | ||
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| # There is contextlib.chdir in Python 3.11, which we should use once | ||
| # it is available everywhere. | ||
| # | ||
| @contextlib.contextmanager | ||
| def context_chdir(path): | ||
| old_cwd = os.getcwd() | ||
| os.chdir(path) | ||
| try: | ||
| yield | ||
| finally: | ||
| os.chdir(old_cwd) | ||
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| def list_filesystems(): | ||
| output = json.loads(subprocess.check_output(["lsblk", "--json", "--paths", "--list", "--noheadings", | ||
| "--output", "NAME,FSTYPE,UUID,MOUNTPOINTS"])) | ||
| filesystems = {} | ||
| for b in output['blockdevices']: | ||
| if b['fstype'] == "btrfs": | ||
| uuid = b['uuid'] | ||
| mps = list(filter(lambda x: x is not None and not x.startswith(TMP_MP_DIR), b['mountpoints'])) | ||
| has_tmp_mp = len(mps) < len(b['mountpoints']) | ||
| if uuid not in filesystems: | ||
| filesystems[uuid] = { | ||
| 'uuid': uuid, | ||
| 'devices': [b['name']], | ||
| 'mountpoints': mps, | ||
| 'has_tmp_mountpoint': has_tmp_mp | ||
| } | ||
| else: | ||
| filesystems[uuid]['devices'] += [b['name']] | ||
| filesystems[uuid]['mountpoints'] += mps | ||
| filesystems[uuid]['has_tmp_mountpoint'] = filesystems[uuid]['has_tmp_mountpoint'] or has_tmp_mp | ||
| return filesystems | ||
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| tmp_mountpoints = set() | ||
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| def add_tmp_mountpoint(db, fs, dev, opt_repair): | ||
| global tmp_mountpoints | ||
| uuid = fs['uuid'] | ||
| if uuid not in tmp_mountpoints: | ||
| debug(f"ADDING {uuid}") | ||
| tmp_mountpoints.add(uuid) | ||
| if uuid in db and db[uuid] > 0: | ||
| db[uuid] += 1 | ||
| else: | ||
| db[uuid] = 1 | ||
| if not fs['has_tmp_mountpoint'] and (db[uuid] == 1 or opt_repair): | ||
| path = TMP_MP_DIR + "/" + uuid | ||
| debug(f"MOUNTING {path}") | ||
| os.makedirs(path, exist_ok=True) | ||
| subprocess.check_call(["mount", dev, path]) | ||
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| def remove_tmp_mountpoint(db, uuid): | ||
| global tmp_mountpoints | ||
| if uuid in tmp_mountpoints: | ||
| debug(f"REMOVING {uuid}") | ||
| tmp_mountpoints.remove(uuid) | ||
| if db[uuid] == 1: | ||
| path = TMP_MP_DIR + "/" + uuid | ||
| try: | ||
| debug(f"UNMOUNTING {path}") | ||
| subprocess.check_call(["umount", path]) | ||
| subprocess.check_call(["rmdir", path]) | ||
| except Exception as err: | ||
| sys.stderr.write(f"Failed to unmount {path}: {err}\n") | ||
| del db[uuid] | ||
| else: | ||
| db[uuid] -= 1 | ||
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| def remove_all_tmp_mountpoints(): | ||
| with mount_database() as db: | ||
| for mp in set(tmp_mountpoints): | ||
| remove_tmp_mountpoint(db, mp) | ||
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| def force_mount_point(db, fs, opt_repair): | ||
| add_tmp_mountpoint(db, fs, fs['devices'][0], opt_repair) | ||
| return TMP_MP_DIR + "/" + fs['uuid'] | ||
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| def get_mount_point(db, fs, opt_mount, opt_repair): | ||
| if len(fs['mountpoints']) > 0: | ||
| remove_tmp_mountpoint(db, fs['uuid']) | ||
| return fs['mountpoints'][0] | ||
| elif opt_mount: | ||
| return force_mount_point(db, fs, opt_repair) | ||
| else: | ||
| return None | ||
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| def get_subvolume_info(mp): | ||
| lines = subprocess.check_output(["btrfs", "subvolume", "list", "-apuq", mp]).splitlines() | ||
| subvols = [] | ||
| for line in lines: | ||
| match = re.match(b"ID (\\d+).*parent (\\d+).*parent_uuid (.*)uuid (.*) path (<FS_TREE>/)?(.*)", line) | ||
| if match: | ||
| pathname = match[6].decode(errors='replace'), | ||
| # Ignore podman btrfs subvolumes, they are an implementation detail. | ||
| if not "containers/storage/btrfs/subvolumes" in pathname: | ||
| subvols += [ | ||
| { | ||
| 'pathname': pathname, | ||
| 'id': int(match[1]), | ||
| 'parent': int(match[2]), | ||
| 'uuid': match[4].decode(), | ||
| 'parent_uuid': None if match[3][0] == ord("-") else match[3].decode().strip() | ||
| } | ||
| ] | ||
| return subvols | ||
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| def get_default_subvolume(mp): | ||
| output = subprocess.check_output(["btrfs", "subvolume", "get-default", mp]) | ||
| match = re.match(b"ID (\\d+).*", output) | ||
| if match: | ||
| return int(match[1]) | ||
| else: | ||
| return None | ||
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| def get_usages(uuid): | ||
| output = subprocess.check_output(["btrfs", "filesystem", "show", "--raw", uuid]) | ||
| usages = {} | ||
| for line in output.splitlines(): | ||
| match = re.match(b".*used\\s+(\\d+)\\s+path\\s+([\\w/]+).*", line) | ||
| if match: | ||
| usages[match[2].decode()] = int(match[1]) | ||
| return usages | ||
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| def poll(opt_mount, opt_repair): | ||
| debug(f"POLL mount {opt_mount} repair {opt_repair}") | ||
| with mount_database() as db: | ||
| filesystems = list_filesystems() | ||
| info = {} | ||
| for fs in filesystems.values(): | ||
| mp = get_mount_point(db, fs, opt_mount, opt_repair) | ||
| if mp: | ||
| try: | ||
| info[fs['uuid']] = { | ||
| 'subvolumes': get_subvolume_info(mp), | ||
| 'default_subvolume': get_default_subvolume(mp), | ||
| 'usages': get_usages(fs['uuid']), | ||
| } | ||
| except Exception as err: | ||
| info[fs['uuid']] = {'error': str(err)} | ||
| return info | ||
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| def cmd_monitor(opt_mount): | ||
| old_infos = poll(opt_mount, opt_repair=False) | ||
| sys.stdout.write(json.dumps(old_infos) + "\n") | ||
| sys.stdout.flush() | ||
| while True: | ||
| time.sleep(5.0) | ||
| new_infos = poll(opt_mount, opt_repair=False) | ||
| if new_infos != old_infos: | ||
| sys.stdout.write(json.dumps(new_infos) + "\n") | ||
| sys.stdout.flush() | ||
| old_infos = new_infos | ||
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| def cmd_poll(opt_mount): | ||
| infos = poll(opt_mount, opt_repair=True) | ||
| sys.stdout.write(json.dumps(infos) + "\n") | ||
| sys.stdout.flush() | ||
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| def cmd_do(uuid, cmd): | ||
| debug(f"DO {uuid} {cmd}") | ||
| with mount_database() as db: | ||
| filesystems = list_filesystems() | ||
| for fs in filesystems.values(): | ||
| if fs['uuid'] == uuid: | ||
| mp = force_mount_point(db, fs, opt_repair=True) | ||
| with context_chdir(mp): | ||
| subprocess.check_call(cmd) | ||
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| def cmd(args): | ||
| if len(args) > 1: | ||
| if args[1] == "poll": | ||
| cmd_poll(len(args) > 2) | ||
| elif args[1] == "monitor": | ||
| cmd_monitor(len(args) > 2) | ||
| elif args[1] == "do": | ||
| cmd_do(args[2], args[3:]) | ||
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| def main(args): | ||
| signal.signal(signal.SIGTERM, lambda _signo, _stack: sys.exit(0)) | ||
| try: | ||
| cmd(args) | ||
| except Exception as err: | ||
| sys.stderr.write(str(err) + "\n") | ||
| sys.exit(1) | ||
| finally: | ||
| remove_all_tmp_mountpoints() | ||
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| main(sys.argv) |
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