ProxMenux/AppImage/scripts/lvm_device_scope.py

# ==========================================================
# ProxMenux Monitor - LVM disk read scope
# Author      : Jonatan
# GitHub      : github.com/jcastro
# Maintainer  : MacRimi
# Copyright   : (c) 2026 MacRimi & contributors
# License     : (GPL-3.0) (https://github.com/MacRimi/ProxMenux/blob/main/LICENSE)
# Version     : 1.0
# Last Updated: 16/10/2026
# ==========================================================
# Description:
# Applies the automatic disk-read policy to LVM metadata scans in both
# Monitor readers. Excluded and idle disks receive no power-mode probe;
# every device built on them is excluded too, and the scan's own reads
# are not taken as activity. No eligible devices means no scan.
# ==========================================================

import json
import re
import subprocess
import threading

_NAME = re.compile(r"[A-Za-z0-9._+-]+")
_scan_lock = threading.Lock()
_scanned_disks = set()


def _topology():
    """Every block device by kernel name: its type, its parents and whether
    it is an LVM physical volume. lsblk reads this from udev, not the disks.
    A RAID or multipath device appears once per member."""
    result = subprocess.run(["lsblk", "-J", "-l", "-o", "KNAME,TYPE,PKNAME,FSTYPE"],
                            capture_output=True, text=True, timeout=5)
    if result.returncode:
        return None
    types, parents, volumes = {}, {}, set()
    for device in json.loads(result.stdout).get("blockdevices") or []:
        name, parent = device.get("kname"), device.get("pkname")
        if not isinstance(name, str) or not _NAME.fullmatch(name):
            return None
        types[name] = device.get("type")
        parents.setdefault(name, set())
        if parent is not None:
            if not isinstance(parent, str) or not _NAME.fullmatch(parent):
                return None
            parents[name].add(parent)
        if device.get("fstype") == "LVM2_member" and device.get("type") != "lvm":
            volumes.add(name)
    return types, parents, volumes


def _disks_under(name, parents, seen=None):
    """The disks a device is built on: itself, or its parents' disks."""
    seen = seen if seen is not None else set()
    if name in seen:
        return set()
    seen.add(name)
    if not parents.get(name):
        return {name}
    found = set()
    for parent in parents[name]:
        found |= _disks_under(parent, parents, seen)
    return found


def lvm_device_args(standby_check):
    """Return [] for an unrestricted scan, --devices args, or None to skip.

    A failed inventory must never fall back to an unrestricted scan. None
    is distinct from []: if every disk is excluded/idle/asleep, callers
    must not start pvs/lvs/vgs at all.
    """
    try:
        from disk_temperature_history import disk_read_policy, excluded_disk_names
        topology = _topology()
        if topology is None:
            return None
        types, parents, volumes = topology
        disks = {name for name, kind in types.items() if kind == "disk"}
        if not disks:
            return None
        excluded = excluded_disk_names()
        blocked = set()
        for disk in sorted(disks):
            # Test policy first: even CHECK POWER MODE is forbidden for an
            # excluded/idle disk. Some USB bridges do not honour -n standby.
            if disk_read_policy(disk, excluded) != "read" or standby_check(disk):
                blocked.add(disk)
        allowed = sorted(f"/dev/{name}" for name in volumes if not (_disks_under(name, parents) & blocked))
        with _scan_lock:
            _scanned_disks.clear()
            _scanned_disks.update(disks - blocked)
        if not blocked:
            return []
        # An explicit list makes LVM open every device in it, so only the
        # physical volumes are named: a RAID, multipath or encrypted volume
        # built on a blocked disk would read that disk too and stays out.
        if not allowed:
            return None
        return ["--devices", ",".join(allowed)]
    except Exception:
        # Unavailable exclusions, topology or policy are not permission to
        # open devices that may have been deliberately excluded.
        return None


def settle_scan_reads():
    """The LVM scan reads the disks it is allowed to. Those reads are its
    own, so they must not make an unused disk look busy at the next check."""
    try:
        from disk_temperature_history import settle_own_reads
        with _scan_lock:
            disks = set(_scanned_disks)
        settle_own_reads(disks)
    except Exception:
        pass