chore(release): v0.1.2

Reviewed-on: #4

README.md

@@ -63,9 +63,14 @@ Everything written into the mirror is made group-readable, and its directories
 group-traversable, so the mirror can be read back by whatever serves it. Neither
 writer does that unaided: the temporary file an encode renames into place is
 created `0600` regardless of the umask, and a straight copy of an existing MP3
-inherits the mode of a source file in a library this tool does not own. Only the
+inherits the mode of a source file in a library this tool does not own.
-group bits are touched; whether the mirror is world-readable stays with the
+
-umask, as does the ownership.
+Directories are handled by clearing the owner and group read/execute bits from
+the process umask, once, at startup. Owner as well as group, because a umask
+carrying `0400` produces directories of mode `0300` — writable and enterable,
+unreadable to the very run that created them. The `other` bits are left where
+the umask puts them: whether the mirror is world-readable is a genuine policy
+question, and so is its ownership.
 
 Mirror files written before this existed are topped up on the next pass. Their
 mtimes are correct, so nothing else would revisit them — and they are not
@@ -94,6 +99,20 @@ music-mirror --source /music --mirror /music-mp3 --subdir "Artist/Album"
 `--subdir` never prunes: a partial pass cannot tell an orphan from a file
 outside its own scope.
 
+### Concurrency
+
+LAME is single-threaded — ffmpeg reports `Threading capabilities: none` for
+`libmp3lame` — so throughput comes entirely from running several encoders at
+once, one process per file. `--jobs` defaults to the CPUs the process may
+actually use, which inside a container means the `cpus:` allowance rather than
+the host's core count. Each pass logs the number it settled on.
+
+As a rough guide, a Zen 3 core encodes about 40–60× realtime at V0 depending on
+clock, so six cores clear roughly 250 hours of audio per hour of wall clock.
+The first full pass is the expensive one; after that only new and changed files
+are touched. Lower `MUSIC_MIRROR_JOBS` if you would rather the NAS stayed
+responsive than finished sooner.
+
 Requires `ffmpeg` and `ffprobe` on `PATH`. The container image provides both.
 
 ## Running it on TrueNAS Scale

music_mirror.py

@@ -16,6 +16,7 @@ makes runs idempotent without a database to keep in step.
 import argparse
 import concurrent.futures
 import fcntl
+import functools
 import logging
 import os
 import re
@@ -83,7 +84,12 @@ MTIME_TOLERANCE_SECONDS = 2
 # that may be tighter still. Directories need the execute bit too, or the group
 # cannot enter them to reach the readable files inside.
 GROUP_READ = 0o040
-GROUP_ENTER = 0o050
+
+# Cleared from the umask so directories this run creates can be listed and
+# entered. Owner as well as group: a umask carrying 0400 -- which is unusual but
+# not ours to assume away -- otherwise produces a mirror tree that not even the
+# process that built it can read back.
+DIRECTORY_ACCESS = 0o550
 
 
 @dataclass
@@ -139,8 +145,13 @@ def make_group_readable(path):
         path.chmod(mode | GROUP_READ)
 
 
+@functools.lru_cache(maxsize=4096)
 def find_cover(directory):
-    """Return an external cover image for a directory, if one is present."""
+    """Return an external cover image for a directory, if one is present.
+
+    Cached because an album's tracks all ask the same question, and the answer
+    costs one stat per candidate name.
+    """
     for name in COVER_NAMES:
         candidate = directory / name
         if candidate.is_file():
@@ -217,7 +228,12 @@ def encode(source, mirror, quality_args, dry_run):
         return Result("encoded", mirror)
 
     mirror.parent.mkdir(parents=True, exist_ok=True)
-    cover = None if has_embedded_picture(source) else find_cover(source.parent)
+    # Probing costs an ffprobe process per file, so only ask when the answer
+    # can change the command. With no cover file beside the track, `-map
+    # 0:v:0?` carries embedded art if there is any and shrugs if there is not.
+    cover = find_cover(source.parent)
+    if cover is not None and has_embedded_picture(source):
+        cover = None
 
     # Read the source's mtime before encoding, not after. If the file is still
     # being written -- a Lidarr import landing mid-pass -- stamping the mirror
@@ -373,6 +389,7 @@ def run_once(scan_root, source_root, mirror_root, quality_args, jobs, dry_run, d
     computed against; they differ only for a partial pass over one directory.
     """
     started = time.monotonic()
+    logger.info("pass starting with %d concurrent encoders", jobs)
     counts = {"encoded": 0, "copied": 0, "skipped": 0, "failed": 0}
     failures = []
 
@@ -418,6 +435,25 @@ def acquire_lock(mirror_root):
     return handle
 
 
+def default_jobs():
+    """Return the number of CPUs this process may actually use.
+
+    os.cpu_count() reports the host's total, which in a container with a `cpus:`
+    limit means starting several times more encoders than there is CPU to run
+    them. libmp3lame is single-threaded, so one process per available CPU is the
+    whole of the concurrency story.
+    """
+    try:
+        quota, period = Path("/sys/fs/cgroup/cpu.max").read_text().split()
+        if quota != "max":
+            return max(1, round(int(quota) / int(period)))
+    except (OSError, ValueError):
+        pass
+    if hasattr(os, "process_cpu_count"):  # 3.13+, respects CPU affinity
+        return os.process_cpu_count() or 4
+    return os.cpu_count() or 4
+
+
 def build_parser():
     """Return the argument parser. Every option also reads an env var, so the
     container can be configured without a command line."""
@@ -443,8 +479,8 @@ def build_parser():
     parser.add_argument(
         "--jobs",
         type=int,
-        default=int(os.getenv("MUSIC_MIRROR_JOBS", "0")) or (os.cpu_count() or 4),
+        default=int(os.getenv("MUSIC_MIRROR_JOBS", "0")) or default_jobs(),
-        help="concurrent encodes (env MUSIC_MIRROR_JOBS; default: CPU count)",
+        help="concurrent encodes (env MUSIC_MIRROR_JOBS; default: available CPUs)",
     )
     parser.add_argument(
         "--interval",
@@ -474,12 +510,14 @@ def main(argv=None):
     logging.basicConfig(format="%(asctime)s %(levelname)s %(message)s", level=logging.INFO)
     args = build_parser().parse_args(argv)
 
-    # Directories are created with 0o777 masked by the umask, so clear the group
+    # Directories are created with 0o777 masked by the umask, so clear the bits
-    # bits from it once here rather than chmod'ing every directory the walk
+    # that matter from it once here rather than chmod'ing every directory the
-    # creates. Files cannot be handled this way -- mkstemp and copy2 both set a
+    # walk creates. The `other` bits are left alone, since whether the mirror is
-    # mode outright -- so they get an explicit chmod instead.
+    # world-readable is a real policy question; owner and group access is not.
+    # Files cannot be handled this way -- mkstemp and copy2 both set a mode
+    # outright, ignoring the umask -- so they get an explicit chmod instead.
     inherited = os.umask(0o077)
-    os.umask(inherited & ~GROUP_ENTER)
+    os.umask(inherited & ~DIRECTORY_ACCESS)
 
     if not args.source or not args.mirror:
         logger.error("both --source and --mirror are required")

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "music-mirror"
-version = "0.1.0"
+version = "0.1.2"
 description = "Maintain a lossy MP3 mirror of a lossless music library"
 readme = "README.md"
 requires-python = ">=3.11"

tests/conftest.py

@@ -27,6 +27,21 @@ def tight_umask():
     os.umask(previous)
 
 
+@pytest.fixture
+def owner_hostile_umask():
+    """Return a callable applying a umask that masks off the owner's read bit.
+
+    Unusual, but it is what produces a mirror tree of mode 0300 -- writable and
+    enterable, unreadable to the very process that built it. Applied on demand
+    rather than for the whole test, because the source library is built by
+    something else entirely and the same umask would make the test's own
+    fixtures unreadable before the run under test even started.
+    """
+    previous = os.umask(0o022)
+    yield lambda: os.umask(0o477)
+    os.umask(previous)
+
+
 @pytest.fixture
 def make_flac():
     """Return a factory writing a short tagged FLAC file."""

tests/test_music_mirror.py

@@ -222,6 +222,27 @@ def test_mirror_directories_are_group_traversable(tmp_path, make_flac, tight_uma
         assert mode & stat.S_IXGRP, directory
 
 
+def test_mirror_directories_survive_an_owner_hostile_umask(
+    tmp_path, make_flac, owner_hostile_umask
+):
+    """A umask carrying 0400 otherwise builds a tree the run cannot read back."""
+    source = tmp_path / "src"
+    mirror = tmp_path / "dst"
+    make_flac(source / "Artist" / "Album" / "a.flac")
+
+    # Applied only now: the library already exists, and the umask under test is
+    # the one the container starts this run with.
+    owner_hostile_umask()
+    run(source, mirror)
+
+    for directory in (mirror, mirror / "Artist", mirror / "Artist" / "Album"):
+        mode = directory.stat().st_mode
+        assert mode & stat.S_IRUSR, directory
+        assert mode & stat.S_IXUSR, directory
+        assert mode & stat.S_IRGRP, directory
+        assert mode & stat.S_IXGRP, directory
+
+
 def test_private_mirror_file_is_repaired_without_re_encoding(tmp_path, make_flac):
     """A mirror written by an older version has a correct mtime, so nothing
     else in the pass would revisit it."""