from __future__ import with_statement import json from invirt.common import * import os from os import rename from os.path import getmtime from contextlib import closing import yaml import re try: loader = yaml.CSafeLoader except: loader = yaml.SafeLoader src_path = '/etc/invirt/master.yaml' src_dirpath = '/etc/invirt/conf.d' cache_path = '/var/lib/invirt/cache.json' lock_path = '/var/lib/invirt/cache.lock' def augment(d1, d2): """Splice dict-tree d2 into d1. Return d1. Example: >>> d = {'a': {'b': 1}, 'c': 2} >>> augment(d, {'a': {'d': 3}}) {'a': {'b', 1, 'd': 3}, 'c': 2} >>> d {'a': {'b', 1, 'd': 3}, 'c': 2} """ for k in d2: if k in d1 and isinstance(d1[k], dict): augment(d1[k], d2[k]) else: d1[k] = d2[k] return d1 def run_parts_list(dirname): """Reimplements Debian's run-parts --list. One difference from run-parts's behavior: run-parts --list /foo/ will give output like /foo//bar, because Python code tends to expect this. Matches documented behavior of run-parts in debianutils v2.28.2, dated 2007. """ # From run-parts(8). lanana_re = re.compile('^[a-z0-9]+$') lsb_re = re.compile('^_?([a-z0-9_.]+-)+[a-z0-9]+$') deb_cron_re = re.compile('^[a-z0-9][a-z0-9-]*$') for name in os.listdir(dirname): if lanana_re.match(name) or lsb_re.match(name) or deb_cron_re.match(name): yield os.path.join(dirname, name) def list_files(): yield src_path for name in run_parts_list(src_dirpath): yield name def load_master(): config = dict() for filename in list_files(): with closing(file(filename)) as f: augment(config, yaml.load(f, loader)) return config def get_src_mtime(): return max(max(getmtime(filename) for filename in list_files()), getmtime(src_dirpath)) def load(force_refresh = False): """ Try loading the configuration from the faster-to-load JSON cache at cache_path. If it doesn't exist or is outdated, load the configuration instead from the original YAML file at src_path and regenerate the cache. I assume I have the permissions to write to the cache directory. """ # Namespace container for state variables, so that they can be updated by # closures. ns = struct() if force_refresh: do_refresh = True else: src_mtime = get_src_mtime() try: cache_mtime = getmtime(cache_path) except OSError: do_refresh = True else: do_refresh = src_mtime + 1 >= cache_mtime # We chose not to simply say # # do_refresh = src_mtime >= cache_time # # because between the getmtime(src_path) and the time the cache is # rewritten, the master configuration may have been updated, so future # checks here would find a cache with a newer mtime than the master # (and thus treat the cache as containing the latest version of the # master). The +1 means that for at least a full second following the # update to the master, this function will refresh the cache, giving us # 1 second to write the cache. Note that if it takes longer than 1 # second to write the cache, then this situation could still arise. # # The getmtime calls should logically be part of the same transaction # as the rest of this function (cache read + conditional cache # refresh), but to wrap everything in an flock would cause the # following cache read to be less streamlined. if not do_refresh: # Try reading from the cache first. This must be transactionally # isolated from concurrent writes to prevent reading an incomplete # (changing) version of the data (but the transaction can share the # lock with other concurrent reads). This isolation is accomplished # using an atomic filesystem rename in the refreshing stage. try: with closing(file(cache_path)) as f: ns.cfg = json.read(f.read()) except: do_refresh = True if do_refresh: # Atomically reload the source and regenerate the cache. The read and # write must be a single transaction, or a stale version may be # written (if another read/write of a more recent configuration # is interleaved). The final atomic rename is to keep this # transactionally isolated from the above cache read. If we fail to # acquire the lock, just try to load the master configuration. try: with lock_file(lock_path): ns.cfg = load_master() try: with closing(file(cache_path + '.tmp', 'w')) as f: f.write(json.write(ns.cfg)) except: pass # silent failure else: rename(cache_path + '.tmp', cache_path) except IOError: ns.cfg = load_master() return ns.cfg dicts = load() structs = dicts2struct(dicts) # vim:et:sw=4:ts=4