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f20929c23f
- master.cf: Enable SMTPS - lock.Mutex: check the return value of lock.acquire - Write debug logs
85 lines
2.6 KiB
Python
85 lines
2.6 KiB
Python
# SPDX-License-Identifier: AGPL-3.0-or-later
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import contextlib
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import errno
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import fcntl
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import logging
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import os
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import pwd
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import threading
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import time
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logger = logging.getLogger(__name__)
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class Mutex:
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"""File and pthread lock based resource mutex"""
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def __init__(self, lock_file):
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self.thread_mutex = threading.Lock()
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self.lock_path = '/var/lock/' + lock_file
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@contextlib.contextmanager
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def lock_threads_only(self):
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"""Acquire the thread lock but not the file lock"""
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if not self.thread_mutex.acquire(timeout=5):
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raise RuntimeError('Could not acquire thread lock')
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try:
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yield
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finally:
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self.thread_mutex.release()
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@contextlib.contextmanager
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def lock_all(self):
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"""Acquire both the thread lock and the file lock"""
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with self.lock_threads_only():
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# Set up
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fd = self._open_lock_file()
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fcntl.lockf(fd, fcntl.LOCK_EX)
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self._chmod_and_chown(fd)
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# Enter context
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try:
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yield
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finally:
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# Clean up
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fcntl.lockf(fd, fcntl.LOCK_UN)
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fd.close()
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def _open_lock_file(self):
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"""Attempt to open lock file for R&W. Raises OSError on failure"""
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attempts = 10
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errno = -1
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fd = None
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# Simulate a spin lock
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while attempts > 0:
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errno, fd = self._try(lambda: open(self.lock_path, 'wb'))
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if errno == 0:
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return fd
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else:
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attempts -= 1
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time.sleep(0.25)
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raise OSError(errno, os.strerror(errno))
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def _chmod_and_chown(self, fd):
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"""If the process UID is root, set fd's mode and ownership to
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appropriate values. If we are not root, only set the mode"""
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if os.getuid() == 0:
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user_info = pwd.getpwnam('plinth')
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os.fchown(fd.fileno(), 0, 0)
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os.fchmod(fd.fileno(), 0o660) # rw-rw----
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fd.truncate(0)
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os.fchown(fd.fileno(), user_info.pw_uid, user_info.pw_gid)
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else:
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errno, _ = self._try(lambda: os.fchmod(fd.fileno(), 0o660))
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if errno != 0:
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logger.warning('chmod failed, lock path %s, errno %d',
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self.lock_path, errno)
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def _try(self, function):
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try:
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return 0, function()
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except OSError as error:
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if error.errno in (errno.EACCES, errno.EPERM):
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return error.errno, None
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else:
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raise
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