CasperSecurity
# -*- test-case-name: twisted.internet.test.test_inotify -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
Very low-level ctypes-based interface to Linux inotify(7).
ctypes and a version of libc which supports inotify system calls are
required.
"""
import ctypes
import ctypes.util
from typing import cast
from twisted.python.filepath import FilePath
class INotifyError(Exception):
"""
Unify all the possible exceptions that can be raised by the INotify API.
"""
def init() -> int:
"""
Create an inotify instance and return the associated file descriptor.
"""
fd = cast(int, libc.inotify_init())
if fd < 0:
raise INotifyError("INotify initialization error.")
return fd
def add(fd: int, path: FilePath, mask: int) -> int:
"""
Add a watch for the given path to the inotify file descriptor, and return
the watch descriptor.
@param fd: The file descriptor returned by C{libc.inotify_init}.
@param path: The path to watch via inotify.
@param mask: Bitmask specifying the events that inotify should monitor.
"""
wd = cast(int, libc.inotify_add_watch(fd, path.asBytesMode().path, mask))
if wd < 0:
raise INotifyError(f"Failed to add watch on '{path!r}' - ({wd!r})")
return wd
def remove(fd: int, wd: int) -> None:
"""
Remove the given watch descriptor from the inotify file descriptor.
"""
# When inotify_rm_watch returns -1 there's an error:
# The errno for this call can be either one of the following:
# EBADF: fd is not a valid file descriptor.
# EINVAL: The watch descriptor wd is not valid; or fd is
# not an inotify file descriptor.
#
# if we can't access the errno here we cannot even raise
# an exception and we need to ignore the problem, one of
# the most common cases is when you remove a directory from
# the filesystem and that directory is observed. When inotify
# tries to call inotify_rm_watch with a non existing directory
# either of the 2 errors might come up because the files inside
# it might have events generated way before they were handled.
# Unfortunately only ctypes in Python 2.6 supports accessing errno:
# http://bugs.python.org/issue1798 and in order to solve
# the problem for previous versions we need to introduce
# code that is quite complex:
# http://stackoverflow.com/questions/661017/access-to-errno-from-python
#
# See #4310 for future resolution of this issue.
libc.inotify_rm_watch(fd, wd)
def initializeModule(libc: ctypes.CDLL) -> None:
"""
Initialize the module, checking if the expected APIs exist and setting the
argtypes and restype for C{inotify_init}, C{inotify_add_watch}, and
C{inotify_rm_watch}.
"""
for function in ("inotify_add_watch", "inotify_init", "inotify_rm_watch"):
if getattr(libc, function, None) is None:
raise ImportError("libc6 2.4 or higher needed")
libc.inotify_init.argtypes = []
libc.inotify_init.restype = ctypes.c_int
libc.inotify_rm_watch.argtypes = [ctypes.c_int, ctypes.c_int]
libc.inotify_rm_watch.restype = ctypes.c_int
libc.inotify_add_watch.argtypes = [ctypes.c_int, ctypes.c_char_p, ctypes.c_uint32]
libc.inotify_add_watch.restype = ctypes.c_int
name = ctypes.util.find_library("c")
if not name:
raise ImportError("Can't find C library.")
libc = ctypes.cdll.LoadLibrary(name)
initializeModule(libc)