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