773edb4a5d
Linux 3.11 introduced O_TMPFILE as a flag to open() sys call. This would enable users to get a fd to an unnamed temporary file. As it's unnamed, it does not require the caller to devise unique names. It is also not accessible through any path. Hence, file creation is race-free. This file is initially unreachable. It is then populated with data(write), metadata(fsetxattr) and fsync'd before being atomically linked into the filesystem in a fully formed state using linkat() sys call. Only after a successful linkat() will the object file will be available for reference. Caveats * Unlike os.rename(), linkat() cannot overwrite destination path if it already exists. If path exists, we unlink and try again. * XFS support for O_TMPFILE was only added in Linux 3.15. * If client disconnects during object upload, although there is no incomplete/stale file on disk, the object directory would persist and is not cleaned up immediately. Change-Id: I8402439fab3aba5d7af449b5e465f89332f606ec Signed-off-by: Prashanth Pai <ppai@redhat.com>
77 lines
2.1 KiB
Python
77 lines
2.1 KiB
Python
# Copyright (c) 2016 OpenStack Foundation
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
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# implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import os
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import ctypes
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from ctypes.util import find_library
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__all__ = ['linkat']
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class Linkat(object):
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# From include/uapi/linux/fcntl.h
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AT_FDCWD = -100
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AT_SYMLINK_FOLLOW = 0x400
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__slots__ = '_c_linkat'
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def __init__(self):
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libc = ctypes.CDLL(find_library('c'), use_errno=True)
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try:
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c_linkat = libc.linkat
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except AttributeError:
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self._c_linkat = None
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return
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c_linkat.argtypes = [ctypes.c_int, ctypes.c_char_p,
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ctypes.c_int, ctypes.c_char_p,
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ctypes.c_int]
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c_linkat.restype = ctypes.c_int
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def errcheck(result, func, arguments):
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if result == -1:
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errno = ctypes.set_errno(0)
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raise IOError(errno, 'linkat: %s' % os.strerror(errno))
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else:
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return result
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c_linkat.errcheck = errcheck
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self._c_linkat = c_linkat
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@property
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def available(self):
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return self._c_linkat is not None
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def __call__(self, olddirfd, oldpath, newdirfd, newpath, flags):
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"""
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linkat() creates a new link (also known as a hard link)
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to an existing file.
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See `man 2 linkat` for more info.
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"""
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if not self.available:
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raise EnvironmentError('linkat not available')
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if not isinstance(olddirfd, int) or not isinstance(newdirfd, int):
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raise TypeError("fd must be an integer.")
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return self._c_linkat(olddirfd, oldpath, newdirfd, newpath, flags)
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linkat = Linkat()
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del Linkat
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