Jim Paris
c5f079f61f
Requires fallocate(2) support with FALLOC_FL_PUNCH_HOLE, as well as a filesystem that supports it (in Linux 3.7, tmpfs, btrfs, xfs, or ext4)
50 lines
1.5 KiB
Python
50 lines
1.5 KiB
Python
# Implementation of hole punching via fallocate, if the OS
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# and filesystem support it.
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try:
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import os
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import ctypes
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import ctypes.util
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def make_fallocate():
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libc_name = ctypes.util.find_library('c')
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libc = ctypes.CDLL(libc_name, use_errno=True)
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_fallocate = libc.fallocate
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_fallocate.restype = ctypes.c_int
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_fallocate.argtypes = [ ctypes.c_int, ctypes.c_int,
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ctypes.c_int64, ctypes.c_int64 ]
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del libc
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del libc_name
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def fallocate(fd, mode, offset, len_):
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res = _fallocate(fd, mode, offset, len_)
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if res != 0: # pragma: no cover
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errno = ctypes.get_errno()
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raise IOError(errno, os.strerror(errno))
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return fallocate
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fallocate = make_fallocate()
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del make_fallocate
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except Exception: # pragma: no cover
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fallocate = None
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FALLOC_FL_KEEP_SIZE = 0x01
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FALLOC_FL_PUNCH_HOLE = 0x02
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def punch_hole(filename, offset, length, ignore_errors = True):
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"""Punch a hole in the file. This isn't well supported, so errors
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are ignored by default."""
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try:
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if fallocate is None: # pragma: no cover
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raise IOError("fallocate not available")
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with open(filename, "r+") as f:
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fallocate(f.fileno(),
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FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE,
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offset, length)
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except IOError: # pragma: no cover
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if ignore_errors:
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return
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raise
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