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v0.5.1
v0.5.1
https://github.com/python/cpython
Tip revision: 74f4bd53e03ded8408bcc2de67cf0f5a4ac5b1a1 authored by Barry Warsaw on 23 February 2012, 15:59:38 UTC
Bump some more copyright years (as per PEP 101), since this is the first
Bump some more copyright years (as per PEP 101), since this is the first
Tip revision: 74f4bd5
_emx_link.py
# _emx_link.py
# Written by Andrew I MacIntyre, December 2002.
"""_emx_link.py is a simplistic emulation of the Unix link(2) library routine
for creating so-called hard links. It is intended to be imported into
the os module in place of the unimplemented (on OS/2) Posix link()
function (os.link()).
We do this on OS/2 by implementing a file copy, with link(2) semantics:-
- the target cannot already exist;
- we hope that the actual file open (if successful) is actually
atomic...
Limitations of this approach/implementation include:-
- no support for correct link counts (EMX stat(target).st_nlink
is always 1);
- thread safety undefined;
- default file permissions (r+w) used, can't be over-ridden;
- implemented in Python so comparatively slow, especially for large
source files;
- need sufficient free disk space to store the copy.
Behaviour:-
- any exception should propagate to the caller;
- want target to be an exact copy of the source, so use binary mode;
- returns None, same as os.link() which is implemented in posixmodule.c;
- target removed in the event of a failure where possible;
- given the motivation to write this emulation came from trying to
support a Unix resource lock implementation, where minimal overhead
during creation of the target is desirable and the files are small,
we read a source block before attempting to create the target so that
we're ready to immediately write some data into it.
"""
import os
import errno
__all__ = ['link']
def link(source, target):
"""link(source, target) -> None
Attempt to hard link the source file to the target file name.
On OS/2, this creates a complete copy of the source file.
"""
s = os.open(source, os.O_RDONLY | os.O_BINARY)
if os.isatty(s):
raise OSError, (errno.EXDEV, 'Cross-device link')
data = os.read(s, 1024)
try:
t = os.open(target, os.O_WRONLY | os.O_BINARY | os.O_CREAT | os.O_EXCL)
except OSError:
os.close(s)
raise
try:
while data:
os.write(t, data)
data = os.read(s, 1024)
except OSError:
os.close(s)
os.close(t)
os.unlink(target)
raise
os.close(s)
os.close(t)
if __name__ == '__main__':
import sys
try:
link(sys.argv[1], sys.argv[2])
except IndexError:
print 'Usage: emx_link <source> <target>'
except OSError:
print 'emx_link: %s' % str(sys.exc_info()[1])