# _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]))
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