80 lines
2.4 KiB
Python
80 lines
2.4 KiB
Python
|
# _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])
|