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eb477f05cf
implement its locking scheme, this module implements a crude link() by way of copying the source to the destination provided the destination doesn't already exist.
79 lines
2.4 KiB
Python
79 lines
2.4 KiB
Python
# _emx_link.py
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# Written by Andrew I MacIntyre, December 2002.
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"""_emx_link.py is a simplistic emulation of the Unix link(2) library routine
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for creating so-called hard links. It is intended to be imported into
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the os module in place of the unimplemented (on OS/2) Posix link()
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function (os.link()).
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We do this on OS/2 by implementing a file copy, with link(2) semantics:-
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- the target cannot already exist;
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- we hope that the actual file open (if successful) is actually
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atomic...
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Limitations of this approach/implementation include:-
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- no support for correct link counts (EMX stat(target).st_nlink
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is always 1);
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- thread safety undefined;
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- default file permissions (r+w) used, can't be over-ridden;
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- implemented in Python so comparatively slow, especially for large
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source files;
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- need sufficient free disk space to store the copy.
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Behaviour:-
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- any exception should propagate to the caller;
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- want target to be an exact copy of the source, so use binary mode;
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- returns None, same as os.link() which is implemented in posixmodule.c;
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- target removed in the event of a failure where possible;
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- given the motivation to write this emulation came from trying to
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support a Unix resource lock implementation, where minimal overhead
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during creation of the target is desirable and the files are small,
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we read a source block before attempting to create the target so that
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we're ready to immediately write some data into it.
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"""
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import os
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import errno
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__all__ = ['link']
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def link(source, target):
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"""link(source, target) -> None
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Attempt to hard link the source file to the target file name.
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On OS/2, this creates a complete copy of the source file.
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"""
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s = os.open(source, os.O_RDONLY | os.O_BINARY)
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if os.isatty(s):
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raise OSError, (errno.EXDEV, 'Cross-device link')
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data = os.read(s, 1024)
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try:
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t = os.open(target, os.O_WRONLY | os.O_BINARY | os.O_CREAT | os.O_EXCL)
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except OSError:
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os.close(s)
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raise
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try:
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while data:
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os.write(t, data)
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data = os.read(s, 1024)
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except OSError:
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os.close(s)
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os.close(t)
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os.unlink(target)
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raise
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os.close(s)
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os.close(t)
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if __name__ == '__main__':
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import sys
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try:
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link(sys.argv[1], sys.argv[2])
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except IndexError:
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print 'Usage: emx_link <source> <target>'
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except OSError:
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print 'emx_link: %s' % str(sys.exc_info()[1])
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