ref: 1717368f640180cab63a870a19d650276172cbfd
dir: /sys/lib/python/plat-os2emx/_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])