Andrew MacIntyre | eb477f0 | 2003-12-02 12:31:09 +0000 | [diff] [blame] | 1 | # _emx_link.py |
| 2 | |
| 3 | # Written by Andrew I MacIntyre, December 2002. |
| 4 | |
Tim Peters | 182b5ac | 2004-07-18 06:16:08 +0000 | [diff] [blame] | 5 | """_emx_link.py is a simplistic emulation of the Unix link(2) library routine |
Andrew MacIntyre | eb477f0 | 2003-12-02 12:31:09 +0000 | [diff] [blame] | 6 | for creating so-called hard links. It is intended to be imported into |
| 7 | the os module in place of the unimplemented (on OS/2) Posix link() |
| 8 | function (os.link()). |
| 9 | |
| 10 | We do this on OS/2 by implementing a file copy, with link(2) semantics:- |
| 11 | - the target cannot already exist; |
| 12 | - we hope that the actual file open (if successful) is actually |
| 13 | atomic... |
| 14 | |
| 15 | Limitations of this approach/implementation include:- |
| 16 | - no support for correct link counts (EMX stat(target).st_nlink |
| 17 | is always 1); |
| 18 | - thread safety undefined; |
| 19 | - default file permissions (r+w) used, can't be over-ridden; |
| 20 | - implemented in Python so comparatively slow, especially for large |
| 21 | source files; |
| 22 | - need sufficient free disk space to store the copy. |
| 23 | |
| 24 | Behaviour:- |
| 25 | - any exception should propagate to the caller; |
| 26 | - want target to be an exact copy of the source, so use binary mode; |
| 27 | - returns None, same as os.link() which is implemented in posixmodule.c; |
| 28 | - target removed in the event of a failure where possible; |
| 29 | - given the motivation to write this emulation came from trying to |
| 30 | support a Unix resource lock implementation, where minimal overhead |
| 31 | during creation of the target is desirable and the files are small, |
| 32 | we read a source block before attempting to create the target so that |
| 33 | we're ready to immediately write some data into it. |
| 34 | """ |
| 35 | |
| 36 | import os |
| 37 | import errno |
| 38 | |
| 39 | __all__ = ['link'] |
| 40 | |
| 41 | def link(source, target): |
| 42 | """link(source, target) -> None |
| 43 | |
| 44 | Attempt to hard link the source file to the target file name. |
| 45 | On OS/2, this creates a complete copy of the source file. |
| 46 | """ |
| 47 | |
| 48 | s = os.open(source, os.O_RDONLY | os.O_BINARY) |
| 49 | if os.isatty(s): |
Collin Winter | e45be28 | 2007-08-23 00:01:55 +0000 | [diff] [blame] | 50 | raise OSError(errno.EXDEV, 'Cross-device link') |
Andrew MacIntyre | eb477f0 | 2003-12-02 12:31:09 +0000 | [diff] [blame] | 51 | data = os.read(s, 1024) |
| 52 | |
| 53 | try: |
| 54 | t = os.open(target, os.O_WRONLY | os.O_BINARY | os.O_CREAT | os.O_EXCL) |
| 55 | except OSError: |
| 56 | os.close(s) |
| 57 | raise |
| 58 | |
| 59 | try: |
| 60 | while data: |
| 61 | os.write(t, data) |
| 62 | data = os.read(s, 1024) |
| 63 | except OSError: |
| 64 | os.close(s) |
| 65 | os.close(t) |
| 66 | os.unlink(target) |
| 67 | raise |
| 68 | |
| 69 | os.close(s) |
| 70 | os.close(t) |
| 71 | |
| 72 | if __name__ == '__main__': |
| 73 | import sys |
| 74 | try: |
| 75 | link(sys.argv[1], sys.argv[2]) |
| 76 | except IndexError: |
Guido van Rossum | be19ed7 | 2007-02-09 05:37:30 +0000 | [diff] [blame] | 77 | print('Usage: emx_link <source> <target>') |
Andrew MacIntyre | eb477f0 | 2003-12-02 12:31:09 +0000 | [diff] [blame] | 78 | except OSError: |
Guido van Rossum | be19ed7 | 2007-02-09 05:37:30 +0000 | [diff] [blame] | 79 | print('emx_link: %s' % str(sys.exc_info()[1])) |