[issue29248] os.readlink fails on Windows

[Eryk Sun]

Eryk Sun added the comment:

os.symlink calls CreateSymbolicLink, which creates the reparse data buffer with the print name stored first, so the offset is always 0. Otherwise we would have noticed this problem already. For example:

    >>> os.symlink('C:\\', 'link', True)
    >>> os.system('fsutil reparsepoint query link')
    Reparse Tag Value : 0xa000000c
    Tag value: Microsoft
    Tag value: Name Surrogate
    Tag value: Symbolic Link

    Reparse Data Length: 0x00000020
    Reparse Data:
    0000:  06 00 0e 00 00 00 06 00  00 00 00 00 43 00 3a 00  ............C.:.
    0010:  5c 00 5c 00 3f 00 3f 00  5c 00 43 00 3a 00 5c 00  \.\.?.?.\.C.:.\.

As you can see above, CreateSymbolicLink stores the "PrintName" DOS path (e.g. "C:\") first, with an offset of 0, followed by the "SubstituteName" NT path (e.g. "\??\C:\").

The "All Users" link, on the other hand, seems to have been created manually with an inverted order. I have ctypes code to manually create a similar link (calling OpenProcessToken/AdjustTokenPrivileges to enable the required privilege and CreateFile/DeviceIoControl to set the reparse point), but I doubt it's worth adding it just to test this bug.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue29248>
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