On Sat, Apr 29, 2017 at 6:45 PM, Tim Chase
<python.l...@tim.thechases.com> wrote:
> Working on some deduplication code, I want do my my best at
> performing an atomic re-hard-linking atop an existing file, akin to
> "ln -f source.txt dest.txt"
>
> However, when I issue
>
> os.link("source.txt", "dest.txt")
>
> it fails with an OSError (EEXISTS). This isn't surprising as it's
> documented. Unfortunately, os.link doesn't support something like
>
> os.link("source.txt", "dest.txt", force=True)
FYI, on Windows this is possible if you use the NTAPI functions
NtOpenFile and NtSetInformationFile instead of WinAPI CreateHardLink.
Using the NT API can also support src_dir_fd, dst_dir_fd, and
follow_symlinks=True [1]. I have a prototype that uses ctypes. I named
this parameter "replace_existing". It's atomic, but it will fail if
the destination is open. An open file can't be unlinked on Windows.
[1]: MSDN claims that "if the path points to a symbolic link, the function
[CreateHardLink] creates a hard link to the target". Unless I'm
misreading, this statement is wrong because it actually links to the
symlink, i.e. the reparse point.
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