shutil.copyfile should use ReFS block-level linking on Windows (by invoking CopyFileW)

[Dico200]

Bug report

Bug description:

shutil.copyfile("./scratch.txt", "./target.txt")

copyfile for copies within a single ReFS volume (or Dev Drive) on Windows 11 does not take advantage of block-level linking capability present in ReFS file system. On the other hand, the kernel automatically does so when you invoke CopyFileW these days. C#/.NET use kernel functions for file copy APIs and automatically take advantage of this too.

Python does not offer an API that takes advantage of block-level linking except for directly invoking CopyFileW using windlls.kernel32 from ctypes.

https://docs.python.org/3/library/shutil.html#shutil-platform-dependent-efficient-copy-operations
CopyFileW should be used instead of streaming data from one file to another, at least in circumstances where block-level linking is possible.

Relevant code:

cpython/Lib/shutil.py

Line 313 in e93c30d

with open(src, 'rb') as fsrc:

CPython versions tested on:

3.9

Operating systems tested on:

Windows

[cmaloney]

This was looked at in 2018 and decided against in gh-77852 which added the platform-specific optimizations because it was slower (see: #77852 (comment) high level, for details see: #7160 (comment) and the comments starting at #7160 (comment)).

In 2019 it looks like more discussion of CopyFileW occured (gh-83087) with the leaning "use CopyFile" everywhere. It sounds like in newer Windows this might be faster (so this should be gated by a windows version potentially), would need benchmarks to validate.