RFR: 8264744: (fs) Use file cloning in Linux version of Files::copy method [v12]

[Alan Bateman]

On Fri, 2 Sep 2022 01:37:59 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> Add file cloning to `java.nio.channels.FileChannel::transferTo` and `java.nio.file.Files.copy(Path,Path)`.
>
> Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8264744: Reduce noise of negligible diffs in UnixFileSystem

The updated implementation changes in 62461a2d look okay but I'm not sure about the updates to the CopyAndMove test. If I read it correctly, it tries to find the mount point where a COW file system is mounted and use it as an additional test directory. I don't think we should want tests trying to use these locations as test directories, even if running with permissions.

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PR: https://git.openjdk.org/jdk/pull/9486