RFR: 6980847: (fs) Files.copy needs to be tuned [v5]

[Alan Bateman]

On Thu, 16 Jun 2022 23:36:34 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> Modify `UnixCopyFile.copyFile()` to set the transfer size to the least common multiple of the source and destination file block sizes if the block sizes are not equal. Modify `WindowsFileCopy.copy()` to set `COPY_FILE_NO_BUFFERING` in the flags passed to `CopyFileEx()` if the size of the transfer is greater than a threshold.
>
> Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   6980847: Use temporary direct buffer for user-space copy

src/java.base/unix/native/libnio/fs/UnixCopyFile.c line 158:

> 156:             if (errno == EINVAL || errno == ENOSYS) {
> 157:                 // Fall back to copying via user-space buffers
> 158:                 char buf[MIN_TRANSFER_SIZE];

We can't have the fallback path using 16k of stack here.

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PR: https://git.openjdk.org/jdk/pull/9161