RFR: 8292562: (fc) Use copy_file_range in FileChannel::transferTo on Linux

[Brian Burkhalter]

On Fri, 19 Aug 2022 06:42:08 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> Add `copy_file_range(2)` to the native Linux implementation of `FileChannel::transferTo`.
>
> src/java.base/unix/native/libnio/ch/FileChannelImpl.c line 186:
> 
>> 184:             switch (errno) {
>> 185:                 case EINTR:
>> 186:                 case EINVAL:
> 
> For EINVAL we could return IOS_INTERRUPTED if you want.

Did you intend `EINTR`?

> src/java.base/unix/native/libnio/ch/FileChannelImpl.c line 192:
> 
>> 190:                 default:
>> 191:                     JNU_ThrowIOExceptionWithLastError(env, "Copy failed");
>> 192:                     return IOS_THROWN;
> 
> Would you mind checking if we have tests that exercise transferTo when the target WritableByteChannel is to a file opened in append mode? Asking because copy_file_range will fall and I'm wondering what the existing behavior is.

Given https://bugs.openjdk.org/browse/JDK-4950302 I suppose the existing code(`sendfile`) will fail as well but I'll check.

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PR: https://git.openjdk.org/jdk/pull/9925