Add copy_file_range() for Linux and Android

[ArniDagur]

This is my first PR to libc, so I looked at how splice() is implemented and modelled it after that.

See http://man7.org/linux/man-pages/man2/copy_file_range.2.html

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @gnzlbg (or someone else) soon.

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[gnzlbg]

When was this function added and in which header is it defined?

You might need to update libc-test/build.sh to only test it when the appropriate header is included, but it might be that the linux and android versions used in CI aren't new enough.

[ArniDagur]

copy_file_range is supported in kernels 4.5 and above. It is a part of unistd.h in glibc. A mistake in this PR relates to the fact that there's only a wrapper present in glibc, but not musl.

[gnzlbg]

I see, well let me know when CI is green.

[ArniDagur]

Just now, copy_file_range support for musl got merged. Does that mean it's fine to include it here immediately?

[gnzlbg]

That would require upgrading the musl versions used here on CI.

[bors]

☔ The latest upstream changes (presumably #1510) made this pull request unmergeable. Please resolve the merge conflicts.

[gnzlbg]

This needs rebasing

[gnzlbg]

@ArniDagur we have recently upgraded the musl version, would you mind rebasing this to see if it passes tests and can be merged? Let me know if there is anything I can help you with!

[ArniDagur]

@gnzlbg The musl tests still fail.

[gnzlbg]

That probably means that the musl version used by CI still does not support this API.

[mati865]

It was added in 1.1.24 (the same as on the CI) but it requires _GNU_SOURCE.
IIUC it's not enabled on purpose:

libc/libc-test/build.rs

Line 2076 in 122ca90

cfg.define("_GNU_SOURCE", None);

[JohnTitor]

Triage: copy_file_range is now added for Linux/GNU but not for musl or Android. I couldn't find any reference that it's available on Android but I think it's fine to support musl skipping the test. Anyway, a rebase would be hard and it'd be better to open a new PR for it, so I'm going to close this PR. Thanks!