RFR: 8291067: macOS should use O_CLOEXEC instead of FD_CLOEXEC

[David Holmes]

On Mon, 1 Aug 2022 16:15:26 GMT, Gerard Ziemski <gziemski at openjdk.org> wrote:

>> I see now it is just not comments but also the code. Again sorry but if the Linux workarounds are for Linux then they don't belong in the BSD code. That just confuses anyone who looks at this code later. If there were eventually an os_posix shared version of this then it wouldn't include Linux specific workarounds.
>
> This is not a **workaround** but an improvement to the robustness of the code, that applies equally to both Linux and macOS, by taking an advantage of what once was a new feature, but now is just a more reliable mechanism for making sure that the forked/child process does not get access to unintended "leaked" file descriptor from the parent. The original comment came from Linux, but we can change it, to apply equally to both Linux/macOS.
> 
> I will refactor this common POSIX code, though they are not 100% exactly the same - Linux uses `open64()`, while macOS uses `open()`.

The comment says:

> On ancient Linux kernels the O_CLOEXEC flag will be ignored and we fall back to using FD_CLOEXEC (see below).

so that is a workaround to handle ancient Linux kernels, and such a workaround has no meaning for BSD unless it too has ancient versions that ignored O_CLOEXEC.

That said, how ancient are we talking about? That comment may be irrelevant today given the minimum supported kernel versions we have.

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PR: https://git.openjdk.org/jdk/pull/9663