Thanks both for looking, and thanks for the explanation Ilmari. Pushed with your improvements. The 4 CI systems run the tests (Windows and Mac by special always-expected-to-work case, Linux and FreeBSD by successful pre-flight perl test of O_DIRECT), and I also tested three unusual systems, two that skip for different reasons and one that will henceforth run this test on the build farm so I wanted to confirm locally first:
Linux/tmpfs: 1..0 # SKIP pre-flight test if we can open a file with O_DIRECT failed: Invalid argument OpenBSD: t/004_io_direct.pl .............. skipped: no O_DIRECT illumos: t/004_io_direct.pl .............. ok (Format different because those last two are autoconf, no meson on my collection of Vagrant images yet...)
