FreeBSD: Enable Direct IO by default

[behlendorf]

Motivation and Context

Enable Direct IO for FreeBSD.

Description

Commits 25eb538, 1786825, and 8dc452d resolve the remaining known issues with Direct IO on FreeBSD. Enable it by default on all platforms.

How Has This Been Tested?

Locally tested in the PRs which resolved the above remaining issues. Additional tests to be done by the CI.

@markjdb thanks for sorting out these issues. Unless you know of any other problems let's enable this by default.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[markjdb]

@markjdb thanks for sorting out these issues. Unless you know of any other problems let's enable this by default.

I believe @bwatkinson is still characterizing a problem with O_DIRECT reads - there is some discussion going on in an email thread, so we should hold off until that's resolved.