OpenZFS: Extend `posix_fadvise(2)` support to FreeBSD

[koobs]

OpenZFS added posix_fadvise(2) support in PR #13694 only for Linux (See also: PR #9807 and PR #10308).

FreeBSD supports posix_fadvise(2) in all supported versions.

This issue tracks extending OpenZFS support for posix_fadvise(2) to FreeBSD

[macdice]

FWIW here is the draft patch I had working a few years ago: macdice/freebsd@48cc228

[macdice]

Updated for recent-ish FreeBSD tree, with a few minor policy changes to be in sync with what was committed for Linux. But this probably needs to be turned into an OpenZFS patch... freebsd/freebsd-src@main...macdice:freebsd:fadvise-zfs

[macdice]

I got some help on VFS locking stuff from @mjguzik and made openzfs#13958, so let's see if we can get this over the line...

[koobs]

I got some help on VFS locking stuff from @mjguzik and made openzfs#13958, so let's see if we can get this over the line...

Weeeeeeeeeeeeeee, you got this mate, thank you so much for referencing it here :D 💪🏽