PEFS and advisory locking on ZFS

Hi,
I maintain the PEFS port/project (https://github.com/freebsd-pefs/pefs/) which is an encrypted file system which transparently runs on top of other file systems.

I've updated it to work OK however someone has discovered that if it's running on top of ZFS then locking doesn't work, >1 process can  own a lock (as tested with lockf)

It FreeBSD 13.1-RC1 (tested with releng/13.1-n250053-6fe29001573 GENERIC arm64) - when testing on -current (14.0-CURRENT #1 main-3468cd95c) it does work.

I tried implemented VOP_ADVLOCK but it didn't help (not really surprising but still).

The test is pretty simple, if /testtank is ZFS, then:

# Create crypto FS
sudo mkdir -p /testtank/test/pefs
echo test123 >keyfile
sudo pefs addchain -fZj keyfile /testtank/test/pefs

# Mount it and add the key
sudo pefs mount /testtank/test/pefs /testtank/test/pefs
sudo pefs addkey -cj keyhole /testtank/test/pefs

# Test locking
sudo lockf -k -t 0 /testtank/test/pefs/lock sleep 5 &
sudo lockf -k -t 0 /testtank/test/pefs/lock echo foo

When it's working the second lockf will print:
lockf: /testtank/test/pefs/lock: already locked

ZFS itself is fine, the lock test passes if PEFS isn't mounted, and on the same version PEFS on UFS works fine also.

I plan on bisecting it but if anyone has a suggestion I'm all ears.

Thanks.

--
Daniel O'Connor
"The nice thing about standards is that there
are so many of them to choose from."
 -- Andrew Tanenbaum