File duplication on NFSv4 exported ZFS filesystems to centos client

[Jordan Ladora]

Curious phenomenon of file pseudo-dup with exported ZFS filesystems on
FreeBSD 10.3-REL NFSv4 export to a centos7 client.


*FreeBSD server-*

zpool create zpool_nfsv4 ...

zfs create zpool_nfsv4/zfs2

zfs create zpool_nfsv4/zfs3


/etc/exports-

V4: /

/zpool_nfsv4

/zpool_nfsv4/zfs2

/zpool_nfsv4/zfs3


zfs unshare -a


*Centos client-*

mkdir /zpool_nfsv4

mkdir /zpool_nfsv4_zfs2

mkdir /zpool_nfsv4_zfs3

mount -t nfs4 -o rw,intr,hard,proto=tcp,nodev,noexec,nosuid
10.0.100.100:/zpool_nfsv4
/zpool_nfsv4

mount -t nfs4 -o rw,intr,hard,proto=tcp,nodev,noexec,nosuid
10.0.100.100:/zpool_nfsv4/zfs2
/zpool_nfsv4_zfs2

mount -t nfs4 -o rw,intr,hard,proto=tcp,nodev,noexec,nosuid
10.0.100.100:/zpool_nfsv4/zfs3
/zpool_nfsv4_zfs3


The FreeBSD share and centos client have the same username (nfsuser),
groupname, and user:group IDs, which also owns the exported /zpool_nfsv4,
so UID/GIDs map correctly on the client and permissions work fine.

The unexpected behavior happens when the user touches a file on the
client's share of either /zpool_nfsv4/zfs2 or /zpool_nfsv4/zfs3-

sudo -u nfsuser touch /zpool_nfs4_zfs2/testfile  # centos client

...this new file then also appears immediately on the client's share mount
at-

/zpool_nfs4_zfs3/testfile

...but not at /zpool_nfs4 (the top-level zfs). It is not duplicated on the
server and there it only appears [in the correct location] at-

/zpool_nfs4/zfs2/testfile  # freebsd server

If I unmount the share and remount it, it looks the same (you still see the
duplicate file on the client) and ‘testfile’ can be manipulated on the
client from either location.

This also doesn't happen if touching a file on the top-level dir
(/zpool_nfsv4) on the client (in other words, there is no duplication seen
on the client if nfsuser touches e.g. /zpool_nfsv4/testfile).

This seems similar to this (https://serverfault.com/quest
ions/535318/creating-two-nfs-shares-from-same-server-but-
when-mounted-both-point-to-same-d) thread with NFSv4 exports on a centos
server, but I cannot find anything similar to what I see here with a
FreeBSD NFSv4 server.

It seems to me that two of the zfs filesystems (zfs1 and zfs2) are mapping
to the same place on the client, but I'm not sure how to deal with this...