Bug#949577: nfs-kernel-server: Unable to see sub-mounted filesystems with nohide set

[Kyle Robbertze <kyle@paddatrapper.com>]

Package: nfs-kernel-server
Version: 1:1.3.4-2.5
Severity: normal

Dear Maintainer,

We use NFSv3 to mount /home on our lab machines. The mount is a ZFS
filesystem with snapshot visibility enabled (this makes
/home/.zfs/snapshot be visibile to users so that they can restore files
if needed). We are using standard /etc/exports, and the ZFS sharenfs
option is disabled.

Since the upgrade to Buster from Stretch, we are unable to view the
contents of snapshots under .zfs/snapshot/<snapshot_name>, but can
accurately see the list of snapshots in .zfs/snapshot. Each ZFS snapshot
is a separate file system, mounted under the snapshot name in
.zfs/snapshot. The nohide option has no effect on whether we can see them
or not.

The /etc/exports below is a snippet of the file, but represents the
base case where we are encountering this issue. I am not sure if it is a
bug in NFS, ZFS or a user issue.

Thanks
Kyle

-- Package-specific info:
-- rpcinfo --
   program vers proto   port  service
    100000    4   tcp    111  portmapper
    100000    3   tcp    111  portmapper
    100000    2   tcp    111  portmapper
    100000    4   udp    111  portmapper
    100000    3   udp    111  portmapper
    100000    2   udp    111  portmapper
    100005    1   udp  55442  mountd
    100005    1   tcp  39107  mountd
    100005    2   udp  34059  mountd
    100005    2   tcp  56283  mountd
    100005    3   udp  38252  mountd
    100005    3   tcp  46465  mountd
    100003    3   tcp   2049  nfs
    100003    4   tcp   2049  nfs
    100227    3   tcp   2049
    100003    3   udp   2049  nfs
    100227    3   udp   2049
    100021    1   udp  58819  nlockmgr
    100021    3   udp  58819  nlockmgr
    100021    4   udp  58819  nlockmgr
    100021    1   tcp  37101  nlockmgr
    100021    3   tcp  37101  nlockmgr
    100021    4   tcp  37101  nlockmgr
-- /etc/default/nfs-kernel-server --
RPCNFSDCOUNT=8
RPCNFSDPRIORITY=0
RPCMOUNTDOPTS="--manage-gids"
NEED_SVCGSSD=""
RPCSVCGSSDOPTS=""
-- /etc/exports --
[...]
# ssh.aims.ac.za (old and new)_
/export    10.1.29.6(rw,fsid=0,insecure,no_subtree_check,async)
/export/home.aims    10.1.29.6(rw,nohide,insecure,no_subtree_check,async)
[...]
-- /proc/fs/nfs/exports --
# Version 1.1
# Path Client(Flags) # IPs

-- System Information:
Debian Release: bullseye/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.4.0-3-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_ZA.UTF-8, LC_CTYPE=en_ZA.UTF-8 (charmap=UTF-8), 
LANGUAGE=en_ZA:en (charmap=UTF-8)
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages nfs-kernel-server depends on:
ii  keyutils      1.6-6
ii  libblkid1     2.34-0.1
ii  libc6         2.29-9
ii  libcap2       1:2.27-1
ii  libsqlite3-0  3.30.1+fossil191229-1
ii  libtirpc3     1.2.5-1
ii  libwrap0      7.6.q-30
ii  lsb-base      11.1.0
ii  netbase       6.0
ii  nfs-common    1:1.3.4-2.5+b1
ii  ucf           3.0038+nmu1

nfs-kernel-server recommends no packages.

nfs-kernel-server suggests no packages.

-- no debconf information