Received-SPF: pass (google.com: domain of linux-nfs+bounces-3523-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Message-ID: <2c2f8e77-33c8-4836-b7e7-785938755e03@cipixia.com>
Date: Sun, 2 Jun 2024 19:43:06 -0700
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Content-Language: en-US
To: linux-nfs@vger.kernel.org
From: Matt Kinni <matt@cipixia.com>
Subject: exports option "mountpoint" ignored in nfsv4, works in v3
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit

Wasn't sure if this was a bug or just an outdated manpage, but the
"mountpoint" option will _not_ stop a v4 client from mounting an
unmounted server directory in Fedora 40 with kernel 6.8.10-300 and
nfs-utils-2.6.4-0.rc6.fc40.x86_64, however it _does_ work as expected if
the client mounts with v3 instead:

# setup
mkdir /mnt/nfs_localhost && mkdir /srv/somemountpoint
chmod 777 /srv/somemountpoint

# in /etc/exports:
/srv                    *(rw,all_squash,fsid=0)
/srv/somemountpoint     *(rw,all_squash,mountpoint)

# in /etc/nfs.conf:
[nfsd]
port=20049
vers3=y
vers4=y

# try mounting with nfs v3 while /srv/somemountpoint is a plain dir:
mount localhost:/srv/somemountpoint /mnt/nfs_localhost -t nfs -o vers=3

(cmd output)> mount.nfs: mounting localhost:/srv/somemountpoint failed,
reason given by server: No such file or directory
(log says)> rpc.mountd[5313]: request to export an unmounted filesystem:
/srv/somemountpoint

# so far so good
# but now try doing the same thing with v4:
mount localhost:/somemountpoint /mnt/nfs_localhost -t nfs -o vers=4.2
(works without error)

If I `mount -o bind /tmp /srv/somemountpoint` the v3 command works as
expected, but the v4 command always works regardless of whether the
underlying folder is a mount point or not.  Is this intended behavior?

The exports(5) manpage does not say anything about the "mountpoint" or
"mp" options not being valid for NFSv4, so I would expect the same
behavior regardless of what "-o vers=..." is supplied by the client
mount command.