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From:   Benjamin Maynard <benmaynard@google.com>
Date:   Mon, 18 Jan 2021 17:57:54 +0000
Message-ID: <CA+QRt4vb=DjgcOqGLtfdfKiDaqKED825xNpNyQaaK-df5tCSRQ@mail.gmail.com>
Subject: Linux 5.11 Kernel: NFS re-export errors with older nfs-utils package versions
To:     linux-nfs@vger.kernel.org
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Hi,

I was recently experimenting with NFS re-exporting using the new patch
set that is in the Linux 5.11 kernel
(https://patchwork.kernel.org/project/linux-nfs/list/?series=393561).

After applying these patches, I consistently faced an error when
trying to perform a previously working NFS re-export: "exportfs:
/files does not support NFS export".

I (with help from some other interested parties) began troubleshooting
and after stepping through each patch individually we identified that
the error only occurred when the following patch was applied:
https://patchwork.kernel.org/project/linux-nfs/patch/20201130220319.501064-3-trond.myklebust@hammerspace.com/.

This patch prevents re-exporting if subtree checking is enabled on the
originating NFS server. The strange thing was that no_subtree_check
export option was already set on the export from the originating NFS
Filer, but the error message persisted.

After lots of troubleshooting, eventually we tried updating NFS Utils
from 1.3.4 to 2.5.2 and we were able to successfully perform
re-export. It appears that the old version of the nfs-utils package
was the cause of the issue.

I appreciate that 1.3.4 is a very old version of nfs-utils, but it is
the default version that ships with Ubuntu and Debian and the error
message does not immediately point to the outdated version being the
cause of the problem.

I was wondering if it was possible to detail the requirement for a
more recent version of nfs-utils in the NFS Re-exporting section of
the Wiki (http://wiki.linux-nfs.org/wiki/index.php/NFS_re-export) to
help others who may encounter this problem in the future?


Kind Regards
Benjamin Maynard