[Bug 1871214] Re: [SRU] nfsd doesn't start if exports depend on mount

[Robie Basak]

I've just finished speaking to Rodrigo about Bionic and Eoan. We think
that a different resolution for Bionic and Eoan might be more suitable,
and Rodrigo will investigate this. In the meantime, I'll leave the
current uploads for Bionic and Eoan in the queue in case we decide to
use them after all, but until we decide, please hold them in the queue.

** Changed in: nfs-utils (Ubuntu Bionic)
       Status: In Progress => Incomplete

** Changed in: nfs-utils (Ubuntu Eoan)
       Status: In Progress => Incomplete

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Title:
  [SRU] nfsd doesn't start if exports depend on mount

Status in nfs-utils package in Ubuntu:
  Fix Released
Status in nfs-utils source package in Bionic:
  Incomplete
Status in nfs-utils source package in Eoan:
  Incomplete
Status in nfs-utils source package in Focal:
  Fix Committed
Status in nfs-utils source package in Groovy:
  Fix Released

Bug description:
  Reproduced in Bionic and Focal, packages 1:1.3.4-2.1ubuntu5.2 and
  1:1.3.4-2.5ubuntu3 respectively.

  Steps to reproduce:

  1) Set up a ISCSI client to a 1GB+ volume, mount it in /data and set fstab to mount at boot
  2) Create a folder in /data like /data/dir1 and set up /etc/exports to export it
  3) Reboot
  4) Notice nfs-server does not start. Check journalctl and see it was because of "exportfs -r" returning -1 because /data/dir1 is not available.

  In Xenial (1:1.2.8-9ubuntu12.2), exportfs always returns 0, so this
  bug is not present there.

  This can be workaroundable in two ways:

  1) Editing nfs-server.service and adding "-" in
  "ExecStartPre=/usr/sbin/exportfs -r" to be
  "ExecStartPre=-/usr/sbin/exportfs -r". This will retain xenial
  behavior.

  2) Editing nfs-server.service and removing "Before=remote-fs-
  pre.target" and adding "RequiresMountsFor=/data". This will cause the
  systemd service load ordering to change, and nfs-server will wait for
  /data to be available.

  #2 is the upstream approach with commit [0] where this new comment
  identifies mount dependencies and automatically sets up
  RequiresMountFor.

  [0] http://git.linux-nfs.org/?p=steved/nfs-
  utils.git;a=commitdiff;h=4776bd0599420f9d073c9e2601ed438062dccd19

  =======================================================================

  [Impact]

  Users attempting to export folders from iSCSI or any remote mounted
  filesystem will experience their exports not being available at system
  start up, requiring workarounds or manual intervention.

  [Test case]

  1. Reproducing the bug:

  1a. Set up a ISCSI client to a 1GB+ volume
  1b. Format /dev/<device> using mkfs.xfs
  1c. Mount it in /data and set fstab as follows to mount at boot

  UUID="<uuid_from_blkid>" /data xfs defaults,auto,_netdev 0 0

  1d. Create a folder in /data like /data/dir1 and set permissions as
  follows

  chmod 777 /data/dir1
  chown nobody:nogroup /data/dir1

  1e. Set up /etc/exports as follows to export it

  /data/dir1 *(rw,async,root_squash,subtree_check)

  1f. Reboot
  1g. Notice nfs-server does not start. Running "showmount -e" displays error.

  2. No cleanup necessary

  3. Install the updated package that contains the fix

  4. Confirming the fix:

  4a. Reboot
  4b. Notice nfs-server starts sucessfully, "showmount -e" displays the exports.

  [Regression Potential]

  Regression potential is minimal. The dependency commit only moves code
  around and the actual fix only introduces an external systemd-
  generator without changing actual pre-existing code.

  I tested and confirmed that the fix introduced [0] also covers the fix
  removed [1], so there should not be any regression on this particular
  code change as well.

  [1] http://git.linux-nfs.org/?p=steved/nfs-
  utils.git;a=commitdiff;h=1e41488f428cd36b200b48b84d31446e38dfdc50

  [Other Info]

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