From f6b2e0052d9c4a22c36e38a402c14f6f42603843 Mon Sep 17 00:00:00 2001
From: Felix Uhl <github@mail.felix-uhl.de>
Date: Thu, 22 Aug 2024 17:51:15 +0200
Subject: [PATCH] zfs_fs: Fix errors when not changing mountpoint

Running `zfs set mountpoint=/mnt/my-ds tank/my-ds`, ZFS may try to
unmount the dataset even if the mountpoint didn't change.
To avoid the confusing error message, this command is now only run when
the mountpoint actually changes.
---
 lib/types/zfs_fs.nix | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/lib/types/zfs_fs.nix b/lib/types/zfs_fs.nix
index 813d75a..7e6b7bb 100644
--- a/lib/types/zfs_fs.nix
+++ b/lib/types/zfs_fs.nix
@@ -73,7 +73,7 @@
               "pbkdf2salt"
               "keyformat"
             ];
-            updateOptions = builtins.removeAttrs config.options onetimeProperties;
+            updateOptions = builtins.removeAttrs config.options (onetimeProperties ++ [ "mountpoint" ]);
             mountpoint = config.options.mountpoint or config.mountpoint;
           in
           ''
@@ -84,12 +84,15 @@
             else
               zfs set ${lib.concatStringsSep " " (lib.mapAttrsToList (n: v: "${n}=${v}") updateOptions)} ${config._name}
               ${lib.optionalString (mountpoint != null) ''
-                # zfs will try unmount the dataset to change the mountpoint
-                # but this might fail if the dataset is in use
-                if ! zfs set mountpoint=${mountpoint} ${config._name}; then
-                  echo "Failed to set mountpoint to '${mountpoint}' for ${config._name}." >&2
-                  echo "You may need to run when the pool is not mounted i.e. in a recovery system:" >&2
-                  echo "  zfs set mountpoint=${mountpoint} ${config._name}" >&2
+                if [[ "$(zfs get -H -o value mountpoint ${config._name})" != "${mountpoint}" ]]; then
+                  echo "Changing mountpoint to '${mountpoint}' for ${config._name}..."
+                  # zfs will try unmount the dataset to change the mountpoint
+                  # but this might fail if the dataset is in use
+                  if ! zfs set mountpoint=${mountpoint} ${config._name}; then
+                    echo "Failed to set mountpoint to '${mountpoint}' for ${config._name}." >&2
+                    echo "You may need to run when the pool is not mounted i.e. in a recovery system:" >&2
+                    echo "  zfs set mountpoint=${mountpoint} ${config._name}" >&2
+                  fi
                 fi
               ''}
             ''}