From: Adam Bell <adam.bell@canonical.com>
Date: 10 Mar 2022 22:22:39 +0700
Subject: ZFS snapshots causing grub.cfg generation failure

In the situation where ZFS snapshots do not contain a .../etc directory, the
generation of /b/g/grub.cfg silently fails, providing no "linux" kernel lines in
the /b/g/grub.cfg file. This patch prevents this type of failure from occurring.
This issue is especially apparent on systems running in FIPS mode with ZFS
boot+root pools.

Patch-Name: grubcfg-zfs-snapshot-generation-failure.patch
---
diff --git a/util/grub.d/10_linux_zfs.in b/util/grub.d/10_linux_zfs.in
index d9b79e2..4dd1609 100755
--- a/util/grub.d/10_linux_zfs.in
+++ b/util/grub.d/10_linux_zfs.in
@@ -520,11 +520,15 @@ get_dataset_info() {
 
     umount "${mntdir}" || true
     # We needed to look in / for snapshots on root dataset, umount the snapshot for etc before zfs lazily unmount it
-    case "${etc_dir}" in /.zfs/snapshot/*/etc)
-        snapshot_path="$(findmnt -n -o TARGET -T ${etc_dir})"
-        umount "${snapshot_path}" || true
-        ;;
-    esac
+    # This process only needs to run if the snapshot contains an .../etc path,
+    #  otherwise the build process may silently fail and produce no kernel lines in grub.cfg
+    if [ -e "${etc_dir}" ]; then
+        case "${etc_dir}" in /.zfs/snapshot/*/etc)
+            snapshot_path="$(findmnt -n -o TARGET -T ${etc_dir})"
+            umount "${snapshot_path}" || true
+            ;;
+        esac
+    fi
 }
 
 # Scan available boot options and returns in a formatted list