dracut: support mountpoint=legacy for root dataset

Support mountpoint=legacy for the root dataset in the dracut zfs support
scripts.

mountpoint=/ or mountpoint=/sysroot also works.

Change zfs-env-bootfs.service to add zfsutil to BOOTFSFLAGS only for
non-legacy root datasets, using the support function
determine_rootflags() added to zfs-lib.sh.

Signed-off-by: Rafael Kitover <[email protected]>

Author: rkitover

contrib/dracut/90zfs/zfs-env-bootfs.service.in

@@ -11,12 +11,7 @@ ExecStart=/bin/sh -c '
     . /lib/dracut-zfs-lib.sh;                                                                  \
     decode_root_args || exit 0;                                                                \
     [ "$root" = "zfs:AUTO" ] && root="$(@sbindir@/zpool list -H -o bootfs | grep -m1 -vFx -)"; \
-    rootflags="$(getarg rootflags=)";                                                          \
-    case ",$rootflags," in                                                                     \
-        *,zfsutil,*) ;;                                                                        \
-        ,,) rootflags=zfsutil ;;                                                               \
-        *)  rootflags="zfsutil,$rootflags" ;;                                                  \
-    esac;                                                                                      \
+    determine_rootflags; \
     exec systemctl set-environment BOOTFS="$root" BOOTFSFLAGS="$rootflags"'
 
 [Install]

contrib/dracut/90zfs/zfs-lib.sh.in

@@ -118,3 +118,19 @@ decode_root_args() {
 
     return 1
 }
+
+# Gets rootflags and adds zfsutil for non-legacy mountpoints.
+# Requires that decode_root_args() has already been called and $root is set.
+determine_rootflags() {
+    rootflags="$(getarg rootflags=)"
+
+    mountpoint="$(zfs get -H -o value mountpoint "$root")"
+
+    if [ "$mountpoint" != legacy ]; then
+        case ",$rootflags," in
+            *,zfsutil,*) ;;
+            ,,) rootflags=zfsutil ;;
+            *)  rootflags="zfsutil,$rootflags" ;;
+        esac
+    fi
+}