btrfs: add hostonly check

modules.d/90btrfs/check

@@ -1,10 +1,22 @@
 #!/bin/bash
 
 # We depend on udev-rules being loaded
-[ "$1" = "-d" ] && exit 0
+[[ "$1" = "-d" ]] && exit 0
 
 # if we don't have btrfs (btrfsctl) installed on the host system,
 # no point in trying to support it in the initramfs.
 which btrfsctl >/dev/null 2>&1 || exit 1
 
+. $dracutfunctions
+[[ $debug ]] && set -x
+
+is_btrfs() { get_fs_type /dev/block/$1 |grep -q btrfs; }
+
+if [[ "$1" = "-h" ]]; then
+    rootdev=$(find_root_block_device)
+    if [[ $rootdev ]]; then
+	is_btrfs "$rootdev" || exit 1
+    fi
+fi
+
 exit 0