1 files changed, 3 insertions, 1 deletions

diff --git a/xorriso-layer.sh b/xorriso-layer.sh
index 886e174..b8f6ede 100755
--- a/xorriso-layer.sh
+++ b/xorriso-layer.sh
@@ -4,10 +4,12 @@ outdev=debian-live-8.4.0-amd64-standard.btrfs.layered.iso
 indev=debian-live-8.4.0-amd64-standard.btrfs.iso
 volid=SamizdatLive
 btrfs_layer_iso_path=live/layer.btrfs
-btrfs_layer_filesystem=debian-live-8.4.0-amd64-standard.layer.snapshot.2016-04-22.222941.btrfs
+btrfs_layer_filesystem="$1"
 
 die() { printf '%s\n' "$*"; exit 1; }
 
+[ -f "$btrfs_layer_filesystem" ] || die "Usage: $0 <layer.btrfs>"
+
 set -ex
 
 cp --reflink "$indev" "$outdev"~