Check if null_blk supports zoned devices

nullb

@@ -38,6 +38,10 @@ function _error() {
 	exit 1
 }
 
+function _warn() {
+	echo "WARNING: $@"
+}
+
 function _msg() {
 	echo "INFO: $@"
 }
@@ -53,6 +57,9 @@ function _check_setup() {
 	if ! grep -q configfs /proc/filesystems; then
 		_error "configfs not mounted"
 	fi
+	if ! grep -q zoned "$SYSFS/features"; then
+		_warn "null_blk module does not support zoned devices"
+	fi
 }
 
 function _check_cd() {