Constant MLFQ_TREE_SAMPLE_VERSION 

pub const MLFQ_TREE_SAMPLE_VERSION: u32 = crate::bpf_intf::mlfq_consts_MLFQ_TREE_SAMPLE_VERSION /* 4u32 */;

Record-layout version tag of the emitted training samples, from enum mlfq_consts in src/bpf/intf.h.