bpf is called via an operations vector described by the following struct:
struct bpf_ops {
void (*bpf_attach)(struct ifnet *, u_int, u_int, struct bpf_if **);
void (*bpf_detach)(struct ifnet *);
void (*bpf_change_type)(struct ifnet *, u_int, u_int);
void (*bpf_tap)(struct bpf_if *, u_char *, u_int);
void (*bpf_mtap)(struct bpf_if *, struct mbuf *);
void (*bpf_mtap2)(struct bpf_if *, void *, u_int, struct mbuf *);
void (*bpf_mtap_af)(struct bpf_if *, uint32_t, struct mbuf *);
void (*bpf_mtap_et)(struct bpf_if *, uint16_t, struct mbuf *);
void (*bpf_mtap_sl_in)(struct bpf_if *, u_char *, struct mbuf **);
void (*bpf_mtap_sl_out)(struct bpf_if *, u_char *, struct mbuf *);
};
This vector is found from
struct bpf_ops * bpf_ops. It is either a “stub” implementation or a real implementation, depending on whether
bpf is absent or present in the kernel, respectively.