grehdr
const struct gre_base_hdr *grehdr;
grehdr = skb_header_pointer(skb, dataoff, sizeof(_grehdr), &_grehdr);
if (!grehdr || (grehdr->flags & GRE_VERSION) != GRE_VERSION_1) {
if (grehdr->protocol != GRE_PROTO_PPP) {
pr_debug("Unsupported GRE proto(0x%x)\n", ntohs(grehdr->protocol));
struct grehdr *greh = header;
ol4_len = sizeof(struct grehdr);
struct grehdr greh;
struct grehdr greh;
hdr.ip6hdr.payload_len = bpf_htons(skb->len + sizeof(struct grehdr));