FUN_XDP_HEADROOM
(PAGE_SIZE - FUN_XDP_HEADROOM - VLAN_ETH_HLEN - FUN_RX_TAILROOM)
xdp_prepare_buff(&xdp, buf_va, FUN_XDP_HEADROOM, skb_frag_size(frags) -
(FUN_RX_TAILROOM + FUN_XDP_HEADROOM), false);
if (xdp_q && headroom == FUN_XDP_HEADROOM) {
headroom = prog ? FUN_XDP_HEADROOM : FUN_RX_HEADROOM;
q->headroom = fp->xdp_prog ? FUN_XDP_HEADROOM : FUN_RX_HEADROOM;