#undef NEED_UDP2
#ifdef HAVE_L2TP
#define NEED_UDP2
#endif
#ifdef HAVE_VXLAN
#define NEED_UDP2
#endif
#undef NEED_ETH4
#ifdef HAVE_TAP
#define NEED_ETH4
#endif
Using ifdef to see if specific protocols or tools are being used in the current deployment, if so, then it declares a new flag using define to indicate requirements
struct headers {
cpu_header_t cpu;
ethernet_t ethernet;
...
#ifdef HAVE_GRE
gre_t gre2;
#endif
#ifdef NEED_UDP2
udp_t udp2;
#endif
#ifdef HAVE_L2TP
l2tp_t l2tp2;
#endif
#ifdef HAVE_VXLAN
vxlan_t vxlan2;
#endif
#ifdef NEED_ETH4
ethernet_t eth4;
#endif
...
}
Using ifdef to see which header fields are required/defined, and based on that they are adding fields to the header struct.
#ifndef _INGRESS_PARSER_P4_
#define _INGRESS_PARSER_P4_
/*------------------ I N G R E S S P A R S E R -----------------------------*/
parser ig_prs_main(packet_in pkt,
/* User */
out headers hdr, out ingress_metadata_t ig_md,
/* Intrinsic */
out ingress_intrinsic_metadata_t ig_intr_md)
{
Checksum()ipv4_checksum;
#ifdef HAVE_NAT
Checksum() tcp_checksum;
Checksum() udp_checksum;
#endif
state start {
pkt.extract(ig_intr_md);
pkt.advance(PORT_METADATA_SIZE);
ig_md.always_zero = 0;
#ifdef HAVE_PPPOE
ig_md.pppoe_ctrl_valid = 0;
ig_md.pppoe_data_valid = 0;
#endif
...
}
...
}
Using ifndef to make sure a main flag isn't being redefined.
Using ifdef to see if NAT is being used, and if so, checksum fields for TCP and UDP are included; also used to see if a flag is defined and if so, a corresponding new field in the start state is added.
/* Still inside `parser ig_prs_main()` function */
#ifdef HAVE_PPPOE
state prs_pppoeCtrl {
pkt.extract(hdr.pppoeC);
ig_md.pppoe_ctrl_valid = 1;
transition accept;
}
state prs_pppoeData {
pkt.extract(hdr.pppoeD);
ig_md.pppoe_data_valid = 1;
transition select(hdr.pppoeD.ppptyp) {
PPPTYPE_IPV4:
prs_ipv4;
PPPTYPE_IPV6:
prs_ipv6;
#ifdef HAVE_MPLS
PPPTYPE_MPLS_UCAST:
prs_mpls0;
#endif
default:
prs_pppoeDataCtrl;
}
}
state prs_pppoeDataCtrl {
ig_md.pppoe_ctrl_valid = 1;
transition accept;
}
#endif
ifdef flags being used to define new states and to add new cases/matches to transitions select blocks
/* Still inside parser ig_prs_main() function */
state prs_ipv4 {
pkt.extract(hdr.ipv4);
ipv4_checksum.add(hdr.ipv4);
ig_md.ipv4_valid = 1;
ig_md.l4_lookup = pkt.lookahead<l4_lookup_t>();
#ifdef HAVE_NAT
tcp_checksum.subtract({hdr.ipv4.src_addr});
tcp_checksum.subtract({hdr.ipv4.dst_addr});
udp_checksum.subtract({hdr.ipv4.src_addr});
udp_checksum.subtract({hdr.ipv4.dst_addr});
#endif
...
}
ifdef being used to do secific calculations inside a state
control ig_ctl(inout headers hdr, inout ingress_metadata_t ig_md,
in ingress_intrinsic_metadata_t ig_intr_md,
in ingress_intrinsic_metadata_from_parser_t ig_prsr_md,
inout ingress_intrinsic_metadata_for_deparser_t ig_dprsr_md,
inout ingress_intrinsic_metadata_for_tm_t ig_tm_md)
{
#ifdef HAVE_NOHW
apply {
if (ig_intr_md.ingress_port == CPU_PORT) {
ig_tm_md.ucast_egress_port =(PortId_t) hdr.cpu.port;
ig_tm_md.bypass_egress = 1;
hdr.cpu.setInvalid();
} else {
hdr.cpu.setValid();
hdr.cpu.port = ig_md.ingress_id;
ig_tm_md.ucast_egress_port = CPU_PORT;
ig_tm_md.bypass_egress = 1;
}
}
#else
IngressControlBundle() ig_ctl_bundle;
#ifdef HAVE_MPLS
IngressControlMPLS()ig_ctl_mpls;
#endif
...
apply {
...
}
#endif
}
Here the ifdef and else directives are used to evaluate the flag and depending on that it either inserts an apply block or instantiate predefined control blocks and an apply block
#ifdef HAVE_TUN
control IngressControlTunnel(...)
{
#ifdef HAVE_L2TP
SubIntId_t l2tp_hit;
#endif
...
}
#endif
Using ifdef to include the main control block in this file and to define new variables based on the respective flags
/* Still inside `control IngressControlTunnel()` function*/
#ifdef HAVE_GRE
action act_tunnel_gre(SubIntId_t port) {
hdr.ethernet.ethertype = hdr.gre.gretyp;
ig_md.source_id = port;
...
}
#endif
Using ifdef to define actions