Initial commitmain

Signed-off-by: Toni Uhlig <matzeton@googlemail.com>

15 files changed, 671 insertions, 0 deletions

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..3edcf37
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,53 @@
+CC=clang-20
+IF=lo
+ifneq ($(DEBUG),)
+BPF_CFLAGS+=-DXDP_DEBUG=1
+endif
+
+all: xdp_udp_handler.o xdp_loader user_server user_client
+
+run: all
+	sudo ./xdp_loader $(IF)
+
+clean:
+	rm -f ./xdp_udp_handler.o ./xdp_loader ./user_server ./user_client
+	rm -f ./fit.log ./rtt.dat ./rtt_tmp.dat
+
+detach:
+	sudo bpftool net detach xdp dev $(IF)
+
+benchmark: all
+	@echo 'Running benchmark in user space..'
+	./user_server &
+	./user_client >./rtt_tmp.dat
+	cp ./rtt_tmp.dat ./rtt.dat
+	./gnuplot.script
+	mv -v rtt.png benchmark-user-with-burst.png
+	# use only the last 90 data points
+	tail -n90 ./rtt_tmp.dat >./rtt.dat
+	./gnuplot.script
+	mv -v rtt.png benchmark-user.png
+	@echo 'Running benchmark with XDP..'
+	$(MAKE) detach
+	$(MAKE) run
+	./user_client >./rtt_tmp.dat
+	cp ./rtt_tmp.dat ./rtt.dat
+	./gnuplot.script
+	mv -v rtt.png benchmark-xdp-with-burst.png
+	# use only the last 90 data points
+	tail -n90 ./rtt_tmp.dat >./rtt.dat
+	./gnuplot.script
+	mv -v rtt.png benchmark-xdp.png
+	$(MAKE) detach
+
+xdp_udp_handler.o: xdp_udp_handler.c xdp_parser.h xdp_checksum.h
+	$(CC) -Wall -Wextra -O3 -g -target bpf -D__TARGET_ARCH_x86 $(BPF_CFLAGS) -c xdp_udp_handler.c -o xdp_udp_handler.o
+
+xdp_loader: xdp_loader.c
+	$(CC) -Wall -Wextra -O3 -g $(CFLAGS) xdp_loader.c -o xdp_loader $(shell pkg-config --cflags --libs libbpf) $(LDFLAGS)
+
+user_server: user_server.c
+	$(CC) -Wall -Wextra -O3 -g $(CFLAGS) user_server.c -o user_server
+
+user_client: user_client.c
+	$(CC) -Wall -Wextra -O3 -g $(CFLAGS) user_client.c -o user_client
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..1f013d6
--- /dev/null
+++ b/README.md
@@ -0,0 +1,13 @@
+Testing the performance of ring0 for packet decoding and manipulation.
+
+Just run: `make benchmark`, that's it!
+
+XDP (ring0):
+
+![XDP](benchmark-xdp.png)
+![XDP with bursts](benchmark-xdp-with-burst.png)
+
+Classic (ring3):
+
+![Userspace](benchmark-user.png)
+![Userspace with bursts](benchmark-user-with-burst.png)
diff --git a/benchmark-user-with-burst.png b/benchmark-user-with-burst.png
new file mode 100644
index 0000000..f0d669c
--- /dev/null
+++ b/benchmark-user-with-burst.png
diff --git a/benchmark-user.png b/benchmark-user.png
new file mode 100644
index 0000000..bf544b9
--- /dev/null
+++ b/benchmark-user.png
diff --git a/benchmark-xdp-with-burst.png b/benchmark-xdp-with-burst.png
new file mode 100644
index 0000000..c5f0bcb
--- /dev/null
+++ b/benchmark-xdp-with-burst.png
diff --git a/benchmark-xdp.png b/benchmark-xdp.png
new file mode 100644
index 0000000..1226523
--- /dev/null
+++ b/benchmark-xdp.png
diff --git a/common.h b/common.h
new file mode 100644
index 0000000..da4cb92
--- /dev/null
+++ b/common.h
@@ -0,0 +1,5 @@
+#define UDP_PORT 50000
+#define MAX_UDP_PACKETS 100
+
+#define PAYLOAD_REQUEST 0x01, 0x08, 0x00, 0x00, 0x05, 0x01, 0x01, 0x01, 0x05, 0x22, 0x01
+#define PAYLOAD_RESPONSE 0x01, 0x04, 0x00, 0x00, 0x05, 0x01, 0x01, 0x02
diff --git a/gnuplot.script b/gnuplot.script
new file mode 100755
index 0000000..a75243a
--- /dev/null
+++ b/gnuplot.script
@@ -0,0 +1,12 @@
+#!/usr/bin/env gnuplot
+
+set terminal png
+set output "rtt.png"
+f(x) = mean_rtt
+fit f(x) 'rtt.dat' u 1:2 via mean_rtt
+stddev_rtt = sqrt(FIT_WSSR / (FIT_NDF + 1 ))
+set title "Packets vs. RTT"
+set xlabel "Packet Number"
+set ylabel "RTT in usec"
+
+plot "rtt.dat" with lines, mean_rtt w l lt 3, stddev_rtt w l lt 3 lc rgb '#bbbbdd'
diff --git a/user_client.c b/user_client.c
new file mode 100644
index 0000000..68c79af
--- /dev/null
+++ b/user_client.c
@@ -0,0 +1,85 @@
+// udp client driver program
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <strings.h>
+#include <sys/socket.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "common.h"
+
+static const unsigned char payload_request[] = { PAYLOAD_REQUEST, 0xFF};
+
+struct {
+    unsigned long long int send_start;
+    unsigned long long int received_end;
+} timings[MAX_UDP_PACKETS];
+
+static int set_ts(unsigned long long int * const out) {
+  struct timeval tv = {};
+
+  if (gettimeofday(&tv, NULL) != 0)
+    return 1;
+
+  *out = (tv.tv_sec * 1000 * 1000) + tv.tv_usec;
+  return 0;
+}
+
+int main() {
+  char buffer[BUFSIZ];
+  int sockfd;
+  struct sockaddr_in servaddr = {};
+
+  servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");
+  servaddr.sin_port = htons(UDP_PORT);
+  servaddr.sin_family = AF_INET;
+  sockfd = socket(AF_INET, SOCK_DGRAM, 0);
+  if (sockfd < 0) {
+    perror("udp socket");
+    return 1;
+  }
+
+  if (connect(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0) {
+    perror("udp connect");
+    return 1;
+  }
+
+  size_t i;
+  ssize_t n;
+  for (i = 0; i < MAX_UDP_PACKETS; ++i) {
+    if (set_ts(&timings[i].send_start) != 0) {
+      n = -1;
+      break;
+    }
+
+    n = sendto(sockfd, payload_request, sizeof(payload_request), 0, NULL, 0);
+    if (n < 0) {
+      perror("udp sendto");
+      break;
+    }
+
+    n = recvfrom(sockfd, buffer, sizeof(buffer), 0, (struct sockaddr *)NULL,
+                 NULL);
+    if (n < 0) {
+      perror("udp recvfrom");
+      break;
+    }
+
+    if (set_ts(&timings[i].received_end) != 0) {
+      n = -1;
+      break;
+    }
+  }
+
+  close(sockfd);
+
+  printf("# packet_number rtt\n");
+  for (size_t i = 0; i < MAX_UDP_PACKETS; ++i) {
+    printf("%zu %lld\n", i, timings[i].received_end - timings[i].send_start);
+  }
+
+  return !(i == MAX_UDP_PACKETS);
+}
diff --git a/user_server.c b/user_server.c
new file mode 100644
index 0000000..de2054f
--- /dev/null
+++ b/user_server.c
@@ -0,0 +1,52 @@
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <stdio.h>
+#include <strings.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "common.h"
+
+static const unsigned char payload_response[] = {PAYLOAD_RESPONSE};
+
+int main() {
+  unsigned char buffer[BUFSIZ];
+  int listenfd;
+  socklen_t len;
+  struct sockaddr_in servaddr = {};
+  struct sockaddr_in cliaddr;
+
+  listenfd = socket(AF_INET, SOCK_DGRAM, 0);
+  servaddr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+  servaddr.sin_port = htons(UDP_PORT);
+  servaddr.sin_family = AF_INET;
+
+  if (bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) != 0) {
+    perror("udp bind");
+    return 1;
+  }
+
+  size_t i;
+  ssize_t n;
+  for (i = 0; i < MAX_UDP_PACKETS; ++i) {
+    len = sizeof(cliaddr);
+    n = recvfrom(listenfd, buffer, sizeof(buffer), 0,
+                 (struct sockaddr *)&cliaddr, &len);
+    if (n < 0) {
+      perror("udp recvfrom");
+      break;
+    }
+
+    n = sendto(listenfd, payload_response, sizeof(payload_response), 0,
+               (struct sockaddr *)&cliaddr, sizeof(cliaddr));
+    if (n < 0) {
+      perror("udp sendto");
+      break;
+    }
+  }
+
+  close(listenfd);
+
+  return !(i == MAX_UDP_PACKETS);
+}
diff --git a/xdp_checksum.h b/xdp_checksum.h
new file mode 100644
index 0000000..1d35565
--- /dev/null
+++ b/xdp_checksum.h
@@ -0,0 +1,94 @@
+#ifndef XDP_CHECKSUM_H
+#define XDP_CHECKSUM_H 1
+
+#include <linux/ip.h>
+#include <linux/udp.h>
+#include <stdlib.h>
+
+static __always_inline __u16 ip_checksum(struct iphdr *iph) {
+  __u32 sum = 0;
+  __u16 *ptr = (__u16 *)iph;
+
+// IP header is iph->ihl * 4 bytes in size --> iph->ihl * 2 16 bit works
+#pragma unroll
+  for (int i = 0; i < 10; i++) { // max 20 bytes (5 * 4)
+    if (i >= iph->ihl * 2)
+      break;
+    if (i == 5)
+      continue; // checksum field at offset 10–11, skip for calc
+    sum += (__u32)ptr[i];
+  }
+
+  while (sum >> 16)
+    sum = (sum & 0xFFFF) + (sum >> 16);
+
+  return ~sum;
+}
+
+static __always_inline __u16 csum_fold_helper(__u32 sum) {
+  while (sum >> 16)
+    sum = (sum & 0xffff) + (sum >> 16);
+  return ~sum;
+}
+
+static __always_inline __u16 csum_add(__u32 sum, __u32 value) {
+  sum += value;
+  return sum;
+}
+
+static __always_inline __u32 csum16_add(__u32 sum, __u16 val) {
+  sum += val;
+  if (sum > 0xffff)
+    sum -= 0xffff;
+  return sum;
+}
+
+static __always_inline __u16 udp_checksum(struct iphdr *iph,
+                                          struct udphdr *udph, void *data_end) {
+  __u32 sum = 0;
+
+  // IP header source/dest address + layer4 protocol
+  sum = csum16_add(sum, (__u16)(iph->saddr >> 16));
+  sum = csum16_add(sum, (__u16)(iph->saddr & 0xffff));
+  sum = csum16_add(sum, (__u16)(iph->daddr >> 16));
+  sum = csum16_add(sum, (__u16)(iph->daddr & 0xffff));
+  sum = csum16_add(sum, __constant_htons(IPPROTO_UDP));
+  // UDP header length
+  sum = csum16_add(sum, udph->len);
+  // UDP header checksum
+  __u16 *ptr = (__u16 *)udph;
+#pragma unroll
+  for (size_t i = 0; i < sizeof(struct udphdr) / 2; i++) {
+    if ((void *)(ptr + 1) > data_end)
+      break;
+    sum = csum16_add(sum, *ptr);
+    ptr++;
+  }
+
+  // UDP payload checksum
+  void *payload = (void *)udph + sizeof(struct udphdr);
+  int payload_len = __constant_ntohs(udph->len) - sizeof(struct udphdr);
+  ptr = (__u16 *)payload;
+
+  for (int i = 0; i < 256; i++) { // max 512 bytes
+    if (payload_len <= 0)
+      break;
+    if ((void *)(ptr + 1) > data_end)
+      break;
+    sum = csum16_add(sum, *ptr);
+    ptr++;
+    payload_len -= 2;
+  }
+
+  // if payload length off: pad wiuth null
+  if (payload_len == 1) {
+    __u8 *last = (__u8 *)ptr;
+    if ((void *)(last + 1) <= data_end) {
+      sum = csum16_add(sum, (*last) << 8);
+    }
+  }
+
+  return csum_fold_helper(sum);
+}
+
+#endif
diff --git a/xdp_loader.c b/xdp_loader.c
new file mode 100644
index 0000000..6f620b8
--- /dev/null
+++ b/xdp_loader.c
@@ -0,0 +1,70 @@
+#include <arpa/inet.h>
+#include <errno.h>
+#include <net/if.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <bpf/bpf.h>
+#include <bpf/libbpf.h>
+#include <linux/if_link.h>
+
+int main(int argc, char **argv) {
+  if (argc != 2) {
+    fprintf(stderr, "Usage: %s <iface>\n", argv[0]);
+    return 1;
+  }
+
+  const char *const iface = argv[1];
+
+  int ifindex = if_nametoindex(iface);
+  if (!ifindex) {
+    perror("if_nametoindex");
+    return 1;
+  }
+
+  struct bpf_object *obj;
+  int prog_fd;
+  const char *const xdp_file = "xdp_udp_handler.o";
+
+  obj = bpf_object__open_file(xdp_file, NULL);
+  if (!obj) {
+    fprintf(stderr, "Error opening BPF object file: `%s'\n", xdp_file);
+    return 1;
+  }
+
+  if (bpf_object__load(obj)) {
+    fprintf(stderr, "Error loading BPF object\n");
+    return 1;
+  }
+
+  struct bpf_program *const prog =
+      bpf_object__find_program_by_name(obj, "xdp_udp_handler");
+  if (!prog) {
+    fprintf(stderr, "Couldn't find program\n");
+    return 1;
+  }
+
+  prog_fd = bpf_program__fd(prog);
+  if (prog_fd < 0) {
+    fprintf(stderr, "Invalid program FD\n");
+    return 1;
+  }
+
+  printf("Attaching BPF program in driver (native) mode..\n");
+  if (bpf_xdp_attach(ifindex, prog_fd,
+                     XDP_FLAGS_UPDATE_IF_NOEXIST | XDP_FLAGS_DRV_MODE,
+                     NULL) < 0) {
+    perror("bpf_xdp_attach");
+    printf("Attaching BPF program in kernel mode..\n");
+    if (bpf_xdp_attach(ifindex, prog_fd, XDP_FLAGS_UPDATE_IF_NOEXIST, NULL) <
+        0) {
+      perror("bpf_xdp_attach");
+      return 1;
+    }
+  }
+
+  printf("XDP program loaded\n");
+  return 0;
+}
diff --git a/xdp_manip.h b/xdp_manip.h
new file mode 100644
index 0000000..70eba28
--- /dev/null
+++ b/xdp_manip.h
@@ -0,0 +1,28 @@
+#ifndef XDP_MANIP_H
+#define XDP_MANIP_H 1
+
+#include <linux/if_ether.h>
+#include <linux/ip.h>
+#include <linux/udp.h>
+
+static __always_inline void swap_eth_addr(struct ethhdr *const ethhdr) {
+  unsigned char src_eth[ETH_ALEN];
+
+  __builtin_memcpy(src_eth, ethhdr->h_source, sizeof(ethhdr->h_source));
+  __builtin_memcpy(ethhdr->h_source, ethhdr->h_dest, sizeof(ethhdr->h_source));
+  __builtin_memcpy(ethhdr->h_dest, src_eth, sizeof(src_eth));
+}
+
+static __always_inline void swap_ip4_addr(struct iphdr *const iphdr) {
+  __be32 src_ip = iphdr->saddr;
+  iphdr->saddr = iphdr->daddr;
+  iphdr->daddr = src_ip;
+}
+
+static __always_inline void swap_udp_port(struct udphdr *const udphdr) {
+  __be16 src_port = udphdr->source;
+  udphdr->source = udphdr->dest;
+  udphdr->dest = src_port;
+}
+
+#endif
diff --git a/xdp_parser.h b/xdp_parser.h
new file mode 100644
index 0000000..a227204
--- /dev/null
+++ b/xdp_parser.h
@@ -0,0 +1,132 @@
+#ifndef XDP_PARSER_H
+#define XDP_PARSER_H 1
+
+#include <linux/if_ether.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <linux/udp.h>
+#include <stdlib.h>
+
+#ifndef VLAN_MAX_DEPTH
+#define VLAN_MAX_DEPTH 2
+#endif
+
+#define VLAN_VID_MASK 0x0fff /* VLAN Identifier */
+
+struct hdr_cursor {
+  union {
+    void *pos;
+    __u8 *pos_u8;
+  };
+};
+
+struct vlan_hdr {
+  __be16 h_vlan_TCI;
+  __be16 h_vlan_encapsulated_proto;
+};
+
+struct collect_vlans {
+  __u16 id[VLAN_MAX_DEPTH];
+};
+
+static __always_inline int proto_is_vlan(__u16 h_proto) {
+  return !!(h_proto == __constant_htons(ETH_P_8021Q) ||
+            h_proto == __constant_htons(ETH_P_8021AD));
+}
+
+static __always_inline int parse_ethhdr_vlan(struct hdr_cursor *nh,
+                                             void *data_end,
+                                             struct ethhdr **ethhdr,
+                                             struct collect_vlans *vlans) {
+  struct ethhdr *eth = nh->pos;
+  int hdrsize = sizeof(*eth);
+  struct vlan_hdr *vlh;
+  __u16 h_proto;
+  int i;
+
+  if (nh->pos + hdrsize > data_end)
+    return -1;
+
+  nh->pos += hdrsize;
+  *ethhdr = eth;
+  vlh = nh->pos;
+  h_proto = eth->h_proto;
+
+#pragma unroll
+  for (i = 0; i < VLAN_MAX_DEPTH; i++) {
+    if (!proto_is_vlan(h_proto))
+      break;
+
+    if (vlh + 1 > (struct vlan_hdr *)data_end)
+      break;
+
+    h_proto = vlh->h_vlan_encapsulated_proto;
+    if (vlans) /* collect VLAN ids */
+      vlans->id[i] = (__constant_ntohs(vlh->h_vlan_TCI) & VLAN_VID_MASK);
+
+    vlh++;
+  }
+
+  nh->pos = vlh;
+  return h_proto; /* network-byte-order */
+}
+
+static __always_inline int parse_ethhdr(struct hdr_cursor *nh, void *data_end,
+                                        struct ethhdr **ethhdr) {
+  return parse_ethhdr_vlan(nh, data_end, ethhdr, NULL);
+}
+
+static __always_inline int parse_ip6hdr(struct hdr_cursor *nh, void *data_end,
+                                        struct ipv6hdr **ip6hdr) {
+  struct ipv6hdr *ip6h = nh->pos;
+
+  if (ip6h + 1 > (struct ipv6hdr *)data_end)
+    return -1;
+
+  nh->pos = ip6h + 1;
+  *ip6hdr = ip6h;
+
+  return ip6h->nexthdr;
+}
+
+static __always_inline int parse_iphdr(struct hdr_cursor *nh, void *data_end,
+                                       struct iphdr **iphdr) {
+  struct iphdr *iph = (struct iphdr *)nh->pos;
+  size_t hdrsize;
+
+  if (iph + 1 > (struct iphdr *)data_end)
+    return -1;
+
+  hdrsize = iph->ihl * 4;
+  if (hdrsize < sizeof(*iph))
+    return -1;
+
+  /* Variable-length IPv4 header, need to use byte-based arithmetic */
+  if (nh->pos + hdrsize > data_end)
+    return -1;
+
+  nh->pos += hdrsize;
+  *iphdr = iph;
+
+  return iph->protocol;
+}
+
+static __always_inline int parse_udphdr(struct hdr_cursor *nh, void *data_end,
+                                        struct udphdr **udphdr) {
+  int len;
+  struct udphdr *h = nh->pos;
+
+  if (h + 1 > (struct udphdr *)data_end)
+    return -1;
+
+  nh->pos = h + 1;
+  *udphdr = h;
+
+  len = __constant_ntohs(h->len) - sizeof(struct udphdr);
+  if (len < 0)
+    return -1;
+
+  return len;
+}
+
+#endif
diff --git a/xdp_udp_handler.c b/xdp_udp_handler.c
new file mode 100644
index 0000000..930667f
--- /dev/null
+++ b/xdp_udp_handler.c
@@ -0,0 +1,127 @@
+#include <linux/bpf.h>
+#include <linux/in.h>
+
+#include <bpf/bpf_helpers.h>
+
+#include "xdp_checksum.h"
+#include "xdp_manip.h"
+#include "xdp_parser.h"
+
+#ifdef XDP_DEBUG
+#define dbg_bpf_printk(fmt, args...) bpf_printk(fmt, ##args)
+#else
+#define dbg_bpf_printk(fmt, args...)
+#endif
+
+#include "common.h"
+
+SEC("xdp")
+int xdp_udp_handler(struct xdp_md *ctx) {
+  void *data_end = (void *)(long)ctx->data_end;
+  void *data = (void *)(long)ctx->data;
+  __u32 action = XDP_PASS; /* Default action */
+  struct hdr_cursor nh = {.pos = data};
+  int nh_type;
+  struct ethhdr *ethhdr;
+  struct iphdr *iphdr = NULL;
+  struct ipv6hdr *ip6hdr = NULL;
+  struct udphdr *udphdr;
+  static const __u8 payload_request[] = {PAYLOAD_REQUEST};
+  static const __u32 payload_request_size = sizeof(payload_request);
+  static const __u8 payload_response[] = {PAYLOAD_RESPONSE};
+  __u32 payload_size;
+
+  nh_type = parse_ethhdr(&nh, data_end, &ethhdr);
+
+  switch (__constant_ntohs(nh_type)) {
+  case ETH_P_IP:
+    nh_type = parse_iphdr(&nh, data_end, &iphdr);
+    break;
+  case ETH_P_IPV6:
+    nh_type = parse_ip6hdr(&nh, data_end, &ip6hdr);
+    break;
+  default:
+    goto out;
+  }
+
+  if (nh_type != IPPROTO_UDP) {
+    goto out;
+  }
+  if (parse_udphdr(&nh, data_end, &udphdr) < 0) {
+    action = XDP_ABORTED;
+    goto out;
+  }
+  if (udphdr->dest != __constant_htons(UDP_PORT)) {
+    goto out;
+  }
+
+  payload_size = (__u8 *)data_end - (__u8 *)nh.pos;
+  if (payload_size < payload_request_size) {
+    goto out;
+  }
+
+  if (nh.pos_u8 + payload_request_size + 1 > (__u8 *)data_end) {
+    goto out;
+  }
+  if (__builtin_memcmp(nh.pos_u8, payload_request, sizeof(payload_request)) !=
+      0) {
+    goto out;
+  }
+
+  dbg_bpf_printk("Received UDP Ping Request #%u with size %u", nh.pos_u8[11],
+                 payload_size);
+
+  /* Shrink UDP packet for Ping Reply */
+  if (bpf_xdp_adjust_tail(ctx, payload_request_size - payload_size) != 0) {
+    return XDP_ABORTED;
+  }
+
+  /* Set data pointers (may not be valid anymore) */
+  data = (void *)(long)ctx->data;
+  data_end = (void *)(long)ctx->data_end;
+  nh.pos = data;
+
+  if (parse_ethhdr(&nh, data_end, &ethhdr) < 0) {
+    action = XDP_ABORTED;
+    goto out;
+  }
+
+  payload_size -= 4;
+
+  if (iphdr != NULL) {
+    if (parse_iphdr(&nh, data_end, &iphdr) < 0) {
+      action = XDP_ABORTED;
+      goto out;
+    }
+    if (parse_udphdr(&nh, data_end, &udphdr) < 0) {
+      action = XDP_ABORTED;
+      goto out;
+    }
+    swap_eth_addr(ethhdr);
+    udphdr->len = __constant_htons(payload_size + sizeof(*udphdr));
+    iphdr->tot_len =
+        __constant_htons(iphdr->ihl * 4 + payload_size + sizeof(*udphdr));
+    swap_ip4_addr(iphdr);
+    iphdr->check = ip_checksum(iphdr);
+    if (nh.pos_u8 + sizeof(payload_response) > (__u8 *)data_end) {
+      action = XDP_ABORTED;
+      goto out;
+    }
+    __builtin_memcpy(nh.pos_u8, payload_response, sizeof(payload_response));
+    swap_udp_port(udphdr);
+    udphdr->check = udp_checksum(iphdr, udphdr, data_end);
+  } else if (ip6hdr != NULL) {
+    parse_ip6hdr(&nh, data_end, &ip6hdr);
+    goto out; // TODO: Implement!
+  } else {
+    action = XDP_ABORTED;
+    goto out;
+  }
+
+  action = XDP_TX;
+out:
+  return action;
+}
+
+char _license[] SEC("license") =
+    "GPL"; // Please keep this to prevent tainting kernel