bpf: add bpf_xdp_adjust_tail sample prog
adding bpf's sample program which is using bpf_xdp_adjust_tail helper
by generating ICMPv4 "packet to big" message if ingress packet's size is
bigger then 600 bytes
Signed-off-by: Nikita V. Shirokov <tehnerd@tehnerd.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
diff --git a/samples/bpf/xdp_adjust_tail_user.c b/samples/bpf/xdp_adjust_tail_user.c
new file mode 100644
index 0000000..f621a54
--- /dev/null
+++ b/samples/bpf/xdp_adjust_tail_user.c
@@ -0,0 +1,142 @@
+/* SPDX-License-Identifier: GPL-2.0
+ * Copyright (c) 2018 Facebook
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+#include <linux/bpf.h>
+#include <linux/if_link.h>
+#include <assert.h>
+#include <errno.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/resource.h>
+#include <arpa/inet.h>
+#include <netinet/ether.h>
+#include <unistd.h>
+#include <time.h>
+#include "bpf_load.h"
+#include "libbpf.h"
+#include "bpf_util.h"
+
+#define STATS_INTERVAL_S 2U
+
+static int ifindex = -1;
+static __u32 xdp_flags;
+
+static void int_exit(int sig)
+{
+ if (ifindex > -1)
+ bpf_set_link_xdp_fd(ifindex, -1, xdp_flags);
+ exit(0);
+}
+
+/* simple "icmp packet too big sent" counter
+ */
+static void poll_stats(unsigned int kill_after_s)
+{
+ time_t started_at = time(NULL);
+ __u64 value = 0;
+ int key = 0;
+
+
+ while (!kill_after_s || time(NULL) - started_at <= kill_after_s) {
+ sleep(STATS_INTERVAL_S);
+
+ assert(bpf_map_lookup_elem(map_fd[0], &key, &value) == 0);
+
+ printf("icmp \"packet too big\" sent: %10llu pkts\n", value);
+ }
+}
+
+static void usage(const char *cmd)
+{
+ printf("Start a XDP prog which send ICMP \"packet too big\" \n"
+ "messages if ingress packet is bigger then MAX_SIZE bytes\n");
+ printf("Usage: %s [...]\n", cmd);
+ printf(" -i <ifindex> Interface Index\n");
+ printf(" -T <stop-after-X-seconds> Default: 0 (forever)\n");
+ printf(" -S use skb-mode\n");
+ printf(" -N enforce native mode\n");
+ printf(" -h Display this help\n");
+}
+
+int main(int argc, char **argv)
+{
+ unsigned char opt_flags[256] = {};
+ unsigned int kill_after_s = 0;
+ const char *optstr = "i:T:SNh";
+ struct rlimit r = {RLIM_INFINITY, RLIM_INFINITY};
+ char filename[256];
+ int opt;
+ int i;
+
+
+ for (i = 0; i < strlen(optstr); i++)
+ if (optstr[i] != 'h' && 'a' <= optstr[i] && optstr[i] <= 'z')
+ opt_flags[(unsigned char)optstr[i]] = 1;
+
+ while ((opt = getopt(argc, argv, optstr)) != -1) {
+
+ switch (opt) {
+ case 'i':
+ ifindex = atoi(optarg);
+ break;
+ case 'T':
+ kill_after_s = atoi(optarg);
+ break;
+ case 'S':
+ xdp_flags |= XDP_FLAGS_SKB_MODE;
+ break;
+ case 'N':
+ xdp_flags |= XDP_FLAGS_DRV_MODE;
+ break;
+ default:
+ usage(argv[0]);
+ return 1;
+ }
+ opt_flags[opt] = 0;
+ }
+
+ for (i = 0; i < strlen(optstr); i++) {
+ if (opt_flags[(unsigned int)optstr[i]]) {
+ fprintf(stderr, "Missing argument -%c\n", optstr[i]);
+ usage(argv[0]);
+ return 1;
+ }
+ }
+
+ if (setrlimit(RLIMIT_MEMLOCK, &r)) {
+ perror("setrlimit(RLIMIT_MEMLOCK, RLIM_INFINITY)");
+ return 1;
+ }
+
+ snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+
+ if (load_bpf_file(filename)) {
+ printf("%s", bpf_log_buf);
+ return 1;
+ }
+
+ if (!prog_fd[0]) {
+ printf("load_bpf_file: %s\n", strerror(errno));
+ return 1;
+ }
+
+ signal(SIGINT, int_exit);
+ signal(SIGTERM, int_exit);
+
+ if (bpf_set_link_xdp_fd(ifindex, prog_fd[0], xdp_flags) < 0) {
+ printf("link set xdp fd failed\n");
+ return 1;
+ }
+
+ poll_stats(kill_after_s);
+
+ bpf_set_link_xdp_fd(ifindex, -1, xdp_flags);
+
+ return 0;
+}