/* 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 <net/if.h>
#include <arpa/inet.h>
#include <netinet/ether.h>
#include <unistd.h>
#include <time.h>
#include <bpf/bpf.h>
#include <bpf/libbpf.h>

#define STATS_INTERVAL_S 2U
#define MAX_PCKT_SIZE 600

static int ifindex = -1;
static __u32 xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST;
static __u32 prog_id;

static void int_exit(int sig)
{
        __u32 curr_prog_id = 0;

        if (ifindex > -1) {
                if (bpf_xdp_query_id(ifindex, xdp_flags, &curr_prog_id)) {
                        printf("bpf_xdp_query_id failed\n");
                        exit(1);
                }
                if (prog_id == curr_prog_id)
                        bpf_xdp_detach(ifindex, xdp_flags, NULL);
                else if (!curr_prog_id)
                        printf("couldn't find a prog id on a given iface\n");
                else
                        printf("program on interface changed, not removing\n");
        }
        exit(0);
}

/* simple "icmp packet too big sent" counter
 */
static void poll_stats(unsigned int map_fd, 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, &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 <ifname|ifindex> Interface\n");
        printf("    -T <stop-after-X-seconds> Default: 0 (forever)\n");
        printf("    -P <MAX_PCKT_SIZE> Default: %u\n", MAX_PCKT_SIZE);
        printf("    -S use skb-mode\n");
        printf("    -N enforce native mode\n");
        printf("    -F force loading prog\n");
        printf("    -h Display this help\n");
}

int main(int argc, char **argv)
{
        unsigned char opt_flags[256] = {};
        const char *optstr = "i:T:P:SNFh";
        struct bpf_prog_info info = {};
        __u32 info_len = sizeof(info);
        unsigned int kill_after_s = 0;
        int i, prog_fd, map_fd, opt;
        struct bpf_program *prog;
        struct bpf_object *obj;
        __u32 max_pckt_size = 0;
        __u32 key = 0;
        char filename[256];
        int err;

        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 = if_nametoindex(optarg);
                        if (!ifindex)
                                ifindex = atoi(optarg);
                        break;
                case 'T':
                        kill_after_s = atoi(optarg);
                        break;
                case 'P':
                        max_pckt_size = atoi(optarg);
                        break;
                case 'S':
                        xdp_flags |= XDP_FLAGS_SKB_MODE;
                        break;
                case 'N':
                        /* default, set below */
                        break;
                case 'F':
                        xdp_flags &= ~XDP_FLAGS_UPDATE_IF_NOEXIST;
                        break;
                default:
                        usage(argv[0]);
                        return 1;
                }
                opt_flags[opt] = 0;
        }

        if (!(xdp_flags & XDP_FLAGS_SKB_MODE))
                xdp_flags |= XDP_FLAGS_DRV_MODE;

        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 (!ifindex) {
                fprintf(stderr, "Invalid ifname\n");
                return 1;
        }

        snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);

        obj = bpf_object__open_file(filename, NULL);
        if (libbpf_get_error(obj))
                return 1;

        prog = bpf_object__next_program(obj, NULL);
        bpf_program__set_type(prog, BPF_PROG_TYPE_XDP);

        err = bpf_object__load(obj);
        if (err)
                return 1;

        prog_fd = bpf_program__fd(prog);

        /* static global var 'max_pcktsz' is accessible from .data section */
        if (max_pckt_size) {
                map_fd = bpf_object__find_map_fd_by_name(obj, "xdp_adju.data");
                if (map_fd < 0) {
                        printf("finding a max_pcktsz map in obj file failed\n");
                        return 1;
                }
                bpf_map_update_elem(map_fd, &key, &max_pckt_size, BPF_ANY);
        }

        /* fetch icmpcnt map */
        map_fd = bpf_object__find_map_fd_by_name(obj, "icmpcnt");
        if (map_fd < 0) {
                printf("finding a icmpcnt map in obj file failed\n");
                return 1;
        }

        signal(SIGINT, int_exit);
        signal(SIGTERM, int_exit);

        if (bpf_xdp_attach(ifindex, prog_fd, xdp_flags, NULL) < 0) {
                printf("link set xdp fd failed\n");
                return 1;
        }

        err = bpf_prog_get_info_by_fd(prog_fd, &info, &info_len);
        if (err) {
                printf("can't get prog info - %s\n", strerror(errno));
                return 1;
        }
        prog_id = info.id;

        poll_stats(map_fd, kill_after_s);
        int_exit(0);

        return 0;
}