/* eBPF example program:
 *
 * - Creates arraymap in kernel with 4 bytes keys and 8 byte values
 *
 * - Loads eBPF program
 *
 *   The eBPF program accesses the map passed in to store two pieces of
 *   information. The number of invocations of the program, which maps
 *   to the number of packets received, is stored to key 0. Key 1 is
 *   incremented on each iteration by the number of bytes stored in
 *   the skb.
 *
 * - Attaches the new program to a cgroup using BPF_PROG_ATTACH
 *
 * - Every second, reads map[0] and map[1] to see how many bytes and
 *   packets were seen on any socket of tasks in the given cgroup.
 */

#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <string.h>
#include <unistd.h>
#include <assert.h>
#include <errno.h>
#include <fcntl.h>

#include <linux/bpf.h>

#include "libbpf.h"

enum {
        MAP_KEY_PACKETS,
        MAP_KEY_BYTES,
};

char bpf_log_buf[BPF_LOG_BUF_SIZE];

static int prog_load(int map_fd, int verdict)
{
        struct bpf_insn prog[] = {
                BPF_MOV64_REG(BPF_REG_6, BPF_REG_1), /* save r6 so it's not clobbered by BPF_CALL */

                /* Count packets */
                BPF_MOV64_IMM(BPF_REG_0, MAP_KEY_PACKETS), /* r0 = 0 */
                BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4), /* *(u32 *)(fp - 4) = r0 */
                BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
                BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = fp - 4 */
                BPF_LD_MAP_FD(BPF_REG_1, map_fd), /* load map fd to r1 */
                BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
                BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
                BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */
                BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */

                /* Count bytes */
                BPF_MOV64_IMM(BPF_REG_0, MAP_KEY_BYTES), /* r0 = 1 */
                BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4), /* *(u32 *)(fp - 4) = r0 */
                BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
                BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = fp - 4 */
                BPF_LD_MAP_FD(BPF_REG_1, map_fd),
                BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
                BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
                BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_6, offsetof(struct __sk_buff, len)), /* r1 = skb->len */
                BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */

                BPF_MOV64_IMM(BPF_REG_0, verdict), /* r0 = verdict */
                BPF_EXIT_INSN(),
        };
        size_t insns_cnt = sizeof(prog) / sizeof(struct bpf_insn);

        return bpf_load_program(BPF_PROG_TYPE_CGROUP_SKB,
                                prog, insns_cnt, "GPL", 0,
                                bpf_log_buf, BPF_LOG_BUF_SIZE);
}

static int usage(const char *argv0)
{
        printf("Usage: %s [-d] [-D] <cg-path> <egress|ingress>\n", argv0);
        printf("        -d      Drop Traffic\n");
        printf("        -D      Detach filter, and exit\n");
        return EXIT_FAILURE;
}

static int attach_filter(int cg_fd, int type, int verdict)
{
        int prog_fd, map_fd, ret, key;
        long long pkt_cnt, byte_cnt;

        map_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY,
                                sizeof(key), sizeof(byte_cnt),
                                256, 0);
        if (map_fd < 0) {
                printf("Failed to create map: '%s'\n", strerror(errno));
                return EXIT_FAILURE;
        }

        prog_fd = prog_load(map_fd, verdict);
        printf("Output from kernel verifier:\n%s\n-------\n", bpf_log_buf);

        if (prog_fd < 0) {
                printf("Failed to load prog: '%s'\n", strerror(errno));
                return EXIT_FAILURE;
        }

        ret = bpf_prog_attach(prog_fd, cg_fd, type, 0);
        if (ret < 0) {
                printf("Failed to attach prog to cgroup: '%s'\n",
                       strerror(errno));
                return EXIT_FAILURE;
        }
        while (1) {
                key = MAP_KEY_PACKETS;
                assert(bpf_map_lookup_elem(map_fd, &key, &pkt_cnt) == 0);

                key = MAP_KEY_BYTES;
                assert(bpf_map_lookup_elem(map_fd, &key, &byte_cnt) == 0);

                printf("cgroup received %lld packets, %lld bytes\n",
                       pkt_cnt, byte_cnt);
                sleep(1);
        }

        return EXIT_SUCCESS;
}

int main(int argc, char **argv)
{
        int detach_only = 0, verdict = 1;
        enum bpf_attach_type type;
        int opt, cg_fd, ret;

        while ((opt = getopt(argc, argv, "Dd")) != -1) {
                switch (opt) {
                case 'd':
                        verdict = 0;
                        break;
                case 'D':
                        detach_only = 1;
                        break;
                default:
                        return usage(argv[0]);
                }
        }

        if (argc - optind < 2)
                return usage(argv[0]);

        if (strcmp(argv[optind + 1], "ingress") == 0)
                type = BPF_CGROUP_INET_INGRESS;
        else if (strcmp(argv[optind + 1], "egress") == 0)
                type = BPF_CGROUP_INET_EGRESS;
        else
                return usage(argv[0]);

        cg_fd = open(argv[optind], O_DIRECTORY | O_RDONLY);
        if (cg_fd < 0) {
                printf("Failed to open cgroup path: '%s'\n", strerror(errno));
                return EXIT_FAILURE;
        }

        if (detach_only) {
                ret = bpf_prog_detach(cg_fd, type);
                printf("bpf_prog_detach() returned '%s' (%d)\n",
                       strerror(errno), errno);
        } else
                ret = attach_filter(cg_fd, type, verdict);

        return ret;
}