/*      $NetBSD: bpfopen.c,v 1.2 2021/08/19 03:27:05 yamaguchi Exp $    */

/*
 * Copyright (c) 2021 Internet Initiative Japan Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__RCSID("$NetBSD: bpfopen.c,v 1.2 2021/08/19 03:27:05 yamaguchi Exp $");

#include <sys/param.h>
#include <sys/ioctl.h>

#include <net/if.h>
#include <net/bpf.h>

#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <poll.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <unistd.h>

#include <util.h>

enum {
        ARG_PROG = 0,
        ARG_HOST,
        ARG_IFNAME,
        ARG_NUM
};

enum {
        PFD_BPF = 0,
        PFD_NUM
};

static void     sighandler(int);
static void     log_debug(const char *, ...) __printflike(1, 2);
static int      bpf_open(void);
static void     bpf_close(int);
static void     bpf_read(int);

static sig_atomic_t      quit;
static bool              daemonize = false;
static int               verbose = 0;
static const char       *path_pid = "/var/run/bpfopen.pid";
static const char       *path_bpf = "/dev/bpf";
static const char       *ifname = NULL;

static void
usage(void)
{

        fprintf(stderr, "%s [-vd] [-p pidfile] [-b devbpf ] <ifname>\n"
            "\t-v: verbose\n"
            "\t-d: daemon mode\n",
            getprogname());
        exit(1);
}

int
main(int argc, char *argv[])
{
        int bpfd;
        int ch;

        while ((ch = getopt(argc, argv, "b:dp:v")) != -1) {
                switch (ch) {
                case 'b':
                        path_bpf = optarg;
                        break;
                case 'd':
                        daemonize = true;
                        break;
                case 'p':
                        path_pid = optarg;
                        break;
                case 'v':
                        verbose++;
                        break;
                default:
                        usage();
                }
        }

        argc -= optind;
        argv += optind;

        if (argc != 1)
                usage();

        ifname = argv[0];

        bpfd = bpf_open();
        if (bpfd < 0)
                err(1, "bpf_open");
        log_debug("bpf opened");

        if (daemonize) {
                if (daemon(1, 1) != 0) {
                        bpf_close(bpfd);
                        err(1, "daemon");
                }
                log_debug("daemonized");

                if (pidfile(path_pid) != 0) {
                        bpf_close(bpfd);
                        err(1, "pidfile");
                }
        }

        bpf_read(bpfd);
        bpf_close(bpfd);
        if (daemonize)
                pidfile_clean();

        return 0;
}

static void
sighandler(int signo)
{

        quit = 1;
}

static void
log_debug(const char *fmt, ...)
{
        va_list ap;

        if (verbose <= 0)
                return;

        va_start(ap, fmt);
        vfprintf(stderr, fmt, ap);
        va_end(ap);

        fprintf(stderr, "\n");
}

static int
bpf_open(void)
{
        struct ifreq ifr;
        int bpfd;

        bpfd = open(path_bpf, O_RDONLY);
        if (bpfd < 0) {
                log_debug("open: %s", strerror(errno));
                return -1;
        }

        memset(&ifr, 0, sizeof(ifr));
        strlcpy(ifr.ifr_name, ifname, sizeof(ifr.ifr_name));

        if (ioctl(bpfd, BIOCSETIF, &ifr) != 0) {
                log_debug("BIOCSETIF: %s", strerror(errno));
                goto close_bpfd;
        }

        if (ioctl(bpfd, BIOCPROMISC, NULL) != 0) {
                log_debug("BIOCPROMISC: %s", strerror(errno));
                goto close_bpfd;
        }

        return bpfd;

close_bpfd:
        close(bpfd);

        return -1;
}

static void
bpf_close(int bpfd)
{

        close(bpfd);
}

static void
bpf_read(int bpfd)
{
        struct pollfd pfd[PFD_NUM];
        int nfds;
        char *buf;
        u_int bufsiz;
        ssize_t n;

        if (ioctl(bpfd, BIOCGBLEN, &bufsiz) != 0) {
                bufsiz = BPF_DFLTBUFSIZE;
                log_debug("BIOCGBLEN: %s, use default size %u",
                    strerror(errno), bufsiz);
        }

        bufsiz = MIN(bufsiz, BPF_DFLTBUFSIZE * 4);

        buf = malloc(bufsiz);
        if (buf == NULL) {
                log_debug("malloc: %s", strerror(errno));
                return;
        }

        quit = 0;
        signal(SIGTERM, sighandler);
        signal(SIGQUIT, sighandler);
        signal(SIGINT, sighandler);
        signal(SIGHUP, sighandler);

        log_debug("start reading %s, bufsiz=%u", ifname, bufsiz);

        while (quit == 0) {
                pfd[PFD_BPF].fd = bpfd;
                pfd[PFD_BPF].events = POLLIN;

                nfds = poll(pfd, PFD_NUM, 1 * 1000);
                if (nfds == -1 && errno != EINTR) {
                        warn("poll");
                        quit = 1;
                }

                if (nfds > 0 && (pfd[PFD_BPF].revents & POLLIN)) {
                        /* read & drop */
                        memset(buf, 0, bufsiz);
                        n = read(pfd[PFD_BPF].fd, buf, bufsiz);
                        if (n < 0)
                                quit = 1;
                }
        }

        log_debug("finish reading %s", ifname);
        free(buf);
}