int wait_snd(int sock)
{
    fd_set RD, WR, EXP;
    struct timespec ts;
    int R;

    FD_ZERO(&RD);
    FD_ZERO(&WR);
    FD_ZERO(&EXP);

    FD_SET(sock, &WR);

    ts.tv_sec = 0;
    ts.tv_nsec = 100;

reselect:
    R = select(sock+1, NULL, &WR, NULL, NULL);
    switch (R)
    {
    case 0:
    case 1:
        return R;
    case -1:
    default:
        switch(errno)
        {
        case EINTR:
            goto reselect;
        default:
            return -errno;
        }
    }
}

int main()
{
...
    clock_gettime(CLOCK_MONOTONIC, &ts_a);
_sendto:
    if (wait_snd(sockfd) != 1)
        goto _sendto;
    ret = sendto(sockfd, buf, fsize, 0, (struct sockaddr *)&sockaddr, sizeof(struct sockaddr_ll));
    if (ret < 0) {
        if (errno == ENOBUFS)
        {
             printf("ENOBUFS catched\n");
             printf("Retrrying a packet...\n");
             goto _sendto;
        }
        if (errno == EAGAIN)
        {
             printf("EAGAIN catched\n");
             printf("Retrrying a packet...\n");
             goto _sendto;
        }
        fprintf(stderr, "sendto %s (%d): %s (%d)\n", ifmac2name(sockaddr.sll_addr, mactable), fsize, strerror(errno), errno);
             goto _sendto;
    }
    clock_gettime(CLOCK_MONOTONIC, &ts_b);
    if (ret != fsize)
        printf("%d\n", ret), exit(0);
    snd_bytes += ret;
    snd_nsec += ((ts_b.tv_nsec < ts_a.tv_nsec) ? ((NSECS_IN_SEC - ts_a.tv_nsec) + ts_b.tv_nsec) : (ts_b.tv_nsec - ts_a.tv_nsec));
...
}