/* vi: set sw=4 ts=4: */
/*
 * DHCPv6 client.
 *
 * 2011-11.
 * WARNING: THIS CODE IS INCOMPLETE. IT IS NOWHERE NEAR
 * TO BE READY FOR PRODUCTION USE.
 *
 * Copyright (C) 2011 Denys Vlasenko.
 *
 * Licensed under GPLv2, see file LICENSE in this source tree.
 */

//config:config UDHCPC6
//config:       bool "udhcp client for DHCPv6 (udhcpc6)"
//config:       default n  # not yet ready
//config:       depends on FEATURE_IPV6
//config:       help
//config:         udhcpc6 is a DHCPv6 client

//applet:IF_UDHCPC6(APPLET(udhcpc6, BB_DIR_USR_BIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_UDHCPC6) += d6_dhcpc.o d6_packet.o d6_socket.o common.o socket.o signalpipe.o


#include <syslog.h>
/* Override ENABLE_FEATURE_PIDFILE - ifupdown needs our pidfile to always exist */
#define WANT_PIDFILE 1
#include "common.h"
#include "dhcpd.h"
#include "dhcpc.h"
#include "d6_common.h"

#include <netinet/if_ether.h>
#include <netpacket/packet.h>
#include <linux/filter.h>

/* "struct client_config_t client_config" is in bb_common_bufsiz1 */


#if ENABLE_LONG_OPTS
static const char udhcpc6_longopts[] ALIGN1 =
        "interface\0"      Required_argument "i"
        "now\0"            No_argument       "n"
        "pidfile\0"        Required_argument "p"
        "quit\0"           No_argument       "q"
        "release\0"        No_argument       "R"
        "request\0"        Required_argument "r"
        "script\0"         Required_argument "s"
        "timeout\0"        Required_argument "T"
        "retries\0"        Required_argument "t"
        "tryagain\0"       Required_argument "A"
        "syslog\0"         No_argument       "S"
        "request-option\0" Required_argument "O"
        "no-default-options\0" No_argument   "o"
        "foreground\0"     No_argument       "f"
        "background\0"     No_argument       "b"
///     IF_FEATURE_UDHCPC_ARPING("arping\0"     No_argument       "a")
        IF_FEATURE_UDHCP_PORT("client-port\0"   Required_argument "P")
        ;
#endif
/* Must match getopt32 option string order */
enum {
        OPT_i = 1 << 0,
        OPT_n = 1 << 1,
        OPT_p = 1 << 2,
        OPT_q = 1 << 3,
        OPT_R = 1 << 4,
        OPT_r = 1 << 5,
        OPT_s = 1 << 6,
        OPT_T = 1 << 7,
        OPT_t = 1 << 8,
        OPT_S = 1 << 9,
        OPT_A = 1 << 10,
        OPT_O = 1 << 11,
        OPT_o = 1 << 12,
        OPT_x = 1 << 13,
        OPT_f = 1 << 14,
/* The rest has variable bit positions, need to be clever */
        OPTBIT_f = 14,
        USE_FOR_MMU(             OPTBIT_b,)
        ///IF_FEATURE_UDHCPC_ARPING(OPTBIT_a,)
        IF_FEATURE_UDHCP_PORT(   OPTBIT_P,)
        USE_FOR_MMU(             OPT_b = 1 << OPTBIT_b,)
        ///IF_FEATURE_UDHCPC_ARPING(OPT_a = 1 << OPTBIT_a,)
        IF_FEATURE_UDHCP_PORT(   OPT_P = 1 << OPTBIT_P,)
};


/*** Utility functions ***/

static void *d6_find_option(uint8_t *option, uint8_t *option_end, unsigned code)
{
        /* "length minus 4" */
        int len_m4 = option_end - option - 4;
        while (len_m4 >= 0) {
                /* Next option's len is too big? */
                if (option[3] > len_m4)
                        return NULL; /* yes. bogus packet! */
                /* So far we treat any opts with code >255
                 * or len >255 as bogus, and stop at once.
                 * This simplifies big-endian handling.
                 */
                if (option[0] != 0 || option[2] != 0)
                        return NULL;
                /* Option seems to be valid */
                /* Does its code match? */
                if (option[1] == code)
                        return option; /* yes! */
                option += option[3] + 4;
                len_m4 -= option[3] + 4;
        }
        return NULL;
}

static void *d6_copy_option(uint8_t *option, uint8_t *option_end, unsigned code)
{
        uint8_t *opt = d6_find_option(option, option_end, code);
        if (!opt)
                return opt;
        return memcpy(xmalloc(opt[3] + 4), opt, opt[3] + 4);
}

static void *d6_store_blob(void *dst, const void *src, unsigned len)
{
        memcpy(dst, src, len);
        return dst + len;
}


/*** Script execution code ***/

static char** new_env(void)
{
        client6_data.env_ptr = xrealloc_vector(client6_data.env_ptr, 3, client6_data.env_idx);
        return &client6_data.env_ptr[client6_data.env_idx++];
}

/* put all the parameters into the environment */
static void option_to_env(uint8_t *option, uint8_t *option_end)
{
        /* "length minus 4" */
        int len_m4 = option_end - option - 4;
        while (len_m4 >= 0) {
                uint32_t v32;
                char ipv6str[sizeof("ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff")];

                if (option[0] != 0 || option[2] != 0)
                        break;

                switch (option[1]) {
                //case D6_OPT_CLIENTID:
                //case D6_OPT_SERVERID:
                case D6_OPT_IA_NA:
                case D6_OPT_IA_PD:
                        option_to_env(option + 16, option + 4 + option[3]);
                        break;
                //case D6_OPT_IA_TA:
                case D6_OPT_IAADDR:
/*   0                   1                   2                   3
 *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |          OPTION_IAADDR        |          option-len           |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                                                               |
 * |                         IPv6 address                          |
 * |                                                               |
 * |                                                               |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                      preferred-lifetime                       |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                        valid-lifetime                         |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 */
                        sprint_nip6(ipv6str, option + 4);
                        *new_env() = xasprintf("ipv6=%s", ipv6str);

                        move_from_unaligned32(v32, option + 4 + 16 + 4);
                        *new_env() = xasprintf("lease=%u", (unsigned)v32);
                        break;

                //case D6_OPT_ORO:
                //case D6_OPT_PREFERENCE:
                //case D6_OPT_ELAPSED_TIME:
                //case D6_OPT_RELAY_MSG:
                //case D6_OPT_AUTH:
                //case D6_OPT_UNICAST:
                //case D6_OPT_STATUS_CODE:
                //case D6_OPT_RAPID_COMMIT:
                //case D6_OPT_USER_CLASS:
                //case D6_OPT_VENDOR_CLASS:
                //case D6_OPT_VENDOR_OPTS:
                //case D6_OPT_INTERFACE_ID:
                //case D6_OPT_RECONF_MSG:
                //case D6_OPT_RECONF_ACCEPT:

                case D6_OPT_IAPREFIX:
/*  0                   1                   2                   3
 *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |        OPTION_IAPREFIX        |         option-length         |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                      preferred-lifetime                       |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                        valid-lifetime                         |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * | prefix-length |                                               |
 * +-+-+-+-+-+-+-+-+          IPv6 prefix                          |
 * |                           (16 octets)                         |
 * |                                                               |
 * |               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |               |
 * +-+-+-+-+-+-+-+-+
 */
                        //move_from_unaligned32(v32, option + 4 + 4);
                        //*new_env() = xasprintf("lease=%u", (unsigned)v32);

                        sprint_nip6(ipv6str, option + 4 + 4 + 1);
                        *new_env() = xasprintf("ipv6prefix=%s/%u", ipv6str, (unsigned)(option[4 + 4]));
                }
                option += 4 + option[3];
                len_m4 -= 4 + option[3];
        }
}

static char **fill_envp(struct d6_packet *packet)
{
        char **envp, **curr;

        client6_data.env_ptr = NULL;
        client6_data.env_idx = 0;

        *new_env() = xasprintf("interface=%s", client_config.interface);

        if (packet)
                option_to_env(packet->d6_options, packet->d6_options + sizeof(packet->d6_options));

        envp = curr = client6_data.env_ptr;
        while (*curr)
                putenv(*curr++);

        return envp;
}

/* Call a script with a par file and env vars */
static void d6_run_script(struct d6_packet *packet, const char *name)
{
        char **envp, **curr;
        char *argv[3];

        envp = fill_envp(packet);

        /* call script */
        log1("Executing %s %s", client_config.script, name);
        argv[0] = (char*) client_config.script;
        argv[1] = (char*) name;
        argv[2] = NULL;
        spawn_and_wait(argv);

        for (curr = envp; *curr; curr++) {
                log2(" %s", *curr);
                bb_unsetenv_and_free(*curr);
        }
        free(envp);
}


/*** Sending/receiving packets ***/

static ALWAYS_INLINE uint32_t random_xid(void)
{
        uint32_t t = rand() & htonl(0x00ffffff);
        return t;
}

/* Initialize the packet with the proper defaults */
static uint8_t *init_d6_packet(struct d6_packet *packet, char type, uint32_t xid)
{
        struct d6_option *clientid;

        memset(packet, 0, sizeof(*packet));

        packet->d6_xid32 = xid;
        packet->d6_msg_type = type;

        clientid = (void*)client_config.clientid;
        return d6_store_blob(packet->d6_options, clientid, clientid->len + 2+2);
}

static uint8_t *add_d6_client_options(uint8_t *ptr)
{
        return ptr;
        //uint8_t c;
        //int i, end, len;

        /* Add a "param req" option with the list of options we'd like to have
         * from stubborn DHCP servers. Pull the data from the struct in common.c.
         * No bounds checking because it goes towards the head of the packet. */
        //...

        /* Add -x options if any */
        //...
}

static int d6_mcast_from_client_config_ifindex(struct d6_packet *packet, uint8_t *end)
{
        static const uint8_t FF02__1_2[16] = {
                0xFF, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x02,
        };

        return d6_send_raw_packet(
                packet, (end - (uint8_t*) packet),
                /*src*/ NULL, CLIENT_PORT6,
                /*dst*/ (struct in6_addr*)FF02__1_2, SERVER_PORT6, MAC_BCAST_ADDR,
                client_config.ifindex
        );
}

/* Milticast a DHCPv6 Solicit packet to the network, with an optionally requested IP.
 *
 * RFC 3315 17.1.1. Creation of Solicit Messages
 *
 * The client MUST include a Client Identifier option to identify itself
 * to the server.  The client includes IA options for any IAs to which
 * it wants the server to assign addresses.  The client MAY include
 * addresses in the IAs as a hint to the server about addresses for
 * which the client has a preference. ...
 *
 * The client uses IA_NA options to request the assignment of non-
 * temporary addresses and uses IA_TA options to request the assignment
 * of temporary addresses.  Either IA_NA or IA_TA options, or a
 * combination of both, can be included in DHCP messages.
 *
 * The client SHOULD include an Option Request option (see section 22.7)
 * to indicate the options the client is interested in receiving.  The
 * client MAY additionally include instances of those options that are
 * identified in the Option Request option, with data values as hints to
 * the server about parameter values the client would like to have
 * returned.
 *
 * The client includes a Reconfigure Accept option (see section 22.20)
 * if the client is willing to accept Reconfigure messages from the
 * server.
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        OPTION_CLIENTID        |          option-len           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                                                               .
      .                              DUID                             .
      .                        (variable length)                      .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          OPTION_IA_NA         |          option-len           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        IAID (4 octets)                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              T1                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              T2                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                         IA_NA-options                         .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          OPTION_IAADDR        |          option-len           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                         IPv6 address                          |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      preferred-lifetime                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        valid-lifetime                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                                                               .
      .                        IAaddr-options                         .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           OPTION_ORO          |           option-len          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    requested-option-code-1    |    requested-option-code-2    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     OPTION_RECONF_ACCEPT      |               0               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 */
/* NOINLINE: limit stack usage in caller */
static NOINLINE int send_d6_discover(uint32_t xid, struct in6_addr *requested_ipv6)
{
        struct d6_packet packet;
        uint8_t *opt_ptr;
        unsigned len;

        /* Fill in: msg type, client id */
        opt_ptr = init_d6_packet(&packet, D6_MSG_SOLICIT, xid);

        /* Create new IA_NA, optionally with included IAADDR with requested IP */
        free(client6_data.ia_na);
        len = requested_ipv6 ? 2+2+4+4+4 + 2+2+16+4+4 : 2+2+4+4+4;
        client6_data.ia_na = xzalloc(len);
        client6_data.ia_na->code = D6_OPT_IA_NA;
        client6_data.ia_na->len = len - 4;
        *(uint32_t*)client6_data.ia_na->data = rand(); /* IAID */
        if (requested_ipv6) {
                struct d6_option *iaaddr = (void*)(client6_data.ia_na->data + 4+4+4);
                iaaddr->code = D6_OPT_IAADDR;
                iaaddr->len = 16+4+4;
                memcpy(iaaddr->data, requested_ipv6, 16);
        }
        opt_ptr = d6_store_blob(opt_ptr, client6_data.ia_na, len);

        /* Add options:
         * "param req" option according to -O, options specified with -x
         */
        opt_ptr = add_d6_client_options(opt_ptr);

        bb_info_msg("Sending discover...");
        return d6_mcast_from_client_config_ifindex(&packet, opt_ptr);
}

/* Multicast a DHCPv6 request message
 *
 * RFC 3315 18.1.1. Creation and Transmission of Request Messages
 *
 * The client uses a Request message to populate IAs with addresses and
 * obtain other configuration information.  The client includes one or
 * more IA options in the Request message.  The server then returns
 * addresses and other information about the IAs to the client in IA
 * options in a Reply message.
 *
 * The client generates a transaction ID and inserts this value in the
 * "transaction-id" field.
 *
 * The client places the identifier of the destination server in a
 * Server Identifier option.
 *
 * The client MUST include a Client Identifier option to identify itself
 * to the server.  The client adds any other appropriate options,
 * including one or more IA options (if the client is requesting that
 * the server assign it some network addresses).
 *
 * The client MUST include an Option Request option (see section 22.7)
 * to indicate the options the client is interested in receiving.  The
 * client MAY include options with data values as hints to the server
 * about parameter values the client would like to have returned.
 *
 * The client includes a Reconfigure Accept option (see section 22.20)
 * indicating whether or not the client is willing to accept Reconfigure
 * messages from the server.
 */
/* NOINLINE: limit stack usage in caller */
static NOINLINE int send_d6_select(uint32_t xid)
{
        struct d6_packet packet;
        uint8_t *opt_ptr;

        /* Fill in: msg type, client id */
        opt_ptr = init_d6_packet(&packet, D6_MSG_REQUEST, xid);

        /* server id */
        opt_ptr = d6_store_blob(opt_ptr, client6_data.server_id, client6_data.server_id->len + 2+2);
        /* IA NA (contains requested IP) */
        opt_ptr = d6_store_blob(opt_ptr, client6_data.ia_na, client6_data.ia_na->len + 2+2);

        /* Add options:
         * "param req" option according to -O, options specified with -x
         */
        opt_ptr = add_d6_client_options(opt_ptr);

        bb_info_msg("Sending select...");
        return d6_mcast_from_client_config_ifindex(&packet, opt_ptr);
}

/* Unicast or broadcast a DHCP renew message
 *
 * RFC 3315 18.1.3. Creation and Transmission of Renew Messages
 *
 * To extend the valid and preferred lifetimes for the addresses
 * associated with an IA, the client sends a Renew message to the server
 * from which the client obtained the addresses in the IA containing an
 * IA option for the IA.  The client includes IA Address options in the
 * IA option for the addresses associated with the IA.  The server
 * determines new lifetimes for the addresses in the IA according to the
 * administrative configuration of the server.  The server may also add
 * new addresses to the IA.  The server may remove addresses from the IA
 * by setting the preferred and valid lifetimes of those addresses to
 * zero.
 *
 * The server controls the time at which the client contacts the server
 * to extend the lifetimes on assigned addresses through the T1 and T2
 * parameters assigned to an IA.
 *
 * At time T1 for an IA, the client initiates a Renew/Reply message
 * exchange to extend the lifetimes on any addresses in the IA.  The
 * client includes an IA option with all addresses currently assigned to
 * the IA in its Renew message.
 *
 * If T1 or T2 is set to 0 by the server (for an IA_NA) or there are no
 * T1 or T2 times (for an IA_TA), the client may send a Renew or Rebind
 * message, respectively, at the client's discretion.
 *
 * The client sets the "msg-type" field to RENEW.  The client generates
 * a transaction ID and inserts this value in the "transaction-id"
 * field.
 *
 * The client places the identifier of the destination server in a
 * Server Identifier option.
 *
 * The client MUST include a Client Identifier option to identify itself
 * to the server.  The client adds any appropriate options, including
 * one or more IA options.  The client MUST include the list of
 * addresses the client currently has associated with the IAs in the
 * Renew message.
 *
 * The client MUST include an Option Request option (see section 22.7)
 * to indicate the options the client is interested in receiving.  The
 * client MAY include options with data values as hints to the server
 * about parameter values the client would like to have returned.
 */
/* NOINLINE: limit stack usage in caller */
static NOINLINE int send_d6_renew(uint32_t xid, struct in6_addr *server_ipv6, struct in6_addr *our_cur_ipv6)
{
        struct d6_packet packet;
        uint8_t *opt_ptr;

        /* Fill in: msg type, client id */
        opt_ptr = init_d6_packet(&packet, DHCPREQUEST, xid);

        /* server id */
        opt_ptr = d6_store_blob(opt_ptr, client6_data.server_id, client6_data.server_id->len + 2+2);
        /* IA NA (contains requested IP) */
        opt_ptr = d6_store_blob(opt_ptr, client6_data.ia_na, client6_data.ia_na->len + 2+2);

        /* Add options:
         * "param req" option according to -O, options specified with -x
         */
        opt_ptr = add_d6_client_options(opt_ptr);

        bb_info_msg("Sending renew...");
        if (server_ipv6)
                return d6_send_kernel_packet(
                        &packet, (opt_ptr - (uint8_t*) &packet),
                        our_cur_ipv6, CLIENT_PORT6,
                        server_ipv6, SERVER_PORT6
                );
        return d6_mcast_from_client_config_ifindex(&packet, opt_ptr);
}

/* Unicast a DHCP release message */
static int send_d6_release(struct in6_addr *server_ipv6, struct in6_addr *our_cur_ipv6)
{
        struct d6_packet packet;
        uint8_t *opt_ptr;

        /* Fill in: msg type, client id */
        opt_ptr = init_d6_packet(&packet, D6_MSG_RELEASE, random_xid());
        /* server id */
        opt_ptr = d6_store_blob(opt_ptr, client6_data.server_id, client6_data.server_id->len + 2+2);
        /* IA NA (contains our current IP) */
        opt_ptr = d6_store_blob(opt_ptr, client6_data.ia_na, client6_data.ia_na->len + 2+2);

        bb_info_msg("Sending release...");
        return d6_send_kernel_packet(
                &packet, (opt_ptr - (uint8_t*) &packet),
                our_cur_ipv6, CLIENT_PORT6,
                server_ipv6, SERVER_PORT6
        );
}

/* Returns -1 on errors that are fatal for the socket, -2 for those that aren't */
/* NOINLINE: limit stack usage in caller */
static NOINLINE int d6_recv_raw_packet(struct in6_addr *peer_ipv6
        UNUSED_PARAM
        , struct d6_packet *d6_pkt, int fd)
{
        int bytes;
        struct ip6_udp_d6_packet packet;

        bytes = safe_read(fd, &packet, sizeof(packet));
        if (bytes < 0) {
                log1("Packet read error, ignoring");
                /* NB: possible down interface, etc. Caller should pause. */
                return bytes; /* returns -1 */
        }

        if (bytes < (int) (sizeof(packet.ip6) + sizeof(packet.udp))) {
                log1("Packet is too short, ignoring");
                return -2;
        }

        if (bytes < sizeof(packet.ip6) + ntohs(packet.ip6.ip6_plen)) {
                /* packet is bigger than sizeof(packet), we did partial read */
                log1("Oversized packet, ignoring");
                return -2;
        }

        /* ignore any extra garbage bytes */
        bytes = sizeof(packet.ip6) + ntohs(packet.ip6.ip6_plen);

        /* make sure its the right packet for us, and that it passes sanity checks */
        if (packet.ip6.ip6_nxt != IPPROTO_UDP
         || (packet.ip6.ip6_vfc >> 4) != 6
         || packet.udp.dest != htons(CLIENT_PORT6)
        /* || bytes > (int) sizeof(packet) - can't happen */
         || packet.udp.len != packet.ip6.ip6_plen
        ) {
                log1("Unrelated/bogus packet, ignoring");
                return -2;
        }

//How to do this for ipv6?
//      /* verify UDP checksum. IP header has to be modified for this */
//      memset(&packet.ip, 0, offsetof(struct iphdr, protocol));
//      /* ip.xx fields which are not memset: protocol, check, saddr, daddr */
//      packet.ip.tot_len = packet.udp.len; /* yes, this is needed */
//      check = packet.udp.check;
//      packet.udp.check = 0;
//      if (check && check != inet_cksum((uint16_t *)&packet, bytes)) {
//              log1("Packet with bad UDP checksum received, ignoring");
//              return -2;
//      }

        log1("Received a packet");
        d6_dump_packet(&packet.data);

        bytes -= sizeof(packet.ip6) + sizeof(packet.udp);
        memcpy(d6_pkt, &packet.data, bytes);
        return bytes;
}


/*** Main ***/

static int sockfd = -1;

#define LISTEN_NONE   0
#define LISTEN_KERNEL 1
#define LISTEN_RAW    2
static smallint listen_mode;

/* initial state: (re)start DHCP negotiation */
#define INIT_SELECTING  0
/* discover was sent, DHCPOFFER reply received */
#define REQUESTING      1
/* select/renew was sent, DHCPACK reply received */
#define BOUND           2
/* half of lease passed, want to renew it by sending unicast renew requests */
#define RENEWING        3
/* renew requests were not answered, lease is almost over, send broadcast renew */
#define REBINDING       4
/* manually requested renew (SIGUSR1) */
#define RENEW_REQUESTED 5
/* release, possibly manually requested (SIGUSR2) */
#define RELEASED        6
static smallint state;

static int d6_raw_socket(int ifindex)
{
        int fd;
        struct sockaddr_ll sock;

        /*
         * Comment:
         *
         *      I've selected not to see LL header, so BPF doesn't see it, too.
         *      The filter may also pass non-IP and non-ARP packets, but we do
         *      a more complete check when receiving the message in userspace.
         *
         * and filter shamelessly stolen from:
         *
         *      http://www.flamewarmaster.de/software/dhcpclient/
         *
         * There are a few other interesting ideas on that page (look under
         * "Motivation").  Use of netlink events is most interesting.  Think
         * of various network servers listening for events and reconfiguring.
         * That would obsolete sending HUP signals and/or make use of restarts.
         *
         * Copyright: 2006, 2007 Stefan Rompf <sux@loplof.de>.
         * License: GPL v2.
         *
         * TODO: make conditional?
         */
#if 0
        static const struct sock_filter filter_instr[] = {
                /* load 9th byte (protocol) */
                BPF_STMT(BPF_LD|BPF_B|BPF_ABS, 9),
                /* jump to L1 if it is IPPROTO_UDP, else to L4 */
                BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, IPPROTO_UDP, 0, 6),
                /* L1: load halfword from offset 6 (flags and frag offset) */
                BPF_STMT(BPF_LD|BPF_H|BPF_ABS, 6),
                /* jump to L4 if any bits in frag offset field are set, else to L2 */
                BPF_JUMP(BPF_JMP|BPF_JSET|BPF_K, 0x1fff, 4, 0),
                /* L2: skip IP header (load index reg with header len) */
                BPF_STMT(BPF_LDX|BPF_B|BPF_MSH, 0),
                /* load udp destination port from halfword[header_len + 2] */
                BPF_STMT(BPF_LD|BPF_H|BPF_IND, 2),
                /* jump to L3 if udp dport is CLIENT_PORT6, else to L4 */
                BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, 68, 0, 1),
                /* L3: accept packet */
                BPF_STMT(BPF_RET|BPF_K, 0xffffffff),
                /* L4: discard packet */
                BPF_STMT(BPF_RET|BPF_K, 0),
        };
        static const struct sock_fprog filter_prog = {
                .len = sizeof(filter_instr) / sizeof(filter_instr[0]),
                /* casting const away: */
                .filter = (struct sock_filter *) filter_instr,
        };
#endif

        log1("Opening raw socket on ifindex %d", ifindex); //log2?

        fd = xsocket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IPV6));
        log1("Got raw socket fd %d", fd); //log2?

        sock.sll_family = AF_PACKET;
        sock.sll_protocol = htons(ETH_P_IPV6);
        sock.sll_ifindex = ifindex;
        xbind(fd, (struct sockaddr *) &sock, sizeof(sock));

#if 0
        if (CLIENT_PORT6 == 546) {
                /* Use only if standard port is in use */
                /* Ignoring error (kernel may lack support for this) */
                if (setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &filter_prog,
                                sizeof(filter_prog)) >= 0)
                        log1("Attached filter to raw socket fd %d", fd); // log?
        }
#endif

        log1("Created raw socket");

        return fd;
}

static void change_listen_mode(int new_mode)
{
        log1("Entering listen mode: %s",
                new_mode != LISTEN_NONE
                        ? (new_mode == LISTEN_KERNEL ? "kernel" : "raw")
                        : "none"
        );

        listen_mode = new_mode;
        if (sockfd >= 0) {
                close(sockfd);
                sockfd = -1;
        }
        if (new_mode == LISTEN_KERNEL)
                sockfd = udhcp_listen_socket(/*INADDR_ANY,*/ CLIENT_PORT6, client_config.interface);
        else if (new_mode != LISTEN_NONE)
                sockfd = d6_raw_socket(client_config.ifindex);
        /* else LISTEN_NONE: sockfd stays closed */
}

/* Called only on SIGUSR1 */
static void perform_renew(void)
{
        bb_info_msg("Performing a DHCP renew");
        switch (state) {
        case BOUND:
                change_listen_mode(LISTEN_KERNEL);
        case RENEWING:
        case REBINDING:
                state = RENEW_REQUESTED;
                break;
        case RENEW_REQUESTED: /* impatient are we? fine, square 1 */
                d6_run_script(NULL, "deconfig");
        case REQUESTING:
        case RELEASED:
                change_listen_mode(LISTEN_RAW);
                state = INIT_SELECTING;
                break;
        case INIT_SELECTING:
                break;
        }
}

static void perform_d6_release(struct in6_addr *server_ipv6, struct in6_addr *our_cur_ipv6)
{
        /* send release packet */
        if (state == BOUND || state == RENEWING || state == REBINDING) {
                bb_info_msg("Unicasting a release");
                send_d6_release(server_ipv6, our_cur_ipv6); /* unicast */
                d6_run_script(NULL, "deconfig");
        }
        bb_info_msg("Entering released state");

        change_listen_mode(LISTEN_NONE);
        state = RELEASED;
}

///static uint8_t* alloc_dhcp_option(int code, const char *str, int extra)
///{
///     uint8_t *storage;
///     int len = strnlen(str, 255);
///     storage = xzalloc(len + extra + OPT_DATA);
///     storage[OPT_CODE] = code;
///     storage[OPT_LEN] = len + extra;
///     memcpy(storage + extra + OPT_DATA, str, len);
///     return storage;
///}

#if BB_MMU
static void client_background(void)
{
        bb_daemonize(0);
        logmode &= ~LOGMODE_STDIO;
        /* rewrite pidfile, as our pid is different now */
        write_pidfile(client_config.pidfile);
}
#endif

//usage:#if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 1
//usage:# define IF_UDHCP_VERBOSE(...) __VA_ARGS__
//usage:#else
//usage:# define IF_UDHCP_VERBOSE(...)
//usage:#endif
//usage:#define udhcpc6_trivial_usage
//usage:       "[-fbnq"IF_UDHCP_VERBOSE("v")"oR] [-i IFACE] [-r IP] [-s PROG] [-p PIDFILE]\n"
//usage:       "        [-x OPT:VAL]... [-O OPT]..." IF_FEATURE_UDHCP_PORT(" [-P N]")
//usage:#define udhcpc6_full_usage "\n"
//usage:        IF_LONG_OPTS(
//usage:     "\n        -i,--interface IFACE    Interface to use (default eth0)"
//usage:     "\n        -p,--pidfile FILE       Create pidfile"
//usage:     "\n        -s,--script PROG        Run PROG at DHCP events (default "CONFIG_UDHCPC_DEFAULT_SCRIPT")"
//usage:     "\n        -B,--broadcast          Request broadcast replies"
//usage:     "\n        -t,--retries N          Send up to N discover packets"
//usage:     "\n        -T,--timeout N          Pause between packets (default 3 seconds)"
//usage:     "\n        -A,--tryagain N         Wait N seconds after failure (default 20)"
//usage:     "\n        -f,--foreground         Run in foreground"
//usage:        USE_FOR_MMU(
//usage:     "\n        -b,--background         Background if lease is not obtained"
//usage:        )
//usage:     "\n        -n,--now                Exit if lease is not obtained"
//usage:     "\n        -q,--quit               Exit after obtaining lease"
//usage:     "\n        -R,--release            Release IP on exit"
//usage:     "\n        -S,--syslog             Log to syslog too"
//usage:        IF_FEATURE_UDHCP_PORT(
//usage:     "\n        -P,--client-port N      Use port N (default 546)"
//usage:        )
////usage:      IF_FEATURE_UDHCPC_ARPING(
////usage:     "\n      -a,--arping             Use arping to validate offered address"
////usage:      )
//usage:     "\n        -O,--request-option OPT Request option OPT from server (cumulative)"
//usage:     "\n        -o,--no-default-options Don't request any options (unless -O is given)"
//usage:     "\n        -r,--request IP         Request this IP address"
//usage:     "\n        -x OPT:VAL              Include option OPT in sent packets (cumulative)"
//usage:     "\n                                Examples of string, numeric, and hex byte opts:"
//usage:     "\n                                -x hostname:bbox - option 12"
//usage:     "\n                                -x lease:3600 - option 51 (lease time)"
//usage:     "\n                                -x 0x3d:0100BEEFC0FFEE - option 61 (client id)"
//usage:        IF_UDHCP_VERBOSE(
//usage:     "\n        -v                      Verbose"
//usage:        )
//usage:        )
//usage:        IF_NOT_LONG_OPTS(
//usage:     "\n        -i IFACE        Interface to use (default eth0)"
//usage:     "\n        -p FILE         Create pidfile"
//usage:     "\n        -s PROG         Run PROG at DHCP events (default "CONFIG_UDHCPC_DEFAULT_SCRIPT")"
//usage:     "\n        -B              Request broadcast replies"
//usage:     "\n        -t N            Send up to N discover packets"
//usage:     "\n        -T N            Pause between packets (default 3 seconds)"
//usage:     "\n        -A N            Wait N seconds (default 20) after failure"
//usage:     "\n        -f              Run in foreground"
//usage:        USE_FOR_MMU(
//usage:     "\n        -b              Background if lease is not obtained"
//usage:        )
//usage:     "\n        -n              Exit if lease is not obtained"
//usage:     "\n        -q              Exit after obtaining lease"
//usage:     "\n        -R              Release IP on exit"
//usage:     "\n        -S              Log to syslog too"
//usage:        IF_FEATURE_UDHCP_PORT(
//usage:     "\n        -P N            Use port N (default 546)"
//usage:        )
////usage:      IF_FEATURE_UDHCPC_ARPING(
////usage:     "\n      -a              Use arping to validate offered address"
////usage:      )
//usage:     "\n        -O OPT          Request option OPT from server (cumulative)"
//usage:     "\n        -o              Don't request any options (unless -O is given)"
//usage:     "\n        -r IP           Request this IP address"
//usage:     "\n        -x OPT:VAL      Include option OPT in sent packets (cumulative)"
//usage:     "\n                        Examples of string, numeric, and hex byte opts:"
//usage:     "\n                        -x hostname:bbox - option 12"
//usage:     "\n                        -x lease:3600 - option 51 (lease time)"
//usage:     "\n                        -x 0x3d:0100BEEFC0FFEE - option 61 (client id)"
//usage:        IF_UDHCP_VERBOSE(
//usage:     "\n        -v              Verbose"
//usage:        )
//usage:        )
//usage:     "\nSignals:"
//usage:     "\n        USR1    Renew lease"
//usage:     "\n        USR2    Release lease"


int udhcpc6_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int udhcpc6_main(int argc UNUSED_PARAM, char **argv)
{
        const char *str_r;
        IF_FEATURE_UDHCP_PORT(char *str_P;)
        void *clientid_mac_ptr;
        llist_t *list_O = NULL;
        llist_t *list_x = NULL;
        int tryagain_timeout = 20;
        int discover_timeout = 3;
        int discover_retries = 3;
        struct in6_addr srv6_buf;
        struct in6_addr ipv6_buf;
        struct in6_addr *requested_ipv6;
        uint32_t xid = 0;
        int packet_num;
        int timeout; /* must be signed */
        unsigned already_waited_sec;
        unsigned opt;
        int max_fd;
        int retval;
        fd_set rfds;

        /* Default options */
        IF_FEATURE_UDHCP_PORT(SERVER_PORT6 = 547;)
        IF_FEATURE_UDHCP_PORT(CLIENT_PORT6 = 546;)
        client_config.interface = "eth0";
        client_config.script = CONFIG_UDHCPC_DEFAULT_SCRIPT;

        /* Parse command line */
        /* O,x: list; -T,-t,-A take numeric param */
        opt_complementary = "O::x::T+:t+:A+" IF_UDHCP_VERBOSE(":vv") ;
        IF_LONG_OPTS(applet_long_options = udhcpc6_longopts;)
        opt = getopt32(argv, "i:np:qRr:s:T:t:SA:O:ox:f"
                USE_FOR_MMU("b")
                ///IF_FEATURE_UDHCPC_ARPING("a")
                IF_FEATURE_UDHCP_PORT("P:")
                "v"
                , &client_config.interface, &client_config.pidfile, &str_r /* i,p */
                , &client_config.script /* s */
                , &discover_timeout, &discover_retries, &tryagain_timeout /* T,t,A */
                , &list_O
                , &list_x
                IF_FEATURE_UDHCP_PORT(, &str_P)
                IF_UDHCP_VERBOSE(, &dhcp_verbose)
        );
        requested_ipv6 = NULL;
        if (opt & OPT_r) {
                if (inet_pton(AF_INET6, str_r, &ipv6_buf) <= 0)
                        bb_error_msg_and_die("bad IPv6 address '%s'", str_r);
                requested_ipv6 = &ipv6_buf;
        }
#if ENABLE_FEATURE_UDHCP_PORT
        if (opt & OPT_P) {
                CLIENT_PORT6 = xatou16(str_P);
                SERVER_PORT6 = CLIENT_PORT6 + 1;
        }
#endif
        while (list_O) {
                char *optstr = llist_pop(&list_O);
                unsigned n = bb_strtou(optstr, NULL, 0);
                if (errno || n > 254) {
                        n = udhcp_option_idx(optstr);
                        n = dhcp_optflags[n].code;
                }
                client_config.opt_mask[n >> 3] |= 1 << (n & 7);
        }
        if (!(opt & OPT_o)) {
                /*
                unsigned i, n;
                for (i = 0; (n = dhcp_optflags[i].code) != 0; i++) {
                        if (dhcp_optflags[i].flags & OPTION_REQ) {
                                client_config.opt_mask[n >> 3] |= 1 << (n & 7);
                        }
                }
                */
        }
        while (list_x) {
                char *optstr = llist_pop(&list_x);
                char *colon = strchr(optstr, ':');
                if (colon)
                        *colon = ' ';
                /* now it looks similar to udhcpd's config file line:
                 * "optname optval", using the common routine: */
                udhcp_str2optset(optstr, &client_config.options);
        }

        if (udhcp_read_interface(client_config.interface,
                        &client_config.ifindex,
                        NULL,
                        client_config.client_mac)

        ) {
                return 1;
        }

        /* Create client ID based on mac, set clientid_mac_ptr */
        {
                struct d6_option *clientid;
                clientid = xzalloc(2+2+2+2+6);
                clientid->code = D6_OPT_CLIENTID;
                clientid->len = 2+2+6;
                clientid->data[1] = 3; /* DUID-LL */
                clientid->data[3] = 1; /* ethernet */
                clientid_mac_ptr = clientid->data + 2+2;
                memcpy(clientid_mac_ptr, client_config.client_mac, 6);
                client_config.clientid = (void*)clientid;
        }

#if !BB_MMU
        /* on NOMMU reexec (i.e., background) early */
        if (!(opt & OPT_f)) {
                bb_daemonize_or_rexec(0 /* flags */, argv);
                logmode = LOGMODE_NONE;
        }
#endif
        if (opt & OPT_S) {
                openlog(applet_name, LOG_PID, LOG_DAEMON);
                logmode |= LOGMODE_SYSLOG;
        }

        /* Make sure fd 0,1,2 are open */
        bb_sanitize_stdio();
        /* Equivalent of doing a fflush after every \n */
        setlinebuf(stdout);
        /* Create pidfile */
        write_pidfile(client_config.pidfile);
        /* Goes to stdout (unless NOMMU) and possibly syslog */
        bb_info_msg("%s (v"BB_VER") started", applet_name);
        /* Set up the signal pipe */
        udhcp_sp_setup();
        /* We want random_xid to be random... */
        srand(monotonic_us());

        state = INIT_SELECTING;
        d6_run_script(NULL, "deconfig");
        change_listen_mode(LISTEN_RAW);
        packet_num = 0;
        timeout = 0;
        already_waited_sec = 0;

        /* Main event loop. select() waits on signal pipe and possibly
         * on sockfd.
         * "continue" statements in code below jump to the top of the loop.
         */
        for (;;) {
                struct timeval tv;
                struct d6_packet packet;
                uint8_t *packet_end;
                /* silence "uninitialized!" warning */
                unsigned timestamp_before_wait = timestamp_before_wait;

                //bb_error_msg("sockfd:%d, listen_mode:%d", sockfd, listen_mode);

                /* Was opening raw or udp socket here
                 * if (listen_mode != LISTEN_NONE && sockfd < 0),
                 * but on fast network renew responses return faster
                 * than we open sockets. Thus this code is moved
                 * to change_listen_mode(). Thus we open listen socket
                 * BEFORE we send renew request (see "case BOUND:"). */

                max_fd = udhcp_sp_fd_set(&rfds, sockfd);

                tv.tv_sec = timeout - already_waited_sec;
                tv.tv_usec = 0;
                retval = 0;
                /* If we already timed out, fall through with retval = 0, else... */
                if ((int)tv.tv_sec > 0) {
                        log1("Waiting on select %u seconds", (int)tv.tv_sec);
                        timestamp_before_wait = (unsigned)monotonic_sec();
                        retval = select(max_fd + 1, &rfds, NULL, NULL, &tv);
                        if (retval < 0) {
                                /* EINTR? A signal was caught, don't panic */
                                if (errno == EINTR) {
                                        already_waited_sec += (unsigned)monotonic_sec() - timestamp_before_wait;
                                        continue;
                                }
                                /* Else: an error occured, panic! */
                                bb_perror_msg_and_die("select");
                        }
                }

                /* If timeout dropped to zero, time to become active:
                 * resend discover/renew/whatever
                 */
                if (retval == 0) {
                        /* When running on a bridge, the ifindex may have changed
                         * (e.g. if member interfaces were added/removed
                         * or if the status of the bridge changed).
                         * Refresh ifindex and client_mac:
                         */
                        if (udhcp_read_interface(client_config.interface,
                                        &client_config.ifindex,
                                        NULL,
                                        client_config.client_mac)
                        ) {
                                goto ret0; /* iface is gone? */
                        }
                        memcpy(clientid_mac_ptr, client_config.client_mac, 6);

                        /* We will restart the wait in any case */
                        already_waited_sec = 0;

                        switch (state) {
                        case INIT_SELECTING:
                                if (!discover_retries || packet_num < discover_retries) {
                                        if (packet_num == 0)
                                                xid = random_xid();
                                        /* multicast */
                                        send_d6_discover(xid, requested_ipv6);
                                        timeout = discover_timeout;
                                        packet_num++;
                                        continue;
                                }
 leasefail:
                                d6_run_script(NULL, "leasefail");
#if BB_MMU /* -b is not supported on NOMMU */
                                if (opt & OPT_b) { /* background if no lease */
                                        bb_info_msg("No lease, forking to background");
                                        client_background();
                                        /* do not background again! */
                                        opt = ((opt & ~OPT_b) | OPT_f);
                                } else
#endif
                                if (opt & OPT_n) { /* abort if no lease */
                                        bb_info_msg("No lease, failing");
                                        retval = 1;
                                        goto ret;
                                }
                                /* wait before trying again */
                                timeout = tryagain_timeout;
                                packet_num = 0;
                                continue;
                        case REQUESTING:
                                if (!discover_retries || packet_num < discover_retries) {
                                        /* send multicast select packet */
                                        send_d6_select(xid);
                                        timeout = discover_timeout;
                                        packet_num++;
                                        continue;
                                }
                                /* Timed out, go back to init state.
                                 * "discover...select...discover..." loops
                                 * were seen in the wild. Treat them similarly
                                 * to "no response to discover" case */
                                change_listen_mode(LISTEN_RAW);
                                state = INIT_SELECTING;
                                goto leasefail;
                        case BOUND:
                                /* 1/2 lease passed, enter renewing state */
                                state = RENEWING;
                                client_config.first_secs = 0; /* make secs field count from 0 */
                                change_listen_mode(LISTEN_KERNEL);
                                log1("Entering renew state");
                                /* fall right through */
                        case RENEW_REQUESTED: /* manual (SIGUSR1) renew */
                        case_RENEW_REQUESTED:
                        case RENEWING:
                                if (timeout > 60) {
                                        /* send an unicast renew request */
                        /* Sometimes observed to fail (EADDRNOTAVAIL) to bind
                         * a new UDP socket for sending inside send_renew.
                         * I hazard to guess existing listening socket
                         * is somehow conflicting with it, but why is it
                         * not deterministic then?! Strange.
                         * Anyway, it does recover by eventually failing through
                         * into INIT_SELECTING state.
                         */
                                        send_d6_renew(xid, &srv6_buf, requested_ipv6);
                                        timeout >>= 1;
                                        continue;
                                }
                                /* Timed out, enter rebinding state */
                                log1("Entering rebinding state");
                                state = REBINDING;
                                /* fall right through */
                        case REBINDING:
                                /* Switch to bcast receive */
                                change_listen_mode(LISTEN_RAW);
                                /* Lease is *really* about to run out,
                                 * try to find DHCP server using broadcast */
                                if (timeout > 0) {
                                        /* send a broadcast renew request */
                                        send_d6_renew(xid, /*server_ipv6:*/ NULL, requested_ipv6);
                                        timeout >>= 1;
                                        continue;
                                }
                                /* Timed out, enter init state */
                                bb_info_msg("Lease lost, entering init state");
                                d6_run_script(NULL, "deconfig");
                                state = INIT_SELECTING;
                                client_config.first_secs = 0; /* make secs field count from 0 */
                                /*timeout = 0; - already is */
                                packet_num = 0;
                                continue;
                        /* case RELEASED: */
                        }
                        /* yah, I know, *you* say it would never happen */
                        timeout = INT_MAX;
                        continue; /* back to main loop */
                } /* if select timed out */

                /* select() didn't timeout, something happened */

                /* Is it a signal? */
                /* note: udhcp_sp_read checks FD_ISSET before reading */
                switch (udhcp_sp_read(&rfds)) {
                case SIGUSR1:
                        client_config.first_secs = 0; /* make secs field count from 0 */
                        already_waited_sec = 0;
                        perform_renew();
                        if (state == RENEW_REQUESTED) {
                                /* We might be either on the same network
                                 * (in which case renew might work),
                                 * or we might be on a completely different one
                                 * (in which case renew won't ever succeed).
                                 * For the second case, must make sure timeout
                                 * is not too big, or else we can send
                                 * futile renew requests for hours.
                                 * (Ab)use -A TIMEOUT value (usually 20 sec)
                                 * as a cap on the timeout.
                                 */
                                if (timeout > tryagain_timeout)
                                        timeout = tryagain_timeout;
                                goto case_RENEW_REQUESTED;
                        }
                        /* Start things over */
                        packet_num = 0;
                        /* Kill any timeouts, user wants this to hurry along */
                        timeout = 0;
                        continue;
                case SIGUSR2:
                        perform_d6_release(&srv6_buf, requested_ipv6);
                        timeout = INT_MAX;
                        continue;
                case SIGTERM:
                        bb_info_msg("Received SIGTERM");
                        goto ret0;
                }

                /* Is it a packet? */
                if (listen_mode == LISTEN_NONE || !FD_ISSET(sockfd, &rfds))
                        continue; /* no */

                {
                        int len;

                        /* A packet is ready, read it */
                        if (listen_mode == LISTEN_KERNEL)
                                len = d6_recv_kernel_packet(&srv6_buf, &packet, sockfd);
                        else
                                len = d6_recv_raw_packet(&srv6_buf, &packet, sockfd);
                        if (len == -1) {
                                /* Error is severe, reopen socket */
                                bb_info_msg("Read error: %s, reopening socket", strerror(errno));
                                sleep(discover_timeout); /* 3 seconds by default */
                                change_listen_mode(listen_mode); /* just close and reopen */
                        }
                        /* If this packet will turn out to be unrelated/bogus,
                         * we will go back and wait for next one.
                         * Be sure timeout is properly decreased. */
                        already_waited_sec += (unsigned)monotonic_sec() - timestamp_before_wait;
                        if (len < 0)
                                continue;
                        packet_end = (uint8_t*)&packet + len;
                }

                if ((packet.d6_xid32 & htonl(0x00ffffff)) != xid) {
                        log1("xid %x (our is %x), ignoring packet",
                                (unsigned)(packet.d6_xid32 & htonl(0x00ffffff)), (unsigned)xid);
                        continue;
                }

                switch (state) {
                case INIT_SELECTING:
                        if (packet.d6_msg_type == D6_MSG_ADVERTISE)
                                goto type_is_ok;
                        /* DHCPv6 has "Rapid Commit", when instead of Advertise,
                         * server sends Reply right away.
                         * Fall through to check for this case.
                         */
                case REQUESTING:
                case RENEWING:
                case RENEW_REQUESTED:
                case REBINDING:
                        if (packet.d6_msg_type == D6_MSG_REPLY) {
                                uint32_t lease_seconds;
                                struct d6_option *option, *iaaddr;
 type_is_ok:
                                option = d6_find_option(packet.d6_options, packet_end, D6_OPT_STATUS_CODE);
                                if (option && option->data[4] != 0) {
                                        /* return to init state */
                                        bb_info_msg("Received DHCP NAK (%u)", option->data[4]);
                                        d6_run_script(&packet, "nak");
                                        if (state != REQUESTING)
                                                d6_run_script(NULL, "deconfig");
                                        change_listen_mode(LISTEN_RAW);
                                        sleep(3); /* avoid excessive network traffic */
                                        state = INIT_SELECTING;
                                        client_config.first_secs = 0; /* make secs field count from 0 */
                                        requested_ipv6 = NULL;
                                        timeout = 0;
                                        packet_num = 0;
                                        already_waited_sec = 0;
                                        continue;
                                }
                                option = d6_copy_option(packet.d6_options, packet_end, D6_OPT_SERVERID);
                                if (!option) {
                                        bb_error_msg("no server ID, ignoring packet");
                                        continue;
                                        /* still selecting - this server looks bad */
                                }
//Note: we do not bother comparing server IDs in Advertise and Reply msgs.
//server_id variable is used solely for creation of proper server_id option
//in outgoing packets. (why DHCPv6 even introduced it is a mystery).
                                free(client6_data.server_id);
                                client6_data.server_id = option;
                                if (packet.d6_msg_type == D6_MSG_ADVERTISE) {
                                        /* enter requesting state */
                                        state = REQUESTING;
                                        timeout = 0;
                                        packet_num = 0;
                                        already_waited_sec = 0;
                                        continue;
                                }
                                /* It's a D6_MSG_REPLY */
/*
 * RFC 3315 18.1.8. Receipt of Reply Messages
 *
 * Upon the receipt of a valid Reply message in response to a Solicit
 * (with a Rapid Commit option), Request, Confirm, Renew, Rebind or
 * Information-request message, the client extracts the configuration
 * information contained in the Reply.  The client MAY choose to report
 * any status code or message from the status code option in the Reply
 * message.
 *
 * The client SHOULD perform duplicate address detection [17] on each of
 * the addresses in any IAs it receives in the Reply message before
 * using that address for traffic.  If any of the addresses are found to
 * be in use on the link, the client sends a Decline message to the
 * server as described in section 18.1.7.
 *
 * If the Reply was received in response to a Solicit (with a Rapid
 * Commit option), Request, Renew or Rebind message, the client updates
 * the information it has recorded about IAs from the IA options
 * contained in the Reply message:
 *
 * -  Record T1 and T2 times.
 *
 * -  Add any new addresses in the IA option to the IA as recorded by
 *    the client.
 *
 * -  Update lifetimes for any addresses in the IA option that the
 *    client already has recorded in the IA.
 *
 * -  Discard any addresses from the IA, as recorded by the client, that
 *    have a valid lifetime of 0 in the IA Address option.
 *
 * -  Leave unchanged any information about addresses the client has
 *    recorded in the IA but that were not included in the IA from the
 *    server.
 *
 * Management of the specific configuration information is detailed in
 * the definition of each option in section 22.
 *
 * If the client receives a Reply message with a Status Code containing
 * UnspecFail, the server is indicating that it was unable to process
 * the message due to an unspecified failure condition.  If the client
 * retransmits the original message to the same server to retry the
 * desired operation, the client MUST limit the rate at which it
 * retransmits the message and limit the duration of the time during
 * which it retransmits the message.
 *
 * When the client receives a Reply message with a Status Code option
 * with the value UseMulticast, the client records the receipt of the
 * message and sends subsequent messages to the server through the
 * interface on which the message was received using multicast.  The
 * client resends the original message using multicast.
 *
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |          OPTION_IA_NA         |          option-len           |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                        IAID (4 octets)                        |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                              T1                               |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                              T2                               |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                                                               |
 * .                         IA_NA-options                         .
 * .                                                               .
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *
 *
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |          OPTION_IAADDR        |          option-len           |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                                                               |
 * |                         IPv6 address                          |
 * |                                                               |
 * |                                                               |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                      preferred-lifetime                       |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                        valid-lifetime                         |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * .                                                               .
 * .                        IAaddr-options                         .
 * .                                                               .
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 */
                                free(client6_data.ia_na);
                                client6_data.ia_na = d6_copy_option(packet.d6_options, packet_end, D6_OPT_IA_NA);
                                if (!client6_data.ia_na) {
                                        bb_error_msg("no %s option, ignoring packet", "IA_NA");
                                        continue;
                                }
                                if (client6_data.ia_na->len < (4 + 4 + 4) + (2 + 2 + 16 + 4 + 4)) {
                                        bb_error_msg("IA_NA option is too short:%d bytes", client6_data.ia_na->len);
                                        continue;
                                }
                                iaaddr = d6_find_option(client6_data.ia_na->data + 4 + 4 + 4,
                                                client6_data.ia_na->data + client6_data.ia_na->len,
                                                D6_OPT_IAADDR
                                );
                                if (!iaaddr) {
                                        bb_error_msg("no %s option, ignoring packet", "IAADDR");
                                        continue;
                                }
                                if (iaaddr->len < (16 + 4 + 4)) {
                                        bb_error_msg("IAADDR option is too short:%d bytes", iaaddr->len);
                                        continue;
                                }
                                /* Note: the address is sufficiently aligned for cast:
                                 * we _copied_ IA-NA, and copy is always well-aligned.
                                 */
                                requested_ipv6 = (struct in6_addr*) iaaddr->data;
                                move_from_unaligned32(lease_seconds, iaaddr->data + 16 + 4);
                                lease_seconds = ntohl(lease_seconds);
                                /* paranoia: must not be too small and not prone to overflows */
                                if (lease_seconds < 0x10)
                                        lease_seconds = 0x10;
/// TODO: check for 0 lease time?
                                if (lease_seconds >= 0x10000000)
                                        lease_seconds = 0x0fffffff;
                                /* enter bound state */
                                timeout = lease_seconds / 2;
                                bb_info_msg("Lease obtained, lease time %u",
                                        /*inet_ntoa(temp_addr),*/ (unsigned)lease_seconds);
                                d6_run_script(&packet, state == REQUESTING ? "bound" : "renew");

                                state = BOUND;
                                change_listen_mode(LISTEN_NONE);
                                if (opt & OPT_q) { /* quit after lease */
                                        goto ret0;
                                }
                                /* future renew failures should not exit (JM) */
                                opt &= ~OPT_n;
#if BB_MMU /* NOMMU case backgrounded earlier */
                                if (!(opt & OPT_f)) {
                                        client_background();
                                        /* do not background again! */
                                        opt = ((opt & ~OPT_b) | OPT_f);
                                }
#endif
                                already_waited_sec = 0;
                                continue; /* back to main loop */
                        }
                        continue;
                /* case BOUND: - ignore all packets */
                /* case RELEASED: - ignore all packets */
                }
                /* back to main loop */
        } /* for (;;) - main loop ends */

 ret0:
        if (opt & OPT_R) /* release on quit */
                perform_d6_release(&srv6_buf, requested_ipv6);
        retval = 0;
 ret:
        /*if (client_config.pidfile) - remove_pidfile has its own check */
                remove_pidfile(client_config.pidfile);
        return retval;
}