source: MondoRescue/tags/3.2.2/mindi-busybox/networking/udhcp/dhcpc.c @ 3715

/* vi: set sw=4 ts=4: */
/*
 * udhcp client
 *
 * Russ Dill <Russ.Dill@asu.edu> July 2001
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
#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 <asm/types.h>
#if (defined(__GLIBC__) && __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 1 && __GLIBC_MINOR__ < 2) || defined(_NEWLIB_VERSION)
# include <netpacket/packet.h>
# include <net/ethernet.h>
#else
# include <linux/if_packet.h>
# include <linux/if_ether.h>
#endif
#include <linux/filter.h>

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


#if ENABLE_LONG_OPTS
static const char udhcpc_longopts[] ALIGN1 =
    "clientid-none\0"  No_argument       "C"
    "vendorclass\0"    Required_argument "V"
    "hostname\0"       Required_argument "H"
    "fqdn\0"           Required_argument "F"
    "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"
    "broadcast\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_C = 1 << 0,
    OPT_V = 1 << 1,
    OPT_H = 1 << 2,
    OPT_h = 1 << 3,
    OPT_F = 1 << 4,
    OPT_i = 1 << 5,
    OPT_n = 1 << 6,
    OPT_p = 1 << 7,
    OPT_q = 1 << 8,
    OPT_R = 1 << 9,
    OPT_r = 1 << 10,
    OPT_s = 1 << 11,
    OPT_T = 1 << 12,
    OPT_t = 1 << 13,
    OPT_S = 1 << 14,
    OPT_A = 1 << 15,
    OPT_O = 1 << 16,
    OPT_o = 1 << 17,
    OPT_x = 1 << 18,
    OPT_f = 1 << 19,
    OPT_B = 1 << 20,
/* The rest has variable bit positions, need to be clever */
    OPTBIT_B = 20,
    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,)
};


/*** Script execution code ***/

/* get a rough idea of how long an option will be (rounding up...) */
static const uint8_t len_of_option_as_string[] = {
    [OPTION_IP              ] = sizeof("255.255.255.255 "),
    [OPTION_IP_PAIR         ] = sizeof("255.255.255.255 ") * 2,
    [OPTION_STATIC_ROUTES   ] = sizeof("255.255.255.255/32 255.255.255.255 "),
    [OPTION_6RD             ] = sizeof("32 128 ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff 255.255.255.255 "),
    [OPTION_STRING          ] = 1,
    [OPTION_STRING_HOST     ] = 1,
#if ENABLE_FEATURE_UDHCP_RFC3397
    [OPTION_DNS_STRING      ] = 1, /* unused */
    /* Hmmm, this severely overestimates size if SIP_SERVERS option
     * is in domain name form: N-byte option in binary form
     * mallocs ~16*N bytes. But it is freed almost at once.
     */
    [OPTION_SIP_SERVERS     ] = sizeof("255.255.255.255 "),
#endif
//  [OPTION_BOOLEAN         ] = sizeof("yes "),
    [OPTION_U8              ] = sizeof("255 "),
    [OPTION_U16             ] = sizeof("65535 "),
//  [OPTION_S16             ] = sizeof("-32768 "),
    [OPTION_U32             ] = sizeof("4294967295 "),
    [OPTION_S32             ] = sizeof("-2147483684 "),
};

/* note: ip is a pointer to an IP in network order, possibly misaliged */
static int sprint_nip(char *dest, const char *pre, const uint8_t *ip)
{
    return sprintf(dest, "%s%u.%u.%u.%u", pre, ip[0], ip[1], ip[2], ip[3]);
}

/* really simple implementation, just count the bits */
static int mton(uint32_t mask)
{
    int i = 0;
    mask = ntohl(mask); /* 111110000-like bit pattern */
    while (mask) {
        i++;
        mask <<= 1;
    }
    return i;
}

/* Check if a given label represents a valid DNS label
 * Return pointer to the first character after the label upon success,
 * NULL otherwise.
 * See RFC1035, 2.3.1
 */
/* We don't need to be particularly anal. For example, allowing _, hyphen
 * at the end, or leading and trailing dots would be ok, since it
 * can't be used for attacks. (Leading hyphen can be, if someone uses
 * cmd "$hostname"
 * in the script: then hostname may be treated as an option)
 */
static const char *valid_domain_label(const char *label)
{
    unsigned char ch;
    unsigned pos = 0;

    for (;;) {
        ch = *label;
        if ((ch|0x20) < 'a' || (ch|0x20) > 'z') {
            if (pos == 0) {
                /* label must begin with letter */
                return NULL;
            }
            if (ch < '0' || ch > '9') {
                if (ch == '\0' || ch == '.')
                    return label;
                /* DNS allows only '-', but we are more permissive */
                if (ch != '-' && ch != '_')
                    return NULL;
            }
        }
        label++;
        pos++;
        //Do we want this?
        //if (pos > 63) /* NS_MAXLABEL; labels must be 63 chars or less */
        //  return NULL;
    }
}

/* Check if a given name represents a valid DNS name */
/* See RFC1035, 2.3.1 */
static int good_hostname(const char *name)
{
    //const char *start = name;

    for (;;) {
        name = valid_domain_label(name);
        if (!name)
            return 0;
        if (!name[0])
            return 1;
            //Do we want this?
            //return ((name - start) < 1025); /* NS_MAXDNAME */
        name++;
    }
}

/* Create "opt_name=opt_value" string */
static NOINLINE char *xmalloc_optname_optval(uint8_t *option, const struct dhcp_optflag *optflag, const char *opt_name)
{
    unsigned upper_length;
    int len, type, optlen;
    char *dest, *ret;

    /* option points to OPT_DATA, need to go back to get OPT_LEN */
    len = option[-OPT_DATA + OPT_LEN];

    type = optflag->flags & OPTION_TYPE_MASK;
    optlen = dhcp_option_lengths[type];
    upper_length = len_of_option_as_string[type]
        * ((unsigned)(len + optlen - 1) / (unsigned)optlen);

    dest = ret = xmalloc(upper_length + strlen(opt_name) + 2);
    dest += sprintf(ret, "%s=", opt_name);

    while (len >= optlen) {
        switch (type) {
        case OPTION_IP:
        case OPTION_IP_PAIR:
            dest += sprint_nip(dest, "", option);
            if (type == OPTION_IP)
                break;
            dest += sprint_nip(dest, "/", option + 4);
            break;
//      case OPTION_BOOLEAN:
//          dest += sprintf(dest, *option ? "yes" : "no");
//          break;
        case OPTION_U8:
            dest += sprintf(dest, "%u", *option);
            break;
//      case OPTION_S16:
        case OPTION_U16: {
            uint16_t val_u16;
            move_from_unaligned16(val_u16, option);
            dest += sprintf(dest, "%u", ntohs(val_u16));
            break;
        }
        case OPTION_S32:
        case OPTION_U32: {
            uint32_t val_u32;
            move_from_unaligned32(val_u32, option);
            dest += sprintf(dest, type == OPTION_U32 ? "%lu" : "%ld", (unsigned long) ntohl(val_u32));
            break;
        }
        /* Note: options which use 'return' instead of 'break'
         * (for example, OPTION_STRING) skip the code which handles
         * the case of list of options.
         */
        case OPTION_STRING:
        case OPTION_STRING_HOST:
            memcpy(dest, option, len);
            dest[len] = '\0';
            if (type == OPTION_STRING_HOST && !good_hostname(dest))
                safe_strncpy(dest, "bad", len);
            return ret;
        case OPTION_STATIC_ROUTES: {
            /* Option binary format:
             * mask [one byte, 0..32]
             * ip [big endian, 0..4 bytes depending on mask]
             * router [big endian, 4 bytes]
             * may be repeated
             *
             * We convert it to a string "IP/MASK ROUTER IP2/MASK2 ROUTER2"
             */
            const char *pfx = "";

            while (len >= 1 + 4) { /* mask + 0-byte ip + router */
                uint32_t nip;
                uint8_t *p;
                unsigned mask;
                int bytes;

                mask = *option++;
                if (mask > 32)
                    break;
                len--;

                nip = 0;
                p = (void*) &nip;
                bytes = (mask + 7) / 8; /* 0 -> 0, 1..8 -> 1, 9..16 -> 2 etc */
                while (--bytes >= 0) {
                    *p++ = *option++;
                    len--;
                }
                if (len < 4)
                    break;

                /* print ip/mask */
                dest += sprint_nip(dest, pfx, (void*) &nip);
                pfx = " ";
                dest += sprintf(dest, "/%u ", mask);
                /* print router */
                dest += sprint_nip(dest, "", option);
                option += 4;
                len -= 4;
            }

            return ret;
        }
        case OPTION_6RD:
            /* Option binary format (see RFC 5969):
             *  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_6RD   | option-length |  IPv4MaskLen  |  6rdPrefixLen |
             * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             * |                           6rdPrefix                           |
             * ...                        (16 octets)                        ...
             * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             * ...                   6rdBRIPv4Address(es)                    ...
             * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             * We convert it to a string
             * "IPv4MaskLen 6rdPrefixLen 6rdPrefix 6rdBRIPv4Address..."
             *
             * Sanity check: ensure that our length is at least 22 bytes, that
             * IPv4MaskLen <= 32,
             * 6rdPrefixLen <= 128,
             * 6rdPrefixLen + (32 - IPv4MaskLen) <= 128
             * (2nd condition need no check - it follows from 1st and 3rd).
             * Else, return envvar with empty value ("optname=")
             */
            if (len >= (1 + 1 + 16 + 4)
             && option[0] <= 32
             && (option[1] + 32 - option[0]) <= 128
            ) {
                /* IPv4MaskLen */
                dest += sprintf(dest, "%u ", *option++);
                /* 6rdPrefixLen */
                dest += sprintf(dest, "%u ", *option++);
                /* 6rdPrefix */
                dest += sprint_nip6(dest, /* "", */ option);
                option += 16;
                len -= 1 + 1 + 16 + 4;
                /* "+ 4" above corresponds to the length of IPv4 addr
                 * we consume in the loop below */
                while (1) {
                    /* 6rdBRIPv4Address(es) */
                    dest += sprint_nip(dest, " ", option);
                    option += 4;
                    len -= 4; /* do we have yet another 4+ bytes? */
                    if (len < 0)
                        break; /* no */
                }
            }

            return ret;
#if ENABLE_FEATURE_UDHCP_RFC3397
        case OPTION_DNS_STRING:
            /* unpack option into dest; use ret for prefix (i.e., "optname=") */
            dest = dname_dec(option, len, ret);
            if (dest) {
                free(ret);
                return dest;
            }
            /* error. return "optname=" string */
            return ret;
        case OPTION_SIP_SERVERS:
            /* Option binary format:
             * type: byte
             * type=0: domain names, dns-compressed
             * type=1: IP addrs
             */
            option++;
            len--;
            if (option[-1] == 0) {
                dest = dname_dec(option, len, ret);
                if (dest) {
                    free(ret);
                    return dest;
                }
            } else
            if (option[-1] == 1) {
                const char *pfx = "";
                while (1) {
                    len -= 4;
                    if (len < 0)
                        break;
                    dest += sprint_nip(dest, pfx, option);
                    pfx = " ";
                    option += 4;
                }
            }
            return ret;
#endif
        } /* switch */

        /* If we are here, try to format any remaining data
         * in the option as another, similarly-formatted option
         */
        option += optlen;
        len -= optlen;
// TODO: it can be a list only if (optflag->flags & OPTION_LIST).
// Should we bail out/warn if we see multi-ip option which is
// not allowed to be such (for example, DHCP_BROADCAST)? -
        if (len < optlen /* || !(optflag->flags & OPTION_LIST) */)
            break;
        *dest++ = ' ';
        *dest = '\0';
    } /* while */

    return ret;
}

/* put all the parameters into the environment */
static char **fill_envp(struct dhcp_packet *packet)
{
    int envc;
    int i;
    char **envp, **curr;
    const char *opt_name;
    uint8_t *temp;
    uint8_t overload = 0;

#define BITMAP unsigned
#define BBITS (sizeof(BITMAP) * 8)
#define BMASK(i) (1 << (i & (sizeof(BITMAP) * 8 - 1)))
#define FOUND_OPTS(i) (found_opts[(unsigned)i / BBITS])
    BITMAP found_opts[256 / BBITS];

    memset(found_opts, 0, sizeof(found_opts));

    /* We need 6 elements for:
     * "interface=IFACE"
     * "ip=N.N.N.N" from packet->yiaddr
     * "siaddr=IP" from packet->siaddr_nip (unless 0)
     * "boot_file=FILE" from packet->file (unless overloaded)
     * "sname=SERVER_HOSTNAME" from packet->sname (unless overloaded)
     * terminating NULL
     */
    envc = 6;
    /* +1 element for each option, +2 for subnet option: */
    if (packet) {
        /* note: do not search for "pad" (0) and "end" (255) options */
//TODO: change logic to scan packet _once_
        for (i = 1; i < 255; i++) {
            temp = udhcp_get_option(packet, i);
            if (temp) {
                if (i == DHCP_OPTION_OVERLOAD)
                    overload = *temp;
                else if (i == DHCP_SUBNET)
                    envc++; /* for $mask */
                envc++;
                /*if (i != DHCP_MESSAGE_TYPE)*/
                FOUND_OPTS(i) |= BMASK(i);
            }
        }
    }
    curr = envp = xzalloc(sizeof(envp[0]) * envc);

    *curr = xasprintf("interface=%s", client_config.interface);
    putenv(*curr++);

    if (!packet)
        return envp;

    /* Export BOOTP fields. Fields we don't (yet?) export:
     * uint8_t op;      // always BOOTREPLY
     * uint8_t htype;   // hardware address type. 1 = 10mb ethernet
     * uint8_t hlen;    // hardware address length
     * uint8_t hops;    // used by relay agents only
     * uint32_t xid;
     * uint16_t secs;   // elapsed since client began acquisition/renewal
     * uint16_t flags;  // only one flag so far: bcast. Never set by server
     * uint32_t ciaddr; // client IP (usually == yiaddr. can it be different
     *                  // if during renew server wants to give us differn IP?)
     * uint32_t gateway_nip; // relay agent IP address
     * uint8_t chaddr[16]; // link-layer client hardware address (MAC)
     * TODO: export gateway_nip as $giaddr?
     */
    /* Most important one: yiaddr as $ip */
    *curr = xmalloc(sizeof("ip=255.255.255.255"));
    sprint_nip(*curr, "ip=", (uint8_t *) &packet->yiaddr);
    putenv(*curr++);
    if (packet->siaddr_nip) {
        /* IP address of next server to use in bootstrap */
        *curr = xmalloc(sizeof("siaddr=255.255.255.255"));
        sprint_nip(*curr, "siaddr=", (uint8_t *) &packet->siaddr_nip);
        putenv(*curr++);
    }
    if (!(overload & FILE_FIELD) && packet->file[0]) {
        /* watch out for invalid packets */
        *curr = xasprintf("boot_file=%."DHCP_PKT_FILE_LEN_STR"s", packet->file);
        putenv(*curr++);
    }
    if (!(overload & SNAME_FIELD) && packet->sname[0]) {
        /* watch out for invalid packets */
        *curr = xasprintf("sname=%."DHCP_PKT_SNAME_LEN_STR"s", packet->sname);
        putenv(*curr++);
    }

    /* Export known DHCP options */
    opt_name = dhcp_option_strings;
    i = 0;
    while (*opt_name) {
        uint8_t code = dhcp_optflags[i].code;
        BITMAP *found_ptr = &FOUND_OPTS(code);
        BITMAP found_mask = BMASK(code);
        if (!(*found_ptr & found_mask))
            goto next;
        *found_ptr &= ~found_mask; /* leave only unknown options */
        temp = udhcp_get_option(packet, code);
        *curr = xmalloc_optname_optval(temp, &dhcp_optflags[i], opt_name);
        putenv(*curr++);
        if (code == DHCP_SUBNET) {
            /* Subnet option: make things like "$ip/$mask" possible */
            uint32_t subnet;
            move_from_unaligned32(subnet, temp);
            *curr = xasprintf("mask=%u", mton(subnet));
            putenv(*curr++);
        }
 next:
        opt_name += strlen(opt_name) + 1;
        i++;
    }
    /* Export unknown options */
    for (i = 0; i < 256;) {
        BITMAP bitmap = FOUND_OPTS(i);
        if (!bitmap) {
            i += BBITS;
            continue;
        }
        if (bitmap & BMASK(i)) {
            unsigned len, ofs;

            temp = udhcp_get_option(packet, i);
            /* udhcp_get_option returns ptr to data portion,
             * need to go back to get len
             */
            len = temp[-OPT_DATA + OPT_LEN];
            *curr = xmalloc(sizeof("optNNN=") + 1 + len*2);
            ofs = sprintf(*curr, "opt%u=", i);
            *bin2hex(*curr + ofs, (void*) temp, len) = '\0';
            putenv(*curr++);
        }
        i++;
    }

    return envp;
}

/* Call a script with a par file and env vars */
static void udhcp_run_script(struct dhcp_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)
{
    return rand();
}

/* Initialize the packet with the proper defaults */
static void init_packet(struct dhcp_packet *packet, char type)
{
    uint16_t secs;

    /* Fill in: op, htype, hlen, cookie fields; message type option: */
    udhcp_init_header(packet, type);

    packet->xid = random_xid();

    client_config.last_secs = monotonic_sec();
    if (client_config.first_secs == 0)
        client_config.first_secs = client_config.last_secs;
    secs = client_config.last_secs - client_config.first_secs;
    packet->secs = htons(secs);

    memcpy(packet->chaddr, client_config.client_mac, 6);
    if (client_config.clientid)
        udhcp_add_binary_option(packet, client_config.clientid);
}

static void add_client_options(struct dhcp_packet *packet)
{
    int i, end, len;

    udhcp_add_simple_option(packet, DHCP_MAX_SIZE, htons(IP_UDP_DHCP_SIZE));

    /* 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. */
    end = udhcp_end_option(packet->options);
    len = 0;
    for (i = 1; i < DHCP_END; i++) {
        if (client_config.opt_mask[i >> 3] & (1 << (i & 7))) {
            packet->options[end + OPT_DATA + len] = i;
            len++;
        }
    }
    if (len) {
        packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
        packet->options[end + OPT_LEN] = len;
        packet->options[end + OPT_DATA + len] = DHCP_END;
    }

    if (client_config.vendorclass)
        udhcp_add_binary_option(packet, client_config.vendorclass);
    if (client_config.hostname)
        udhcp_add_binary_option(packet, client_config.hostname);
    if (client_config.fqdn)
        udhcp_add_binary_option(packet, client_config.fqdn);

    /* Request broadcast replies if we have no IP addr */
    if ((option_mask32 & OPT_B) && packet->ciaddr == 0)
        packet->flags |= htons(BROADCAST_FLAG);

    /* Add -x options if any */
    {
        struct option_set *curr = client_config.options;
        while (curr) {
            udhcp_add_binary_option(packet, curr->data);
            curr = curr->next;
        }
//      if (client_config.sname)
//          strncpy((char*)packet->sname, client_config.sname, sizeof(packet->sname) - 1);
//      if (client_config.boot_file)
//          strncpy((char*)packet->file, client_config.boot_file, sizeof(packet->file) - 1);
    }

    // This will be needed if we remove -V VENDOR_STR in favor of
    // -x vendor:VENDOR_STR
    //if (!udhcp_find_option(packet.options, DHCP_VENDOR))
    //  /* not set, set the default vendor ID */
    //  ...add (DHCP_VENDOR, "udhcp "BB_VER) opt...
}

/* RFC 2131
 * 4.4.4 Use of broadcast and unicast
 *
 * The DHCP client broadcasts DHCPDISCOVER, DHCPREQUEST and DHCPINFORM
 * messages, unless the client knows the address of a DHCP server.
 * The client unicasts DHCPRELEASE messages to the server. Because
 * the client is declining the use of the IP address supplied by the server,
 * the client broadcasts DHCPDECLINE messages.
 *
 * When the DHCP client knows the address of a DHCP server, in either
 * INIT or REBOOTING state, the client may use that address
 * in the DHCPDISCOVER or DHCPREQUEST rather than the IP broadcast address.
 * The client may also use unicast to send DHCPINFORM messages
 * to a known DHCP server. If the client receives no response to DHCP
 * messages sent to the IP address of a known DHCP server, the DHCP
 * client reverts to using the IP broadcast address.
 */

static int raw_bcast_from_client_config_ifindex(struct dhcp_packet *packet)
{
    return udhcp_send_raw_packet(packet,
        /*src*/ INADDR_ANY, CLIENT_PORT,
        /*dst*/ INADDR_BROADCAST, SERVER_PORT, MAC_BCAST_ADDR,
        client_config.ifindex);
}

/* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
/* NOINLINE: limit stack usage in caller */
static NOINLINE int send_discover(uint32_t xid, uint32_t requested)
{
    struct dhcp_packet packet;

    /* Fill in: op, htype, hlen, cookie, chaddr fields,
     * random xid field (we override it below),
     * client-id option (unless -C), message type option:
     */
    init_packet(&packet, DHCPDISCOVER);

    packet.xid = xid;
    if (requested)
        udhcp_add_simple_option(&packet, DHCP_REQUESTED_IP, requested);

    /* Add options: maxsize,
     * optionally: hostname, fqdn, vendorclass,
     * "param req" option according to -O, options specified with -x
     */
    add_client_options(&packet);

    bb_info_msg("Sending discover...");
    return raw_bcast_from_client_config_ifindex(&packet);
}

/* Broadcast a DHCP request message */
/* RFC 2131 3.1 paragraph 3:
 * "The client _broadcasts_ a DHCPREQUEST message..."
 */
/* NOINLINE: limit stack usage in caller */
static NOINLINE int send_select(uint32_t xid, uint32_t server, uint32_t requested)
{
    struct dhcp_packet packet;
    struct in_addr addr;

/*
 * RFC 2131 4.3.2 DHCPREQUEST message
 * ...
 * If the DHCPREQUEST message contains a 'server identifier'
 * option, the message is in response to a DHCPOFFER message.
 * Otherwise, the message is a request to verify or extend an
 * existing lease. If the client uses a 'client identifier'
 * in a DHCPREQUEST message, it MUST use that same 'client identifier'
 * in all subsequent messages. If the client included a list
 * of requested parameters in a DHCPDISCOVER message, it MUST
 * include that list in all subsequent messages.
 */
    /* Fill in: op, htype, hlen, cookie, chaddr fields,
     * random xid field (we override it below),
     * client-id option (unless -C), message type option:
     */
    init_packet(&packet, DHCPREQUEST);

    packet.xid = xid;
    udhcp_add_simple_option(&packet, DHCP_REQUESTED_IP, requested);

    udhcp_add_simple_option(&packet, DHCP_SERVER_ID, server);

    /* Add options: maxsize,
     * optionally: hostname, fqdn, vendorclass,
     * "param req" option according to -O, and options specified with -x
     */
    add_client_options(&packet);

    addr.s_addr = requested;
    bb_info_msg("Sending select for %s...", inet_ntoa(addr));
    return raw_bcast_from_client_config_ifindex(&packet);
}

/* Unicast or broadcast a DHCP renew message */
/* NOINLINE: limit stack usage in caller */
static NOINLINE int send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr)
{
    struct dhcp_packet packet;

/*
 * RFC 2131 4.3.2 DHCPREQUEST message
 * ...
 * DHCPREQUEST generated during RENEWING state:
 *
 * 'server identifier' MUST NOT be filled in, 'requested IP address'
 * option MUST NOT be filled in, 'ciaddr' MUST be filled in with
 * client's IP address. In this situation, the client is completely
 * configured, and is trying to extend its lease. This message will
 * be unicast, so no relay agents will be involved in its
 * transmission.  Because 'giaddr' is therefore not filled in, the
 * DHCP server will trust the value in 'ciaddr', and use it when
 * replying to the client.
 */
    /* Fill in: op, htype, hlen, cookie, chaddr fields,
     * random xid field (we override it below),
     * client-id option (unless -C), message type option:
     */
    init_packet(&packet, DHCPREQUEST);

    packet.xid = xid;
    packet.ciaddr = ciaddr;

    /* Add options: maxsize,
     * optionally: hostname, fqdn, vendorclass,
     * "param req" option according to -O, and options specified with -x
     */
    add_client_options(&packet);

    bb_info_msg("Sending renew...");
    if (server)
        return udhcp_send_kernel_packet(&packet,
            ciaddr, CLIENT_PORT,
            server, SERVER_PORT);
    return raw_bcast_from_client_config_ifindex(&packet);
}

#if ENABLE_FEATURE_UDHCPC_ARPING
/* Broadcast a DHCP decline message */
/* NOINLINE: limit stack usage in caller */
static NOINLINE int send_decline(/*uint32_t xid,*/ uint32_t server, uint32_t requested)
{
    struct dhcp_packet packet;

    /* Fill in: op, htype, hlen, cookie, chaddr, random xid fields,
     * client-id option (unless -C), message type option:
     */
    init_packet(&packet, DHCPDECLINE);

#if 0
    /* RFC 2131 says DHCPDECLINE's xid is randomly selected by client,
     * but in case the server is buggy and wants DHCPDECLINE's xid
     * to match the xid which started entire handshake,
     * we use the same xid we used in initial DHCPDISCOVER:
     */
    packet.xid = xid;
#endif
    /* DHCPDECLINE uses "requested ip", not ciaddr, to store offered IP */
    udhcp_add_simple_option(&packet, DHCP_REQUESTED_IP, requested);

    udhcp_add_simple_option(&packet, DHCP_SERVER_ID, server);

    bb_info_msg("Sending decline...");
    return raw_bcast_from_client_config_ifindex(&packet);
}
#endif

/* Unicast a DHCP release message */
static int send_release(uint32_t server, uint32_t ciaddr)
{
    struct dhcp_packet packet;

    /* Fill in: op, htype, hlen, cookie, chaddr, random xid fields,
     * client-id option (unless -C), message type option:
     */
    init_packet(&packet, DHCPRELEASE);

    /* DHCPRELEASE uses ciaddr, not "requested ip", to store IP being released */
    packet.ciaddr = ciaddr;

    udhcp_add_simple_option(&packet, DHCP_SERVER_ID, server);

    bb_info_msg("Sending release...");
    return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
}

/* 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 udhcp_recv_raw_packet(struct dhcp_packet *dhcp_pkt, int fd)
{
    int bytes;
    struct ip_udp_dhcp_packet packet;
    uint16_t check;
#ifdef PACKET_AUXDATA
    unsigned char cmsgbuf[CMSG_LEN(sizeof(struct tpacket_auxdata))];
    struct cmsghdr *cmsg;
#endif
    struct iovec iov;
    struct msghdr msg;

#ifdef PACKET_AUXDATA
    /* used to use just safe_read(fd, &packet, sizeof(packet))
     * but we need to check for TP_STATUS_CSUMNOTREADY :(
     */
    iov.iov_base = &packet;
    iov.iov_len = sizeof(packet);
    memset(&msg, 0, sizeof(msg));
    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;
    msg.msg_control = cmsgbuf;
    msg.msg_controllen = sizeof(cmsgbuf);
    for (;;) {
        bytes = recvmsg(fd, &msg, 0);
        if (bytes < 0) {
            if (errno == EINTR)
                continue;
            log1("Packet read error, ignoring");
            /* NB: possible down interface, etc. Caller should pause. */
            return bytes; /* returns -1 */
        }
        break;
    }
#else
    memset(&packet, 0, sizeof(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 */
    }
#endif

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

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

    /* ignore any extra garbage bytes */
    bytes = ntohs(packet.ip.tot_len);

    /* make sure its the right packet for us, and that it passes sanity checks */
    if (packet.ip.protocol != IPPROTO_UDP
     || packet.ip.version != IPVERSION
     || packet.ip.ihl != (sizeof(packet.ip) >> 2)
     || packet.udp.dest != htons(CLIENT_PORT)
    /* || bytes > (int) sizeof(packet) - can't happen */
     || ntohs(packet.udp.len) != (uint16_t)(bytes - sizeof(packet.ip))
    ) {
        log1("Unrelated/bogus packet, ignoring");
        return -2;
    }

    /* verify IP checksum */
    check = packet.ip.check;
    packet.ip.check = 0;
    if (check != inet_cksum((uint16_t *)&packet.ip, sizeof(packet.ip))) {
        log1("Bad IP header checksum, ignoring");
        return -2;
    }

#ifdef PACKET_AUXDATA
    for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
        if (cmsg->cmsg_level == SOL_PACKET
         && cmsg->cmsg_type == PACKET_AUXDATA
        ) {
            /* some VMs don't checksum UDP and TCP data
             * they send to the same physical machine,
             * here we detect this case:
             */
            struct tpacket_auxdata *aux = (void *)CMSG_DATA(cmsg);
            if (aux->tp_status & TP_STATUS_CSUMNOTREADY)
                goto skip_udp_sum_check;
        }
    }
#endif

    /* 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;
    }
#ifdef PACKET_AUXDATA
 skip_udp_sum_check:
#endif

    if (packet.data.cookie != htonl(DHCP_MAGIC)) {
        bb_info_msg("Packet with bad magic, ignoring");
        return -2;
    }

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

    bytes -= sizeof(packet.ip) + sizeof(packet.udp);
    memcpy(dhcp_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 udhcp_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?
     */
    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_PORT, 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,
    };

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

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

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

    if (CLIENT_PORT == 68) {
        /* 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"); // log?
    }

#ifdef PACKET_AUXDATA
    if (setsockopt(fd, SOL_PACKET, PACKET_AUXDATA,
            &const_int_1, sizeof(int)) < 0
    ) {
        if (errno != ENOPROTOOPT)
            log1("Can't set PACKET_AUXDATA on raw socket");
    }
#else
    sock.sll_family = AF_PACKET;
    sock.sll_protocol = htons(ETH_P_IP);
    sock.sll_ifindex = ifindex;
    xbind(fd, (struct sockaddr *) &sock, sizeof(sock));
#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_PORT, client_config.interface);
    else if (new_mode != LISTEN_NONE)
        sockfd = udhcp_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 */
        udhcp_run_script(NULL, "deconfig");
    case REQUESTING:
    case RELEASED:
        change_listen_mode(LISTEN_RAW);
        state = INIT_SELECTING;
        break;
    case INIT_SELECTING:
        break;
    }
}

static void perform_release(uint32_t server_addr, uint32_t requested_ip)
{
    char buffer[sizeof("255.255.255.255")];
    struct in_addr temp_addr;

    /* send release packet */
    if (state == BOUND || state == RENEWING || state == REBINDING) {
        temp_addr.s_addr = server_addr;
        strcpy(buffer, inet_ntoa(temp_addr));
        temp_addr.s_addr = requested_ip;
        bb_info_msg("Unicasting a release of %s to %s",
                inet_ntoa(temp_addr), buffer);
        send_release(server_addr, requested_ip); /* unicast */
        udhcp_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 udhcpc_trivial_usage
//usage:       "[-fbnq"IF_UDHCP_VERBOSE("v")"oCRB] [-i IFACE] [-r IP] [-s PROG] [-p PIDFILE]\n"
//usage:       "    [-V VENDOR] [-x OPT:VAL]... [-O OPT]..." IF_FEATURE_UDHCP_PORT(" [-P N]")
//usage:#define udhcpc_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 68)"
//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:     "\n    -F,--fqdn NAME      Ask server to update DNS mapping for NAME"
//usage:     "\n    -V,--vendorclass VENDOR Vendor identifier (default 'udhcp VERSION')"
//usage:     "\n    -C,--clientid-none  Don't send MAC as client identifier"
//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 68)"
//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:     "\n    -F NAME     Ask server to update DNS mapping for NAME"
//usage:     "\n    -V VENDOR   Vendor identifier (default 'udhcp VERSION')"
//usage:     "\n    -C      Don't send MAC as client identifier"
//usage:    IF_UDHCP_VERBOSE(
//usage:     "\n    -v      Verbose"
//usage:    )
//usage:    )
//usage:     "\nSignals:"
//usage:     "\n    USR1    Renew lease"
//usage:     "\n    USR2    Release lease"


int udhcpc_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int udhcpc_main(int argc UNUSED_PARAM, char **argv)
{
    uint8_t *temp, *message;
    const char *str_V, *str_h, *str_F, *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;
    uint32_t server_addr = server_addr; /* for compiler */
    uint32_t requested_ip = 0;
    uint32_t xid = xid; /* for compiler */
    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_PORT = 67;)
    IF_FEATURE_UDHCP_PORT(CLIENT_PORT = 68;)
    client_config.interface = "eth0";
    client_config.script = CONFIG_UDHCPC_DEFAULT_SCRIPT;
    str_V = "udhcp "BB_VER;

    /* 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 = udhcpc_longopts;)
    opt = getopt32(argv, "CV:H:h:F:i:np:qRr:s:T:t:SA:O:ox:fB"
        USE_FOR_MMU("b")
        IF_FEATURE_UDHCPC_ARPING("a")
        IF_FEATURE_UDHCP_PORT("P:")
        "v"
        , &str_V, &str_h, &str_h, &str_F
        , &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)
    );
    if (opt & (OPT_h|OPT_H)) {
        //msg added 2011-11
        bb_error_msg("option -h NAME is deprecated, use -x hostname:NAME");
        client_config.hostname = alloc_dhcp_option(DHCP_HOST_NAME, str_h, 0);
    }
    if (opt & OPT_F) {
        /* FQDN option format: [0x51][len][flags][0][0]<fqdn> */
        client_config.fqdn = alloc_dhcp_option(DHCP_FQDN, str_F, 3);
        /* Flag bits: 0000NEOS
         * S: 1 = Client requests server to update A RR in DNS as well as PTR
         * O: 1 = Server indicates to client that DNS has been updated regardless
         * E: 1 = Name is in DNS format, i.e. <4>host<6>domain<3>com<0>,
         *    not "host.domain.com". Format 0 is obsolete.
         * N: 1 = Client requests server to not update DNS (S must be 0 then)
         * Two [0] bytes which follow are deprecated and must be 0.
         */
        client_config.fqdn[OPT_DATA + 0] = 0x1;
        /*client_config.fqdn[OPT_DATA + 1] = 0; - xzalloc did it */
        /*client_config.fqdn[OPT_DATA + 2] = 0; */
    }
    if (opt & OPT_r)
        requested_ip = inet_addr(str_r);
#if ENABLE_FEATURE_UDHCP_PORT
    if (opt & OPT_P) {
        CLIENT_PORT = xatou16(str_P);
        SERVER_PORT = CLIENT_PORT - 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;
    }

    clientid_mac_ptr = NULL;
    if (!(opt & OPT_C) && !udhcp_find_option(client_config.options, DHCP_CLIENT_ID)) {
        /* not suppressed and not set, set the default client ID */
        client_config.clientid = alloc_dhcp_option(DHCP_CLIENT_ID, "", 7);
        client_config.clientid[OPT_DATA] = 1; /* type: ethernet */
        clientid_mac_ptr = client_config.clientid + OPT_DATA+1;
        memcpy(clientid_mac_ptr, client_config.client_mac, 6);
    }
    if (str_V[0] != '\0') {
        // can drop -V, str_V, client_config.vendorclass,
        // but need to add "vendor" to the list of recognized
        // string opts for this to work;
        // and need to tweak add_client_options() too...
        // ...so the question is, should we?
        //bb_error_msg("option -V VENDOR is deprecated, use -x vendor:VENDOR");
        client_config.vendorclass = alloc_dhcp_option(DHCP_VENDOR, str_V, 0);
    }

#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;
    udhcp_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 dhcp_packet packet;
        /* 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? */
            }
            if (clientid_mac_ptr)
                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();
                    /* broadcast */
                    send_discover(xid, requested_ip);
                    timeout = discover_timeout;
                    packet_num++;
                    continue;
                }
 leasefail:
                udhcp_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 broadcast select packet */
                    send_select(xid, server_addr, requested_ip);
                    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_renew(xid, server_addr, requested_ip);
                    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_renew(xid, 0 /*INADDR_ANY*/, requested_ip);
                    timeout >>= 1;
                    continue;
                }
                /* Timed out, enter init state */
                bb_info_msg("Lease lost, entering init state");
                udhcp_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_release(server_addr, requested_ip);
            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 = udhcp_recv_kernel_packet(&packet, sockfd);
            else
                len = udhcp_recv_raw_packet(&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;
        }

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

        /* Ignore packets that aren't for us */
        if (packet.hlen != 6
         || memcmp(packet.chaddr, client_config.client_mac, 6) != 0
        ) {
//FIXME: need to also check that last 10 bytes are zero
            log1("chaddr does not match, ignoring packet"); // log2?
            continue;
        }

        message = udhcp_get_option(&packet, DHCP_MESSAGE_TYPE);
        if (message == NULL) {
            bb_error_msg("no message type option, ignoring packet");
            continue;
        }

        switch (state) {
        case INIT_SELECTING:
            /* Must be a DHCPOFFER */
            if (*message == DHCPOFFER) {
/* What exactly is server's IP? There are several values.
 * Example DHCP offer captured with tchdump:
 *
 * 10.34.25.254:67 > 10.34.25.202:68 // IP header's src
 * BOOTP fields:
 * Your-IP 10.34.25.202
 * Server-IP 10.34.32.125   // "next server" IP
 * Gateway-IP 10.34.25.254  // relay's address (if DHCP relays are in use)
 * DHCP options:
 * DHCP-Message Option 53, length 1: Offer
 * Server-ID Option 54, length 4: 10.34.255.7       // "server ID"
 * Default-Gateway Option 3, length 4: 10.34.25.254 // router
 *
 * We think that real server IP (one to use in renew/release)
 * is one in Server-ID option. But I am not 100% sure.
 * IP header's src and Gateway-IP (same in this example)
 * might work too.
 * "Next server" and router are definitely wrong ones to use, though...
 */
                temp = udhcp_get_option(&packet, DHCP_SERVER_ID);
                if (!temp) {
                    bb_error_msg("no server ID, ignoring packet");
                    continue;
                    /* still selecting - this server looks bad */
                }
                /* it IS unaligned sometimes, don't "optimize" */
                move_from_unaligned32(server_addr, temp);
                /*xid = packet.xid; - already is */
                requested_ip = packet.yiaddr;

                /* enter requesting state */
                state = REQUESTING;
                timeout = 0;
                packet_num = 0;
                already_waited_sec = 0;
            }
            continue;
        case REQUESTING:
        case RENEWING:
        case RENEW_REQUESTED:
        case REBINDING:
            if (*message == DHCPACK) {
                uint32_t lease_seconds;
                struct in_addr temp_addr;

                temp = udhcp_get_option(&packet, DHCP_LEASE_TIME);
                if (!temp) {
                    bb_error_msg("no lease time with ACK, using 1 hour lease");
                    lease_seconds = 60 * 60;
                } else {
                    /* it IS unaligned sometimes, don't "optimize" */
                    move_from_unaligned32(lease_seconds, temp);
                    lease_seconds = ntohl(lease_seconds);
                    /* paranoia: must not be too small and not prone to overflows */
                    if (lease_seconds < 0x10)
                        lease_seconds = 0x10;
                    if (lease_seconds >= 0x10000000)
                        lease_seconds = 0x0fffffff;
                }
#if ENABLE_FEATURE_UDHCPC_ARPING
                if (opt & OPT_a) {
/* RFC 2131 3.1 paragraph 5:
 * "The client receives the DHCPACK message with configuration
 * parameters. The client SHOULD perform a final check on the
 * parameters (e.g., ARP for allocated network address), and notes
 * the duration of the lease specified in the DHCPACK message. At this
 * point, the client is configured. If the client detects that the
 * address is already in use (e.g., through the use of ARP),
 * the client MUST send a DHCPDECLINE message to the server and restarts
 * the configuration process..." */
                    if (!arpping(packet.yiaddr,
                            NULL,
                            (uint32_t) 0,
                            client_config.client_mac,
                            client_config.interface)
                    ) {
                        bb_info_msg("Offered address is in use "
                            "(got ARP reply), declining");
                        send_decline(/*xid,*/ server_addr, packet.yiaddr);

                        if (state != REQUESTING)
                            udhcp_run_script(NULL, "deconfig");
                        change_listen_mode(LISTEN_RAW);
                        state = INIT_SELECTING;
                        client_config.first_secs = 0; /* make secs field count from 0 */
                        requested_ip = 0;
                        timeout = tryagain_timeout;
                        packet_num = 0;
                        already_waited_sec = 0;
                        continue; /* back to main loop */
                    }
                }
#endif
                /* enter bound state */
                timeout = lease_seconds / 2;
                temp_addr.s_addr = packet.yiaddr;
                bb_info_msg("Lease of %s obtained, lease time %u",
                    inet_ntoa(temp_addr), (unsigned)lease_seconds);
                requested_ip = packet.yiaddr;
                udhcp_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
                /* make future renew packets use different xid */
                /* xid = random_xid(); ...but why bother? */
                already_waited_sec = 0;
                continue; /* back to main loop */
            }
            if (*message == DHCPNAK) {
                /* return to init state */
                bb_info_msg("Received DHCP NAK");
                udhcp_run_script(&packet, "nak");
                if (state != REQUESTING)
                    udhcp_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_ip = 0;
                timeout = 0;
                packet_num = 0;
                already_waited_sec = 0;
            }
            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_release(server_addr, requested_ip);
    retval = 0;
 ret:
    /*if (client_config.pidfile) - remove_pidfile has its own check */
        remove_pidfile(client_config.pidfile);
    return retval;
}