qemu/slirp/slirp.c

/*
 * libslirp glue
 *
 * Copyright (c) 2004-2008 Fabrice Bellard
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
#include "qemu-common.h"
#include "qemu/timer.h"
#include "sysemu/char.h"
#include "slirp.h"
#include "hw/hw.h"

/* host loopback address */
struct in_addr loopback_addr;
/* host loopback network mask */
unsigned long loopback_mask;

/* emulated hosts use the MAC addr 52:55:IP:IP:IP:IP */
static const uint8_t special_ethaddr[ETH_ALEN] = {
    0x52, 0x55, 0x00, 0x00, 0x00, 0x00
};

u_int curtime;

static QTAILQ_HEAD(slirp_instances, Slirp) slirp_instances =
    QTAILQ_HEAD_INITIALIZER(slirp_instances);

static struct in_addr dns_addr;
static u_int dns_addr_time;

#define TIMEOUT_FAST 2  /* milliseconds */
#define TIMEOUT_SLOW 499  /* milliseconds */
/* for the aging of certain requests like DNS */
#define TIMEOUT_DEFAULT 1000  /* milliseconds */

#ifdef _WIN32

int get_dns_addr(struct in_addr *pdns_addr)
{
    FIXED_INFO *FixedInfo=NULL;
    ULONG    BufLen;
    DWORD    ret;
    IP_ADDR_STRING *pIPAddr;
    struct in_addr tmp_addr;

    if (dns_addr.s_addr != 0 && (curtime - dns_addr_time) < TIMEOUT_DEFAULT) {
        *pdns_addr = dns_addr;
        return 0;
    }

    FixedInfo = (FIXED_INFO *)GlobalAlloc(GPTR, sizeof(FIXED_INFO));
    BufLen = sizeof(FIXED_INFO);

    if (ERROR_BUFFER_OVERFLOW == GetNetworkParams(FixedInfo, &BufLen)) {
        if (FixedInfo) {
            GlobalFree(FixedInfo);
            FixedInfo = NULL;
        }
        FixedInfo = GlobalAlloc(GPTR, BufLen);
    }

    if ((ret = GetNetworkParams(FixedInfo, &BufLen)) != ERROR_SUCCESS) {
        printf("GetNetworkParams failed. ret = %08x\n", (u_int)ret );
        if (FixedInfo) {
            GlobalFree(FixedInfo);
            FixedInfo = NULL;
        }
        return -1;
    }

    pIPAddr = &(FixedInfo->DnsServerList);
    inet_aton(pIPAddr->IpAddress.String, &tmp_addr);
    *pdns_addr = tmp_addr;
    dns_addr = tmp_addr;
    dns_addr_time = curtime;
    if (FixedInfo) {
        GlobalFree(FixedInfo);
        FixedInfo = NULL;
    }
    return 0;
}

static void winsock_cleanup(void)
{
    WSACleanup();
}

#else

static struct stat dns_addr_stat;

int get_dns_addr(struct in_addr *pdns_addr)
{
    char buff[512];
    char buff2[257];
    FILE *f;
    int found = 0;
    struct in_addr tmp_addr;

    if (dns_addr.s_addr != 0) {
        struct stat old_stat;
        if ((curtime - dns_addr_time) < TIMEOUT_DEFAULT) {
            *pdns_addr = dns_addr;
            return 0;
        }
        old_stat = dns_addr_stat;
        if (stat("/etc/resolv.conf", &dns_addr_stat) != 0)
            return -1;
        if ((dns_addr_stat.st_dev == old_stat.st_dev)
            && (dns_addr_stat.st_ino == old_stat.st_ino)
            && (dns_addr_stat.st_size == old_stat.st_size)
            && (dns_addr_stat.st_mtime == old_stat.st_mtime)) {
            *pdns_addr = dns_addr;
            return 0;
        }
    }

    f = fopen("/etc/resolv.conf", "r");
    if (!f)
        return -1;

#ifdef DEBUG
    fprintf(stderr, "IP address of your DNS(s): ");
#endif
    while (fgets(buff, 512, f) != NULL) {
        if (sscanf(buff, "nameserver%*[ \t]%256s", buff2) == 1) {
            if (!inet_aton(buff2, &tmp_addr))
                continue;
            /* If it's the first one, set it to dns_addr */
            if (!found) {
                *pdns_addr = tmp_addr;
                dns_addr = tmp_addr;
                dns_addr_time = curtime;
            }
#ifdef DEBUG
            else
                fprintf(stderr, ", ");
#endif
            if (++found > 3) {
#ifdef DEBUG
                fprintf(stderr, "(more)");
#endif
                break;
            }
#ifdef DEBUG
            else
                fprintf(stderr, "%s", inet_ntoa(tmp_addr));
#endif
        }
    }
    fclose(f);
    if (!found)
        return -1;
    return 0;
}

#endif

static void slirp_init_once(void)
{
    static int initialized;
#ifdef _WIN32
    WSADATA Data;
#endif

    if (initialized) {
        return;
    }
    initialized = 1;

#ifdef _WIN32
    WSAStartup(MAKEWORD(2,0), &Data);
    atexit(winsock_cleanup);
#endif

    loopback_addr.s_addr = htonl(INADDR_LOOPBACK);
    loopback_mask = htonl(IN_CLASSA_NET);
}

static void slirp_state_save(QEMUFile *f, void *opaque);
static int slirp_state_load(QEMUFile *f, void *opaque, int version_id);

Slirp *slirp_init(int restricted, struct in_addr vnetwork,
                  struct in_addr vnetmask, struct in_addr vhost,
                  const char *vhostname, const char *tftp_path,
                  const char *bootfile, struct in_addr vdhcp_start,
                  struct in_addr vnameserver, const char **vdnssearch,
                  void *opaque)
{
    Slirp *slirp = g_malloc0(sizeof(Slirp));

    slirp_init_once();

    slirp->restricted = restricted;

    if_init(slirp);
    ip_init(slirp);

    /* Initialise mbufs *after* setting the MTU */
    m_init(slirp);

    slirp->vnetwork_addr = vnetwork;
    slirp->vnetwork_mask = vnetmask;
    slirp->vhost_addr = vhost;
    if (vhostname) {
        pstrcpy(slirp->client_hostname, sizeof(slirp->client_hostname),
                vhostname);
    }
    slirp->tftp_prefix = g_strdup(tftp_path);
    slirp->bootp_filename = g_strdup(bootfile);
    slirp->vdhcp_startaddr = vdhcp_start;
    slirp->vnameserver_addr = vnameserver;

    if (vdnssearch) {
        translate_dnssearch(slirp, vdnssearch);
    }

    slirp->opaque = opaque;

    register_savevm(NULL, "slirp", 0, 3,
                    slirp_state_save, slirp_state_load, slirp);

    QTAILQ_INSERT_TAIL(&slirp_instances, slirp, entry);

    return slirp;
}

void slirp_cleanup(Slirp *slirp)
{
    QTAILQ_REMOVE(&slirp_instances, slirp, entry);

    unregister_savevm(NULL, "slirp", slirp);

    ip_cleanup(slirp);
    m_cleanup(slirp);

    g_free(slirp->vdnssearch);
    g_free(slirp->tftp_prefix);
    g_free(slirp->bootp_filename);
    g_free(slirp);
}

#define CONN_CANFSEND(so) (((so)->so_state & (SS_FCANTSENDMORE|SS_ISFCONNECTED)) == SS_ISFCONNECTED)
#define CONN_CANFRCV(so) (((so)->so_state & (SS_FCANTRCVMORE|SS_ISFCONNECTED)) == SS_ISFCONNECTED)

static void slirp_update_timeout(uint32_t *timeout)
{
    Slirp *slirp;
    uint32_t t;

    if (*timeout <= TIMEOUT_FAST) {
        return;
    }

    t = MIN(1000, *timeout);

    /* If we have tcp timeout with slirp, then we will fill @timeout with
     * more precise value.
     */
    QTAILQ_FOREACH(slirp, &slirp_instances, entry) {
        if (slirp->time_fasttimo) {
            *timeout = TIMEOUT_FAST;
            return;
        }
        if (slirp->do_slowtimo) {
            t = MIN(TIMEOUT_SLOW, t);
        }
    }
    *timeout = t;
}

void slirp_pollfds_fill(GArray *pollfds, uint32_t *timeout)
{
    Slirp *slirp;
    struct socket *so, *so_next;

    if (QTAILQ_EMPTY(&slirp_instances)) {
        return;
    }

    /*
     * First, TCP sockets
     */

    QTAILQ_FOREACH(slirp, &slirp_instances, entry) {
        /*
         * *_slowtimo needs calling if there are IP fragments
         * in the fragment queue, or there are TCP connections active
         */
        slirp->do_slowtimo = ((slirp->tcb.so_next != &slirp->tcb) ||
                (&slirp->ipq.ip_link != slirp->ipq.ip_link.next));

        for (so = slirp->tcb.so_next; so != &slirp->tcb;
                so = so_next) {
            int events = 0;

            so_next = so->so_next;

            so->pollfds_idx = -1;

            /*
             * See if we need a tcp_fasttimo
             */
            if (slirp->time_fasttimo == 0 &&
                so->so_tcpcb->t_flags & TF_DELACK) {
                slirp->time_fasttimo = curtime; /* Flag when want a fasttimo */
            }

            /*
             * NOFDREF can include still connecting to local-host,
             * newly socreated() sockets etc. Don't want to select these.
             */
            if (so->so_state & SS_NOFDREF || so->s == -1) {
                continue;
            }

            /*
             * Set for reading sockets which are accepting
             */
            if (so->so_state & SS_FACCEPTCONN) {
                GPollFD pfd = {
                    .fd = so->s,
                    .events = G_IO_IN | G_IO_HUP | G_IO_ERR,
                };
                so->pollfds_idx = pollfds->len;
                g_array_append_val(pollfds, pfd);
                continue;
            }

            /*
             * Set for writing sockets which are connecting
             */
            if (so->so_state & SS_ISFCONNECTING) {
                GPollFD pfd = {
                    .fd = so->s,
                    .events = G_IO_OUT | G_IO_ERR,
                };
                so->pollfds_idx = pollfds->len;
                g_array_append_val(pollfds, pfd);
                continue;
            }

            /*
             * Set for writing if we are connected, can send more, and
             * we have something to send
             */
            if (CONN_CANFSEND(so) && so->so_rcv.sb_cc) {
                events |= G_IO_OUT | G_IO_ERR;
            }

            /*
             * Set for reading (and urgent data) if we are connected, can
             * receive more, and we have room for it XXX /2 ?
             */
            if (CONN_CANFRCV(so) &&
                (so->so_snd.sb_cc < (so->so_snd.sb_datalen/2))) {
                events |= G_IO_IN | G_IO_HUP | G_IO_ERR | G_IO_PRI;
            }

            if (events) {
                GPollFD pfd = {
                    .fd = so->s,
                    .events = events,
                };
                so->pollfds_idx = pollfds->len;
                g_array_append_val(pollfds, pfd);
            }
        }

        /*
         * UDP sockets
         */
        for (so = slirp->udb.so_next; so != &slirp->udb;
                so = so_next) {
            so_next = so->so_next;

            so->pollfds_idx = -1;

            /*
             * See if it's timed out
             */
            if (so->so_expire) {
                if (so->so_expire <= curtime) {
                    udp_detach(so);
                    continue;
                } else {
                    slirp->do_slowtimo = true; /* Let socket expire */
                }
            }

            /*
             * When UDP packets are received from over the
             * link, they're sendto()'d straight away, so
             * no need for setting for writing
             * Limit the number of packets queued by this session
             * to 4.  Note that even though we try and limit this
             * to 4 packets, the session could have more queued
             * if the packets needed to be fragmented
             * (XXX <= 4 ?)
             */
            if ((so->so_state & SS_ISFCONNECTED) && so->so_queued <= 4) {
                GPollFD pfd = {
                    .fd = so->s,
                    .events = G_IO_IN | G_IO_HUP | G_IO_ERR,
                };
                so->pollfds_idx = pollfds->len;
                g_array_append_val(pollfds, pfd);
            }
        }

        /*
         * ICMP sockets
         */
        for (so = slirp->icmp.so_next; so != &slirp->icmp;
                so = so_next) {
            so_next = so->so_next;

            so->pollfds_idx = -1;

            /*
             * See if it's timed out
             */
            if (so->so_expire) {
                if (so->so_expire <= curtime) {
                    icmp_detach(so);
                    continue;
                } else {
                    slirp->do_slowtimo = true; /* Let socket expire */
                }
            }

            if (so->so_state & SS_ISFCONNECTED) {
                GPollFD pfd = {
                    .fd = so->s,
                    .events = G_IO_IN | G_IO_HUP | G_IO_ERR,
                };
                so->pollfds_idx = pollfds->len;
                g_array_append_val(pollfds, pfd);
            }
        }
    }
    slirp_update_timeout(timeout);
}

void slirp_pollfds_poll(GArray *pollfds, int select_error)
{
    Slirp *slirp;
    struct socket *so, *so_next;
    int ret;

    if (QTAILQ_EMPTY(&slirp_instances)) {
        return;
    }

    curtime = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);

    QTAILQ_FOREACH(slirp, &slirp_instances, entry) {
        /*
         * See if anything has timed out
         */
        if (slirp->time_fasttimo &&
            ((curtime - slirp->time_fasttimo) >= TIMEOUT_FAST)) {
            tcp_fasttimo(slirp);
            slirp->time_fasttimo = 0;
        }
        if (slirp->do_slowtimo &&
            ((curtime - slirp->last_slowtimo) >= TIMEOUT_SLOW)) {
            ip_slowtimo(slirp);
            tcp_slowtimo(slirp);
            slirp->last_slowtimo = curtime;
        }

        /*
         * Check sockets
         */
        if (!select_error) {
            /*
             * Check TCP sockets
             */
            for (so = slirp->tcb.so_next; so != &slirp->tcb;
                    so = so_next) {
                int revents;

                so_next = so->so_next;

                revents = 0;
                if (so->pollfds_idx != -1) {
                    revents = g_array_index(pollfds, GPollFD,
                                            so->pollfds_idx).revents;
                }

                if (so->so_state & SS_NOFDREF || so->s == -1) {
                    continue;
                }

                /*
                 * Check for URG data
                 * This will soread as well, so no need to
                 * test for G_IO_IN below if this succeeds
                 */
                if (revents & G_IO_PRI) {
                    sorecvoob(so);
                }
                /*
                 * Check sockets for reading
                 */
                else if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR)) {
                    /*
                     * Check for incoming connections
                     */
                    if (so->so_state & SS_FACCEPTCONN) {
                        tcp_connect(so);
                        continue;
                    } /* else */
                    ret = soread(so);

                    /* Output it if we read something */
                    if (ret > 0) {
                        tcp_output(sototcpcb(so));
                    }
                }

                /*
                 * Check sockets for writing
                 */
                if (!(so->so_state & SS_NOFDREF) &&
                        (revents & (G_IO_OUT | G_IO_ERR))) {
                    /*
                     * Check for non-blocking, still-connecting sockets
                     */
                    if (so->so_state & SS_ISFCONNECTING) {
                        /* Connected */
                        so->so_state &= ~SS_ISFCONNECTING;

                        ret = send(so->s, (const void *) &ret, 0, 0);
                        if (ret < 0) {
                            /* XXXXX Must fix, zero bytes is a NOP */
                            if (errno == EAGAIN || errno == EWOULDBLOCK ||
                                errno == EINPROGRESS || errno == ENOTCONN) {
                                continue;
                            }

                            /* else failed */
                            so->so_state &= SS_PERSISTENT_MASK;
                            so->so_state |= SS_NOFDREF;
                        }
                        /* else so->so_state &= ~SS_ISFCONNECTING; */

                        /*
                         * Continue tcp_input
                         */
                        tcp_input((struct mbuf *)NULL, sizeof(struct ip), so);
                        /* continue; */
                    } else {
                        ret = sowrite(so);
                    }
                    /*
                     * XXXXX If we wrote something (a lot), there
                     * could be a need for a window update.
                     * In the worst case, the remote will send
                     * a window probe to get things going again
                     */
                }

                /*
                 * Probe a still-connecting, non-blocking socket
                 * to check if it's still alive
                 */
#ifdef PROBE_CONN
                if (so->so_state & SS_ISFCONNECTING) {
                    ret = qemu_recv(so->s, &ret, 0, 0);

                    if (ret < 0) {
                        /* XXX */
                        if (errno == EAGAIN || errno == EWOULDBLOCK ||
                            errno == EINPROGRESS || errno == ENOTCONN) {
                            continue; /* Still connecting, continue */
                        }

                        /* else failed */
                        so->so_state &= SS_PERSISTENT_MASK;
                        so->so_state |= SS_NOFDREF;

                        /* tcp_input will take care of it */
                    } else {
                        ret = send(so->s, &ret, 0, 0);
                        if (ret < 0) {
                            /* XXX */
                            if (errno == EAGAIN || errno == EWOULDBLOCK ||
                                errno == EINPROGRESS || errno == ENOTCONN) {
                                continue;
                            }
                            /* else failed */
                            so->so_state &= SS_PERSISTENT_MASK;
                            so->so_state |= SS_NOFDREF;
                        } else {
                            so->so_state &= ~SS_ISFCONNECTING;
                        }

                    }
                    tcp_input((struct mbuf *)NULL, sizeof(struct ip), so);
                } /* SS_ISFCONNECTING */
#endif
            }

            /*
             * Now UDP sockets.
             * Incoming packets are sent straight away, they're not buffered.
             * Incoming UDP data isn't buffered either.
             */
            for (so = slirp->udb.so_next; so != &slirp->udb;
                    so = so_next) {
                int revents;

                so_next = so->so_next;

                revents = 0;
                if (so->pollfds_idx != -1) {
                    revents = g_array_index(pollfds, GPollFD,
                            so->pollfds_idx).revents;
                }

                if (so->s != -1 &&
                    (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR))) {
                    sorecvfrom(so);
                }
            }

            /*
             * Check incoming ICMP relies.
             */
            for (so = slirp->icmp.so_next; so != &slirp->icmp;
                    so = so_next) {
                    int revents;

                    so_next = so->so_next;

                    revents = 0;
                    if (so->pollfds_idx != -1) {
                        revents = g_array_index(pollfds, GPollFD,
                                                so->pollfds_idx).revents;
                    }

                    if (so->s != -1 &&
                        (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR))) {
                    icmp_receive(so);
                }
            }
        }

        if_start(slirp);
    }
}

static void arp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
{
    struct arphdr *ah = (struct arphdr *)(pkt + ETH_HLEN);
    uint8_t arp_reply[max(ETH_HLEN + sizeof(struct arphdr), 64)];
    struct ethhdr *reh = (struct ethhdr *)arp_reply;
    struct arphdr *rah = (struct arphdr *)(arp_reply + ETH_HLEN);
    int ar_op;
    struct ex_list *ex_ptr;

    ar_op = ntohs(ah->ar_op);
    switch(ar_op) {
    case ARPOP_REQUEST:
        if (ah->ar_tip == ah->ar_sip) {
            /* Gratuitous ARP */
            arp_table_add(slirp, ah->ar_sip, ah->ar_sha);
            return;
        }

        if ((ah->ar_tip & slirp->vnetwork_mask.s_addr) ==
            slirp->vnetwork_addr.s_addr) {
            if (ah->ar_tip == slirp->vnameserver_addr.s_addr ||
                ah->ar_tip == slirp->vhost_addr.s_addr)
                goto arp_ok;
            for (ex_ptr = slirp->exec_list; ex_ptr; ex_ptr = ex_ptr->ex_next) {
                if (ex_ptr->ex_addr.s_addr == ah->ar_tip)
                    goto arp_ok;
            }
            return;
        arp_ok:
            memset(arp_reply, 0, sizeof(arp_reply));

            arp_table_add(slirp, ah->ar_sip, ah->ar_sha);

            /* ARP request for alias/dns mac address */
            memcpy(reh->h_dest, pkt + ETH_ALEN, ETH_ALEN);
            memcpy(reh->h_source, special_ethaddr, ETH_ALEN - 4);
            memcpy(&reh->h_source[2], &ah->ar_tip, 4);
            reh->h_proto = htons(ETH_P_ARP);

            rah->ar_hrd = htons(1);
            rah->ar_pro = htons(ETH_P_IP);
            rah->ar_hln = ETH_ALEN;
            rah->ar_pln = 4;
            rah->ar_op = htons(ARPOP_REPLY);
            memcpy(rah->ar_sha, reh->h_source, ETH_ALEN);
            rah->ar_sip = ah->ar_tip;
            memcpy(rah->ar_tha, ah->ar_sha, ETH_ALEN);
            rah->ar_tip = ah->ar_sip;
            slirp_output(slirp->opaque, arp_reply, sizeof(arp_reply));
        }
        break;
    case ARPOP_REPLY:
        arp_table_add(slirp, ah->ar_sip, ah->ar_sha);
        break;
    default:
        break;
    }
}

void slirp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
{
    struct mbuf *m;
    int proto;

    if (pkt_len < ETH_HLEN)
        return;

    proto = ntohs(*(uint16_t *)(pkt + 12));
    switch(proto) {
    case ETH_P_ARP:
        arp_input(slirp, pkt, pkt_len);
        break;
    case ETH_P_IP:
        m = m_get(slirp);
        if (!m)
            return;
        /* Note: we add to align the IP header */
        if (M_FREEROOM(m) < pkt_len + 2) {
            m_inc(m, pkt_len + 2);
        }
        m->m_len = pkt_len + 2;
        memcpy(m->m_data + 2, pkt, pkt_len);

        m->m_data += 2 + ETH_HLEN;
        m->m_len -= 2 + ETH_HLEN;

        ip_input(m);
        break;
    default:
        break;
    }
}

/* Output the IP packet to the ethernet device. Returns 0 if the packet must be
 * re-queued.
 */
int if_encap(Slirp *slirp, struct mbuf *ifm)
{
    uint8_t buf[1600];
    struct ethhdr *eh = (struct ethhdr *)buf;
    uint8_t ethaddr[ETH_ALEN];
    const struct ip *iph = (const struct ip *)ifm->m_data;

    if (ifm->m_len + ETH_HLEN > sizeof(buf)) {
        return 1;
    }

    if (iph->ip_dst.s_addr == 0) {
        /* 0.0.0.0 can not be a destination address, something went wrong,
         * avoid making it worse */
        return 1;
    }
    if (!arp_table_search(slirp, iph->ip_dst.s_addr, ethaddr)) {
        uint8_t arp_req[ETH_HLEN + sizeof(struct arphdr)];
        struct ethhdr *reh = (struct ethhdr *)arp_req;
        struct arphdr *rah = (struct arphdr *)(arp_req + ETH_HLEN);

        if (!ifm->arp_requested) {
            /* If the client addr is not known, send an ARP request */
            memset(reh->h_dest, 0xff, ETH_ALEN);
            memcpy(reh->h_source, special_ethaddr, ETH_ALEN - 4);
            memcpy(&reh->h_source[2], &slirp->vhost_addr, 4);
            reh->h_proto = htons(ETH_P_ARP);
            rah->ar_hrd = htons(1);
            rah->ar_pro = htons(ETH_P_IP);
            rah->ar_hln = ETH_ALEN;
            rah->ar_pln = 4;
            rah->ar_op = htons(ARPOP_REQUEST);

            /* source hw addr */
            memcpy(rah->ar_sha, special_ethaddr, ETH_ALEN - 4);
            memcpy(&rah->ar_sha[2], &slirp->vhost_addr, 4);

            /* source IP */
            rah->ar_sip = slirp->vhost_addr.s_addr;

            /* target hw addr (none) */
            memset(rah->ar_tha, 0, ETH_ALEN);

            /* target IP */
            rah->ar_tip = iph->ip_dst.s_addr;
            slirp->client_ipaddr = iph->ip_dst;
            slirp_output(slirp->opaque, arp_req, sizeof(arp_req));
            ifm->arp_requested = true;

            /* Expire request and drop outgoing packet after 1 second */
            ifm->expiration_date = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + 1000000000ULL;
        }
        return 0;
    } else {
        memcpy(eh->h_dest, ethaddr, ETH_ALEN);
        memcpy(eh->h_source, special_ethaddr, ETH_ALEN - 4);
        /* XXX: not correct */
        memcpy(&eh->h_source[2], &slirp->vhost_addr, 4);
        eh->h_proto = htons(ETH_P_IP);
        memcpy(buf + sizeof(struct ethhdr), ifm->m_data, ifm->m_len);
        slirp_output(slirp->opaque, buf, ifm->m_len + ETH_HLEN);
        return 1;
    }
}

/* Drop host forwarding rule, return 0 if found. */
int slirp_remove_hostfwd(Slirp *slirp, int is_udp, struct in_addr host_addr,
                         int host_port)
{
    struct socket *so;
    struct socket *head = (is_udp ? &slirp->udb : &slirp->tcb);
    struct sockaddr_in addr;
    int port = htons(host_port);
    socklen_t addr_len;

    for (so = head->so_next; so != head; so = so->so_next) {
        addr_len = sizeof(addr);
        if ((so->so_state & SS_HOSTFWD) &&
            getsockname(so->s, (struct sockaddr *)&addr, &addr_len) == 0 &&
            addr.sin_addr.s_addr == host_addr.s_addr &&
            addr.sin_port == port) {
            close(so->s);
            sofree(so);
            return 0;
        }
    }

    return -1;
}

int slirp_add_hostfwd(Slirp *slirp, int is_udp, struct in_addr host_addr,
                      int host_port, struct in_addr guest_addr, int guest_port)
{
    if (!guest_addr.s_addr) {
        guest_addr = slirp->vdhcp_startaddr;
    }
    if (is_udp) {
        if (!udp_listen(slirp, host_addr.s_addr, htons(host_port),
                        guest_addr.s_addr, htons(guest_port), SS_HOSTFWD))
            return -1;
    } else {
        if (!tcp_listen(slirp, host_addr.s_addr, htons(host_port),
                        guest_addr.s_addr, htons(guest_port), SS_HOSTFWD))
            return -1;
    }
    return 0;
}

int slirp_add_exec(Slirp *slirp, int do_pty, const void *args,
                   struct in_addr *guest_addr, int guest_port)
{
    if (!guest_addr->s_addr) {
        guest_addr->s_addr = slirp->vnetwork_addr.s_addr |
            (htonl(0x0204) & ~slirp->vnetwork_mask.s_addr);
    }
    if ((guest_addr->s_addr & slirp->vnetwork_mask.s_addr) !=
        slirp->vnetwork_addr.s_addr ||
        guest_addr->s_addr == slirp->vhost_addr.s_addr ||
        guest_addr->s_addr == slirp->vnameserver_addr.s_addr) {
        return -1;
    }
    return add_exec(&slirp->exec_list, do_pty, (char *)args, *guest_addr,
                    htons(guest_port));
}

ssize_t slirp_send(struct socket *so, const void *buf, size_t len, int flags)
{
    if (so->s == -1 && so->extra) {
        qemu_chr_fe_write(so->extra, buf, len);
        return len;
    }

    return send(so->s, buf, len, flags);
}

static struct socket *
slirp_find_ctl_socket(Slirp *slirp, struct in_addr guest_addr, int guest_port)
{
    struct socket *so;

    for (so = slirp->tcb.so_next; so != &slirp->tcb; so = so->so_next) {
        if (so->so_faddr.s_addr == guest_addr.s_addr &&
            htons(so->so_fport) == guest_port) {
            return so;
        }
    }
    return NULL;
}

size_t slirp_socket_can_recv(Slirp *slirp, struct in_addr guest_addr,
                             int guest_port)
{
    struct iovec iov[2];
    struct socket *so;

    so = slirp_find_ctl_socket(slirp, guest_addr, guest_port);

    if (!so || so->so_state & SS_NOFDREF) {
        return 0;
    }

    if (!CONN_CANFRCV(so) || so->so_snd.sb_cc >= (so->so_snd.sb_datalen/2)) {
        return 0;
    }

    return sopreprbuf(so, iov, NULL);
}

void slirp_socket_recv(Slirp *slirp, struct in_addr guest_addr, int guest_port,
                       const uint8_t *buf, int size)
{
    int ret;
    struct socket *so = slirp_find_ctl_socket(slirp, guest_addr, guest_port);

    if (!so)
        return;

    ret = soreadbuf(so, (const char *)buf, size);

    if (ret > 0)
        tcp_output(sototcpcb(so));
}

static void slirp_tcp_save(QEMUFile *f, struct tcpcb *tp)
{
    int i;

    qemu_put_sbe16(f, tp->t_state);
    for (i = 0; i < TCPT_NTIMERS; i++)
        qemu_put_sbe16(f, tp->t_timer[i]);
    qemu_put_sbe16(f, tp->t_rxtshift);
    qemu_put_sbe16(f, tp->t_rxtcur);
    qemu_put_sbe16(f, tp->t_dupacks);
    qemu_put_be16(f, tp->t_maxseg);
    qemu_put_sbyte(f, tp->t_force);
    qemu_put_be16(f, tp->t_flags);
    qemu_put_be32(f, tp->snd_una);
    qemu_put_be32(f, tp->snd_nxt);
    qemu_put_be32(f, tp->snd_up);
    qemu_put_be32(f, tp->snd_wl1);
    qemu_put_be32(f, tp->snd_wl2);
    qemu_put_be32(f, tp->iss);
    qemu_put_be32(f, tp->snd_wnd);
    qemu_put_be32(f, tp->rcv_wnd);
    qemu_put_be32(f, tp->rcv_nxt);
    qemu_put_be32(f, tp->rcv_up);
    qemu_put_be32(f, tp->irs);
    qemu_put_be32(f, tp->rcv_adv);
    qemu_put_be32(f, tp->snd_max);
    qemu_put_be32(f, tp->snd_cwnd);
    qemu_put_be32(f, tp->snd_ssthresh);
    qemu_put_sbe16(f, tp->t_idle);
    qemu_put_sbe16(f, tp->t_rtt);
    qemu_put_be32(f, tp->t_rtseq);
    qemu_put_sbe16(f, tp->t_srtt);
    qemu_put_sbe16(f, tp->t_rttvar);
    qemu_put_be16(f, tp->t_rttmin);
    qemu_put_be32(f, tp->max_sndwnd);
    qemu_put_byte(f, tp->t_oobflags);
    qemu_put_byte(f, tp->t_iobc);
    qemu_put_sbe16(f, tp->t_softerror);
    qemu_put_byte(f, tp->snd_scale);
    qemu_put_byte(f, tp->rcv_scale);
    qemu_put_byte(f, tp->request_r_scale);
    qemu_put_byte(f, tp->requested_s_scale);
    qemu_put_be32(f, tp->ts_recent);
    qemu_put_be32(f, tp->ts_recent_age);
    qemu_put_be32(f, tp->last_ack_sent);
}

static void slirp_sbuf_save(QEMUFile *f, struct sbuf *sbuf)
{
    uint32_t off;

    qemu_put_be32(f, sbuf->sb_cc);
    qemu_put_be32(f, sbuf->sb_datalen);
    off = (uint32_t)(sbuf->sb_wptr - sbuf->sb_data);
    qemu_put_sbe32(f, off);
    off = (uint32_t)(sbuf->sb_rptr - sbuf->sb_data);
    qemu_put_sbe32(f, off);
    qemu_put_buffer(f, (unsigned char*)sbuf->sb_data, sbuf->sb_datalen);
}

static void slirp_socket_save(QEMUFile *f, struct socket *so)
{
    qemu_put_be32(f, so->so_urgc);
    qemu_put_be32(f, so->so_faddr.s_addr);
    qemu_put_be32(f, so->so_laddr.s_addr);
    qemu_put_be16(f, so->so_fport);
    qemu_put_be16(f, so->so_lport);
    qemu_put_byte(f, so->so_iptos);
    qemu_put_byte(f, so->so_emu);
    qemu_put_byte(f, so->so_type);
    qemu_put_be32(f, so->so_state);
    slirp_sbuf_save(f, &so->so_rcv);
    slirp_sbuf_save(f, &so->so_snd);
    slirp_tcp_save(f, so->so_tcpcb);
}

static void slirp_bootp_save(QEMUFile *f, Slirp *slirp)
{
    int i;

    for (i = 0; i < NB_BOOTP_CLIENTS; i++) {
        qemu_put_be16(f, slirp->bootp_clients[i].allocated);
        qemu_put_buffer(f, slirp->bootp_clients[i].macaddr, 6);
    }
}

static void slirp_state_save(QEMUFile *f, void *opaque)
{
    Slirp *slirp = opaque;
    struct ex_list *ex_ptr;

    for (ex_ptr = slirp->exec_list; ex_ptr; ex_ptr = ex_ptr->ex_next)
        if (ex_ptr->ex_pty == 3) {
            struct socket *so;
            so = slirp_find_ctl_socket(slirp, ex_ptr->ex_addr,
                                       ntohs(ex_ptr->ex_fport));
            if (!so)
                continue;

            qemu_put_byte(f, 42);
            slirp_socket_save(f, so);
        }
    qemu_put_byte(f, 0);

    qemu_put_be16(f, slirp->ip_id);

    slirp_bootp_save(f, slirp);
}

static void slirp_tcp_load(QEMUFile *f, struct tcpcb *tp)
{
    int i;

    tp->t_state = qemu_get_sbe16(f);
    for (i = 0; i < TCPT_NTIMERS; i++)
        tp->t_timer[i] = qemu_get_sbe16(f);
    tp->t_rxtshift = qemu_get_sbe16(f);
    tp->t_rxtcur = qemu_get_sbe16(f);
    tp->t_dupacks = qemu_get_sbe16(f);
    tp->t_maxseg = qemu_get_be16(f);
    tp->t_force = qemu_get_sbyte(f);
    tp->t_flags = qemu_get_be16(f);
    tp->snd_una = qemu_get_be32(f);
    tp->snd_nxt = qemu_get_be32(f);
    tp->snd_up = qemu_get_be32(f);
    tp->snd_wl1 = qemu_get_be32(f);
    tp->snd_wl2 = qemu_get_be32(f);
    tp->iss = qemu_get_be32(f);
    tp->snd_wnd = qemu_get_be32(f);
    tp->rcv_wnd = qemu_get_be32(f);
    tp->rcv_nxt = qemu_get_be32(f);
    tp->rcv_up = qemu_get_be32(f);
    tp->irs = qemu_get_be32(f);
    tp->rcv_adv = qemu_get_be32(f);
    tp->snd_max = qemu_get_be32(f);
    tp->snd_cwnd = qemu_get_be32(f);
    tp->snd_ssthresh = qemu_get_be32(f);
    tp->t_idle = qemu_get_sbe16(f);
    tp->t_rtt = qemu_get_sbe16(f);
    tp->t_rtseq = qemu_get_be32(f);
    tp->t_srtt = qemu_get_sbe16(f);
    tp->t_rttvar = qemu_get_sbe16(f);
    tp->t_rttmin = qemu_get_be16(f);
    tp->max_sndwnd = qemu_get_be32(f);
    tp->t_oobflags = qemu_get_byte(f);
    tp->t_iobc = qemu_get_byte(f);
    tp->t_softerror = qemu_get_sbe16(f);
    tp->snd_scale = qemu_get_byte(f);
    tp->rcv_scale = qemu_get_byte(f);
    tp->request_r_scale = qemu_get_byte(f);
    tp->requested_s_scale = qemu_get_byte(f);
    tp->ts_recent = qemu_get_be32(f);
    tp->ts_recent_age = qemu_get_be32(f);
    tp->last_ack_sent = qemu_get_be32(f);
    tcp_template(tp);
}

static int slirp_sbuf_load(QEMUFile *f, struct sbuf *sbuf)
{
    uint32_t off, sb_cc, sb_datalen;

    sb_cc = qemu_get_be32(f);
    sb_datalen = qemu_get_be32(f);

    sbreserve(sbuf, sb_datalen);

    if (sbuf->sb_datalen != sb_datalen)
        return -ENOMEM;

    sbuf->sb_cc = sb_cc;

    off = qemu_get_sbe32(f);
    sbuf->sb_wptr = sbuf->sb_data + off;
    off = qemu_get_sbe32(f);
    sbuf->sb_rptr = sbuf->sb_data + off;
    qemu_get_buffer(f, (unsigned char*)sbuf->sb_data, sbuf->sb_datalen);

    return 0;
}

static int slirp_socket_load(QEMUFile *f, struct socket *so)
{
    if (tcp_attach(so) < 0)
        return -ENOMEM;

    so->so_urgc = qemu_get_be32(f);
    so->so_faddr.s_addr = qemu_get_be32(f);
    so->so_laddr.s_addr = qemu_get_be32(f);
    so->so_fport = qemu_get_be16(f);
    so->so_lport = qemu_get_be16(f);
    so->so_iptos = qemu_get_byte(f);
    so->so_emu = qemu_get_byte(f);
    so->so_type = qemu_get_byte(f);
    so->so_state = qemu_get_be32(f);
    if (slirp_sbuf_load(f, &so->so_rcv) < 0)
        return -ENOMEM;
    if (slirp_sbuf_load(f, &so->so_snd) < 0)
        return -ENOMEM;
    slirp_tcp_load(f, so->so_tcpcb);

    return 0;
}

static void slirp_bootp_load(QEMUFile *f, Slirp *slirp)
{
    int i;

    for (i = 0; i < NB_BOOTP_CLIENTS; i++) {
        slirp->bootp_clients[i].allocated = qemu_get_be16(f);
        qemu_get_buffer(f, slirp->bootp_clients[i].macaddr, 6);
    }
}

static int slirp_state_load(QEMUFile *f, void *opaque, int version_id)
{
    Slirp *slirp = opaque;
    struct ex_list *ex_ptr;

    while (qemu_get_byte(f)) {
        int ret;
        struct socket *so = socreate(slirp);

        if (!so)
            return -ENOMEM;

        ret = slirp_socket_load(f, so);

        if (ret < 0)
            return ret;

        if ((so->so_faddr.s_addr & slirp->vnetwork_mask.s_addr) !=
            slirp->vnetwork_addr.s_addr) {
            return -EINVAL;
        }
        for (ex_ptr = slirp->exec_list; ex_ptr; ex_ptr = ex_ptr->ex_next) {
            if (ex_ptr->ex_pty == 3 &&
                so->so_faddr.s_addr == ex_ptr->ex_addr.s_addr &&
                so->so_fport == ex_ptr->ex_fport) {
                break;
            }
        }
        if (!ex_ptr)
            return -EINVAL;

        so->extra = (void *)ex_ptr->ex_exec;
    }

    if (version_id >= 2) {
        slirp->ip_id = qemu_get_be16(f);
    }

    if (version_id >= 3) {
        slirp_bootp_load(f, slirp);
    }

    return 0;
}