sd-network: IPv4 link-local support [v2]

Implements IPv4LL with respect to RFC 3927
(http://tools.ietf.org/rfc/rfc3927.txt) and integrates it
with networkd. Majority of the IPv4LL state machine is
taken from avahi (http://avahi.org/) project's autoip.

IPv4LL can be enabled by IPv4LL=yes under [Network]
section of .network file.

IPv4LL works independent of DHCP but if DHCP lease is
aquired, then LL address will be dropped.

[tomegun: removed a trailing newline and a compiler warning]

4 files changed, 684 insertions, 0 deletions

diff --git a/src/libsystemd-network/ipv4ll-internal.h b/src/libsystemd-network/ipv4ll-internal.h
new file mode 100644
index 0000000000..fe5ef8e2b8
--- /dev/null
+++ b/src/libsystemd-network/ipv4ll-internal.h
@@ -0,0 +1,38 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+#pragma once
+
+/***
+  This file is part of systemd.
+
+  Copyright (C) 2014 Axis Communications AB. All rights reserved.
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd 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
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <netinet/if_ether.h>
+
+#include "sparse-endian.h"
+#include "socket-util.h"
+
+int arp_network_bind_raw_socket(int index, union sockaddr_union *link);
+int arp_network_send_raw_socket(int fd, const union sockaddr_union *link,
+                                        const struct ether_arp *arp);
+
+void arp_packet_init(struct ether_arp *arp);
+void arp_packet_probe(struct ether_arp *arp, be32_t pa, const struct ether_addr *ha);
+void arp_packet_announcement(struct ether_arp *arp, be32_t pa, const struct ether_addr *ha);
+int arp_packet_verify_headers(struct ether_arp *arp);
+
+#define log_ipv4ll(ll, fmt, ...) log_meta(LOG_DEBUG, __FILE__, __LINE__, __func__, "IPv4LL: " fmt, ##__VA_ARGS__)
diff --git a/src/libsystemd-network/ipv4ll-network.c b/src/libsystemd-network/ipv4ll-network.c
new file mode 100644
index 0000000000..51734d7e4d
--- /dev/null
+++ b/src/libsystemd-network/ipv4ll-network.c
@@ -0,0 +1,56 @@
+/***
+  This file is part of systemd.
+
+  Copyright (C) 2014 Axis Communications AB. All rights reserved.
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd 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
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include "util.h"
+#include "ipv4ll-internal.h"
+
+int arp_network_send_raw_socket(int fd, const union sockaddr_union *link,
+                                        const struct ether_arp *arp) {
+        assert(arp);
+        assert(link);
+        assert(fd >= 0);
+
+        if (sendto(fd, arp, sizeof(struct ether_arp), 0, &link->sa, sizeof(link->ll)) < 0)
+                return -errno;
+
+        return 0;
+}
+
+int arp_network_bind_raw_socket(int index, union sockaddr_union *link) {
+        int s;
+
+        assert(index > 0);
+        assert(link);
+
+        s = socket(PF_PACKET, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, htons(ETH_P_ARP));
+        if (s < 0)
+                return -errno;
+
+        link->ll.sll_family = AF_PACKET;
+        link->ll.sll_ifindex = index;
+        link->ll.sll_protocol = htons(ETH_P_ARP);
+        link->ll.sll_halen = ETH_ALEN;
+
+        if (bind(s, &link->sa, sizeof(link->ll)) < 0) {
+                close_nointr_nofail(s);
+                return -errno;
+        }
+
+        return s;
+}
diff --git a/src/libsystemd-network/ipv4ll-packet.c b/src/libsystemd-network/ipv4ll-packet.c
new file mode 100644
index 0000000000..2b6c73ab4b
--- /dev/null
+++ b/src/libsystemd-network/ipv4ll-packet.c
@@ -0,0 +1,71 @@
+/***
+  This file is part of systemd.
+
+  Copyright (C) 2014 Axis Communications AB. All rights reserved.
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd 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
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+#include <arpa/inet.h>
+
+#include "util.h"
+#include "ipv4ll-internal.h"
+
+void arp_packet_init(struct ether_arp *arp) {
+        assert(arp);
+
+        memzero(arp, sizeof(struct ether_arp));
+        /* Header */
+        arp->ea_hdr.ar_hrd = htons(ARPHRD_ETHER); /* HTYPE */
+        arp->ea_hdr.ar_pro = htons(ETHERTYPE_IP); /* PTYPE */
+        arp->ea_hdr.ar_hln = ETH_ALEN; /* HLEN */
+        arp->ea_hdr.ar_pln = sizeof arp->arp_spa; /* PLEN */
+        arp->ea_hdr.ar_op = htons(ARPOP_REQUEST); /* REQUEST */
+}
+
+void arp_packet_probe(struct ether_arp *arp, be32_t pa, const struct ether_addr *ha) {
+        assert(ha);
+
+        arp_packet_init(arp);
+        memcpy(arp->arp_sha, ha, ETH_ALEN);
+        memcpy(arp->arp_tpa, &pa, sizeof(pa));
+}
+
+void arp_packet_announcement(struct ether_arp *arp, be32_t pa, const struct ether_addr *ha) {
+        assert(ha);
+
+        arp_packet_init(arp);
+        memcpy(arp->arp_sha, ha, ETH_ALEN);
+        memcpy(arp->arp_tpa, &pa, sizeof(pa));
+        memcpy(arp->arp_spa, &pa, sizeof(pa));
+}
+
+int arp_packet_verify_headers(struct ether_arp *arp) {
+        assert(arp);
+
+        if (arp->ea_hdr.ar_hrd != htons(ARPHRD_ETHER)) {
+                log_ipv4ll(NULL, "ignoring packet: header is not ARPHRD_ETHER");
+                return -EINVAL;
+        }
+        if (arp->ea_hdr.ar_pro != htons(ETHERTYPE_IP)) {
+                log_ipv4ll(NULL, "ignoring packet: protocol is not ETHERTYPE_IP");
+                return -EINVAL;
+        }
+        if (arp->ea_hdr.ar_op != htons(ARPOP_REQUEST) &&
+            arp->ea_hdr.ar_op != htons(ARPOP_REPLY)) {
+                log_ipv4ll(NULL, "ignoring packet: operation is not ARPOP_REQUEST or ARPOP_REPLY");
+                return -EINVAL;
+        }
+
+        return 0;
+}
diff --git a/src/libsystemd-network/sd-ipv4ll.c b/src/libsystemd-network/sd-ipv4ll.c
new file mode 100644
index 0000000000..c6f6e01431
--- /dev/null
+++ b/src/libsystemd-network/sd-ipv4ll.c
@@ -0,0 +1,519 @@
+/***
+  This file is part of systemd.
+
+  Copyright (C) 2014 Axis Communications AB. All rights reserved.
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd 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
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <stdlib.h>
+#include <errno.h>
+#include <string.h>
+#include <stdio.h>
+#include <arpa/inet.h>
+
+#include "util.h"
+#include "list.h"
+
+#include "ipv4ll-internal.h"
+#include "sd-ipv4ll.h"
+
+/* Constants from the RFC */
+#define PROBE_WAIT 1
+#define PROBE_NUM 3
+#define PROBE_MIN 1
+#define PROBE_MAX 2
+#define ANNOUNCE_WAIT 2
+#define ANNOUNCE_NUM 2
+#define ANNOUNCE_INTERVAL 2
+#define MAX_CONFLICTS 10
+#define RATE_LIMIT_INTERVAL 60
+#define DEFEND_INTERVAL 10
+
+#define IPV4LL_NETWORK 0xA9FE0000L
+#define IPV4LL_NETMASK 0xFFFF0000L
+
+typedef enum IPv4LLTrigger{
+        IPV4LL_TRIGGER_NULL,
+        IPV4LL_TRIGGER_PACKET,
+        IPV4LL_TRIGGER_TIMEOUT,
+        _IPV4LL_TRIGGER_MAX,
+        _IPV4LL_TRIGGER_INVALID = -1
+} IPv4LLTrigger;
+
+typedef enum IPv4LLState {
+        IPV4LL_STATE_INIT,
+        IPV4LL_STATE_WAITING_PROBE,
+        IPV4LL_STATE_PROBING,
+        IPV4LL_STATE_WAITING_ANNOUNCE,
+        IPV4LL_STATE_ANNOUNCING,
+        IPV4LL_STATE_RUNNING,
+        _IPV4LL_STATE_MAX,
+        _IPV4LL_STATE_INVALID = -1
+} IPv4LLState;
+
+struct sd_ipv4ll {
+        IPv4LLState state;
+        int index;
+        int fd;
+        union sockaddr_union link;
+        int iteration;
+        int conflict;
+        sd_event_source *receive_message;
+        sd_event_source *timer;
+        usec_t next_wakeup;
+        usec_t defend_window;
+        int next_wakeup_valid;
+        be32_t address;
+        /* External */
+        be32_t claimed_address;
+        struct ether_addr mac_addr;
+        sd_event *event;
+        int event_priority;
+        sd_ipv4ll_cb_t cb;
+        void* userdata;
+};
+
+static void ipv4ll_run_state_machine(sd_ipv4ll *ll, IPv4LLTrigger trigger, void *trigger_data);
+
+static void ipv4ll_set_state(sd_ipv4ll *ll, IPv4LLState st, int reset_counter) {
+
+        assert(ll);
+        assert(st < _IPV4LL_STATE_MAX);
+
+        if (st == ll->state && !reset_counter) {
+                ll->iteration++;
+        } else {
+                ll->state = st;
+                ll->iteration = 0;
+        }
+}
+
+static int ipv4ll_client_notify(sd_ipv4ll *ll, int event) {
+        assert(ll);
+
+        if (ll->cb)
+                ll->cb(ll, event, ll->userdata);
+
+        return 0;
+}
+
+static int ipv4ll_stop(sd_ipv4ll *ll, int event) {
+        assert(ll);
+
+        ll->receive_message = sd_event_source_unref(ll->receive_message);
+        if (ll->fd >= 0)
+                close_nointr_nofail(ll->fd);
+        ll->fd = -1;
+
+        ll->timer = sd_event_source_unref(ll->timer);
+
+        ipv4ll_client_notify(ll, event);
+
+        ll->claimed_address = 0;
+
+        ipv4ll_set_state (ll, IPV4LL_STATE_INIT, 1);
+
+        log_ipv4ll(ll, "STOPPED");
+
+        return 0;
+}
+
+static be32_t ipv4ll_pick_address(sd_ipv4ll *ll) {
+        be32_t addr;
+
+        assert(ll);
+
+        if (ll->address) {
+                do {
+                        uint32_t r = random_u32() & 0x0000FFFF;
+                        addr = htonl(IPV4LL_NETWORK | r);
+                } while (addr == ll->address ||
+                        (ntohl(addr) & IPV4LL_NETMASK) != IPV4LL_NETWORK ||
+                        (ntohl(addr) & 0x0000FF00) == 0x0000 ||
+                        (ntohl(addr) & 0x0000FF00) == 0xFF00);
+        } else {
+                uint32_t a = 1;
+                int i;
+
+                for (i = 0; i < ETH_ALEN; i++)
+                        a += ll->mac_addr.ether_addr_octet[i]*i;
+                a = (a % 0xFE00) + 0x0100;
+                addr = htonl(IPV4LL_NETWORK | (uint32_t) a);
+        }
+
+        return addr;
+}
+
+static int ipv4ll_timer(sd_event_source *s, uint64_t usec, void *userdata) {
+        sd_ipv4ll *ll = (sd_ipv4ll*)userdata;
+
+        assert(ll);
+
+        ll->next_wakeup_valid = 0;
+        ipv4ll_run_state_machine(ll, IPV4LL_TRIGGER_TIMEOUT, NULL);
+
+        return 0;
+}
+
+static void ipv4ll_set_next_wakeup (sd_ipv4ll *ll, int sec, int random_sec) {
+        usec_t next_timeout = 0;
+        usec_t time_now = 0;
+
+        assert(sec >= 0);
+        assert(random_sec >= 0);
+        assert(ll);
+
+        next_timeout = sec * USEC_PER_SEC;
+
+        if (random_sec)
+                next_timeout += random_u32() % (random_sec * USEC_PER_SEC);
+
+        if (sd_event_get_now_monotonic(ll->event, &time_now) < 0)
+                time_now = now(CLOCK_MONOTONIC);
+
+        ll->next_wakeup = time_now + next_timeout;
+        ll->next_wakeup_valid = 1;
+}
+
+static bool ipv4ll_arp_conflict (sd_ipv4ll *ll, struct ether_arp *arp) {
+        assert(ll);
+        assert(arp);
+
+        if (memcmp(arp->arp_spa, &ll->address, sizeof(ll->address)) == 0 &&
+            memcmp(arp->arp_sha, &ll->mac_addr, ETH_ALEN) != 0)
+                return true;
+
+        return false;
+}
+
+static bool ipv4ll_arp_probe_conflict (sd_ipv4ll *ll, struct ether_arp *arp) {
+        assert(ll);
+        assert(arp);
+
+        if (ipv4ll_arp_conflict(ll, arp))
+                return true;
+
+        if (memcmp(arp->arp_tpa, &ll->address, sizeof(ll->address)) == 0 &&
+            memcmp(arp->arp_sha, &ll->mac_addr, ETH_ALEN))
+                return true;
+
+        return false;
+}
+
+static void ipv4ll_run_state_machine(sd_ipv4ll *ll, IPv4LLTrigger trigger, void *trigger_data) {
+        struct ether_arp out_packet;
+        int out_packet_ready = 0;
+        int r = 0;
+
+        assert(ll);
+        assert(trigger < _IPV4LL_TRIGGER_MAX);
+
+        if (ll->state == IPV4LL_STATE_INIT) {
+
+                log_ipv4ll(ll, "PROBE");
+                ipv4ll_set_state(ll, IPV4LL_STATE_WAITING_PROBE, 1);
+                ipv4ll_set_next_wakeup(ll, 0, PROBE_WAIT);
+
+        } else if ((ll->state == IPV4LL_STATE_WAITING_PROBE && trigger == IPV4LL_TRIGGER_TIMEOUT) ||
+                (ll->state == IPV4LL_STATE_PROBING && trigger == IPV4LL_TRIGGER_TIMEOUT && ll->iteration < PROBE_NUM-2)) {
+
+                /* Send a probe */
+                arp_packet_probe(&out_packet, ll->address, &ll->mac_addr);
+                out_packet_ready = 1;
+                ipv4ll_set_state(ll, IPV4LL_STATE_PROBING, 0);
+
+                ipv4ll_set_next_wakeup(ll, PROBE_MIN, (PROBE_MAX-PROBE_MIN));
+
+        } else if (ll->state == IPV4LL_STATE_PROBING && trigger == IPV4LL_TRIGGER_TIMEOUT && ll->iteration >= PROBE_NUM-2) {
+
+                /* Send the last probe */
+                arp_packet_probe(&out_packet, ll->address, &ll->mac_addr);
+                out_packet_ready = 1;
+                ipv4ll_set_state(ll, IPV4LL_STATE_WAITING_ANNOUNCE, 1);
+
+                ipv4ll_set_next_wakeup(ll, ANNOUNCE_WAIT, 0);
+
+        } else if ((ll->state == IPV4LL_STATE_WAITING_ANNOUNCE && trigger == IPV4LL_TRIGGER_TIMEOUT) ||
+                (ll->state == IPV4LL_STATE_ANNOUNCING && trigger == IPV4LL_TRIGGER_TIMEOUT && ll->iteration < ANNOUNCE_NUM-1)) {
+
+                /* Send announcement packet */
+                arp_packet_announcement(&out_packet, ll->address, &ll->mac_addr);
+                out_packet_ready = 1;
+                ipv4ll_set_state(ll, IPV4LL_STATE_ANNOUNCING, 0);
+
+                ipv4ll_set_next_wakeup(ll, ANNOUNCE_INTERVAL, 0);
+
+                if (ll->iteration == 0) {
+                        log_ipv4ll(ll, "ANNOUNCE");
+                        ll->claimed_address = ll->address;
+                        r = ipv4ll_client_notify(ll, IPV4LL_EVENT_BIND);
+                        ll->conflict = 0;
+                }
+
+        } else if ((ll->state == IPV4LL_STATE_ANNOUNCING && trigger == IPV4LL_TRIGGER_TIMEOUT &&
+                    ll->iteration >= ANNOUNCE_NUM-1)) {
+
+                ipv4ll_set_state(ll, IPV4LL_STATE_RUNNING, 0);
+                ll->next_wakeup_valid = 0;
+
+        } else if (trigger == IPV4LL_TRIGGER_PACKET) {
+
+                int conflicted = 0;
+                usec_t time_now;
+                struct ether_arp* in_packet = (struct ether_arp*)trigger_data;
+
+                assert(in_packet);
+
+                if (IN_SET(ll->state, IPV4LL_STATE_ANNOUNCING, IPV4LL_STATE_RUNNING)) {
+
+                        if (ipv4ll_arp_conflict(ll, in_packet)) {
+
+                                r = sd_event_get_now_monotonic(ll->event, &time_now);
+                                if (r < 0)
+                                        goto out;
+
+                                /* Defend address */
+                                if (time_now > ll->defend_window) {
+                                        ll->defend_window = time_now + DEFEND_INTERVAL * USEC_PER_SEC;
+                                        arp_packet_announcement(&out_packet, ll->address, &ll->mac_addr);
+                                        out_packet_ready = 1;
+                                } else
+                                        conflicted = 1;
+                        }
+
+                } else if (IN_SET(ll->state, IPV4LL_STATE_WAITING_PROBE,
+                                             IPV4LL_STATE_PROBING,
+                                             IPV4LL_STATE_WAITING_ANNOUNCE)) {
+
+                        conflicted = ipv4ll_arp_probe_conflict(ll, in_packet);
+                }
+
+                if (conflicted) {
+                        log_ipv4ll(ll, "CONFLICT");
+                        r = ipv4ll_client_notify(ll, IPV4LL_EVENT_CONFLICT);
+                        ll->claimed_address = 0;
+
+                        /* Pick a new address */
+                        ll->address = ipv4ll_pick_address(ll);
+                        ll->conflict++;
+                        ll->defend_window = 0;
+                        ipv4ll_set_state(ll, IPV4LL_STATE_WAITING_PROBE, 1);
+
+                        if (ll->conflict >= MAX_CONFLICTS) {
+                                log_ipv4ll(ll, "MAX_CONFLICTS");
+                                ipv4ll_set_next_wakeup(ll, RATE_LIMIT_INTERVAL, PROBE_WAIT);
+                        } else
+                                ipv4ll_set_next_wakeup(ll, 0, PROBE_WAIT);
+
+                }
+        }
+
+        if (out_packet_ready) {
+                r = arp_network_send_raw_socket(ll->fd, &ll->link, &out_packet);
+                if (r < 0) {
+                        log_ipv4ll(ll, "failed to send arp packet out");
+                        goto out;
+                }
+        }
+
+        if (ll->next_wakeup_valid) {
+                ll->timer = sd_event_source_unref(ll->timer);
+                r = sd_event_add_monotonic(ll->event, &ll->timer,
+                                   ll->next_wakeup, 0, ipv4ll_timer, ll);
+                if (r < 0)
+                        goto out;
+
+                r = sd_event_source_set_priority(ll->timer, ll->event_priority);
+                if (r < 0)
+                        goto out;
+        }
+
+out:
+        if (r < 0)
+                ipv4ll_stop(ll, r);
+}
+
+static int ipv4ll_receive_message(sd_event_source *s, int fd,
+                                  uint32_t revents, void *userdata) {
+        int r;
+        struct ether_arp arp;
+        sd_ipv4ll *ll = (sd_ipv4ll*)userdata;
+
+        assert(ll);
+
+        r = read(fd, &arp, sizeof(struct ether_arp));
+        if (r < (int) sizeof(struct ether_arp))
+                return 0;
+
+        r = arp_packet_verify_headers(&arp);
+        if (r < 0)
+                return 0;
+
+        ipv4ll_run_state_machine(ll, IPV4LL_TRIGGER_PACKET, &arp);
+
+        return 0;
+}
+
+int sd_ipv4ll_set_index(sd_ipv4ll *ll, int interface_index) {
+        assert_return(ll, -EINVAL);
+        assert_return(interface_index >= -1, -EINVAL);
+        assert_return(ll->state == IPV4LL_STATE_INIT, -EBUSY);
+
+        ll->index = interface_index;
+
+        return 0;
+}
+
+int sd_ipv4ll_set_mac(sd_ipv4ll *ll, const struct ether_addr *addr) {
+        assert_return(ll, -EINVAL);
+        assert_return(ll->state == IPV4LL_STATE_INIT, -EBUSY);
+
+        memcpy(&ll->mac_addr.ether_addr_octet, addr, ETH_ALEN);
+
+        return 0;
+}
+
+int sd_ipv4ll_detach_event(sd_ipv4ll *ll) {
+        assert_return(ll, -EINVAL);
+
+        ll->event = sd_event_unref(ll->event);
+
+        return 0;
+}
+
+int sd_ipv4ll_attach_event(sd_ipv4ll *ll, sd_event *event, int priority) {
+        int r;
+
+        assert_return(ll, -EINVAL);
+        assert_return(!ll->event, -EBUSY);
+
+        if (event)
+                ll->event = sd_event_ref(event);
+        else {
+                r = sd_event_default(&ll->event);
+                if (r < 0) {
+                        ipv4ll_stop(ll, IPV4LL_EVENT_STOP);
+                        return r;
+                }
+        }
+
+        ll->event_priority = priority;
+
+        return 0;
+}
+
+int sd_ipv4ll_set_callback(sd_ipv4ll *ll, sd_ipv4ll_cb_t cb, void *userdata) {
+        assert_return(ll, -EINVAL);
+
+        ll->cb = cb;
+        ll->userdata = userdata;
+
+        return 0;
+}
+
+int sd_ipv4ll_get_address(sd_ipv4ll *ll, struct in_addr *address){
+        assert_return(ll, -EINVAL);
+        assert_return(address, -EINVAL);
+
+        if (ll->claimed_address == 0) {
+                return -ENOENT;
+        }
+
+        address->s_addr = ll->claimed_address;
+        return 0;
+}
+
+int sd_ipv4ll_start (sd_ipv4ll *ll) {
+        int r;
+
+        assert_return(ll, -EINVAL);
+        assert_return(ll->event, -EINVAL);
+        assert_return(ll->index > 0, -EINVAL);
+        assert_return(ll->state == IPV4LL_STATE_INIT, -EBUSY);
+
+        r = arp_network_bind_raw_socket(ll->index, &ll->link);
+
+        if (r < 0)
+                goto out;
+
+        ll->fd = r;
+        ll->conflict = 0;
+        ll->defend_window = 0;
+        ll->claimed_address = 0;
+
+        if (ll->address == 0)
+                ll->address = ipv4ll_pick_address(ll);
+
+        ipv4ll_set_state (ll, IPV4LL_STATE_INIT, 1);
+
+        r = sd_event_add_io(ll->event, &ll->receive_message, ll->fd,
+                            EPOLLIN, ipv4ll_receive_message, ll);
+        if (r < 0)
+                goto out;
+
+        r = sd_event_source_set_priority(ll->receive_message, ll->event_priority);
+        if (r < 0)
+                goto out;
+
+        r = sd_event_add_monotonic(ll->event, &ll->timer, now(CLOCK_MONOTONIC), 0,
+                                   ipv4ll_timer, ll);
+
+        if (r < 0)
+                goto out;
+
+        r = sd_event_source_set_priority(ll->timer, ll->event_priority);
+
+out:
+        if (r < 0)
+                ipv4ll_stop(ll, IPV4LL_EVENT_STOP);
+
+        return 0;
+}
+
+int sd_ipv4ll_stop(sd_ipv4ll *ll) {
+        return ipv4ll_stop(ll, IPV4LL_EVENT_STOP);
+}
+
+void sd_ipv4ll_free (sd_ipv4ll *ll) {
+        if (!ll)
+                return;
+
+        sd_ipv4ll_stop(ll);
+        sd_ipv4ll_detach_event(ll);
+
+        free(ll);
+}
+
+DEFINE_TRIVIAL_CLEANUP_FUNC(sd_ipv4ll*, sd_ipv4ll_free);
+#define _cleanup_ipv4ll_free_ _cleanup_(sd_ipv4ll_freep)
+
+int sd_ipv4ll_new(sd_ipv4ll **ret) {
+        _cleanup_ipv4ll_free_ sd_ipv4ll *ll = NULL;
+
+        assert_return(ret, -EINVAL);
+
+        ll = new0(sd_ipv4ll, 1);
+        if (!ll)
+                return -ENOMEM;
+
+        ll->state = IPV4LL_STATE_INIT;
+        ll->index = -1;
+        ll->fd = -1;
+
+        *ret = ll;
+        ll = NULL;
+
+        return 0;
+}