src/libsystemd-network/sd-ipv4acd.c - systemd-stable - Rivoreo Source Code Repositories

 /* SPDX-License-Identifier: LGPL-2.1+ */
 /***
   Copyright © 2014 Axis Communications AB. All rights reserved.
 ***/

 #include <arpa/inet.h>
 #include <errno.h>
 #include <netinet/if_ether.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

 #include "sd-ipv4acd.h"

 #include "alloc-util.h"
 #include "arp-util.h"
 #include "ether-addr-util.h"
 #include "event-util.h"
 #include "fd-util.h"
 #include "in-addr-util.h"
 #include "list.h"
 #include "random-util.h"
 #include "siphash24.h"
 #include "string-util.h"
 #include "time-util.h"

 /* Constants from the RFC */
 #define PROBE_WAIT_USEC (1U * USEC_PER_SEC)
 #define PROBE_NUM 3U
 #define PROBE_MIN_USEC (1U * USEC_PER_SEC)
 #define PROBE_MAX_USEC (2U * USEC_PER_SEC)
 #define ANNOUNCE_WAIT_USEC (2U * USEC_PER_SEC)
 #define ANNOUNCE_NUM 2U
 #define ANNOUNCE_INTERVAL_USEC (2U * USEC_PER_SEC)
 #define MAX_CONFLICTS 10U
 #define RATE_LIMIT_INTERVAL_USEC (60U * USEC_PER_SEC)
 #define DEFEND_INTERVAL_USEC (10U * USEC_PER_SEC)

 typedef enum IPv4ACDState {
         IPV4ACD_STATE_INIT,
         IPV4ACD_STATE_STARTED,
         IPV4ACD_STATE_WAITING_PROBE,
         IPV4ACD_STATE_PROBING,
         IPV4ACD_STATE_WAITING_ANNOUNCE,
         IPV4ACD_STATE_ANNOUNCING,
         IPV4ACD_STATE_RUNNING,
         _IPV4ACD_STATE_MAX,
         _IPV4ACD_STATE_INVALID = -1
 } IPv4ACDState;

 struct sd_ipv4acd {
         unsigned n_ref;

         IPv4ACDState state;
         int ifindex;
         int fd;

         unsigned n_iteration;
         unsigned n_conflict;

         sd_event_source *receive_message_event_source;
         sd_event_source *timer_event_source;

         usec_t defend_window;
         be32_t address;

         /* External */
         struct ether_addr mac_addr;

         sd_event *event;
         int event_priority;
         sd_ipv4acd_callback_t callback;
         void* userdata;
 };

 #define log_ipv4acd_errno(acd, error, fmt, ...) log_internal(LOG_DEBUG, error, PROJECT_FILE, __LINE__, __func__, "IPV4ACD: " fmt, ##__VA_ARGS__)
 #define log_ipv4acd(acd, fmt, ...) log_ipv4acd_errno(acd, 0, fmt, ##__VA_ARGS__)

 static void ipv4acd_set_state(sd_ipv4acd *acd, IPv4ACDState st, bool reset_counter) {
         assert(acd);
         assert(st < _IPV4ACD_STATE_MAX);

         if (st == acd->state && !reset_counter)
                 acd->n_iteration++;
         else {
                 acd->state = st;
                 acd->n_iteration = 0;
         }
 }

 static void ipv4acd_reset(sd_ipv4acd *acd) {
         assert(acd);

         (void) event_source_disable(acd->timer_event_source);
         acd->receive_message_event_source = sd_event_source_unref(acd->receive_message_event_source);

         acd->fd = safe_close(acd->fd);

         ipv4acd_set_state(acd, IPV4ACD_STATE_INIT, true);
 }

 static sd_ipv4acd *ipv4acd_free(sd_ipv4acd *acd) {
         assert(acd);

         acd->timer_event_source = sd_event_source_unref(acd->timer_event_source);

         ipv4acd_reset(acd);
         sd_ipv4acd_detach_event(acd);

         return mfree(acd);
 }

 DEFINE_TRIVIAL_REF_UNREF_FUNC(sd_ipv4acd, sd_ipv4acd, ipv4acd_free);

 int sd_ipv4acd_new(sd_ipv4acd **ret) {
         _cleanup_(sd_ipv4acd_unrefp) sd_ipv4acd *acd = NULL;

         assert_return(ret, -EINVAL);

         acd = new(sd_ipv4acd, 1);
         if (!acd)
                 return -ENOMEM;

         *acd = (sd_ipv4acd) {
                 .n_ref = 1,
                 .state = IPV4ACD_STATE_INIT,
                 .ifindex = -1,
                 .fd = -1,
         };

         *ret = TAKE_PTR(acd);

         return 0;
 }

 static void ipv4acd_client_notify(sd_ipv4acd *acd, int event) {
         assert(acd);

         if (!acd->callback)
                 return;

         acd->callback(acd, event, acd->userdata);
 }

 int sd_ipv4acd_stop(sd_ipv4acd *acd) {
         assert_return(acd, -EINVAL);

         ipv4acd_reset(acd);

         log_ipv4acd(acd, "STOPPED");

         ipv4acd_client_notify(acd, SD_IPV4ACD_EVENT_STOP);

         return 0;
 }

 static int ipv4acd_on_timeout(sd_event_source *s, uint64_t usec, void *userdata);

 static int ipv4acd_set_next_wakeup(sd_ipv4acd *acd, usec_t usec, usec_t random_usec) {
         usec_t next_timeout, time_now;

         assert(acd);

         next_timeout = usec;

         if (random_usec > 0)
                 next_timeout += (usec_t) random_u64() % random_usec;

         assert_se(sd_event_now(acd->event, clock_boottime_or_monotonic(), &time_now) >= 0);

         return event_reset_time(acd->event, &acd->timer_event_source,
                                 clock_boottime_or_monotonic(),
                                 time_now + next_timeout, 0,
                                 ipv4acd_on_timeout, acd,
                                 acd->event_priority, "ipv4acd-timer", true);
 }

 static bool ipv4acd_arp_conflict(sd_ipv4acd *acd, struct ether_arp *arp) {
         assert(acd);
         assert(arp);

         /* see the BPF */
         if (memcmp(arp->arp_spa, &acd->address, sizeof(acd->address)) == 0)
                 return true;

         /* the TPA matched instead of the SPA, this is not a conflict */
         return false;
 }

 static int ipv4acd_on_timeout(sd_event_source *s, uint64_t usec, void *userdata) {
         sd_ipv4acd *acd = userdata;
         int r = 0;

         assert(acd);

         switch (acd->state) {

         case IPV4ACD_STATE_STARTED:
                 ipv4acd_set_state(acd, IPV4ACD_STATE_WAITING_PROBE, true);

                 if (acd->n_conflict >= MAX_CONFLICTS) {
                         char ts[FORMAT_TIMESPAN_MAX];
                         log_ipv4acd(acd, "Max conflicts reached, delaying by %s", format_timespan(ts, sizeof(ts), RATE_LIMIT_INTERVAL_USEC, 0));

                         r = ipv4acd_set_next_wakeup(acd, RATE_LIMIT_INTERVAL_USEC, PROBE_WAIT_USEC);
                         if (r < 0)
                                 goto fail;
                 } else {
                         r = ipv4acd_set_next_wakeup(acd, 0, PROBE_WAIT_USEC);
                         if (r < 0)
                                 goto fail;
                 }

                 break;

         case IPV4ACD_STATE_WAITING_PROBE:
         case IPV4ACD_STATE_PROBING:
                 /* Send a probe */
                 r = arp_send_probe(acd->fd, acd->ifindex, acd->address, &acd->mac_addr);
                 if (r < 0) {
                         log_ipv4acd_errno(acd, r, "Failed to send ARP probe: %m");
                         goto fail;
                 } else {
                         _cleanup_free_ char *address = NULL;
                         union in_addr_union addr = { .in.s_addr = acd->address };

                         (void) in_addr_to_string(AF_INET, &addr, &address);
                         log_ipv4acd(acd, "Probing %s", strna(address));
                 }

                 if (acd->n_iteration < PROBE_NUM - 2) {
                         ipv4acd_set_state(acd, IPV4ACD_STATE_PROBING, false);

                         r = ipv4acd_set_next_wakeup(acd, PROBE_MIN_USEC, (PROBE_MAX_USEC-PROBE_MIN_USEC));
                         if (r < 0)
                                 goto fail;
                 } else {
                         ipv4acd_set_state(acd, IPV4ACD_STATE_WAITING_ANNOUNCE, true);

                         r = ipv4acd_set_next_wakeup(acd, ANNOUNCE_WAIT_USEC, 0);
                         if (r < 0)
                                 goto fail;
                 }

                 break;

         case IPV4ACD_STATE_ANNOUNCING:
                 if (acd->n_iteration >= ANNOUNCE_NUM - 1) {
                         ipv4acd_set_state(acd, IPV4ACD_STATE_RUNNING, false);
                         break;
                 }

                 _fallthrough_;
         case IPV4ACD_STATE_WAITING_ANNOUNCE:
                 /* Send announcement packet */
                 r = arp_send_announcement(acd->fd, acd->ifindex, acd->address, &acd->mac_addr);
                 if (r < 0) {
                         log_ipv4acd_errno(acd, r, "Failed to send ARP announcement: %m");
                         goto fail;
                 } else
                         log_ipv4acd(acd, "ANNOUNCE");

                 ipv4acd_set_state(acd, IPV4ACD_STATE_ANNOUNCING, false);

                 r = ipv4acd_set_next_wakeup(acd, ANNOUNCE_INTERVAL_USEC, 0);
                 if (r < 0)
                         goto fail;

                 if (acd->n_iteration == 0) {
                         acd->n_conflict = 0;
                         ipv4acd_client_notify(acd, SD_IPV4ACD_EVENT_BIND);
                 }

                 break;

         default:
                 assert_not_reached("Invalid state.");
         }

         return 0;

 fail:
         sd_ipv4acd_stop(acd);
         return 0;
 }

 static void ipv4acd_on_conflict(sd_ipv4acd *acd) {
         _cleanup_free_ char *address = NULL;
         union in_addr_union addr = { .in.s_addr = acd->address };

         assert(acd);

         acd->n_conflict++;

         (void) in_addr_to_string(AF_INET, &addr, &address);
         log_ipv4acd(acd, "Conflict on %s (%u)", strna(address), acd->n_conflict);

         ipv4acd_reset(acd);
         ipv4acd_client_notify(acd, SD_IPV4ACD_EVENT_CONFLICT);
 }

 static int ipv4acd_on_packet(
                 sd_event_source *s,
                 int fd,
                 uint32_t revents,
                 void *userdata) {

         sd_ipv4acd *acd = userdata;
         struct ether_arp packet;
         ssize_t n;
         int r;

         assert(s);
         assert(acd);
         assert(fd >= 0);

         n = recv(fd, &packet, sizeof(struct ether_arp), 0);
         if (n < 0) {
                 if (IN_SET(errno, EAGAIN, EINTR))
                         return 0;

                 log_ipv4acd_errno(acd, errno, "Failed to read ARP packet: %m");
                 goto fail;
         }
         if ((size_t) n != sizeof(struct ether_arp)) {
                 log_ipv4acd(acd, "Ignoring too short ARP packet.");
                 return 0;
         }

         switch (acd->state) {

         case IPV4ACD_STATE_ANNOUNCING:
         case IPV4ACD_STATE_RUNNING:

                 if (ipv4acd_arp_conflict(acd, &packet)) {
                         usec_t ts;

                         assert_se(sd_event_now(acd->event, clock_boottime_or_monotonic(), &ts) >= 0);

                         /* Defend address */
                         if (ts > acd->defend_window) {
                                 acd->defend_window = ts + DEFEND_INTERVAL_USEC;
                                 r = arp_send_announcement(acd->fd, acd->ifindex, acd->address, &acd->mac_addr);
                                 if (r < 0) {
                                         log_ipv4acd_errno(acd, r, "Failed to send ARP announcement: %m");
                                         goto fail;
                                 } else
                                         log_ipv4acd(acd, "DEFEND");

                         } else
                                 ipv4acd_on_conflict(acd);
                 }
                 break;

         case IPV4ACD_STATE_WAITING_PROBE:
         case IPV4ACD_STATE_PROBING:
         case IPV4ACD_STATE_WAITING_ANNOUNCE:
                 /* BPF ensures this packet indicates a conflict */
                 ipv4acd_on_conflict(acd);
                 break;

         default:
                 assert_not_reached("Invalid state.");
         }

         return 0;

 fail:
         sd_ipv4acd_stop(acd);
         return 0;
 }

 int sd_ipv4acd_set_ifindex(sd_ipv4acd *acd, int ifindex) {
         assert_return(acd, -EINVAL);
         assert_return(ifindex > 0, -EINVAL);
         assert_return(acd->state == IPV4ACD_STATE_INIT, -EBUSY);

         acd->ifindex = ifindex;

         return 0;
 }

 int sd_ipv4acd_set_mac(sd_ipv4acd *acd, const struct ether_addr *addr) {
         assert_return(acd, -EINVAL);
         assert_return(addr, -EINVAL);
         assert_return(acd->state == IPV4ACD_STATE_INIT, -EBUSY);

         acd->mac_addr = *addr;

         return 0;
 }

 int sd_ipv4acd_detach_event(sd_ipv4acd *acd) {
         assert_return(acd, -EINVAL);

         acd->event = sd_event_unref(acd->event);

         return 0;
 }

 int sd_ipv4acd_attach_event(sd_ipv4acd *acd, sd_event *event, int64_t priority) {
         int r;

         assert_return(acd, -EINVAL);
         assert_return(!acd->event, -EBUSY);

         if (event)
                 acd->event = sd_event_ref(event);
         else {
                 r = sd_event_default(&acd->event);
                 if (r < 0)
                         return r;
         }

         acd->event_priority = priority;

         return 0;
 }

 int sd_ipv4acd_set_callback(sd_ipv4acd *acd, sd_ipv4acd_callback_t cb, void *userdata) {
         assert_return(acd, -EINVAL);

         acd->callback = cb;
         acd->userdata = userdata;

         return 0;
 }

 int sd_ipv4acd_set_address(sd_ipv4acd *acd, const struct in_addr *address) {
         assert_return(acd, -EINVAL);
         assert_return(address, -EINVAL);
         assert_return(acd->state == IPV4ACD_STATE_INIT, -EBUSY);

         acd->address = address->s_addr;

         return 0;
 }

 int sd_ipv4acd_is_running(sd_ipv4acd *acd) {
         assert_return(acd, false);

         return acd->state != IPV4ACD_STATE_INIT;
 }

 int sd_ipv4acd_start(sd_ipv4acd *acd, bool reset_conflicts) {
         int r;

         assert_return(acd, -EINVAL);
         assert_return(acd->event, -EINVAL);
         assert_return(acd->ifindex > 0, -EINVAL);
         assert_return(acd->address != 0, -EINVAL);
         assert_return(!ether_addr_is_null(&acd->mac_addr), -EINVAL);
         assert_return(acd->state == IPV4ACD_STATE_INIT, -EBUSY);

         r = arp_network_bind_raw_socket(acd->ifindex, acd->address, &acd->mac_addr);
         if (r < 0)
                 return r;

         safe_close(acd->fd);
         acd->fd = r;
         acd->defend_window = 0;

         if (reset_conflicts)
                 acd->n_conflict = 0;

         r = sd_event_add_io(acd->event, &acd->receive_message_event_source, acd->fd, EPOLLIN, ipv4acd_on_packet, acd);
         if (r < 0)
                 goto fail;

         r = sd_event_source_set_priority(acd->receive_message_event_source, acd->event_priority);
         if (r < 0)
                 goto fail;

         (void) sd_event_source_set_description(acd->receive_message_event_source, "ipv4acd-receive-message");

         r = ipv4acd_set_next_wakeup(acd, 0, 0);
         if (r < 0)
                 goto fail;

         ipv4acd_set_state(acd, IPV4ACD_STATE_STARTED, true);
         return 0;

 fail:
         ipv4acd_reset(acd);
         return r;
 }
	/* SPDX-License-Identifier: LGPL-2.1+ */
	/***
	Copyright © 2014 Axis Communications AB. All rights reserved.
	***/

	#include <arpa/inet.h>
	#include <errno.h>
	#include <netinet/if_ether.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>

	#include "sd-ipv4acd.h"

	#include "alloc-util.h"
	#include "arp-util.h"
	#include "ether-addr-util.h"
	#include "event-util.h"
	#include "fd-util.h"
	#include "in-addr-util.h"
	#include "list.h"
	#include "random-util.h"
	#include "siphash24.h"
	#include "string-util.h"
	#include "time-util.h"

	/* Constants from the RFC */
	#define PROBE_WAIT_USEC (1U * USEC_PER_SEC)
	#define PROBE_NUM 3U
	#define PROBE_MIN_USEC (1U * USEC_PER_SEC)
	#define PROBE_MAX_USEC (2U * USEC_PER_SEC)
	#define ANNOUNCE_WAIT_USEC (2U * USEC_PER_SEC)
	#define ANNOUNCE_NUM 2U
	#define ANNOUNCE_INTERVAL_USEC (2U * USEC_PER_SEC)
	#define MAX_CONFLICTS 10U
	#define RATE_LIMIT_INTERVAL_USEC (60U * USEC_PER_SEC)
	#define DEFEND_INTERVAL_USEC (10U * USEC_PER_SEC)

	typedef enum IPv4ACDState {
	IPV4ACD_STATE_INIT,
	IPV4ACD_STATE_STARTED,
	IPV4ACD_STATE_WAITING_PROBE,
	IPV4ACD_STATE_PROBING,
	IPV4ACD_STATE_WAITING_ANNOUNCE,
	IPV4ACD_STATE_ANNOUNCING,
	IPV4ACD_STATE_RUNNING,
	_IPV4ACD_STATE_MAX,
	_IPV4ACD_STATE_INVALID = -1
	} IPv4ACDState;

	struct sd_ipv4acd {
	unsigned n_ref;

	IPv4ACDState state;
	int ifindex;
	int fd;

	unsigned n_iteration;
	unsigned n_conflict;

	sd_event_source *receive_message_event_source;
	sd_event_source *timer_event_source;

	usec_t defend_window;
	be32_t address;

	/* External */
	struct ether_addr mac_addr;

	sd_event *event;
	int event_priority;
	sd_ipv4acd_callback_t callback;
	void* userdata;
	};

	#define log_ipv4acd_errno(acd, error, fmt, ...) log_internal(LOG_DEBUG, error, PROJECT_FILE, __LINE__, __func__, "IPV4ACD: " fmt, ##__VA_ARGS__)
	#define log_ipv4acd(acd, fmt, ...) log_ipv4acd_errno(acd, 0, fmt, ##__VA_ARGS__)

	static void ipv4acd_set_state(sd_ipv4acd *acd, IPv4ACDState st, bool reset_counter) {
	assert(acd);
	assert(st < _IPV4ACD_STATE_MAX);

	if (st == acd->state && !reset_counter)
	acd->n_iteration++;
	else {
	acd->state = st;
	acd->n_iteration = 0;
	}
	}

	static void ipv4acd_reset(sd_ipv4acd *acd) {
	assert(acd);

	(void) event_source_disable(acd->timer_event_source);
	acd->receive_message_event_source = sd_event_source_unref(acd->receive_message_event_source);

	acd->fd = safe_close(acd->fd);

	ipv4acd_set_state(acd, IPV4ACD_STATE_INIT, true);
	}

	static sd_ipv4acd ipv4acd_free(sd_ipv4acd acd) {
	assert(acd);

	acd->timer_event_source = sd_event_source_unref(acd->timer_event_source);

	ipv4acd_reset(acd);
	sd_ipv4acd_detach_event(acd);

	return mfree(acd);
	}

	DEFINE_TRIVIAL_REF_UNREF_FUNC(sd_ipv4acd, sd_ipv4acd, ipv4acd_free);

	int sd_ipv4acd_new(sd_ipv4acd **ret) {
	_cleanup_(sd_ipv4acd_unrefp) sd_ipv4acd *acd = NULL;

	assert_return(ret, -EINVAL);

	acd = new(sd_ipv4acd, 1);
	if (!acd)
	return -ENOMEM;

	*acd = (sd_ipv4acd) {
	.n_ref = 1,
	.state = IPV4ACD_STATE_INIT,
	.ifindex = -1,
	.fd = -1,
	};

	*ret = TAKE_PTR(acd);

	return 0;
	}

	static void ipv4acd_client_notify(sd_ipv4acd *acd, int event) {
	assert(acd);

	if (!acd->callback)
	return;

	acd->callback(acd, event, acd->userdata);
	}

	int sd_ipv4acd_stop(sd_ipv4acd *acd) {
	assert_return(acd, -EINVAL);

	ipv4acd_reset(acd);

	log_ipv4acd(acd, "STOPPED");

	ipv4acd_client_notify(acd, SD_IPV4ACD_EVENT_STOP);

	return 0;
	}

	static int ipv4acd_on_timeout(sd_event_source s, uint64_t usec, void userdata);

	static int ipv4acd_set_next_wakeup(sd_ipv4acd *acd, usec_t usec, usec_t random_usec) {
	usec_t next_timeout, time_now;

	assert(acd);

	next_timeout = usec;

	if (random_usec > 0)
	next_timeout += (usec_t) random_u64() % random_usec;

	assert_se(sd_event_now(acd->event, clock_boottime_or_monotonic(), &time_now) >= 0);

	return event_reset_time(acd->event, &acd->timer_event_source,
	clock_boottime_or_monotonic(),
	time_now + next_timeout, 0,
	ipv4acd_on_timeout, acd,
	acd->event_priority, "ipv4acd-timer", true);
	}

	static bool ipv4acd_arp_conflict(sd_ipv4acd acd, struct ether_arp arp) {
	assert(acd);
	assert(arp);

	/* see the BPF */
	if (memcmp(arp->arp_spa, &acd->address, sizeof(acd->address)) == 0)
	return true;

	/* the TPA matched instead of the SPA, this is not a conflict */
	return false;
	}

	static int ipv4acd_on_timeout(sd_event_source s, uint64_t usec, void userdata) {
	sd_ipv4acd *acd = userdata;
	int r = 0;

	assert(acd);

	switch (acd->state) {

	case IPV4ACD_STATE_STARTED:
	ipv4acd_set_state(acd, IPV4ACD_STATE_WAITING_PROBE, true);

	if (acd->n_conflict >= MAX_CONFLICTS) {
	char ts[FORMAT_TIMESPAN_MAX];
	log_ipv4acd(acd, "Max conflicts reached, delaying by %s", format_timespan(ts, sizeof(ts), RATE_LIMIT_INTERVAL_USEC, 0));

	r = ipv4acd_set_next_wakeup(acd, RATE_LIMIT_INTERVAL_USEC, PROBE_WAIT_USEC);
	if (r < 0)
	goto fail;
	} else {
	r = ipv4acd_set_next_wakeup(acd, 0, PROBE_WAIT_USEC);
	if (r < 0)
	goto fail;
	}

	break;

	case IPV4ACD_STATE_WAITING_PROBE:
	case IPV4ACD_STATE_PROBING:
	/* Send a probe */
	r = arp_send_probe(acd->fd, acd->ifindex, acd->address, &acd->mac_addr);
	if (r < 0) {
	log_ipv4acd_errno(acd, r, "Failed to send ARP probe: %m");
	goto fail;
	} else {
	_cleanup_free_ char *address = NULL;
	union in_addr_union addr = { .in.s_addr = acd->address };

	(void) in_addr_to_string(AF_INET, &addr, &address);
	log_ipv4acd(acd, "Probing %s", strna(address));
	}

	if (acd->n_iteration < PROBE_NUM - 2) {
	ipv4acd_set_state(acd, IPV4ACD_STATE_PROBING, false);

	r = ipv4acd_set_next_wakeup(acd, PROBE_MIN_USEC, (PROBE_MAX_USEC-PROBE_MIN_USEC));
	if (r < 0)
	goto fail;
	} else {
	ipv4acd_set_state(acd, IPV4ACD_STATE_WAITING_ANNOUNCE, true);

	r = ipv4acd_set_next_wakeup(acd, ANNOUNCE_WAIT_USEC, 0);
	if (r < 0)
	goto fail;
	}

	break;

	case IPV4ACD_STATE_ANNOUNCING:
	if (acd->n_iteration >= ANNOUNCE_NUM - 1) {
	ipv4acd_set_state(acd, IPV4ACD_STATE_RUNNING, false);
	break;
	}

	_fallthrough_;
	case IPV4ACD_STATE_WAITING_ANNOUNCE:
	/* Send announcement packet */
	r = arp_send_announcement(acd->fd, acd->ifindex, acd->address, &acd->mac_addr);
	if (r < 0) {
	log_ipv4acd_errno(acd, r, "Failed to send ARP announcement: %m");
	goto fail;
	} else
	log_ipv4acd(acd, "ANNOUNCE");

	ipv4acd_set_state(acd, IPV4ACD_STATE_ANNOUNCING, false);

	r = ipv4acd_set_next_wakeup(acd, ANNOUNCE_INTERVAL_USEC, 0);
	if (r < 0)
	goto fail;

	if (acd->n_iteration == 0) {
	acd->n_conflict = 0;
	ipv4acd_client_notify(acd, SD_IPV4ACD_EVENT_BIND);
	}

	break;

	default:
	assert_not_reached("Invalid state.");
	}

	return 0;

	fail:
	sd_ipv4acd_stop(acd);
	return 0;
	}

	static void ipv4acd_on_conflict(sd_ipv4acd *acd) {
	_cleanup_free_ char *address = NULL;
	union in_addr_union addr = { .in.s_addr = acd->address };

	assert(acd);

	acd->n_conflict++;

	(void) in_addr_to_string(AF_INET, &addr, &address);
	log_ipv4acd(acd, "Conflict on %s (%u)", strna(address), acd->n_conflict);

	ipv4acd_reset(acd);
	ipv4acd_client_notify(acd, SD_IPV4ACD_EVENT_CONFLICT);
	}

	static int ipv4acd_on_packet(
	sd_event_source *s,
	int fd,
	uint32_t revents,
	void *userdata) {

	sd_ipv4acd *acd = userdata;
	struct ether_arp packet;
	ssize_t n;
	int r;

	assert(s);
	assert(acd);
	assert(fd >= 0);

	n = recv(fd, &packet, sizeof(struct ether_arp), 0);
	if (n < 0) {
	if (IN_SET(errno, EAGAIN, EINTR))
	return 0;

	log_ipv4acd_errno(acd, errno, "Failed to read ARP packet: %m");
	goto fail;
	}
	if ((size_t) n != sizeof(struct ether_arp)) {
	log_ipv4acd(acd, "Ignoring too short ARP packet.");
	return 0;
	}

	switch (acd->state) {

	case IPV4ACD_STATE_ANNOUNCING:
	case IPV4ACD_STATE_RUNNING:

	if (ipv4acd_arp_conflict(acd, &packet)) {
	usec_t ts;

	assert_se(sd_event_now(acd->event, clock_boottime_or_monotonic(), &ts) >= 0);

	/* Defend address */
	if (ts > acd->defend_window) {
	acd->defend_window = ts + DEFEND_INTERVAL_USEC;
	r = arp_send_announcement(acd->fd, acd->ifindex, acd->address, &acd->mac_addr);
	if (r < 0) {
	log_ipv4acd_errno(acd, r, "Failed to send ARP announcement: %m");
	goto fail;
	} else
	log_ipv4acd(acd, "DEFEND");

	} else
	ipv4acd_on_conflict(acd);
	}
	break;

	case IPV4ACD_STATE_WAITING_PROBE:
	case IPV4ACD_STATE_PROBING:
	case IPV4ACD_STATE_WAITING_ANNOUNCE:
	/* BPF ensures this packet indicates a conflict */
	ipv4acd_on_conflict(acd);
	break;

	default:
	assert_not_reached("Invalid state.");
	}

	return 0;

	fail:
	sd_ipv4acd_stop(acd);
	return 0;
	}

	int sd_ipv4acd_set_ifindex(sd_ipv4acd *acd, int ifindex) {
	assert_return(acd, -EINVAL);
	assert_return(ifindex > 0, -EINVAL);
	assert_return(acd->state == IPV4ACD_STATE_INIT, -EBUSY);

	acd->ifindex = ifindex;

	return 0;
	}

	int sd_ipv4acd_set_mac(sd_ipv4acd acd, const struct ether_addr addr) {
	assert_return(acd, -EINVAL);
	assert_return(addr, -EINVAL);
	assert_return(acd->state == IPV4ACD_STATE_INIT, -EBUSY);

	acd->mac_addr = *addr;

	return 0;
	}

	int sd_ipv4acd_detach_event(sd_ipv4acd *acd) {
	assert_return(acd, -EINVAL);

	acd->event = sd_event_unref(acd->event);

	return 0;
	}

	int sd_ipv4acd_attach_event(sd_ipv4acd acd, sd_event event, int64_t priority) {
	int r;

	assert_return(acd, -EINVAL);
	assert_return(!acd->event, -EBUSY);

	if (event)
	acd->event = sd_event_ref(event);
	else {
	r = sd_event_default(&acd->event);
	if (r < 0)
	return r;
	}

	acd->event_priority = priority;

	return 0;
	}

	int sd_ipv4acd_set_callback(sd_ipv4acd acd, sd_ipv4acd_callback_t cb, void userdata) {
	assert_return(acd, -EINVAL);

	acd->callback = cb;
	acd->userdata = userdata;

	return 0;
	}

	int sd_ipv4acd_set_address(sd_ipv4acd acd, const struct in_addr address) {
	assert_return(acd, -EINVAL);
	assert_return(address, -EINVAL);
	assert_return(acd->state == IPV4ACD_STATE_INIT, -EBUSY);

	acd->address = address->s_addr;

	return 0;
	}

	int sd_ipv4acd_is_running(sd_ipv4acd *acd) {
	assert_return(acd, false);

	return acd->state != IPV4ACD_STATE_INIT;
	}

	int sd_ipv4acd_start(sd_ipv4acd *acd, bool reset_conflicts) {
	int r;

	assert_return(acd, -EINVAL);
	assert_return(acd->event, -EINVAL);
	assert_return(acd->ifindex > 0, -EINVAL);
	assert_return(acd->address != 0, -EINVAL);
	assert_return(!ether_addr_is_null(&acd->mac_addr), -EINVAL);
	assert_return(acd->state == IPV4ACD_STATE_INIT, -EBUSY);

	r = arp_network_bind_raw_socket(acd->ifindex, acd->address, &acd->mac_addr);
	if (r < 0)
	return r;

	safe_close(acd->fd);
	acd->fd = r;
	acd->defend_window = 0;

	if (reset_conflicts)
	acd->n_conflict = 0;

	r = sd_event_add_io(acd->event, &acd->receive_message_event_source, acd->fd, EPOLLIN, ipv4acd_on_packet, acd);
	if (r < 0)
	goto fail;

	r = sd_event_source_set_priority(acd->receive_message_event_source, acd->event_priority);
	if (r < 0)
	goto fail;

	(void) sd_event_source_set_description(acd->receive_message_event_source, "ipv4acd-receive-message");

	r = ipv4acd_set_next_wakeup(acd, 0, 0);
	if (r < 0)
	goto fail;

	ipv4acd_set_state(acd, IPV4ACD_STATE_STARTED, true);
	return 0;

	fail:
	ipv4acd_reset(acd);
	return r;
	}