1 /**
2  * @file
3  * Address Resolution Protocol module for IP over Ethernet
4  *
5  * Functionally, ARP is divided into two parts. The first maps an IP address
6  * to a physical address when sending a packet, and the second part answers
7  * requests from other machines for our physical address.
8  *
9  * This implementation complies with RFC 826 (Ethernet ARP). It supports
10  * Gratuitous ARP from RFC3220 (IP Mobility Support for IPv4) section 4.6
11  * if an interface calls etharp_gratuitous(our_netif) upon address change.
12  */
13 
14 /*
15  * Copyright (c) 2001-2003 Swedish Institute of Computer Science.
16  * Copyright (c) 2003-2004 Leon Woestenberg <leon.woestenberg@axon.tv>
17  * Copyright (c) 2003-2004 Axon Digital Design B.V., The Netherlands.
18  * All rights reserved.
19  *
20  * Redistribution and use in source and binary forms, with or without modification,
21  * are permitted provided that the following conditions are met:
22  *
23  * 1. Redistributions of source code must retain the above copyright notice,
24  *    this list of conditions and the following disclaimer.
25  * 2. Redistributions in binary form must reproduce the above copyright notice,
26  *    this list of conditions and the following disclaimer in the documentation
27  *    and/or other materials provided with the distribution.
28  * 3. The name of the author may not be used to endorse or promote products
29  *    derived from this software without specific prior written permission.
30  *
31  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
32  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
33  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
34  * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
35  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
36  * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
37  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
38  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
39  * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
40  * OF SUCH DAMAGE.
41  *
42  * This file is part of the lwIP TCP/IP stack.
43  *
44  */
45 
46 #include "lwip/opt.h"
47 
48 #if LWIP_IPV4 && LWIP_ARP /* don't build if not configured for use in lwipopts.h */
49 
50 #include "lwip/etharp.h"
51 #include "lwip/stats.h"
52 #include "lwip/snmp.h"
53 #include "lwip/dhcp.h"
54 #include "lwip/autoip.h"
55 #include "lwip/acd.h"
56 #include "lwip/prot/iana.h"
57 #include "netif/ethernet.h"
58 
59 #include <string.h>
60 
61 #ifdef LWIP_HOOK_FILENAME
62 #include LWIP_HOOK_FILENAME
63 #endif
64 
65 /** Re-request a used ARP entry 1 minute before it would expire to prevent
66  *  breaking a steadily used connection because the ARP entry timed out. */
67 #define ARP_AGE_REREQUEST_USED_UNICAST   (ARP_MAXAGE - 30)
68 #define ARP_AGE_REREQUEST_USED_BROADCAST (ARP_MAXAGE - 15)
69 
70 /** the time an ARP entry stays pending after first request,
71  *  for ARP_TMR_INTERVAL = 1000, this is
72  *  10 seconds.
73  *
74  *  @internal Keep this number at least 2, otherwise it might
75  *  run out instantly if the timeout occurs directly after a request.
76  */
77 #define ARP_MAXPENDING 5
78 
79 /** ARP states */
80 enum etharp_state {
81   ETHARP_STATE_EMPTY = 0,
82   ETHARP_STATE_PENDING,
83   ETHARP_STATE_STABLE,
84   ETHARP_STATE_STABLE_REREQUESTING_1,
85   ETHARP_STATE_STABLE_REREQUESTING_2
86 #if ETHARP_SUPPORT_STATIC_ENTRIES
87   , ETHARP_STATE_STATIC
88 #endif /* ETHARP_SUPPORT_STATIC_ENTRIES */
89 };
90 
91 struct etharp_entry {
92 #if ARP_QUEUEING
93   /** Pointer to queue of pending outgoing packets on this ARP entry. */
94   struct etharp_q_entry *q;
95 #else /* ARP_QUEUEING */
96   /** Pointer to a single pending outgoing packet on this ARP entry. */
97   struct pbuf *q;
98 #endif /* ARP_QUEUEING */
99   ip4_addr_t ipaddr;
100   struct netif *netif;
101   struct eth_addr ethaddr;
102   u16_t ctime;
103   u8_t state;
104 };
105 
106 static struct etharp_entry arp_table[ARP_TABLE_SIZE];
107 
108 #if !LWIP_NETIF_HWADDRHINT
109 static netif_addr_idx_t etharp_cached_entry;
110 #endif /* !LWIP_NETIF_HWADDRHINT */
111 
112 /** Try hard to create a new entry - we want the IP address to appear in
113     the cache (even if this means removing an active entry or so). */
114 #define ETHARP_FLAG_TRY_HARD     1
115 #define ETHARP_FLAG_FIND_ONLY    2
116 #if ETHARP_SUPPORT_STATIC_ENTRIES
117 #define ETHARP_FLAG_STATIC_ENTRY 4
118 #endif /* ETHARP_SUPPORT_STATIC_ENTRIES */
119 
120 #if LWIP_NETIF_HWADDRHINT
121 #define ETHARP_SET_ADDRHINT(netif, addrhint)  do { if (((netif) != NULL) && ((netif)->hints != NULL)) { \
122                                               (netif)->hints->addr_hint = (addrhint); }} while(0)
123 #else /* LWIP_NETIF_HWADDRHINT */
124 #define ETHARP_SET_ADDRHINT(netif, addrhint)  (etharp_cached_entry = (addrhint))
125 #endif /* LWIP_NETIF_HWADDRHINT */
126 
127 
128 /* Check for maximum ARP_TABLE_SIZE */
129 #if (ARP_TABLE_SIZE > NETIF_ADDR_IDX_MAX)
130 #error "ARP_TABLE_SIZE must fit in an s16_t, you have to reduce it in your lwipopts.h"
131 #endif
132 
133 
134 static err_t etharp_request_dst(struct netif *netif, const ip4_addr_t *ipaddr, const struct eth_addr *hw_dst_addr);
135 static err_t etharp_raw(struct netif *netif,
136                         const struct eth_addr *ethsrc_addr, const struct eth_addr *ethdst_addr,
137                         const struct eth_addr *hwsrc_addr, const ip4_addr_t *ipsrc_addr,
138                         const struct eth_addr *hwdst_addr, const ip4_addr_t *ipdst_addr,
139                         const u16_t opcode);
140 
141 #if ARP_QUEUEING
142 /**
143  * Free a complete queue of etharp entries
144  *
145  * @param q a queue of etharp_q_entry's to free
146  */
147 static void
free_etharp_q(struct etharp_q_entry * q)148 free_etharp_q(struct etharp_q_entry *q)
149 {
150   struct etharp_q_entry *r;
151   LWIP_ASSERT("q != NULL", q != NULL);
152   while (q) {
153     r = q;
154     q = q->next;
155     LWIP_ASSERT("r->p != NULL", (r->p != NULL));
156     pbuf_free(r->p);
157     memp_free(MEMP_ARP_QUEUE, r);
158   }
159 }
160 #else /* ARP_QUEUEING */
161 
162 /** Compatibility define: free the queued pbuf */
163 #define free_etharp_q(q) pbuf_free(q)
164 
165 #endif /* ARP_QUEUEING */
166 
167 /** Clean up ARP table entries */
168 static void
etharp_free_entry(int i)169 etharp_free_entry(int i)
170 {
171   /* remove from SNMP ARP index tree */
172   mib2_remove_arp_entry(arp_table[i].netif, &arp_table[i].ipaddr);
173   /* and empty packet queue */
174   if (arp_table[i].q != NULL) {
175     /* remove all queued packets */
176     LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_free_entry: freeing entry %"U16_F", packet queue %p.\n", (u16_t)i, (void *)(arp_table[i].q)));
177     free_etharp_q(arp_table[i].q);
178     arp_table[i].q = NULL;
179   }
180   /* recycle entry for re-use */
181   arp_table[i].state = ETHARP_STATE_EMPTY;
182 #ifdef LWIP_DEBUG
183   /* for debugging, clean out the complete entry */
184   arp_table[i].ctime = 0;
185   arp_table[i].netif = NULL;
186   ip4_addr_set_zero(&arp_table[i].ipaddr);
187   arp_table[i].ethaddr = ethzero;
188 #endif /* LWIP_DEBUG */
189 }
190 
191 /**
192  * Clears expired entries in the ARP table.
193  *
194  * This function should be called every ARP_TMR_INTERVAL milliseconds (1 second),
195  * in order to expire entries in the ARP table.
196  */
197 void
etharp_tmr(void)198 etharp_tmr(void)
199 {
200   int i;
201 
202   LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer\n"));
203   /* remove expired entries from the ARP table */
204   for (i = 0; i < ARP_TABLE_SIZE; ++i) {
205     u8_t state = arp_table[i].state;
206     if (state != ETHARP_STATE_EMPTY
207 #if ETHARP_SUPPORT_STATIC_ENTRIES
208         && (state != ETHARP_STATE_STATIC)
209 #endif /* ETHARP_SUPPORT_STATIC_ENTRIES */
210        ) {
211       arp_table[i].ctime++;
212       if ((arp_table[i].ctime >= ARP_MAXAGE) ||
213           ((arp_table[i].state == ETHARP_STATE_PENDING)  &&
214            (arp_table[i].ctime >= ARP_MAXPENDING))) {
215         /* pending or stable entry has become old! */
216         LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer: expired %s entry %d.\n",
217                                    arp_table[i].state >= ETHARP_STATE_STABLE ? "stable" : "pending", i));
218         /* clean up entries that have just been expired */
219         etharp_free_entry(i);
220       } else if (arp_table[i].state == ETHARP_STATE_STABLE_REREQUESTING_1) {
221         /* Don't send more than one request every 2 seconds. */
222         arp_table[i].state = ETHARP_STATE_STABLE_REREQUESTING_2;
223       } else if (arp_table[i].state == ETHARP_STATE_STABLE_REREQUESTING_2) {
224         /* Reset state to stable, so that the next transmitted packet will
225            re-send an ARP request. */
226         arp_table[i].state = ETHARP_STATE_STABLE;
227       } else if (arp_table[i].state == ETHARP_STATE_PENDING) {
228         /* still pending, resend an ARP query */
229         etharp_request(arp_table[i].netif, &arp_table[i].ipaddr);
230       }
231     }
232   }
233 }
234 
235 /**
236  * Search the ARP table for a matching or new entry.
237  *
238  * If an IP address is given, return a pending or stable ARP entry that matches
239  * the address. If no match is found, create a new entry with this address set,
240  * but in state ETHARP_EMPTY. The caller must check and possibly change the
241  * state of the returned entry.
242  *
243  * If ipaddr is NULL, return a initialized new entry in state ETHARP_EMPTY.
244  *
245  * In all cases, attempt to create new entries from an empty entry. If no
246  * empty entries are available and ETHARP_FLAG_TRY_HARD flag is set, recycle
247  * old entries. Heuristic choose the least important entry for recycling.
248  *
249  * @param ipaddr IP address to find in ARP cache, or to add if not found.
250  * @param flags See @ref etharp_state
251  * @param netif netif related to this address (used for NETIF_HWADDRHINT)
252  *
253  * @return The ARP entry index that matched or is created, ERR_MEM if no
254  * entry is found or could be recycled.
255  */
256 static s16_t
etharp_find_entry(const ip4_addr_t * ipaddr,u8_t flags,struct netif * netif)257 etharp_find_entry(const ip4_addr_t *ipaddr, u8_t flags, struct netif *netif)
258 {
259   s16_t old_pending = ARP_TABLE_SIZE, old_stable = ARP_TABLE_SIZE;
260   s16_t empty = ARP_TABLE_SIZE;
261   s16_t i = 0;
262   /* oldest entry with packets on queue */
263   s16_t old_queue = ARP_TABLE_SIZE;
264   /* its age */
265   u16_t age_queue = 0, age_pending = 0, age_stable = 0;
266 
267   LWIP_UNUSED_ARG(netif);
268 
269   /**
270    * a) do a search through the cache, remember candidates
271    * b) select candidate entry
272    * c) create new entry
273    */
274 
275   /* a) in a single search sweep, do all of this
276    * 1) remember the first empty entry (if any)
277    * 2) remember the oldest stable entry (if any)
278    * 3) remember the oldest pending entry without queued packets (if any)
279    * 4) remember the oldest pending entry with queued packets (if any)
280    * 5) search for a matching IP entry, either pending or stable
281    *    until 5 matches, or all entries are searched for.
282    */
283 
284   for (i = 0; i < ARP_TABLE_SIZE; ++i) {
285     u8_t state = arp_table[i].state;
286     /* no empty entry found yet and now we do find one? */
287     if ((empty == ARP_TABLE_SIZE) && (state == ETHARP_STATE_EMPTY)) {
288       LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_find_entry: found empty entry %d\n", (int)i));
289       /* remember first empty entry */
290       empty = i;
291     } else if (state != ETHARP_STATE_EMPTY) {
292       LWIP_ASSERT("state == ETHARP_STATE_PENDING || state >= ETHARP_STATE_STABLE",
293                   state == ETHARP_STATE_PENDING || state >= ETHARP_STATE_STABLE);
294       /* if given, does IP address match IP address in ARP entry? */
295       if (ipaddr && ip4_addr_eq(ipaddr, &arp_table[i].ipaddr)
296 #if ETHARP_TABLE_MATCH_NETIF
297           && ((netif == NULL) || (netif == arp_table[i].netif))
298 #endif /* ETHARP_TABLE_MATCH_NETIF */
299          ) {
300         LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_find_entry: found matching entry %d\n", (int)i));
301         /* found exact IP address match, simply bail out */
302         return i;
303       }
304       /* pending entry? */
305       if (state == ETHARP_STATE_PENDING) {
306         /* pending with queued packets? */
307         if (arp_table[i].q != NULL) {
308           if (arp_table[i].ctime >= age_queue) {
309             old_queue = i;
310             age_queue = arp_table[i].ctime;
311           }
312         } else
313           /* pending without queued packets? */
314         {
315           if (arp_table[i].ctime >= age_pending) {
316             old_pending = i;
317             age_pending = arp_table[i].ctime;
318           }
319         }
320         /* stable entry? */
321       } else if (state >= ETHARP_STATE_STABLE) {
322 #if ETHARP_SUPPORT_STATIC_ENTRIES
323         /* don't record old_stable for static entries since they never expire */
324         if (state < ETHARP_STATE_STATIC)
325 #endif /* ETHARP_SUPPORT_STATIC_ENTRIES */
326         {
327           /* remember entry with oldest stable entry in oldest, its age in maxtime */
328           if (arp_table[i].ctime >= age_stable) {
329             old_stable = i;
330             age_stable = arp_table[i].ctime;
331           }
332         }
333       }
334     }
335   }
336   /* { we have no match } => try to create a new entry */
337 
338   /* don't create new entry, only search? */
339   if (((flags & ETHARP_FLAG_FIND_ONLY) != 0) ||
340       /* or no empty entry found and not allowed to recycle? */
341       ((empty == ARP_TABLE_SIZE) && ((flags & ETHARP_FLAG_TRY_HARD) == 0))) {
342     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_find_entry: no empty entry found and not allowed to recycle\n"));
343     return (s16_t)ERR_MEM;
344   }
345 
346   /* b) choose the least destructive entry to recycle:
347    * 1) empty entry
348    * 2) oldest stable entry
349    * 3) oldest pending entry without queued packets
350    * 4) oldest pending entry with queued packets
351    *
352    * { ETHARP_FLAG_TRY_HARD is set at this point }
353    */
354 
355   /* 1) empty entry available? */
356   if (empty < ARP_TABLE_SIZE) {
357     i = empty;
358     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_find_entry: selecting empty entry %d\n", (int)i));
359   } else {
360     /* 2) found recyclable stable entry? */
361     if (old_stable < ARP_TABLE_SIZE) {
362       /* recycle oldest stable*/
363       i = old_stable;
364       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_find_entry: selecting oldest stable entry %d\n", (int)i));
365       /* no queued packets should exist on stable entries */
366       LWIP_ASSERT("arp_table[i].q == NULL", arp_table[i].q == NULL);
367       /* 3) found recyclable pending entry without queued packets? */
368     } else if (old_pending < ARP_TABLE_SIZE) {
369       /* recycle oldest pending */
370       i = old_pending;
371       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_find_entry: selecting oldest pending entry %d (without queue)\n", (int)i));
372       /* 4) found recyclable pending entry with queued packets? */
373     } else if (old_queue < ARP_TABLE_SIZE) {
374       /* recycle oldest pending (queued packets are free in etharp_free_entry) */
375       i = old_queue;
376       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_find_entry: selecting oldest pending entry %d, freeing packet queue %p\n", (int)i, (void *)(arp_table[i].q)));
377       /* no empty or recyclable entries found */
378     } else {
379       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_find_entry: no empty or recyclable entries found\n"));
380       return (s16_t)ERR_MEM;
381     }
382 
383     /* { empty or recyclable entry found } */
384     LWIP_ASSERT("i < ARP_TABLE_SIZE", i < ARP_TABLE_SIZE);
385     etharp_free_entry(i);
386   }
387 
388   LWIP_ASSERT("i < ARP_TABLE_SIZE", i < ARP_TABLE_SIZE);
389   LWIP_ASSERT("arp_table[i].state == ETHARP_STATE_EMPTY",
390               arp_table[i].state == ETHARP_STATE_EMPTY);
391 
392   /* IP address given? */
393   if (ipaddr != NULL) {
394     /* set IP address */
395     ip4_addr_copy(arp_table[i].ipaddr, *ipaddr);
396   }
397   arp_table[i].ctime = 0;
398 #if ETHARP_TABLE_MATCH_NETIF
399   arp_table[i].netif = netif;
400 #endif /* ETHARP_TABLE_MATCH_NETIF */
401   return (s16_t)i;
402 }
403 
404 /**
405  * Update (or insert) a IP/MAC address pair in the ARP cache.
406  *
407  * If a pending entry is resolved, any queued packets will be sent
408  * at this point.
409  *
410  * @param netif netif related to this entry (used for NETIF_ADDRHINT)
411  * @param ipaddr IP address of the inserted ARP entry.
412  * @param ethaddr Ethernet address of the inserted ARP entry.
413  * @param flags See @ref etharp_state
414  *
415  * @return
416  * - ERR_OK Successfully updated ARP cache.
417  * - ERR_MEM If we could not add a new ARP entry when ETHARP_FLAG_TRY_HARD was set.
418  * - ERR_ARG Non-unicast address given, those will not appear in ARP cache.
419  *
420  * @see pbuf_free()
421  */
422 static err_t
etharp_update_arp_entry(struct netif * netif,const ip4_addr_t * ipaddr,struct eth_addr * ethaddr,u8_t flags)423 etharp_update_arp_entry(struct netif *netif, const ip4_addr_t *ipaddr, struct eth_addr *ethaddr, u8_t flags)
424 {
425   s16_t i;
426   LWIP_ASSERT("netif->hwaddr_len == ETH_HWADDR_LEN", netif->hwaddr_len == ETH_HWADDR_LEN);
427   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_update_arp_entry: %"U16_F".%"U16_F".%"U16_F".%"U16_F" - %02"X16_F":%02"X16_F":%02"X16_F":%02"X16_F":%02"X16_F":%02"X16_F"\n",
428               ip4_addr1_16(ipaddr), ip4_addr2_16(ipaddr), ip4_addr3_16(ipaddr), ip4_addr4_16(ipaddr),
429               (u16_t)ethaddr->addr[0], (u16_t)ethaddr->addr[1], (u16_t)ethaddr->addr[2],
430               (u16_t)ethaddr->addr[3], (u16_t)ethaddr->addr[4], (u16_t)ethaddr->addr[5]));
431   /* non-unicast address? */
432   if (ip4_addr_isany(ipaddr) ||
433       ip4_addr_isbroadcast(ipaddr, netif) ||
434       ip4_addr_ismulticast(ipaddr)) {
435     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_update_arp_entry: will not add non-unicast IP address to ARP cache\n"));
436     return ERR_ARG;
437   }
438   /* find or create ARP entry */
439   i = etharp_find_entry(ipaddr, flags, netif);
440   /* bail out if no entry could be found */
441   if (i < 0) {
442     return (err_t)i;
443   }
444 
445 #if ETHARP_SUPPORT_STATIC_ENTRIES
446   if (flags & ETHARP_FLAG_STATIC_ENTRY) {
447     /* record static type */
448     arp_table[i].state = ETHARP_STATE_STATIC;
449   } else if (arp_table[i].state == ETHARP_STATE_STATIC) {
450     /* found entry is a static type, don't overwrite it */
451     return ERR_VAL;
452   } else
453 #endif /* ETHARP_SUPPORT_STATIC_ENTRIES */
454   {
455     /* mark it stable */
456     arp_table[i].state = ETHARP_STATE_STABLE;
457   }
458 
459   /* record network interface */
460   arp_table[i].netif = netif;
461   /* insert in SNMP ARP index tree */
462   mib2_add_arp_entry(netif, &arp_table[i].ipaddr);
463 
464   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_update_arp_entry: updating stable entry %"S16_F"\n", i));
465   /* update address */
466   SMEMCPY(&arp_table[i].ethaddr, ethaddr, ETH_HWADDR_LEN);
467   /* reset time stamp */
468   arp_table[i].ctime = 0;
469   /* this is where we will send out queued packets! */
470 #if ARP_QUEUEING
471   while (arp_table[i].q != NULL) {
472     struct pbuf *p;
473     /* remember remainder of queue */
474     struct etharp_q_entry *q = arp_table[i].q;
475     /* pop first item off the queue */
476     arp_table[i].q = q->next;
477     /* get the packet pointer */
478     p = q->p;
479     /* now queue entry can be freed */
480     memp_free(MEMP_ARP_QUEUE, q);
481 #else /* ARP_QUEUEING */
482   if (arp_table[i].q != NULL) {
483     struct pbuf *p = arp_table[i].q;
484     arp_table[i].q = NULL;
485 #endif /* ARP_QUEUEING */
486     /* send the queued IP packet */
487     ethernet_output(netif, p, (struct eth_addr *)(netif->hwaddr), ethaddr, ETHTYPE_IP);
488     /* free the queued IP packet */
489     pbuf_free(p);
490   }
491   return ERR_OK;
492 }
493 
494 #if ETHARP_SUPPORT_STATIC_ENTRIES
495 /** Add a new static entry to the ARP table. If an entry exists for the
496  * specified IP address, this entry is overwritten.
497  * If packets are queued for the specified IP address, they are sent out.
498  *
499  * @param ipaddr IP address for the new static entry
500  * @param ethaddr ethernet address for the new static entry
501  * @return See return values of etharp_add_static_entry
502  */
503 err_t
504 etharp_add_static_entry(const ip4_addr_t *ipaddr, struct eth_addr *ethaddr)
505 {
506   struct netif *netif;
507   LWIP_ASSERT_CORE_LOCKED();
508   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_add_static_entry: %"U16_F".%"U16_F".%"U16_F".%"U16_F" - %02"X16_F":%02"X16_F":%02"X16_F":%02"X16_F":%02"X16_F":%02"X16_F"\n",
509               ip4_addr1_16(ipaddr), ip4_addr2_16(ipaddr), ip4_addr3_16(ipaddr), ip4_addr4_16(ipaddr),
510               (u16_t)ethaddr->addr[0], (u16_t)ethaddr->addr[1], (u16_t)ethaddr->addr[2],
511               (u16_t)ethaddr->addr[3], (u16_t)ethaddr->addr[4], (u16_t)ethaddr->addr[5]));
512 
513   netif = ip4_route(ipaddr);
514   if (netif == NULL) {
515     return ERR_RTE;
516   }
517 
518   return etharp_update_arp_entry(netif, ipaddr, ethaddr, ETHARP_FLAG_TRY_HARD | ETHARP_FLAG_STATIC_ENTRY);
519 }
520 
521 /** Remove a static entry from the ARP table previously added with a call to
522  * etharp_add_static_entry.
523  *
524  * @param ipaddr IP address of the static entry to remove
525  * @return ERR_OK: entry removed
526  *         ERR_MEM: entry wasn't found
527  *         ERR_ARG: entry wasn't a static entry but a dynamic one
528  */
529 err_t
530 etharp_remove_static_entry(const ip4_addr_t *ipaddr)
531 {
532   s16_t i;
533   LWIP_ASSERT_CORE_LOCKED();
534   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_remove_static_entry: %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
535               ip4_addr1_16(ipaddr), ip4_addr2_16(ipaddr), ip4_addr3_16(ipaddr), ip4_addr4_16(ipaddr)));
536 
537   /* find or create ARP entry */
538   i = etharp_find_entry(ipaddr, ETHARP_FLAG_FIND_ONLY, NULL);
539   /* bail out if no entry could be found */
540   if (i < 0) {
541     return (err_t)i;
542   }
543 
544   if (arp_table[i].state != ETHARP_STATE_STATIC) {
545     /* entry wasn't a static entry, cannot remove it */
546     return ERR_ARG;
547   }
548   /* entry found, free it */
549   etharp_free_entry(i);
550   return ERR_OK;
551 }
552 #endif /* ETHARP_SUPPORT_STATIC_ENTRIES */
553 
554 /**
555  * Remove all ARP table entries of the specified netif.
556  *
557  * @param netif points to a network interface
558  */
559 void
560 etharp_cleanup_netif(struct netif *netif)
561 {
562   int i;
563 
564   for (i = 0; i < ARP_TABLE_SIZE; ++i) {
565     u8_t state = arp_table[i].state;
566     if ((state != ETHARP_STATE_EMPTY) && (arp_table[i].netif == netif)) {
567       etharp_free_entry(i);
568     }
569   }
570 }
571 
572 /**
573  * Finds (stable) ethernet/IP address pair from ARP table
574  * using interface and IP address index.
575  * @note the addresses in the ARP table are in network order!
576  *
577  * @param netif points to interface index
578  * @param ipaddr points to the (network order) IP address index
579  * @param eth_ret points to return pointer
580  * @param ip_ret points to return pointer
581  * @return table index if found, -1 otherwise
582  */
583 ssize_t
584 etharp_find_addr(struct netif *netif, const ip4_addr_t *ipaddr,
585                  struct eth_addr **eth_ret, const ip4_addr_t **ip_ret)
586 {
587   s16_t i;
588 
589   LWIP_ASSERT("eth_ret != NULL && ip_ret != NULL",
590               eth_ret != NULL && ip_ret != NULL);
591 
592   LWIP_UNUSED_ARG(netif);
593 
594   i = etharp_find_entry(ipaddr, ETHARP_FLAG_FIND_ONLY, netif);
595   if ((i >= 0) && (arp_table[i].state >= ETHARP_STATE_STABLE)) {
596     *eth_ret = &arp_table[i].ethaddr;
597     *ip_ret = &arp_table[i].ipaddr;
598     return i;
599   }
600   return -1;
601 }
602 
603 /**
604  * Possibility to iterate over stable ARP table entries
605  *
606  * @param i entry number, 0 to ARP_TABLE_SIZE
607  * @param ipaddr return value: IP address
608  * @param netif return value: points to interface
609  * @param eth_ret return value: ETH address
610  * @return 1 on valid index, 0 otherwise
611  */
612 int
613 etharp_get_entry(size_t i, ip4_addr_t **ipaddr, struct netif **netif, struct eth_addr **eth_ret)
614 {
615   LWIP_ASSERT("ipaddr != NULL", ipaddr != NULL);
616   LWIP_ASSERT("netif != NULL", netif != NULL);
617   LWIP_ASSERT("eth_ret != NULL", eth_ret != NULL);
618 
619   if ((i < ARP_TABLE_SIZE) && (arp_table[i].state >= ETHARP_STATE_STABLE)) {
620     *ipaddr  = &arp_table[i].ipaddr;
621     *netif   = arp_table[i].netif;
622     *eth_ret = &arp_table[i].ethaddr;
623     return 1;
624   } else {
625     return 0;
626   }
627 }
628 
629 /**
630  * Responds to ARP requests to us. Upon ARP replies to us, add entry to cache
631  * send out queued IP packets. Updates cache with snooped address pairs.
632  *
633  * Should be called for incoming ARP packets. The pbuf in the argument
634  * is freed by this function.
635  *
636  * @param p The ARP packet that arrived on netif. Is freed by this function.
637  * @param netif The lwIP network interface on which the ARP packet pbuf arrived.
638  *
639  * @see pbuf_free()
640  */
641 void
642 etharp_input(struct pbuf *p, struct netif *netif)
643 {
644   struct etharp_hdr *hdr;
645   /* these are aligned properly, whereas the ARP header fields might not be */
646   ip4_addr_t sipaddr, dipaddr;
647   u8_t for_us, from_us;
648 
649   LWIP_ASSERT_CORE_LOCKED();
650 
651   LWIP_ERROR("netif != NULL", (netif != NULL), return;);
652 
653   hdr = (struct etharp_hdr *)p->payload;
654 
655   /* RFC 826 "Packet Reception": */
656   if ((hdr->hwtype != PP_HTONS(LWIP_IANA_HWTYPE_ETHERNET)) ||
657       (hdr->hwlen != ETH_HWADDR_LEN) ||
658       (hdr->protolen != sizeof(ip4_addr_t)) ||
659       (hdr->proto != PP_HTONS(ETHTYPE_IP)))  {
660     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
661                 ("etharp_input: packet dropped, wrong hw type, hwlen, proto, protolen or ethernet type (%"U16_F"/%"U16_F"/%"U16_F"/%"U16_F")\n",
662                  hdr->hwtype, (u16_t)hdr->hwlen, hdr->proto, (u16_t)hdr->protolen));
663     ETHARP_STATS_INC(etharp.proterr);
664     ETHARP_STATS_INC(etharp.drop);
665     pbuf_free(p);
666     return;
667   }
668   ETHARP_STATS_INC(etharp.recv);
669 
670 #if LWIP_ACD
671   /* We have to check if a host already has configured our ip address and
672    * continuously check if there is a host with this IP-address so we can
673    * detect collisions.
674    * acd_arp_reply ensures the detection of conflicts. It will handle possible
675    * defending or retreating and will make sure a new IP address is selected.
676    * etharp_input does not need to handle packets that originate "from_us".
677    */
678   acd_arp_reply(netif, hdr);
679 #endif /* LWIP_ACD */
680 
681   /* Copy struct ip4_addr_wordaligned to aligned ip4_addr, to support compilers without
682    * structure packing (not using structure copy which breaks strict-aliasing rules). */
683   IPADDR_WORDALIGNED_COPY_TO_IP4_ADDR_T(&sipaddr, &hdr->sipaddr);
684   IPADDR_WORDALIGNED_COPY_TO_IP4_ADDR_T(&dipaddr, &hdr->dipaddr);
685 
686   /* this interface is not configured? */
687   if (ip4_addr_isany_val(*netif_ip4_addr(netif))) {
688     for_us = 0;
689     from_us = 0;
690   } else {
691     /* ARP packet directed to us? */
692     for_us = (u8_t)ip4_addr_eq(&dipaddr, netif_ip4_addr(netif));
693     /* ARP packet from us? */
694     from_us = (u8_t)ip4_addr_eq(&sipaddr, netif_ip4_addr(netif));
695   }
696 
697   /* ARP message directed to us?
698       -> add IP address in ARP cache; assume requester wants to talk to us,
699          can result in directly sending the queued packets for this host.
700      ARP message not directed to us?
701       ->  update the source IP address in the cache, if present */
702   etharp_update_arp_entry(netif, &sipaddr, &(hdr->shwaddr),
703                           for_us ? ETHARP_FLAG_TRY_HARD : ETHARP_FLAG_FIND_ONLY);
704 
705   /* now act on the message itself */
706   switch (hdr->opcode) {
707     /* ARP request? */
708     case PP_HTONS(ARP_REQUEST):
709       /* ARP request. If it asked for our address, we send out a
710        * reply. In any case, we time-stamp any existing ARP entry,
711        * and possibly send out an IP packet that was queued on it. */
712 
713       LWIP_DEBUGF (ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_input: incoming ARP request\n"));
714       /* ARP request for our address? */
715       if (for_us && !from_us) {
716         /* send ARP response */
717         etharp_raw(netif,
718                    (struct eth_addr *)netif->hwaddr, &hdr->shwaddr,
719                    (struct eth_addr *)netif->hwaddr, netif_ip4_addr(netif),
720                    &hdr->shwaddr, &sipaddr,
721                    ARP_REPLY);
722         /* we are not configured? */
723       } else if (ip4_addr_isany_val(*netif_ip4_addr(netif))) {
724         /* { for_us == 0 and netif->ip_addr.addr == 0 } */
725         LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_input: we are unconfigured, ARP request ignored.\n"));
726         /* request was not directed to us */
727       } else {
728         /* { for_us == 0 and netif->ip_addr.addr != 0 } */
729         LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_input: ARP request was not for us.\n"));
730       }
731       break;
732     case PP_HTONS(ARP_REPLY):
733       /* ARP reply. We already updated the ARP cache earlier. */
734       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_input: incoming ARP reply\n"));
735       break;
736     default:
737       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_input: ARP unknown opcode type %"S16_F"\n", lwip_htons(hdr->opcode)));
738       ETHARP_STATS_INC(etharp.err);
739       break;
740   }
741   /* free ARP packet */
742   pbuf_free(p);
743 }
744 
745 /** Just a small helper function that sends a pbuf to an ethernet address
746  * in the arp_table specified by the index 'arp_idx'.
747  */
748 static err_t
749 etharp_output_to_arp_index(struct netif *netif, struct pbuf *q, netif_addr_idx_t arp_idx)
750 {
751   LWIP_ASSERT("arp_table[arp_idx].state >= ETHARP_STATE_STABLE",
752               arp_table[arp_idx].state >= ETHARP_STATE_STABLE);
753   /* if arp table entry is about to expire: re-request it,
754      but only if its state is ETHARP_STATE_STABLE to prevent flooding the
755      network with ARP requests if this address is used frequently. */
756   if (arp_table[arp_idx].state == ETHARP_STATE_STABLE) {
757     if (arp_table[arp_idx].ctime >= ARP_AGE_REREQUEST_USED_BROADCAST) {
758       /* issue a standard request using broadcast */
759       if (etharp_request(netif, &arp_table[arp_idx].ipaddr) == ERR_OK) {
760         arp_table[arp_idx].state = ETHARP_STATE_STABLE_REREQUESTING_1;
761       }
762     } else if (arp_table[arp_idx].ctime >= ARP_AGE_REREQUEST_USED_UNICAST) {
763       /* issue a unicast request (for 15 seconds) to prevent unnecessary broadcast */
764       if (etharp_request_dst(netif, &arp_table[arp_idx].ipaddr, &arp_table[arp_idx].ethaddr) == ERR_OK) {
765         arp_table[arp_idx].state = ETHARP_STATE_STABLE_REREQUESTING_1;
766       }
767     }
768   }
769 
770   return ethernet_output(netif, q, (struct eth_addr *)(netif->hwaddr), &arp_table[arp_idx].ethaddr, ETHTYPE_IP);
771 }
772 
773 /**
774  * Resolve and fill-in Ethernet address header for outgoing IP packet.
775  *
776  * For IP multicast and broadcast, corresponding Ethernet addresses
777  * are selected and the packet is transmitted on the link.
778  *
779  * For unicast addresses, the packet is submitted to etharp_query(). In
780  * case the IP address is outside the local network, the IP address of
781  * the gateway is used.
782  *
783  * @param netif The lwIP network interface which the IP packet will be sent on.
784  * @param q The pbuf(s) containing the IP packet to be sent.
785  * @param ipaddr The IP address of the packet destination.
786  *
787  * @return
788  * - ERR_RTE No route to destination (no gateway to external networks),
789  * or the return type of either etharp_query() or ethernet_output().
790  */
791 err_t
792 etharp_output(struct netif *netif, struct pbuf *q, const ip4_addr_t *ipaddr)
793 {
794   const struct eth_addr *dest;
795   struct eth_addr mcastaddr;
796   const ip4_addr_t *dst_addr = ipaddr;
797 
798   LWIP_ASSERT_CORE_LOCKED();
799   LWIP_ASSERT("netif != NULL", netif != NULL);
800   LWIP_ASSERT("q != NULL", q != NULL);
801   LWIP_ASSERT("ipaddr != NULL", ipaddr != NULL);
802 
803   /* Determine on destination hardware address. Broadcasts and multicasts
804    * are special, other IP addresses are looked up in the ARP table. */
805 
806   /* broadcast destination IP address? */
807   if (ip4_addr_isbroadcast(ipaddr, netif)) {
808     /* broadcast on Ethernet also */
809     dest = (const struct eth_addr *)&ethbroadcast;
810     /* multicast destination IP address? */
811   } else if (ip4_addr_ismulticast(ipaddr)) {
812     /* Hash IP multicast address to MAC address.*/
813     mcastaddr.addr[0] = LL_IP4_MULTICAST_ADDR_0;
814     mcastaddr.addr[1] = LL_IP4_MULTICAST_ADDR_1;
815     mcastaddr.addr[2] = LL_IP4_MULTICAST_ADDR_2;
816     mcastaddr.addr[3] = ip4_addr2(ipaddr) & 0x7f;
817     mcastaddr.addr[4] = ip4_addr3(ipaddr);
818     mcastaddr.addr[5] = ip4_addr4(ipaddr);
819     /* destination Ethernet address is multicast */
820     dest = &mcastaddr;
821     /* unicast destination IP address? */
822   } else {
823     netif_addr_idx_t i;
824     /* outside local network? if so, this can neither be a global broadcast nor
825        a subnet broadcast. */
826     if (!ip4_addr_net_eq(ipaddr, netif_ip4_addr(netif), netif_ip4_netmask(netif)) &&
827         !ip4_addr_islinklocal(ipaddr)) {
828 #if LWIP_AUTOIP
829       struct ip_hdr *iphdr = LWIP_ALIGNMENT_CAST(struct ip_hdr *, q->payload);
830       /* According to RFC 3297, chapter 2.6.2 (Forwarding Rules), a packet with
831          a link-local source address must always be "directly to its destination
832          on the same physical link. The host MUST NOT send the packet to any
833          router for forwarding". */
834       if (!ip4_addr_islinklocal(&iphdr->src))
835 #endif /* LWIP_AUTOIP */
836       {
837 #ifdef LWIP_HOOK_ETHARP_GET_GW
838         /* For advanced routing, a single default gateway might not be enough, so get
839            the IP address of the gateway to handle the current destination address. */
840         dst_addr = LWIP_HOOK_ETHARP_GET_GW(netif, ipaddr);
841         if (dst_addr == NULL)
842 #endif /* LWIP_HOOK_ETHARP_GET_GW */
843         {
844           /* interface has default gateway? */
845           if (!ip4_addr_isany_val(*netif_ip4_gw(netif))) {
846             /* send to hardware address of default gateway IP address */
847             dst_addr = netif_ip4_gw(netif);
848             /* no default gateway available */
849           } else {
850             /* no route to destination error (default gateway missing) */
851             return ERR_RTE;
852           }
853         }
854       }
855     }
856 #if LWIP_NETIF_HWADDRHINT
857     if (netif->hints != NULL) {
858       /* per-pcb cached entry was given */
859       netif_addr_idx_t etharp_cached_entry = netif->hints->addr_hint;
860       if (etharp_cached_entry < ARP_TABLE_SIZE) {
861 #endif /* LWIP_NETIF_HWADDRHINT */
862         if ((arp_table[etharp_cached_entry].state >= ETHARP_STATE_STABLE) &&
863 #if ETHARP_TABLE_MATCH_NETIF
864             (arp_table[etharp_cached_entry].netif == netif) &&
865 #endif
866             (ip4_addr_eq(dst_addr, &arp_table[etharp_cached_entry].ipaddr))) {
867           /* the per-pcb-cached entry is stable and the right one! */
868           ETHARP_STATS_INC(etharp.cachehit);
869           return etharp_output_to_arp_index(netif, q, etharp_cached_entry);
870         }
871 #if LWIP_NETIF_HWADDRHINT
872       }
873     }
874 #endif /* LWIP_NETIF_HWADDRHINT */
875 
876     /* find stable entry: do this here since this is a critical path for
877        throughput and etharp_find_entry() is kind of slow */
878     for (i = 0; i < ARP_TABLE_SIZE; i++) {
879       if ((arp_table[i].state >= ETHARP_STATE_STABLE) &&
880 #if ETHARP_TABLE_MATCH_NETIF
881           (arp_table[i].netif == netif) &&
882 #endif
883           (ip4_addr_eq(dst_addr, &arp_table[i].ipaddr))) {
884         /* found an existing, stable entry */
885         ETHARP_SET_ADDRHINT(netif, i);
886         return etharp_output_to_arp_index(netif, q, i);
887       }
888     }
889     /* no stable entry found, use the (slower) query function:
890        queue on destination Ethernet address belonging to ipaddr */
891     return etharp_query(netif, dst_addr, q);
892   }
893 
894   /* continuation for multicast/broadcast destinations */
895   /* obtain source Ethernet address of the given interface */
896   /* send packet directly on the link */
897   return ethernet_output(netif, q, (struct eth_addr *)(netif->hwaddr), dest, ETHTYPE_IP);
898 }
899 
900 /**
901  * Send an ARP request for the given IP address and/or queue a packet.
902  *
903  * If the IP address was not yet in the cache, a pending ARP cache entry
904  * is added and an ARP request is sent for the given address. The packet
905  * is queued on this entry.
906  *
907  * If the IP address was already pending in the cache, a new ARP request
908  * is sent for the given address. The packet is queued on this entry.
909  *
910  * If the IP address was already stable in the cache, and a packet is
911  * given, it is directly sent and no ARP request is sent out.
912  *
913  * If the IP address was already stable in the cache, and no packet is
914  * given, an ARP request is sent out.
915  *
916  * @param netif The lwIP network interface on which ipaddr
917  * must be queried for.
918  * @param ipaddr The IP address to be resolved.
919  * @param q If non-NULL, a pbuf that must be delivered to the IP address.
920  * q is not freed by this function.
921  *
922  * @note q must only be ONE packet, not a packet queue!
923  *
924  * @return
925  * - ERR_BUF Could not make room for Ethernet header.
926  * - ERR_MEM Hardware address unknown, and no more ARP entries available
927  *   to query for address or queue the packet.
928  * - ERR_MEM Could not queue packet due to memory shortage.
929  * - ERR_RTE No route to destination (no gateway to external networks).
930  * - ERR_ARG Non-unicast address given, those will not appear in ARP cache.
931  *
932  */
933 err_t
934 etharp_query(struct netif *netif, const ip4_addr_t *ipaddr, struct pbuf *q)
935 {
936   struct eth_addr *srcaddr = (struct eth_addr *)netif->hwaddr;
937   err_t result = ERR_MEM;
938   int is_new_entry = 0;
939   s16_t i_err;
940   netif_addr_idx_t i;
941 
942   /* non-unicast address? */
943   if (ip4_addr_isbroadcast(ipaddr, netif) ||
944       ip4_addr_ismulticast(ipaddr) ||
945       ip4_addr_isany(ipaddr)) {
946     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: will not add non-unicast IP address to ARP cache\n"));
947     return ERR_ARG;
948   }
949 
950   /* find entry in ARP cache, ask to create entry if queueing packet */
951   i_err = etharp_find_entry(ipaddr, ETHARP_FLAG_TRY_HARD, netif);
952 
953   /* could not find or create entry? */
954   if (i_err < 0) {
955     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: could not create ARP entry\n"));
956     if (q) {
957       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: packet dropped\n"));
958       ETHARP_STATS_INC(etharp.memerr);
959     }
960     return (err_t)i_err;
961   }
962   LWIP_ASSERT("type overflow", (size_t)i_err < NETIF_ADDR_IDX_MAX);
963   i = (netif_addr_idx_t)i_err;
964 
965   /* mark a fresh entry as pending (we just sent a request) */
966   if (arp_table[i].state == ETHARP_STATE_EMPTY) {
967     is_new_entry = 1;
968     arp_table[i].state = ETHARP_STATE_PENDING;
969     /* record network interface for re-sending arp request in etharp_tmr */
970     arp_table[i].netif = netif;
971   }
972 
973   /* { i is either a STABLE or (new or existing) PENDING entry } */
974   LWIP_ASSERT("arp_table[i].state == PENDING or STABLE",
975               ((arp_table[i].state == ETHARP_STATE_PENDING) ||
976                (arp_table[i].state >= ETHARP_STATE_STABLE)));
977 
978   /* do we have a new entry? or an implicit query request? */
979   if (is_new_entry || (q == NULL)) {
980     /* try to resolve it; send out ARP request */
981     result = etharp_request(netif, ipaddr);
982     if (result != ERR_OK) {
983       /* ARP request couldn't be sent */
984       /* We don't re-send arp request in etharp_tmr, but we still queue packets,
985          since this failure could be temporary, and the next packet calling
986          etharp_query again could lead to sending the queued packets. */
987     } else {
988       /* ARP request successfully sent */
989       if ((arp_table[i].state == ETHARP_STATE_PENDING) && !is_new_entry) {
990         /* A new ARP request has been sent for a pending entry. Reset the ctime to
991            not let it expire too fast. */
992         LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: reset ctime for entry %"S16_F"\n", (s16_t)i));
993         arp_table[i].ctime = 0;
994       }
995     }
996     if (q == NULL) {
997       return result;
998     }
999   }
1000 
1001   /* packet given? */
1002   LWIP_ASSERT("q != NULL", q != NULL);
1003   /* stable entry? */
1004   if (arp_table[i].state >= ETHARP_STATE_STABLE) {
1005     /* we have a valid IP->Ethernet address mapping */
1006     ETHARP_SET_ADDRHINT(netif, i);
1007     /* send the packet */
1008     result = ethernet_output(netif, q, srcaddr, &(arp_table[i].ethaddr), ETHTYPE_IP);
1009     /* pending entry? (either just created or already pending */
1010   } else if (arp_table[i].state == ETHARP_STATE_PENDING) {
1011     /* entry is still pending, queue the given packet 'q' */
1012     struct pbuf *p;
1013     int copy_needed = 0;
1014     /* IF q includes a pbuf that must be copied, copy the whole chain into a
1015      * new PBUF_RAM. See the definition of PBUF_NEEDS_COPY for details. */
1016     p = q;
1017     while (p) {
1018       LWIP_ASSERT("no packet queues allowed!", (p->len != p->tot_len) || (p->next == NULL));
1019       if (PBUF_NEEDS_COPY(p)) {
1020         copy_needed = 1;
1021         break;
1022       }
1023       p = p->next;
1024     }
1025     if (copy_needed) {
1026       /* copy the whole packet into new pbufs */
1027       p = pbuf_clone(PBUF_LINK, PBUF_RAM, q);
1028     } else {
1029       /* referencing the old pbuf is enough */
1030       p = q;
1031       pbuf_ref(p);
1032     }
1033     /* packet could be taken over? */
1034     if (p != NULL) {
1035       /* queue packet ... */
1036 #if ARP_QUEUEING
1037       struct etharp_q_entry *new_entry;
1038       /* allocate a new arp queue entry */
1039       new_entry = (struct etharp_q_entry *)memp_malloc(MEMP_ARP_QUEUE);
1040       if (new_entry != NULL) {
1041         unsigned int qlen = 0;
1042         new_entry->next = NULL;
1043         new_entry->p = p;
1044         if (arp_table[i].q != NULL) {
1045           /* queue was already existent, append the new entry to the end */
1046           struct etharp_q_entry *r;
1047           r = arp_table[i].q;
1048           qlen++;
1049           while (r->next != NULL) {
1050             r = r->next;
1051             qlen++;
1052           }
1053           r->next = new_entry;
1054         } else {
1055           /* queue did not exist, first item in queue */
1056           arp_table[i].q = new_entry;
1057         }
1058 #if ARP_QUEUE_LEN
1059         if (qlen >= ARP_QUEUE_LEN) {
1060           struct etharp_q_entry *old;
1061           old = arp_table[i].q;
1062           arp_table[i].q = arp_table[i].q->next;
1063           pbuf_free(old->p);
1064           memp_free(MEMP_ARP_QUEUE, old);
1065         }
1066 #endif
1067         LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: queued packet %p on ARP entry %"U16_F"\n", (void *)q, i));
1068         result = ERR_OK;
1069       } else {
1070         /* the pool MEMP_ARP_QUEUE is empty */
1071         pbuf_free(p);
1072         LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: could not queue a copy of PBUF_REF packet %p (out of memory)\n", (void *)q));
1073         result = ERR_MEM;
1074       }
1075 #else /* ARP_QUEUEING */
1076       /* always queue one packet per ARP request only, freeing a previously queued packet */
1077       if (arp_table[i].q != NULL) {
1078         LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: dropped previously queued packet %p for ARP entry %"U16_F"\n", (void *)q, (u16_t)i));
1079         pbuf_free(arp_table[i].q);
1080       }
1081       arp_table[i].q = p;
1082       result = ERR_OK;
1083       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: queued packet %p on ARP entry %"U16_F"\n", (void *)q, (u16_t)i));
1084 #endif /* ARP_QUEUEING */
1085     } else {
1086       ETHARP_STATS_INC(etharp.memerr);
1087       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: could not queue a copy of PBUF_REF packet %p (out of memory)\n", (void *)q));
1088       result = ERR_MEM;
1089     }
1090   }
1091   return result;
1092 }
1093 
1094 /**
1095  * Send a raw ARP packet (opcode and all addresses can be modified)
1096  *
1097  * @param netif the lwip network interface on which to send the ARP packet
1098  * @param ethsrc_addr the source MAC address for the ethernet header
1099  * @param ethdst_addr the destination MAC address for the ethernet header
1100  * @param hwsrc_addr the source MAC address for the ARP protocol header
1101  * @param ipsrc_addr the source IP address for the ARP protocol header
1102  * @param hwdst_addr the destination MAC address for the ARP protocol header
1103  * @param ipdst_addr the destination IP address for the ARP protocol header
1104  * @param opcode the type of the ARP packet
1105  * @return ERR_OK if the ARP packet has been sent
1106  *         ERR_MEM if the ARP packet couldn't be allocated
1107  *         any other err_t on failure
1108  */
1109 static err_t
1110 etharp_raw(struct netif *netif, const struct eth_addr *ethsrc_addr,
1111            const struct eth_addr *ethdst_addr,
1112            const struct eth_addr *hwsrc_addr, const ip4_addr_t *ipsrc_addr,
1113            const struct eth_addr *hwdst_addr, const ip4_addr_t *ipdst_addr,
1114            const u16_t opcode)
1115 {
1116   struct pbuf *p;
1117   err_t result = ERR_OK;
1118   struct etharp_hdr *hdr;
1119 
1120   LWIP_ASSERT("netif != NULL", netif != NULL);
1121 
1122   /* allocate a pbuf for the outgoing ARP request packet */
1123   p = pbuf_alloc(PBUF_LINK, SIZEOF_ETHARP_HDR, PBUF_RAM);
1124   /* could allocate a pbuf for an ARP request? */
1125   if (p == NULL) {
1126     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
1127                 ("etharp_raw: could not allocate pbuf for ARP request.\n"));
1128     ETHARP_STATS_INC(etharp.memerr);
1129     return ERR_MEM;
1130   }
1131   LWIP_ASSERT("check that first pbuf can hold struct etharp_hdr",
1132               (p->len >= SIZEOF_ETHARP_HDR));
1133 
1134   hdr = (struct etharp_hdr *)p->payload;
1135   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_raw: sending raw ARP packet.\n"));
1136   hdr->opcode = lwip_htons(opcode);
1137 
1138   LWIP_ASSERT("netif->hwaddr_len must be the same as ETH_HWADDR_LEN for etharp!",
1139               (netif->hwaddr_len == ETH_HWADDR_LEN));
1140 
1141   /* Write the ARP MAC-Addresses */
1142   SMEMCPY(&hdr->shwaddr, hwsrc_addr, ETH_HWADDR_LEN);
1143   SMEMCPY(&hdr->dhwaddr, hwdst_addr, ETH_HWADDR_LEN);
1144   /* Copy struct ip4_addr_wordaligned to aligned ip4_addr, to support compilers without
1145    * structure packing. */
1146   IPADDR_WORDALIGNED_COPY_FROM_IP4_ADDR_T(&hdr->sipaddr, ipsrc_addr);
1147   IPADDR_WORDALIGNED_COPY_FROM_IP4_ADDR_T(&hdr->dipaddr, ipdst_addr);
1148 
1149   hdr->hwtype = PP_HTONS(LWIP_IANA_HWTYPE_ETHERNET);
1150   hdr->proto = PP_HTONS(ETHTYPE_IP);
1151   /* set hwlen and protolen */
1152   hdr->hwlen = ETH_HWADDR_LEN;
1153   hdr->protolen = sizeof(ip4_addr_t);
1154 
1155   /* send ARP query */
1156 #if LWIP_AUTOIP
1157   /* If we are using Link-Local, all ARP packets that contain a Link-Local
1158    * 'sender IP address' MUST be sent using link-layer broadcast instead of
1159    * link-layer unicast. (See RFC3927 Section 2.5, last paragraph) */
1160   if (ip4_addr_islinklocal(ipsrc_addr)) {
1161     ethernet_output(netif, p, ethsrc_addr, &ethbroadcast, ETHTYPE_ARP);
1162   } else
1163 #endif /* LWIP_AUTOIP */
1164   {
1165     ethernet_output(netif, p, ethsrc_addr, ethdst_addr, ETHTYPE_ARP);
1166   }
1167 
1168   ETHARP_STATS_INC(etharp.xmit);
1169   /* free ARP query packet */
1170   pbuf_free(p);
1171   p = NULL;
1172   /* could not allocate pbuf for ARP request */
1173 
1174   return result;
1175 }
1176 
1177 /**
1178  * Send an ARP request packet asking for ipaddr to a specific eth address.
1179  * Used to send unicast request to refresh the ARP table just before an entry
1180  * times out
1181  *
1182  * @param netif the lwip network interface on which to send the request
1183  * @param ipaddr the IP address for which to ask
1184  * @param hw_dst_addr the ethernet address to send this packet to
1185  * @return ERR_OK if the request has been sent
1186  *         ERR_MEM if the ARP packet couldn't be allocated
1187  *         any other err_t on failure
1188  */
1189 static err_t
1190 etharp_request_dst(struct netif *netif, const ip4_addr_t *ipaddr, const struct eth_addr *hw_dst_addr)
1191 {
1192   return etharp_raw(netif, (struct eth_addr *)netif->hwaddr, hw_dst_addr,
1193                     (struct eth_addr *)netif->hwaddr, netif_ip4_addr(netif), &ethzero,
1194                     ipaddr, ARP_REQUEST);
1195 }
1196 
1197 /**
1198  * Send an ARP request packet asking for ipaddr.
1199  *
1200  * @param netif the lwip network interface on which to send the request
1201  * @param ipaddr the IP address for which to ask
1202  * @return ERR_OK if the request has been sent
1203  *         ERR_MEM if the ARP packet couldn't be allocated
1204  *         any other err_t on failure
1205  */
1206 err_t
1207 etharp_request(struct netif *netif, const ip4_addr_t *ipaddr)
1208 {
1209   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_request: sending ARP request.\n"));
1210   return etharp_request_dst(netif, ipaddr, &ethbroadcast);
1211 }
1212 
1213 #if LWIP_ACD
1214 /**
1215  * Send an ARP request packet probing for an ipaddr.
1216  * Used to send probe messages for address conflict detection.
1217  *
1218  * @param netif the lwip network interface on which to send the request
1219  * @param ipaddr the IP address to probe
1220  * @return ERR_OK if the request has been sent
1221  *         ERR_MEM if the ARP packet couldn't be allocated
1222  *         any other err_t on failure
1223  */
1224 err_t
1225 etharp_acd_probe(struct netif *netif, const ip4_addr_t *ipaddr)
1226 {
1227   return etharp_raw(netif, (struct eth_addr *)netif->hwaddr, &ethbroadcast,
1228                     (struct eth_addr *)netif->hwaddr, IP4_ADDR_ANY4, &ethzero,
1229                     ipaddr, ARP_REQUEST);
1230 }
1231 
1232 /**
1233  * Send an ARP request packet announcing an ipaddr.
1234  * Used to send announce messages for address conflict detection.
1235  *
1236  * @param netif the lwip network interface on which to send the request
1237  * @param ipaddr the IP address to announce
1238  * @return ERR_OK if the request has been sent
1239  *         ERR_MEM if the ARP packet couldn't be allocated
1240  *         any other err_t on failure
1241  */
1242 err_t
1243 etharp_acd_announce(struct netif *netif, const ip4_addr_t *ipaddr)
1244 {
1245   return etharp_raw(netif, (struct eth_addr *)netif->hwaddr, &ethbroadcast,
1246                     (struct eth_addr *)netif->hwaddr, ipaddr, &ethzero,
1247                     ipaddr, ARP_REQUEST);
1248 }
1249 #endif /* LWIP_ACD */
1250 
1251 #endif /* LWIP_IPV4 && LWIP_ARP */
1252