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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  * Gratuitious 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_ARP || LWIP_ETHERNET
49 
50 #include "lwip/ip_addr.h"
51 #include "lwip/def.h"
52 #include "lwip/ip.h"
53 #include "lwip/stats.h"
54 #include "lwip/snmp.h"
55 #include "lwip/dhcp.h"
56 #include "lwip/autoip.h"
57 #include "netif/etharp.h"
58 
59 #if PPPOE_SUPPORT
60 #include "netif/ppp_oe.h"
61 #endif /* PPPOE_SUPPORT */
62 
63 #include <string.h>
64 
65 const struct eth_addr ethbroadcast = {{0xff,0xff,0xff,0xff,0xff,0xff}};
66 const struct eth_addr ethzero = {{0,0,0,0,0,0}};
67 
68 #if LWIP_ARP /* don't build if not configured for use in lwipopts.h */
69 
70 /** the time an ARP entry stays valid after its last update,
71  *  for ARP_TMR_INTERVAL = 5000, this is
72  *  (240 * 5) seconds = 20 minutes.
73  */
74 #define ARP_MAXAGE 240
75 /** the time an ARP entry stays pending after first request,
76  *  for ARP_TMR_INTERVAL = 5000, this is
77  *  (2 * 5) seconds = 10 seconds.
78  *
79  *  @internal Keep this number at least 2, otherwise it might
80  *  run out instantly if the timeout occurs directly after a request.
81  */
82 #define ARP_MAXPENDING 2
83 
84 #define HWTYPE_ETHERNET 1
85 
86 enum etharp_state {
87   ETHARP_STATE_EMPTY = 0,
88   ETHARP_STATE_PENDING,
89   ETHARP_STATE_STABLE
90 };
91 
92 struct etharp_entry {
93 #if ARP_QUEUEING
94   /** Pointer to queue of pending outgoing packets on this ARP entry. */
95   struct etharp_q_entry *q;
96 #else /* ARP_QUEUEING */
97   /** Pointer to a single pending outgoing packet on this ARP entry. */
98   struct pbuf *q;
99 #endif /* ARP_QUEUEING */
100   ip_addr_t ipaddr;
101   struct eth_addr ethaddr;
102 #if LWIP_SNMP
103   struct netif *netif;
104 #endif /* LWIP_SNMP */
105   u8_t state;
106   u8_t ctime;
107 #if ETHARP_SUPPORT_STATIC_ENTRIES
108   u8_t static_entry;
109 #endif /* ETHARP_SUPPORT_STATIC_ENTRIES */
110 };
111 
112 static struct etharp_entry arp_table[ARP_TABLE_SIZE];
113 
114 #if !LWIP_NETIF_HWADDRHINT
115 static u8_t etharp_cached_entry;
116 #endif /* !LWIP_NETIF_HWADDRHINT */
117 
118 /** Try hard to create a new entry - we want the IP address to appear in
119     the cache (even if this means removing an active entry or so). */
120 #define ETHARP_FLAG_TRY_HARD     1
121 #define ETHARP_FLAG_FIND_ONLY    2
122 #define ETHARP_FLAG_STATIC_ENTRY 4
123 
124 #if LWIP_NETIF_HWADDRHINT
125 #define ETHARP_SET_HINT(netif, hint)  if (((netif) != NULL) && ((netif)->addr_hint != NULL))  \
126                                       *((netif)->addr_hint) = (hint);
127 #else /* LWIP_NETIF_HWADDRHINT */
128 #define ETHARP_SET_HINT(netif, hint)  (etharp_cached_entry = (hint))
129 #endif /* LWIP_NETIF_HWADDRHINT */
130 
131 static err_t update_arp_entry(struct netif *netif, ip_addr_t *ipaddr, struct eth_addr *ethaddr, u8_t flags);
132 
133 
134 /* Some checks, instead of etharp_init(): */
135 #if (LWIP_ARP && (ARP_TABLE_SIZE > 0x7f))
136   #error "ARP_TABLE_SIZE must fit in an s8_t, you have to reduce it in your lwipopts.h"
137 #endif
138 
139 
140 #if ARP_QUEUEING
141 /**
142  * Free a complete queue of etharp entries
143  *
144  * @param q a qeueue of etharp_q_entry's to free
145  */
146 static void
free_etharp_q(struct etharp_q_entry * q)147 free_etharp_q(struct etharp_q_entry *q)
148 {
149   struct etharp_q_entry *r;
150   LWIP_ASSERT("q != NULL", q != NULL);
151   LWIP_ASSERT("q->p != NULL", q->p != 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
free_entry(int i)169 free_entry(int i)
170 {
171   /* remove from SNMP ARP index tree */
172   snmp_delete_arpidx_tree(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_timer: 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 #if ETHARP_SUPPORT_STATIC_ENTRIES
183   arp_table[i].static_entry = 0;
184 #endif /* ETHARP_SUPPORT_STATIC_ENTRIES */
185 #ifdef LWIP_DEBUG
186   /* for debugging, clean out the complete entry */
187   arp_table[i].ctime = 0;
188 #if LWIP_SNMP
189   arp_table[i].netif = NULL;
190 #endif /* LWIP_SNMP */
191   ip_addr_set_zero(&arp_table[i].ipaddr);
192   arp_table[i].ethaddr = ethzero;
193 #endif /* LWIP_DEBUG */
194 }
195 
196 /**
197  * Clears expired entries in the ARP table.
198  *
199  * This function should be called every ETHARP_TMR_INTERVAL milliseconds (5 seconds),
200  * in order to expire entries in the ARP table.
201  */
202 void
etharp_tmr(void)203 etharp_tmr(void)
204 {
205   u8_t i;
206 
207   LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer\n"));
208   /* remove expired entries from the ARP table */
209   for (i = 0; i < ARP_TABLE_SIZE; ++i) {
210     u8_t state = arp_table[i].state;
211     if (state != ETHARP_STATE_EMPTY
212 #if ETHARP_SUPPORT_STATIC_ENTRIES
213       && (arp_table[i].static_entry == 0)
214 #endif /* ETHARP_SUPPORT_STATIC_ENTRIES */
215       ) {
216       arp_table[i].ctime++;
217       if ((arp_table[i].ctime >= ARP_MAXAGE) ||
218           ((arp_table[i].state == ETHARP_STATE_PENDING)  &&
219            (arp_table[i].ctime >= ARP_MAXPENDING))) {
220         /* pending or stable entry has become old! */
221         LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer: expired %s entry %"U16_F".\n",
222              arp_table[i].state == ETHARP_STATE_STABLE ? "stable" : "pending", (u16_t)i));
223         /* clean up entries that have just been expired */
224         free_entry(i);
225       }
226 #if ARP_QUEUEING
227       /* still pending entry? (not expired) */
228       if (arp_table[i].state == ETHARP_STATE_PENDING) {
229         /* resend an ARP query here? */
230       }
231 #endif /* ARP_QUEUEING */
232     }
233   }
234 }
235 
236 /**
237  * Search the ARP table for a matching or new entry.
238  *
239  * If an IP address is given, return a pending or stable ARP entry that matches
240  * the address. If no match is found, create a new entry with this address set,
241  * but in state ETHARP_EMPTY. The caller must check and possibly change the
242  * state of the returned entry.
243  *
244  * If ipaddr is NULL, return a initialized new entry in state ETHARP_EMPTY.
245  *
246  * In all cases, attempt to create new entries from an empty entry. If no
247  * empty entries are available and ETHARP_FLAG_TRY_HARD flag is set, recycle
248  * old entries. Heuristic choose the least important entry for recycling.
249  *
250  * @param ipaddr IP address to find in ARP cache, or to add if not found.
251  * @param flags @see definition of ETHARP_FLAG_*
252  * @param netif netif related to this address (used for NETIF_HWADDRHINT)
253  *
254  * @return The ARP entry index that matched or is created, ERR_MEM if no
255  * entry is found or could be recycled.
256  */
257 static s8_t
find_entry(ip_addr_t * ipaddr,u8_t flags)258 find_entry(ip_addr_t *ipaddr, u8_t flags)
259 {
260   s8_t old_pending = ARP_TABLE_SIZE, old_stable = ARP_TABLE_SIZE;
261   s8_t empty = ARP_TABLE_SIZE;
262   u8_t i = 0, age_pending = 0, age_stable = 0;
263   /* oldest entry with packets on queue */
264   s8_t old_queue = ARP_TABLE_SIZE;
265   /* its age */
266   u8_t age_queue = 0;
267 
268   /**
269    * a) do a search through the cache, remember candidates
270    * b) select candidate entry
271    * c) create new entry
272    */
273 
274   /* a) in a single search sweep, do all of this
275    * 1) remember the first empty entry (if any)
276    * 2) remember the oldest stable entry (if any)
277    * 3) remember the oldest pending entry without queued packets (if any)
278    * 4) remember the oldest pending entry with queued packets (if any)
279    * 5) search for a matching IP entry, either pending or stable
280    *    until 5 matches, or all entries are searched for.
281    */
282 
283   for (i = 0; i < ARP_TABLE_SIZE; ++i) {
284     u8_t state = arp_table[i].state;
285     /* no empty entry found yet and now we do find one? */
286     if ((empty == ARP_TABLE_SIZE) && (state == ETHARP_STATE_EMPTY)) {
287       LWIP_DEBUGF(ETHARP_DEBUG, ("find_entry: found empty entry %"U16_F"\n", (u16_t)i));
288       /* remember first empty entry */
289       empty = i;
290     } else if (state != ETHARP_STATE_EMPTY) {
291       LWIP_ASSERT("state == ETHARP_STATE_PENDING || state == ETHARP_STATE_STABLE",
292         state == ETHARP_STATE_PENDING || state == ETHARP_STATE_STABLE);
293       /* if given, does IP address match IP address in ARP entry? */
294       if (ipaddr && ip_addr_cmp(ipaddr, &arp_table[i].ipaddr)) {
295         LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: found matching entry %"U16_F"\n", (u16_t)i));
296         /* found exact IP address match, simply bail out */
297         return i;
298       }
299       /* pending entry? */
300       if (state == ETHARP_STATE_PENDING) {
301         /* pending with queued packets? */
302         if (arp_table[i].q != NULL) {
303           if (arp_table[i].ctime >= age_queue) {
304             old_queue = i;
305             age_queue = arp_table[i].ctime;
306           }
307         } else
308         /* pending without queued packets? */
309         {
310           if (arp_table[i].ctime >= age_pending) {
311             old_pending = i;
312             age_pending = arp_table[i].ctime;
313           }
314         }
315       /* stable entry? */
316       } else if (state == ETHARP_STATE_STABLE) {
317 #if ETHARP_SUPPORT_STATIC_ENTRIES
318         /* don't record old_stable for static entries since they never expire */
319         if (arp_table[i].static_entry == 0)
320 #endif /* ETHARP_SUPPORT_STATIC_ENTRIES */
321         {
322           /* remember entry with oldest stable entry in oldest, its age in maxtime */
323           if (arp_table[i].ctime >= age_stable) {
324             old_stable = i;
325             age_stable = arp_table[i].ctime;
326           }
327         }
328       }
329     }
330   }
331   /* { we have no match } => try to create a new entry */
332 
333   /* don't create new entry, only search? */
334   if (((flags & ETHARP_FLAG_FIND_ONLY) != 0) ||
335       /* or no empty entry found and not allowed to recycle? */
336       ((empty == ARP_TABLE_SIZE) && ((flags & ETHARP_FLAG_TRY_HARD) == 0))) {
337     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: no empty entry found and not allowed to recycle\n"));
338     return (s8_t)ERR_MEM;
339   }
340 
341   /* b) choose the least destructive entry to recycle:
342    * 1) empty entry
343    * 2) oldest stable entry
344    * 3) oldest pending entry without queued packets
345    * 4) oldest pending entry with queued packets
346    *
347    * { ETHARP_FLAG_TRY_HARD is set at this point }
348    */
349 
350   /* 1) empty entry available? */
351   if (empty < ARP_TABLE_SIZE) {
352     i = empty;
353     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting empty entry %"U16_F"\n", (u16_t)i));
354   } else {
355     /* 2) found recyclable stable entry? */
356     if (old_stable < ARP_TABLE_SIZE) {
357       /* recycle oldest stable*/
358       i = old_stable;
359       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting oldest stable entry %"U16_F"\n", (u16_t)i));
360       /* no queued packets should exist on stable entries */
361       LWIP_ASSERT("arp_table[i].q == NULL", arp_table[i].q == NULL);
362     /* 3) found recyclable pending entry without queued packets? */
363     } else if (old_pending < ARP_TABLE_SIZE) {
364       /* recycle oldest pending */
365       i = old_pending;
366       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting oldest pending entry %"U16_F" (without queue)\n", (u16_t)i));
367     /* 4) found recyclable pending entry with queued packets? */
368     } else if (old_queue < ARP_TABLE_SIZE) {
369       /* recycle oldest pending (queued packets are free in free_entry) */
370       i = old_queue;
371       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: selecting oldest pending entry %"U16_F", freeing packet queue %p\n", (u16_t)i, (void *)(arp_table[i].q)));
372       /* no empty or recyclable entries found */
373     } else {
374       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("find_entry: no empty or recyclable entries found\n"));
375       return (s8_t)ERR_MEM;
376     }
377 
378     /* { empty or recyclable entry found } */
379     LWIP_ASSERT("i < ARP_TABLE_SIZE", i < ARP_TABLE_SIZE);
380     free_entry(i);
381   }
382 
383   LWIP_ASSERT("i < ARP_TABLE_SIZE", i < ARP_TABLE_SIZE);
384   LWIP_ASSERT("arp_table[i].state == ETHARP_STATE_EMPTY",
385     arp_table[i].state == ETHARP_STATE_EMPTY);
386 
387   /* IP address given? */
388   if (ipaddr != NULL) {
389     /* set IP address */
390     ip_addr_copy(arp_table[i].ipaddr, *ipaddr);
391   }
392   arp_table[i].ctime = 0;
393 #if ETHARP_SUPPORT_STATIC_ENTRIES
394   arp_table[i].static_entry = 0;
395 #endif /* ETHARP_SUPPORT_STATIC_ENTRIES */
396   return (err_t)i;
397 }
398 
399 /**
400  * Send an IP packet on the network using netif->linkoutput
401  * The ethernet header is filled in before sending.
402  *
403  * @params netif the lwIP network interface on which to send the packet
404  * @params p the packet to send, p->payload pointing to the (uninitialized) ethernet header
405  * @params src the source MAC address to be copied into the ethernet header
406  * @params dst the destination MAC address to be copied into the ethernet header
407  * @return ERR_OK if the packet was sent, any other err_t on failure
408  */
409 static err_t
etharp_send_ip(struct netif * netif,struct pbuf * p,struct eth_addr * src,struct eth_addr * dst)410 etharp_send_ip(struct netif *netif, struct pbuf *p, struct eth_addr *src, struct eth_addr *dst)
411 {
412   struct eth_hdr *ethhdr = (struct eth_hdr *)p->payload;
413 
414   LWIP_ASSERT("netif->hwaddr_len must be the same as ETHARP_HWADDR_LEN for etharp!",
415               (netif->hwaddr_len == ETHARP_HWADDR_LEN));
416   ETHADDR32_COPY(&ethhdr->dest, dst);
417   ETHADDR16_COPY(&ethhdr->src, src);
418   ethhdr->type = PP_HTONS(ETHTYPE_IP);
419   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_send_ip: sending packet %p\n", (void *)p));
420   /* send the packet */
421   return netif->linkoutput(netif, p);
422 }
423 
424 /**
425  * Update (or insert) a IP/MAC address pair in the ARP cache.
426  *
427  * If a pending entry is resolved, any queued packets will be sent
428  * at this point.
429  *
430  * @param netif netif related to this entry (used for NETIF_ADDRHINT)
431  * @param ipaddr IP address of the inserted ARP entry.
432  * @param ethaddr Ethernet address of the inserted ARP entry.
433  * @param flags @see definition of ETHARP_FLAG_*
434  *
435  * @return
436  * - ERR_OK Succesfully updated ARP cache.
437  * - ERR_MEM If we could not add a new ARP entry when ETHARP_FLAG_TRY_HARD was set.
438  * - ERR_ARG Non-unicast address given, those will not appear in ARP cache.
439  *
440  * @see pbuf_free()
441  */
442 static err_t
update_arp_entry(struct netif * netif,ip_addr_t * ipaddr,struct eth_addr * ethaddr,u8_t flags)443 update_arp_entry(struct netif *netif, ip_addr_t *ipaddr, struct eth_addr *ethaddr, u8_t flags)
444 {
445   s8_t i;
446   LWIP_ASSERT("netif->hwaddr_len == ETHARP_HWADDR_LEN", netif->hwaddr_len == ETHARP_HWADDR_LEN);
447   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("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",
448     ip4_addr1_16(ipaddr), ip4_addr2_16(ipaddr), ip4_addr3_16(ipaddr), ip4_addr4_16(ipaddr),
449     ethaddr->addr[0], ethaddr->addr[1], ethaddr->addr[2],
450     ethaddr->addr[3], ethaddr->addr[4], ethaddr->addr[5]));
451   /* non-unicast address? */
452   if (ip_addr_isany(ipaddr) ||
453       ip_addr_isbroadcast(ipaddr, netif) ||
454       ip_addr_ismulticast(ipaddr)) {
455     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("update_arp_entry: will not add non-unicast IP address to ARP cache\n"));
456     return ERR_ARG;
457   }
458   /* find or create ARP entry */
459   i = find_entry(ipaddr, flags);
460   /* bail out if no entry could be found */
461   if (i < 0) {
462     return (err_t)i;
463   }
464 
465 #if ETHARP_SUPPORT_STATIC_ENTRIES
466   if (flags & ETHARP_FLAG_STATIC_ENTRY) {
467     /* record static type */
468     arp_table[i].static_entry = 1;
469   }
470 #endif /* ETHARP_SUPPORT_STATIC_ENTRIES */
471 
472   /* mark it stable */
473   arp_table[i].state = ETHARP_STATE_STABLE;
474 
475 #if LWIP_SNMP
476   /* record network interface */
477   arp_table[i].netif = netif;
478 #endif /* LWIP_SNMP */
479   /* insert in SNMP ARP index tree */
480   snmp_insert_arpidx_tree(netif, &arp_table[i].ipaddr);
481 
482   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("update_arp_entry: updating stable entry %"S16_F"\n", (s16_t)i));
483   /* update address */
484   ETHADDR32_COPY(&arp_table[i].ethaddr, ethaddr);
485   /* reset time stamp */
486   arp_table[i].ctime = 0;
487   /* this is where we will send out queued packets! */
488 #if ARP_QUEUEING
489   while (arp_table[i].q != NULL) {
490     struct pbuf *p;
491     /* remember remainder of queue */
492     struct etharp_q_entry *q = arp_table[i].q;
493     /* pop first item off the queue */
494     arp_table[i].q = q->next;
495     /* get the packet pointer */
496     p = q->p;
497     /* now queue entry can be freed */
498     memp_free(MEMP_ARP_QUEUE, q);
499 #else /* ARP_QUEUEING */
500   if (arp_table[i].q != NULL) {
501     struct pbuf *p = arp_table[i].q;
502     arp_table[i].q = NULL;
503 #endif /* ARP_QUEUEING */
504     /* send the queued IP packet */
505     etharp_send_ip(netif, p, (struct eth_addr*)(netif->hwaddr), ethaddr);
506     /* free the queued IP packet */
507     pbuf_free(p);
508   }
509   return ERR_OK;
510 }
511 
512 #if ETHARP_SUPPORT_STATIC_ENTRIES
513 /** Add a new static entry to the ARP table. If an entry exists for the
514  * specified IP address, this entry is overwritten.
515  * If packets are queued for the specified IP address, they are sent out.
516  *
517  * @param ipaddr IP address for the new static entry
518  * @param ethaddr ethernet address for the new static entry
519  * @return @see return values of etharp_add_static_entry
520  */
521 err_t
522 etharp_add_static_entry(ip_addr_t *ipaddr, struct eth_addr *ethaddr)
523 {
524   struct netif *netif;
525   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",
526     ip4_addr1_16(ipaddr), ip4_addr2_16(ipaddr), ip4_addr3_16(ipaddr), ip4_addr4_16(ipaddr),
527     ethaddr->addr[0], ethaddr->addr[1], ethaddr->addr[2],
528     ethaddr->addr[3], ethaddr->addr[4], ethaddr->addr[5]));
529 
530   netif = ip_route(ipaddr);
531   if (netif == NULL) {
532     return ERR_RTE;
533   }
534 
535   return update_arp_entry(netif, ipaddr, ethaddr, ETHARP_FLAG_TRY_HARD | ETHARP_FLAG_STATIC_ENTRY);
536 }
537 
538 /** Remove a static entry from the ARP table previously added with a call to
539  * etharp_add_static_entry.
540  *
541  * @param ipaddr IP address of the static entry to remove
542  * @return ERR_OK: entry removed
543  *         ERR_MEM: entry wasn't found
544  *         ERR_ARG: entry wasn't a static entry but a dynamic one
545  */
546 err_t
547 etharp_remove_static_entry(ip_addr_t *ipaddr)
548 {
549   s8_t i;
550   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_remove_static_entry: %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
551     ip4_addr1_16(ipaddr), ip4_addr2_16(ipaddr), ip4_addr3_16(ipaddr), ip4_addr4_16(ipaddr)));
552 
553   /* find or create ARP entry */
554   i = find_entry(ipaddr, ETHARP_FLAG_FIND_ONLY);
555   /* bail out if no entry could be found */
556   if (i < 0) {
557     return (err_t)i;
558   }
559 
560   if ((arp_table[i].state != ETHARP_STATE_STABLE) ||
561     (arp_table[i].static_entry == 0)) {
562     /* entry wasn't a static entry, cannot remove it */
563     return ERR_ARG;
564   }
565   /* entry found, free it */
566   free_entry(i);
567   return ERR_OK;
568 }
569 #endif /* ETHARP_SUPPORT_STATIC_ENTRIES */
570 
571 /**
572  * Finds (stable) ethernet/IP address pair from ARP table
573  * using interface and IP address index.
574  * @note the addresses in the ARP table are in network order!
575  *
576  * @param netif points to interface index
577  * @param ipaddr points to the (network order) IP address index
578  * @param eth_ret points to return pointer
579  * @param ip_ret points to return pointer
580  * @return table index if found, -1 otherwise
581  */
582 s8_t
583 etharp_find_addr(struct netif *netif, ip_addr_t *ipaddr,
584          struct eth_addr **eth_ret, ip_addr_t **ip_ret)
585 {
586   s8_t i;
587 
588   LWIP_ASSERT("eth_ret != NULL && ip_ret != NULL",
589     eth_ret != NULL && ip_ret != NULL);
590 
591   LWIP_UNUSED_ARG(netif);
592 
593   i = find_entry(ipaddr, ETHARP_FLAG_FIND_ONLY);
594   if((i >= 0) && arp_table[i].state == ETHARP_STATE_STABLE) {
595       *eth_ret = &arp_table[i].ethaddr;
596       *ip_ret = &arp_table[i].ipaddr;
597       return i;
598   }
599   return -1;
600 }
601 
602 #if ETHARP_TRUST_IP_MAC
603 /**
604  * Updates the ARP table using the given IP packet.
605  *
606  * Uses the incoming IP packet's source address to update the
607  * ARP cache for the local network. The function does not alter
608  * or free the packet. This function must be called before the
609  * packet p is passed to the IP layer.
610  *
611  * @param netif The lwIP network interface on which the IP packet pbuf arrived.
612  * @param p The IP packet that arrived on netif.
613  *
614  * @return NULL
615  *
616  * @see pbuf_free()
617  */
618 static void
619 etharp_ip_input(struct netif *netif, struct pbuf *p)
620 {
621   struct eth_hdr *ethhdr;
622   struct ip_hdr *iphdr;
623   ip_addr_t iphdr_src;
624   LWIP_ERROR("netif != NULL", (netif != NULL), return;);
625 
626   /* Only insert an entry if the source IP address of the
627      incoming IP packet comes from a host on the local network. */
628   ethhdr = (struct eth_hdr *)p->payload;
629   iphdr = (struct ip_hdr *)((u8_t*)ethhdr + SIZEOF_ETH_HDR);
630 #if ETHARP_SUPPORT_VLAN
631   if (ethhdr->type == PP_HTONS(ETHTYPE_VLAN)) {
632     iphdr = (struct ip_hdr *)((u8_t*)ethhdr + SIZEOF_ETH_HDR + SIZEOF_VLAN_HDR);
633   }
634 #endif /* ETHARP_SUPPORT_VLAN */
635 
636   ip_addr_copy(iphdr_src, iphdr->src);
637 
638   /* source is not on the local network? */
639   if (!ip_addr_netcmp(&iphdr_src, &(netif->ip_addr), &(netif->netmask))) {
640     /* do nothing */
641     return;
642   }
643 
644   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_ip_input: updating ETHARP table.\n"));
645   /* update the source IP address in the cache, if present */
646   /* @todo We could use ETHARP_FLAG_TRY_HARD if we think we are going to talk
647    * back soon (for example, if the destination IP address is ours. */
648   update_arp_entry(netif, &iphdr_src, &(ethhdr->src), ETHARP_FLAG_FIND_ONLY);
649 }
650 #endif /* ETHARP_TRUST_IP_MAC */
651 
652 /**
653  * Responds to ARP requests to us. Upon ARP replies to us, add entry to cache
654  * send out queued IP packets. Updates cache with snooped address pairs.
655  *
656  * Should be called for incoming ARP packets. The pbuf in the argument
657  * is freed by this function.
658  *
659  * @param netif The lwIP network interface on which the ARP packet pbuf arrived.
660  * @param ethaddr Ethernet address of netif.
661  * @param p The ARP packet that arrived on netif. Is freed by this function.
662  *
663  * @return NULL
664  *
665  * @see pbuf_free()
666  */
667 static void
668 etharp_arp_input(struct netif *netif, struct eth_addr *ethaddr, struct pbuf *p)
669 {
670   struct etharp_hdr *hdr;
671   struct eth_hdr *ethhdr;
672   /* these are aligned properly, whereas the ARP header fields might not be */
673   ip_addr_t sipaddr, dipaddr;
674   u8_t for_us;
675 #if LWIP_AUTOIP
676   const u8_t * ethdst_hwaddr;
677 #endif /* LWIP_AUTOIP */
678 
679   LWIP_ERROR("netif != NULL", (netif != NULL), return;);
680 
681   /* drop short ARP packets: we have to check for p->len instead of p->tot_len here
682      since a struct etharp_hdr is pointed to p->payload, so it musn't be chained! */
683   if (p->len < SIZEOF_ETHARP_PACKET) {
684     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
685       ("etharp_arp_input: packet dropped, too short (%"S16_F"/%"S16_F")\n", p->tot_len,
686       (s16_t)SIZEOF_ETHARP_PACKET));
687     ETHARP_STATS_INC(etharp.lenerr);
688     ETHARP_STATS_INC(etharp.drop);
689     pbuf_free(p);
690     return;
691   }
692 
693   ethhdr = (struct eth_hdr *)p->payload;
694   hdr = (struct etharp_hdr *)((u8_t*)ethhdr + SIZEOF_ETH_HDR);
695 #if ETHARP_SUPPORT_VLAN
696   if (ethhdr->type == PP_HTONS(ETHTYPE_VLAN)) {
697     hdr = (struct etharp_hdr *)(((u8_t*)ethhdr) + SIZEOF_ETH_HDR + SIZEOF_VLAN_HDR);
698   }
699 #endif /* ETHARP_SUPPORT_VLAN */
700 
701   /* RFC 826 "Packet Reception": */
702   if ((hdr->hwtype != PP_HTONS(HWTYPE_ETHERNET)) ||
703       (hdr->hwlen != ETHARP_HWADDR_LEN) ||
704       (hdr->protolen != sizeof(ip_addr_t)) ||
705       (hdr->proto != PP_HTONS(ETHTYPE_IP)))  {
706     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
707       ("etharp_arp_input: packet dropped, wrong hw type, hwlen, proto, protolen or ethernet type (%"U16_F"/%"U16_F"/%"U16_F"/%"U16_F")\n",
708       hdr->hwtype, hdr->hwlen, hdr->proto, hdr->protolen));
709     ETHARP_STATS_INC(etharp.proterr);
710     ETHARP_STATS_INC(etharp.drop);
711     pbuf_free(p);
712     return;
713   }
714   ETHARP_STATS_INC(etharp.recv);
715 
716 #if LWIP_AUTOIP
717   /* We have to check if a host already has configured our random
718    * created link local address and continously check if there is
719    * a host with this IP-address so we can detect collisions */
720   autoip_arp_reply(netif, hdr);
721 #endif /* LWIP_AUTOIP */
722 
723   /* Copy struct ip_addr2 to aligned ip_addr, to support compilers without
724    * structure packing (not using structure copy which breaks strict-aliasing rules). */
725   IPADDR2_COPY(&sipaddr, &hdr->sipaddr);
726   IPADDR2_COPY(&dipaddr, &hdr->dipaddr);
727 
728   /* this interface is not configured? */
729   if (ip_addr_isany(&netif->ip_addr)) {
730     for_us = 0;
731   } else {
732     /* ARP packet directed to us? */
733     for_us = (u8_t)ip_addr_cmp(&dipaddr, &(netif->ip_addr));
734   }
735 
736   /* ARP message directed to us?
737       -> add IP address in ARP cache; assume requester wants to talk to us,
738          can result in directly sending the queued packets for this host.
739      ARP message not directed to us?
740       ->  update the source IP address in the cache, if present */
741   update_arp_entry(netif, &sipaddr, &(hdr->shwaddr),
742                    for_us ? ETHARP_FLAG_TRY_HARD : ETHARP_FLAG_FIND_ONLY);
743 
744   /* now act on the message itself */
745   switch (hdr->opcode) {
746   /* ARP request? */
747   case PP_HTONS(ARP_REQUEST):
748     /* ARP request. If it asked for our address, we send out a
749      * reply. In any case, we time-stamp any existing ARP entry,
750      * and possiby send out an IP packet that was queued on it. */
751 
752     LWIP_DEBUGF (ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: incoming ARP request\n"));
753     /* ARP request for our address? */
754     if (for_us) {
755 
756       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: replying to ARP request for our IP address\n"));
757       /* Re-use pbuf to send ARP reply.
758          Since we are re-using an existing pbuf, we can't call etharp_raw since
759          that would allocate a new pbuf. */
760       hdr->opcode = htons(ARP_REPLY);
761 
762       IPADDR2_COPY(&hdr->dipaddr, &hdr->sipaddr);
763       IPADDR2_COPY(&hdr->sipaddr, &netif->ip_addr);
764 
765       LWIP_ASSERT("netif->hwaddr_len must be the same as ETHARP_HWADDR_LEN for etharp!",
766                   (netif->hwaddr_len == ETHARP_HWADDR_LEN));
767 #if LWIP_AUTOIP
768       /* If we are using Link-Local, all ARP packets that contain a Link-Local
769        * 'sender IP address' MUST be sent using link-layer broadcast instead of
770        * link-layer unicast. (See RFC3927 Section 2.5, last paragraph) */
771       ethdst_hwaddr = ip_addr_islinklocal(&netif->ip_addr) ? (u8_t*)(ethbroadcast.addr) : hdr->shwaddr.addr;
772 #endif /* LWIP_AUTOIP */
773 
774       ETHADDR16_COPY(&hdr->dhwaddr, &hdr->shwaddr);
775 #if LWIP_AUTOIP
776       ETHADDR16_COPY(&ethhdr->dest, ethdst_hwaddr);
777 #else  /* LWIP_AUTOIP */
778       ETHADDR16_COPY(&ethhdr->dest, &hdr->shwaddr);
779 #endif /* LWIP_AUTOIP */
780       ETHADDR16_COPY(&hdr->shwaddr, ethaddr);
781       ETHADDR16_COPY(&ethhdr->src, ethaddr);
782 
783       /* hwtype, hwaddr_len, proto, protolen and the type in the ethernet header
784          are already correct, we tested that before */
785 
786       /* return ARP reply */
787       netif->linkoutput(netif, p);
788     /* we are not configured? */
789     } else if (ip_addr_isany(&netif->ip_addr)) {
790       /* { for_us == 0 and netif->ip_addr.addr == 0 } */
791       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: we are unconfigured, ARP request ignored.\n"));
792     /* request was not directed to us */
793     } else {
794       /* { for_us == 0 and netif->ip_addr.addr != 0 } */
795       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: ARP request was not for us.\n"));
796     }
797     break;
798   case PP_HTONS(ARP_REPLY):
799     /* ARP reply. We already updated the ARP cache earlier. */
800     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: incoming ARP reply\n"));
801 #if (LWIP_DHCP && DHCP_DOES_ARP_CHECK)
802     /* DHCP wants to know about ARP replies from any host with an
803      * IP address also offered to us by the DHCP server. We do not
804      * want to take a duplicate IP address on a single network.
805      * @todo How should we handle redundant (fail-over) interfaces? */
806     dhcp_arp_reply(netif, &sipaddr);
807 #endif /* (LWIP_DHCP && DHCP_DOES_ARP_CHECK) */
808     break;
809   default:
810     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: ARP unknown opcode type %"S16_F"\n", htons(hdr->opcode)));
811     ETHARP_STATS_INC(etharp.err);
812     break;
813   }
814   /* free ARP packet */
815   pbuf_free(p);
816 }
817 
818 /**
819  * Resolve and fill-in Ethernet address header for outgoing IP packet.
820  *
821  * For IP multicast and broadcast, corresponding Ethernet addresses
822  * are selected and the packet is transmitted on the link.
823  *
824  * For unicast addresses, the packet is submitted to etharp_query(). In
825  * case the IP address is outside the local network, the IP address of
826  * the gateway is used.
827  *
828  * @param netif The lwIP network interface which the IP packet will be sent on.
829  * @param q The pbuf(s) containing the IP packet to be sent.
830  * @param ipaddr The IP address of the packet destination.
831  *
832  * @return
833  * - ERR_RTE No route to destination (no gateway to external networks),
834  * or the return type of either etharp_query() or etharp_send_ip().
835  */
836 err_t
837 etharp_output(struct netif *netif, struct pbuf *q, ip_addr_t *ipaddr)
838 {
839   struct eth_addr *dest, mcastaddr;
840 
841   /* make room for Ethernet header - should not fail */
842   if (pbuf_header(q, sizeof(struct eth_hdr)) != 0) {
843     /* bail out */
844     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
845       ("etharp_output: could not allocate room for header.\n"));
846     LINK_STATS_INC(link.lenerr);
847     return ERR_BUF;
848   }
849 
850   /* assume unresolved Ethernet address */
851   dest = NULL;
852   /* Determine on destination hardware address. Broadcasts and multicasts
853    * are special, other IP addresses are looked up in the ARP table. */
854 
855   /* broadcast destination IP address? */
856   if (ip_addr_isbroadcast(ipaddr, netif)) {
857     /* broadcast on Ethernet also */
858     dest = (struct eth_addr *)&ethbroadcast;
859   /* multicast destination IP address? */
860   } else if (ip_addr_ismulticast(ipaddr)) {
861     /* Hash IP multicast address to MAC address.*/
862     mcastaddr.addr[0] = 0x01;
863     mcastaddr.addr[1] = 0x00;
864     mcastaddr.addr[2] = 0x5e;
865     mcastaddr.addr[3] = ip4_addr2(ipaddr) & 0x7f;
866     mcastaddr.addr[4] = ip4_addr3(ipaddr);
867     mcastaddr.addr[5] = ip4_addr4(ipaddr);
868     /* destination Ethernet address is multicast */
869     dest = &mcastaddr;
870   /* unicast destination IP address? */
871   } else {
872     /* outside local network? */
873     if (!ip_addr_netcmp(ipaddr, &(netif->ip_addr), &(netif->netmask)) &&
874         !ip_addr_islinklocal(ipaddr)) {
875 #if LWIP_AUTOIP
876       struct ip_hdr *iphdr = (struct ip_hdr*)((u8_t*)q->payload +
877         sizeof(struct eth_hdr));
878       /* According to RFC 3297, chapter 2.6.2 (Forwarding Rules), a packet with
879          a link-local source address must always be "directly to its destination
880          on the same physical link. The host MUST NOT send the packet to any
881          router for forwarding". */
882       if (!ip_addr_islinklocal(&iphdr->src))
883 #endif /* LWIP_AUTOIP */
884       {
885         /* interface has default gateway? */
886         if (!ip_addr_isany(&netif->gw)) {
887           /* send to hardware address of default gateway IP address */
888           ipaddr = &(netif->gw);
889         /* no default gateway available */
890         } else {
891           /* no route to destination error (default gateway missing) */
892           return ERR_RTE;
893         }
894       }
895     }
896 #if LWIP_NETIF_HWADDRHINT
897     if (netif->addr_hint != NULL) {
898       /* per-pcb cached entry was given */
899       u8_t etharp_cached_entry = *(netif->addr_hint);
900       if (etharp_cached_entry < ARP_TABLE_SIZE) {
901 #endif /* LWIP_NETIF_HWADDRHINT */
902         if ((arp_table[etharp_cached_entry].state == ETHARP_STATE_STABLE) &&
903             (ip_addr_cmp(ipaddr, &arp_table[etharp_cached_entry].ipaddr))) {
904           /* the per-pcb-cached entry is stable and the right one! */
905           ETHARP_STATS_INC(etharp.cachehit);
906           return etharp_send_ip(netif, q, (struct eth_addr*)(netif->hwaddr),
907             &arp_table[etharp_cached_entry].ethaddr);
908         }
909 #if LWIP_NETIF_HWADDRHINT
910       }
911     }
912 #endif /* LWIP_NETIF_HWADDRHINT */
913     /* queue on destination Ethernet address belonging to ipaddr */
914     return etharp_query(netif, ipaddr, q);
915   }
916 
917   /* continuation for multicast/broadcast destinations */
918   /* obtain source Ethernet address of the given interface */
919   /* send packet directly on the link */
920   return etharp_send_ip(netif, q, (struct eth_addr*)(netif->hwaddr), dest);
921 }
922 
923 /**
924  * Send an ARP request for the given IP address and/or queue a packet.
925  *
926  * If the IP address was not yet in the cache, a pending ARP cache entry
927  * is added and an ARP request is sent for the given address. The packet
928  * is queued on this entry.
929  *
930  * If the IP address was already pending in the cache, a new ARP request
931  * is sent for the given address. The packet is queued on this entry.
932  *
933  * If the IP address was already stable in the cache, and a packet is
934  * given, it is directly sent and no ARP request is sent out.
935  *
936  * If the IP address was already stable in the cache, and no packet is
937  * given, an ARP request is sent out.
938  *
939  * @param netif The lwIP network interface on which ipaddr
940  * must be queried for.
941  * @param ipaddr The IP address to be resolved.
942  * @param q If non-NULL, a pbuf that must be delivered to the IP address.
943  * q is not freed by this function.
944  *
945  * @note q must only be ONE packet, not a packet queue!
946  *
947  * @return
948  * - ERR_BUF Could not make room for Ethernet header.
949  * - ERR_MEM Hardware address unknown, and no more ARP entries available
950  *   to query for address or queue the packet.
951  * - ERR_MEM Could not queue packet due to memory shortage.
952  * - ERR_RTE No route to destination (no gateway to external networks).
953  * - ERR_ARG Non-unicast address given, those will not appear in ARP cache.
954  *
955  */
956 err_t
957 etharp_query(struct netif *netif, ip_addr_t *ipaddr, struct pbuf *q)
958 {
959   struct eth_addr * srcaddr = (struct eth_addr *)netif->hwaddr;
960   err_t result = ERR_MEM;
961   s8_t i; /* ARP entry index */
962 
963   /* non-unicast address? */
964   if (ip_addr_isbroadcast(ipaddr, netif) ||
965       ip_addr_ismulticast(ipaddr) ||
966       ip_addr_isany(ipaddr)) {
967     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: will not add non-unicast IP address to ARP cache\n"));
968     return ERR_ARG;
969   }
970 
971   /* find entry in ARP cache, ask to create entry if queueing packet */
972   i = find_entry(ipaddr, ETHARP_FLAG_TRY_HARD);
973 
974   /* could not find or create entry? */
975   if (i < 0) {
976     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: could not create ARP entry\n"));
977     if (q) {
978       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: packet dropped\n"));
979       ETHARP_STATS_INC(etharp.memerr);
980     }
981     return (err_t)i;
982   }
983 
984   /* mark a fresh entry as pending (we just sent a request) */
985   if (arp_table[i].state == ETHARP_STATE_EMPTY) {
986     arp_table[i].state = ETHARP_STATE_PENDING;
987   }
988 
989   /* { i is either a STABLE or (new or existing) PENDING entry } */
990   LWIP_ASSERT("arp_table[i].state == PENDING or STABLE",
991   ((arp_table[i].state == ETHARP_STATE_PENDING) ||
992    (arp_table[i].state == ETHARP_STATE_STABLE)));
993 
994   /* do we have a pending entry? or an implicit query request? */
995   if ((arp_table[i].state == ETHARP_STATE_PENDING) || (q == NULL)) {
996     /* try to resolve it; send out ARP request */
997     result = etharp_request(netif, ipaddr);
998     if (result != ERR_OK) {
999       /* ARP request couldn't be sent */
1000       /* We don't re-send arp request in etharp_tmr, but we still queue packets,
1001          since this failure could be temporary, and the next packet calling
1002          etharp_query again could lead to sending the queued packets. */
1003     }
1004     if (q == NULL) {
1005       return result;
1006     }
1007   }
1008 
1009   /* packet given? */
1010   LWIP_ASSERT("q != NULL", q != NULL);
1011   /* stable entry? */
1012   if (arp_table[i].state == ETHARP_STATE_STABLE) {
1013     /* we have a valid IP->Ethernet address mapping */
1014     ETHARP_SET_HINT(netif, i);
1015     /* send the packet */
1016     result = etharp_send_ip(netif, q, srcaddr, &(arp_table[i].ethaddr));
1017   /* pending entry? (either just created or already pending */
1018   } else if (arp_table[i].state == ETHARP_STATE_PENDING) {
1019     /* entry is still pending, queue the given packet 'q' */
1020     struct pbuf *p;
1021     int copy_needed = 0;
1022     /* IF q includes a PBUF_REF, PBUF_POOL or PBUF_RAM, we have no choice but
1023      * to copy the whole queue into a new PBUF_RAM (see bug #11400)
1024      * PBUF_ROMs can be left as they are, since ROM must not get changed. */
1025     p = q;
1026     while (p) {
1027       LWIP_ASSERT("no packet queues allowed!", (p->len != p->tot_len) || (p->next == 0));
1028       if(p->type != PBUF_ROM) {
1029         copy_needed = 1;
1030         break;
1031       }
1032       p = p->next;
1033     }
1034     if(copy_needed) {
1035       /* copy the whole packet into new pbufs */
1036       p = pbuf_alloc(PBUF_RAW, p->tot_len, PBUF_RAM);
1037       if(p != NULL) {
1038         if (pbuf_copy(p, q) != ERR_OK) {
1039           pbuf_free(p);
1040           p = NULL;
1041         }
1042       }
1043     } else {
1044       /* referencing the old pbuf is enough */
1045       p = q;
1046       pbuf_ref(p);
1047     }
1048     /* packet could be taken over? */
1049     if (p != NULL) {
1050       /* queue packet ... */
1051 #if ARP_QUEUEING
1052       struct etharp_q_entry *new_entry;
1053       /* allocate a new arp queue entry */
1054       new_entry = (struct etharp_q_entry *)memp_malloc(MEMP_ARP_QUEUE);
1055       if (new_entry != NULL) {
1056         new_entry->next = 0;
1057         new_entry->p = p;
1058         if(arp_table[i].q != NULL) {
1059           /* queue was already existent, append the new entry to the end */
1060           struct etharp_q_entry *r;
1061           r = arp_table[i].q;
1062           while (r->next != NULL) {
1063             r = r->next;
1064           }
1065           r->next = new_entry;
1066         } else {
1067           /* queue did not exist, first item in queue */
1068           arp_table[i].q = new_entry;
1069         }
1070         LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: queued packet %p on ARP entry %"S16_F"\n", (void *)q, (s16_t)i));
1071         result = ERR_OK;
1072       } else {
1073         /* the pool MEMP_ARP_QUEUE is empty */
1074         pbuf_free(p);
1075         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));
1076         result = ERR_MEM;
1077       }
1078 #else /* ARP_QUEUEING */
1079       /* always queue one packet per ARP request only, freeing a previously queued packet */
1080       if (arp_table[i].q != NULL) {
1081         LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: dropped previously queued packet %p for ARP entry %"S16_F"\n", (void *)q, (s16_t)i));
1082         pbuf_free(arp_table[i].q);
1083       }
1084       arp_table[i].q = p;
1085       result = ERR_OK;
1086       LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: queued packet %p on ARP entry %"S16_F"\n", (void *)q, (s16_t)i));
1087 #endif /* ARP_QUEUEING */
1088     } else {
1089       ETHARP_STATS_INC(etharp.memerr);
1090       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));
1091       result = ERR_MEM;
1092     }
1093   }
1094   return result;
1095 }
1096 
1097 /**
1098  * Send a raw ARP packet (opcode and all addresses can be modified)
1099  *
1100  * @param netif the lwip network interface on which to send the ARP packet
1101  * @param ethsrc_addr the source MAC address for the ethernet header
1102  * @param ethdst_addr the destination MAC address for the ethernet header
1103  * @param hwsrc_addr the source MAC address for the ARP protocol header
1104  * @param ipsrc_addr the source IP address for the ARP protocol header
1105  * @param hwdst_addr the destination MAC address for the ARP protocol header
1106  * @param ipdst_addr the destination IP address for the ARP protocol header
1107  * @param opcode the type of the ARP packet
1108  * @return ERR_OK if the ARP packet has been sent
1109  *         ERR_MEM if the ARP packet couldn't be allocated
1110  *         any other err_t on failure
1111  */
1112 #if !LWIP_AUTOIP
1113 static
1114 #endif /* LWIP_AUTOIP */
1115 err_t
1116 etharp_raw(struct netif *netif, const struct eth_addr *ethsrc_addr,
1117            const struct eth_addr *ethdst_addr,
1118            const struct eth_addr *hwsrc_addr, const ip_addr_t *ipsrc_addr,
1119            const struct eth_addr *hwdst_addr, const ip_addr_t *ipdst_addr,
1120            const u16_t opcode)
1121 {
1122   struct pbuf *p;
1123   err_t result = ERR_OK;
1124   struct eth_hdr *ethhdr;
1125   struct etharp_hdr *hdr;
1126 #if LWIP_AUTOIP
1127   const u8_t * ethdst_hwaddr;
1128 #endif /* LWIP_AUTOIP */
1129 
1130   /* allocate a pbuf for the outgoing ARP request packet */
1131   p = pbuf_alloc(PBUF_RAW, SIZEOF_ETHARP_PACKET, PBUF_RAM);
1132   /* could allocate a pbuf for an ARP request? */
1133   if (p == NULL) {
1134     LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
1135       ("etharp_raw: could not allocate pbuf for ARP request.\n"));
1136     ETHARP_STATS_INC(etharp.memerr);
1137     return ERR_MEM;
1138   }
1139   LWIP_ASSERT("check that first pbuf can hold struct etharp_hdr",
1140               (p->len >= SIZEOF_ETHARP_PACKET));
1141 
1142   ethhdr = (struct eth_hdr *)p->payload;
1143   hdr = (struct etharp_hdr *)((u8_t*)ethhdr + SIZEOF_ETH_HDR);
1144   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_raw: sending raw ARP packet.\n"));
1145   hdr->opcode = htons(opcode);
1146 
1147   LWIP_ASSERT("netif->hwaddr_len must be the same as ETHARP_HWADDR_LEN for etharp!",
1148               (netif->hwaddr_len == ETHARP_HWADDR_LEN));
1149 #if LWIP_AUTOIP
1150   /* If we are using Link-Local, all ARP packets that contain a Link-Local
1151    * 'sender IP address' MUST be sent using link-layer broadcast instead of
1152    * link-layer unicast. (See RFC3927 Section 2.5, last paragraph) */
1153   ethdst_hwaddr = ip_addr_islinklocal(ipsrc_addr) ? (u8_t*)(ethbroadcast.addr) : ethdst_addr->addr;
1154 #endif /* LWIP_AUTOIP */
1155   /* Write the ARP MAC-Addresses */
1156   ETHADDR16_COPY(&hdr->shwaddr, hwsrc_addr);
1157   ETHADDR16_COPY(&hdr->dhwaddr, hwdst_addr);
1158   /* Write the Ethernet MAC-Addresses */
1159 #if LWIP_AUTOIP
1160   ETHADDR16_COPY(&ethhdr->dest, ethdst_hwaddr);
1161 #else  /* LWIP_AUTOIP */
1162   ETHADDR16_COPY(&ethhdr->dest, ethdst_addr);
1163 #endif /* LWIP_AUTOIP */
1164   ETHADDR16_COPY(&ethhdr->src, ethsrc_addr);
1165   /* Copy struct ip_addr2 to aligned ip_addr, to support compilers without
1166    * structure packing. */
1167   IPADDR2_COPY(&hdr->sipaddr, ipsrc_addr);
1168   IPADDR2_COPY(&hdr->dipaddr, ipdst_addr);
1169 
1170   hdr->hwtype = PP_HTONS(HWTYPE_ETHERNET);
1171   hdr->proto = PP_HTONS(ETHTYPE_IP);
1172   /* set hwlen and protolen */
1173   hdr->hwlen = ETHARP_HWADDR_LEN;
1174   hdr->protolen = sizeof(ip_addr_t);
1175 
1176   ethhdr->type = PP_HTONS(ETHTYPE_ARP);
1177   /* send ARP query */
1178   result = netif->linkoutput(netif, p);
1179   ETHARP_STATS_INC(etharp.xmit);
1180   /* free ARP query packet */
1181   pbuf_free(p);
1182   p = NULL;
1183   /* could not allocate pbuf for ARP request */
1184 
1185   return result;
1186 }
1187 
1188 /**
1189  * Send an ARP request packet asking for ipaddr.
1190  *
1191  * @param netif the lwip network interface on which to send the request
1192  * @param ipaddr the IP address for which to ask
1193  * @return ERR_OK if the request has been sent
1194  *         ERR_MEM if the ARP packet couldn't be allocated
1195  *         any other err_t on failure
1196  */
1197 err_t
1198 etharp_request(struct netif *netif, ip_addr_t *ipaddr)
1199 {
1200   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_request: sending ARP request.\n"));
1201   return etharp_raw(netif, (struct eth_addr *)netif->hwaddr, &ethbroadcast,
1202                     (struct eth_addr *)netif->hwaddr, &netif->ip_addr, &ethzero,
1203                     ipaddr, ARP_REQUEST);
1204 }
1205 #endif /* LWIP_ARP */
1206 
1207 /**
1208  * Process received ethernet frames. Using this function instead of directly
1209  * calling ip_input and passing ARP frames through etharp in ethernetif_input,
1210  * the ARP cache is protected from concurrent access.
1211  *
1212  * @param p the recevied packet, p->payload pointing to the ethernet header
1213  * @param netif the network interface on which the packet was received
1214  */
1215 err_t
1216 ethernet_input(struct pbuf *p, struct netif *netif)
1217 {
1218   struct eth_hdr* ethhdr;
1219   u16_t type;
1220   s16_t ip_hdr_offset = SIZEOF_ETH_HDR;
1221 
1222   if (p->len <= SIZEOF_ETH_HDR) {
1223     /* a packet with only an ethernet header (or less) is not valid for us */
1224     ETHARP_STATS_INC(etharp.proterr);
1225     ETHARP_STATS_INC(etharp.drop);
1226     goto free_and_return;
1227   }
1228 
1229   /* points to packet payload, which starts with an Ethernet header */
1230   ethhdr = (struct eth_hdr *)p->payload;
1231   LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE,
1232     ("ethernet_input: dest:%"X8_F":%"X8_F":%"X8_F":%"X8_F":%"X8_F":%"X8_F", src:%"X8_F":%"X8_F":%"X8_F":%"X8_F":%"X8_F":%"X8_F", type:%"X16_F"\n",
1233      (unsigned)ethhdr->dest.addr[0], (unsigned)ethhdr->dest.addr[1], (unsigned)ethhdr->dest.addr[2],
1234      (unsigned)ethhdr->dest.addr[3], (unsigned)ethhdr->dest.addr[4], (unsigned)ethhdr->dest.addr[5],
1235      (unsigned)ethhdr->src.addr[0], (unsigned)ethhdr->src.addr[1], (unsigned)ethhdr->src.addr[2],
1236      (unsigned)ethhdr->src.addr[3], (unsigned)ethhdr->src.addr[4], (unsigned)ethhdr->src.addr[5],
1237      (unsigned)htons(ethhdr->type)));
1238 
1239   type = ethhdr->type;
1240 #if ETHARP_SUPPORT_VLAN
1241   if (type == PP_HTONS(ETHTYPE_VLAN)) {
1242     struct eth_vlan_hdr *vlan = (struct eth_vlan_hdr*)(((char*)ethhdr) + SIZEOF_ETH_HDR);
1243     if (p->len <= SIZEOF_ETH_HDR + SIZEOF_VLAN_HDR) {
1244       /* a packet with only an ethernet/vlan header (or less) is not valid for us */
1245       ETHARP_STATS_INC(etharp.proterr);
1246       ETHARP_STATS_INC(etharp.drop);
1247       goto free_and_return;
1248     }
1249 #ifdef ETHARP_VLAN_CHECK /* if not, allow all VLANs */
1250     if (VLAN_ID(vlan) != ETHARP_VLAN_CHECK) {
1251       /* silently ignore this packet: not for our VLAN */
1252       pbuf_free(p);
1253       return ERR_OK;
1254     }
1255 #endif /* ETHARP_VLAN_CHECK */
1256     type = vlan->tpid;
1257     ip_hdr_offset = SIZEOF_ETH_HDR + SIZEOF_VLAN_HDR;
1258   }
1259 #endif /* ETHARP_SUPPORT_VLAN */
1260 
1261 #if LWIP_ARP_FILTER_NETIF
1262   netif = LWIP_ARP_FILTER_NETIF_FN(p, netif, htons(type));
1263 #endif /* LWIP_ARP_FILTER_NETIF*/
1264 
1265   switch (type) {
1266 #if LWIP_ARP
1267     /* IP packet? */
1268     case PP_HTONS(ETHTYPE_IP):
1269       if (!(netif->flags & NETIF_FLAG_ETHARP)) {
1270         goto free_and_return;
1271       }
1272 #if ETHARP_TRUST_IP_MAC
1273       /* update ARP table */
1274       etharp_ip_input(netif, p);
1275 #endif /* ETHARP_TRUST_IP_MAC */
1276       /* skip Ethernet header */
1277       if(pbuf_header(p, -ip_hdr_offset)) {
1278         LWIP_ASSERT("Can't move over header in packet", 0);
1279         goto free_and_return;
1280       } else {
1281         /* pass to IP layer */
1282         ip_input(p, netif);
1283       }
1284       break;
1285 
1286     case PP_HTONS(ETHTYPE_ARP):
1287       if (!(netif->flags & NETIF_FLAG_ETHARP)) {
1288         goto free_and_return;
1289       }
1290       /* pass p to ARP module */
1291       etharp_arp_input(netif, (struct eth_addr*)(netif->hwaddr), p);
1292       break;
1293 #endif /* LWIP_ARP */
1294 #if PPPOE_SUPPORT
1295     case PP_HTONS(ETHTYPE_PPPOEDISC): /* PPP Over Ethernet Discovery Stage */
1296       pppoe_disc_input(netif, p);
1297       break;
1298 
1299     case PP_HTONS(ETHTYPE_PPPOE): /* PPP Over Ethernet Session Stage */
1300       pppoe_data_input(netif, p);
1301       break;
1302 #endif /* PPPOE_SUPPORT */
1303 
1304     default:
1305       ETHARP_STATS_INC(etharp.proterr);
1306       ETHARP_STATS_INC(etharp.drop);
1307       goto free_and_return;
1308   }
1309 
1310   /* This means the pbuf is freed or consumed,
1311      so the caller doesn't have to free it again */
1312   return ERR_OK;
1313 
1314 free_and_return:
1315   pbuf_free(p);
1316   return ERR_OK;
1317 }
1318 #endif /* LWIP_ARP || LWIP_ETHERNET */
1319