网络数据包头部在linux网络协议栈中的变化
2015-09-10 22:46
483 查看
接收时使用skb_pull()不断去掉各层协议头部；发送时使用skb_push()不断添加各层协议头部。
先说说接收：
再来看看发送过程中的填充头部：
先说说接收：
150 * eth_type_trans - determine the packet's protocol ID.
151 * @skb: received socket data
152 * @dev: receiving network device
153 *
154 * The rule here is that we
155 * assume 802.3 if the type field is short enough to be a length.
156 * This is normal practice and works for any 'now in use' protocol.
157 */
158 __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
159 {
160 struct ethhdr *eth;
161 unsigned char *rawp;
162
163 skb->dev = dev;
164 skb_reset_mac_header(skb);
165 skb_pull(skb, ETH_HLEN);
166 eth = eth_hdr(skb);
167
168 if (unlikely(is_multicast_ether_addr(eth->h_dest))) {
169 if (!compare_ether_addr_64bits(eth->h_dest, dev->broadcast))
170 skb->pkt_type = PACKET_BROADCAST;
171 else
172 skb->pkt_type = PACKET_MULTICAST;
173 }
174
175 /*
176 * This ALLMULTI check should be redundant by 1.4
177 * so don't forget to remove it.
178 *
179 * Seems, you forgot to remove it. All silly devices
180 * seems to set IFF_PROMISC.
181 */
182
183 else if (1 /*dev->flags&IFF_PROMISC */ ) {
184 if (unlikely(compare_ether_addr_64bits(eth->h_dest, dev->dev_addr)))
185 skb->pkt_type = PACKET_OTHERHOST;
186 }
187
188 /*
189 * Some variants of DSA tagging don't have an ethertype field
190 * at all, so we check here whether one of those tagging
191 * variants has been configured on the receiving interface,
192 * and if so, set skb->protocol without looking at the packet.
193 */
194 if (netdev_uses_dsa_tags(dev))
195 return htons(ETH_P_DSA);
196 if (netdev_uses_trailer_tags(dev))
197 return htons(ETH_P_TRAILER);
198
199 if (ntohs(eth->h_proto) >= 1536)
200 return eth->h_proto;
201
202 rawp = skb->data;
203
204 /*
205 * This is a magic hack to spot IPX packets. Older Novell breaks
206 * the protocol design and runs IPX over 802.3 without an 802.2 LLC
207 * layer. We look for FFFF which isn't a used 802.2 SSAP/DSAP. This
208 * won't work for fault tolerant netware but does for the rest.
209 */
210 if (*(unsigned short *)rawp == 0xFFFF)
211 return htons(ETH_P_802_3);
212
213 /*
214 * Real 802.2 LLC
215 */
216 return htons(ETH_P_802_2);
217 }
218 EXPORT_SYMBOL(eth_type_trans);193 static int ip_local_deliver_finish(struct sk_buff *skb)
194 {
195 struct net *net = dev_net(skb->dev);
196
197 __skb_pull(skb, ip_hdrlen(skb));
198
199 /* Point into the IP datagram, just past the header. */
200 skb_reset_transport_header(skb);
201
202 rcu_read_lock();
203 {
204 int protocol = ip_hdr(skb)->protocol;
205 int hash, raw;
206 const struct net_protocol *ipprot;
207
208 resubmit:
209 raw = raw_local_deliver(skb, protocol);
210
211 hash = protocol & (MAX_INET_PROTOS - 1);
212 ipprot = rcu_dereference(inet_protos[hash]);
213 if (ipprot != NULL) {
214 int ret;
215
216 if (!net_eq(net, &init_net) && !ipprot->netns_ok) {
217 if (net_ratelimit())
218 printk("%s: proto %d isn't netns-ready\n",
219 __func__, protocol);
220 kfree_skb(skb);
221 goto out;
222 }
223
224 if (!ipprot->no_policy) {
225 if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) {
226 kfree_skb(skb);
227 goto out;
228 }
229 nf_reset(skb);
230 }
231 ret = ipprot->handler(skb);
232 if (ret < 0) {
233 protocol = -ret;
234 goto resubmit;
235 }
236 IP_INC_STATS_BH(net, IPSTATS_MIB_INDELIVERS);
237 } else {
238 if (!raw) {
239 if (xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) {
240 IP_INC_STATS_BH(net, IPSTATS_MIB_INUNKNOWNPROTOS);
241 icmp_send(skb, ICMP_DEST_UNREACH,
242 ICMP_PROT_UNREACH, 0);
243 }
244 } else
245 IP_INC_STATS_BH(net, IPSTATS_MIB_INDELIVERS);
246 kfree_skb(skb);
247 }
248 }
249 out:
250 rcu_read_unlock();
251
252 return 0;
253 }5224 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
5225 struct tcphdr *th, unsigned len)
5226 {
5227 struct tcp_sock *tp = tcp_sk(sk);
5228 int res;
5229
5230 /*
5231 * Header prediction.
5232 * The code loosely follows the one in the famous
5233 * "30 instruction TCP receive" Van Jacobson mail.
5234 *
5235 * Van's trick is to deposit buffers into socket queue
5236 * on a device interrupt, to call tcp_recv function
5237 * on the receive process context and checksum and copy
5238 * the buffer to user space. smart...
5239 *
5240 * Our current scheme is not silly either but we take the
5241 * extra cost of the net_bh soft interrupt processing...
5242 * We do checksum and copy also but from device to kernel.
5243 */
5244
5245 tp->rx_opt.saw_tstamp = 0;
5246
5247 /* pred_flags is 0xS?10 << 16 + snd_wnd
5248 * if header_prediction is to be made
5249 * 'S' will always be tp->tcp_header_len >> 2
5250 * '?' will be 0 for the fast path, otherwise pred_flags is 0 to
5251 * turn it off (when there are holes in the receive
5252 * space for instance)
5253 * PSH flag is ignored.
5254 */
5255
5256 if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5257 TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5258 !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5259 int tcp_header_len = tp->tcp_header_len;
5260
5261 /* Timestamp header prediction: tcp_header_len
5262 * is automatically equal to th->doff*4 due to pred_flags
5263 * match.
5264 */
5265
5266 /* Check timestamp */
5267 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5268 /* No? Slow path! */
5269 if (!tcp_parse_aligned_timestamp(tp, th))
5270 goto slow_path;
5271
5272 /* If PAWS failed, check it more carefully in slow path */
5273 if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5274 goto slow_path;
5275
5276 /* DO NOT update ts_recent here, if checksum fails
5277 * and timestamp was corrupted part, it will result
5278 * in a hung connection since we will drop all
5279 * future packets due to the PAWS test.
5280 */
5281 }
5282
5283 if (len <= tcp_header_len) {
5284 /* Bulk data transfer: sender */
5285 if (len == tcp_header_len) {
5286 /* Predicted packet is in window by definition.
5287 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5288 * Hence, check seq<=rcv_wup reduces to:
5289 */
5290 if (tcp_header_len ==
5291 (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5292 tp->rcv_nxt == tp->rcv_wup)
5293 tcp_store_ts_recent(tp);
5294
5295 /* We know that such packets are checksummed
5296 * on entry.
5297 */
5298 tcp_ack(sk, skb, 0);
5299 __kfree_skb(skb);
5300 tcp_data_snd_check(sk);
5301 return 0;
5302 } else { /* Header too small */
5303 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5304 goto discard;
5305 }
5306 } else {
5307 int eaten = 0;
5308 int copied_early = 0;
5309
5310 if (tp->copied_seq == tp->rcv_nxt &&
5311 len - tcp_header_len <= tp->ucopy.len) {
5312 #ifdef CONFIG_NET_DMA
5313 if (tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
5314 copied_early = 1;
5315 eaten = 1;
5316 }
5317 #endif
5318 if (tp->ucopy.task == current &&
5319 sock_owned_by_user(sk) && !copied_early) {
5320 __set_current_state(TASK_RUNNING);
5321
5322 if (!tcp_copy_to_iovec(sk, skb, tcp_header_len))
5323 eaten = 1;
5324 }
5325 if (eaten) {
5326 /* Predicted packet is in window by definition.
5327 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5328 * Hence, check seq<=rcv_wup reduces to:
5329 */
5330 if (tcp_header_len ==
5331 (sizeof(struct tcphdr) +
5332 TCPOLEN_TSTAMP_ALIGNED) &&
5333 tp->rcv_nxt == tp->rcv_wup)
5334 tcp_store_ts_recent(tp);
5335
5336 tcp_rcv_rtt_measure_ts(sk, skb);
5337
5338 __skb_pull(skb, tcp_header_len);
5339 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
5340 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITSTOUSER);
5341 }
5342 if (copied_early)
5343 tcp_cleanup_rbuf(sk, skb->len);
5344 }
5345 if (!eaten) {
5346 if (tcp_checksum_complete_user(sk, skb))
5347 goto csum_error;
5348
5349 /* Predicted packet is in window by definition.
5350 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5351 * Hence, check seq<=rcv_wup reduces to:
5352 */
5353 if (tcp_header_len ==
5354 (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5355 tp->rcv_nxt == tp->rcv_wup)
5356 tcp_store_ts_recent(tp);
5357
5358 tcp_rcv_rtt_measure_ts(sk, skb);
5359
5360 if ((int)skb->truesize > sk->sk_forward_alloc)
5361 goto step5;
5362
5363 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
5364
5365 /* Bulk data transfer: receiver */
5366 __skb_pull(skb, tcp_header_len);
5367 __skb_queue_tail(&sk->sk_receive_queue, skb);
5368 skb_set_owner_r(skb, sk);
5369 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
5370 }
5371
5372 tcp_event_data_recv(sk, skb);
5373
5374 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5375 /* Well, only one small jumplet in fast path... */
5376 tcp_ack(sk, skb, FLAG_DATA);
5377 tcp_data_snd_check(sk);
5378 if (!inet_csk_ack_scheduled(sk))
5379 goto no_ack;
5380 }
5381
5382 if (!copied_early || tp->rcv_nxt != tp->rcv_wup)
5383 __tcp_ack_snd_check(sk, 0);
5384 no_ack:
5385 #ifdef CONFIG_NET_DMA
5386 if (copied_early)
5387 __skb_queue_tail(&sk->sk_async_wait_queue, skb);
5388 else
5389 #endif
5390 if (eaten)
5391 __kfree_skb(skb);
5392 else
5393 sk->sk_data_ready(sk, 0);
5394 return 0;
5395 }
5396 }
5397
5398 slow_path:
5399 if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
5400 goto csum_error;
5401
5402 /*
5403 * Standard slow path.
5404 */
5405
5406 res = tcp_validate_incoming(sk, skb, th, 1);
5407 if (res <= 0)
5408 return -res;
5409
5410 step5:
5411 if (th->ack && tcp_ack(sk, skb, FLAG_SLOWPATH) < 0)
5412 goto discard;
5413
5414 tcp_rcv_rtt_measure_ts(sk, skb);
5415
5416 /* Process urgent data. */
5417 tcp_urg(sk, skb, th);
5418
5419 /* step 7: process the segment text */
5420 tcp_data_queue(sk, skb);
5421
5422 tcp_data_snd_check(sk);
5423 tcp_ack_snd_check(sk);
5424 return 0;
5425
5426 csum_error:
5427 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5428
5429 discard:
5430 __kfree_skb(skb);
5431 return 0;
5432 }再来看看发送过程中的填充头部：
777 /* This routine actually transmits TCP packets queued in by
778 * tcp_do_sendmsg(). This is used by both the initial
779 * transmission and possible later retransmissions.
780 * All SKB's seen here are completely headerless. It is our
781 * job to build the TCP header, and pass the packet down to
782 * IP so it can do the same plus pass the packet off to the
783 * device.
784 *
785 * We are working here with either a clone of the original
786 * SKB, or a fresh unique copy made by the retransmit engine.
787 */
788 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
789 gfp_t gfp_mask)
790 {
791 const struct inet_connection_sock *icsk = inet_csk(sk);
792 struct inet_sock *inet;
793 struct tcp_sock *tp;
794 struct tcp_skb_cb *tcb;
795 struct tcp_out_options opts;
796 unsigned tcp_options_size, tcp_header_size;
797 struct tcp_md5sig_key *md5;
798 struct tcphdr *th;
799 int err;
800
801 BUG_ON(!skb || !tcp_skb_pcount(skb));
802
803 /* If congestion control is doing timestamping, we must
804 * take such a timestamp before we potentially clone/copy.
805 */
806 if (icsk->icsk_ca_ops->flags & TCP_CONG_RTT_STAMP)
807 __net_timestamp(skb);
808
809 if (likely(clone_it)) {
810 if (unlikely(skb_cloned(skb)))
811 skb = pskb_copy(skb, gfp_mask);
812 else
813 skb = skb_clone(skb, gfp_mask);
814 if (unlikely(!skb))
815 return -ENOBUFS;
816 }
817
818 inet = inet_sk(sk);
819 tp = tcp_sk(sk);
820 tcb = TCP_SKB_CB(skb);
821 memset(&opts, 0, sizeof(opts));
822
823 if (unlikely(tcb->flags & TCPCB_FLAG_SYN))
824 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
825 else
826 tcp_options_size = tcp_established_options(sk, skb, &opts,
827 &md5);
828 tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
829
830 if (tcp_packets_in_flight(tp) == 0)
831 tcp_ca_event(sk, CA_EVENT_TX_START);
832
833 skb_push(skb, tcp_header_size);
834 skb_reset_transport_header(skb);
835 skb_set_owner_w(skb, sk);
836
837 /* Build TCP header and checksum it. */
838 th = tcp_hdr(skb);
839 th->source = inet->inet_sport;
840 th->dest = inet->inet_dport;
841 th->seq = htonl(tcb->seq);
842 th->ack_seq = htonl(tp->rcv_nxt);
843 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
844 tcb->flags);
845
846 if (unlikely(tcb->flags & TCPCB_FLAG_SYN)) {
847 /* RFC1323: The window in SYN & SYN/ACK segments
848 * is never scaled.
849 */
850 th->window = htons(min(tp->rcv_wnd, 65535U));
851 } else {
852 th->window = htons(tcp_select_window(sk));
853 }
854 th->check = 0;
855 th->urg_ptr = 0;
856
857 /* The urg_mode check is necessary during a below snd_una win probe */
858 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
859 if (before(tp->snd_up, tcb->seq + 0x10000)) {
860 th->urg_ptr = htons(tp->snd_up - tcb->seq);
861 th->urg = 1;
862 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
863 th->urg_ptr = 0xFFFF;
864 th->urg = 1;
865 }
866 }
867
868 tcp_options_write((__be32 *)(th + 1), tp, &opts);
869 if (likely((tcb->flags & TCPCB_FLAG_SYN) == 0))
870 TCP_ECN_send(sk, skb, tcp_header_size);
871
872 #ifdef CONFIG_TCP_MD5SIG
873 /* Calculate the MD5 hash, as we have all we need now */
874 if (md5) {
875 sk->sk_route_caps &= ~NETIF_F_GSO_MASK;
876 tp->af_specific->calc_md5_hash(opts.hash_location,
877 md5, sk, NULL, skb);
878 }
879 #endif
880
881 icsk->icsk_af_ops->send_check(sk, skb->len, skb);
882
883 if (likely(tcb->flags & TCPCB_FLAG_ACK))
884 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
885
886 if (skb->len != tcp_header_size)
887 tcp_event_data_sent(tp, skb, sk);
888
889 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
890 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
891
892 err = icsk->icsk_af_ops->queue_xmit(skb, 0);
893 if (likely(err <= 0))
894 return err;
895
896 tcp_enter_cwr(sk, 1);
897
898 return net_xmit_eval(err);
899 }314 int ip_queue_xmit(struct sk_buff *skb, int ipfragok)
315 {
316 struct sock *sk = skb->sk;
317 struct inet_sock *inet = inet_sk(sk);
318 struct ip_options *opt = inet->opt;
319 struct rtable *rt;
320 struct iphdr *iph;
321
322 /* Skip all of this if the packet is already routed,
323 * f.e. by something like SCTP.
324 */
325 rt = skb_rtable(skb);
326 if (rt != NULL)
327 goto packet_routed;
328
329 /* Make sure we can route this packet. */
330 rt = (struct rtable *)__sk_dst_check(sk, 0);
331 if (rt == NULL) {
332 __be32 daddr;
333
334 /* Use correct destination address if we have options. */
335 daddr = inet->inet_daddr;
336 if(opt && opt->srr)
337 daddr = opt->faddr;
338
339 {
340 struct flowi fl = { .oif = sk->sk_bound_dev_if,
341 .mark = sk->sk_mark,
342 .nl_u = { .ip4_u =
343 { .daddr = daddr,
344 .saddr = inet->inet_saddr,
345 .tos = RT_CONN_FLAGS(sk) } },
346 .proto = sk->sk_protocol,
347 .flags = inet_sk_flowi_flags(sk),
348 .uli_u = { .ports =
349 { .sport = inet->inet_sport,
350 .dport = inet->inet_dport } } };
351
352 /* If this fails, retransmit mechanism of transport layer will
353 * keep trying until route appears or the connection times
354 * itself out.
355 */
356 security_sk_classify_flow(sk, &fl);
357 if (ip_route_output_flow(sock_net(sk), &rt, &fl, sk, 0))
358 goto no_route;
359 }
360 sk_setup_caps(sk, &rt->u.dst);
361 }
362 skb_dst_set(skb, dst_clone(&rt->u.dst));
363
364 packet_routed:
365 if (opt && opt->is_strictroute && rt->rt_dst != rt->rt_gateway)
366 goto no_route;
367
368 /* OK, we know where to send it, allocate and build IP header. */
369 skb_push(skb, sizeof(struct iphdr) + (opt ? opt->optlen : 0));
370 skb_reset_network_header(skb);
371 iph = ip_hdr(skb);
372 *((__be16 *)iph) = htons((4 << 12) | (5 << 8) | (inet->tos & 0xff));
373 if (ip_dont_fragment(sk, &rt->u.dst) && !ipfragok)
374 iph->frag_off = htons(IP_DF);
375 else
376 iph->frag_off = 0;
377 iph->ttl = ip_select_ttl(inet, &rt->u.dst);
378 iph->protocol = sk->sk_protocol;
379 iph->saddr = rt->rt_src;
380 iph->daddr = rt->rt_dst;
381 /* Transport layer set skb->h.foo itself. */
382
383 if (opt && opt->optlen) {
384 iph->ihl += opt->optlen >> 2;
385 ip_options_build(skb, opt, inet->inet_daddr, rt, 0);
386 }
387
388 ip_select_ident_more(iph, &rt->u.dst, sk,
389 (skb_shinfo(skb)->gso_segs ?: 1) - 1);
390
391 skb->priority = sk->sk_priority;
392 skb->mark = sk->sk_mark;
393
394 return ip_local_out(skb);
395
396 no_route:
397 IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTNOROUTES);
398 kfree_skb(skb);
399 return -EHOSTUNREACH;
400 }178 static inline int ip_finish_output2(struct sk_buff *skb)
179 {
180 struct dst_entry *dst = skb_dst(skb);
181 struct rtable *rt = (struct rtable *)dst;
182 struct net_device *dev = dst->dev;
183 unsigned int hh_len = LL_RESERVED_SPACE(dev);
184
185 if (rt->rt_type == RTN_MULTICAST) {
186 IP_UPD_PO_STATS(dev_net(dev), IPSTATS_MIB_OUTMCAST, skb->len);
187 } else if (rt->rt_type == RTN_BROADCAST)
188 IP_UPD_PO_STATS(dev_net(dev), IPSTATS_MIB_OUTBCAST, skb->len);
189
190 /* Be paranoid, rather than too clever. */
191 if (unlikely(skb_headroom(skb) < hh_len && dev->header_ops)) {
192 struct sk_buff *skb2;
193
194 skb2 = skb_realloc_headroom(skb, LL_RESERVED_SPACE(dev));
195 if (skb2 == NULL) {
196 kfree_skb(skb);
197 return -ENOMEM;
198 }
199 if (skb->sk)
200 skb_set_owner_w(skb2, skb->sk);
201 kfree_skb(skb);
202 skb = skb2;
203 }
204
205 if (dst->hh)
206 return neigh_hh_output(dst->hh, skb); //添加eth头部
207 else if (dst->neighbour)
208 return dst->neighbour->output(skb); //添加eth头部
209
210 if (net_ratelimit())
211 printk(KERN_DEBUG "ip_finish_output2: No header cache and no neighbour!\n");
212 kfree_skb(skb);
213 return -EINVAL;
214 }//以太网头部填充函数之一
302 static inline int neigh_hh_output(struct hh_cache *hh, struct sk_buff *skb)
303 {
304 unsigned seq;
305 int hh_len;
306
307 do {
308 int hh_alen;
309
310 seq = read_seqbegin(&hh->hh_lock);
311 hh_len = hh->hh_len;
312 hh_alen = HH_DATA_ALIGN(hh_len);
313 memcpy(skb->data - hh_alen, hh->hh_data, hh_alen);
314 } while (read_seqretry(&hh->hh_lock, seq));
315
316 skb_push(skb, hh_len);
317 return hh->hh_output(skb);
318 }//以太网头部填充函数之二
1195 int neigh_resolve_output(struct sk_buff *skb)
1196 {
1197 struct dst_entry *dst = skb_dst(skb);
1198 struct neighbour *neigh;
1199 int rc = 0;
1200
1201 if (!dst || !(neigh = dst->neighbour))
1202 goto discard;
1203
1204 __skb_pull(skb, skb_network_offset(skb));
1205
1206 if (!neigh_event_send(neigh, skb)) {
1207 int err;
1208 struct net_device *dev = neigh->dev;
1209 if (dev->header_ops->cache && !dst->hh) {
1210 write_lock_bh(&neigh->lock);
1211 if (!dst->hh)
1212 neigh_hh_init(neigh, dst, dst->ops->protocol);
1213 err = dev_hard_header(skb, dev, ntohs(skb->protocol),
1214 neigh->ha, NULL, skb->len);
1215 write_unlock_bh(&neigh->lock);
1216 } else {
1217 read_lock_bh(&neigh->lock);
1218 err = dev_hard_header(skb, dev, ntohs(skb->protocol),
1219 neigh->ha, NULL, skb->len);
1220 read_unlock_bh(&neigh->lock);
1221 }
1222 if (err >= 0)
1223 rc = neigh->ops->queue_xmit(skb);
1224 else
1225 goto out_kfree_skb;
1226 }
1227 out:
1228 return rc;
1229 discard:
1230 NEIGH_PRINTK1("neigh_resolve_output: dst=%p neigh=%p\n",
1231 dst, dst ? dst->neighbour : NULL);
1232 out_kfree_skb:
1233 rc = -EINVAL;
1234 kfree_skb(skb);
1235 goto out;
1236 }
1237 EXPORT_SYMBOL(neigh_resolve_output);1280 static inline int dev_hard_header(struct sk_buff *skb, struct net_device *dev,
1281 unsigned short type,
1282 const void *daddr, const void *saddr,
1283 unsigned len)
1284 {
1285 if (!dev->header_ops || !dev->header_ops->create)
1286 return 0;
1287
1288 return dev->header_ops->create(skb, dev, type, daddr, saddr, len);//调用eth_header
1289 }79 int eth_header(struct sk_buff *skb, struct net_device *dev,
80 unsigned short type,
81 const void *daddr, const void *saddr, unsigned len)
82 {
83 struct ethhdr *eth = (struct ethhdr *)skb_push(skb, ETH_HLEN);
84
85 if (type != ETH_P_802_3 && type != ETH_P_802_2)
86 eth->h_proto = htons(type);
87 else
88 eth->h_proto = htons(len);
89
90 /*
91 * Set the source hardware address.
92 */
93
94 if (!saddr)
95 saddr = dev->dev_addr;
96 memcpy(eth->h_source, saddr, ETH_ALEN);
97
98 if (daddr) {
99 memcpy(eth->h_dest, daddr, ETH_ALEN);
100 return ETH_HLEN;
101 }
102
103 /*
104 * Anyway, the loopback-device should never use this function...
105 */
106
107 if (dev->flags & (IFF_LOOPBACK | IFF_NOARP)) {
108 memset(eth->h_dest, 0, ETH_ALEN);
109 return ETH_HLEN;
110 }
111
112 return -ETH_HLEN;
113 }
114 EXPORT_SYMBOL(eth_header);
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