datapath/forward.c

   1 /*
   2  * Distributed under the terms of the GNU GPL version 2.
   3  * Copyright (c) 2007, 2008 The Board of Trustees of The Leland
   4  * Stanford Junior University
   5  */
   6
   7 #include <linux/netdevice.h>
   8 #include <linux/etherdevice.h>
   9 #include <linux/if_ether.h>
  10 #include <linux/if_vlan.h>
  11 #include <linux/in.h>
  12 #include <linux/ip.h>
  13 #include <linux/tcp.h>
  14 #include <linux/udp.h>
  15 #include <linux/in6.h>
  16 #include <asm/uaccess.h>
  17 #include <linux/types.h>
  18 #include <net/checksum.h>
  19 #include "forward.h"
  20 #include "datapath.h"
  21 #include "chain.h"
  22 #include "flow.h"
  23
  24 /* FIXME: do we need to use GFP_ATOMIC everywhere here? */
  25
  26 static int make_writable(struct sk_buff **);
  27
  28 static struct sk_buff *retrieve_skb(uint32_t id);
  29 static void discard_skb(uint32_t id);
  30
  31 /* 'skb' was received on port 'p', which may be a physical switch port, the
  32  * local port, or a null pointer.  Process it according to 'chain'.  Returns 0
  33  * if successful, in which case 'skb' is destroyed, or -ESRCH if there is no
  34  * matching flow, in which case 'skb' still belongs to the caller. */
  35 int run_flow_through_tables(struct sw_chain *chain, struct sk_buff *skb,
  36                             struct net_bridge_port *p)
  37 {
  38         /* Ethernet address used as the destination for STP frames. */
  39         static const uint8_t stp_eth_addr[ETH_ALEN]
  40                 = { 0x01, 0x80, 0xC2, 0x00, 0x00, 0x01 };
  41         struct sw_flow_key key;
  42         struct sw_flow *flow;
  43
  44         if (flow_extract(skb, p ? p->port_no : OFPP_NONE, &key)
  45             && (chain->dp->flags & OFPC_FRAG_MASK) == OFPC_FRAG_DROP) {
  46                 /* Drop fragment. */
  47                 kfree_skb(skb);
  48                 return 0;
  49         }
  50         if (p && p->flags & (OFPPFL_NO_RECV | OFPPFL_NO_RECV_STP) &&
  51             p->flags & (compare_ether_addr(key.dl_dst, stp_eth_addr)
  52                         ? OFPPFL_NO_RECV : OFPPFL_NO_RECV_STP)) {
  53                 kfree_skb(skb);
  54                 return 0;
  55         }
  56
  57         flow = chain_lookup(chain, &key);
  58         if (likely(flow != NULL)) {
  59                 flow_used(flow, skb);
  60                 execute_actions(chain->dp, skb, &key,
  61                                 flow->actions, flow->n_actions, 0);
  62                 return 0;
  63         } else {
  64                 return -ESRCH;
  65         }
  66 }
  67
  68 /* 'skb' was received on port 'p', which may be a physical switch port, the
  69  * local port, or a null pointer.  Process it according to 'chain', sending it
  70  * up to the controller if no flow matches.  Takes ownership of 'skb'. */
  71 void fwd_port_input(struct sw_chain *chain, struct sk_buff *skb,
  72                     struct net_bridge_port *p)
  73 {
  74         if (run_flow_through_tables(chain, skb, p))
  75                 dp_output_control(chain->dp, skb, fwd_save_skb(skb),
  76                                   chain->dp->miss_send_len,
  77                                   OFPR_NO_MATCH);
  78 }
  79
  80 static int do_output(struct datapath *dp, struct sk_buff *skb, size_t max_len,
  81                      int out_port, int ignore_no_fwd)
  82 {
  83         if (!skb)
  84                 return -ENOMEM;
  85         return (likely(out_port != OFPP_CONTROLLER)
  86                 ? dp_output_port(dp, skb, out_port, ignore_no_fwd)
  87                 : dp_output_control(dp, skb, fwd_save_skb(skb),
  88                                          max_len, OFPR_ACTION));
  89 }
  90
  91 void execute_actions(struct datapath *dp, struct sk_buff *skb,
  92                      const struct sw_flow_key *key,
  93                      const struct ofp_action *actions, int n_actions,
  94                      int ignore_no_fwd)
  95 {
  96         /* Every output action needs a separate clone of 'skb', but the common
  97          * case is just a single output action, so that doing a clone and
  98          * then freeing the original skbuff is wasteful.  So the following code
  99          * is slightly obscure just to avoid that. */
 100         int prev_port;
 101         size_t max_len=0;        /* Initialze to make compiler happy */
 102         uint16_t eth_proto;
 103         int i;
 104
 105         prev_port = -1;
 106         eth_proto = ntohs(key->dl_type);
 107
 108         for (i = 0; i < n_actions; i++) {
 109                 const struct ofp_action *a = &actions[i];
 110
 111                 if (prev_port != -1) {
 112                         do_output(dp, skb_clone(skb, GFP_ATOMIC),
 113                                   max_len, prev_port, ignore_no_fwd);
 114                         prev_port = -1;
 115                 }
 116
 117                 if (likely(a->type == htons(OFPAT_OUTPUT))) {
 118                         prev_port = ntohs(a->arg.output.port);
 119                         max_len = ntohs(a->arg.output.max_len);
 120                 } else {
 121                         if (!make_writable(&skb)) {
 122                                 if (net_ratelimit())
 123                                     printk("make_writable failed\n");
 124                                 break;
 125                         }
 126                         skb = execute_setter(skb, eth_proto, key, a);
 127                         if (!skb) {
 128                                 if (net_ratelimit())
 129                                         printk("execute_setter lost skb\n");
 130                                 return;
 131                         }
 132                 }
 133         }
 134         if (prev_port != -1)
 135                 do_output(dp, skb, max_len, prev_port, ignore_no_fwd);
 136         else
 137                 kfree_skb(skb);
 138 }
 139
 140 /* Updates 'sum', which is a field in 'skb''s data, given that a 4-byte field
 141  * covered by the sum has been changed from 'from' to 'to'.  If set,
 142  * 'pseudohdr' indicates that the field is in the TCP or UDP pseudo-header.
 143  * Based on nf_proto_csum_replace4. */
 144 static void update_csum(__sum16 *sum, struct sk_buff *skb,
 145                         __be32 from, __be32 to, int pseudohdr)
 146 {
 147         __be32 diff[] = { ~from, to };
 148         if (skb->ip_summed != CHECKSUM_PARTIAL) {
 149                 *sum = csum_fold(csum_partial((char *)diff, sizeof(diff),
 150                                 ~csum_unfold(*sum)));
 151                 if (skb->ip_summed == CHECKSUM_COMPLETE && pseudohdr)
 152                         skb->csum = ~csum_partial((char *)diff, sizeof(diff),
 153                                                 ~skb->csum);
 154         } else if (pseudohdr)
 155                 *sum = ~csum_fold(csum_partial((char *)diff, sizeof(diff),
 156                                 csum_unfold(*sum)));
 157 }
 158
 159 static void modify_nh(struct sk_buff *skb, uint16_t eth_proto,
 160                         uint8_t nw_proto, const struct ofp_action *a)
 161 {
 162         if (eth_proto == ETH_P_IP) {
 163                 struct iphdr *nh = ip_hdr(skb);
 164                 uint32_t new, *field;
 165
 166                 new = a->arg.nw_addr;
 167
 168                 if (a->type == htons(OFPAT_SET_NW_SRC))
 169                         field = &nh->saddr;
 170                 else
 171                         field = &nh->daddr;
 172
 173                 if (nw_proto == IPPROTO_TCP) {
 174                         struct tcphdr *th = tcp_hdr(skb);
 175                         update_csum(&th->check, skb, *field, new, 1);
 176                 } else if (nw_proto == IPPROTO_UDP) {
 177                         struct udphdr *th = udp_hdr(skb);
 178                         update_csum(&th->check, skb, *field, new, 1);
 179                 }
 180                 update_csum(&nh->check, skb, *field, new, 0);
 181                 *field = new;
 182         }
 183 }
 184
 185 static void modify_th(struct sk_buff *skb, uint16_t eth_proto,
 186                         uint8_t nw_proto, const struct ofp_action *a)
 187 {
 188         if (eth_proto == ETH_P_IP) {
 189                 uint16_t new, *field;
 190
 191                 new = a->arg.tp;
 192
 193                 if (nw_proto == IPPROTO_TCP) {
 194                         struct tcphdr *th = tcp_hdr(skb);
 195
 196                         if (a->type == htons(OFPAT_SET_TP_SRC))
 197                                 field = &th->source;
 198                         else
 199                                 field = &th->dest;
 200
 201                         update_csum(&th->check, skb, *field, new, 1);
 202                         *field = new;
 203                 } else if (nw_proto == IPPROTO_UDP) {
 204                         struct udphdr *th = udp_hdr(skb);
 205
 206                         if (a->type == htons(OFPAT_SET_TP_SRC))
 207                                 field = &th->source;
 208                         else
 209                                 field = &th->dest;
 210
 211                         update_csum(&th->check, skb, *field, new, 1);
 212                         *field = new;
 213                 }
 214         }
 215 }
 216
 217 static struct sk_buff *vlan_pull_tag(struct sk_buff *skb)
 218 {
 219         struct vlan_ethhdr *vh = vlan_eth_hdr(skb);
 220         struct ethhdr *eh;
 221
 222
 223         /* Verify we were given a vlan packet */
 224         if (vh->h_vlan_proto != htons(ETH_P_8021Q))
 225                 return skb;
 226
 227         memmove(skb->data + VLAN_HLEN, skb->data, 2 * VLAN_ETH_ALEN);
 228
 229         eh = (struct ethhdr *)skb_pull(skb, VLAN_HLEN);
 230
 231         skb->protocol = eh->h_proto;
 232         skb->mac_header += VLAN_HLEN;
 233
 234         return skb;
 235 }
 236
 237 static struct sk_buff *modify_vlan(struct sk_buff *skb,
 238                 const struct sw_flow_key *key, const struct ofp_action *a)
 239 {
 240         uint16_t new_id = ntohs(a->arg.vlan_id);
 241
 242         if (new_id != OFP_VLAN_NONE) {
 243                 if (key->dl_vlan != htons(OFP_VLAN_NONE)) {
 244                         /* Modify vlan id, but maintain other TCI values */
 245                         struct vlan_ethhdr *vh = vlan_eth_hdr(skb);
 246                         vh->h_vlan_TCI = (vh->h_vlan_TCI
 247                                         & ~(htons(VLAN_VID_MASK))) | a->arg.vlan_id;
 248                 } else  {
 249                         /* Add vlan header */
 250
 251                         /* xxx The vlan_put_tag function, doesn't seem to work
 252                          * xxx reliably when it attempts to use the hardware-accelerated
 253                          * xxx version.  We'll directly use the software version
 254                          * xxx until the problem can be diagnosed.
 255                          */
 256                         skb = __vlan_put_tag(skb, new_id);
 257                 }
 258         } else  {
 259                 /* Remove an existing vlan header if it exists */
 260                 vlan_pull_tag(skb);
 261         }
 262
 263         return skb;
 264 }
 265
 266 struct sk_buff *execute_setter(struct sk_buff *skb, uint16_t eth_proto,
 267                         const struct sw_flow_key *key, const struct ofp_action *a)
 268 {
 269         switch (ntohs(a->type)) {
 270         case OFPAT_SET_DL_VLAN:
 271                 skb = modify_vlan(skb, key, a);
 272                 break;
 273
 274         case OFPAT_SET_DL_SRC: {
 275                 struct ethhdr *eh = eth_hdr(skb);
 276                 memcpy(eh->h_source, a->arg.dl_addr, sizeof eh->h_source);
 277                 break;
 278         }
 279         case OFPAT_SET_DL_DST: {
 280                 struct ethhdr *eh = eth_hdr(skb);
 281                 memcpy(eh->h_dest, a->arg.dl_addr, sizeof eh->h_dest);
 282                 break;
 283         }
 284
 285         case OFPAT_SET_NW_SRC:
 286         case OFPAT_SET_NW_DST:
 287                 modify_nh(skb, eth_proto, key->nw_proto, a);
 288                 break;
 289
 290         case OFPAT_SET_TP_SRC:
 291         case OFPAT_SET_TP_DST:
 292                 modify_th(skb, eth_proto, key->nw_proto, a);
 293                 break;
 294
 295         default:
 296                 if (net_ratelimit())
 297                         printk("execute_setter: unknown action: %d\n", ntohs(a->type));
 298         }
 299
 300         return skb;
 301 }
 302
 303 static int
 304 recv_features_request(struct sw_chain *chain, const struct sender *sender,
 305                       const void *msg)
 306 {
 307         return dp_send_features_reply(chain->dp, sender);
 308 }
 309
 310 static int
 311 recv_get_config_request(struct sw_chain *chain, const struct sender *sender,
 312                         const void *msg)
 313 {
 314         return dp_send_config_reply(chain->dp, sender);
 315 }
 316
 317 static int
 318 recv_set_config(struct sw_chain *chain, const struct sender *sender,
 319                 const void *msg)
 320 {
 321         const struct ofp_switch_config *osc = msg;
 322         int flags;
 323
 324         flags = ntohs(osc->flags) & (OFPC_SEND_FLOW_EXP | OFPC_FRAG_MASK);
 325         if ((flags & OFPC_FRAG_MASK) != OFPC_FRAG_NORMAL
 326             && (flags & OFPC_FRAG_MASK) != OFPC_FRAG_DROP) {
 327                 flags = (flags & ~OFPC_FRAG_MASK) | OFPC_FRAG_DROP;
 328         }
 329         chain->dp->flags = flags;
 330
 331         chain->dp->miss_send_len = ntohs(osc->miss_send_len);
 332
 333         return 0;
 334 }
 335
 336 static int
 337 recv_packet_out(struct sw_chain *chain, const struct sender *sender,
 338                 const void *msg)
 339 {
 340         const struct ofp_packet_out *opo = msg;
 341         struct sk_buff *skb;
 342         struct vlan_ethhdr *mac;
 343         int nh_ofs;
 344         struct sw_flow_key key;
 345         int n_actions = ntohs(opo->n_actions);
 346         int act_len = n_actions * sizeof opo->actions[0];
 347
 348         if (act_len > (ntohs(opo->header.length) - sizeof *opo)) {
 349                 if (net_ratelimit())
 350                         printk("message too short for number of actions\n");
 351                 return -EINVAL;
 352         }
 353
 354         if (ntohl(opo->buffer_id) == (uint32_t) -1) {
 355                 int data_len = ntohs(opo->header.length) - sizeof *opo - act_len;
 356
 357                 /* FIXME: there is likely a way to reuse the data in msg. */
 358                 skb = alloc_skb(data_len, GFP_ATOMIC);
 359                 if (!skb)
 360                         return -ENOMEM;
 361
 362                 /* FIXME?  We don't reserve NET_IP_ALIGN or NET_SKB_PAD since
 363                  * we're just transmitting this raw without examining anything
 364                  * at those layers. */
 365                 memcpy(skb_put(skb, data_len), &opo->actions[n_actions], data_len);
 366
 367                 skb_set_mac_header(skb, 0);
 368                 mac = vlan_eth_hdr(skb);
 369                 if (likely(mac->h_vlan_proto != htons(ETH_P_8021Q)))
 370                         nh_ofs = sizeof(struct ethhdr);
 371                 else
 372                         nh_ofs = sizeof(struct vlan_ethhdr);
 373                 skb_set_network_header(skb, nh_ofs);
 374         } else {
 375                 skb = retrieve_skb(ntohl(opo->buffer_id));
 376                 if (!skb)
 377                         return -ESRCH;
 378         }
 379
 380         dp_set_origin(chain->dp, ntohs(opo->in_port), skb);
 381
 382         flow_extract(skb, ntohs(opo->in_port), &key);
 383         execute_actions(chain->dp, skb, &key, opo->actions, n_actions, 1);
 384
 385         return 0;
 386 }
 387
 388 static int
 389 recv_port_mod(struct sw_chain *chain, const struct sender *sender,
 390               const void *msg)
 391 {
 392         const struct ofp_port_mod *opm = msg;
 393
 394         dp_update_port_flags(chain->dp, opm);
 395
 396         return 0;
 397 }
 398
 399 static int
 400 recv_echo_request(struct sw_chain *chain, const struct sender *sender,
 401                   const void *msg)
 402 {
 403         return dp_send_echo_reply(chain->dp, sender, msg);
 404 }
 405
 406 static int
 407 recv_echo_reply(struct sw_chain *chain, const struct sender *sender,
 408                   const void *msg)
 409 {
 410         return 0;
 411 }
 412
 413 static int
 414 add_flow(struct sw_chain *chain, const struct ofp_flow_mod *ofm)
 415 {
 416         int error = -ENOMEM;
 417         int i;
 418         int n_actions;
 419         struct sw_flow *flow;
 420
 421
 422         /* To prevent loops, make sure there's no action to send to the
 423          * OFP_TABLE virtual port.
 424          */
 425         n_actions = (ntohs(ofm->header.length) - sizeof *ofm)
 426                         / sizeof *ofm->actions;
 427         for (i=0; i<n_actions; i++) {
 428                 const struct ofp_action *a = &ofm->actions[i];
 429
 430                 if (a->type == htons(OFPAT_OUTPUT)
 431                                         && (a->arg.output.port == htons(OFPP_TABLE)
 432                                                 || a->arg.output.port == htons(OFPP_NONE)
 433                                                 || a->arg.output.port == ofm->match.in_port)) {
 434                         /* xxx Send fancy new error message? */
 435                         goto error;
 436                 }
 437         }
 438
 439         /* Allocate memory. */
 440         flow = flow_alloc(n_actions, GFP_ATOMIC);
 441         if (flow == NULL)
 442                 goto error;
 443
 444         /* Fill out flow. */
 445         flow_extract_match(&flow->key, &ofm->match);
 446         flow->priority = flow->key.wildcards ? ntohs(ofm->priority) : -1;
 447         flow->idle_timeout = ntohs(ofm->idle_timeout);
 448         flow->hard_timeout = ntohs(ofm->hard_timeout);
 449         flow->used = jiffies;
 450         flow->n_actions = n_actions;
 451         flow->init_time = jiffies;
 452         flow->byte_count = 0;
 453         flow->packet_count = 0;
 454         spin_lock_init(&flow->lock);
 455         memcpy(flow->actions, ofm->actions, n_actions * sizeof *flow->actions);
 456
 457         /* Act. */
 458         error = chain_insert(chain, flow);
 459         if (error)
 460                 goto error_free_flow;
 461         error = 0;
 462         if (ntohl(ofm->buffer_id) != (uint32_t) -1) {
 463                 struct sk_buff *skb = retrieve_skb(ntohl(ofm->buffer_id));
 464                 if (skb) {
 465                         struct sw_flow_key key;
 466                         flow_used(flow, skb);
 467                         flow_extract(skb, ntohs(ofm->match.in_port), &key);
 468                         execute_actions(chain->dp, skb, &key, ofm->actions, n_actions, 0);
 469                 }
 470                 else
 471                         error = -ESRCH;
 472         }
 473         return error;
 474
 475 error_free_flow:
 476         flow_free(flow);
 477 error:
 478         if (ntohl(ofm->buffer_id) != (uint32_t) -1)
 479                 discard_skb(ntohl(ofm->buffer_id));
 480         return error;
 481 }
 482
 483 static int
 484 recv_flow(struct sw_chain *chain, const struct sender *sender, const void *msg)
 485 {
 486         const struct ofp_flow_mod *ofm = msg;
 487         uint16_t command = ntohs(ofm->command);
 488
 489         if (command == OFPFC_ADD) {
 490                 return add_flow(chain, ofm);
 491         }  else if (command == OFPFC_DELETE) {
 492                 struct sw_flow_key key;
 493                 flow_extract_match(&key, &ofm->match);
 494                 return chain_delete(chain, &key, 0, 0) ? 0 : -ESRCH;
 495         } else if (command == OFPFC_DELETE_STRICT) {
 496                 struct sw_flow_key key;
 497                 uint16_t priority;
 498                 flow_extract_match(&key, &ofm->match);
 499                 priority = key.wildcards ? ntohs(ofm->priority) : -1;
 500                 return chain_delete(chain, &key, priority, 1) ? 0 : -ESRCH;
 501         } else {
 502                 return -ENOTSUPP;
 503         }
 504 }
 505
 506 /* 'msg', which is 'length' bytes long, was received across Netlink from
 507  * 'sender'.  Apply it to 'chain'. */
 508 int
 509 fwd_control_input(struct sw_chain *chain, const struct sender *sender,
 510                   const void *msg, size_t length)
 511 {
 512
 513         struct openflow_packet {
 514                 size_t min_size;
 515                 int (*handler)(struct sw_chain *, const struct sender *,
 516                                const void *);
 517         };
 518
 519         static const struct openflow_packet packets[] = {
 520                 [OFPT_FEATURES_REQUEST] = {
 521                         sizeof (struct ofp_header),
 522                         recv_features_request,
 523                 },
 524                 [OFPT_GET_CONFIG_REQUEST] = {
 525                         sizeof (struct ofp_header),
 526                         recv_get_config_request,
 527                 },
 528                 [OFPT_SET_CONFIG] = {
 529                         sizeof (struct ofp_switch_config),
 530                         recv_set_config,
 531                 },
 532                 [OFPT_PACKET_OUT] = {
 533                         sizeof (struct ofp_packet_out),
 534                         recv_packet_out,
 535                 },
 536                 [OFPT_FLOW_MOD] = {
 537                         sizeof (struct ofp_flow_mod),
 538                         recv_flow,
 539                 },
 540                 [OFPT_PORT_MOD] = {
 541                         sizeof (struct ofp_port_mod),
 542                         recv_port_mod,
 543                 },
 544                 [OFPT_ECHO_REQUEST] = {
 545                         sizeof (struct ofp_header),
 546                         recv_echo_request,
 547                 },
 548                 [OFPT_ECHO_REPLY] = {
 549                         sizeof (struct ofp_header),
 550                         recv_echo_reply,
 551                 },
 552         };
 553
 554         struct ofp_header *oh;
 555
 556         oh = (struct ofp_header *) msg;
 557         if (oh->version != OFP_VERSION) {
 558                 dp_send_error_msg(chain->dp, sender, OFPET_BAD_REQUEST,
 559                                   OFPBRC_BAD_VERSION, msg, length);
 560                 return -EINVAL;
 561         }
 562         if (ntohs(oh->length) > length)
 563                 return -EINVAL;
 564
 565         if (oh->type < ARRAY_SIZE(packets)) {
 566                 const struct openflow_packet *pkt = &packets[oh->type];
 567                 if (pkt->handler) {
 568                         if (length < pkt->min_size)
 569                                 return -EFAULT;
 570                         return pkt->handler(chain, sender, msg);
 571                 }
 572         }
 573         dp_send_error_msg(chain->dp, sender, OFPET_BAD_REQUEST,
 574                           OFPBRC_BAD_TYPE, msg, length);
 575         return -EINVAL;
 576 }
 577
 578 /* Packet buffering. */
 579
 580 #define OVERWRITE_SECS  1
 581 #define OVERWRITE_JIFFIES (OVERWRITE_SECS * HZ)
 582
 583 struct packet_buffer {
 584         struct sk_buff *skb;
 585         uint32_t cookie;
 586         unsigned long exp_jiffies;
 587 };
 588
 589 static struct packet_buffer buffers[N_PKT_BUFFERS];
 590 static unsigned int buffer_idx;
 591 static DEFINE_SPINLOCK(buffer_lock);
 592
 593 uint32_t fwd_save_skb(struct sk_buff *skb)
 594 {
 595         struct sk_buff *old_skb = NULL;
 596         struct packet_buffer *p;
 597         unsigned long int flags;
 598         uint32_t id;
 599
 600         spin_lock_irqsave(&buffer_lock, flags);
 601         buffer_idx = (buffer_idx + 1) & PKT_BUFFER_MASK;
 602         p = &buffers[buffer_idx];
 603         if (p->skb) {
 604                 /* Don't buffer packet if existing entry is less than
 605                  * OVERWRITE_SECS old. */
 606                 if (time_before(jiffies, p->exp_jiffies)) {
 607                         spin_unlock_irqrestore(&buffer_lock, flags);
 608                         return -1;
 609                 } else {
 610                         /* Defer kfree_skb() until interrupts re-enabled. */
 611                         old_skb = p->skb;
 612                 }
 613         }
 614         /* Don't use maximum cookie value since the all-bits-1 id is
 615          * special. */
 616         if (++p->cookie >= (1u << PKT_COOKIE_BITS) - 1)
 617                 p->cookie = 0;
 618         skb_get(skb);
 619         p->skb = skb;
 620         p->exp_jiffies = jiffies + OVERWRITE_JIFFIES;
 621         id = buffer_idx | (p->cookie << PKT_BUFFER_BITS);
 622         spin_unlock_irqrestore(&buffer_lock, flags);
 623
 624         if (old_skb)
 625                 kfree_skb(old_skb);
 626
 627         return id;
 628 }
 629
 630 static struct sk_buff *retrieve_skb(uint32_t id)
 631 {
 632         unsigned long int flags;
 633         struct sk_buff *skb = NULL;
 634         struct packet_buffer *p;
 635
 636         spin_lock_irqsave(&buffer_lock, flags);
 637         p = &buffers[id & PKT_BUFFER_MASK];
 638         if (p->cookie == id >> PKT_BUFFER_BITS) {
 639                 skb = p->skb;
 640                 p->skb = NULL;
 641         } else {
 642                 printk("cookie mismatch: %x != %x\n",
 643                                 id >> PKT_BUFFER_BITS, p->cookie);
 644         }
 645         spin_unlock_irqrestore(&buffer_lock, flags);
 646
 647         return skb;
 648 }
 649
 650 void fwd_discard_all(void)
 651 {
 652         int i;
 653
 654         for (i = 0; i < N_PKT_BUFFERS; i++) {
 655                 struct sk_buff *skb;
 656                 unsigned long int flags;
 657
 658                 /* Defer kfree_skb() until interrupts re-enabled. */
 659                 spin_lock_irqsave(&buffer_lock, flags);
 660                 skb = buffers[i].skb;
 661                 buffers[i].skb = NULL;
 662                 spin_unlock_irqrestore(&buffer_lock, flags);
 663
 664                 kfree_skb(skb);
 665         }
 666 }
 667
 668 static void discard_skb(uint32_t id)
 669 {
 670         struct sk_buff *old_skb = NULL;
 671         unsigned long int flags;
 672         struct packet_buffer *p;
 673
 674         spin_lock_irqsave(&buffer_lock, flags);
 675         p = &buffers[id & PKT_BUFFER_MASK];
 676         if (p->cookie == id >> PKT_BUFFER_BITS) {
 677                 /* Defer kfree_skb() until interrupts re-enabled. */
 678                 old_skb = p->skb;
 679                 p->skb = NULL;
 680         }
 681         spin_unlock_irqrestore(&buffer_lock, flags);
 682
 683         if (old_skb)
 684                 kfree_skb(old_skb);
 685 }
 686
 687 void fwd_exit(void)
 688 {
 689         fwd_discard_all();
 690 }
 691
 692 /* Utility functions. */
 693
 694 /* Makes '*pskb' writable, possibly copying it and setting '*pskb' to point to
 695  * the copy.
 696  * Returns 1 if successful, 0 on failure. */
 697 static int
 698 make_writable(struct sk_buff **pskb)
 699 {
 700         /* Based on skb_make_writable() in net/netfilter/core.c. */
 701         struct sk_buff *nskb;
 702
 703         /* Not exclusive use of packet?  Must copy. */
 704         if (skb_shared(*pskb) || skb_cloned(*pskb))
 705                 goto copy_skb;
 706
 707         return pskb_may_pull(*pskb, 40); /* FIXME? */
 708
 709 copy_skb:
 710         nskb = skb_copy(*pskb, GFP_ATOMIC);
 711         if (!nskb)
 712                 return 0;
 713         BUG_ON(skb_is_nonlinear(nskb));
 714
 715         /* Rest of kernel will get very unhappy if we pass it a
 716            suddenly-orphaned skbuff */
 717         if ((*pskb)->sk)
 718                 skb_set_owner_w(nskb, (*pskb)->sk);
 719         kfree_skb(*pskb);
 720         *pskb = nskb;
 721         return 1;
 722 }