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