text: /*
   * Copyright (c) 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016 Nicira, Inc.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at:
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  #include <config.h>
  #include "packets.h"
  #include <arpa/inet.h>
  #include <sys/socket.h>
  #include <netinet/in.h>
  #include <netinet/ip6.h>
  #include <netinet/icmp6.h>
  #include <stdlib.h>
  #include "byte-order.h"
  #include "csum.h"
  #include "crc32c.h"
  #include "flow.h"
  #include "openvswitch/hmap.h"
  #include "openvswitch/dynamic-string.h"
  #include "ovs-thread.h"
  #include "odp-util.h"
  #include "dp-packet.h"
  #include "unaligned.h"
  
  const struct in6_addr in6addr_exact = IN6ADDR_EXACT_INIT;
  const struct in6_addr in6addr_all_hosts = IN6ADDR_ALL_HOSTS_INIT;
  
  struct in6_addr
  flow_tnl_dst(const struct flow_tnl *tnl)
  {
      return tnl->ip_dst ? in6_addr_mapped_ipv4(tnl->ip_dst) : tnl->ipv6_dst;
  }
  
  struct in6_addr
  flow_tnl_src(const struct flow_tnl *tnl)
  {
      return tnl->ip_src ? in6_addr_mapped_ipv4(tnl->ip_src) : tnl->ipv6_src;
  }
  
  /* Parses 's' as a 16-digit hexadecimal number representing a datapath ID.  On
   * success stores the dpid into '*dpidp' and returns true, on failure stores 0
   * into '*dpidp' and returns false.
   *
   * Rejects an all-zeros dpid as invalid. */
  bool
  dpid_from_string(const char *s, uint64_t *dpidp)
  {
      *dpidp = (strlen(s) == 16 && strspn(s, "0123456789abcdefABCDEF") == 16
                ? strtoull(s, NULL, 16)
                : 0);
      return *dpidp != 0;
  }
  
  /* Returns true if 'ea' is a reserved address, that a bridge must never
   * forward, false otherwise.
   *
   * If you change this function's behavior, please update corresponding
   * documentation in vswitch.xml at the same time. */
  bool
  eth_addr_is_reserved(const struct eth_addr ea)
  {
      struct eth_addr_node {
          struct hmap_node hmap_node;
          const uint64_t ea64;
      };
  
      static struct eth_addr_node nodes[] = {
          /* STP, IEEE pause frames, and other reserved protocols. */
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c2000000ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c2000001ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c2000002ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c2000003ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c2000004ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c2000005ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c2000006ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c2000007ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c2000008ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c2000009ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c200000aULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c200000bULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c200000cULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c200000dULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c200000eULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x0180c200000fULL },
  
          /* Extreme protocols. */
          { HMAP_NODE_NULL_INITIALIZER, 0x00e02b000000ULL }, /* EDP. */
          { HMAP_NODE_NULL_INITIALIZER, 0x00e02b000004ULL }, /* EAPS. */
          { HMAP_NODE_NULL_INITIALIZER, 0x00e02b000006ULL }, /* EAPS. */
  
          /* Cisco protocols. */
          { HMAP_NODE_NULL_INITIALIZER, 0x01000c000000ULL }, /* ISL. */
          { HMAP_NODE_NULL_INITIALIZER, 0x01000cccccccULL }, /* PAgP, UDLD, CDP,
                                                              * DTP, VTP. */
          { HMAP_NODE_NULL_INITIALIZER, 0x01000ccccccdULL }, /* PVST+. */
          { HMAP_NODE_NULL_INITIALIZER, 0x01000ccdcdcdULL }, /* STP Uplink Fast,
                                                              * FlexLink. */
  
          /* Cisco CFM. */
          { HMAP_NODE_NULL_INITIALIZER, 0x01000cccccc0ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x01000cccccc1ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x01000cccccc2ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x01000cccccc3ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x01000cccccc4ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x01000cccccc5ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x01000cccccc6ULL },
          { HMAP_NODE_NULL_INITIALIZER, 0x01000cccccc7ULL },
      };
  
      static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
      struct eth_addr_node *node;
      static struct hmap addrs;
      uint64_t ea64;
  
      if (ovsthread_once_start(&once)) {
          hmap_init(&addrs);
          for (node = nodes; node < &nodes[ARRAY_SIZE(nodes)]; node++) {
              hmap_insert(&addrs, &node->hmap_node, hash_uint64(node->ea64));
          }
          ovsthread_once_done(&once);
      }
  
      ea64 = eth_addr_to_uint64(ea);
      HMAP_FOR_EACH_IN_BUCKET (node, hmap_node, hash_uint64(ea64), &addrs) {
          if (node->ea64 == ea64) {
              return true;
          }
      }
      return false;
  }
  
  bool
  eth_addr_from_string(const char *s, struct eth_addr *ea)
  {
      if (ovs_scan(s, ETH_ADDR_SCAN_FMT, ETH_ADDR_SCAN_ARGS(*ea))) {
          return true;
      } else {
          *ea = eth_addr_zero;
          return false;
      }
  }
  
  /* Fills 'b' with a Reverse ARP packet with Ethernet source address 'eth_src'.
   * This function is used by Open vSwitch to compose packets in cases where
   * context is important but content doesn't (or shouldn't) matter.
   *
   * The returned packet has enough headroom to insert an 802.1Q VLAN header if
   * desired. */
  void
  compose_rarp(struct dp_packet *b, const struct eth_addr eth_src)
  {
      struct eth_header *eth;
      struct arp_eth_header *arp;
  
      dp_packet_clear(b);
      dp_packet_prealloc_tailroom(b, 2 + ETH_HEADER_LEN + VLAN_HEADER_LEN
                               + ARP_ETH_HEADER_LEN);
      dp_packet_reserve(b, 2 + VLAN_HEADER_LEN);
      eth = dp_packet_put_uninit(b, sizeof *eth);
      eth->eth_dst = eth_addr_broadcast;
      eth->eth_src = eth_src;
      eth->eth_type = htons(ETH_TYPE_RARP);
  
      arp = dp_packet_put_uninit(b, sizeof *arp);
      arp->ar_hrd = htons(ARP_HRD_ETHERNET);
      arp->ar_pro = htons(ARP_PRO_IP);
      arp->ar_hln = sizeof arp->ar_sha;
      arp->ar_pln = sizeof arp->ar_spa;
      arp->ar_op = htons(ARP_OP_RARP);
      arp->ar_sha = eth_src;
      put_16aligned_be32(&arp->ar_spa, htonl(0));
      arp->ar_tha = eth_src;
      put_16aligned_be32(&arp->ar_tpa, htonl(0));
  
      dp_packet_reset_offsets(b);
      dp_packet_set_l3(b, arp);
  }
  
  /* Insert VLAN header according to given TCI. Packet passed must be Ethernet
   * packet.  Ignores the CFI bit of 'tci' using 0 instead.
   *
   * Also adjusts the layer offsets accordingly. */
  void
  eth_push_vlan(struct dp_packet *packet, ovs_be16 tpid, ovs_be16 tci)
  {
      struct vlan_eth_header *veh;
  
      /* Insert new 802.1Q header. */
      veh = dp_packet_resize_l2(packet, VLAN_HEADER_LEN);
      memmove(veh, (char *)veh + VLAN_HEADER_LEN, 2 * ETH_ADDR_LEN);
      veh->veth_type = tpid;
      veh->veth_tci = tci & htons(~VLAN_CFI);
  }
  
  /* Removes outermost VLAN header (if any is present) from 'packet'.
   *
   * 'packet->l2_5' should initially point to 'packet''s outer-most VLAN header
   * or may be NULL if there are no VLAN headers. */
  void
  eth_pop_vlan(struct dp_packet *packet)
  {
      struct vlan_eth_header *veh = dp_packet_l2(packet);
  
      if (veh && dp_packet_size(packet) >= sizeof *veh
          && eth_type_vlan(veh->veth_type)) {
  
          memmove((char *)veh + VLAN_HEADER_LEN, veh, 2 * ETH_ADDR_LEN);
          dp_packet_resize_l2(packet, -VLAN_HEADER_LEN);
      }
  }
  
  /* Set ethertype of the packet. */
  static void
  set_ethertype(struct dp_packet *packet, ovs_be16 eth_type)
  {
      struct eth_header *eh = dp_packet_l2(packet);
  
      if (!eh) {
          return;
      }
  
      if (eth_type_vlan(eh->eth_type)) {
          ovs_be16 *p;
          char *l2_5 = dp_packet_l2_5(packet);
  
          p = ALIGNED_CAST(ovs_be16 *,
                           (l2_5 ? l2_5 : (char *)dp_packet_l3(packet)) - 2);
          *p = eth_type;
      } else {
          eh->eth_type = eth_type;
      }
  }
  
  static bool is_mpls(struct dp_packet *packet)
  {
      return packet->l2_5_ofs != UINT16_MAX;
  }
  
  /* Set time to live (TTL) of an MPLS label stack entry (LSE). */
  void
  set_mpls_lse_ttl(ovs_be32 *lse, uint8_t ttl)
  {
      *lse &= ~htonl(MPLS_TTL_MASK);
      *lse |= htonl((ttl << MPLS_TTL_SHIFT) & MPLS_TTL_MASK);
  }
  
  /* Set traffic class (TC) of an MPLS label stack entry (LSE). */
  void
  set_mpls_lse_tc(ovs_be32 *lse, uint8_t tc)
  {
      *lse &= ~htonl(MPLS_TC_MASK);
      *lse |= htonl((tc << MPLS_TC_SHIFT) & MPLS_TC_MASK);
  }
  
  /* Set label of an MPLS label stack entry (LSE). */
  void
  set_mpls_lse_label(ovs_be32 *lse, ovs_be32 label)
  {
      *lse &= ~htonl(MPLS_LABEL_MASK);
      *lse |= htonl((ntohl(label) << MPLS_LABEL_SHIFT) & MPLS_LABEL_MASK);
  }
  
  /* Set bottom of stack (BoS) bit of an MPLS label stack entry (LSE). */
  void
  set_mpls_lse_bos(ovs_be32 *lse, uint8_t bos)
  {
      *lse &= ~htonl(MPLS_BOS_MASK);
      *lse |= htonl((bos << MPLS_BOS_SHIFT) & MPLS_BOS_MASK);
  }
  
  /* Compose an MPLS label stack entry (LSE) from its components:
   * label, traffic class (TC), time to live (TTL) and
   * bottom of stack (BoS) bit. */
  ovs_be32
  set_mpls_lse_values(uint8_t ttl, uint8_t tc, uint8_t bos, ovs_be32 label)
  {
      ovs_be32 lse = htonl(0);
      set_mpls_lse_ttl(&lse, ttl);
      set_mpls_lse_tc(&lse, tc);
      set_mpls_lse_bos(&lse, bos);
      set_mpls_lse_label(&lse, label);
      return lse;
  }
  
  /* Set MPLS label stack entry to outermost MPLS header.*/
  void
  set_mpls_lse(struct dp_packet *packet, ovs_be32 mpls_lse)
  {
      /* Packet type should be MPLS to set label stack entry. */
      if (is_mpls(packet)) {
          struct mpls_hdr *mh = dp_packet_l2_5(packet);
  
          /* Update mpls label stack entry. */
          put_16aligned_be32(&mh->mpls_lse, mpls_lse);
      }
  }
  
  /* Push MPLS label stack entry 'lse' onto 'packet' as the outermost MPLS
   * header.  If 'packet' does not already have any MPLS labels, then its
   * Ethertype is changed to 'ethtype' (which must be an MPLS Ethertype). */
  void
  push_mpls(struct dp_packet *packet, ovs_be16 ethtype, ovs_be32 lse)
  {
      char * header;
      size_t len;
  
      if (!eth_type_mpls(ethtype)) {
          return;
      }
  
      if (!is_mpls(packet)) {
          /* Set MPLS label stack offset. */
          packet->l2_5_ofs = packet->l3_ofs;
      }
  
      set_ethertype(packet, ethtype);
  
      /* Push new MPLS shim header onto packet. */
      len = packet->l2_5_ofs;
      header = dp_packet_resize_l2_5(packet, MPLS_HLEN);
      memmove(header, header + MPLS_HLEN, len);
      memcpy(header + len, &lse, sizeof lse);
  }
  
  /* If 'packet' is an MPLS packet, removes its outermost MPLS label stack entry.
   * If the label that was removed was the only MPLS label, changes 'packet''s
   * Ethertype to 'ethtype' (which ordinarily should not be an MPLS
   * Ethertype). */
  void
  pop_mpls(struct dp_packet *packet, ovs_be16 ethtype)
  {
      if (is_mpls(packet)) {
          struct mpls_hdr *mh = dp_packet_l2_5(packet);
          size_t len = packet->l2_5_ofs;
  
          set_ethertype(packet, ethtype);
          if (get_16aligned_be32(&mh->mpls_lse) & htonl(MPLS_BOS_MASK)) {
              dp_packet_set_l2_5(packet, NULL);
          }
          /* Shift the l2 header forward. */
          memmove((char*)dp_packet_data(packet) + MPLS_HLEN, dp_packet_data(packet), len);
          dp_packet_resize_l2_5(packet, -MPLS_HLEN);
      }
  }
  
  /* Converts hex digits in 'hex' to an Ethernet packet in '*packetp'.  The
   * caller must free '*packetp'.  On success, returns NULL.  On failure, returns
   * an error message and stores NULL in '*packetp'.
   *
   * Aligns the L3 header of '*packetp' on a 32-bit boundary. */
  const char *
  eth_from_hex(const char *hex, struct dp_packet **packetp)
  {
      struct dp_packet *packet;
  
      /* Use 2 bytes of headroom to 32-bit align the L3 header. */
      packet = *packetp = dp_packet_new_with_headroom(strlen(hex) / 2, 2);
  
      if (dp_packet_put_hex(packet, hex, NULL)[0] != '\0') {
          dp_packet_delete(packet);
          *packetp = NULL;
          return "Trailing garbage in packet data";
      }
  
      if (dp_packet_size(packet) < ETH_HEADER_LEN) {
          dp_packet_delete(packet);
          *packetp = NULL;
          return "Packet data too short for Ethernet";
      }
  
      return NULL;
  }
  
  void
  eth_format_masked(const struct eth_addr eth,
                    const struct eth_addr *mask, struct ds *s)
  {
      ds_put_format(s, ETH_ADDR_FMT, ETH_ADDR_ARGS(eth));
      if (mask && !eth_mask_is_exact(*mask)) {
          ds_put_format(s, "/"ETH_ADDR_FMT, ETH_ADDR_ARGS(*mask));
      }
  }
  
  /* Given the IP netmask 'netmask', returns the number of bits of the IP address
   * that it specifies, that is, the number of 1-bits in 'netmask'.
   *
   * If 'netmask' is not a CIDR netmask (see ip_is_cidr()), the return value will
   * still be in the valid range but isn't otherwise meaningful. */
  int
  ip_count_cidr_bits(ovs_be32 netmask)
  {
      return 32 - ctz32(ntohl(netmask));
  }
  
  void
  ip_format_masked(ovs_be32 ip, ovs_be32 mask, struct ds *s)
  {
      ds_put_format(s, IP_FMT, IP_ARGS(ip));
      if (mask != OVS_BE32_MAX) {
          if (ip_is_cidr(mask)) {
              ds_put_format(s, "/%d", ip_count_cidr_bits(mask));
          } else {
              ds_put_format(s, "/"IP_FMT, IP_ARGS(mask));
          }
      }
  }
  
  /* Parses string 's', which must be an IP address.  Stores the IP address into
   * '*ip'.  Returns true if successful, otherwise false. */
  bool
  ip_parse(const char *s, ovs_be32 *ip)
  {
      return inet_pton(AF_INET, s, ip) == 1;
  }
  
  /* Parses string 's', which must be an IP address with an optional netmask or
   * CIDR prefix length.  Stores the IP address into '*ip', netmask into '*mask',
   * (255.255.255.255, if 's' lacks a netmask), and number of scanned characters
   * into '*n'.
   *
   * Returns NULL if successful, otherwise an error message that the caller must
   * free(). */
  char * OVS_WARN_UNUSED_RESULT
  ip_parse_masked_len(const char *s, int *n, ovs_be32 *ip,
                      ovs_be32 *mask)
  {
      int prefix;
  
      if (ovs_scan_len(s, n, IP_SCAN_FMT"/"IP_SCAN_FMT,
                   IP_SCAN_ARGS(ip), IP_SCAN_ARGS(mask))) {
          /* OK. */
      } else if (ovs_scan_len(s, n, IP_SCAN_FMT"/%d",
                              IP_SCAN_ARGS(ip), &prefix)) {
          if (prefix < 0 || prefix > 32) {
              return xasprintf("%s: IPv4 network prefix bits not between 0 and "
                                "32, inclusive", s);
          }
          *mask = be32_prefix_mask(prefix);
      } else if (ovs_scan_len(s, n, IP_SCAN_FMT, IP_SCAN_ARGS(ip))) {
          *mask = OVS_BE32_MAX;
      } else {
          return xasprintf("%s: invalid IP address", s);
      }
      return NULL;
  }
  
  /* This function is similar to ip_parse_masked_len(), but doesn't return the
   * number of scanned characters and expects 's' to end after the ip/(optional)
   * mask.
   *
   * Returns NULL if successful, otherwise an error message that the caller must
   * free(). */
  char * OVS_WARN_UNUSED_RESULT
  ip_parse_masked(const char *s, ovs_be32 *ip, ovs_be32 *mask)
  {
      int n = 0;
  
      char *error = ip_parse_masked_len(s, &n, ip, mask);
      if (!error && s[n]) {
          return xasprintf("%s: invalid IP address", s);
      }
      return error;
  }
  
  /* Similar to ip_parse_masked_len(), but the mask, if present, must be a CIDR
   * mask and is returned as a prefix len in '*plen'. */
  char * OVS_WARN_UNUSED_RESULT
  ip_parse_cidr_len(const char *s, int *n, ovs_be32 *ip, unsigned int *plen)
  {
      ovs_be32 mask;
      char *error;
  
      error = ip_parse_masked_len(s, n, ip, &mask);
      if (error) {
          return error;
      }
  
      if (!ip_is_cidr(mask)) {
          return xasprintf("%s: CIDR network required", s);
      }
      *plen = ip_count_cidr_bits(mask);
      return NULL;
  }
  
  /* Similar to ip_parse_cidr_len(), but doesn't return the number of scanned
   * characters and expects 's' to be NULL terminated at the end of the
   * ip/(optional) cidr. */
  char * OVS_WARN_UNUSED_RESULT
  ip_parse_cidr(const char *s, ovs_be32 *ip, unsigned int *plen)
  {
      int n = 0;
  
      char *error = ip_parse_cidr_len(s, &n, ip, plen);
      if (!error && s[n]) {
          return xasprintf("%s: invalid IP address", s);
      }
      return error;
  }
  
  /* Parses string 's', which must be an IPv6 address.  Stores the IPv6 address
   * into '*ip'.  Returns true if successful, otherwise false. */
  bool
  ipv6_parse(const char *s, struct in6_addr *ip)
  {
      return inet_pton(AF_INET6, s, ip) == 1;
  }
  
  /* Parses string 's', which must be an IPv6 address with an optional netmask or
   * CIDR prefix length.  Stores the IPv6 address into '*ip' and the netmask into
   * '*mask' (if 's' does not contain a netmask, all-one-bits is assumed), and
   * number of scanned characters into '*n'.
   *
   * Returns NULL if successful, otherwise an error message that the caller must
   * free(). */
  char * OVS_WARN_UNUSED_RESULT
  ipv6_parse_masked_len(const char *s, int *n, struct in6_addr *ip,
                        struct in6_addr *mask)
  {
      char ipv6_s[IPV6_SCAN_LEN + 1];
      int prefix;
  
      if (ovs_scan_len(s, n, " "IPV6_SCAN_FMT, ipv6_s)
          && ipv6_parse(ipv6_s, ip)) {
          if (ovs_scan_len(s, n, "/%d", &prefix)) {
              if (prefix < 0 || prefix > 128) {
                  return xasprintf("%s: IPv6 network prefix bits not between 0 "
                                   "and 128, inclusive", s);
              }
              *mask = ipv6_create_mask(prefix);
          } else if (ovs_scan_len(s, n, "/"IPV6_SCAN_FMT, ipv6_s)) {
               if (!ipv6_parse(ipv6_s, mask)) {
                   return xasprintf("%s: Invalid IPv6 mask", s);
               }
              /* OK. */
          } else {
              /* OK. No mask. */
              *mask = in6addr_exact;
          }
          return NULL;
      }
      return xasprintf("%s: invalid IPv6 address", s);
  }
  
  /* This function is similar to ipv6_parse_masked_len(), but doesn't return the
   * number of scanned characters and expects 's' to end following the
   * ipv6/(optional) mask. */
  char * OVS_WARN_UNUSED_RESULT
  ipv6_parse_masked(const char *s, struct in6_addr *ip, struct in6_addr *mask)
  {
      int n = 0;
  
      char *error = ipv6_parse_masked_len(s, &n, ip, mask);
      if (!error && s[n]) {
          return xasprintf("%s: invalid IPv6 address", s);
      }
      return error;
  }
  
  /* Similar to ipv6_parse_masked_len(), but the mask, if present, must be a CIDR
   * mask and is returned as a prefix length in '*plen'. */
  char * OVS_WARN_UNUSED_RESULT
  ipv6_parse_cidr_len(const char *s, int *n, struct in6_addr *ip,
                      unsigned int *plen)
  {
      struct in6_addr mask;
      char *error;
  
      error = ipv6_parse_masked_len(s, n, ip, &mask);
      if (error) {
          return error;
      }
  
      if (!ipv6_is_cidr(&mask)) {
          return xasprintf("%s: IPv6 CIDR network required", s);
      }
      *plen = ipv6_count_cidr_bits(&mask);
      return NULL;
  }
  
  /* Similar to ipv6_parse_cidr_len(), but doesn't return the number of scanned
   * characters and expects 's' to end after the ipv6/(optional) cidr. */
  char * OVS_WARN_UNUSED_RESULT
  ipv6_parse_cidr(const char *s, struct in6_addr *ip, unsigned int *plen)
  {
      int n = 0;
  
      char *error = ipv6_parse_cidr_len(s, &n, ip, plen);
      if (!error && s[n]) {
          return xasprintf("%s: invalid IPv6 address", s);
      }
      return error;
  }
  
  /* Stores the string representation of the IPv6 address 'addr' into the
   * character array 'addr_str', which must be at least INET6_ADDRSTRLEN
   * bytes long. */
  void
  ipv6_format_addr(const struct in6_addr *addr, struct ds *s)
  {
      char *dst;
  
      ds_reserve(s, s->length + INET6_ADDRSTRLEN);
  
      dst = s->string + s->length;
      inet_ntop(AF_INET6, addr, dst, INET6_ADDRSTRLEN);
      s->length += strlen(dst);
  }
  
  /* Same as print_ipv6_addr, but optionally encloses the address in square
   * brackets. */
  void
  ipv6_format_addr_bracket(const struct in6_addr *addr, struct ds *s,
                           bool bracket)
  {
      if (bracket) {
          ds_put_char(s, '[');
      }
      ipv6_format_addr(addr, s);
      if (bracket) {
          ds_put_char(s, ']');
      }
  }
  
  void
  ipv6_format_mapped(const struct in6_addr *addr, struct ds *s)
  {
      if (IN6_IS_ADDR_V4MAPPED(addr)) {
          ds_put_format(s, IP_FMT, addr->s6_addr[12], addr->s6_addr[13],
                                   addr->s6_addr[14], addr->s6_addr[15]);
      } else {
          ipv6_format_addr(addr, s);
      }
  }
  
  void
  ipv6_format_masked(const struct in6_addr *addr, const struct in6_addr *mask,
                     struct ds *s)
  {
      ipv6_format_addr(addr, s);
      if (mask && !ipv6_mask_is_exact(mask)) {
          if (ipv6_is_cidr(mask)) {
              int cidr_bits = ipv6_count_cidr_bits(mask);
              ds_put_format(s, "/%d", cidr_bits);
          } else {
              ds_put_char(s, '/');
              ipv6_format_addr(mask, s);
          }
      }
  }
  
  /* Stores the string representation of the IPv6 address 'addr' into the
   * character array 'addr_str', which must be at least INET6_ADDRSTRLEN
   * bytes long. If addr is IPv4-mapped, store an IPv4 dotted-decimal string. */
  const char *
  ipv6_string_mapped(char *addr_str, const struct in6_addr *addr)
  {
      ovs_be32 ip;
      ip = in6_addr_get_mapped_ipv4(addr);
      if (ip) {
          return inet_ntop(AF_INET, &ip, addr_str, INET6_ADDRSTRLEN);
      } else {
          return inet_ntop(AF_INET6, addr, addr_str, INET6_ADDRSTRLEN);
      }
  }
  
  #ifdef s6_addr32
  #define s6_addrX s6_addr32
  #define IPV6_FOR_EACH(VAR) for (int VAR = 0; VAR < 4; VAR++)
  #else
  #define s6_addrX s6_addr
  #define IPV6_FOR_EACH(VAR) for (int VAR = 0; VAR < 16; VAR++)
  #endif
  
  struct in6_addr
  ipv6_addr_bitand(const struct in6_addr *a, const struct in6_addr *b)
  {
     struct in6_addr dst;
     IPV6_FOR_EACH (i) {
         dst.s6_addrX[i] = a->s6_addrX[i] & b->s6_addrX[i];
     }
     return dst;
  }
  
  struct in6_addr
  ipv6_addr_bitxor(const struct in6_addr *a, const struct in6_addr *b)
  {
     struct in6_addr dst;
     IPV6_FOR_EACH (i) {
         dst.s6_addrX[i] = a->s6_addrX[i] ^ b->s6_addrX[i];
     }
     return dst;
  }
  
  bool
  ipv6_is_zero(const struct in6_addr *a)
  {
     IPV6_FOR_EACH (i) {
         if (a->s6_addrX[i]) {
             return false;
         }
     }
     return true;
  }
  
  /* Returns an in6_addr consisting of 'mask' high-order 1-bits and 128-N
   * low-order 0-bits. */
  struct in6_addr
  ipv6_create_mask(int mask)
  {
      struct in6_addr netmask;
      uint8_t *netmaskp = &netmask.s6_addr[0];
  
      memset(&netmask, 0, sizeof netmask);
      while (mask > 8) {
          *netmaskp = 0xff;
          netmaskp++;
          mask -= 8;
      }
  
      if (mask) {
          *netmaskp = 0xff << (8 - mask);
      }
  
      return netmask;
  }
  
  /* Given the IPv6 netmask 'netmask', returns the number of bits of the IPv6
   * address that it specifies, that is, the number of 1-bits in 'netmask'.
   * 'netmask' must be a CIDR netmask (see ipv6_is_cidr()).
   *
   * If 'netmask' is not a CIDR netmask (see ipv6_is_cidr()), the return value
   * will still be in the valid range but isn't otherwise meaningful. */
  int
  ipv6_count_cidr_bits(const struct in6_addr *netmask)
  {
      int i;
      int count = 0;
      const uint8_t *netmaskp = &netmask->s6_addr[0];
  
      for (i=0; i<16; i++) {
          if (netmaskp[i] == 0xff) {
              count += 8;
          } else {
              uint8_t nm;
  
              for(nm = netmaskp[i]; nm; nm <<= 1) {
                  count++;
              }
              break;
          }
  
      }
  
      return count;
  }
  
  /* Returns true if 'netmask' is a CIDR netmask, that is, if it consists of N
   * high-order 1-bits and 128-N low-order 0-bits. */
  bool
  ipv6_is_cidr(const struct in6_addr *netmask)
  {
      const uint8_t *netmaskp = &netmask->s6_addr[0];
      int i;
  
      for (i=0; i<16; i++) {
          if (netmaskp[i] != 0xff) {
              uint8_t x = ~netmaskp[i];
              if (x & (x + 1)) {
                  return false;
              }
              while (++i < 16) {
                  if (netmaskp[i]) {
                      return false;
                  }
              }
          }
      }
  
      return true;
  }
  
  /* Populates 'b' with an Ethernet II packet headed with the given 'eth_dst',
   * 'eth_src' and 'eth_type' parameters.  A payload of 'size' bytes is allocated
   * in 'b' and returned.  This payload may be populated with appropriate
   * information by the caller.  Sets 'b''s 'frame' pointer and 'l3' offset to
   * the Ethernet header and payload respectively.  Aligns b->l3 on a 32-bit
   * boundary.
   *
   * The returned packet has enough headroom to insert an 802.1Q VLAN header if
   * desired. */
  void *
  eth_compose(struct dp_packet *b, const struct eth_addr eth_dst,
              const struct eth_addr eth_src, uint16_t eth_type,
              size_t size)
  {
      void *data;
      struct eth_header *eth;
  
      dp_packet_clear(b);
  
      /* The magic 2 here ensures that the L3 header (when it is added later)
       * will be 32-bit aligned. */
      dp_packet_prealloc_tailroom(b, 2 + ETH_HEADER_LEN + VLAN_HEADER_LEN + size);
      dp_packet_reserve(b, 2 + VLAN_HEADER_LEN);
      eth = dp_packet_put_uninit(b, ETH_HEADER_LEN);
      data = dp_packet_put_zeros(b, size);
  
      eth->eth_dst = eth_dst;
      eth->eth_src = eth_src;
      eth->eth_type = htons(eth_type);
  
      dp_packet_reset_offsets(b);
      dp_packet_set_l3(b, data);
  
      return data;
  }
  
  static void
  packet_set_ipv4_addr(struct dp_packet *packet,
                       ovs_16aligned_be32 *addr, ovs_be32 new_addr)
  {
      struct ip_header *nh = dp_packet_l3(packet);
      ovs_be32 old_addr = get_16aligned_be32(addr);
      size_t l4_size = dp_packet_l4_size(packet);
  
      if (nh->ip_proto == IPPROTO_TCP && l4_size >= TCP_HEADER_LEN) {
          struct tcp_header *th = dp_packet_l4(packet);
  
          th->tcp_csum = recalc_csum32(th->tcp_csum, old_addr, new_addr);
      } else if (nh->ip_proto == IPPROTO_UDP && l4_size >= UDP_HEADER_LEN ) {
          struct udp_header *uh = dp_packet_l4(packet);
  
          if (uh->udp_csum) {
              uh->udp_csum = recalc_csum32(uh->udp_csum, old_addr, new_addr);
              if (!uh->udp_csum) {
                  uh->udp_csum = htons(0xffff);
              }
          }
      }
      nh->ip_csum = recalc_csum32(nh->ip_csum, old_addr, new_addr);
      put_16aligned_be32(addr, new_addr);
  }
  
  /* Returns true, if packet contains at least one routing header where
   * segements_left > 0.
   *
   * This function assumes that L3 and L4 offsets are set in the packet. */
  static bool
  packet_rh_present(struct dp_packet *packet, uint8_t *nexthdr)
  {
      const struct ovs_16aligned_ip6_hdr *nh;
      size_t len;
      size_t remaining;
      uint8_t *data = dp_packet_l3(packet);
  
      remaining = packet->l4_ofs - packet->l3_ofs;
      if (remaining < sizeof *nh) {
          return false;
      }
      nh = ALIGNED_CAST(struct ovs_16aligned_ip6_hdr *, data);
      data += sizeof *nh;
      remaining -= sizeof *nh;
      *nexthdr = nh->ip6_nxt;
  
      while (1) {
          if ((*nexthdr != IPPROTO_HOPOPTS)
                  && (*nexthdr != IPPROTO_ROUTING)
                  && (*nexthdr != IPPROTO_DSTOPTS)
                  && (*nexthdr != IPPROTO_AH)
                  && (*nexthdr != IPPROTO_FRAGMENT)) {
              /* It's either a terminal header (e.g., TCP, UDP) or one we
               * don't understand.  In either case, we're done with the
               * packet, so use it to fill in 'nw_proto'. */
              break;
          }
  
          /* We only verify that at least 8 bytes of the next header are
           * available, but many of these headers are longer.  Ensure that
           * accesses within the extension header are within those first 8
           * bytes. All extension headers are required to be at least 8
           * bytes. */
          if (remaining < 8) {
              return false;
          }
  
          if (*nexthdr == IPPROTO_AH) {
              /* A standard AH definition isn't available, but the fields
               * we care about are in the same location as the generic
               * option header--only the header length is calculated
               * differently. */
              const struct ip6_ext *ext_hdr = (struct ip6_ext *)data;
  
              *nexthdr = ext_hdr->ip6e_nxt;
              len = (ext_hdr->ip6e_len + 2) * 4;
          } else if (*nexthdr == IPPROTO_FRAGMENT) {
              const struct ovs_16aligned_ip6_frag *frag_hdr
                  = ALIGNED_CAST(struct ovs_16aligned_ip6_frag *, data);
  
              *nexthdr = frag_hdr->ip6f_nxt;
              len = sizeof *frag_hdr;
          } else if (*nexthdr == IPPROTO_ROUTING) {
              const struct ip6_rthdr *rh = (struct ip6_rthdr *)data;
  
              if (rh->ip6r_segleft > 0) {
                  return true;
              }
  
              *nexthdr = rh->ip6r_nxt;
              len = (rh->ip6r_len + 1) * 8;
          } else {
              const struct ip6_ext *ext_hdr = (struct ip6_ext *)data;
  
              *nexthdr = ext_hdr->ip6e_nxt;
              len = (ext_hdr->ip6e_len + 1) * 8;
          }
  
          if (remaining < len) {
              return false;
          }
          remaining -= len;
          data += len;
      }
  
      return false;
  }
  
  static void
  packet_update_csum128(struct dp_packet *packet, uint8_t proto,
                       ovs_16aligned_be32 addr[4], const ovs_be32 new_addr[4])
  {
      size_t l4_size = dp_packet_l4_size(packet);
  
      if (proto == IPPROTO_TCP && l4_size >= TCP_HEADER_LEN) {
          struct tcp_header *th = dp_packet_l4(packet);
  
          th->tcp_csum = recalc_csum128(th->tcp_csum, addr, new_addr);
      } else if (proto == IPPROTO_UDP && l4_size >= UDP_HEADER_LEN) {
          struct udp_header *uh = dp_packet_l4(packet);
  
          if (uh->udp_csum) {
              uh->udp_csum = recalc_csum128(uh->udp_csum, addr, new_addr);
              if (!uh->udp_csum) {
                  uh->udp_csum = htons(0xffff);
              }
          }
      } else if (proto == IPPROTO_ICMPV6 &&
                 l4_size >= sizeof(struct icmp6_header)) {
          struct icmp6_header *icmp = dp_packet_l4(packet);
  
          icmp->icmp6_cksum = recalc_csum128(icmp->icmp6_cksum, addr, new_addr);
      }
  }
  
  static void
  packet_set_ipv6_addr(struct dp_packet *packet, uint8_t proto,
                       ovs_16aligned_be32 addr[4], const ovs_be32 new_addr[4],
                       bool recalculate_csum)
  {
      if (recalculate_csum) {
          packet_update_csum128(packet, proto, addr, new_addr);
      }
      memcpy(addr, new_addr, sizeof(ovs_be32[4]));
  }
  
  static void
  packet_set_ipv6_flow_label(ovs_16aligned_be32 *flow_label, ovs_be32 flow_key)
  {
      ovs_be32 old_label = get_16aligned_be32(flow_label);
      ovs_be32 new_label = (old_label & htonl(~IPV6_LABEL_MASK)) | flow_key;
      put_16aligned_be32(flow_label, new_label);
  }
  
  static void
  packet_set_ipv6_tc(ovs_16aligned_be32 *flow_label, uint8_t tc)
  {
      ovs_be32 old_label = get_16aligned_be32(flow_label);
      ovs_be32 new_label = (old_label & htonl(0xF00FFFFF)) | htonl(tc << 20);
      put_16aligned_be32(flow_label, new_label);
  }
  
  /* Modifies the IPv4 header fields of 'packet' to be consistent with 'src',
   * 'dst', 'tos', and 'ttl'.  Updates 'packet''s L4 checksums as appropriate.
   * 'packet' must contain a valid IPv4 packet with correctly populated l[347]
   * markers. */
  void
  packet_set_ipv4(struct dp_packet *packet, ovs_be32 src, ovs_be32 dst,
                  uint8_t tos, uint8_t ttl)
  {
      struct ip_header *nh = dp_packet_l3(packet);
  
      if (get_16aligned_be32(&nh->ip_src) != src) {
          packet_set_ipv4_addr(packet, &nh->ip_src, src);
      }
  
      if (get_16aligned_be32(&nh->ip_dst) != dst) {
          packet_set_ipv4_addr(packet, &nh->ip_dst, dst);
      }
  
      if (nh->ip_tos != tos) {
          uint8_t *field = &nh->ip_tos;
  
          nh->ip_csum = recalc_csum16(nh->ip_csum, htons((uint16_t) *field),
                                      htons((uint16_t) tos));
          *field = tos;
      }
  
      if (nh->ip_ttl != ttl) {
          uint8_t *field = &nh->ip_ttl;
  
          nh->ip_csum = recalc_csum16(nh->ip_csum, htons(*field << 8),
                                      htons(ttl << 8));
          *field = ttl;
      }
  }
  
  /* Modifies the IPv6 header fields of 'packet' to be consistent with 'src',
   * 'dst', 'traffic class', and 'next hop'.  Updates 'packet''s L4 checksums as
   * appropriate. 'packet' must contain a valid IPv6 packet with correctly
   * populated l[34] offsets. */
  void
  packet_set_ipv6(struct dp_packet *packet, const ovs_be32 src[4],
                  const ovs_be32 dst[4], uint8_t key_tc, ovs_be32 key_fl,
                  uint8_t key_hl)
  {
      struct ovs_16aligned_ip6_hdr *nh = dp_packet_l3(packet);
      uint8_t proto = 0;
      bool rh_present;
  
      rh_present = packet_rh_present(packet, &proto);
  
      if (memcmp(&nh->ip6_src, src, sizeof(ovs_be32[4]))) {
          packet_set_ipv6_addr(packet, proto, nh->ip6_src.be32, src, true);
      }
  
      if (memcmp(&nh->ip6_dst, dst, sizeof(ovs_be32[4]))) {
          packet_set_ipv6_addr(packet, proto, nh->ip6_dst.be32, dst,
                               !rh_present);
      }
  
      packet_set_ipv6_tc(&nh->ip6_flow, key_tc);
      packet_set_ipv6_flow_label(&nh->ip6_flow, key_fl);
      nh->ip6_hlim = key_hl;
  }
  
  static void
  packet_set_port(ovs_be16 *port, ovs_be16 new_port, ovs_be16 *csum)
  {
      if (*port != new_port) {
          *csum = recalc_csum16(*csum, *port, new_port);
          *port = new_port;
      }
  }
  
  /* Sets the TCP source and destination port ('src' and 'dst' respectively) of
   * the TCP header contained in 'packet'.  'packet' must be a valid TCP packet
   * with its l4 offset properly populated. */
  void
  packet_set_tcp_port(struct dp_packet *packet, ovs_be16 src, ovs_be16 dst)
  {
      struct tcp_header *th = dp_packet_l4(packet);
  
      packet_set_port(&th->tcp_src, src, &th->tcp_csum);
      packet_set_port(&th->tcp_dst, dst, &th->tcp_csum);
  }
  
  /* Sets the UDP source and destination port ('src' and 'dst' respectively) of
   * the UDP header contained in 'packet'.  'packet' must be a valid UDP packet
   * with its l4 offset properly populated. */
  void
  packet_set_udp_port(struct dp_packet *packet, ovs_be16 src, ovs_be16 dst)
  {
      struct udp_header *uh = dp_packet_l4(packet);
  
      if (uh->udp_csum) {
          packet_set_port(&uh->udp_src, src, &uh->udp_csum);
          packet_set_port(&uh->udp_dst, dst, &uh->udp_csum);
  
          if (!uh->udp_csum) {
              uh->udp_csum = htons(0xffff);
          }
      } else {
          uh->udp_src = src;
          uh->udp_dst = dst;
      }
  }
  
  /* Sets the SCTP source and destination port ('src' and 'dst' respectively) of
   * the SCTP header contained in 'packet'.  'packet' must be a valid SCTP packet
   * with its l4 offset properly populated. */
  void
  packet_set_sctp_port(struct dp_packet *packet, ovs_be16 src, ovs_be16 dst)
  {
      struct sctp_header *sh = dp_packet_l4(packet);
      ovs_be32 old_csum, old_correct_csum, new_csum;
      uint16_t tp_len = dp_packet_l4_size(packet);
  
      old_csum = get_16aligned_be32(&sh->sctp_csum);
      put_16aligned_be32(&sh->sctp_csum, 0);
      old_correct_csum = crc32c((void *)sh, tp_len);
  
      sh->sctp_src = src;
      sh->sctp_dst = dst;
  
      new_csum = crc32c((void *)sh, tp_len);
      put_16aligned_be32(&sh->sctp_csum, old_csum ^ old_correct_csum ^ new_csum);
  }
  
  /* Sets the ICMP type and code of the ICMP header contained in 'packet'.
   * 'packet' must be a valid ICMP packet with its l4 offset properly
   * populated. */
  void
  packet_set_icmp(struct dp_packet *packet, uint8_t type, uint8_t code)
  {
      struct icmp_header *ih = dp_packet_l4(packet);
      ovs_be16 orig_tc = htons(ih->icmp_type << 8 | ih->icmp_code);
      ovs_be16 new_tc = htons(type << 8 | code);
  
      if (orig_tc != new_tc) {
          ih->icmp_type = type;
          ih->icmp_code = code;
  
          ih->icmp_csum = recalc_csum16(ih->icmp_csum, orig_tc, new_tc);
      }
  }
  
  void
  packet_set_nd(struct dp_packet *packet, const ovs_be32 target[4],
                const struct eth_addr sll, const struct eth_addr tll)
  {
      struct ovs_nd_msg *ns;
      struct ovs_nd_opt *nd_opt;
      int bytes_remain = dp_packet_l4_size(packet);
  
      if (OVS_UNLIKELY(bytes_remain < sizeof(*ns))) {
          return;
      }
  
      ns = dp_packet_l4(packet);
      nd_opt = &ns->options[0];
      bytes_remain -= sizeof(*ns);
  
      if (memcmp(&ns->target, target, sizeof(ovs_be32[4]))) {
          packet_set_ipv6_addr(packet, IPPROTO_ICMPV6,
                               ns->target.be32,
                               target, true);
      }
  
      while (bytes_remain >= ND_OPT_LEN && nd_opt->nd_opt_len != 0) {
          if (nd_opt->nd_opt_type == ND_OPT_SOURCE_LINKADDR
              && nd_opt->nd_opt_len == 1) {
              if (!eth_addr_equals(nd_opt->nd_opt_mac, sll)) {
                  ovs_be16 *csum = &(ns->icmph.icmp6_cksum);
  
                  *csum = recalc_csum48(*csum, nd_opt->nd_opt_mac, sll);
                  nd_opt->nd_opt_mac = sll;
              }
  
              /* A packet can only contain one SLL or TLL option */
              break;
          } else if (nd_opt->nd_opt_type == ND_OPT_TARGET_LINKADDR
                     && nd_opt->nd_opt_len == 1) {
              if (!eth_addr_equals(nd_opt->nd_opt_mac, tll)) {
                  ovs_be16 *csum = &(ns->icmph.icmp6_cksum);
  
                  *csum = recalc_csum48(*csum, nd_opt->nd_opt_mac, tll);
                  nd_opt->nd_opt_mac = tll;
              }
  
              /* A packet can only contain one SLL or TLL option */
              break;
          }
  
          nd_opt += nd_opt->nd_opt_len;
          bytes_remain -= nd_opt->nd_opt_len * ND_OPT_LEN;
      }
  }
  
  const char *
  packet_tcp_flag_to_string(uint32_t flag)
  {
      switch (flag) {
      case TCP_FIN:
          return "fin";
      case TCP_SYN:
          return "syn";
      case TCP_RST:
          return "rst";
      case TCP_PSH:
          return "psh";
      case TCP_ACK:
          return "ack";
      case TCP_URG:
          return "urg";
      case TCP_ECE:
          return "ece";
      case TCP_CWR:
          return "cwr";
      case TCP_NS:
          return "ns";
      case 0x200:
          return "[200]";
      case 0x400:
          return "[400]";
      case 0x800:
          return "[800]";
      default:
          return NULL;
      }
  }
  
  /* Appends a string representation of the TCP flags value 'tcp_flags'
   * (e.g. from struct flow.tcp_flags or obtained via TCP_FLAGS) to 's', in the
   * format used by tcpdump. */
  void
  packet_format_tcp_flags(struct ds *s, uint16_t tcp_flags)
  {
      if (!tcp_flags) {
          ds_put_cstr(s, "none");
          return;
      }
  
      if (tcp_flags & TCP_SYN) {
          ds_put_char(s, 'S');
      }
      if (tcp_flags & TCP_FIN) {
          ds_put_char(s, 'F');
      }
      if (tcp_flags & TCP_PSH) {
          ds_put_char(s, 'P');
      }
      if (tcp_flags & TCP_RST) {
          ds_put_char(s, 'R');
      }
      if (tcp_flags & TCP_URG) {
          ds_put_char(s, 'U');
      }
      if (tcp_flags & TCP_ACK) {
          ds_put_char(s, '.');
      }
      if (tcp_flags & TCP_ECE) {
          ds_put_cstr(s, "E");
      }
      if (tcp_flags & TCP_CWR) {
          ds_put_cstr(s, "C");
      }
      if (tcp_flags & TCP_NS) {
          ds_put_cstr(s, "N");
      }
      if (tcp_flags & 0x200) {
          ds_put_cstr(s, "[200]");
      }
      if (tcp_flags & 0x400) {
          ds_put_cstr(s, "[400]");
      }
      if (tcp_flags & 0x800) {
          ds_put_cstr(s, "[800]");
      }
  }
  
  #define ARP_PACKET_SIZE  (2 + ETH_HEADER_LEN + VLAN_HEADER_LEN + \
                            ARP_ETH_HEADER_LEN)
  
  /* Clears 'b' and replaces its contents by an ARP frame with the specified
   * 'arp_op', 'arp_sha', 'arp_tha', 'arp_spa', and 'arp_tpa'.  The outer
   * Ethernet frame is initialized with Ethernet source 'arp_sha' and destination
   * 'arp_tha', except that destination ff:ff:ff:ff:ff:ff is used instead if
   * 'broadcast' is true.  Points the L3 header to the ARP header. */
  void
  compose_arp(struct dp_packet *b, uint16_t arp_op,
              const struct eth_addr arp_sha, const struct eth_addr arp_tha,
              bool broadcast, ovs_be32 arp_spa, ovs_be32 arp_tpa)
  {
      compose_arp__(b);
  
      struct eth_header *eth = dp_packet_l2(b);
      eth->eth_dst = broadcast ? eth_addr_broadcast : arp_tha;
      eth->eth_src = arp_sha;
  
      struct arp_eth_header *arp = dp_packet_l3(b);
      arp->ar_op = htons(arp_op);
      arp->ar_sha = arp_sha;
      arp->ar_tha = arp_tha;
      put_16aligned_be32(&arp->ar_spa, arp_spa);
      put_16aligned_be32(&arp->ar_tpa, arp_tpa);
  }
  
  /* Clears 'b' and replaces its contents by an ARP frame.  Sets the fields in
   * the Ethernet and ARP headers that are fixed for ARP frames to those fixed
   * values, and zeroes the other fields.  Points the L3 header to the ARP
   * header. */
  void
  compose_arp__(struct dp_packet *b)
  {
      dp_packet_clear(b);
      dp_packet_prealloc_tailroom(b, ARP_PACKET_SIZE);
      dp_packet_reserve(b, 2 + VLAN_HEADER_LEN);
  
      struct eth_header *eth = dp_packet_put_zeros(b, sizeof *eth);
      eth->eth_type = htons(ETH_TYPE_ARP);
  
      struct arp_eth_header *arp = dp_packet_put_zeros(b, sizeof *arp);
      arp->ar_hrd = htons(ARP_HRD_ETHERNET);
      arp->ar_pro = htons(ARP_PRO_IP);
      arp->ar_hln = sizeof arp->ar_sha;
      arp->ar_pln = sizeof arp->ar_spa;
  
      dp_packet_reset_offsets(b);
      dp_packet_set_l3(b, arp);
  }
  
  /* This function expects packet with ethernet header with correct
   * l3 pointer set. */
  static void *
  compose_ipv6(struct dp_packet *packet, uint8_t proto,
               const struct in6_addr *src, const struct in6_addr *dst,
               uint8_t key_tc, ovs_be32 key_fl, uint8_t key_hl, int size)
  {
      struct ip6_hdr *nh;
      void *data;
  
      /* Copy 'src' and 'dst' to temporary buffers to prevent misaligned
       * accesses. */
      ovs_be32 sbuf[4], dbuf[4];
      memcpy(sbuf, src, sizeof sbuf);
      memcpy(dbuf, dst, sizeof dbuf);
  
      nh = dp_packet_l3(packet);
      nh->ip6_vfc = 0x60;
      nh->ip6_nxt = proto;
      nh->ip6_plen = htons(size);
      data = dp_packet_put_zeros(packet, size);
      dp_packet_set_l4(packet, data);
      packet_set_ipv6(packet, sbuf, dbuf, key_tc, key_fl, key_hl);
      return data;
  }
  
  /* Compose an IPv6 Neighbor Discovery Neighbor Solicitation message. */
  void
  compose_nd_ns(struct dp_packet *b, const struct eth_addr eth_src,
                const struct in6_addr *ipv6_src, const struct in6_addr *ipv6_dst)
  {
      struct in6_addr sn_addr;
      struct eth_addr eth_dst;
      struct ovs_nd_msg *ns;
      struct ovs_nd_opt *nd_opt;
      uint32_t icmp_csum;
  
      in6_addr_solicited_node(&sn_addr, ipv6_dst);
      ipv6_multicast_to_ethernet(&eth_dst, &sn_addr);
  
      eth_compose(b, eth_dst, eth_src, ETH_TYPE_IPV6, IPV6_HEADER_LEN);
      ns = compose_ipv6(b, IPPROTO_ICMPV6, ipv6_src, &sn_addr,
                        0, 0, 255, ND_MSG_LEN + ND_OPT_LEN);
  
      ns->icmph.icmp6_type = ND_NEIGHBOR_SOLICIT;
      ns->icmph.icmp6_code = 0;
      put_16aligned_be32(&ns->rso_flags, htonl(0));
  
      nd_opt = &ns->options[0];
      nd_opt->nd_opt_type = ND_OPT_SOURCE_LINKADDR;
      nd_opt->nd_opt_len = 1;
  
      /* Copy target address to temp buffer to prevent misaligned access. */
      ovs_be32 tbuf[4];
      memcpy(tbuf, ipv6_dst->s6_addr, sizeof tbuf);
      packet_set_nd(b, tbuf, eth_src, eth_addr_zero);
  
      ns->icmph.icmp6_cksum = 0;
      icmp_csum = packet_csum_pseudoheader6(dp_packet_l3(b));
      ns->icmph.icmp6_cksum = csum_finish(csum_continue(icmp_csum, ns,
                                                        ND_MSG_LEN + ND_OPT_LEN));
  }
  
  /* Compose an IPv6 Neighbor Discovery Neighbor Advertisement message. */
  void
  compose_nd_na(struct dp_packet *b,
                const struct eth_addr eth_src, const struct eth_addr eth_dst,
                const struct in6_addr *ipv6_src, const struct in6_addr *ipv6_dst,
                ovs_be32 rso_flags)
  {
      struct ovs_nd_msg *na;
      struct ovs_nd_opt *nd_opt;
      uint32_t icmp_csum;
  
      eth_compose(b, eth_dst, eth_src, ETH_TYPE_IPV6, IPV6_HEADER_LEN);
      na = compose_ipv6(b, IPPROTO_ICMPV6, ipv6_src, ipv6_dst,
                        0, 0, 255, ND_MSG_LEN + ND_OPT_LEN);
  
      na->icmph.icmp6_type = ND_NEIGHBOR_ADVERT;
      na->icmph.icmp6_code = 0;
      put_16aligned_be32(&na->rso_flags, rso_flags);
  
      nd_opt = &na->options[0];
      nd_opt->nd_opt_type = ND_OPT_TARGET_LINKADDR;
      nd_opt->nd_opt_len = 1;
  
      /* Copy target address to temp buffer to prevent misaligned access. */
      ovs_be32 tbuf[4];
      memcpy(tbuf, ipv6_src->s6_addr, sizeof tbuf);
      packet_set_nd(b, tbuf, eth_addr_zero, eth_src);
  
      na->icmph.icmp6_cksum = 0;
      icmp_csum = packet_csum_pseudoheader6(dp_packet_l3(b));
      na->icmph.icmp6_cksum = csum_finish(csum_continue(icmp_csum, na,
                                                        ND_MSG_LEN + ND_OPT_LEN));
  }
  
  uint32_t
  packet_csum_pseudoheader(const struct ip_header *ip)
  {
      uint32_t partial = 0;
  
      partial = csum_add32(partial, get_16aligned_be32(&ip->ip_src));
      partial = csum_add32(partial, get_16aligned_be32(&ip->ip_dst));
      partial = csum_add16(partial, htons(ip->ip_proto));
      partial = csum_add16(partial, htons(ntohs(ip->ip_tot_len) -
                                          IP_IHL(ip->ip_ihl_ver) * 4));
  
      return partial;
  }
  
  #ifndef __CHECKER__
  uint32_t
  packet_csum_pseudoheader6(const struct ovs_16aligned_ip6_hdr *ip6)
  {
      uint32_t partial = 0;
  
      partial = csum_add32(partial, get_16aligned_be32(&(ip6->ip6_src.be32[0])));
      partial = csum_add32(partial, get_16aligned_be32(&(ip6->ip6_src.be32[1])));
      partial = csum_add32(partial, get_16aligned_be32(&(ip6->ip6_src.be32[2])));
      partial = csum_add32(partial, get_16aligned_be32(&(ip6->ip6_src.be32[3])));
  
      partial = csum_add32(partial, get_16aligned_be32(&(ip6->ip6_dst.be32[0])));
      partial = csum_add32(partial, get_16aligned_be32(&(ip6->ip6_dst.be32[1])));
      partial = csum_add32(partial, get_16aligned_be32(&(ip6->ip6_dst.be32[2])));
      partial = csum_add32(partial, get_16aligned_be32(&(ip6->ip6_dst.be32[3])));
  
      partial = csum_add16(partial, htons(ip6->ip6_nxt));
      partial = csum_add16(partial, ip6->ip6_plen);
  
      return partial;
  }
  #endif
  
  void
  IP_ECN_set_ce(struct dp_packet *pkt, bool is_ipv6)
  {
      if (is_ipv6) {
          ovs_16aligned_be32 *ip6 = dp_packet_l3(pkt);
  
          put_16aligned_be32(ip6, get_16aligned_be32(ip6) |
                                  htonl(IP_ECN_CE << 20));
      } else {
          struct ip_header *nh = dp_packet_l3(pkt);
          uint8_t tos = nh->ip_tos;
  
          tos |= IP_ECN_CE;
          if (nh->ip_tos != tos) {
              nh->ip_csum = recalc_csum16(nh->ip_csum, htons(nh->ip_tos),
                                          htons((uint16_t) tos));
              nh->ip_tos = tos;
          }
      }
  }
  