l2sess_node.c

Go to the documentation of this file.

/*
 * Copyright (c) 2016 Cisco and/or its affiliates.
 * 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 <netinet/in.h>
#include <vlib/vlib.h>
#include <vnet/vnet.h>
#include <vnet/pg/pg.h>
#include <vppinfra/error.h>
#include <acl/l2sess.h>
#include <vnet/l2/l2_classify.h>


typedef struct
{
  u32 next_index;
  u32 sw_if_index;
  u32 trace_flags;
  u32 session_tables[2];
  u32 session_nexts[2];
  u8 l4_proto;
} l2sess_trace_t;

/* packet trace format function */

#define _(node_name, node_var, is_out, is_ip6, is_track) \
static u8 * format_## node_var ##_trace (u8 * s, va_list * args)      \
{  \
  CLIB_UNUSED (vlib_main_t * vm) = va_arg (*args, vlib_main_t *); \
  CLIB_UNUSED (vlib_node_t * node) = va_arg (*args, vlib_node_t *); \
  l2sess_trace_t * t = va_arg (*args, l2sess_trace_t *); \
 \
  s = format (s, node_name ": sw_if_index %d, next index %d trace_flags %08x L4 proto %d\n" \
                           "                 tables [ %d, %d ] nexts [ %d, %d ]", \
              t->sw_if_index, t->next_index, t->trace_flags, t->l4_proto, \
              t->session_tables[0], t->session_tables[1], \
              t->session_nexts[0], t->session_nexts[1]); \
  return s; \
}
foreach_l2sess_node
#undef _
#define foreach_l2sess_error \
_(SWAPPED, "Mac swap packets processed")
  typedef enum
{
#define _(sym,str) L2SESS_ERROR_##sym,
  foreach_l2sess_error
#undef _
    L2SESS_N_ERROR,
} l2sess_error_t;

static char *l2sess_error_strings[] = {
#define _(sym,string) string,
  foreach_l2sess_error
#undef _
};

typedef enum
{
  L2SESS_NEXT_DROP,
  L2SESS_N_NEXT,
} l2sess_next_t;

u8
l2sess_get_l4_proto (vlib_buffer_t * b0, int node_is_ip6)
{
  u8 proto;
  int proto_offset;
  if (node_is_ip6)
    {
      proto_offset = 20;
    }
  else
    {
      proto_offset = 23;
    }
  proto = *((u8 *) vlib_buffer_get_current (b0) + proto_offset);
  return proto;
}


u8
l2sess_get_tcp_flags (vlib_buffer_t * b0, int node_is_ip6)
{
  u8 flags;
  int flags_offset;
  if (node_is_ip6)
    {
      flags_offset = 14 + 40 + 13;      /* FIXME: no extension headers assumed */
    }
  else
    {
      flags_offset = 14 + 20 + 13;
    }
  flags = *((u8 *) vlib_buffer_get_current (b0) + flags_offset);
  return flags;
}

static inline int
l4_tcp_or_udp (u8 proto)
{
  return ((proto == 6) || (proto == 17));
}

void
l2sess_get_session_tables (l2sess_main_t * sm, u32 sw_if_index,
                           int node_is_out, int node_is_ip6, u8 l4_proto,
                           u32 * session_tables)
{
/*
 * Based on the direction, l3 and l4 protocol, fill a u32[2] array:
 * [0] is index for the "direct match" path, [1] is for "mirrored match".
 * Store the indices of the tables to add the session to in session_tables[]
 */
  l2_output_classify_main_t *l2om = &l2_output_classify_main;
  l2_input_classify_main_t *l2im = &l2_input_classify_main;

  u32 output_table_index;
  u32 input_table_index;

  if (!l4_tcp_or_udp (l4_proto))
    {
      return;
    }

  if (node_is_ip6)
    {
      vec_validate_init_empty (l2im->
                               classify_table_index_by_sw_if_index
                               [L2_INPUT_CLASSIFY_TABLE_IP6], sw_if_index,
                               ~0);
      input_table_index =
        l2im->
        classify_table_index_by_sw_if_index[L2_INPUT_CLASSIFY_TABLE_IP6]
        [sw_if_index];
      vec_validate_init_empty (l2om->
                               classify_table_index_by_sw_if_index
                               [L2_OUTPUT_CLASSIFY_TABLE_IP6], sw_if_index,
                               ~0);
      output_table_index =
        l2om->
        classify_table_index_by_sw_if_index[L2_OUTPUT_CLASSIFY_TABLE_IP6]
        [sw_if_index];
    }
  else
    {
      vec_validate_init_empty (l2im->
                               classify_table_index_by_sw_if_index
                               [L2_INPUT_CLASSIFY_TABLE_IP4], sw_if_index,
                               ~0);
      input_table_index =
        l2im->
        classify_table_index_by_sw_if_index[L2_INPUT_CLASSIFY_TABLE_IP4]
        [sw_if_index];
      vec_validate_init_empty (l2om->
                               classify_table_index_by_sw_if_index
                               [L2_OUTPUT_CLASSIFY_TABLE_IP4], sw_if_index,
                               ~0);
      output_table_index =
        l2om->
        classify_table_index_by_sw_if_index[L2_OUTPUT_CLASSIFY_TABLE_IP4]
        [sw_if_index];
    }

  if (node_is_out)
    {
      session_tables[0] = output_table_index;
      session_tables[1] = input_table_index;
    }
  else
    {
      session_tables[0] = input_table_index;
      session_tables[1] = output_table_index;
    }
}

void
l2sess_get_session_nexts (l2sess_main_t * sm, u32 sw_if_index,
                          int node_is_out, int node_is_ip6, u8 l4_proto,
                          u32 * session_nexts)
{
/*
 * Based on the direction, l3 and l4 protocol, fill a u32[2] array:
 * [0] is the index for the "direct match" path, [1] is for "mirrored match".
 * Store the match_next_index in session_nexts[] for a new session entry which is being added to session tables.
 */
  u32 input_node_index;
  u32 output_node_index;

  if (!l4_tcp_or_udp (l4_proto))
    {
      return;
    }

  input_node_index =
    sm->next_slot_track_node_by_is_ip6_is_out[node_is_ip6][0];
  output_node_index =
    sm->next_slot_track_node_by_is_ip6_is_out[node_is_ip6][1];

  if (node_is_out)
    {
      session_nexts[0] = output_node_index;
      session_nexts[1] = input_node_index;
    }
  else
    {
      session_nexts[0] = input_node_index;
      session_nexts[1] = output_node_index;
    }
}


static inline void
swap_bytes (vlib_buffer_t * b0, int off_a, int off_b, int nbytes)
{
  u8 tmp;
  u8 *pa = vlib_buffer_get_current (b0) + off_a;
  u8 *pb = vlib_buffer_get_current (b0) + off_b;
  while (nbytes--)
    {
      tmp = *pa;
      *pa++ = *pb;
      *pb++ = tmp;
    }
}

/*
 * This quite pro[bv]ably is a terrible idea performance wise. Moreso doing it twice.
 * Would having a long (ish) chunk of memory work better for this ?
 * We will see when we get to the performance of this.
 */
void
l2sess_flip_l3l4_fields (vlib_buffer_t * b0, int node_is_ip6, u8 l4_proto)
{
  if (!l4_tcp_or_udp (l4_proto))
    {
      return;
    }
  if (node_is_ip6)
    {
      swap_bytes (b0, 22, 38, 16);      /* L3 */
      swap_bytes (b0, 54, 56, 2);       /* L4 (when no EH!) */
    }
  else
    {
      swap_bytes (b0, 26, 30, 4);       /* L3 */
      swap_bytes (b0, 34, 36, 2);       /* L4 */
    }
}

void
l2sess_add_session (vlib_buffer_t * b0, int node_is_out, int node_is_ip6,
                    u32 session_table, u32 session_match_next,
                    u32 opaque_index)
{
  vnet_classify_main_t *cm = &vnet_classify_main;
  u32 action = 0;
  u32 metadata = 0;

#ifdef DEBUG_SESSIONS
  printf ("Adding session to table %d with next %d\n", session_table,
          session_match_next);
#endif
  vnet_classify_add_del_session (cm, session_table,
                                 vlib_buffer_get_current (b0),
                                 session_match_next, opaque_index, 0, action,
                                 metadata, 1);
}



static void *
get_ptr_to_offset (vlib_buffer_t * b0, int offset)
{
  u8 *p = vlib_buffer_get_current (b0) + offset;
  return p;
}


/*
 * FIXME: Hardcoded offsets are ugly, although if casting to structs one
 * would need to take care about alignment.. So let's for now be naive and simple.
 */

void
session_store_ip4_l3l4_info (vlib_buffer_t * b0, l2s_session_t * sess,
                             int node_is_out)
{
  clib_memcpy (&sess->side[1 - node_is_out].addr.ip4,
               get_ptr_to_offset (b0, 26), 4);
  clib_memcpy (&sess->side[node_is_out].addr.ip4, get_ptr_to_offset (b0, 30),
               4);
  sess->side[1 - node_is_out].port =
    ntohs (*(u16 *) get_ptr_to_offset (b0, 34));
  sess->side[node_is_out].port = ntohs (*(u16 *) get_ptr_to_offset (b0, 36));
}

void
session_store_ip6_l3l4_info (vlib_buffer_t * b0, l2s_session_t * sess,
                             int node_is_out)
{
  clib_memcpy (&sess->side[1 - node_is_out].addr.ip6,
               get_ptr_to_offset (b0, 22), 16);
  clib_memcpy (&sess->side[node_is_out].addr.ip4, get_ptr_to_offset (b0, 38),
               16);
  sess->side[1 - node_is_out].port =
    ntohs (*(u16 *) get_ptr_to_offset (b0, 54));
  sess->side[node_is_out].port = ntohs (*(u16 *) get_ptr_to_offset (b0, 56));
}

static void
build_match_from_session (l2sess_main_t * sm, u8 * match,
                          l2s_session_t * sess, int is_out)
{
  if (sess->is_ip6)
    {
      match[20] = sess->l4_proto;
      clib_memcpy (&match[22], &sess->side[1 - is_out].addr.ip6, 16);
      clib_memcpy (&match[38], &sess->side[is_out].addr.ip4, 16);
      *(u16 *) & match[54] = htons (sess->side[1 - is_out].port);
      *(u16 *) & match[56] = htons (sess->side[is_out].port);
    }
  else
    {
      match[23] = sess->l4_proto;
      clib_memcpy (&match[26], &sess->side[1 - is_out].addr.ip6, 4);
      clib_memcpy (&match[30], &sess->side[is_out].addr.ip4, 4);
      *(u16 *) & match[34] = htons (sess->side[1 - is_out].port);
      *(u16 *) & match[36] = htons (sess->side[is_out].port);
    }
}

static void
delete_session (l2sess_main_t * sm, u32 sw_if_index, u32 session_index)
{
  vnet_classify_main_t *cm = &vnet_classify_main;
  u8 match[5 * 16];             /* For building the mock of the packet to delete the classifier session */
  u32 session_tables[2] = { ~0, ~0 };
  l2s_session_t *sess = sm->sessions + session_index;
  if (pool_is_free (sm->sessions, sess))
    {
      sm->counter_attempted_delete_free_session++;
      return;
    }
  l2sess_get_session_tables (sm, sw_if_index, 0, sess->is_ip6, sess->l4_proto,
                             session_tables);
  if (session_tables[1] != ~0)
    {
      build_match_from_session (sm, match, sess, 1);
      vnet_classify_add_del_session (cm, session_tables[1], match, 0, 0, 0, 0,
                                     0, 0);
    }
  if (session_tables[1] != ~0)
    {
      build_match_from_session (sm, match, sess, 1);
      vnet_classify_add_del_session (cm, session_tables[1], match, 0, 0, 0, 0,
                                     0, 0);
    }
  pool_put (sm->sessions, sess);
}

static void
udp_session_account_buffer (vlib_buffer_t * b0, l2s_session_t * s,
                            int which_side, u64 now)
{
  l2s_session_side_t *ss = &s->side[which_side];
  ss->active_time = now;
  ss->n_packets++;
  ss->n_bytes += b0->current_data + b0->current_length;
}

static inline u64
udp_session_get_timeout (l2sess_main_t * sm, l2s_session_t * sess, u64 now)
{
  return (sm->udp_session_idle_timeout);
}

static void
tcp_session_account_buffer (vlib_buffer_t * b0, l2s_session_t * s,
                            int which_side, u64 now)
{
  l2s_session_side_t *ss = &s->side[which_side];
  ss->active_time = now;
  ss->n_packets++;
  ss->n_bytes += b0->current_data + b0->current_length;
  /* Very very lightweight TCP state tracking: just record which flags were seen */
  s->tcp_flags_seen |=
    l2sess_get_tcp_flags (b0, s->is_ip6) << (8 * which_side);
}

/*
 * Since we are tracking for the purposes of timing the sessions out,
 * we mostly care about two states: established (maximize the idle timeouts)
 * and transient (halfopen/halfclosed/reset) - we need to have a reasonably short timeout to
 * quickly get rid of sessions but not short enough to violate the TCP specs.
 */

static inline u64
tcp_session_get_timeout (l2sess_main_t * sm, l2s_session_t * sess, u64 now)
{
  /* seen both SYNs and ACKs but not FINs means we are in establshed state */
  u16 masked_flags =
    sess->tcp_flags_seen & ((TCP_FLAGS_RSTFINACKSYN << 8) +
                            TCP_FLAGS_RSTFINACKSYN);
  if (((TCP_FLAGS_ACKSYN << 8) + TCP_FLAGS_ACKSYN) == masked_flags)
    {
      return (sm->tcp_session_idle_timeout);
    }
  else
    {
      return (sm->tcp_session_transient_timeout);
    }
}

static inline u64
session_get_timeout (l2sess_main_t * sm, l2s_session_t * sess, u64 now)
{
  u64 timeout;

  switch (sess->l4_proto)
    {
    case 6:
      timeout = tcp_session_get_timeout (sm, sess, now);
      break;
    case 17:
      timeout = udp_session_get_timeout (sm, sess, now);
      break;
    default:
      timeout = 0;
    }

  return timeout;
}

static inline u64
get_session_last_active_time(l2s_session_t * sess)
{
  u64 last_active =
    sess->side[0].active_time >
    sess->side[1].active_time ? sess->side[0].active_time : sess->side[1].
    active_time;
  return last_active;
}

static int
session_is_alive (l2sess_main_t * sm, l2s_session_t * sess, u64 now, u64 *last_active_cache)
{
  u64 last_active = get_session_last_active_time(sess);
  u64 timeout = session_get_timeout (sm, sess, now);
  int is_alive = ((now - last_active) < timeout);
  if (last_active_cache)
    *last_active_cache = last_active;
  return is_alive;
}

static void
check_idle_sessions (l2sess_main_t * sm, u32 sw_if_index, u64 now)
{
  sm->timer_wheel_next_expiring_time = 0;
  sm->data_from_advancing_timing_wheel
    =
    timing_wheel_advance (&sm->timing_wheel, now,
                          sm->data_from_advancing_timing_wheel,
                          &sm->timer_wheel_next_expiring_time);
#ifdef DEBUG_SESSIONS_VERBOSE
  {
    clib_time_t *ct = &sm->vlib_main->clib_time;
    f64 ctime;
    ctime = now * ct->seconds_per_clock;
    clib_warning ("Now        : %U", format_time_interval, "h:m:s:u", ctime);
    ctime = sm->timer_wheel_next_expiring_time * ct->seconds_per_clock;
    clib_warning ("Next expire: %U", format_time_interval, "h:m:s:u", ctime);
    clib_warning ("Expired items: %d",
                  (int) vec_len (sm->data_from_advancing_timing_wheel));
  }
#endif

  sm->timer_wheel_next_expiring_time = now + sm->timer_wheel_tick;
  if (PREDICT_FALSE ( 0 == sm->data_from_advancing_timing_wheel )) {
    return;
  }

  if (PREDICT_FALSE (_vec_len (sm->data_from_advancing_timing_wheel) > 0))
    {
      uword i;
      for (i = 0; i < _vec_len (sm->data_from_advancing_timing_wheel); i++)
        {
          u32 session_index = sm->data_from_advancing_timing_wheel[i];
          if (!pool_is_free_index (sm->sessions, session_index))
            {
              l2s_session_t *sess = sm->sessions + session_index;
              u64 last_active;
              if (session_is_alive (sm, sess, now, &last_active))
                {
#ifdef DEBUG_SESSIONS
              clib_warning ("Restarting timer for session %d", (int) session_index);
#endif
                    /* Pretend we did this in the past, at last_active moment */
                    timing_wheel_insert (&sm->timing_wheel,
                                         last_active + session_get_timeout (sm, sess,
                                                                    last_active),
                                         session_index);
                }
              else
                {
#ifdef DEBUG_SESSIONS
              clib_warning ("Deleting session %d", (int) session_index);
#endif
              delete_session (sm, sw_if_index, session_index);
                }
            }
        }
      _vec_len (sm->data_from_advancing_timing_wheel) = 0;
    }
}

static uword
l2sess_node_fn (vlib_main_t * vm,
                vlib_node_runtime_t * node, vlib_frame_t * frame,
                int node_is_out, int node_is_ip6, int node_is_track,
                u32 *feat_next_node_index)
{
  u32 n_left_from, *from, *to_next;
  l2sess_next_t next_index;
  u32 pkts_swapped = 0;
  u32 feature_bitmap0;
  u32 trace_flags0;

  l2sess_main_t *sm = &l2sess_main;

  from = vlib_frame_vector_args (frame);
  n_left_from = frame->n_vectors;
  next_index = node->cached_next_index;

  while (n_left_from > 0)
    {
      u32 n_left_to_next;

      vlib_get_next_frame (vm, node, next_index, to_next, n_left_to_next);

      /* Only a single loop for now for simplicity */

      while (n_left_from > 0 && n_left_to_next > 0)
        {
          u32 bi0;
          vlib_buffer_t *b0;
          u32 next0 = L2SESS_NEXT_DROP;
          u32 sw_if_index0;
          //ethernet_header_t *en0;

          /* speculatively enqueue b0 to the current next frame */
          bi0 = from[0];
          to_next[0] = bi0;
          from += 1;
          to_next += 1;
          n_left_from -= 1;
          n_left_to_next -= 1;

          b0 = vlib_get_buffer (vm, bi0);
          //en0 = vlib_buffer_get_current (b0);

/*
 *     node_is_out : 1 = is output, 0 = is input
 *     node_is_ip6 : 1 = is ip6, 0 = is ip4
 *     node_is_track : 1 = is a state tracking node, 0 - is a session addition node
 *
 *     The below code adjust the behavior according to these parameters.
 */
          {
            u32 session_tables[2] = { ~0, ~0 };
            u32 session_nexts[2] = { ~0, ~0 };
            u8 l4_proto;
            u64 now = clib_cpu_time_now ();

            trace_flags0 = 0;
            if (node_is_out)
              {
                sw_if_index0 = vnet_buffer (b0)->sw_if_index[VLIB_TX];
              }
            else
              {
                sw_if_index0 = vnet_buffer (b0)->sw_if_index[VLIB_RX];
              }
            /* potentially also remove the nodes here */
            feature_bitmap0 = vnet_buffer (b0)->l2.feature_bitmap;

            if (node_is_track)
              {
                u32 sess_index = vnet_buffer (b0)->l2_classify.opaque_index;
                l2s_session_t *sess = sm->sessions + sess_index;
                l4_proto = sess->l4_proto;

                if (session_is_alive (sm, sess, now, 0))
                  {
                    if (6 == l4_proto)
                      {
                        tcp_session_account_buffer (b0, sess, node_is_out,
                                                    now);
                      }
                    else
                      {
                        udp_session_account_buffer (b0, sess, node_is_out,
                                                    now);
                      }
                  }
                else
                  {
                    timing_wheel_delete (&sm->timing_wheel, sess_index);
                    delete_session (sm, sw_if_index0, sess_index);
                    /* FIXME: drop the packet that hit the obsolete node, for now. We really ought to recycle it. */
                    next0 = 0;
                  }
              }
            else
              {
                /*
                 * "-add" node: take l2opaque which arrived to us, and deduce
                 * the tables out of that. ~0 means the topmost classifier table
                 * applied for this AF on the RX(for input)/TX(for output)) sw_if_index.
                 * Also add the mirrored session to the paired table.
                 */
                l2s_session_t *sess;
                u32 sess_index;

                l4_proto = l2sess_get_l4_proto (b0, node_is_ip6);

                pool_get (sm->sessions, sess);
                sess_index = sess - sm->sessions;
                sess->create_time = now;
                sess->side[node_is_out].active_time = now;
                sess->side[1 - node_is_out].active_time = now;
                sess->l4_proto = l4_proto;
                sess->is_ip6 = node_is_ip6;
                if (node_is_ip6)
                  {
                    session_store_ip6_l3l4_info (b0, sess, node_is_out);
                  }
                else
                  {
                    session_store_ip4_l3l4_info (b0, sess, node_is_out);
                  }

                l2sess_get_session_tables (sm, sw_if_index0, node_is_out,
                                           node_is_ip6, l4_proto,
                                           session_tables);
                l2sess_get_session_nexts (sm, sw_if_index0, node_is_out,
                                          node_is_ip6, l4_proto,
                                          session_nexts);
                l2sess_flip_l3l4_fields (b0, node_is_ip6, l4_proto);
                if (session_tables[1] != ~0)
                  {
                    l2sess_add_session (b0, node_is_out, node_is_ip6,
                                        session_tables[1], session_nexts[1],
                                        sess_index);
                  }
                l2sess_flip_l3l4_fields (b0, node_is_ip6, l4_proto);
                if (session_tables[0] != ~0)
                  {
                    l2sess_add_session (b0, node_is_out, node_is_ip6,
                                        session_tables[0], session_nexts[0],
                                        sess_index);
                  }
                if (6 == sess->l4_proto)
                  {
                    tcp_session_account_buffer (b0, sess, node_is_out, now);
                  }
                else
                  {
                    udp_session_account_buffer (b0, sess, node_is_out, now);
                  }
                timing_wheel_insert (&sm->timing_wheel,
                                     now + session_get_timeout (sm, sess,
                                                                now),
                                     sess_index);
              }

            if (now >= sm->timer_wheel_next_expiring_time)
              {
                check_idle_sessions (sm, sw_if_index0, now);
              }

            next0 = feat_bitmap_get_next_node_index (feat_next_node_index,
                                                   feature_bitmap0);

            if (next0 >= node->n_next_nodes)
              {
                trace_flags0 |= 1;
              }

            if (PREDICT_FALSE ((node->flags & VLIB_NODE_FLAG_TRACE)
                               && (b0->flags & VLIB_BUFFER_IS_TRACED)))
              {
                l2sess_trace_t *t =
                  vlib_add_trace (vm, node, b0, sizeof (*t));
                t->sw_if_index = sw_if_index0;
                t->next_index = next0;
                t->trace_flags = trace_flags0;
                t->l4_proto = l4_proto;
                t->session_tables[0] = session_tables[0];
                t->session_tables[1] = session_tables[1];
                t->session_nexts[0] = session_nexts[0];
                t->session_nexts[1] = session_nexts[1];
              }

          }
          pkts_swapped += 1;
          if (next0 >= node->n_next_nodes)
            {
              next0 = 0;
            }

          /* verify speculative enqueue, maybe switch current next frame */
          vlib_validate_buffer_enqueue_x1 (vm, node, next_index,
                                           to_next, n_left_to_next,
                                           bi0, next0);
        }

      vlib_put_next_frame (vm, node, next_index, n_left_to_next);
    }
  vlib_node_increment_counter (vm, node->node_index,
                               L2SESS_ERROR_SWAPPED, pkts_swapped);
  return frame->n_vectors;
}


#define _(node_name, node_var, is_out, is_ip6, is_track) \
static uword                                             \
node_var ## node_fn (vlib_main_t * vm,                   \
                  vlib_node_runtime_t * node,            \
                  vlib_frame_t * frame)                  \
{                                                        \
  l2sess_main_t *sm = &l2sess_main;                      \
  return l2sess_node_fn(vm, node, frame,                 \
                        is_out, is_ip6, is_track,        \
                        sm->node_var ## _feat_next_node_index);  \
}                                                        \
VLIB_REGISTER_NODE (node_var) = {                        \
  .function = node_var ## node_fn,                       \
  .name = node_name,                                     \
  .vector_size = sizeof (u32),                           \
  .format_trace = format_ ## node_var ## _trace,         \
  .type = VLIB_NODE_TYPE_INTERNAL,                       \
                                                         \
  .n_errors = ARRAY_LEN(l2sess_error_strings),           \
  .error_strings = l2sess_error_strings,                 \
                                                         \
  .n_next_nodes = L2SESS_N_NEXT,                         \
  .next_nodes = {                                        \
        [L2SESS_NEXT_DROP] = "error-drop",               \
  },                                                     \
};
foreach_l2sess_node
#undef _