# Introduction
Maximum Transmission Unit is a term used to describe the maximum sized "thingy" that can be sent out an interface. It can refer to the maximum frame size that a NIC can send. On Ethernet that would include the Ethernet header but typically not the IGF. It can refer to the maximum packet size, that is, on Ethernet an MTU of 1500, would allow an IPv4 packet of 1500 bytes, that would result in an Ethernet frame of 1518 bytes.

# MTU in VPP
VPP allows setting of the physical payload MTU. I.e. not including L2 overhead. Setting the hardware MTU will program the NIC.
This MTU will be inherited by all software interfaces.

VPP also allows setting of the payload MTU for software interfaces. Independently of the MTU set on the hardware. If the software payload MTU is set higher than the capability of the NIC, the packet will be dropped.

In addition VPP supports setting the MTU of individual network layer protocols. IPv4, IPv6 or MPLS. For example an IPv4 MTU of 1500 (includes the IPv4 header) will fit in a hardware payload MTU of 1500.

_Note we might consider changing the hardware payload MTU to hardware MTU_. That is, the MTU includes all L2 framing. Then the payload MTU can be calculated based on the interface's configuration. E.g. 802.1q tags etc.

There are currently no checks or warnings if e.g. the user configures a per-protocol MTU larger than the underlying payload MTU. If that happens packets will be fragmented or dropped.

## Data structures
The hardware payload MTU is stored in the max_packet_bytes variable in the vnet_hw_interface_t structure.

The software MTU (previously max_l3_packet_bytes) is in vnet_sw_interface_t->in mtu[VNET_N_MTU].

# API

## Set physical MTU

This API message is used to set the physical MTU. It is currently limited to Ethernet interfaces. Note, this programs the NIC.

```
autoreply define hw_interface_set_mtu
{
 u32 client_index;
 u32 context;
 u32 sw_if_index;
 u16 mtu;
};
```

## Set the L2 payload MTU (not including the L2 header) and per-protocol MTUs

This API message sets the L3 payload MTU. E.g. on Ethernet it is the maximum size of the Ethernet payload. If a value is left as 0, then the default is picked from VNET_MTU_L3.

```
autoreply define sw_interface_set_mtu
{
 u32 client_index;
 u32 context;
 u32 sw_if_index;
 /* $$$$ Replace with enum */
 u32 mtu[4]; /* 0 - L3, 1 - IP4, 2 - IP6, 3 - MPLS */
};

```

## Get interface MTU

The various MTUs on an interface can be queried with the sw_interface_
/*
 * 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.
 */
/**
 * @file
 * @brief LISP sub-interfaces.
 *
 */
#include <vnet/lisp-gpe/lisp_gpe_tenant.h>
#include <vnet/lisp-gpe/lisp_gpe_sub_interface.h>
#include <vnet/fib/fib_table.h>
#include <vnet/interface.h>

/**
 * @brief Pool of all l3-sub-interfaces
 */
static lisp_gpe_sub_interface_t *lisp_gpe_sub_interface_pool;

/**
 * A DB of all LISP L3 sub-interfaces. The key is:{VNI,l-RLOC}
 */
static uword *lisp_gpe_sub_interfaces;

/**
 * A DB of all VNET L3 sub-interfaces. The key is:{VNI,l-RLOC}
 * Used in the data-plane for interface lookup on decap.
 */
uword *lisp_gpe_sub_interfaces_sw_if_index;

/**
 * The next available sub-interface ID. FIXME
 */
static u32 lisp_gpe_sub_interface_id;


static index_t
lisp_gpe_sub_interface_db_find (const ip_address_t * lrloc, u32 vni)
{
  uword *p;

  lisp_gpe_sub_interface_key_t key;

  memset (&key, 0, sizeof (key));
  ip_address_copy (&key.local_rloc, lrloc);
  key.vni = vni;
  p = hash_get_mem (lisp_gpe_sub_interfaces, &key);

  if (NULL == p)
    return (INDEX_INVALID);
  else
    return (p[0]);
}

static void
lisp_gpe_sub_interface_db_insert (const lisp_gpe_sub_interface_t * l3s)
{
  hash_set_mem (lisp_gpe_sub_interfaces,
		l3s->key, l3s - lisp_gpe_sub_interface_pool);
  hash_set_mem (lisp_gpe_sub_interfaces_sw_if_index,
		l3s->key, l3s->sw_if_index);
}

static void
lisp_gpe_sub_interface_db_remove (const lisp_gpe_sub_interface_t * l3s)
{
  hash_unset_mem (lisp_gpe_sub_interfaces, l3s->key);
  hash_unset_mem (lisp_gpe_sub_interfaces_sw_if_index, l3s->key);
}

lisp_gpe_sub_interface_t *
lisp_gpe_sub_interface_get_i (index_t l3si)
{
  return (pool_elt_at_index (lisp_gpe_sub_interface_pool, l3si));
}

static void
lisp_gpe_sub_interface_set_table (u32 sw_if_index, u32 table_id)
{
  fib_node_index_t fib_index;

  fib_index = fib_table_find_or_create_and_lock (FIB_PROTOCOL_IP4, table_id,
						 FIB_SOURCE_LISP);
  ASSERT (FIB_NODE_INDEX_INVALID != fib_index);

  vec_validate (ip4_main.fib_index_by_sw_if_index, sw_if_index);
  ip4_main.fib_index_by_sw_if_index[sw_if_index] = fib_index;

  fib_index = fib_table_find_or_create_and_lock (FIB_PROTOCOL_IP6, table_id,
						 FIB_SOURCE_LISP);
  ASSERT (FIB_NODE_INDEX_INVALID != fib_index);

  vec_validate (ip6_main.fib_index_by_sw_if_index, sw_if_index);
  ip6_main.fib_index_by_sw_if_index[sw_if_index] = fib_index;
}

static void
lisp_gpe_sub_interface_unset_table (u32 sw_if_index, u32 table_id)
{
  fib_table_unlock (ip4_main.fib_index_by_sw_if_index[sw_if_index],
		    FIB_PROTOCOL_IP4, FIB_SOURCE_LISP);
  ip4_main.fib_index_by_sw_if_index[sw_if_index] = 0;
  ip4_sw_interface_enable_disable (sw_if_index, 0);

  fib_table_unlock (ip6_main.fib_index_by_sw_if_index[sw_if_index],
		    FIB_PROTOCOL_IP6, FIB_SOURCE_LISP);
  ip6_main.fib_index_by_sw_if_index[sw_if_index] = 0;
  ip6_sw_interface_enable_disable (sw_if_index, 0);
}

index_t
lisp_gpe_sub_interface_find_or_create_and_lock (const ip_address_t * lrloc,
						u32 overlay_table_id, u32 vni)
{
  lisp_gpe_sub_interface_t *l3s;
  index_t l3si;

  l3si = lisp_gpe_sub_interface_db_find (lrloc, vni);

  if (INDEX_INVALID == l3si)
    {
      u32 main_sw_if_index, sub_sw_if_index;

      /*
       * find the main interface from the VNI
       */
      main_sw_if_index =
	lisp_gpe_tenant_l3_iface_add_or_lock (vni, overlay_table_id,
					      1 /* with_default_route */ );

      vnet_sw_interface_t sub_itf_template = {
	.type = VNET_SW_INTERFACE_TYPE_SUB,
	.flood_class = VNET_FLOOD_CLASS_NORMAL,
	.sup_sw_if_index = main_sw_if_index,
	.sub.id = lisp_gpe_sub_interface_id++,
      };

      if (NULL != vnet_create_sw_interface (vnet_get_main (),
					    &sub_itf_template,
					    &sub_sw_if_index))
	return (INDEX_INVALID);

      pool_get (lisp_gpe_sub_interface_pool, l3s);
      memset (l3s, 0, sizeof (*l3s));
      l3s->key = clib_mem_alloc (sizeof (*l3s->key));
      memset (l3s->key, 0, sizeof (*l3s->key));

      ip_address_copy (&l3s->key->local_rloc, lrloc);
      l3s->key->vni = vni;
      l3s->main_sw_if_index = main_sw_if_index;
      l3s->sw_if_index = sub_sw_if_index;
      l3s->eid_table_id = overlay_table_id;

      l3si = (l3s - lisp_gpe_sub_interface_pool);

      // FIXME. enable When we get an adj
      ip6_sw_interface_enable_disable (l3s->sw_if_index, 1);
      ip4_sw_interface_enable_disable (l3s->sw_if_index, 1);

      vnet_sw_interface_set_flags (vnet_get_main (),
				   l3s->sw_if_index,
				   VNET_SW_INTERFACE_FLAG_ADMIN_UP);

      lisp_gpe_sub_interface_db_insert (l3s);
    }
  else
    {
      l3s = lisp_gpe_sub_interface_get_i (l3si);
      l3s->eid_table_id = overlay_table_id;
    }

  lisp_gpe_sub_interface_set_table (l3s->sw_if_index, l3s->eid_table_id);
  l3s->locks++;

  return (l3si);
}

void
lisp_gpe_sub_interface_unlock (index_t l3si)
{
  lisp_gpe_sub_interface_t *l3s;

  l3s = lisp_gpe_sub_interface_get_i (l3si);

  ASSERT (0 != l3s->locks);
  l3s->locks--;

  if (0 == l3s->locks)
    {
      lisp_gpe_sub_interface_unset_table (l3s->sw_if_index,
					  l3s->eid_table_id);

      lisp_gpe_tenant_l3_iface_unlock (l3s->key->vni);
      vnet_sw_interface_set_flags (vnet_get_main (), l3s->sw_if_index, 0);
      vnet_delete_sub_interface (l3s->sw_if_index);

      lisp_gpe_sub_interface_db_remove (l3s);

      clib_mem_free (l3s->key);
      pool_put (lisp_gpe_sub_interface_pool, l3s);
    }
}

const lisp_gpe_sub_interface_t *
lisp_gpe_sub_interface_get (index_t l3si)
{
  return (lisp_gpe_sub_interface_get_i (l3si));
}

u8 *
format_lisp_gpe_sub_interface (u8 * s, va_list * ap)
{
  lisp_gpe_sub_interface_t *l3s = va_arg (*ap, lisp_gpe_sub_interface_t *);
  vnet_main_t *vnm = vnet_get_main ();

  s = format (s, "%-16U",
	      format_vnet_sw_interface_name,
	      vnm, vnet_get_sw_interface (vnm, l3s->sw_if_index));
  s = format (s, "%=8d", l3s->key->vni);
  s = format (s, "%=15d", l3s->sw_if_index);
  s = format (s, "%U", format_ip_address, &l3s->key->local_rloc);

  return (s);
}

/** CLI command to show LISP-GPE interfaces. */
static clib_error_t *
lisp_gpe_sub_interface_show (vlib_main_t * vm,
			     unformat_input_t * input,
			     vlib_cli_command_t * cmd)
{
  lisp_gpe_sub_interface_t *l3s;

  vlib_cli_output (vm, "%-16s%=8s%=15s%s", "Name", "VNI", "sw_if_index",
		   "local RLOC");

  /* *INDENT-OFF* */
  pool_foreach (l3s, lisp_gpe_sub_interface_pool,
  ({
    vlib_cli_output (vm, "%U", format_lisp_gpe_sub_interface, l3s);
  }));
  /* *INDENT-ON* */

  return 0;
}

/* *INDENT-OFF* */
VLIB_CLI_COMMAND (lisp_gpe_sub_interface_command) = {
  .path = "show gpe sub-interface",
  .short_help = "show gpe sub-interface",
  .function = lisp_gpe_sub_interface_show,
};
/* *INDENT-ON* */

static clib_error_t *
lisp_gpe_sub_interface_module_init (vlib_main_t * vm)
{
  lisp_gpe_sub_interfaces =
    hash_create_mem (0,
		     sizeof (lisp_gpe_sub_interface_key_t), sizeof (uword));
  lisp_gpe_sub_interfaces_sw_if_index =
    hash_create_mem (0,
		     sizeof (lisp_gpe_sub_interface_key_t), sizeof (uword));

  return (NULL);
}

VLIB_INIT_FUNCTION (lisp_gpe_sub_interface_module_init);

/*
 * fd.io coding-style-patch-verification: ON
 *
 * Local Variables:
 * eval: (c-set-style "gnu")
 * End:
 */