Diff: lwip/core/netif.c

Revision:

0:350011bf8be7

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lwip/core/netif.c	Tue Nov 23 14:15:36 2010 +0000
@@ -0,0 +1,752 @@
+/**
+ * @file
+ * lwIP network interface abstraction
+ *
+ */
+
+/*
+ * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification,
+ * are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
+ * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
+ * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
+ * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
+ * OF SUCH DAMAGE.
+ *
+ * This file is part of the lwIP TCP/IP stack.
+ *
+ * Author: Adam Dunkels <adam@sics.se>
+ *
+ */
+
+#include "lwip/opt.h"
+
+#include "lwip/def.h"
+#include "lwip/ip_addr.h"
+#include "lwip/netif.h"
+#include "lwip/tcp_impl.h"
+#include "lwip/snmp.h"
+#include "lwip/igmp.h"
+#include "netif/etharp.h"
+#include "lwip/stats.h"
+#if ENABLE_LOOPBACK
+#include "lwip/sys.h"
+#if LWIP_NETIF_LOOPBACK_MULTITHREADING
+#include "lwip/tcpip.h"
+#endif /* LWIP_NETIF_LOOPBACK_MULTITHREADING */
+#endif /* ENABLE_LOOPBACK */
+
+#if LWIP_AUTOIP
+#include "lwip/autoip.h"
+#endif /* LWIP_AUTOIP */
+#if LWIP_DHCP
+#include "lwip/dhcp.h"
+#endif /* LWIP_DHCP */
+
+#if LWIP_NETIF_STATUS_CALLBACK
+#define NETIF_STATUS_CALLBACK(n) do{ if (n->status_callback) { (n->status_callback)(n); }}while(0)
+#else
+#define NETIF_STATUS_CALLBACK(n)
+#endif /* LWIP_NETIF_STATUS_CALLBACK */ 
+
+#if LWIP_NETIF_LINK_CALLBACK
+#define NETIF_LINK_CALLBACK(n) do{ if (n->link_callback) { (n->link_callback)(n); }}while(0)
+#else
+#define NETIF_LINK_CALLBACK(n)
+#endif /* LWIP_NETIF_LINK_CALLBACK */ 
+
+struct netif *netif_list;
+struct netif *netif_default;
+
+#if LWIP_HAVE_LOOPIF
+static struct netif loop_netif;
+
+/**
+ * Initialize a lwip network interface structure for a loopback interface
+ *
+ * @param netif the lwip network interface structure for this loopif
+ * @return ERR_OK if the loopif is initialized
+ *         ERR_MEM if private data couldn't be allocated
+ */
+static err_t
+netif_loopif_init(struct netif *netif)
+{
+  /* initialize the snmp variables and counters inside the struct netif
+   * ifSpeed: no assumption can be made!
+   */
+  NETIF_INIT_SNMP(netif, snmp_ifType_softwareLoopback, 0);
+
+  netif->name[0] = 'l';
+  netif->name[1] = 'o';
+  netif->output = netif_loop_output;
+  return ERR_OK;
+}
+#endif /* LWIP_HAVE_LOOPIF */
+
+void
+netif_init(void)
+{
+#if LWIP_HAVE_LOOPIF
+  ip_addr_t loop_ipaddr, loop_netmask, loop_gw;
+  IP4_ADDR(&loop_gw, 127,0,0,1);
+  IP4_ADDR(&loop_ipaddr, 127,0,0,1);
+  IP4_ADDR(&loop_netmask, 255,0,0,0);
+
+#if NO_SYS
+  netif_add(&loop_netif, &loop_ipaddr, &loop_netmask, &loop_gw, NULL, netif_loopif_init, ip_input);
+#else  /* NO_SYS */
+  netif_add(&loop_netif, &loop_ipaddr, &loop_netmask, &loop_gw, NULL, netif_loopif_init, tcpip_input);
+#endif /* NO_SYS */
+  netif_set_up(&loop_netif);
+
+#endif /* LWIP_HAVE_LOOPIF */
+}
+
+/**
+ * Add a network interface to the list of lwIP netifs.
+ *
+ * @param netif a pre-allocated netif structure
+ * @param ipaddr IP address for the new netif
+ * @param netmask network mask for the new netif
+ * @param gw default gateway IP address for the new netif
+ * @param state opaque data passed to the new netif
+ * @param init callback function that initializes the interface
+ * @param input callback function that is called to pass
+ * ingress packets up in the protocol layer stack.
+ *
+ * @return netif, or NULL if failed.
+ */
+struct netif *
+netif_add(struct netif *netif, ip_addr_t *ipaddr, ip_addr_t *netmask,
+  ip_addr_t *gw, void *state, netif_init_fn init, netif_input_fn input)
+{
+  static u8_t netifnum = 0;
+
+  LWIP_ASSERT("No init function given", init != NULL);
+
+  /* reset new interface configuration state */
+  ip_addr_set_zero(&netif->ip_addr);
+  ip_addr_set_zero(&netif->netmask);
+  ip_addr_set_zero(&netif->gw);
+  netif->flags = 0;
+#if LWIP_DHCP
+  /* netif not under DHCP control by default */
+  netif->dhcp = NULL;
+#endif /* LWIP_DHCP */
+#if LWIP_AUTOIP
+  /* netif not under AutoIP control by default */
+  netif->autoip = NULL;
+#endif /* LWIP_AUTOIP */
+#if LWIP_NETIF_STATUS_CALLBACK
+  netif->status_callback = NULL;
+#endif /* LWIP_NETIF_STATUS_CALLBACK */
+#if LWIP_NETIF_LINK_CALLBACK
+  netif->link_callback = NULL;
+#endif /* LWIP_NETIF_LINK_CALLBACK */
+#if LWIP_IGMP
+  netif->igmp_mac_filter = NULL;
+#endif /* LWIP_IGMP */
+#if ENABLE_LOOPBACK
+  netif->loop_first = NULL;
+  netif->loop_last = NULL;
+#endif /* ENABLE_LOOPBACK */
+
+  /* remember netif specific state information data */
+  netif->state = state;
+  netif->num = netifnum++;
+  netif->input = input;
+#if LWIP_NETIF_HWADDRHINT
+  netif->addr_hint = NULL;
+#endif /* LWIP_NETIF_HWADDRHINT*/
+#if ENABLE_LOOPBACK && LWIP_LOOPBACK_MAX_PBUFS
+  netif->loop_cnt_current = 0;
+#endif /* ENABLE_LOOPBACK && LWIP_LOOPBACK_MAX_PBUFS */
+
+  netif_set_addr(netif, ipaddr, netmask, gw);
+
+  /* call user specified initialization function for netif */
+  if (init(netif) != ERR_OK) {
+    return NULL;
+  }
+
+  /* add this netif to the list */
+  netif->next = netif_list;
+  netif_list = netif;
+  snmp_inc_iflist();
+
+#if LWIP_IGMP
+  /* start IGMP processing */
+  if (netif->flags & NETIF_FLAG_IGMP) {
+    igmp_start(netif);
+  }
+#endif /* LWIP_IGMP */
+
+  LWIP_DEBUGF(NETIF_DEBUG, ("netif: added interface %c%c IP addr ",
+    netif->name[0], netif->name[1]));
+  ip_addr_debug_print(NETIF_DEBUG, ipaddr);
+  LWIP_DEBUGF(NETIF_DEBUG, (" netmask "));
+  ip_addr_debug_print(NETIF_DEBUG, netmask);
+  LWIP_DEBUGF(NETIF_DEBUG, (" gw "));
+  ip_addr_debug_print(NETIF_DEBUG, gw);
+  LWIP_DEBUGF(NETIF_DEBUG, ("\n"));
+  return netif;
+}
+
+/**
+ * Change IP address configuration for a network interface (including netmask
+ * and default gateway).
+ *
+ * @param netif the network interface to change
+ * @param ipaddr the new IP address
+ * @param netmask the new netmask
+ * @param gw the new default gateway
+ */
+void
+netif_set_addr(struct netif *netif, ip_addr_t *ipaddr, ip_addr_t *netmask,
+    ip_addr_t *gw)
+{
+  netif_set_ipaddr(netif, ipaddr);
+  netif_set_netmask(netif, netmask);
+  netif_set_gw(netif, gw);
+}
+
+/**
+ * Remove a network interface from the list of lwIP netifs.
+ *
+ * @param netif the network interface to remove
+ */
+void
+netif_remove(struct netif *netif)
+{
+  if (netif == NULL) {
+    return;
+  }
+
+#if LWIP_IGMP
+  /* stop IGMP processing */
+  if (netif->flags & NETIF_FLAG_IGMP) {
+    igmp_stop(netif);
+  }
+#endif /* LWIP_IGMP */
+  if (netif_is_up(netif)) {
+    /* set netif down before removing (call callback function) */
+    netif_set_down(netif);
+  }
+
+  snmp_delete_ipaddridx_tree(netif);
+
+  /*  is it the first netif? */
+  if (netif_list == netif) {
+    netif_list = netif->next;
+  } else {
+    /*  look for netif further down the list */
+    struct netif * tmpNetif;
+    for (tmpNetif = netif_list; tmpNetif != NULL; tmpNetif = tmpNetif->next) {
+      if (tmpNetif->next == netif) {
+        tmpNetif->next = netif->next;
+        break;
+      }
+    }
+    if (tmpNetif == NULL)
+      return; /*  we didn't find any netif today */
+  }
+  snmp_dec_iflist();
+  /* this netif is default? */
+  if (netif_default == netif) {
+    /* reset default netif */
+    netif_set_default(NULL);
+  }
+  LWIP_DEBUGF( NETIF_DEBUG, ("netif_remove: removed netif\n") );
+}
+
+/**
+ * Find a network interface by searching for its name
+ *
+ * @param name the name of the netif (like netif->name) plus concatenated number
+ * in ascii representation (e.g. 'en0')
+ */
+struct netif *
+netif_find(char *name)
+{
+  struct netif *netif;
+  u8_t num;
+
+  if (name == NULL) {
+    return NULL;
+  }
+
+  num = name[2] - '0';
+
+  for(netif = netif_list; netif != NULL; netif = netif->next) {
+    if (num == netif->num &&
+       name[0] == netif->name[0] &&
+       name[1] == netif->name[1]) {
+      LWIP_DEBUGF(NETIF_DEBUG, ("netif_find: found %c%c\n", name[0], name[1]));
+      return netif;
+    }
+  }
+  LWIP_DEBUGF(NETIF_DEBUG, ("netif_find: didn't find %c%c\n", name[0], name[1]));
+  return NULL;
+}
+
+/**
+ * Change the IP address of a network interface
+ *
+ * @param netif the network interface to change
+ * @param ipaddr the new IP address
+ *
+ * @note call netif_set_addr() if you also want to change netmask and
+ * default gateway
+ */
+void
+netif_set_ipaddr(struct netif *netif, ip_addr_t *ipaddr)
+{
+  /* TODO: Handling of obsolete pcbs */
+  /* See:  http://mail.gnu.org/archive/html/lwip-users/2003-03/msg00118.html */
+#if LWIP_TCP
+  struct tcp_pcb *pcb;
+  struct tcp_pcb_listen *lpcb;
+
+  /* address is actually being changed? */
+  if ((ip_addr_cmp(ipaddr, &(netif->ip_addr))) == 0) {
+    /* extern struct tcp_pcb *tcp_active_pcbs; defined by tcp.h */
+    LWIP_DEBUGF(NETIF_DEBUG | LWIP_DBG_STATE, ("netif_set_ipaddr: netif address being changed\n"));
+    pcb = tcp_active_pcbs;
+    while (pcb != NULL) {
+      /* PCB bound to current local interface address? */
+      if (ip_addr_cmp(&(pcb->local_ip), &(netif->ip_addr))
+#if LWIP_AUTOIP
+        /* connections to link-local addresses must persist (RFC3927 ch. 1.9) */
+        && !ip_addr_islinklocal(&(pcb->local_ip))
+#endif /* LWIP_AUTOIP */
+        ) {
+        /* this connection must be aborted */
+        struct tcp_pcb *next = pcb->next;
+        LWIP_DEBUGF(NETIF_DEBUG | LWIP_DBG_STATE, ("netif_set_ipaddr: aborting TCP pcb %p\n", (void *)pcb));
+        tcp_abort(pcb);
+        pcb = next;
+      } else {
+        pcb = pcb->next;
+      }
+    }
+    for (lpcb = tcp_listen_pcbs.listen_pcbs; lpcb != NULL; lpcb = lpcb->next) {
+      /* PCB bound to current local interface address? */
+      if ((!(ip_addr_isany(&(lpcb->local_ip)))) &&
+          (ip_addr_cmp(&(lpcb->local_ip), &(netif->ip_addr)))) {
+        /* The PCB is listening to the old ipaddr and
+         * is set to listen to the new one instead */
+        ip_addr_set(&(lpcb->local_ip), ipaddr);
+      }
+    }
+  }
+#endif
+  snmp_delete_ipaddridx_tree(netif);
+  snmp_delete_iprteidx_tree(0,netif);
+  /* set new IP address to netif */
+  ip_addr_set(&(netif->ip_addr), ipaddr);
+  snmp_insert_ipaddridx_tree(netif);
+  snmp_insert_iprteidx_tree(0,netif);
+
+  LWIP_DEBUGF(NETIF_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("netif: IP address of interface %c%c set to %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
+    netif->name[0], netif->name[1],
+    ip4_addr1_16(&netif->ip_addr),
+    ip4_addr2_16(&netif->ip_addr),
+    ip4_addr3_16(&netif->ip_addr),
+    ip4_addr4_16(&netif->ip_addr)));
+}
+
+/**
+ * Change the default gateway for a network interface
+ *
+ * @param netif the network interface to change
+ * @param gw the new default gateway
+ *
+ * @note call netif_set_addr() if you also want to change ip address and netmask
+ */
+void
+netif_set_gw(struct netif *netif, ip_addr_t *gw)
+{
+  ip_addr_set(&(netif->gw), gw);
+  LWIP_DEBUGF(NETIF_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("netif: GW address of interface %c%c set to %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
+    netif->name[0], netif->name[1],
+    ip4_addr1_16(&netif->gw),
+    ip4_addr2_16(&netif->gw),
+    ip4_addr3_16(&netif->gw),
+    ip4_addr4_16(&netif->gw)));
+}
+
+/**
+ * Change the netmask of a network interface
+ *
+ * @param netif the network interface to change
+ * @param netmask the new netmask
+ *
+ * @note call netif_set_addr() if you also want to change ip address and
+ * default gateway
+ */
+void
+netif_set_netmask(struct netif *netif, ip_addr_t *netmask)
+{
+  snmp_delete_iprteidx_tree(0, netif);
+  /* set new netmask to netif */
+  ip_addr_set(&(netif->netmask), netmask);
+  snmp_insert_iprteidx_tree(0, netif);
+  LWIP_DEBUGF(NETIF_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("netif: netmask of interface %c%c set to %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
+    netif->name[0], netif->name[1],
+    ip4_addr1_16(&netif->netmask),
+    ip4_addr2_16(&netif->netmask),
+    ip4_addr3_16(&netif->netmask),
+    ip4_addr4_16(&netif->netmask)));
+}
+
+/**
+ * Set a network interface as the default network interface
+ * (used to output all packets for which no specific route is found)
+ *
+ * @param netif the default network interface
+ */
+void
+netif_set_default(struct netif *netif)
+{
+  if (netif == NULL) {
+    /* remove default route */
+    snmp_delete_iprteidx_tree(1, netif);
+  } else {
+    /* install default route */
+    snmp_insert_iprteidx_tree(1, netif);
+  }
+  netif_default = netif;
+  LWIP_DEBUGF(NETIF_DEBUG, ("netif: setting default interface %c%c\n",
+           netif ? netif->name[0] : '\'', netif ? netif->name[1] : '\''));
+}
+
+/**
+ * Bring an interface up, available for processing
+ * traffic.
+ * 
+ * @note: Enabling DHCP on a down interface will make it come
+ * up once configured.
+ * 
+ * @see dhcp_start()
+ */ 
+void netif_set_up(struct netif *netif)
+{
+  if (!(netif->flags & NETIF_FLAG_UP)) {
+    netif->flags |= NETIF_FLAG_UP;
+    
+#if LWIP_SNMP
+    snmp_get_sysuptime(&netif->ts);
+#endif /* LWIP_SNMP */
+
+    NETIF_STATUS_CALLBACK(netif);
+
+    if (netif->flags & NETIF_FLAG_LINK_UP) {
+#if LWIP_ARP
+      /* For Ethernet network interfaces, we would like to send a "gratuitous ARP" */ 
+      if (netif->flags & (NETIF_FLAG_ETHARP)) {
+        etharp_gratuitous(netif);
+      }
+#endif /* LWIP_ARP */
+
+#if LWIP_IGMP
+      /* resend IGMP memberships */
+      if (netif->flags & NETIF_FLAG_IGMP) {
+        igmp_report_groups( netif);
+      }
+#endif /* LWIP_IGMP */
+    }
+  }
+}
+
+/**
+ * Bring an interface down, disabling any traffic processing.
+ *
+ * @note: Enabling DHCP on a down interface will make it come
+ * up once configured.
+ * 
+ * @see dhcp_start()
+ */ 
+void netif_set_down(struct netif *netif)
+{
+  if (netif->flags & NETIF_FLAG_UP) {
+    netif->flags &= ~NETIF_FLAG_UP;
+#if LWIP_SNMP
+    snmp_get_sysuptime(&netif->ts);
+#endif
+
+    NETIF_STATUS_CALLBACK(netif);
+  }
+}
+
+#if LWIP_NETIF_STATUS_CALLBACK
+/**
+ * Set callback to be called when interface is brought up/down
+ */
+void netif_set_status_callback(struct netif *netif, netif_status_callback_fn status_callback)
+{
+  if (netif) {
+    netif->status_callback = status_callback;
+  }
+}
+#endif /* LWIP_NETIF_STATUS_CALLBACK */
+
+/**
+ * Called by a driver when its link goes up
+ */
+void netif_set_link_up(struct netif *netif )
+{
+  if (!(netif->flags & NETIF_FLAG_LINK_UP)) {
+    netif->flags |= NETIF_FLAG_LINK_UP;
+
+#if LWIP_DHCP
+    if (netif->dhcp) {
+      dhcp_network_changed(netif);
+    }
+#endif /* LWIP_DHCP */
+
+#if LWIP_AUTOIP
+    if (netif->autoip) {
+      autoip_network_changed(netif);
+    }
+#endif /* LWIP_AUTOIP */
+
+    if (netif->flags & NETIF_FLAG_UP) {
+#if LWIP_ARP
+      /* For Ethernet network interfaces, we would like to send a "gratuitous ARP" */ 
+      if (netif->flags & NETIF_FLAG_ETHARP) {
+        etharp_gratuitous(netif);
+      }
+#endif /* LWIP_ARP */
+
+#if LWIP_IGMP
+      /* resend IGMP memberships */
+      if (netif->flags & NETIF_FLAG_IGMP) {
+        igmp_report_groups( netif);
+      }
+#endif /* LWIP_IGMP */
+    }
+    NETIF_LINK_CALLBACK(netif);
+  }
+}
+
+/**
+ * Called by a driver when its link goes down
+ */
+void netif_set_link_down(struct netif *netif )
+{
+  if (netif->flags & NETIF_FLAG_LINK_UP) {
+    netif->flags &= ~NETIF_FLAG_LINK_UP;
+    NETIF_LINK_CALLBACK(netif);
+  }
+}
+
+#if LWIP_NETIF_LINK_CALLBACK
+/**
+ * Set callback to be called when link is brought up/down
+ */
+void netif_set_link_callback(struct netif *netif, netif_status_callback_fn link_callback)
+{
+  if (netif) {
+    netif->link_callback = link_callback;
+  }
+}
+#endif /* LWIP_NETIF_LINK_CALLBACK */
+
+#if ENABLE_LOOPBACK
+/**
+ * Send an IP packet to be received on the same netif (loopif-like).
+ * The pbuf is simply copied and handed back to netif->input.
+ * In multithreaded mode, this is done directly since netif->input must put
+ * the packet on a queue.
+ * In callback mode, the packet is put on an internal queue and is fed to
+ * netif->input by netif_poll().
+ *
+ * @param netif the lwip network interface structure
+ * @param p the (IP) packet to 'send'
+ * @param ipaddr the ip address to send the packet to (not used)
+ * @return ERR_OK if the packet has been sent
+ *         ERR_MEM if the pbuf used to copy the packet couldn't be allocated
+ */
+err_t
+netif_loop_output(struct netif *netif, struct pbuf *p,
+       ip_addr_t *ipaddr)
+{
+  struct pbuf *r;
+  err_t err;
+  struct pbuf *last;
+#if LWIP_LOOPBACK_MAX_PBUFS
+  u8_t clen = 0;
+#endif /* LWIP_LOOPBACK_MAX_PBUFS */
+  /* If we have a loopif, SNMP counters are adjusted for it,
+   * if not they are adjusted for 'netif'. */
+#if LWIP_SNMP
+#if LWIP_HAVE_LOOPIF
+  struct netif *stats_if = &loop_netif;
+#else /* LWIP_HAVE_LOOPIF */
+  struct netif *stats_if = netif;
+#endif /* LWIP_HAVE_LOOPIF */
+#endif /* LWIP_SNMP */
+  SYS_ARCH_DECL_PROTECT(lev);
+  LWIP_UNUSED_ARG(ipaddr);
+
+  /* Allocate a new pbuf */
+  r = pbuf_alloc(PBUF_LINK, p->tot_len, PBUF_RAM);
+  if (r == NULL) {
+    LINK_STATS_INC(link.memerr);
+    LINK_STATS_INC(link.drop);
+    snmp_inc_ifoutdiscards(stats_if);
+    return ERR_MEM;
+  }
+#if LWIP_LOOPBACK_MAX_PBUFS
+  clen = pbuf_clen(r);
+  /* check for overflow or too many pbuf on queue */
+  if(((netif->loop_cnt_current + clen) < netif->loop_cnt_current) ||
+     ((netif->loop_cnt_current + clen) > LWIP_LOOPBACK_MAX_PBUFS)) {
+    pbuf_free(r);
+    LINK_STATS_INC(link.memerr);
+    LINK_STATS_INC(link.drop);
+    snmp_inc_ifoutdiscards(stats_if);
+    return ERR_MEM;
+  }
+  netif->loop_cnt_current += clen;
+#endif /* LWIP_LOOPBACK_MAX_PBUFS */
+
+  /* Copy the whole pbuf queue p into the single pbuf r */
+  if ((err = pbuf_copy(r, p)) != ERR_OK) {
+    pbuf_free(r);
+    LINK_STATS_INC(link.memerr);
+    LINK_STATS_INC(link.drop);
+    snmp_inc_ifoutdiscards(stats_if);
+    return err;
+  }
+
+  /* Put the packet on a linked list which gets emptied through calling
+     netif_poll(). */
+
+  /* let last point to the last pbuf in chain r */
+  for (last = r; last->next != NULL; last = last->next);
+
+  SYS_ARCH_PROTECT(lev);
+  if(netif->loop_first != NULL) {
+    LWIP_ASSERT("if first != NULL, last must also be != NULL", netif->loop_last != NULL);
+    netif->loop_last->next = r;
+    netif->loop_last = last;
+  } else {
+    netif->loop_first = r;
+    netif->loop_last = last;
+  }
+  SYS_ARCH_UNPROTECT(lev);
+
+  LINK_STATS_INC(link.xmit);
+  snmp_add_ifoutoctets(stats_if, p->tot_len);
+  snmp_inc_ifoutucastpkts(stats_if);
+
+#if LWIP_NETIF_LOOPBACK_MULTITHREADING
+  /* For multithreading environment, schedule a call to netif_poll */
+  tcpip_callback((tcpip_callback_fn)netif_poll, netif);
+#endif /* LWIP_NETIF_LOOPBACK_MULTITHREADING */
+
+  return ERR_OK;
+}
+
+/**
+ * Call netif_poll() in the main loop of your application. This is to prevent
+ * reentering non-reentrant functions like tcp_input(). Packets passed to
+ * netif_loop_output() are put on a list that is passed to netif->input() by
+ * netif_poll().
+ */
+void
+netif_poll(struct netif *netif)
+{
+  struct pbuf *in;
+  /* If we have a loopif, SNMP counters are adjusted for it,
+   * if not they are adjusted for 'netif'. */
+#if LWIP_SNMP
+#if LWIP_HAVE_LOOPIF
+  struct netif *stats_if = &loop_netif;
+#else /* LWIP_HAVE_LOOPIF */
+  struct netif *stats_if = netif;
+#endif /* LWIP_HAVE_LOOPIF */
+#endif /* LWIP_SNMP */
+  SYS_ARCH_DECL_PROTECT(lev);
+
+  do {
+    /* Get a packet from the list. With SYS_LIGHTWEIGHT_PROT=1, this is protected */
+    SYS_ARCH_PROTECT(lev);
+    in = netif->loop_first;
+    if (in != NULL) {
+      struct pbuf *in_end = in;
+#if LWIP_LOOPBACK_MAX_PBUFS
+      u8_t clen = pbuf_clen(in);
+      /* adjust the number of pbufs on queue */
+      LWIP_ASSERT("netif->loop_cnt_current underflow",
+        ((netif->loop_cnt_current - clen) < netif->loop_cnt_current));
+      netif->loop_cnt_current -= clen;
+#endif /* LWIP_LOOPBACK_MAX_PBUFS */
+      while (in_end->len != in_end->tot_len) {
+        LWIP_ASSERT("bogus pbuf: len != tot_len but next == NULL!", in_end->next != NULL);
+        in_end = in_end->next;
+      }
+      /* 'in_end' now points to the last pbuf from 'in' */
+      if (in_end == netif->loop_last) {
+        /* this was the last pbuf in the list */
+        netif->loop_first = netif->loop_last = NULL;
+      } else {
+        /* pop the pbuf off the list */
+        netif->loop_first = in_end->next;
+        LWIP_ASSERT("should not be null since first != last!", netif->loop_first != NULL);
+      }
+      /* De-queue the pbuf from its successors on the 'loop_' list. */
+      in_end->next = NULL;
+    }
+    SYS_ARCH_UNPROTECT(lev);
+
+    if (in != NULL) {
+      LINK_STATS_INC(link.recv);
+      snmp_add_ifinoctets(stats_if, in->tot_len);
+      snmp_inc_ifinucastpkts(stats_if);
+      /* loopback packets are always IP packets! */
+      if (ip_input(in, netif) != ERR_OK) {
+        pbuf_free(in);
+      }
+      /* Don't reference the packet any more! */
+      in = NULL;
+    }
+  /* go on while there is a packet on the list */
+  } while (netif->loop_first != NULL);
+}
+
+#if !LWIP_NETIF_LOOPBACK_MULTITHREADING
+/**
+ * Calls netif_poll() for every netif on the netif_list.
+ */
+void
+netif_poll_all(void)
+{
+  struct netif *netif = netif_list;
+  /* loop through netifs */
+  while (netif != NULL) {
+    netif_poll(netif);
+    /* proceed to next network interface */
+    netif = netif->next;
+  }
+}
+#endif /* !LWIP_NETIF_LOOPBACK_MULTITHREADING */
+#endif /* ENABLE_LOOPBACK */