Squashed commit of the following:

net/netdev:  Add implementation of if_nametoindex() and if indextoname().
    net/pkt:  Raw AF_PACKET sockets now depend on CONFIG_NETDEV_IFINDEX.
    net/procfs:  Tweak to handle traversal of interfaces if CONFIG_NETDEV_IFINDEX is not defined.
    net/netdev.h:  Update netdev_findbyaddr() to use the assigned device index.
    Trivial typo fix
    net/netdev:  Add support for assigned an interface index to a device when it is regisgtered.

include/net/if.h

@@ -247,4 +247,39 @@ struct ifconf
  * Public Function Prototypes
  *******************************************************************************************/
 
+/*******************************************************************************************
+ * Name: if_nametoindex
+ *
+ * Description:
+ *   The if_nametoindex() function returns the interface index corresponding to name ifname.
+ *
+ * Input Parameters:
+ *   ifname - The interface name
+ *
+ * Returned Value:
+ *   The corresponding index if ifname is the name of an interface; otherwise, zero.
+ *
+ *******************************************************************************************/
+
+unsigned int if_nametoindex(FAR const char *ifname);
+
+/*******************************************************************************************
+ * Name: if_indextoname
+ *
+ * Description:
+ *   The if_indextoname() function maps an interface index to its corresponding name.
+ *
+ * Input Parameters:
+ *   ifname  - Points to a buffer of at least IF_NAMESIZE bytes.  if_indextoname() will
+ *             place in this buffer the name of the interface with index ifindex.
+ *
+ * Returned Value:
+ *   If ifindex is an interface index, then the function will return the value supplied by
+ *   ifname. Otherwise, the function returns a NULL pointer and sets errno to indicate the
+*    error.
+ *
+ *******************************************************************************************/
+
+FAR char *if_indextoname(unsigned int ifindex, FAR char *ifname);
+
 #endif /* __INCLUDE_NET_IF_H */

include/nuttx/net/netdev.h

@@ -3,7 +3,7 @@
  * Defines architecture-specific device driver interfaces to the NuttX
  * network.
  *
- *   Copyright (C) 2007, 2009, 2011-2017 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007, 2009, 2011-2018 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Derived largely from portions of uIP with has a similar BSD-styple license:
@@ -241,6 +241,11 @@ struct net_driver_s
 
   uint8_t d_lltype;             /* See enum net_lltype_e */
   uint8_t d_llhdrlen;           /* Link layer header size */
+
+#ifdef CONFIG_NETDEV_IFINDEX
+  uint8_t d_ifindex;            /* Device index */
+#endif
+
   uint16_t d_mtu;               /* Maximum packet size */
 #ifdef CONFIG_NET_TCP
   uint16_t d_recvwndo;          /* TCP receive window size */

net/netdev/Kconfig

@@ -24,4 +24,16 @@ config NETDEV_WIRELESS_IOCTL
 	---help---
 		Enable support for wireless device ioctl() commands
 
+config NETDEV_IFINDEX
+	bool "Enable IF index support"
+	default n
+	---help---
+		Enable support for references devices by an interface index.
+
+		This feature is automatically enabled when raw, PACKET sockets
+		are enabled.
+
+		When enabled, these option also enables the user interfaces:
+		if_nametoindex() and if_indextoname().
+
 endmenu # Network Device Operations

net/netdev/Make.defs

@@ -41,6 +41,10 @@ NETDEV_CSRCS += netdev_count.c netdev_ifconf.c netdev_foreach.c
 NETDEV_CSRCS += netdev_unregister.c netdev_carrier.c netdev_default.c
 NETDEV_CSRCS += netdev_verify.c netdev_lladdrsize.c
 
+ifeq ($(CONFIG_NETDEV_IFINDEX),y)
+NETDEV_CSRCS += netdev_indextoname.c netdev_nametoindex.c
+endif
+
 # Include netdev build support
 
 DEPPATH += --dep-path netdev

net/netdev/netdev.h

@@ -47,6 +47,16 @@
 
 #include <nuttx/net/ip.h>
 
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+/* If CONFIG_NETDEV_IFINDEX is enabled then there is limit to the number of
+ * devices that can be registered due to the nature of some static data.
+ */
+
+#define MAX_IFINDEX  32
+
 /****************************************************************************
  * Public Data
  ****************************************************************************/
@@ -70,6 +80,17 @@ extern "C"
 EXTERN struct net_driver_s *g_netdevices;
 #endif
 
+#ifdef CONFIG_NETDEV_IFINDEX
+/* The set of network devices that have been registered.  This is used to
+ * assign a unique device index to the newly registered device.
+ *
+ * REVISIT:  The width of g_nassigned limits the number of registered
+ * devices to 32 (MAX_IFINDEX).
+ */
+
+EXTERN uint32_t g_devset;
+#endif
+
 /****************************************************************************
  * Public Types
  ****************************************************************************/
@@ -120,9 +141,6 @@ bool netdev_verify(FAR struct net_driver_s *dev);
  * Returned Value:
  *  Pointer to driver on success; null on failure
  *
- * Assumptions:
- *  Called from normal user mode
- *
  ****************************************************************************/
 
 #if CONFIG_NSOCKET_DESCRIPTORS > 0
@@ -144,9 +162,6 @@ FAR struct net_driver_s *netdev_findbyname(FAR const char *ifname);
  * Returned Value:
  *  0:Enumeration completed 1:Enumeration terminated early by callback
  *
- * Assumptions:
- *  Called from normal user mode
- *
  ****************************************************************************/
 
 int netdev_foreach(netdev_callback_t callback, FAR void *arg);
@@ -165,9 +180,6 @@ int netdev_foreach(netdev_callback_t callback, FAR void *arg);
  * Returned Value:
  *  Pointer to driver on success; null on failure
  *
- * Assumptions:
- *  Called from normal user mode
- *
  ****************************************************************************/
 
 #if CONFIG_NSOCKET_DESCRIPTORS > 0
@@ -190,9 +202,6 @@ FAR struct net_driver_s *netdev_findby_ipv4addr(in_addr_t lipaddr,
  * Returned Value:
  *  Pointer to driver on success; null on failure
  *
- * Assumptions:
- *  Called from normal user mode
- *
  ****************************************************************************/
 
 #ifdef CONFIG_NET_IPv6
@@ -205,25 +214,80 @@ FAR struct net_driver_s *netdev_findby_ipv6addr(const net_ipv6addr_t lipaddr,
  * Name: netdev_findbyindex
  *
  * Description:
- *   Find a previously registered network device by its position in the
+ *   Find a previously registered network device by assigned interface index.
- *   list of registered devices.  NOTE that this function is not a safe way
- *   to enumerate network devices:  There could be changes to the list of
- *   registered device causing a given index to be meaningless (unless, of
- *   course, the caller keeps the network locked).
  *
  * Input Parameters:
- *   index - the index of the interface to file
+ *   ifindex - The interface index
  *
  * Returned Value:
- *  Pointer to driver on success; NULL on failure.  This function can only
+ *  Pointer to driver on success; NULL on failure.  This function will return
- *  fail if there are fewer registered interfaces than could be indexed.
+ *  NULL only if there is no device corresponding to the provided index.
- *
- * Assumptions:
- *  Called from normal user mode
  *
  ****************************************************************************/
 
-FAR struct net_driver_s *netdev_findbyindex(int index);
+FAR struct net_driver_s *netdev_findbyindex(int ifindex);
+
+/****************************************************************************
+ * Name: netdev_nextindex
+ *
+ * Description:
+ *   Return the interface index to the next valid device.
+ *
+ * Input Parameters:
+ *   ifindex - The first interface index to check.  Usually in a traversal
+ *             this would be the previous inteface index plus 1.
+ *
+ * Returned Value:
+ *   The interface index for the next network driver.  -ENODEV is returned if
+ *   there are no further devices with assigned interface indices.
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_NETDEV_IFINDEX
+int netdev_nextindex(int ifindex);
+#endif
+
+/****************************************************************************
+ * Name: netdev_indextoname
+ *
+ * Description:
+ *   The if_indextoname() function maps an interface index to its
+ *   corresponding name.
+ *
+ * Input Parameters:
+ *   ifname  - Points to a buffer of at least IF_NAMESIZE bytes.
+ *             if_indextoname() will place in this buffer the name of the
+ *             interface with index ifindex.
+ *
+ * Returned Value:
+ *   If ifindex is an interface index, then the function will return zero
+ *   (OK). Otherwise, the function returns a negated errno value;
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_NETDEV_IFINDEX
+int netdev_indextoname(unsigned int ifindex, FAR char *ifname);
+#endif
+
+/****************************************************************************
+ * Name: netdev_nametoindex
+ *
+ * Description:
+ *   The if_nametoindex() function returns the interface index corresponding
+ *   to name ifname.
+ *
+ * Input Parameters:
+ *   ifname - The interface name
+ *
+ * Returned Value:
+ *   The corresponding index if ifname is the name of an interface;
+ *   otherwise, a negated errno value is returned.
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_NETDEV_IFINDEX
+unsigned int netdev_nametoindex(FAR const char *ifname);
+#endif
 
 /****************************************************************************
  * Name: netdev_default
@@ -244,9 +308,6 @@ FAR struct net_driver_s *netdev_findbyindex(int index);
  * Returned Value:
  *  Pointer to default network driver on success; null on failure
  *
- * Assumptions:
- *  Called from normal user mode
- *
  ****************************************************************************/
 
 #if CONFIG_NSOCKET_DESCRIPTORS > 0
@@ -267,9 +328,6 @@ FAR struct net_driver_s *netdev_default(void);
  * Returned Value:
  *  None
  *
- * Assumptions:
- *  Called from normal user mode
- *
  ****************************************************************************/
 
 #if CONFIG_NSOCKET_DESCRIPTORS > 0
@@ -291,9 +349,6 @@ void netdev_ipv4_txnotify(in_addr_t lipaddr, in_addr_t ripaddr);
  * Returned Value:
  *  None
  *
- * Assumptions:
- *  Called from normal user mode
- *
  ****************************************************************************/
 
 #ifdef CONFIG_NET_IPv6
@@ -316,9 +371,6 @@ void netdev_ipv6_txnotify(FAR const net_ipv6addr_t lipaddr,
  * Returned Value:
  *  None
  *
- * Assumptions:
- *  Called from normal user mode
- *
  ****************************************************************************/
 
 void netdev_txnotify_dev(FAR struct net_driver_s *dev);
@@ -335,9 +387,6 @@ void netdev_txnotify_dev(FAR struct net_driver_s *dev);
  * Returned Value:
  *   The number of network devices
  *
- * Assumptions:
- *  Called from normal user mode
- *
  ****************************************************************************/
 
 #if CONFIG_NSOCKET_DESCRIPTORS > 0

net/netdev/netdev_findbyindex.c

@@ -1,7 +1,7 @@
 /****************************************************************************
  * net/netdev/netdev_findbyindex.c
  *
- *   Copyright (C) 2015 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2015, 2018 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -38,9 +38,9 @@
  ****************************************************************************/
 
 #include <nuttx/config.h>
-#if defined(CONFIG_NET) && CONFIG_NSOCKET_DESCRIPTORS > 0
 
 #include <string.h>
+#include <assert.h>
 #include <errno.h>
 
 #include <nuttx/net/netdev.h>
@@ -48,6 +48,8 @@
 #include "utils/utils.h"
 #include "netdev/netdev.h"
 
+#if CONFIG_NSOCKET_DESCRIPTORS > 0
+
 /****************************************************************************
  * Public Functions
  ****************************************************************************/
@@ -56,33 +58,65 @@
  * Name: netdev_findbyindex
  *
  * Description:
- *   Find a previously registered network device by its position in the
+ *   Find a previously registered network device by assigned interface index.
- *   list of registered devices.  NOTE that this function is not a safe way
- *   to enumerate network devices:  There could be changes to the list of
- *   registered device causing a given index to be meaningless (unless, of
- *   course, the caller keeps the network locked).
  *
  * Input Parameters:
- *   index - the index of the interface to file
+ *   ifindex - The interface index
  *
  * Returned Value:
- *  Pointer to driver on success; NULL on failure.  This function can only
+ *  Pointer to driver on success; NULL on failure.  This function will return
- *  fail if there are fewer registered interfaces than could be indexed.
+ *  NULL only if there is no device corresponding to the provided index.
- *
- * Assumptions:
- *  Called from normal user mode
  *
  ****************************************************************************/
 
-FAR struct net_driver_s *netdev_findbyindex(int index)
+FAR struct net_driver_s *netdev_findbyindex(int ifindex)
 {
   FAR struct net_driver_s *dev;
   int i;
 
+#ifdef CONFIG_NETDEV_IFINDEX
+  /* The bit index is the interface index minus one.  Zero is reserved in
+   * POSIX to mean no interface index.
+   */
+
+  DEBUGASSERT(ifindex > 0 && ifindex <= MAX_IFINDEX);
+  ifindex--;
+  if (ifindex < 0 || ifindex >= MAX_IFINDEX)
+    {
+      return NULL;
+    }
+#endif
+
   net_lock();
+
+#ifdef CONFIG_NETDEV_IFINDEX
+  /* Check if this index has been assigned */
+
+  if ((g_devset & (1L << ifindex)) == 0)
+    {
+      /* This index has not been assigned */
+
+      net_unlock();
+      return NULL;
+    }
+#endif
+
   for (i = 0, dev = g_netdevices; dev; i++, dev = dev->flink)
     {
-      if (i == index)
+#ifdef CONFIG_NETDEV_IFINDEX
+      /* Check if the index matches the index assigned when the device was
+       * registered.
+       */
+
+     if (dev->d_ifindex == ifindex)
+#else
+      /* NOTE that this option is not a safe way to enumerate network
+       * devices:  There could be changes to the list of registered device
+       * causing a given index to be meaningless (unless, of course, the
+       * caller keeps the network locked).
+       */
+      if (i == ifindex)
+#endif
         {
           net_unlock();
           return dev;
@@ -93,4 +127,53 @@ FAR struct net_driver_s *netdev_findbyindex(int index)
   return NULL;
 }
 
-#endif /* CONFIG_NET && CONFIG_NSOCKET_DESCRIPTORS */
+/****************************************************************************
+ * Name: netdev_nextindex
+ *
+ * Description:
+ *   Return the interface index to the next valid device.
+ *
+ * Input Parameters:
+ *   ifindex - The first interface index to check.  Usually in a traversal
+ *             this would be the previous inteface index plus 1.
+ *
+ * Returned Value:
+ *   The interface index for the next network driver.  -ENODEV is returned if
+ *   there are no further devices with assigned interface indices.
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_NETDEV_IFINDEX
+int netdev_nextindex(int ifindex)
+{
+  /* The bit index is the interface index minus one.  Zero is reserved in
+   * POSIX to mean no interface index.
+   */
+
+  DEBUGASSERT(ifindex > 0 && ifindex <= MAX_IFINDEX);
+  ifindex--;
+
+  if (ifindex >= 0 && ifindex < MAX_IFINDEX)
+    {
+      net_lock();
+      for (; ifindex < MAX_IFINDEX; ifindex++)
+        {
+          if ((g_devset & (1L << ifindex)) != 0)
+            {
+               /* NOTE that the index + 1 is returned.  Zero is reserved to
+                * mean no-index in the POSIX standards.
+                */
+
+               net_unlock();
+               return ifindex + 1;
+           }
+        }
+
+      net_unlock();
+    }
+
+  return -ENODEV;
+}
+#endif
+
+#endif /* CONFIG_NSOCKET_DESCRIPTORS */

net/netdev/netdev_register.c

@@ -95,6 +95,17 @@
 
 struct net_driver_s *g_netdevices = NULL;
 
+#ifdef CONFIG_NETDEV_IFINDEX
+/* The set of network devices that have been registered.  This is used to
+ * assign a unique device index to the newly registered device.
+ *
+ * REVISIT:  The width of g_nassigned limits the number of registered
+ * devices to 32 (MAX_IFINDEX).
+ */
+
+uint32_t g_devset;
+#endif
+
 /****************************************************************************
  * Private Functions
  ****************************************************************************/
@@ -146,6 +157,50 @@ static int find_devnum(FAR const char *devfmt)
   return result;
 }
 
+/****************************************************************************
+ * Name: get_ifindex
+ *
+ * Description:
+ *   Assign a unique interface index to the device.
+ *
+ * Input Parameters:
+ *   None
+ *
+ * Returned Value:
+ *   The interface index assigned to the device.  -ENOSPC is returned if
+ *   more the MAX_IFINDEX names have been assigned.
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_NETDEV_IFINDEX
+static int get_ifindex(void)
+{
+  int ndx;
+
+   /* Search for an unused index */
+
+   for (ndx = 0; ndx < MAX_IFINDEX; ndx++)
+     {
+       uint32_t bit = 1L << ndx;
+       if ((g_devset & bit) == 0)
+         {
+           /* Indicate that this index is in use */
+
+           g_devset |= bit;
+
+           /* NOTE that the index + 1 is returned.  Zero is reserved to
+            * mean no-index in the POSIX standards.
+            */
+
+           net_unlock();
+           return ndx + 1;
+         }
+     }
+
+   return -ENOSPC;
+}
+#endif
+
 /****************************************************************************
  * Public Functions
  ****************************************************************************/
@@ -177,6 +232,9 @@ int netdev_register(FAR struct net_driver_s *dev, enum net_lltype_e lltype)
   FAR const char devfmt_str[IFNAMSIZ];
 #endif
   int devnum;
+#ifdef CONFIG_NETDEV_IFINDEX
+  int ifindex;
+#endif
 
   if (dev != NULL)
     {
@@ -285,12 +343,24 @@ int netdev_register(FAR struct net_driver_s *dev, enum net_lltype_e lltype)
       dev->d_conncb = NULL;
       dev->d_devcb = NULL;
 
+      /* We need exclusive access for the following operations */
+
+      net_lock();
+
+#ifdef CONFIG_NETDEV_IFINDEX
+      ifindex = get_ifindex();
+      if (ifindex < 0)
+        {
+          return ifindex;
+        }
+
+      dev->d_ifindex = (uint8_t)ifindex;
+#endif
+
       /* Get the next available device number and assign a device name to
        * the interface
        */
 
-      net_lock();
-
 #ifdef CONFIG_NET_LOOPBACK
       /* The local loopback device is a special case:  There can be only one
        * local loopback device so it is unnumbered.

net/netdev/netdev_unregister.c

@@ -1,7 +1,7 @@
 /****************************************************************************
  * net/netdev/netdev_unregister.c
  *
- *   Copyright (C) 2011, 2015 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2011, 2015, 2018 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -65,6 +65,43 @@
 #  define NETDEV_FORMAT "eth%d"
 #endif
 
+/****************************************************************************
+ * Name: free_ifindex
+ *
+ * Description:
+ *   Free a interface index to the assigned to device.
+ *
+ * Input Parameters:
+ *   dev - Instance of device structure for the unregistered device.
+ *
+ * Returned Value:
+ *   None.
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_NETDEV_IFINDEX
+static inline void free_ifindex(int ndx)
+{
+  uint32_t bit;
+
+  /* The bit index is the interface index minus one.  Zero is reserved in
+   * POSIX to mean no interface index.
+   */
+
+  DEBUGASSERT(ndx > 0 && ndx <= MAX_IFINDEX);
+  ndx--;
+
+  /* Set the bit in g_devset corresponding to the zero based index */
+
+  bit = 1 << ndx;
+
+  /* The bit should be in the set state */
+
+  DEBUGASSERT((g_devset & bit) != 0);
+  g_devset &= ~bit;
+}
+#endif
+
 /****************************************************************************
  * Public Functions
  ****************************************************************************/
@@ -124,6 +161,9 @@ int netdev_unregister(FAR struct net_driver_s *dev)
           curr->flink = NULL;
         }
 
+#ifdef CONFIG_NETDEV_IFINDEX
+      free_ifindex(dev->d_ifindex);
+#endif
       net_unlock();
 
 #ifdef CONFIG_NET_ETHERNET
@@ -135,7 +175,7 @@ int netdev_unregister(FAR struct net_driver_s *dev)
             dev->d_mac.ether.ether_addr_octet[4],
             dev->d_mac.ether.ether_addr_octet[5], dev->d_ifname);
 #else
-      ninfo("Registered dev: %s\n", dev->d_ifname);
+      ninfo("Unregistered dev: %s\n", dev->d_ifname);
 #endif
       return OK;
     }

net/pkt/Kconfig

@@ -9,6 +9,7 @@ config NET_PKT
 	bool "Socket packet socket support"
 	default n
 	depends on NET_ETHERNET || EXPERIMENTAL
+	select NETDEV_IFINDEX
 	---help---
 		Enable or disable support for packet sockets.
 

net/pkt/pkt_sockif.c

@@ -1,7 +1,7 @@
 /****************************************************************************
  * net/socket/pkt_sockif.c
  *
- *   Copyright (C) 2017 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2017-2018 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -47,10 +47,13 @@
 #include <errno.h>
 #include <debug.h>
 
-#include <nuttx/net/net.h>
 #include <netpacket/packet.h>
-#include <socket/socket.h>
 
+#include <nuttx/net/net.h>
+#include <nuttx/net/netdev.h>
+
+#include "netdev/netdev.h"
+#include <socket/socket.h>
 #include "pkt/pkt.h"
 
 #ifdef CONFIG_NET_PKT
@@ -342,16 +345,6 @@ static int pkt_accept(FAR struct socket *psock, FAR struct sockaddr *addr,
 static int pkt_bind(FAR struct socket *psock, FAR const struct sockaddr *addr,
                     socklen_t addrlen)
 {
-#if 0
-  char hwaddr[6] =  /* our MAC for debugging */
-  {
-    0x00, 0xa1, 0xb1, 0xc1, 0xd1, 0xe1
-  };
-#endif
-  char hwaddr[6] =  /* MAC from ifconfig */
-  {
-    0x00, 0xe0, 0xde, 0xad, 0xbe, 0xef
-  };
   int ifindex;
 
   /* Verify that a valid address has been provided */
@@ -368,21 +361,31 @@ static int pkt_bind(FAR struct socket *psock, FAR const struct sockaddr *addr,
   if (psock->s_type == SOCK_RAW)
     {
       FAR struct pkt_conn_s *conn = (FAR struct pkt_conn_s *)psock->s_conn;
+      FAR struct net_driver_s *dev;
 
       /* Look at the addr and identify network interface */
 
       ifindex = ((struct sockaddr_ll*)addr)->sll_ifindex;
 
-#if 0
       /* Get the MAC address of that interface */
 
-      memcpy(hwaddr, g_netdevices->d_mac.ether, 6);
+      dev = netdev_findbyindex(ifindex);
-#endif
+      if (dev == NULL)
+        {
+          return -EADDRNOTAVAIL;
+        }
+
+      /* Only Ethernet is supported */
+
+      if (d_lltype != NET_LL_ETHERNET)
+        {
+          return -EAFNOSUPPORT;
+        }
 
       /* Put ifindex and mac address into connection */
 
       conn->ifindex = ifindex;
-      memcpy(conn->lmac, hwaddr, 6);
+      memcpy(conn->lmac, dev->d_mac.ether.ether_addr_octet, 6);
 
       /* Mark the socket bound */
 

net/procfs/net_procfs.c

@@ -523,6 +523,22 @@ static int netprocfs_readdir(FAR struct fs_dirent_s *dir)
         {
           int devndx = index - DEV_INDEX;
 
+#ifdef CONFIG_NETDEV_IFINDEX
+          /* Make sure the devndx is a valid interface index.
+           *
+           * REVISIT:  That actual underlay indices may be space.  The
+           * way that level1->base.nentries is set-up assumes that
+           * the indexing is continuous and may cause entries to be lost.
+           */
+
+          devndx = netdev_nextindex(devndx);
+          if (devndx < 0)
+            {
+              /* There are no more... one must have been unregistered */
+
+              return -ENOENT;
+            }
+#endif
           /* Find the device corresponding to this device index */
 
           dev = netdev_findbyindex(devndx);

net/udp/udp_finddev.c

@@ -238,7 +238,7 @@ FAR struct net_driver_s *udp_find_raddr_device(FAR struct udp_conn_s *conn)
             }
           else
             {
-              /* Not a suitable IPv6  unicast address for device lookup */
+              /* Not a suitable IPv6 unicast address for device lookup */
 
               return NULL;
             }