AP_Networking: added option for PPP<->ethernet bridge

when NET_OPTIONS is set to enable PPP bridging both an ethernet and a
PPP link will be brought up, with IP forwarding making the PPP remote
endpoint available on the ethernet LAN

libraries/AP_Networking/AP_Networking.cpp

@@ -86,6 +86,20 @@ const AP_Param::GroupInfo AP_Networking::var_info[] = {
     AP_SUBGROUPINFO(param.test_ipaddr, "TEST_IP", 8,  AP_Networking, AP_Networking_IPV4),
 #endif
 
+    // @Param: OPTIONS
+    // @DisplayName: Networking options
+    // @Description: Networking options
+    // @Bitmask: 0:EnablePPP Ethernet gateway
+    // @RebootRequired: True
+    // @User: Advanced
+    AP_GROUPINFO("OPTIONS", 9,  AP_Networking,    param.options, 0),
+
+#if AP_NETWORKING_PPP_GATEWAY_ENABLED
+    // @Group: REMPPP_IP
+    // @Path: AP_Networking_address.cpp
+    AP_SUBGROUPINFO(param.remote_ppp_ip, "REMPPP_IP", 10,  AP_Networking, AP_Networking_IPV4),
+#endif
+    
     AP_GROUPEND
 };
 
@@ -129,8 +143,19 @@ void AP_Networking::init()
     }
 #endif
 
+#if AP_NETWORKING_PPP_GATEWAY_ENABLED
+    if (option_is_set(OPTION::PPP_ETHERNET_GATEWAY)) {
+        /*
+          when we are a PPP/Ethernet gateway we bring up the ethernet first
+         */
+        backend = new AP_Networking_ChibiOS(*this);
+        backend_PPP = new AP_Networking_PPP(*this);
+    }
+#endif
+
+
 #if AP_NETWORKING_BACKEND_PPP
-    if (AP::serialmanager().have_serial(AP_SerialManager::SerialProtocol_PPP, 0)) {
+    if (backend == nullptr && AP::serialmanager().have_serial(AP_SerialManager::SerialProtocol_PPP, 0)) {
         backend = new AP_Networking_PPP(*this);
     }
 #endif
@@ -158,6 +183,13 @@ void AP_Networking::init()
         return;
     }
 
+#if AP_NETWORKING_PPP_GATEWAY_ENABLED
+    if (backend_PPP != nullptr && !backend_PPP->init()) {
+        GCS_SEND_TEXT(MAV_SEVERITY_INFO, "NET: backend_PPP init failed");
+        backend_PPP = nullptr;
+    }
+#endif
+
     announce_address_changes();
 
     GCS_SEND_TEXT(MAV_SEVERITY_INFO,"NET: Initialized");

libraries/AP_Networking/AP_Networking.h

@@ -26,6 +26,7 @@ class AP_Networking
 public:
     friend class AP_Networking_Backend;
     friend class AP_Networking_ChibiOS;
+    friend class AP_Networking_PPP;
     friend class AP_Vehicle;
     friend class Networking_Periph;
 
@@ -149,6 +150,13 @@ public:
 
     static const struct AP_Param::GroupInfo var_info[];
 
+    enum class OPTION {
+        PPP_ETHERNET_GATEWAY=(1U<<0),
+    };
+    bool option_is_set(OPTION option) const {
+        return (param.options.get() & int32_t(option)) != 0;
+    }
+
 private:
     static AP_Networking *singleton;
 
@@ -172,10 +180,18 @@ private:
         AP_Int32 tests;
         AP_Networking_IPV4 test_ipaddr{AP_NETWORKING_TEST_IP};
 #endif
+
+#if AP_NETWORKING_PPP_GATEWAY_ENABLED
+        AP_Networking_IPV4 remote_ppp_ip{AP_NETWORKING_REMOTE_PPP_IP};
+#endif
     } param;
 
     AP_Networking_Backend *backend;
 
+#if AP_NETWORKING_PPP_GATEWAY_ENABLED
+    AP_Networking_Backend *backend_PPP;
+#endif
+
     HAL_Semaphore sem;
 
     enum class NetworkPortType {

libraries/AP_Networking/AP_Networking_Config.h

@@ -119,3 +119,17 @@
 #ifndef AP_NETWORKING_SENDFILE_BUFSIZE
 #define AP_NETWORKING_SENDFILE_BUFSIZE (64*512)
 #endif
+
+#ifndef AP_NETWORKING_PPP_GATEWAY_ENABLED
+#define AP_NETWORKING_PPP_GATEWAY_ENABLED (AP_NETWORKING_BACKEND_CHIBIOS && AP_NETWORKING_BACKEND_PPP)
+#endif
+
+/*
+  the IP address given to the remote end of the PPP link when running
+  as a PPP<->ethernet gateway. If this is on the same subnet as the
+  ethernet interface IP then proxyarp will be used
+ */
+#ifndef AP_NETWORKING_REMOTE_PPP_IP
+#define AP_NETWORKING_REMOTE_PPP_IP "0.0.0.0"
+#endif
+

libraries/AP_Networking/AP_Networking_PPP.cpp

@@ -57,10 +57,17 @@ void AP_Networking_PPP::ppp_status_callback(struct ppp_pcb_s *pcb, int code, voi
     switch (code) {
     case PPPERR_NONE:
         // got new addresses for the link
+#if AP_NETWORKING_PPP_GATEWAY_ENABLED
+        if (driver.frontend.option_is_set(AP_Networking::OPTION::PPP_ETHERNET_GATEWAY)) {
+            GCS_SEND_TEXT(MAV_SEVERITY_INFO, "PPP: got addresses");
+        } else
+#endif
+        {
             driver.activeSettings.ip = ntohl(netif_ip4_addr(pppif)->addr);
             driver.activeSettings.gw = ntohl(netif_ip4_gw(pppif)->addr);
             driver.activeSettings.nm = ntohl(netif_ip4_netmask(pppif)->addr);
             driver.activeSettings.last_change_ms = AP_HAL::millis();
+        }
         break;
 
     case PPPERR_OPEN:
@@ -94,10 +101,13 @@ bool AP_Networking_PPP::init()
         return false;
     }
 
+    const bool ethernet_gateway = frontend.option_is_set(AP_Networking::OPTION::PPP_ETHERNET_GATEWAY);
+    if (!ethernet_gateway) {
         // initialise TCP/IP thread
         LWIP_TCPIP_LOCK();
         tcpip_init(NULL, NULL);
         LWIP_TCPIP_UNLOCK();
+    }
 
     hal.scheduler->delay(100);
     
@@ -127,9 +137,14 @@ void AP_Networking_PPP::ppp_loop(void)
     while (!hal.scheduler->is_system_initialized()) {
         hal.scheduler->delay_microseconds(1000);
     }
+    const bool ppp_gateway = frontend.option_is_set(AP_Networking::OPTION::PPP_ETHERNET_GATEWAY);
+    if (ppp_gateway) {
+        // wait for the ethernet interface to be up
+        AP::network().startup_wait();
+    }
 
     // ensure this thread owns the uart
-    uart->begin(0);
+    uart->begin(AP::serialmanager().find_baudrate(AP_SerialManager::SerialProtocol_PPP, 0));
     uart->set_unbuffered_writes(true);
 
     while (true) {
@@ -137,9 +152,63 @@ void AP_Networking_PPP::ppp_loop(void)
 
         // connect and set as default route
         LWIP_TCPIP_LOCK();
+
+#if AP_NETWORKING_PPP_GATEWAY_ENABLED
+        if (ppp_gateway) {
+            /*
+              when bridging setup the ppp interface with the same IP
+              as the ethernet interface, and set the remote IP address
+              as the local address + 1
+             */
+            ip4_addr_t our_ip, his_ip;
+            const uint32_t ip = frontend.get_ip_active();
+            uint32_t rem_ip = frontend.param.remote_ppp_ip.get_uint32();
+            if (rem_ip == 0) {
+                // use ethernet IP +1 by default
+                rem_ip = ip+1;
+            }
+            our_ip.addr = htonl(ip);
+            his_ip.addr = htonl(rem_ip);
+            ppp_set_ipcp_ouraddr(ppp, &our_ip);
+            ppp_set_ipcp_hisaddr(ppp, &his_ip);
+            if (netif_list != nullptr) {
+                const uint32_t nmask = frontend.get_netmask_param();
+                if ((ip & nmask) == (rem_ip & nmask)) {
+                    // remote PPP IP is on the same subnet as the
+                    // local ethernet IP, so enable proxyarp to avoid
+                    // users having to setup routes in all devices
+                    netif_set_proxyarp(netif_list, &his_ip);
+                }
+            }
+        }
+
+        // connect to the remote end
         ppp_connect(ppp, 0);
 
+        if (ppp_gateway) {
+            extern struct netif *netif_list;
+            /*
+              when we are setup as a PPP gateway we want the pppif to be
+              first in the list so routing works if it is on the same
+              subnet
+            */
+            if (netif_list != nullptr &&
+                netif_list->next != nullptr &&
+                netif_list->next->next == pppif) {
+                netif_list->next->next = nullptr;
+                pppif->next = netif_list;
+                netif_list = pppif;
+            }
+        } else {
             netif_set_default(pppif);
+        }
+#else
+        // normal PPP link, connect to the remote end and set as the
+        // default route
+        ppp_connect(ppp, 0);
+        netif_set_default(pppif);
+#endif // AP_NETWORKING_PPP_GATEWAY_ENABLED
+
         LWIP_TCPIP_UNLOCK();
 
         need_restart = false;

libraries/AP_Networking/config/lwipopts.h

@@ -74,7 +74,6 @@ extern "C"
 #define LWIP_ICMP                  LWIP_IPV4
 
 #define LWIP_SNMP                  LWIP_UDP
-#define MIB2_STATS                 LWIP_SNMP
 #ifdef LWIP_HAVE_MBEDTLS
 #define LWIP_SNMP_V3               (LWIP_SNMP)
 #endif
@@ -255,6 +254,7 @@ a lot of data that needs to be copied, this should be set high. */
 #define LWIP_ARP                1
 #define ARP_TABLE_SIZE          10
 #define ARP_QUEUEING            1
+#define ARP_PROXYARP_SUPPORT    1
 
 
 /* ---------- IP options ---------- */
@@ -263,6 +263,12 @@ a lot of data that needs to be copied, this should be set high. */
    on a device with only one network interface, define this to 0. */
 #define IP_FORWARD              1
 
+/*
+  extra header space when forwarding for adding the ethernet header
+*/
+#define PBUF_LINK_HLEN          16
+
+
 /* IP reassembly and segmentation.These are orthogonal even
  * if they both deal with IP fragments */
 #define IP_REASSEMBLY           1
@@ -302,22 +308,8 @@ a lot of data that needs to be copied, this should be set high. */
 
 /* ---------- Statistics options ---------- */
 
-#define LWIP_STATS              1
+#define LWIP_STATS              0
-#define LWIP_STATS_DISPLAY      1
+#define LWIP_STATS_DISPLAY      0
-
-#if LWIP_STATS
-#define LINK_STATS              1
-#define IP_STATS                1
-#define ICMP_STATS              1
-#define IGMP_STATS              1
-#define IPFRAG_STATS            1
-#define UDP_STATS               1
-#define TCP_STATS               1
-#define MEM_STATS               1
-#define MEMP_STATS              1
-#define PBUF_STATS              1
-#define SYS_STATS               1
-#endif /* LWIP_STATS */
 
 /* ---------- NETBIOS options ---------- */
 #define LWIP_NETBIOS_RESPOND_NAME_QUERY 1
@@ -343,7 +335,10 @@ a lot of data that needs to be copied, this should be set high. */
 #define MSCHAP_SUPPORT          0      /* Set > 0 for MSCHAP */
 #define CBCP_SUPPORT            0      /* Set > 0 for CBCP (NOT FUNCTIONAL!) */
 #define CCP_SUPPORT             0      /* Set > 0 for CCP */
-#define VJ_SUPPORT              1      /* Set > 0 for VJ header compression. */
+/*
+  VJ support disabled due to bugs with IP forwarding
+ */
+#define VJ_SUPPORT              0      /* Set > 0 for VJ header compression. */
 #define MD5_SUPPORT             0      /* Set > 0 for MD5 (see also CHAP) */
 
 #endif /* PPP_SUPPORT */