ring: and int: now correctly recognise gretap interfaces

Previously, libtrace was trying to interpret these as raw IP but
gretap actually delivers bridged Ethernet frames so the initial
header is Ethernet, not IP.

Author: salcock

lib/format_linux_int.c

@@ -393,6 +393,13 @@ linuxnative_get_link_type(const struct libtrace_packet_t *packet)
     uint16_t linktype =
         (((struct libtrace_linuxnative_header *)(packet->buffer))
              ->hdr.sll_hatype);
+    uint16_t proto =
+        (((struct libtrace_linuxnative_header *)(packet->buffer))
+             ->hdr.sll_protocol);
+    if (proto == htons(ETH_P_TEB)) {
+        /* bridged Ethernet frame, regardless of the hatype */
+        return TRACE_TYPE_ETH;
+    }
     return linuxcommon_get_link_type(linktype);
 }
 

lib/format_linux_ring.c

@@ -511,6 +511,11 @@ static libtrace_linktype_t
 linuxring_get_link_type(const struct libtrace_packet_t *packet)
 {
     uint16_t linktype = GET_SOCKADDR_HDR(packet->buffer)->sll_hatype;
+
+    if (GET_SOCKADDR_HDR(packet->buffer)->sll_protocol == htons(ETH_P_TEB)) {
+        /* this is a GRE tunnel with a transparent Ethernet header */
+        return TRACE_TYPE_ETH;
+    }
     return linuxcommon_get_link_type(linktype);
 }