Separate "Ethernet in capture file" and "Ethernet maybe with FCS" dissectors.

Have a dissector that is passed a "struct eth_phdr" pointer, indicating
whether there is an FCS, there is no FCS, or there's maybe an FCS, and
an "eth_maybefcs" dissector, to be called from other dissectors.  The
latter takes no data argument.

That obviates the need for callers of the latter to fill in an
"eth_phdr" structure.

Note in a comment that setting the "assume an FCS" preference overrides
a file format handler in Wiretap saying "we have no FCS".  I seem to
remember that this might be intentional.

Ping-Bug: 9933
Change-Id: I600e1351d468ab31d48369edb96832d6da3e480c
Reviewed-on: https://code.wireshark.org/review/13432
Reviewed-by: Guy Harris <guy@alum.mit.edu>

epan/dissectors/packet-atm.c

@@ -145,7 +145,7 @@ static dissector_handle_t fr_handle;
 static dissector_handle_t llc_handle;
 static dissector_handle_t sscop_handle;
 static dissector_handle_t ppp_handle;
-static dissector_handle_t eth_handle;
+static dissector_handle_t eth_maybefcs_handle;
 static dissector_handle_t ip_handle;
 static dissector_handle_t data_handle;
 
@@ -992,12 +992,9 @@ dissect_reassembled_pdu(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
              * See RFC 2684 section 6.2 "VC Multiplexing of Bridged
              * Protocols".
              */
-            struct eth_phdr eth;
-
             proto_tree_add_item(tree, hf_atm_padding, tvb, 0, 2, ENC_NA);
             next_tvb = tvb_new_subset_remaining(tvb, 2);
-            eth.fcs_len = -1;   /* We don't know whether there's an FCS */
-            call_dissector_with_data(eth_handle, next_tvb, pinfo, tree, &eth);
+            call_dissector(eth_maybefcs_handle, next_tvb, pinfo, tree);
             decoded = TRUE;
           }
           else if (octet[2] == 0x03    && /* NLPID */
@@ -2018,7 +2015,7 @@ proto_reg_handoff_atm(void)
   llc_handle            = find_dissector("llc");
   sscop_handle          = find_dissector("sscop");
   ppp_handle            = find_dissector("ppp");
-  eth_handle            = find_dissector("eth");
+  eth_maybefcs_handle   = find_dissector("eth_maybefcs");
   ip_handle             = find_dissector("ip");
   data_handle           = find_dissector("data");
 

epan/dissectors/packet-cisco-fp-mim.c

@@ -72,7 +72,7 @@ static const true_false_string ooodl_tfs = {
   "Deliver in order (If DA) or Learn (If SA)"
 };
 
-static dissector_handle_t eth_dissector ;
+static dissector_handle_t eth_maybefcs_dissector ;
 
 
 #define FP_PROTO_COL_NAME "FabricPath"
@@ -218,7 +218,6 @@ dissect_fp( tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data _U_
   guint16       dlid     = 0;
   const guint8 *dst_addr = NULL;
   gboolean      dest_ig  = FALSE;
-  struct eth_phdr eth;
 
   col_set_str( pinfo->cinfo, COL_PROTOCOL, FP_PROTO_COL_NAME ) ;
   col_set_str( pinfo->cinfo, COL_INFO, FP_PROTO_COL_INFO ) ;
@@ -295,11 +294,9 @@ dissect_fp( tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data _U_
   /* call the eth dissector */
   next_tvb = tvb_new_subset_remaining( tvb, FP_HEADER_SIZE) ;
   /*
-   * For now, say we don't know whether there's an FCS in the
-   * captured data.
+   * For now, we don't know whether there's an FCS in the captured data.
    */
-  eth.fcs_len = -1;
-  call_dissector_with_data( eth_dissector, next_tvb, pinfo, tree, &eth ) ;
+  call_dissector( eth_maybefcs_dissector, next_tvb, pinfo, tree ) ;
 
   return tvb_captured_length( tvb ) ;
 }
@@ -416,7 +413,7 @@ proto_reg_handoff_fabricpath(void)
      * by the Ethernet dissector.  This needs more work, so we leave this
      * as calling the "eth" dissector as a reminder.
      */
-    eth_dissector = find_dissector( "eth" );
+    eth_maybefcs_dissector = find_dissector( "eth_maybefcs" );
     prefs_initialized = TRUE;
   }
 }

epan/dissectors/packet-epon.c

@@ -54,7 +54,7 @@ static expert_field ei_epon_dpoe_bad = EI_INIT;
 static expert_field ei_epon_dpoe_encrypted_data = EI_INIT;
 static expert_field ei_epon_checksum_bad = EI_INIT;
 
-static dissector_handle_t eth_handle;
+static dissector_handle_t eth_maybefcs_handle;
 
 static gint ett_epon = -1;
 static gint ett_epon_sec = -1;
@@ -79,7 +79,6 @@ dissect_epon(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
   guint       offset = 0;
   guint       dpoe_sec_byte;
   gboolean    dpoe_encrypted = FALSE;
-  struct eth_phdr eth;
 
   /* Start_of_Packet delimiter (/S/) can either happen in byte 1 or byte 2,
    * making the captured preamble either 7 or 6 bytes in length. If the
@@ -200,8 +199,7 @@ dissect_epon(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
      * XXX - is it guaranteed whether the capture will, or won't, have
      * an FCS?
      */
-    eth.fcs_len = -1;
-    call_dissector_with_data(eth_handle, next_tvb, pinfo, tree, &eth);
+    call_dissector(eth_maybefcs_handle, next_tvb, pinfo, tree);
   }
 
   return tvb_captured_length(tvb);
@@ -297,7 +295,7 @@ proto_reg_handoff_epon(void)
   epon_handle = create_dissector_handle(dissect_epon, proto_epon);
   dissector_add_uint("wtap_encap", WTAP_ENCAP_EPON, epon_handle);
 
-  eth_handle = find_dissector("eth");
+  eth_maybefcs_handle = find_dissector("eth_maybefcs");
 }
 
 /*

epan/dissectors/packet-eth.c

@@ -795,7 +795,7 @@ add_ethernet_trailer(packet_info *pinfo, proto_tree *tree, proto_tree *fh_tree,
 /* Called for the Ethernet Wiretap encapsulation type; pass the FCS length
    reported to us, or, if the "assume_fcs" preference is set, pass 4. */
 static int
-dissect_eth_maybefcs(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data)
+dissect_eth(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data)
 {
   struct eth_phdr   *eth = (struct eth_phdr *)data;
   proto_tree        *fh_tree;
@@ -808,6 +808,10 @@ dissect_eth_maybefcs(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *
     tvbuff_t *next_tvb;
     guint total_trailer_length;
 
+    /*
+     * XXX - this overrides Wiretap saying "this packet definitely has
+     * no FCS".
+     */
     total_trailer_length = eth_trailer_length + (eth_assume_fcs ? 4 : 0);
 
     /* Dissect the tvb up to, but not including the trailer */
@@ -818,9 +822,17 @@ dissect_eth_maybefcs(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *
 
     /* Now handle the ethernet trailer and optional FCS */
     next_tvb = tvb_new_subset_remaining(tvb, tvb_captured_length(tvb) - total_trailer_length);
+    /*
+     * XXX - this overrides Wiretap saying "this packet definitely has
+     * no FCS".
+     */
     add_ethernet_trailer(pinfo, tree, fh_tree, hf_eth_trailer, tvb, next_tvb,
                          eth_assume_fcs ? 4 : eth->fcs_len);
   } else {
+    /*
+     * XXX - this overrides Wiretap saying "this packet definitely has
+     * no FCS".
+     */
     dissect_eth_common(tvb, pinfo, tree, eth_assume_fcs ? 4 : eth->fcs_len);
   }
   return tvb_captured_length(tvb);
@@ -843,6 +855,14 @@ dissect_eth_withfcs(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* d
   return tvb_captured_length(tvb);
 }
 
+/* ...and this one's for encapsulated packets that might or might not. */
+static int
+dissect_eth_maybefcs(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
+{
+  dissect_eth_common(tvb, pinfo, tree, eth_assume_fcs ? 4 : -1);
+  return tvb_captured_length(tvb);
+}
+
 void
 proto_register_eth(void)
 {
@@ -1008,7 +1028,7 @@ proto_register_eth(void)
 
   register_dissector("eth_withoutfcs", dissect_eth_withoutfcs, proto_eth);
   register_dissector("eth_withfcs", dissect_eth_withfcs, proto_eth);
-  register_dissector("eth", dissect_eth_maybefcs, proto_eth);
+  register_dissector("eth_maybefcs", dissect_eth_maybefcs, proto_eth);
   eth_tap = register_tap("eth");
 
   register_conversation_table(proto_eth, TRUE, eth_conversation_packet, eth_hostlist_packet);
@@ -1018,7 +1038,7 @@ proto_register_eth(void)
 void
 proto_reg_handoff_eth(void)
 {
-  dissector_handle_t eth_maybefcs_handle, eth_withoutfcs_handle;
+  dissector_handle_t eth_handle, eth_withoutfcs_handle;
 
   /* Get a handle for the Firewall-1 dissector. */
   fw1_handle = find_dissector("fw1");
@@ -1029,8 +1049,8 @@ proto_reg_handoff_eth(void)
   /* Get a handle for the generic data dissector. */
   data_handle = find_dissector("data");
 
-  eth_maybefcs_handle = find_dissector("eth");
-  dissector_add_uint("wtap_encap", WTAP_ENCAP_ETHERNET, eth_maybefcs_handle);
+  eth_handle = create_dissector_handle(dissect_eth, proto_eth);
+  dissector_add_uint("wtap_encap", WTAP_ENCAP_ETHERNET, eth_handle);
 
   eth_withoutfcs_handle = find_dissector("eth_withoutfcs");
   dissector_add_uint("ethertype", ETHERTYPE_ETHBRIDGE, eth_withoutfcs_handle);

epan/dissectors/packet-tzsp.c

@@ -101,7 +101,7 @@ static const value_string tzsp_encapsulation[] = {
 static gint ett_tzsp = -1;
 static gint ett_tag = -1;
 
-static dissector_handle_t eth_handle;
+static dissector_handle_t eth_maybefcs_handle;
 static dissector_handle_t tr_handle;
 static dissector_handle_t ppp_handle;
 static dissector_handle_t fddi_handle;
@@ -289,7 +289,6 @@ dissect_tzsp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_
     guint16             encapsulation = 0;
     const char         *info;
     guint8              type;
-    struct eth_phdr     eth;
 
     col_set_str(pinfo->cinfo, COL_PROTOCOL, "TZSP");
     col_clear(pinfo->cinfo, COL_INFO);
@@ -340,8 +339,7 @@ dissect_tzsp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_
         switch (encapsulation) {
 
         case TZSP_ENCAP_ETHERNET:
-            eth.fcs_len = -1;  /* not known */
-            call_dissector_with_data(eth_handle, next_tvb, pinfo, tree, &eth);
+            call_dissector(eth_maybefcs_handle, next_tvb, pinfo, tree);
             break;
 
         case TZSP_ENCAP_TOKEN_RING:
@@ -556,7 +554,7 @@ proto_reg_handoff_tzsp(void)
     dissector_add_uint("udp.port", UDP_PORT_TZSP, tzsp_handle);
 
     /* Get the data dissector for handling various encapsulation types. */
-    eth_handle = find_dissector("eth");
+    eth_maybefcs_handle = find_dissector("eth_maybefcs");
     tr_handle = find_dissector("tr");
     ppp_handle = find_dissector("ppp_hdlc");
     fddi_handle = find_dissector("fddi");