misc: improve pcap drop trace output

Append <nodename>: <error-string> to pcap drop traces.

The data displays perfectly fine in [vanilla] wireshark, and makes it
100% obvious which node dropped the packet, and why.

Type: feature
Ticket: VPP-1776

Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: I9b964b99da4011b93723354db6ef0b128fca20cb

diff --git a/src/vnet/interface_output.c b/src/vnet/interface_output.c
index 8eb2e67..8e25701 100644 (file)
--- a/src/vnet/interface_output.c
+++ b/src/vnet/interface_output.c
@@ -1177,6 +1177,7 @@ pcap_drop_trace (vlib_main_t * vm,
   u32 bi0;
   i16 save_current_data;
   u16 save_current_length;
+  vlib_error_main_t *em = &vm->error_main;
 
   from = vlib_frame_vector_args (f);
 
@@ -1222,6 +1223,59 @@ pcap_drop_trace (vlib_main_t * vm,
          else if (b0->current_data > 0)
            vlib_buffer_advance (b0, (word) - b0->current_data);
 
+         {
+           vlib_buffer_t *last = b0;
+           u32 error_node_index;
+           int drop_string_len;
+           vlib_node_t *n;
+           /* Length of the error string */
+           int error_string_len =
+             clib_strnlen (em->error_strings_heap[b0->error], 128);
+
+           /* Dig up the drop node */
+           error_node_index = vm->node_main.node_by_error[b0->error];
+           n = vlib_get_node (vm, error_node_index);
+
+           /* Length of full drop string, w/ "nodename: " prepended */
+           drop_string_len = error_string_len + vec_len (n->name) + 2;
+
+           /* Find the last buffer in the chain */
+           while (last->flags & VLIB_BUFFER_NEXT_PRESENT)
+             last = vlib_get_buffer (vm, last->next_buffer);
+
+           /*
+            * Append <nodename>: <error-string> to the capture,
+            * only if we can do that without allocating a new buffer.
+            */
+           if (PREDICT_TRUE ((last->current_data + last->current_length)
+                             < (VLIB_BUFFER_DEFAULT_DATA_SIZE
+                                - drop_string_len)))
+             {
+               clib_memcpy_fast (last->data + last->current_data +
+                                 last->current_length, n->name,
+                                 vec_len (n->name));
+               clib_memcpy_fast (last->data + last->current_data +
+                                 last->current_length + vec_len (n->name),
+                                 ": ", 2);
+               clib_memcpy_fast (last->data + last->current_data +
+                                 last->current_length + vec_len (n->name) +
+                                 2, em->error_strings_heap[b0->error],
+                                 error_string_len);
+               last->current_length += drop_string_len;
+               b0->flags &= ~(VLIB_BUFFER_TOTAL_LENGTH_VALID);
+               pcap_add_buffer (&pp->pcap_main, vm, bi0,
+                                pp->max_bytes_per_pkt);
+               last->current_length -= drop_string_len;
+               b0->current_data = save_current_data;
+               b0->current_length = save_current_length;
+               continue;
+             }
+         }
+
+         /*
+          * Didn't have space in the last buffer, here's the dropped
+          * packet as-is
+          */
          pcap_add_buffer (&pp->pcap_main, vm, bi0, pp->max_bytes_per_pkt);
 
          b0->current_data = save_current_data;