vlib: add postmortem pcap dispatch trace

Inspired by a real-life conundrum: scenario X involves a vpp crash in
ip4-load-balance because vnet_buffer(b)->ip.adj_index[VLIB_TX] is
(still) set to ~0.

The problem takes most of a day to occur, and we need to see the
broken packet's graph trajectory, metadata, etc. to understand the
problem.

Fix a signed/unsigned ASSERT bug in vlib_get_trace_count().

Rename elog_post_mortem_dump() -> vlib_post_mortem_dump(), add
dispatch trace post-mortem dump.

Add FILTER_FLAG_POST_MORTEM so we can (putatively) capture a ludicrous
number of buffer traces, without actually using more than one dispatch
cycle's worth of memory.

Type: improvement

Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: If093202ef071df46e290370bd9b33bf6560d30e6

1 files changed, 2 insertions, 0 deletions

diff --git a/src/vlib/main.h b/src/vlib/main.h
index c582bc12f4e..c420d5f9d28 100644
--- a/src/vlib/main.h
+++ b/src/vlib/main.h
@@ -197,6 +197,7 @@ typedef struct vlib_main_t
   /* Pcap dispatch trace main */
   pcap_main_t dispatch_pcap_main;
   uword dispatch_pcap_enable;
+  uword dispatch_pcap_postmortem;
   u32 *dispatch_buffer_trace_nodes;
   u8 *pcap_buffer;
 
@@ -483,6 +484,7 @@ typedef struct
   u8 *filename;
   int enable;
   int status;
+  int post_mortem;
   u32 packets_to_capture;
   u32 buffer_trace_node_index;
   u32 buffer_traces_to_capture;