VLIB_BUFFER_TRACE_TRAJECTORY宏的作用

可以通過開啟宏VLIB_BUFFER_TRACE_TRAJECTORY，在mbuf里記錄mbuf經過的node個數以及所經過的node的index：

        if (VLIB_BUFFER_TRACE_TRAJECTORY && frame)

        {

            int i;

            int log_index;

            u32 * from;

            from = vlib_frame_vector_args (frame);

            for (i = 0; i < frame->n_vectors; i++)

            {

                vlib_buffer_t *b = vlib_get_buffer (vm, from[i]);

                ASSERT (b->pre_data[0] < 32);

                log_index = b->pre_data[0]++ + 1;

                b->pre_data[log_index] = node->node_index;

            }

            n = node->function (vm, node, frame);

        }

用以下函數打印記錄的node信息

void vlib_dump_context_trace (vlib_main_t*vm, u32 bi)

{

   vlib_node_main_t * vnm = &vm->node_main;

   vlib_buffer_t * b;

   u8 i, n;

   if (VLIB_BUFFER_TRACE_TRAJECTORY)

    {

       b = vlib_get_buffer (vm, bi);

       n = b->pre_data[0];

       fformat(stderr, "Context trace for bi %d b 0x%llx, visited%d\n",

                bi, b, n);

       if (n == 0 || n > 20)

       {

           fformat(stderr, "n is unreasonable\n");

           return;

       }

       for (i = 0; i < n; i++)

       {

           u32 node_index;

           node_index = b->pre_data[i+1];

           if (node_index > vec_len (vnm->nodes))

           {

                fformat(stderr, "Skip bogusnode index %d\n", node_index);

                continue;

           }

           fformat(stderr, "%v (%d)\n",vnm->nodes[node_index]->name,

                    node_index);

       }

    }

   else

    {

       fformat(stderr,

                "in vlib/buffers.h,#define VLIB_BUFFER_TRACE_TRAJECTORY 1\n");

    }

}