init / exit function ordering

The vlib init function subsystem now supports a mix of procedural and
formally-specified ordering constraints. We should eliminate procedural
knowledge wherever possible.

The following schemes are *roughly* equivalent:

static clib_error_t *init_runs_first (vlib_main_t *vm)
{
   clib_error_t *error;

   ... do some stuff...

   if ((error = vlib_call_init_function (init_runs_next)))
     return error;
   ...
}
VLIB_INIT_FUNCTION (init_runs_first);

and

static clib_error_t *init_runs_first (vlib_main_t *vm)
{
   ... do some stuff...
}
VLIB_INIT_FUNCTION (init_runs_first) =
{
    .runs_before = VLIB_INITS("init_runs_next"),
};

The first form will [most likely] call "init_runs_next" on the
spot. The second form means that "init_runs_first" runs before
"init_runs_next," possibly much earlier in the sequence.

Please DO NOT construct sets of init functions where A before B
actually means A *right before* B. It's not necessary - simply combine
A and B - and it leads to hugely annoying debugging exercises when
trying to switch from ad-hoc procedural ordering constraints to formal
ordering constraints.

Change-Id: I5e4353503bf43b4acb11a45fb33c79a5ade8426c
Signed-off-by: Dave Barach <dave@barachs.net>

1 files changed, 10 insertions, 11 deletions

diff --git a/src/vnet/mpls/mpls_input.c b/src/vnet/mpls/mpls_input.c
index 1dd5e326a3c..37fa1aead12 100644
--- a/src/vnet/mpls/mpls_input.c
+++ b/src/vnet/mpls/mpls_input.c
@@ -50,8 +50,8 @@ format_mpls_input_trace (u8 * s, va_list * args)
 #define _(a,b) if (t->next_index == MPLS_INPUT_NEXT_##a) next_name = b;
   foreach_mpls_input_next;
 #undef _
-  
-  s = format (s, "MPLS: next %s[%d]  label %d ttl %d exp %d", 
+
+  s = format (s, "MPLS: next %s[%d]  label %d ttl %d exp %d",
               next_name, t->next_index,
 	      vnet_mpls_uc_get_label(label),
 	      vnet_mpls_uc_get_ttl(label),
@@ -209,9 +209,9 @@ mpls_input_inline (vlib_main_t * vm,
               vlib_increment_simple_counter (cm, thread_index, sw_if_index0, 1);
             }
 
-          if (PREDICT_FALSE(b0->flags & VLIB_BUFFER_IS_TRACED)) 
+          if (PREDICT_FALSE(b0->flags & VLIB_BUFFER_IS_TRACED))
             {
-              mpls_input_trace_t *tr = vlib_add_trace (vm, node, 
+              mpls_input_trace_t *tr = vlib_add_trace (vm, node,
 						       b0, sizeof (*tr));
               tr->next_index = next0;
               tr->label_net_byte_order = *(u32*)h0;
@@ -278,16 +278,15 @@ mpls_setup_nodes (vlib_main_t * vm)
 
 static clib_error_t * mpls_input_init (vlib_main_t * vm)
 {
-  clib_error_t * error; 
-
-  error = vlib_call_init_function (vm, mpls_init);
-  if (error)
-    clib_error_report (error);
-
   mpls_setup_nodes (vm);
 
   return 0;
 }
 
-VLIB_INIT_FUNCTION (mpls_input_init);
+/* *INDENT-OFF* */
+VLIB_INIT_FUNCTION (mpls_input_init) =
+{
+  .runs_after = VLIB_INITS("mpls_init"),
+};
+/* *INDENT-ON* */
 #endif /* CLIB_MARCH_VARIANT */