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, 9 insertions, 4 deletions

diff --git a/src/vnet/dpo/dpo.c b/src/vnet/dpo/dpo.c
index df78456bf60..13ae37a74a8 100644
--- a/src/vnet/dpo/dpo.c
+++ b/src/vnet/dpo/dpo.c
@@ -16,7 +16,7 @@
  * @brief
  * A Data-Path Object is an object that represents actions that are
  * applied to packets are they are switched through VPP.
- * 
+ *
  * The DPO is a base class that is specialised by other objects to provide
  * concrete actions
  *
@@ -267,10 +267,10 @@ dpo_copy (dpo_id_t *dst,
      * the destination is written in a single u64 write - hence atomically w.r.t
      * any packets inflight.
      */
-    *((u64*)dst) = *(u64*)src; 
+    *((u64*)dst) = *(u64*)src;
 
     dpo_lock(dst);
-    dpo_unlock(&tmp);    
+    dpo_unlock(&tmp);
 }
 
 int
@@ -592,7 +592,12 @@ dpo_module_init (vlib_main_t * vm)
     return (NULL);
 }
 
-VLIB_INIT_FUNCTION(dpo_module_init);
+/* *INDENT-OFF* */
+VLIB_INIT_FUNCTION(dpo_module_init) =
+{
+    .runs_before = VLIB_INITS ("ip_main_init"),
+};
+/* *INDENT-ON* */
 
 static clib_error_t *
 dpo_memory_show (vlib_main_t * vm,