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, 10 deletions

diff --git a/src/vnet/udp/udp.c b/src/vnet/udp/udp.c
index d5166d9142e..81bdb8bd0e4 100644
--- a/src/vnet/udp/udp.c
+++ b/src/vnet/udp/udp.c
@@ -395,17 +395,9 @@ udp_init (vlib_main_t * vm)
   ip_main_t *im = &ip_main;
   vlib_thread_main_t *tm = vlib_get_thread_main ();
   u32 num_threads;
-  clib_error_t *error = 0;
   ip_protocol_info_t *pi;
   int i;
 
-  if ((error = vlib_call_init_function (vm, ip_main_init)))
-    return error;
-  if ((error = vlib_call_init_function (vm, ip4_lookup_init)))
-    return error;
-  if ((error = vlib_call_init_function (vm, ip6_lookup_init)))
-    return error;
-
   /*
    * Registrations
    */
@@ -443,10 +435,17 @@ udp_init (vlib_main_t * vm)
 	clib_spinlock_init (&um->peekers_readers_locks[i]);
 	clib_spinlock_init (&um->peekers_write_locks[i]);
       }
-  return error;
+  return 0;
 }
 
-VLIB_INIT_FUNCTION (udp_init);
+/* *INDENT-OFF* */
+VLIB_INIT_FUNCTION (udp_init) =
+{
+  .runs_after = VLIB_INITS("ip_main_init", "ip4_lookup_init",
+                           "ip6_lookup_init"),
+};
+/* *INDENT-ON* */
+
 
 static clib_error_t *
 show_udp_punt_fn (vlib_main_t * vm, unformat_input_t * input,