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, 8 insertions, 6 deletions

diff --git a/src/vpp/stats/stat_segment.c b/src/vpp/stats/stat_segment.c
index 300cfe785e1..bb2ffad8f6d 100644
--- a/src/vpp/stats/stat_segment.c
+++ b/src/vpp/stats/stat_segment.c
@@ -680,11 +680,6 @@ static clib_error_t *
 statseg_init (vlib_main_t * vm)
 {
   stat_segment_main_t *sm = &stat_segment_main;
-  clib_error_t *error;
-
-  /* dependent on unix_input_init */
-  if ((error = vlib_call_init_function (vm, unix_input_init)))
-    return error;
 
   if (sm->socket_name)
     stats_segment_socket_init ();
@@ -692,6 +687,14 @@ statseg_init (vlib_main_t * vm)
   return 0;
 }
 
+/* *INDENT-OFF* */
+VLIB_INIT_FUNCTION (statseg_init) =
+{
+  .runs_after = VLIB_INITS("unix_input_init"),
+};
+/* *INDENT-ON* */
+
+
 clib_error_t *
 stat_segment_register_gauge (u8 * name, stat_segment_update_fn update_fn,
 			     u32 caller_index)
@@ -832,7 +835,6 @@ statseg_sw_interface_add_del (vnet_main_t * vnm, u32 sw_if_index, u32 is_add)
   return 0;
 }
 
-VLIB_INIT_FUNCTION (statseg_init);
 VLIB_EARLY_CONFIG_FUNCTION (statseg_config, "statseg");
 VNET_SW_INTERFACE_ADD_DEL_FUNCTION (statseg_sw_interface_add_del);