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>

3 files changed, 21 insertions, 22 deletions

diff --git a/src/plugins/igmp/igmp.c b/src/plugins/igmp/igmp.c
index 7f828619331..4e2fce1b916 100644
--- a/src/plugins/igmp/igmp.c
+++ b/src/plugins/igmp/igmp.c
@@ -479,24 +479,24 @@ igmp_enable_disable (u32 sw_if_index, u8 enable, igmp_mode_t mode)
 static clib_error_t *
 igmp_init (vlib_main_t * vm)
 {
-  clib_error_t *error;
   igmp_main_t *im = &igmp_main;
 
-  if ((error = vlib_call_init_function (vm, ip4_lookup_init)))
-    return error;
-
   im->igmp_api_client_by_client_index = hash_create (0, sizeof (u32));
 
   im->logger = vlib_log_register_class ("igmp", 0);
 
   IGMP_DBG ("initialized");
 
-  return (error);
+  return (0);
 }
 
-VLIB_INIT_FUNCTION (igmp_init);
 /* *INDENT-OFF* */
-VLIB_PLUGIN_REGISTER () = {
+VLIB_INIT_FUNCTION (igmp_init) =
+{
+  .runs_after = VLIB_INITS("ip4_lookup_init"),
+};
+VLIB_PLUGIN_REGISTER () =
+{
   .version = VPP_BUILD_VER,
   .description = "Internet Group Management Protocol (IGMP)",
 };
diff --git a/src/plugins/igmp/igmp_input.c b/src/plugins/igmp/igmp_input.c
index 83e11ec6cc5..d5f714bc033 100644
--- a/src/plugins/igmp/igmp_input.c
+++ b/src/plugins/igmp/igmp_input.c
@@ -445,19 +445,19 @@ VLIB_REGISTER_NODE (igmp_parse_report_node) =
 static clib_error_t *
 igmp_input_init (vlib_main_t * vm)
 {
-  clib_error_t *error;
-
-  if ((error = vlib_call_init_function (vm, igmp_init)))
-    return error;
-
   ip4_register_protocol (IP_PROTOCOL_IGMP, igmp_input_node.index);
 
   IGMP_DBG ("input-initialized");
 
-  return (error);
+  return (0);
 }
 
-VLIB_INIT_FUNCTION (igmp_input_init);
+/* *INDENT-OFF* */
+VLIB_INIT_FUNCTION (igmp_input_init) =
+{
+  .runs_after = VLIB_INITS("igmp_init"),
+};
+/* *INDENT-ON* */
 
 /*
  * fd.io coding-style-patch-verification: ON
diff --git a/src/plugins/igmp/igmp_ssm_range.c b/src/plugins/igmp/igmp_ssm_range.c
index 3d12712d3db..c74d312b508 100644
--- a/src/plugins/igmp/igmp_ssm_range.c
+++ b/src/plugins/igmp/igmp_ssm_range.c
@@ -138,20 +138,19 @@ VLIB_CLI_COMMAND (igmp_show_timers_command, static) = {
 static clib_error_t *
 igmp_ssm_range_init (vlib_main_t * vm)
 {
-  clib_error_t *error;
-
-  if ((error = vlib_call_init_function (vm, igmp_init)))
-    return error;
-
   igmp_ssm_range_populate ();
 
   IGMP_DBG ("ssm-range-initialized");
 
-  return (error);
+  return (0);
 }
 
-VLIB_INIT_FUNCTION (igmp_ssm_range_init);
-
+/* *INDENT-OFF* */
+VLIB_INIT_FUNCTION (igmp_ssm_range_init) =
+{
+  .runs_after = VLIB_INITS("igmp_init"),
+};
+/* *INDENT-ON* */
 
 /*
  * fd.io coding-style-patch-verification: ON