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>

2 files changed, 13 insertions, 12 deletions

diff --git a/src/plugins/ioam/udp-ping/udp_ping_export.c b/src/plugins/ioam/udp-ping/udp_ping_export.c
index 7a7cad4934a..d25eb1041dd 100644
--- a/src/plugins/ioam/udp-ping/udp_ping_export.c
+++ b/src/plugins/ioam/udp-ping/udp_ping_export.c
@@ -290,15 +290,16 @@ VLIB_CLI_COMMAND (set_udp_ping_export_command, static) = {
 clib_error_t *
 udp_ping_flow_report_init (vlib_main_t * vm)
 {
-  clib_error_t *error;
-
-  if ((error = vlib_call_init_function (vm, flow_report_init)))
-    return error;
-
   return 0;
 }
 
-VLIB_INIT_FUNCTION (udp_ping_flow_report_init);
+/* *INDENT-OFF* */
+VLIB_INIT_FUNCTION (udp_ping_flow_report_init) =
+{
+  .runs_after = VLIB_INITS ("flow_report_init"),
+};
+/* *INDENT-ON* */
+
 
 /*
  * fd.io coding-style-patch-verification: ON
diff --git a/src/plugins/ioam/udp-ping/udp_ping_node.c b/src/plugins/ioam/udp-ping/udp_ping_node.c
index 59e4511eb7d..e5916dbd0e1 100644
--- a/src/plugins/ioam/udp-ping/udp_ping_node.c
+++ b/src/plugins/ioam/udp-ping/udp_ping_node.c
@@ -819,21 +819,21 @@ VLIB_REGISTER_NODE (udp_ping_local, static) =
 static clib_error_t *
 udp_ping_init (vlib_main_t * vm)
 {
-  clib_error_t *error = 0;
-
   udp_ping_main.vlib_main = vm;
   udp_ping_main.vnet_main = vnet_get_main ();
   udp_ping_main.timer_interval = 1e9;
 
-  if ((error = vlib_call_init_function (vm, ip_main_init)))
-    return (error);
-
   ip6_register_protocol (IP_PROTOCOL_IP6_HOP_BY_HOP_OPTIONS,
 			 udp_ping_local.index);
   return 0;
 }
 
-VLIB_INIT_FUNCTION (udp_ping_init);
+/* *INDENT-OFF* */
+VLIB_INIT_FUNCTION (udp_ping_init) =
+{
+  .runs_after = VLIB_INITS("ip_main_init"),
+};
+/* *INDENT-ON* */
 
 /*
  * fd.io coding-style-patch-verification: ON