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, 7 insertions, 6 deletions

diff --git a/src/vlib/linux/pci.c b/src/vlib/linux/pci.c
index 8b614c751a1..20d44cd6d6e 100644
--- a/src/vlib/linux/pci.c
+++ b/src/vlib/linux/pci.c
@@ -1449,13 +1449,9 @@ linux_pci_init (vlib_main_t * vm)
 {
   vlib_pci_main_t *pm = &pci_main;
   vlib_pci_addr_t *addr = 0, *addrs;
-  clib_error_t *error;
 
   pm->vlib_main = vm;
 
-  if ((error = vlib_call_init_function (vm, unix_input_init)))
-    return error;
-
   ASSERT (sizeof (vlib_pci_addr_t) == sizeof (u32));
 
   addrs = vlib_pci_get_all_dev_addrs ();
@@ -1471,10 +1467,15 @@ linux_pci_init (vlib_main_t * vm)
     }
   /* *INDENT-ON* */
 
-  return error;
+  return 0;
 }
 
-VLIB_INIT_FUNCTION (linux_pci_init);
+/* *INDENT-OFF* */
+VLIB_INIT_FUNCTION (linux_pci_init) =
+{
+  .runs_after = VLIB_INITS("unix_input_init"),
+};
+/* *INDENT-ON* */
 
 /*
  * fd.io coding-style-patch-verification: ON