clusterer: controller-support API, gated behind a build-time flag

Groundwork for clusterer_controller (added later in this series): an API the
controller binds to, a way to declare which clusters it manages, and the hooks
that let a controller-managed cluster take its identity at runtime instead of
from the config.

Declaring a managed cluster uses a per-cluster 'cluster_options' modparam - the
same "key=value, key=value" idiom as my_node_info:

    modparam("clusterer", "cluster_options", "cluster_id=1, use_controller=1")

cluster_id is required; use_controller is a 0/1 flag defaulting to 0 (native),
and only use_controller=1 pre-creates the controller-managed stub, which never
touches the DB and is guarded against hijacking a native cluster of the same id.
Native clusters need no cluster_options line at all, and every other clusterer
setting (db_mode, ping_*, my_node_id, sharing_tag, ...) stays a global modparam.
The interim 'use_controller' / 'cluster_id' int modparams (never released) are
kept registered only to fail with a migration hint.

The managed-id set is exported through the ctrl binds (managed_count /
managed_ids) so the controller can cross-check it pre-fork: a managed id with no
matching 'cluster' config has no BIN socket or crypto params, and a 'cluster'
config for an unmanaged id has nothing legitimate to drive. Either mismatch
aborts at startup naming the offending id, rather than half-forming a cluster.

All of it is compiled only under CLUSTERER_CTRL_SUPPORT:
  - the clusterer_ctrl API (clusterer_ctrl.c) and the cluster_options modparam
    plus the load_clusterer_ctrl_binds export;
  - the controller stub pre-create loop, the child_init guard, the shm
    current_id mirror, the on-demand stub, and the shtag_managed /
    controller_managed logic;
  - the per-cluster identity and hybrid-db_mode accessors (cluster_self_id,
    cl_db_mode, GET_CURRENT_ID, use_controller), which get #else fallbacks to
    the stock globals (current_id / db_mode / 0) so their call sites compile to
    the exact upstream object code with no per-site #ifdef. add_node_info's
    internal self_id parameter is gated the same way.

The top-level Makefile exports CLUSTERER_CTRL_SUPPORT=1 iff clusterer_controller
is in the configured build - derived from the include/exclude lists rather than
the current 'modules' subset, so it is stable across 'make all' and a
single-module rebuild - and clusterer/Makefile turns that into the -D.

The point of the gate: a build without clusterer_controller produces the stock
clusterer module. No cluster_options parameter (rejected as unknown), no
behavioural change, no added exports. Verified with
'unifdef -UCLUSTERER_CTRL_SUPPORT' against the base - no semantic difference
from upstream. Enabling the controller rebuilds clusterer with the hooks; the
two are a matched pair.

Author: Lt-Flash

Makefile

@@ -70,6 +70,19 @@ include Makefile.defs
 # always exclude the SVN dir
 override exclude_modules+= .svn $(skip_modules)
 
+# The clusterer module exposes its controller-support API (and the extra
+# cluster_options modparam) only when the clusterer_controller module is part of
+# this build; otherwise it is a stock module.  Mirror the module-selection rule
+# below (built if force-included, else unless excluded) and export the result so
+# clusterer/Makefile can define -DCLUSTERER_CTRL_SUPPORT.  Derived from the
+# configured include/exclude lists (not the current 'modules' subset) so it stays
+# consistent whether you 'make all' or rebuild just modules/clusterer.
+ifneq ($(filter clusterer_controller,$(include_modules)),)
+export CLUSTERER_CTRL_SUPPORT:=1
+else ifeq ($(filter clusterer_controller,$(exclude_modules)),)
+export CLUSTERER_CTRL_SUPPORT:=1
+endif
+
 #always include this modules
 #include_modules?=
 

modules/clusterer/Makefile

@@ -6,4 +6,12 @@ NAME=clusterer.so
 #DEFS+= -DCLUSTERER_DBG
 #DEFS+= -DCLUSTERER_EXTRA_BIN_DBG
 
+# Controller support (the clusterer_ctrl API, the cluster_options modparam and
+# the controller hooks) is compiled only when the clusterer_controller module is
+# part of this build - the top-level Makefile exports CLUSTERER_CTRL_SUPPORT=1 in
+# that case.  A stock build produces the vanilla clusterer module.
+ifeq ($(CLUSTERER_CTRL_SUPPORT),1)
+DEFS+= -DCLUSTERER_CTRL_SUPPORT
+endif
+
 include ../../Makefile.modules