qmp: Dumb down how we run QMP command registration

The way we get QMP commands registered is high tech:

* qapi-commands.py generates qmp_init_marshal() that does the actual work

* it also generates the magic to register it as a MODULE_INIT_QAPI
  function, so it runs when someone calls
  module_call_init(MODULE_INIT_QAPI)

* main() calls module_call_init()

QEMU needs to register a few non-qapified commands.  Same high tech
works: monitor.c has its own qmp_init_marshal() along with the magic
to make it run in module_call_init(MODULE_INIT_QAPI).

QEMU also needs to unregister commands that are not wanted in this
build's configuration (commit 5032a16).  Simple enough:
qmp_unregister_commands_hack().  The difficulty is to make it run
after the generated qmp_init_marshal().  We can't simply run it in
monitor.c's qmp_init_marshal(), because the order in which the
registered functions run is indeterminate.  So qmp_init_marshal()
registers qmp_unregister_commands_hack() separately.  Since
registering *appends* to the list of registered functions, this will
make it run after all the functions that have been registered already.

I suspect it takes a long and expensive computer science education to
not find this silly.

Dumb it down as follows:

* Drop MODULE_INIT_QAPI entirely

* Give the generated qmp_init_marshal() external linkage.

* Call it instead of module_call_init(MODULE_INIT_QAPI)

* Except in QEMU proper, call new monitor_init_qmp_commands() that in
  turn calls the generated qmp_init_marshal(), registers the
  additional commands and unregisters the unwanted ones.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <1488544368-30622-5-git-send-email-armbru@redhat.com>

include/monitor/monitor.h

@@ -16,6 +16,7 @@ extern Monitor *cur_mon;
 
 bool monitor_cur_is_qmp(void);
 
+void monitor_init_qmp_commands(void);
 void monitor_init(Chardev *chr, int flags);
 void monitor_cleanup(void);
 

include/qemu/module.h

@@ -42,7 +42,6 @@ static void __attribute__((constructor)) do_qemu_init_ ## function(void)    \
 typedef enum {
     MODULE_INIT_BLOCK,
     MODULE_INIT_OPTS,
-    MODULE_INIT_QAPI,
     MODULE_INIT_QOM,
     MODULE_INIT_TRACE,
     MODULE_INIT_MAX
@@ -50,7 +49,6 @@ typedef enum {
 
 #define block_init(function) module_init(function, MODULE_INIT_BLOCK)
 #define opts_init(function) module_init(function, MODULE_INIT_OPTS)
-#define qapi_init(function) module_init(function, MODULE_INIT_QAPI)
 #define type_init(function) module_init(function, MODULE_INIT_QOM)
 #define trace_init(function) module_init(function, MODULE_INIT_TRACE)
 

monitor.c

@@ -997,8 +997,10 @@ static void qmp_unregister_commands_hack(void)
 #endif
 }
 
-static void qmp_init_marshal(void)
+void monitor_init_qmp_commands(void)
 {
+    qmp_init_marshal();
+
     qmp_register_command("query-qmp-schema", qmp_query_qmp_schema,
                          QCO_NO_OPTIONS);
     qmp_register_command("device_add", qmp_device_add,
@@ -1006,12 +1008,9 @@ static void qmp_init_marshal(void)
     qmp_register_command("netdev_add", qmp_netdev_add,
                          QCO_NO_OPTIONS);
 
-    /* call it after the rest of qapi_init() */
+    qmp_unregister_commands_hack();
-    register_module_init(qmp_unregister_commands_hack, MODULE_INIT_QAPI);
 }
 
-qapi_init(qmp_init_marshal);
-
 /* set the current CPU defined by the user */
 int monitor_set_cpu(int cpu_index)
 {

qga/main.c

@@ -1321,7 +1321,7 @@ int main(int argc, char **argv)
 
     config->log_level = G_LOG_LEVEL_ERROR | G_LOG_LEVEL_CRITICAL;
 
-    module_call_init(MODULE_INIT_QAPI);
+    qmp_init_marshal();
 
     init_dfl_pathnames();
     config_load(config);

scripts/qapi-commands.py

@@ -208,14 +208,12 @@ def gen_register_command(name, success_response):
 def gen_registry(registry):
     ret = mcgen('''
 
-static void qmp_init_marshal(void)
+void qmp_init_marshal(void)
 {
 ''')
     ret += registry
     ret += mcgen('''
 }
-
-qapi_init(qmp_init_marshal);
 ''')
     return ret
 
@@ -308,6 +306,7 @@ fdecl.write(mcgen('''
 #include "qapi/qmp/qdict.h"
 #include "qapi/error.h"
 
+void qmp_init_marshal(void);
 ''',
                   prefix=prefix))
 

tests/test-qmp-commands.c

@@ -273,7 +273,7 @@ int main(int argc, char **argv)
     g_test_add_func("/0.15/dealloc_types", test_dealloc_types);
     g_test_add_func("/0.15/dealloc_partial", test_dealloc_partial);
 
-    module_call_init(MODULE_INIT_QAPI);
+    qmp_init_marshal();
     g_test_run();
 
     return 0;

vl.c

@@ -2988,7 +2988,7 @@ int main(int argc, char **argv, char **envp)
     qemu_init_exec_dir(argv[0]);
 
     module_call_init(MODULE_INIT_QOM);
-    module_call_init(MODULE_INIT_QAPI);
+    monitor_init_qmp_commands();
 
     qemu_add_opts(&qemu_drive_opts);
     qemu_add_drive_opts(&qemu_legacy_drive_opts);