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>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/monitor/monitor.h b/include/monitor/monitor.h
index e64b944d7c..d2b3aafdb4 100644
--- a/include/monitor/monitor.h
+++ b/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);