Make LXC controller use a private dbus connection & close it

The LXC controller uses dbus to talk to systemd to create
cgroups. This means that each LXC controller instance has
a dbus connection. The DBus daemon is limited to 256
connections by default and we want to be able to run many
1000 of containers.

While the dbus limit could be raised in the config files,
it is simpler to make libvirt LXC controller close its
dbus connection once everything is configured.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

src/Makefile.am

@@ -2381,6 +2381,7 @@ libvirt_lxc_CFLAGS =				\
 		$(PIE_CFLAGS)			\
 		$(LIBNL_CFLAGS)			\
 		$(FUSE_CFLAGS)			\
+		$(DBUS_CFLAGS)			\
 		$(NULL)
 if WITH_BLKID
 libvirt_lxc_CFLAGS += $(BLKID_CFLAGS)

src/lxc/lxc_controller.c

@@ -64,6 +64,7 @@
 #include "virrandom.h"
 #include "virprocess.h"
 #include "virnuma.h"
+#include "virdbus.h"
 #include "rpc/virnetserver.h"
 #include "virstring.h"
 
@@ -2200,6 +2201,12 @@ virLXCControllerRun(virLXCControllerPtr ctrl)
         if (virLXCControllerConsoleSetNonblocking(&(ctrl->consoles[i])) < 0)
             goto cleanup;
 
+    /* We must not hold open a dbus connection for life
+     * of LXC instance, since dbus-daemon is limited to
+     * only a few 100 connections by default
+     */
+    virDBusCloseSystemBus();
+
     rc = virLXCControllerMain(ctrl);
 
     virLXCControllerEventSendExit(ctrl, rc);
@@ -2351,6 +2358,8 @@ int main(int argc, char *argv[])
 
     virEventRegisterDefaultImpl();
 
+    virDBusSetSharedBus(false);
+
     if (!(ctrl = virLXCControllerNew(name)))
         goto cleanup;