migration: Fix global state with Xen.

When doing migration via the QMP command xen_save_devices_state, the
current runstate is not store into the global state section. Also the
current runstate is not the one we want on the receiver side.

During migration, the Xen toolstack paused QEMU before save the devices
state. Also, the toolstack expect QEMU to autostart when the migration is
finished.
So this patch store "running" as it's current runstate.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

include/migration/migration.h

@@ -203,4 +203,5 @@ void register_global_state(void);
 void global_state_set_optional(void);
 void savevm_skip_configuration(void);
 int global_state_store(void);
+void global_state_store_running(void);
 #endif

migration/migration.c

@@ -122,6 +122,13 @@ int global_state_store(void)
     return 0;
 }
 
+void global_state_store_running(void)
+{
+    const char *state = RunState_lookup[RUN_STATE_RUNNING];
+    strncpy((char *)global_state.runstate,
+           state, sizeof(global_state.runstate));
+}
+
 static bool global_state_received(void)
 {
     return global_state.received;

migration/savevm.c

@@ -1394,6 +1394,7 @@ void qmp_xen_save_devices_state(const char *filename, Error **errp)
 
     saved_vm_running = runstate_is_running();
     vm_stop(RUN_STATE_SAVE_VM);
+    global_state_store_running();
 
     f = qemu_fopen(filename, "wb");
     if (!f) {