+/*
+ * vmci_register_vsock_callback() - Register the VSOCK vmci_transport callback.
+ *
+ * The callback will be called when the first host or guest becomes active,
+ * or if they are already active when this function is called.
+ * To unregister the callback, call this function with NULL parameter.
+ *
+ * Returns 0 on success. -EBUSY if a callback is already registered.
+ */
+int vmci_register_vsock_callback(vmci_vsock_cb callback)
+{
+ int err = 0;
+
+ mutex_lock(&vmci_vsock_mutex);
+
+ if (vmci_vsock_transport_cb && callback) {
+ err = -EBUSY;
+ goto out;
+ }
+
+ vmci_vsock_transport_cb = callback;
+
+ if (!vmci_vsock_transport_cb) {
+ vmci_vsock_cb_host_called = false;
+ goto out;
+ }
+
+ if (vmci_guest_code_active())
+ vmci_vsock_transport_cb(false);
+
+ if (vmci_host_users() > 0) {
+ vmci_vsock_cb_host_called = true;
+ vmci_vsock_transport_cb(true);
+ }
+
+out:
+ mutex_unlock(&vmci_vsock_mutex);
+ return err;
+}
+EXPORT_SYMBOL_GPL(vmci_register_vsock_callback);
+
+void vmci_call_vsock_callback(bool is_host)
+{
+ mutex_lock(&vmci_vsock_mutex);
+
+ if (!vmci_vsock_transport_cb)
+ goto out;
+
+ /* In the host, this function could be called multiple times,
+ * but we want to register it only once.
+ */
+ if (is_host) {
+ if (vmci_vsock_cb_host_called)
+ goto out;
+
+ vmci_vsock_cb_host_called = true;
+ }
+
+ vmci_vsock_transport_cb(is_host);
+out:
+ mutex_unlock(&vmci_vsock_mutex);
+}
+