vmm: dbus: graceful shutdown of the DBusApi thread

This commit adds support for graceful shutdown of the DBusApi thread
using `futures::channel::oneshot` channels. By using oneshot channels,
we ensure that the thread has enough time to send a response to the
`VmmShutdown` method call before it is terminated. Without this step,
the thread may be terminated before it can send a response, resulting
in an error message on the client side stating that the message
recipient disconnected from the message bus without providing a reply.

Also changes the default values for DBus service name, object path
and interface name.

Signed-off-by: Omer Faruk Bayram <omer.faruk@sartura.hr>

src/main.rs

@@ -18,6 +18,8 @@ use std::os::unix::io::{FromRawFd, RawFd};
 use std::sync::mpsc::channel;
 use std::sync::{Arc, Mutex};
 use thiserror::Error;
+#[cfg(feature = "dbus_api")]
+use vmm::api::dbus::dbus_api_graceful_shutdown;
 use vmm::config;
 use vmm_sys_util::eventfd::EventFd;
 use vmm_sys_util::signal::block_signal;
@@ -513,7 +515,7 @@ fn start_vmm(toplevel: TopLevel) -> Result<Option<String>, Error> {
 
     let exit_evt = EventFd::new(EFD_NONBLOCK).map_err(Error::CreateExitEventFd)?;
 
-    let vmm_thread = vmm::start_vmm_thread(
+    let vmm_thread_handle = vmm::start_vmm_thread(
         vmm::VmmVersionInfo::new(env!("BUILD_VERSION"), env!("CARGO_PKG_VERSION")),
         &api_socket_path,
         api_socket_fd,
@@ -568,11 +570,15 @@ fn start_vmm(toplevel: TopLevel) -> Result<Option<String>, Error> {
         }
     }
 
-    vmm_thread
+    vmm_thread_handle
+        .thread_handle
         .join()
         .map_err(Error::ThreadJoin)?
         .map_err(Error::VmmThread)?;
 
+    #[cfg(feature = "dbus_api")]
+    dbus_api_graceful_shutdown(vmm_thread_handle.dbus_shutdown_chs);
+
     r.map(|_| api_socket_path)
 }