switch-to-configuration-ng: add timeout to systemd daemon reload/reexecute

Just like `systemctl daemon-reload`/`systemctl daemon-reexec`, we ensure
we don't wait forever for the reload action to finish.

pkgs/by-name/sw/switch-to-configuration-ng/src/src/main.rs

@@ -87,6 +87,12 @@ const DRY_RELOAD_BY_ACTIVATION_LIST_FILE: &str = "/run/nixos/dry-activation-relo
 // Reuse the same default timeout that systemd uses. See https://github.com/systemd/systemd/blob/8b4278d12ec55cc3f96764bc8197e1055fbb6d3f/src/libsystemd/sd-bus/bus-internal.h#L312
 const BUS_TIMEOUT: Duration = Duration::from_secs(25);
 
+// Reuse the same daemon reload/reexecute timeout that systemd uses. See https://github.com/systemd/systemd/blob/5366dbdbd44ba4dc0c914dd4daa1a5297e0b2bde/src/basic/constants.h#L18
+const DAEMON_RELOAD_TIMEOUT: Duration = Duration::from_secs(180);
+
+// Used during times of waiting for D-Bus to process messages.
+const DBUS_PROCESS_TIME: Duration = Duration::from_millis(500);
+
 #[derive(Debug, Clone, PartialEq)]
 enum Action {
     Switch,
@@ -932,7 +938,7 @@ fn block_on_jobs(
             "waiting for submitted jobs to finish, still have {} job(s)",
             submitted_jobs.borrow().len()
         );
-        _ = conn.process(Duration::from_millis(500));
+        _ = conn.process(DBUS_PROCESS_TIME);
     }
 }
 
@@ -987,7 +993,7 @@ fn do_user_switch(parent_exe: String) -> anyhow::Result<()> {
     log::debug!("waiting for nixos activation to finish");
     while !*nixos_activation_done.borrow() {
         _ = dbus_conn
-            .process(Duration::from_secs(500))
+            .process(DBUS_PROCESS_TIME)
             .context("Failed to process dbus messages")?;
     }
 
@@ -1695,10 +1701,18 @@ won't take effect until you reboot the system.
 
         log::debug!("waiting for systemd restart to finish");
 
+        let mut reexec_time_waited = Duration::from_secs(0);
         while *systemd_is_reloading.borrow() {
             _ = dbus_conn
-                .process(Duration::from_millis(500))
+                .process(DBUS_PROCESS_TIME)
                 .context("Failed to process dbus messages")?;
+            reexec_time_waited += DBUS_PROCESS_TIME;
+            if reexec_time_waited >= DAEMON_RELOAD_TIMEOUT {
+                anyhow::bail!(
+                    "systemd daemon reexecute failed, timeout after {:?}",
+                    DAEMON_RELOAD_TIMEOUT
+                );
+            }
         }
     }
 
@@ -1712,10 +1726,18 @@ won't take effect until you reboot the system.
     _ = systemd.reload(); // we don't get a dbus reply here
     log::debug!("waiting for systemd reload to finish");
 
+    let mut reload_time_waited = Duration::from_secs(0);
     while *systemd_is_reloading.borrow() {
         _ = dbus_conn
-            .process(Duration::from_millis(500))
+            .process(DBUS_PROCESS_TIME)
             .context("Failed to process dbus messages")?;
+        reload_time_waited += DBUS_PROCESS_TIME;
+        if reload_time_waited >= DAEMON_RELOAD_TIMEOUT {
+            anyhow::bail!(
+                "systemd daemon reload failed, timeout after {:?}",
+                DAEMON_RELOAD_TIMEOUT
+            );
+        }
     }
 
     dbus_conn