[ssh] Treat stfp thread exit as failure

Author: Sploder12

include/multipass/platform.h

@@ -91,9 +91,8 @@ std::unique_ptr<Process> make_sshfs_server_process(const SSHFSServerConfig& conf
 std::unique_ptr<Process> make_process(std::unique_ptr<ProcessSpec>&& process_spec);
 int symlink_attr_from(const char* path, sftp_attributes_struct* attr);
 
-std::function<int()> make_quit_watchdog(
-    const std::chrono::milliseconds& timeout,
-    const std::function<bool()>& condition); // call while single-threaded; call result later, in dedicated thread
+std::function<int(const std::function<bool()>&)> make_quit_watchdog(
+    const std::chrono::milliseconds& timeout); // call while single-threaded; call result later, in dedicated thread
 
 std::string reinterpret_interface_id(const std::string& ux_id); // give platforms a chance to reinterpret network IDs
 

src/platform/platform_unix.cpp

@@ -186,16 +186,17 @@ timespec make_timespec(std::chrono::duration<Rep, Period> duration)
     return out;
 }
 
-std::function<int()> mp::platform::make_quit_watchdog(const std::chrono::milliseconds& timeout,
-                                                      const std::function<bool()>& condition)
+std::function<int(const std::function<bool()>&)> mp::platform::make_quit_watchdog(
+    const std::chrono::milliseconds& timeout)
 {
-    return [sigset = make_and_block_signals({SIGQUIT, SIGTERM, SIGHUP}), time = make_timespec(timeout), condition]() {
+    return [sigset = make_and_block_signals({SIGQUIT, SIGTERM, SIGHUP}),
+            time = make_timespec(timeout)](const std::function<bool()>& condition) {
         while (condition())
         {
             if (const int sig = sigtimedwait(&sigset, nullptr, &time); sig != -1)
                 return sig;
         }
 
-        return SIGCHLD;
+        return -1;
     };
 }

src/sshfs_mount/sshfs_server.cpp

@@ -105,19 +105,22 @@ int main(int argc, char* argv[])
 
     try
     {
+        auto watchdog =
+            mpp::make_quit_watchdog(std::chrono::milliseconds{500}); // called while there is only one thread
+
         mp::SSHSession session{host, port, username, mp::SSHClientKeyProvider{priv_key_blob}};
         mp::SshfsMount sshfs_mount(std::move(session), source_path, target_path, gid_mappings, uid_mappings);
 
-        auto watchdog = mpp::make_quit_watchdog(std::chrono::milliseconds{2500}, [&sshfs_mount] {
-            return sshfs_mount.alive();
-        }); // called while there is only one thread
-
         // ssh lives on its own thread, use this thread to listen for quit signal
-        if (int sig = watchdog())
+        int sig = watchdog([&sshfs_mount] { return sshfs_mount.alive(); });
+
+        if (sig != -1)
             cout << "Received signal " << sig << ". Stopping" << endl;
+        else
+            cout << "SFTP server thread stopped unexpectedly." << endl;
 
         sshfs_mount.stop();
-        exit(0);
+        exit(sig == -1 ? EXIT_FAILURE : EXIT_SUCCESS);
     }
     catch (const mp::SSHFSMissingError&)
     {