Delete PID file on exit

Register an exit notifier to remove the PID file. By the time atexit()
is called, qemu_write_pidfile() guarantees QEMU owns the PID file,
thus we could safely remove it when exiting.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180907121319.8607-4-marcandre.lureau@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

vl.c

@@ -2560,6 +2560,16 @@ static void qemu_run_exit_notifiers(void)
     notifier_list_notify(&exit_notifiers, NULL);
 }
 
+static const char *pid_file;
+static Notifier qemu_unlink_pidfile_notifier;
+
+static void qemu_unlink_pidfile(Notifier *n, void *data)
+{
+    if (pid_file) {
+        unlink(pid_file);
+    }
+}
+
 bool machine_init_done;
 
 void qemu_add_machine_init_done_notifier(Notifier *notify)
@@ -2884,7 +2894,6 @@ int main(int argc, char **argv, char **envp)
     const char *vga_model = NULL;
     const char *qtest_chrdev = NULL;
     const char *qtest_log = NULL;
-    const char *pid_file = NULL;
     const char *incoming = NULL;
     bool userconfig = true;
     bool nographic = false;
@@ -3911,6 +3920,9 @@ int main(int argc, char **argv, char **envp)
         exit(1);
     }
 
+    qemu_unlink_pidfile_notifier.notify = qemu_unlink_pidfile;
+    qemu_add_exit_notifier(&qemu_unlink_pidfile_notifier);
+
     if (qemu_init_main_loop(&main_loop_err)) {
         error_report_err(main_loop_err);
         exit(1);