trace: split trace_init_file out of trace_init_backends

This is cleaner, and improves error reporting with -daemonize.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-id: 1452174932-28657-4-git-send-email-den@openvz.org
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/trace/control.h b/trace/control.h
index 7905917..d50f399 100644
--- a/trace/control.h
+++ b/trace/control.h
@@ -157,7 +157,7 @@
  *
  * Returns: Whether the backends could be successfully initialized.
  */
-bool trace_init_backends(const char *file);
+bool trace_init_backends(void);
 
 /**
  * trace_init_events:
@@ -170,6 +170,17 @@
  */
 void trace_init_events(const char *file);
 
+/**
+ * trace_init_file:
+ * @file:   Name of trace output file; may be NULL.
+ *          Corresponds to commandline option "-trace file=...".
+ *
+ * Record the name of the output file for the tracing backend.
+ * Exits if no selected backend does not support specifying the
+ * output file, and a non-NULL file was passed.
+ */
+void trace_init_file(const char *file);
+
 
 #include "trace/control-internal.h"