trace: avoid conditional code compilation during option parsing

A default implementation for backend-specific routines is provided in
"trace/default.c", which backends can override by setting "trace_default=no" in
"configure".

Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>

trace/control.h

@@ -0,0 +1,24 @@
+/*
+ * Interface for configuring and controlling the state of tracing events.
+ *
+ * Copyright (C) 2011 Lluís Vilanova <vilanova@ac.upc.edu>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ */
+
+#ifndef TRACE_CONTROL_H
+#define TRACE_CONTROL_H
+
+#include <stdbool.h>
+
+
+/** Initialize the tracing backend.
+ *
+ * @file Name of trace output file; may be NULL.
+ *       Corresponds to commandline option "-trace file=...".
+ * @return Whether the backend could be successfully initialized.
+ */
+bool trace_backend_init(const char *file);
+
+#endif  /* TRACE_CONTROL_H */

trace/default.c

@@ -0,0 +1,21 @@
+/*
+ * Default implementation for backend initialization from commandline.
+ *
+ * Copyright (C) 2011 Lluís Vilanova <vilanova@ac.upc.edu>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ */
+
+#include "trace/control.h"
+
+
+bool trace_backend_init(const char *file)
+{
+    if (file) {
+        fprintf(stderr, "error: -trace file=...: "
+                "option not supported by the selected tracing backend\n");
+        return false;
+    }
+    return true;
+}

trace/simple.c

@@ -16,6 +16,7 @@
 #include <pthread.h>
 #include "qemu-timer.h"
 #include "trace.h"
+#include "trace/control.h"
 
 /** Trace file header event ID */
 #define HEADER_EVENT_ID (~(uint64_t)0) /* avoids conflicting with TraceEventIDs */
@@ -330,7 +331,7 @@ void st_flush_trace_buffer(void)
     flush_trace_file(true);
 }
 
-bool st_init(const char *file)
+bool trace_backend_init(const char *file)
 {
     pthread_t thread;
     pthread_attr_t attr;
@@ -346,10 +347,11 @@ bool st_init(const char *file)
     pthread_sigmask(SIG_SETMASK, &oldset, NULL);
 
     if (ret != 0) {
-        return false;
+        fprintf(stderr, "warning: unable to initialize simple trace backend\n");
+    } else {
+        atexit(st_flush_trace_buffer);
+        st_set_trace_file(file);
     }
 
-    atexit(st_flush_trace_buffer);
-    st_set_trace_file(file);
     return true;
 }

trace/simple.h

@@ -15,7 +15,6 @@
 #include <stdbool.h>
 #include <stdio.h>
 
-#ifdef CONFIG_TRACE_SIMPLE
 typedef uint64_t TraceEventID;
 
 typedef struct {
@@ -37,12 +36,5 @@ void st_print_trace_file_status(FILE *stream, fprintf_function stream_printf);
 void st_set_trace_file_enabled(bool enable);
 bool st_set_trace_file(const char *file);
 void st_flush_trace_buffer(void);
-bool st_init(const char *file);
-#else
-static inline bool st_init(const char *file)
-{
-    return true;
-}
-#endif /* !CONFIG_TRACE_SIMPLE */
 
 #endif /* TRACE_SIMPLE_H */