cpu: Fix TrafficGen trace playback

This patch addresses an issue with trace playback in the TrafficGen
where the trace was reset but the header was not read from the trace
when a captured trace was played back for a second time. This resulted
in parsing errors as the expected message was not found in the trace
file.

The header check is moved to an init funtion which is called by the
constructor and when the trace is reset. This ensures that the trace
header is read each time when the trace is replayed.

This patch also addresses a small formatting issue in a panic.

src/cpu/testers/traffic_gen/generators.cc

@@ -204,14 +204,20 @@ RandomGen::nextPacketTick(bool elastic, Tick delay) const
 
 TraceGen::InputStream::InputStream(const std::string& filename)
     : trace(filename)
+{
+    init();
+}
+
+void
+TraceGen::InputStream::init()
 {
     // Create a protobuf message for the header and read it from the stream
     Message::PacketHeader header_msg;
     if (!trace.read(header_msg)) {
-        panic("Failed to read packet header from %s\n", filename);
+        panic("Failed to read packet header from trace\n");
 
         if (header_msg.tick_freq() != SimClock::Frequency) {
-            panic("Trace %s was recorded with a different tick frequency %d\n",
+            panic("Trace was recorded with a different tick frequency %d\n",
                   header_msg.tick_freq());
         }
     }
@@ -221,6 +227,7 @@ void
 TraceGen::InputStream::reset()
 {
     trace.reset();
+    init();
 }
 
 bool

src/cpu/testers/traffic_gen/generators.hh

@@ -379,6 +379,12 @@ class TraceGen : public BaseGen
          */
         void reset();
 
+        /**
+         * Check the trace header to make sure that it is of the right
+         * format.
+         */
+        void init();
+
         /**
          * Attempt to read a trace element from the stream,
          * and also notify the caller if the end of the file