Added a loglsisten command for listening into the log

loglisten.c

@@ -0,0 +1,95 @@
+/**
+ * This is a means to listen into the stream of log messages from the logv2 
+ * logging system.
+ *
+ * Mark Koennecke, May 2016
+ */
+#include <sics.h>
+#include <logv2.h>
+#include <lld.h>
+
+/*
+  From logv2.c
+*/
+extern int subsystemFromText(const char *text);
+/*=============================================================================*/
+static int listenerList;
+static int callbackRegistered = 0;
+
+typedef struct {
+  SConnection *pCon;
+  char subsystem[64];
+} ListenEntry;
+/*-----------------------------------------------------------------------------*/
+static void LogListenCallback(unsigned int severity, const char *timeStamp, 
+			    const char *subsystem, 
+			    const char *message, void *userData)
+{
+  ListenEntry current;
+  int status, cleanupNeeded = 0;
+
+  status = LLDnodePtr2First(listenerList);
+  while(status != 0){
+    LLDnodeDataTo(listenerList,&current);
+    if(strcmp(current.subsystem,subsystem) == 0) {
+      if(SCisConnected(current.pCon)){
+	SCPureSockWrite(current.pCon,(char *)message,eValue);
+      } else {
+	cleanupNeeded = 1;
+      }
+    }
+    status = LLDnodePtr2Next(listenerList);
+  }
+
+  /*
+    lld lists sometimes get confused when deleting nodes on the fly.
+    This is why this has been put into a separate loop
+  */
+  if(cleanupNeeded){
+    status = LLDnodePtr2First(listenerList);
+    while(status != 0){
+      LLDnodeDataTo(listenerList,&current);
+      if(!SCisConnected(current.pCon)){
+	SCDeleteConnection(current.pCon);
+	LLDnodeDelete(listenerList);
+      }
+      status = LLDnodePtr2Next(listenerList);
+    }
+  }
+
+}
+/*-----------------------------------------------------------------------------*/
+static int LogListenAction(SConnection * pCon, SicsInterp * pSics,
+                            void *pData, int argc, char *argv[])
+{
+  ListenEntry listLog;
+
+  if(argc < 2){ 
+    SCWrite(pCon,"ERROR: need subsystem argument for loglisten", eError);
+    return 0;
+  }
+  
+  if(subsystemFromText(argv[1]) < 0){
+    SCPrintf(pCon,eError, "ERROR: invalid subsystem %s specified", argv[1]);
+    return 0;
+  }
+
+
+  listLog.pCon = SCCopyConnection(pCon);
+  strncpy(listLog.subsystem,argv[1],sizeof(listLog.subsystem));
+  LLDnodeAppendFrom(listenerList,&listLog);
+
+  if(!callbackRegistered){
+    RegisterLogCallback(LogListenCallback,NULL);
+    callbackRegistered = 1;
+  }
+
+  SCSendOK(pCon);
+  return 1;
+}
+/*-----------------------------------------------------------------------------*/
+void LogListenInit(void)
+{
+  listenerList = LLDcreate(sizeof(ListenEntry));
+  AddCmd("loglisten", LogListenAction);
+}