Fix bug in DataHub where it would skip the first record in a set when a filter is being used. Also add comments and update source code logic to make it easier to understand and maintain.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@11008 6f19259b-4bc3-4df7-8a09-765794883524

IntelFrameworkModulePkg/Universal/DataHubDxe/DataHub.c

@@ -286,18 +286,26 @@ DataHubGetNextRecord (
   DATA_HUB_INSTANCE       *Private;
   DATA_HUB_FILTER_DRIVER  *FilterDriver;
   UINT64                  ClassFilter;
-  UINT64                  FilterMonotonicCount;
 
   Private               = DATA_HUB_INSTANCE_FROM_THIS (This);
 
   FilterDriver          = NULL;
-  FilterMonotonicCount  = 0;
   ClassFilter = EFI_DATA_RECORD_CLASS_DEBUG |
     EFI_DATA_RECORD_CLASS_ERROR |
     EFI_DATA_RECORD_CLASS_DATA |
     EFI_DATA_RECORD_CLASS_PROGRESS_CODE;
 
-  if (FilterDriverEvent != NULL) {
+  //
+  // If FilterDriverEvent is NULL, then return the next record
+  //
+  if (FilterDriverEvent == NULL) {
+    *Record = GetNextDataRecord (&Private->DataListHead, ClassFilter, MonotonicCount);
+    if (*Record == NULL) {
+      return EFI_NOT_FOUND;
+    }
+    return EFI_SUCCESS;
+  }
+    
   //
   // For events the beginning is the last unread record. This info is
   // stored in the instance structure, so we must look up the event
@@ -315,53 +323,56 @@ DataHubGetNextRecord (
   //
   ClassFilter = FilterDriver->ClassFilter;
 
-    if (*MonotonicCount == 0) {
   //
-      // Use the MTC from the Filter Driver.
+  // Retrieve the next record or the first record.
   //   
-      FilterMonotonicCount = FilterDriver->GetNextMonotonicCount;
+  if (*MonotonicCount != 0 || FilterDriver->GetNextMonotonicCount == 0) { 
-       
+    *Record = GetNextDataRecord (&Private->DataListHead, ClassFilter, MonotonicCount);
-      //
+    if (*Record == NULL) {
-      // The GetNextMonotonicCount field remembers the last value from the previous time.
-      // But we already processed this vaule, so we need to find the next one.
-      //
-      *Record = GetNextDataRecord (&Private->DataListHead, ClassFilter, &FilterMonotonicCount);
-      if (FilterMonotonicCount != 0) {
-        *MonotonicCount = FilterMonotonicCount;
-      }
-      
-      if ((FilterDriver->GetNextMonotonicCount != 0) && (FilterMonotonicCount == 0)) {
-        //
-        // If there is no new record to get exit now.
-        //
-        *MonotonicCount = 0;
       return EFI_NOT_FOUND;
     }
-    }
+    
-  }
+    if (*MonotonicCount != 0) {
       //
-  // Return the record
+      // If this was not the last record then update the count associated with the filter 
+      //
+      FilterDriver->GetNextMonotonicCount = *MonotonicCount;
+    } else {
+      //
+      // Save the MonotonicCount of the last record which has been read
+      //
+      FilterDriver->GetNextMonotonicCount = (*Record)->LogMonotonicCount;
+    }
+    return EFI_SUCCESS;
+  }
+  
+  //
+  // This is a request to read the first record that has not been read yet.  
+  // Set MonotoicCount to the last record successfuly read
+  //
+  *MonotonicCount = FilterDriver->GetNextMonotonicCount;
+  
+  //
+  // Retrieve the last record successfuly read again, but do not return it since
+  // it has already been returned before.
   //
   *Record = GetNextDataRecord (&Private->DataListHead, ClassFilter, MonotonicCount);
   if (*Record == NULL) {
     return EFI_NOT_FOUND;
   }
   
-  if (FilterDriver != NULL) {
+  if (*MonotonicCount != 0) {
     //
-    // If we have a filter driver update the records that have been read.
+    // Update the count associated with the filter 
-    // If MonotonicCount is zero No more reacords left.
-    //
-    if (*MonotonicCount == 0) {
-      //
-      // Save the current Record MonotonicCount.
-      //
-      FilterDriver->GetNextMonotonicCount = (*Record)->LogMonotonicCount;
-    } else {
-      //
-      // Point to next undread record
     //
     FilterDriver->GetNextMonotonicCount = *MonotonicCount;
+
+    //
+    // Retrieve the record after the last record successfuly read 
+    //  
+    *Record = GetNextDataRecord (&Private->DataListHead, ClassFilter, MonotonicCount);
+    if (*Record == NULL) {
+      return EFI_NOT_FOUND;
     }
   }