Update some comments after understanding things better. Some things which got

me confused were perfectly correct.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@27626 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/add-ons/kernel/partitioning_systems/intel/PartitionMap.cpp

@@ -508,17 +508,19 @@ PrimaryPartition::LogicalPartitionAt(int32 index) const
 void
 PrimaryPartition::AddLogicalPartition(LogicalPartition *partition)
 {
-	if (partition) {
-		partition->SetPrimaryPartition(this);
-		partition->SetPrevious(fTail);
-		if (fTail) {
-			fTail->SetNext(partition);
-			fTail = partition;
-		} else
-			fHead = fTail = partition;
-		partition->SetNext(NULL);
-		fLogicalPartitionCount++;
-	}
+	if (!partition)
+		return;
+
+	partition->SetPrimaryPartition(this);
+	partition->SetPrevious(fTail);
+	if (fTail) {
+		fTail->SetNext(partition);
+		fTail = partition;
+	} else
+		fHead = fTail = partition;
+	partition->SetNext(NULL);
+
+	fLogicalPartitionCount++;
 }
 
 // RemoveLogicalPartition
@@ -538,6 +540,7 @@ PrimaryPartition::RemoveLogicalPartition(LogicalPartition *partition)
 		next->SetPrevious(prev);
 	else
 		fTail = prev;
+
 	fLogicalPartitionCount--;
 
 	partition->SetNext(NULL);

src/add-ons/kernel/partitioning_systems/intel/PartitionMapParser.cpp

@@ -168,7 +168,13 @@ PartitionMapParser::_ParseExtended(PrimaryPartition *primary, off_t offset)
 
 		// Examine the table, there is exactly one extended and one
 		// non-extended logical partition. All four table entries are
-		// examined though.
+		// examined though. If there is no inner extended partition,
+		// the end of the linked list is reached.
+		// The first PTS describing both an "inner extended" parition and a
+		// "data" partition (non extended and not empty) is the start sector
+		// of the primary extended partition. The next PTS in the linked list
+		// is the start sector of the inner extended partition described in
+		// this PTS.
 		LogicalPartition extended;
 		LogicalPartition nonExtended;
 		for (int32 i = 0; error == B_OK && i < 4; i++) {
@@ -224,7 +230,7 @@ PartitionMapParser::_ParseExtended(PrimaryPartition *primary, off_t offset)
 				error = B_NO_MEMORY;
 		}
 
-		// prepare to parse next extended partition
+		// prepare to parse next extended/non-extended partition pair
 		if (error == B_OK && !extended.IsEmpty())
 			offset = extended.Offset();
 		else

src/add-ons/kernel/partitioning_systems/intel/PartitionMapWriter.cpp

@@ -226,23 +226,38 @@ PartitionMapWriter::_WriteExtended(partition_table_sector *pts,
 		return B_BAD_DATA;
 	}
 
+	// NOTE: The OS/2 boot manager needs the first entry to describe the
+	// data partition, while the second entry should describe the "inner
+	// extended" partition.
+
 	// write the table
 	partition_descriptor* descriptor = &(pts->table[0]);
 	partition->GetPartitionDescriptor(descriptor, partition->PTSOffset());
 		// location is relative to this partitions PTS offset
 
-	// setting offset and size of the next partition in the linked list
+	// Set offset and size of the next partition in the linked list.
+	// This is done via a so called "inner extended" partition which is
+	// only used to point to the next PTS location (start sector of the
+	// inner extended partition).
 	descriptor = &(pts->table[1]);
 	LogicalPartition extended;
 	if (next) {
 		extended.SetPTSOffset(partition->PTSOffset());
 		extended.SetOffset(next->PTSOffset());
-		extended.SetSize(next->Size() + next->Offset() - next->PTSOffset());
-			// TODO: The size calculation looks suspicious.
-			// Isn't next->Offset() relative to primary extended patition while
-			// next->PTSOffset() is not?
+
+		// Strictly speaking, the size is not relevant and just needs to
+		// be non-zero. But some operating systems check the size of
+		// inner extended partitions and it needs to include the next data
+		// partition. Therefor the size is the size of the next data partition
+		// plus the offset between the next PTS and the data partition start
+		// offset. This assumes of course that the start offset is behind
+		// the PTS offset, which is actually not dictated by a minimal
+		// specification.
+		extended.SetSize(next->Size() + (next->Offset() - next->PTSOffset()));
+
+		// Use the same extended partition type as the primary extended
+		// partition.
 		extended.SetType(partition->GetPrimaryPartition()->Type());
-			// TODO: Weird.
 
 		extended.GetPartitionDescriptor(descriptor, 0);