ignore GPT partitions that are marked unused by UUID (#178)

Signed-off-by: Avi Deitcher <avi@deitcher.net>

partition/gpt/partition.go

@@ -1,6 +1,7 @@
 package gpt
 
 import (
+	"bytes"
 	"encoding/binary"
 	"fmt"
 	"io"
@@ -15,6 +16,8 @@ import (
 // PartitionEntrySize fixed size of a GPT partition entry
 const PartitionEntrySize = 128
 
+var zeroUUIDBytes = make([]byte, 16)
+
 // Partition represents the structure of a single partition on the disk
 type Partition struct {
 	Start              uint64 // start sector for the partition
@@ -90,6 +93,9 @@ func partitionFromBytes(b []byte, logicalSectorSize, physicalSectorSize int) (*P
 		return nil, fmt.Errorf("data for partition was %d bytes instead of expected %d", len(b), PartitionEntrySize)
 	}
 	// is it all zeroes?
+	if bytes.Equal(b[0:16], zeroUUIDBytes) {
+		return nil, nil
+	}
 	typeGUID, err := uuid.FromBytes(bytesToUUIDBytes(b[0:16]))
 	if err != nil {
 		return nil, fmt.Errorf("unable to read partition type GUID: %v", err)

partition/gpt/table.go

@@ -337,6 +337,9 @@ func readPartitionArrayBytes(b []byte, entrySize, logicalSectorSize, physicalSec
 		if err != nil {
 			return nil, fmt.Errorf("error reading partition entry %d: %v", i, err)
 		}
+		if p == nil {
+			continue
+		}
 		// augment partition information
 		p.Size = (p.End - p.Start + 1) * uint64(logicalSectorSize)
 		parts = append(parts, p)