stages/disks: add logic to resize an existing partition

Fixes coreos#924
This fix will allow users to resize an existing partition without wiping
out an entry from the partition table.

internal/exec/stages/disks/partitions.go

@@ -339,6 +339,7 @@ func (s stage) partitionDisk(dev types.Disk, devAlias string) error {
 		}
 		matches := exists && matchErr == nil
 		wipeEntry := part.WipePartitionEntry != nil && *part.WipePartitionEntry
+		resize := part.ResizePartition != nil && *part.ResizePartition
 
 		// This is a translation of the matrix in the operator notes.
 		switch {
@@ -353,7 +354,17 @@ func (s stage) partitionDisk(dev types.Disk, devAlias string) error {
 		case exists && shouldExist && matches:
 			s.Logger.Info("partition %d found with correct specifications", part.Number)
 		case exists && shouldExist && !wipeEntry && !matches:
-			return fmt.Errorf("Partition %d didn't match: %v", part.Number, matchErr)
+			if resize {
+				s.Logger.Info("partition %d found with resizePartition option, wiping partition entry and recreating", part.Number)
+				var ids []string
+				ids = append(ids, info.GUID, info.TypeGUID)
+				// need to preserve the partition ids for resizing
+				op.PreservePartitionIDs(ids)
+				op.DeletePartition(part.Number)
+				op.CreatePartition(part)
+			} else {
+				return fmt.Errorf("Partition %d didn't match: %v", part.Number, matchErr)
+			}
 		case exists && shouldExist && wipeEntry && !matches:
 			s.Logger.Info("partition %d did not meet specifications, wiping partition entry and recreating", part.Number)
 			op.DeletePartition(part.Number)

internal/sgdisk/sgdisk.go

@@ -25,12 +25,13 @@ import (
 )
 
 type Operation struct {
-	logger    *log.Logger
-	dev       string
-	wipe      bool
-	parts     []Partition
-	deletions []int
-	infos     []int
+	logger       *log.Logger
+	dev          string
+	wipe         bool
+	partitionIDs []string
+	parts        []Partition
+	deletions    []int
+	infos        []int
 }
 
 // We ignore types.Partition.StartMiB/SizeMiB in favor of
@@ -59,6 +60,11 @@ func (op *Operation) DeletePartition(num int) {
 	op.deletions = append(op.deletions, num)
 }
 
+// PreservePartitionIDs preserves the GUID and TypeGUID for a given partition.
+func (op *Operation) PreservePartitionIDs(ids []string) {
+	op.partitionIDs = append(op.partitionIDs, ids...)
+}
+
 func (op *Operation) Info(num int) {
 	op.infos = append(op.infos, num)
 }
@@ -137,6 +143,10 @@ func (op Operation) buildOptions() []string {
 	}
 
 	for _, p := range op.parts {
+		if len(op.partitionIDs) > 0 {
+			p.GUID = &op.partitionIDs[0]
+			p.TypeGUID = &op.partitionIDs[1]
+		}
 		opts = append(opts, fmt.Sprintf("--new=%d:%s:+%s", p.Number, partitionGetStart(p), partitionGetSize(p)))
 		if p.Label != nil {
 			opts = append(opts, fmt.Sprintf("--change-name=%d:%s", p.Number, *p.Label))