Feature: Partitions and UsableBytes (Windows Only)

When collecting HW informations about disks it's also very usefull to understand how much free space is available on each partition.

Here a quick example based on my "Windows support: block" jaypipes#156

block.go

@@ -108,13 +108,14 @@ type Disk struct {
 
 // Partition describes a logical division of a Disk.
 type Partition struct {
-	Disk       *Disk  `json:"-"`
-	Name       string `json:"name"`
-	Label      string `json:"label"`
-	MountPoint string `json:"mount_point"`
-	SizeBytes  uint64 `json:"size_bytes"`
-	Type       string `json:"type"`
-	IsReadOnly bool   `json:"read_only"`
+	Disk        *Disk  `json:"-"`
+	Name        string `json:"name"`
+	Label       string `json:"label"`
+	MountPoint  string `json:"mount_point"`
+	SizeBytes   uint64 `json:"size_bytes"`
+	UsableBytes uint64 `json:"usable_bytes"`
+	Type        string `json:"type"`
+	IsReadOnly  bool   `json:"read_only"`
 }
 
 // BlockInfo describes all disk drives and partitions in the host system.

block_windows.go

@@ -122,12 +122,13 @@ func (ctx *context) blockFillInfo(info *BlockInfo) error {
 						if logicaldisktodiskpartition.Antecedent == desiredAntecedent && logicaldisktodiskpartition.Dependent == desiredDependent {
 							// Appending Partition
 							p := &Partition{
-								Name:       logicaldisk.Caption,
-								Label:      logicaldisk.Caption,
-								SizeBytes:  logicaldisk.Size,
-								MountPoint: logicaldisk.DeviceID,
-								Type:       diskpartition.Type,
-								IsReadOnly: toReadOnly(diskpartition.Access), // TODO: add information
+								Name:        logicaldisk.Caption,
+								Label:       logicaldisk.Caption,
+								SizeBytes:   logicaldisk.Size,
+								UsableBytes: logicaldisk.FreeSpace,
+								MountPoint:  logicaldisk.DeviceID,
+								Type:        diskpartition.Type,
+								IsReadOnly:  toReadOnly(diskpartition.Access), // TODO: add information
 							}
 							disk.Partitions = append(disk.Partitions, p)
 							break