disk: new types LVMVolumeGroup and LVMLogicalVolume

Types to represent LVM2 setups with logical volumes being contained
in volume groups.

LVMVolumeGroup implements the following disk interfaces:
- Entity
- Container
- VolumeContainer

LVMLogicalVolume implements the following disk interfaces:
- Entity
- Container
- Sizeable

Co-Authored-By: Christian Kellner <christian@kellner.me>

internal/disk/lvm.go

@@ -0,0 +1,77 @@
+package disk
+
+import "fmt"
+
+type LVMVolumeGroup struct {
+	Name        string
+	Description string
+
+	LogicalVolumes []LVMLogicalVolume
+}
+
+func (vg *LVMVolumeGroup) IsContainer() bool {
+	return true
+}
+
+func (vg *LVMVolumeGroup) GetItemCount() uint {
+	return uint(len(vg.LogicalVolumes))
+}
+
+func (vg *LVMVolumeGroup) GetChild(n uint) Entity {
+	return &vg.LogicalVolumes[n]
+}
+
+func (vg *LVMVolumeGroup) CreateVolume(mountpoint string, size uint64) (Entity, error) {
+	filesystem := Filesystem{
+		Type:         "xfs",
+		Mountpoint:   mountpoint,
+		FSTabOptions: "defaults",
+		FSTabFreq:    0,
+		FSTabPassNo:  0,
+	}
+
+	lv := LVMLogicalVolume{
+		Size:    size,
+		Payload: &filesystem,
+	}
+
+	vg.LogicalVolumes = append(vg.LogicalVolumes, lv)
+
+	return &vg.LogicalVolumes[len(vg.LogicalVolumes)-1], nil
+}
+
+type LVMLogicalVolume struct {
+	Name    string
+	Size    uint64
+	Payload Entity
+}
+
+func (lv *LVMLogicalVolume) IsContainer() bool {
+	return true
+}
+
+func (lv *LVMLogicalVolume) GetItemCount() uint {
+	if lv.Payload == nil {
+		return 0
+	}
+	return 1
+}
+
+func (lv *LVMLogicalVolume) GetChild(n uint) Entity {
+	if n != 0 {
+		panic(fmt.Sprintf("invalid child index for LVMLogicalVolume: %d != 0", n))
+	}
+	return lv.Payload
+}
+
+func (lv *LVMLogicalVolume) GetSize() uint64 {
+	return lv.Size
+}
+
+func (lv *LVMLogicalVolume) EnsureSize(s uint64) bool {
+	if s > lv.Size {
+		lv.Size = s
+		return true
+	}
+	return false
+}