add TTL support

The volume TTL and file TTL are not necessarily the same. as long as
file TTL is smaller than volume TTL, it'll be fine.

volume TTL is used when assigning file id, e.g.
http://.../dir/assign?ttl=3h

file TTL is used when uploading

go/topology/volume_layout.go

@@ -11,15 +11,17 @@ import (
 // mapping from volume to its locations, inverted from server to volume
 type VolumeLayout struct {
 	rp              *storage.ReplicaPlacement
+	ttl             *storage.TTL
 	vid2location    map[storage.VolumeId]*VolumeLocationList
 	writables       []storage.VolumeId // transient array of writable volume id
 	volumeSizeLimit uint64
 	accessLock      sync.Mutex
 }
 
-func NewVolumeLayout(rp *storage.ReplicaPlacement, volumeSizeLimit uint64) *VolumeLayout {
+func NewVolumeLayout(rp *storage.ReplicaPlacement, ttl *storage.TTL, volumeSizeLimit uint64) *VolumeLayout {
 	return &VolumeLayout{
 		rp:              rp,
+		ttl:             ttl,
 		vid2location:    make(map[storage.VolumeId]*VolumeLocationList),
 		writables:       *new([]storage.VolumeId),
 		volumeSizeLimit: volumeSizeLimit,
@@ -42,6 +44,14 @@ func (vl *VolumeLayout) RegisterVolume(v *storage.VolumeInfo, dn *DataNode) {
 	}
 }
 
+func (vl *VolumeLayout) UnRegisterVolume(v *storage.VolumeInfo, dn *DataNode) {
+	vl.accessLock.Lock()
+	defer vl.accessLock.Unlock()
+
+	vl.removeFromWritable(v.Id)
+	delete(vl.vid2location, v.Id)
+}
+
 func (vl *VolumeLayout) AddToWritable(vid storage.VolumeId) {
 	for _, id := range vl.writables {
 		if vid == id {
@@ -192,6 +202,7 @@ func (vl *VolumeLayout) SetVolumeCapacityFull(vid storage.VolumeId) bool {
 func (vl *VolumeLayout) ToMap() map[string]interface{} {
 	m := make(map[string]interface{})
 	m["replication"] = vl.rp.String()
+	m["ttl"] = vl.ttl.String()
 	m["writables"] = vl.writables
 	//m["locations"] = vl.vid2location
 	return m