add metastore, switching sequence to use it

metastore is for storing metadata. This will be used later when moving
to distributed master mode.

go/metastore/metastore.go

@@ -0,0 +1,35 @@
+package metastore
+
+import (
+	"code.google.com/p/weed-fs/go/util"
+	"errors"
+	"path"
+)
+
+type MetaStoreBacking interface {
+	Get(elem ...string) ([]byte, error)
+	Set(val []byte, elem ...string) error
+  Has(elem ...string) bool
+}
+
+type MetaStore struct {
+	MetaStoreBacking
+}
+
+func (m *MetaStore) SetUint64(val uint64, elem ...string) error {
+	b := make([]byte, 8)
+	util.Uint64toBytes(b, val)
+	return m.Set(b, elem...)
+}
+
+func (m *MetaStore) GetUint64(elem ...string) (val uint64, err error) {
+	if b, e := m.Get(elem...); e == nil && len(b) == 8 {
+		val = util.BytesToUint64(b)
+	} else {
+		if e != nil {
+			return 0, e
+		}
+		err = errors.New("Not found value for " + path.Join(elem...))
+	}
+	return
+}