lib/db: Do all update operations on a single item at once (#5441)

To do so the BlockMap struct has been removed. It behaves like any other prefixed
part of the database, but was not integrated in the recent keyer refactor. Now
the database is only flushed when files are in a consistent state.

lib/db/keyer.go

@@ -73,6 +73,10 @@ type keyer interface {
 	NameFromGlobalVersionKey(key []byte) []byte
 	FolderFromGlobalVersionKey(key []byte) ([]byte, bool)
 
+	// block map key stuff (former BlockMap)
+	GenerateBlockMapKey(key, folder, hash, name []byte) blockMapKey
+	NameFromBlockMapKey(key []byte) []byte
+
 	// file need index
 	GenerateNeedFileKey(key, folder, name []byte) needFileKey
 
@@ -154,6 +158,25 @@ func (k defaultKeyer) FolderFromGlobalVersionKey(key []byte) ([]byte, bool) {
 	return k.folderIdx.Val(binary.BigEndian.Uint32(key[keyPrefixLen:]))
 }
 
+type blockMapKey []byte
+
+func (k defaultKeyer) GenerateBlockMapKey(key, folder, hash, name []byte) blockMapKey {
+	key = resize(key, keyPrefixLen+keyFolderLen+keyHashLen+len(name))
+	key[0] = KeyTypeBlock
+	binary.BigEndian.PutUint32(key[keyPrefixLen:], k.folderIdx.ID(folder))
+	copy(key[keyPrefixLen+keyFolderLen:], hash)
+	copy(key[keyPrefixLen+keyFolderLen+keyHashLen:], name)
+	return key
+}
+
+func (k defaultKeyer) NameFromBlockMapKey(key []byte) []byte {
+	return key[keyPrefixLen+keyFolderLen+keyHashLen:]
+}
+
+func (k blockMapKey) WithoutHashAndName() []byte {
+	return k[:keyPrefixLen+keyFolderLen]
+}
+
 type needFileKey []byte
 
 func (k needFileKey) WithoutName() []byte {