We should pass around db.Instance instead of leveldb.DB

We're going to need the db.Instance to keep some state, and for that to
work we need the same one passed around everywhere. Hence this moves the
leveldb-specific file opening stuff into the db package and exports the
dbInstance type.

lib/db/set.go

@@ -18,14 +18,13 @@ import (
 	"github.com/syncthing/syncthing/lib/osutil"
 	"github.com/syncthing/syncthing/lib/protocol"
 	"github.com/syncthing/syncthing/lib/sync"
-	"github.com/syndtr/goleveldb/leveldb"
 )
 
 type FileSet struct {
 	localVersion map[protocol.DeviceID]int64
 	mutex        sync.Mutex
 	folder       string
-	db           *dbInstance
+	db           *Instance
 	blockmap     *BlockMap
 	localSize    sizeTracker
 	globalSize   sizeTracker
@@ -93,11 +92,11 @@ func (s *sizeTracker) Size() (files, deleted int, bytes int64) {
 	return s.files, s.deleted, s.bytes
 }
 
-func NewFileSet(folder string, db *leveldb.DB) *FileSet {
+func NewFileSet(folder string, db *Instance) *FileSet {
 	var s = FileSet{
 		localVersion: make(map[protocol.DeviceID]int64),
 		folder:       folder,
-		db:           newDBInstance(db),
+		db:           db,
 		blockmap:     NewBlockMap(db, folder),
 		mutex:        sync.NewMutex(),
 	}
@@ -239,17 +238,10 @@ func (s *FileSet) GlobalSize() (files, deleted int, bytes int64) {
 	return s.globalSize.Size()
 }
 
-// ListFolders returns the folder IDs seen in the database.
-func ListFolders(db *leveldb.DB) []string {
-	i := newDBInstance(db)
-	return i.listFolders()
-}
-
 // DropFolder clears out all information related to the given folder from the
 // database.
-func DropFolder(db *leveldb.DB, folder string) {
-	i := newDBInstance(db)
-	i.dropFolder([]byte(folder))
+func DropFolder(db *Instance, folder string) {
+	db.dropFolder([]byte(folder))
 	bm := &BlockMap{
 		db:     db,
 		folder: folder,