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.

cmd/syncthing/main.go

@@ -9,6 +9,7 @@ package main
 import (
 	"bytes"
 	"crypto/tls"
+	"errors"
 	"flag"
 	"fmt"
 	"io/ioutil"
@@ -42,9 +43,6 @@ import (
 	"github.com/syncthing/syncthing/lib/tlsutil"
 	"github.com/syncthing/syncthing/lib/upgrade"
 
-	"github.com/syndtr/goleveldb/leveldb"
-	"github.com/syndtr/goleveldb/leveldb/errors"
-	"github.com/syndtr/goleveldb/leveldb/opt"
 	"github.com/thejerf/suture"
 )
 
@@ -371,7 +369,7 @@ func main() {
 
 		if doUpgrade {
 			// Use leveldb database locks to protect against concurrent upgrades
-			_, err = leveldb.OpenFile(locations[locDatabase], &opt.Options{OpenFilesCacheCapacity: 100})
+			_, err = db.Open(locations[locDatabase])
 			if err != nil {
 				l.Infoln("Attempting upgrade through running Syncthing...")
 				err = upgradeViaRest()
@@ -617,21 +615,7 @@ func syncthingMain() {
 	}
 
 	dbFile := locations[locDatabase]
-	dbOpts := dbOpts(cfg)
-	ldb, err := leveldb.OpenFile(dbFile, dbOpts)
-	if leveldbIsCorrupted(err) {
-		ldb, err = leveldb.RecoverFile(dbFile, dbOpts)
-	}
-	if leveldbIsCorrupted(err) {
-		// The database is corrupted, and we've tried to recover it but it
-		// didn't work. At this point there isn't much to do beyond dropping
-		// the database and reindexing...
-		l.Infoln("Database corruption detected, unable to recover. Reinitializing...")
-		if err := resetDB(); err != nil {
-			l.Fatalln("Remove database:", err)
-		}
-		ldb, err = leveldb.OpenFile(dbFile, dbOpts)
-	}
+	ldb, err := db.Open(dbFile)
 	if err != nil {
 		l.Fatalln("Cannot open database:", err, "- Is another copy of Syncthing already running?")
 	}
@@ -642,7 +626,7 @@ func syncthingMain() {
 
 	// Remove database entries for folders that no longer exist in the config
 	folders := cfg.Folders()
-	for _, folder := range db.ListFolders(ldb) {
+	for _, folder := range ldb.ListFolders() {
 		if _, ok := folders[folder]; !ok {
 			l.Infof("Cleaning data for dropped folder %q", folder)
 			db.DropFolder(ldb, folder)
@@ -881,40 +865,6 @@ func loadConfig(cfgFile string) (*config.Wrapper, string, error) {
 	return cfg, myName, nil
 }
 
-func dbOpts(cfg *config.Wrapper) *opt.Options {
-	// Calculate a suitable database block cache capacity.
-
-	// Default is 8 MiB.
-	blockCacheCapacity := 8 << 20
-	// Increase block cache up to this maximum:
-	const maxCapacity = 64 << 20
-	// ... which we reach when the box has this much RAM:
-	const maxAtRAM = 8 << 30
-
-	if v := cfg.Options().DatabaseBlockCacheMiB; v != 0 {
-		// Use the value from the config, if it's set.
-		blockCacheCapacity = v << 20
-	} else if bytes, err := memorySize(); err == nil {
-		// We start at the default of 8 MiB and use larger values for machines
-		// with more memory.
-
-		if bytes > maxAtRAM {
-			// Cap the cache at maxCapacity when we reach maxAtRam amount of memory
-			blockCacheCapacity = maxCapacity
-		} else if bytes > maxAtRAM/maxCapacity*int64(blockCacheCapacity) {
-			// Grow from the default to maxCapacity at maxAtRam amount of memory
-			blockCacheCapacity = int(bytes * maxCapacity / maxAtRAM)
-		}
-		l.Infoln("Database block cache capacity", blockCacheCapacity/1024, "KiB")
-	}
-
-	return &opt.Options{
-		OpenFilesCacheCapacity: 100,
-		BlockCacheCapacity:     blockCacheCapacity,
-		WriteBuffer:            4 << 20,
-	}
-}
-
 func startAuditing(mainSvc *suture.Supervisor) {
 	auditFile := timestampedLoc(locAuditLog)
 	fd, err := os.OpenFile(auditFile, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0600)
@@ -1166,19 +1116,3 @@ func checkShortIDs(cfg *config.Wrapper) error {
 	}
 	return nil
 }
-
-// A "better" version of leveldb's errors.IsCorrupted.
-func leveldbIsCorrupted(err error) bool {
-	switch {
-	case err == nil:
-		return false
-
-	case errors.IsCorrupted(err):
-		return true
-
-	case strings.Contains(err.Error(), "corrupted"):
-		return true
-	}
-
-	return false
-}