reverse: add longnameParentCache

findLongnameParent has to read the whole directory to find the
right file; add a simple cache to avoid most directory scans.

internal/fusefrontend_reverse/reverse_longnames.go

@@ -3,7 +3,9 @@ package fusefrontend_reverse
 import (
 	"os"
 	"path/filepath"
+	"sync"
 	"syscall"
+	"time"
 
 	"github.com/hanwen/go-fuse/fuse"
 	"github.com/hanwen/go-fuse/fuse/nodefs"
@@ -15,7 +17,37 @@ const (
 	shortNameMax = 176
 )
 
-func (rfs *reverseFS) findLongnameParent(dir string, dirIV []byte, longname string) (string, error) {
+type dirIVNameStruct struct {
+	dirIV [nametransform.DirIVLen]byte
+	name  string
+}
+
+var longnameParentCache map[string]string
+var longnameCacheLock sync.Mutex
+
+// Very simple cache cleaner: Nuke it every hour
+func longnameCacheCleaner() {
+	for {
+		time.Sleep(time.Hour)
+		longnameCacheLock.Lock()
+		longnameParentCache = map[string]string{}
+		longnameCacheLock.Unlock()
+	}
+}
+
+func init() {
+	longnameParentCache = map[string]string{}
+	go longnameCacheCleaner()
+}
+
+// findLongnameParent converts "gocryptfs.longname.XYZ" to the plaintext name
+func (rfs *reverseFS) findLongnameParent(dir string, dirIV []byte, longname string) (plaintextName string, err error) {
+	longnameCacheLock.Lock()
+	hit := longnameParentCache[longname]
+	longnameCacheLock.Unlock()
+	if hit != "" {
+		return hit, nil
+	}
 	absDir := filepath.Join(rfs.args.Cipherdir, dir)
 	dirfd, err := os.Open(absDir)
 	if err != nil {
@@ -25,20 +57,27 @@ func (rfs *reverseFS) findLongnameParent(dir string, dirIV []byte, longname stri
 	if err != nil {
 		return "", err
 	}
-	for _, e := range dirEntries {
-		if len(e) <= shortNameMax {
+	longnameCacheLock.Lock()
+	defer longnameCacheLock.Unlock()
+	for _, plaintextName = range dirEntries {
+		if len(plaintextName) <= shortNameMax {
 			continue
 		}
-		cName := rfs.nameTransform.EncryptName(e, dirIV)
+		cName := rfs.nameTransform.EncryptName(plaintextName, dirIV)
 		if len(cName) <= syscall.NAME_MAX {
 			panic("logic error or wrong shortNameMax constant?")
 		}
 		hName := nametransform.HashLongName(cName)
+		longnameParentCache[hName] = plaintextName
 		if longname == hName {
-			return e, nil
+			hit = plaintextName
 		}
 	}
-	return "", syscall.ENOENT
+	if hit == "" {
+		return "", syscall.ENOENT
+	} else {
+		return hit, nil
+	}
 }
 
 func (rfs *reverseFS) newNameFile(relPath string) (nodefs.File, fuse.Status) {

internal/fusefrontend_reverse/rfs.go

@@ -248,9 +248,15 @@ func (rfs *reverseFS) OpenDir(cipherPath string, context *fuse.Context) ([]fuse.
 	if entries == nil {
 		return nil, status
 	}
+	// Allocate maximum possible number of virtual files.
+	// If all files have long names we need a virtual ".name" file for each,
+	// plus one for gocryptfs.diriv.
+	virtualFiles := make([]fuse.DirEntry, len(entries)+1)
 	// Virtual gocryptfs.diriv file
-	dirIVEntry := fuse.DirEntry{syscall.S_IFREG | 0400, nametransform.DirIVFilename}
-	virtualFiles := []fuse.DirEntry{dirIVEntry}
+	virtualFiles[0] = fuse.DirEntry{syscall.S_IFREG | 0400, nametransform.DirIVFilename}
+	// Actually used entries
+	nVirtual := 1
+
 	// Encrypt names
 	dirIV := deriveDirIV(cipherPath)
 	for i := range entries {
@@ -263,12 +269,13 @@ func (rfs *reverseFS) OpenDir(cipherPath string, context *fuse.Context) ([]fuse.
 			if len(cName) > syscall.NAME_MAX {
 				cName = nametransform.HashLongName(cName)
 				dotNameFile := fuse.DirEntry{syscall.S_IFREG | 0600, cName + nametransform.LongNameSuffix}
-				virtualFiles = append(virtualFiles, dotNameFile)
+				virtualFiles[nVirtual] = dotNameFile
+				nVirtual++
 			}
 		}
 		entries[i].Name = cName
 	}
-	entries = append(entries, virtualFiles...)
+	entries = append(entries, virtualFiles[:nVirtual]...)
 	return entries, fuse.OK
 }