OpenDir performance: Read DirIV once and reuse it for all names

Formerly, we called decryptPath for every name.
That resulted in a directory walk that reads in all diriv files
on the way.

Massive improvement for RM and LS (check performance.txt for details)

VERSION         UNTAR   RM   LS
v0.4               48    5    1.5
v0.5-rc1           56   19    7
v0.5-rc1-1         54    9    4.1   <---- THIS VERSION

4 files changed, 50 insertions, 34 deletions

diff --git a/cryptfs/cryptfs_names.go b/cryptfs/cryptfs_names.go
index 2a5f158..8f8486b 100644
--- a/cryptfs/cryptfs_names.go
+++ b/cryptfs/cryptfs_names.go
@@ -17,7 +17,7 @@ const (
 )
 
 // DecryptName - decrypt base64-encoded encrypted filename "cipherName"
-func (be *CryptFS) decryptName(cipherName string, iv []byte) (string, error) {
+func (be *CryptFS) DecryptName(cipherName string, iv []byte) (string, error) {
 
 	// Make sure relative symlinks still work after encryption
 	// by passing these through unchanged
@@ -91,7 +91,7 @@ func (be *CryptFS) TranslatePathZeroIV(path string, op int) (string, error) {
 		if op == OpEncrypt {
 			newPart = be.encryptName(part, zeroIV)
 		} else {
-			newPart, err = be.decryptName(part, zeroIV)
+			newPart, err = be.DecryptName(part, zeroIV)
 			if err != nil {
 				return "", err
 			}
diff --git a/cryptfs/names_diriv.go b/cryptfs/names_diriv.go
index be7a2b1..ae8545b 100644
--- a/cryptfs/names_diriv.go
+++ b/cryptfs/names_diriv.go
@@ -7,8 +7,8 @@ import (
 	"strings"
 )
 
-// readDirIV - read the "gocryptfs.diriv" file from "dir" (absolute path)
-func (be *CryptFS) readDirIV(dir string) (iv []byte, err error) {
+// readDirIV - read the "gocryptfs.diriv" file from "dir" (absolute ciphertext path)
+func (be *CryptFS) ReadDirIV(dir string) (iv []byte, err error) {
 	ivfile := filepath.Join(dir, DIRIV_FILENAME)
 	Debug.Printf("readDirIV: reading %s\n", ivfile)
 	iv, err = ioutil.ReadFile(ivfile)
@@ -22,7 +22,7 @@ func (be *CryptFS) readDirIV(dir string) (iv []byte, err error) {
 	return iv, nil
 }
 
-// WriteDirIV - create diriv file inside "dir" (absolute path)
+// WriteDirIV - create diriv file inside "dir" (absolute ciphertext path)
 // This function is exported because it is used from pathfs_frontend, main,
 // and also the automated tests.
 func WriteDirIV(dir string) error {
@@ -45,7 +45,7 @@ func (be *CryptFS) EncryptPathDirIV(plainPath string, rootDir string) (string, e
 	var encryptedNames []string
 	plainNames := strings.Split(plainPath, "/")
 	for _, plainName := range plainNames {
-		iv, err := be.readDirIV(wd)
+		iv, err := be.ReadDirIV(wd)
 		if err != nil {
 			return "", err
 		}
@@ -66,11 +66,11 @@ func (be *CryptFS) DecryptPathDirIV(encryptedPath string, rootDir string) (strin
 	encryptedNames := strings.Split(encryptedPath, "/")
 	Debug.Printf("DecryptPathDirIV: decrypting %v\n", encryptedNames)
 	for _, encryptedName := range encryptedNames {
-		iv, err := be.readDirIV(wd)
+		iv, err := be.ReadDirIV(wd)
 		if err != nil {
 			return "", err
 		}
-		plainName, err := be.decryptName(encryptedName, iv)
+		plainName, err := be.DecryptName(encryptedName, iv)
 		if err != nil {
 			return "", err
 		}
diff --git a/pathfs_frontend/fs.go b/pathfs_frontend/fs.go
index e68e6bc..fe9a8b0 100644
--- a/pathfs_frontend/fs.go
+++ b/pathfs_frontend/fs.go
@@ -75,35 +75,41 @@ func (fs *FS) OpenDir(dirName string, context *fuse.Context) ([]fuse.DirEntry, f
 	if err != nil {
 		return nil, fuse.ToStatus(err)
 	}
+	// Read ciphertext directory
 	cipherEntries, status := fs.FileSystem.OpenDir(cDirName, context)
+	if cipherEntries == nil {
+		return nil, status
+	}
+	// Get DirIV (stays zero if DirIV if off)
+	cachedIV := make([]byte, cryptfs.DIRIV_LEN)
+	if fs.args.DirIV {
+		// Read the DirIV once and use it for all later name decryptions
+		cDirAbsPath := filepath.Join(fs.args.Cipherdir, cDirName)
+		cachedIV, err = fs.CryptFS.ReadDirIV(cDirAbsPath)
+		if err != nil {
+			return nil, fuse.ToStatus(err)
+		}
+	}
+	// Decrypt filenames
 	var plain []fuse.DirEntry
-	if cipherEntries != nil {
-		for i := range cipherEntries {
-			cName := cipherEntries[i].Name
-			if dirName == "" && cName == cryptfs.ConfDefaultName {
-				// silently ignore "gocryptfs.conf" in the top level dir
-				continue
-			}
-			if fs.args.DirIV && cName == cryptfs.DIRIV_FILENAME {
-				// silently ignore "gocryptfs.diriv" everywhere if dirIV is enabled
-				continue
-			}
-			var name string
-			if !fs.args.DirIV {
-				name, err = fs.decryptPath(cName)
-			} else {
-				// When dirIV is enabled we need the full path to be able to decrypt it
-				cPath := filepath.Join(cDirName, cName)
-				name, err = fs.decryptPath(cPath)
-				name = filepath.Base(name)
-			}
-			if err != nil {
-				cryptfs.Warn.Printf("Invalid name \"%s\" in dir \"%s\": %s\n", cName, dirName, err)
-				continue
-			}
-			cipherEntries[i].Name = name
-			plain = append(plain, cipherEntries[i])
+	for i := range cipherEntries {
+		cName := cipherEntries[i].Name
+		if dirName == "" && cName == cryptfs.ConfDefaultName {
+			// silently ignore "gocryptfs.conf" in the top level dir
+			continue
+		}
+		if fs.args.DirIV && cName == cryptfs.DIRIV_FILENAME {
+			// silently ignore "gocryptfs.diriv" everywhere if dirIV is enabled
+			continue
+		}
+		var name string
+		name, err = fs.CryptFS.DecryptName(cName, cachedIV)
+		if err != nil {
+			cryptfs.Warn.Printf("Invalid name \"%s\" in dir \"%s\": %s\n", cName, dirName, err)
+			continue
 		}
+		cipherEntries[i].Name = name
+		plain = append(plain, cipherEntries[i])
 	}
 	return plain, status
 }
diff --git a/performance.txt b/performance.txt
new file mode 100644
index 0000000..55678c3
--- /dev/null
+++ b/performance.txt
@@ -0,0 +1,10 @@
+All test performed on tmpfs, /tmp/a mounted on /tmp/b.
+
+UNTAR: tar xfz ../linux-3.0.tar.gz
+LS: ls -lR > /dev/null
+RM: rm -rf linux-3.0
+
+VERSION         UNTAR    LS     RM
+v0.4               48     1.5    5
+v0.5-rc1           56     7     19
+v0.5-rc1-1         54     4.1    9