v2api/reverse: move old fusefrontend_reverse out of the way

fusefrontend_reverse -> fusefrontend_reverse_v1api

11 files changed, 1419 insertions, 0 deletions

diff --git a/internal/fusefrontend_reverse_v1api/ctlsock_interface.go b/internal/fusefrontend_reverse_v1api/ctlsock_interface.go
new file mode 100644
index 0000000..f7b8afd
--- /dev/null
+++ b/internal/fusefrontend_reverse_v1api/ctlsock_interface.go
@@ -0,0 +1,38 @@
+package fusefrontend_reverse
+
+import (
+	"path/filepath"
+	"strings"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/rfjakob/gocryptfs/internal/ctlsocksrv"
+	"github.com/rfjakob/gocryptfs/internal/pathiv"
+)
+
+var _ ctlsocksrv.Interface = &ReverseFS{} // Verify that interface is implemented.
+
+// EncryptPath implements ctlsock.Backend.
+// This is used for the control socket and for the "-exclude" logic.
+func (rfs *ReverseFS) EncryptPath(plainPath string) (string, error) {
+	if rfs.args.PlaintextNames || plainPath == "" {
+		return plainPath, nil
+	}
+	cipherPath := ""
+	parts := strings.Split(plainPath, "/")
+	for _, part := range parts {
+		dirIV := pathiv.Derive(cipherPath, pathiv.PurposeDirIV)
+		encryptedPart := rfs.nameTransform.EncryptName(part, dirIV)
+		if rfs.args.LongNames && len(encryptedPart) > unix.NAME_MAX {
+			encryptedPart = rfs.nameTransform.HashLongName(encryptedPart)
+		}
+		cipherPath = filepath.Join(cipherPath, encryptedPart)
+	}
+	return cipherPath, nil
+}
+
+// DecryptPath implements ctlsock.Backend
+func (rfs *ReverseFS) DecryptPath(cipherPath string) (string, error) {
+	p, err := rfs.decryptPath(cipherPath)
+	return p, err
+}
diff --git a/internal/fusefrontend_reverse_v1api/excluder.go b/internal/fusefrontend_reverse_v1api/excluder.go
new file mode 100644
index 0000000..c44816c
--- /dev/null
+++ b/internal/fusefrontend_reverse_v1api/excluder.go
@@ -0,0 +1,66 @@
+package fusefrontend_reverse
+
+import (
+	"io/ioutil"
+	"os"
+	"strings"
+
+	"github.com/rfjakob/gocryptfs/internal/exitcodes"
+	"github.com/rfjakob/gocryptfs/internal/fusefrontend"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+
+	"github.com/sabhiram/go-gitignore"
+)
+
+// prepareExcluder creates an object to check if paths are excluded
+// based on the patterns specified in the command line.
+func (rfs *ReverseFS) prepareExcluder(args fusefrontend.Args) {
+	if len(args.Exclude) > 0 || len(args.ExcludeWildcard) > 0 || len(args.ExcludeFrom) > 0 {
+		excluder, err := ignore.CompileIgnoreLines(getExclusionPatterns(args)...)
+		if err != nil {
+			tlog.Fatal.Printf("Error compiling exclusion rules: %q", err)
+			os.Exit(exitcodes.ExcludeError)
+		}
+		rfs.excluder = excluder
+	}
+}
+
+// getExclusionPatters prepares a list of patterns to be excluded.
+// Patterns passed in the -exclude command line option are prefixed
+// with a leading '/' to preserve backwards compatibility (before
+// wildcard matching was implemented, exclusions always were matched
+// against the full path).
+func getExclusionPatterns(args fusefrontend.Args) []string {
+	patterns := make([]string, len(args.Exclude)+len(args.ExcludeWildcard))
+	// add -exclude
+	for i, p := range args.Exclude {
+		patterns[i] = "/" + p
+	}
+	// add -exclude-wildcard
+	copy(patterns[len(args.Exclude):], args.ExcludeWildcard)
+	// add -exclude-from
+	for _, file := range args.ExcludeFrom {
+		lines, err := getLines(file)
+		if err != nil {
+			tlog.Fatal.Printf("Error reading exclusion patterns: %q", err)
+			os.Exit(exitcodes.ExcludeError)
+		}
+		patterns = append(patterns, lines...)
+	}
+	return patterns
+}
+
+// getLines reads a file and splits it into lines
+func getLines(file string) ([]string, error) {
+	buffer, err := ioutil.ReadFile(file)
+	if err != nil {
+		return nil, err
+	}
+	return strings.Split(string(buffer), "\n"), nil
+}
+
+// isExcludedPlain finds out if the plaintext path "pPath" is
+// excluded (used when -exclude is passed by the user).
+func (rfs *ReverseFS) isExcludedPlain(pPath string) bool {
+	return rfs.excluder != nil && rfs.excluder.MatchesPath(pPath)
+}
diff --git a/internal/fusefrontend_reverse_v1api/excluder_test.go b/internal/fusefrontend_reverse_v1api/excluder_test.go
new file mode 100644
index 0000000..e19b99f
--- /dev/null
+++ b/internal/fusefrontend_reverse_v1api/excluder_test.go
@@ -0,0 +1,84 @@
+package fusefrontend_reverse
+
+import (
+	"io/ioutil"
+	"os"
+	"reflect"
+	"testing"
+
+	"github.com/rfjakob/gocryptfs/internal/fusefrontend"
+)
+
+func TestShouldNoCreateExcluderIfNoPattersWereSpecified(t *testing.T) {
+	var rfs ReverseFS
+	var args fusefrontend.Args
+	rfs.prepareExcluder(args)
+	if rfs.excluder != nil {
+		t.Error("Should not have created excluder")
+	}
+}
+
+func TestShouldPrefixExcludeValuesWithSlash(t *testing.T) {
+	var args fusefrontend.Args
+	args.Exclude = []string{"file1", "dir1/file2.txt"}
+	args.ExcludeWildcard = []string{"*~", "build/*.o"}
+
+	expected := []string{"/file1", "/dir1/file2.txt", "*~", "build/*.o"}
+
+	patterns := getExclusionPatterns(args)
+	if !reflect.DeepEqual(patterns, expected) {
+		t.Errorf("expected %q, got %q", expected, patterns)
+	}
+}
+
+func TestShouldReadExcludePatternsFromFiles(t *testing.T) {
+	tmpfile1, err := ioutil.TempFile("", "excludetest")
+	if err != nil {
+		t.Fatal(err)
+	}
+	exclude1 := tmpfile1.Name()
+	defer os.Remove(exclude1)
+	defer tmpfile1.Close()
+
+	tmpfile2, err := ioutil.TempFile("", "excludetest")
+	if err != nil {
+		t.Fatal(err)
+	}
+	exclude2 := tmpfile2.Name()
+	defer os.Remove(exclude2)
+	defer tmpfile2.Close()
+
+	tmpfile1.WriteString("file1.1\n")
+	tmpfile1.WriteString("file1.2\n")
+	tmpfile2.WriteString("file2.1\n")
+	tmpfile2.WriteString("file2.2\n")
+
+	var args fusefrontend.Args
+	args.ExcludeWildcard = []string{"cmdline1"}
+	args.ExcludeFrom = []string{exclude1, exclude2}
+
+	// An empty string is returned for the last empty line
+	// It's ignored when the patterns are actually compiled
+	expected := []string{"cmdline1", "file1.1", "file1.2", "", "file2.1", "file2.2", ""}
+
+	patterns := getExclusionPatterns(args)
+	if !reflect.DeepEqual(patterns, expected) {
+		t.Errorf("expected %q, got %q", expected, patterns)
+	}
+}
+
+func TestShouldReturnFalseIfThereAreNoExclusions(t *testing.T) {
+	var rfs ReverseFS
+	if rfs.isExcludedPlain("any/path") {
+		t.Error("Should not exclude any path if no exclusions were specified")
+	}
+}
+
+func TestShouldCallIgnoreParserToCheckExclusion(t *testing.T) {
+	rfs, ignorerMock := createRFSWithMocks()
+
+	rfs.isExcludedPlain("some/path")
+	if ignorerMock.calledWith != "some/path" {
+		t.Error("Failed to call IgnoreParser")
+	}
+}
diff --git a/internal/fusefrontend_reverse_v1api/mocks_test.go b/internal/fusefrontend_reverse_v1api/mocks_test.go
new file mode 100644
index 0000000..fd2f940
--- /dev/null
+++ b/internal/fusefrontend_reverse_v1api/mocks_test.go
@@ -0,0 +1,32 @@
+package fusefrontend_reverse
+
+import (
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+)
+
+type IgnoreParserMock struct {
+	toExclude  string
+	calledWith string
+}
+
+func (parser *IgnoreParserMock) MatchesPath(f string) bool {
+	parser.calledWith = f
+	return f == parser.toExclude
+}
+
+type NameTransformMock struct {
+	nametransform.NameTransform
+}
+
+func (n *NameTransformMock) DecryptName(cipherName string, iv []byte) (string, error) {
+	return "mockdecrypt_" + cipherName, nil
+}
+
+func createRFSWithMocks() (*ReverseFS, *IgnoreParserMock) {
+	ignorerMock := &IgnoreParserMock{}
+	nameTransformMock := &NameTransformMock{}
+	var rfs ReverseFS
+	rfs.excluder = ignorerMock
+	rfs.nameTransform = nameTransformMock
+	return &rfs, ignorerMock
+}
diff --git a/internal/fusefrontend_reverse_v1api/reverse_longnames.go b/internal/fusefrontend_reverse_v1api/reverse_longnames.go
new file mode 100644
index 0000000..f1576d2
--- /dev/null
+++ b/internal/fusefrontend_reverse_v1api/reverse_longnames.go
@@ -0,0 +1,126 @@
+package fusefrontend_reverse
+
+import (
+	"log"
+	"path/filepath"
+	"sync"
+	"syscall"
+	"time"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/hanwen/go-fuse/v2/fuse"
+	"github.com/hanwen/go-fuse/v2/fuse/nodefs"
+
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+	"github.com/rfjakob/gocryptfs/internal/pathiv"
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+const (
+	// File names are padded to 16-byte multiples, encrypted and
+	// base64-encoded. We can encode at most 176 bytes to stay below the 255
+	// bytes limit:
+	// * base64(176 bytes) = 235 bytes
+	// * base64(192 bytes) = 256 bytes (over 255!)
+	// But the PKCS#7 padding is at least one byte. This means we can only use
+	// 175 bytes for the file name.
+	shortNameMax = 175
+)
+
+// longnameParentCache maps dir+"/"+longname to plaintextname.
+// Yes, the combination of relative plaintext dir path and encrypted
+// longname is strange, but works fine as a map index.
+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 initLongnameCache() {
+	if longnameParentCache != nil {
+		return
+	}
+	longnameParentCache = map[string]string{}
+	go longnameCacheCleaner()
+}
+
+// findLongnameParent converts "longname" = "gocryptfs.longname.XYZ" to the
+// plaintext name. "dir" = relative plaintext path to the directory the
+// longname file is in, "dirIV" = directory IV of the directory.
+func (rfs *ReverseFS) findLongnameParent(dir string, dirIV []byte, longname string) (plaintextName string, err error) {
+	longnameCacheLock.Lock()
+	hit := longnameParentCache[dir+"/"+longname]
+	longnameCacheLock.Unlock()
+	if hit != "" {
+		return hit, nil
+	}
+	dirfd, err := syscallcompat.OpenDirNofollow(rfs.args.Cipherdir, filepath.Dir(dir))
+	if err != nil {
+		tlog.Warn.Printf("findLongnameParent: OpenDirNofollow failed: %v\n", err)
+		return "", err
+	}
+	fd, err := syscallcompat.Openat(dirfd, filepath.Base(dir), syscall.O_RDONLY|syscall.O_DIRECTORY|syscall.O_NOFOLLOW, 0)
+	syscall.Close(dirfd)
+	if err != nil {
+		tlog.Warn.Printf("findLongnameParent: Openat failed: %v\n", err)
+		return "", err
+	}
+	dirEntries, err := syscallcompat.Getdents(fd)
+	syscall.Close(fd)
+	if err != nil {
+		tlog.Warn.Printf("findLongnameParent: Getdents failed: %v\n", err)
+		return "", err
+	}
+	longnameCacheLock.Lock()
+	defer longnameCacheLock.Unlock()
+	for _, entry := range dirEntries {
+		plaintextName := entry.Name
+		if len(plaintextName) <= shortNameMax {
+			continue
+		}
+		cName := rfs.nameTransform.EncryptName(plaintextName, dirIV)
+		if len(cName) <= unix.NAME_MAX {
+			// Entry should have been skipped by the "continue" above
+			log.Panic("logic error or wrong shortNameMax constant?")
+		}
+		hName := rfs.nameTransform.HashLongName(cName)
+		longnameParentCache[dir+"/"+hName] = plaintextName
+		if longname == hName {
+			hit = plaintextName
+		}
+	}
+	if hit == "" {
+		return "", syscall.ENOENT
+	}
+	return hit, nil
+}
+
+func (rfs *ReverseFS) newNameFile(relPath string) (nodefs.File, fuse.Status) {
+	dotName := filepath.Base(relPath)                       // gocryptfs.longname.XYZ.name
+	longname := nametransform.RemoveLongNameSuffix(dotName) // gocryptfs.longname.XYZ
+	// cipher directory
+	cDir := nametransform.Dir(relPath)
+	// plain directory
+	pDir, err := rfs.decryptPath(cDir)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	dirIV := pathiv.Derive(cDir, pathiv.PurposeDirIV)
+	// plain name
+	pName, err := rfs.findLongnameParent(pDir, dirIV, longname)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	content := []byte(rfs.nameTransform.EncryptName(pName, dirIV))
+	parentFile := filepath.Join(pDir, pName)
+	return rfs.newVirtualFile(content, rfs.args.Cipherdir, parentFile, inoTagNameFile)
+}
diff --git a/internal/fusefrontend_reverse_v1api/rfile.go b/internal/fusefrontend_reverse_v1api/rfile.go
new file mode 100644
index 0000000..68f7309
--- /dev/null
+++ b/internal/fusefrontend_reverse_v1api/rfile.go
@@ -0,0 +1,209 @@
+package fusefrontend_reverse
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"path/filepath"
+	"syscall"
+
+	// In newer Go versions, this has moved to just "sync/syncmap".
+	"golang.org/x/sync/syncmap"
+
+	"github.com/hanwen/go-fuse/v2/fuse"
+	"github.com/hanwen/go-fuse/v2/fuse/nodefs"
+
+	"github.com/rfjakob/gocryptfs/internal/contentenc"
+	"github.com/rfjakob/gocryptfs/internal/pathiv"
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+type reverseFile struct {
+	// Embed nodefs.defaultFile for a ENOSYS implementation of all methods
+	nodefs.File
+	// Backing FD
+	fd *os.File
+	// File header (contains the IV)
+	header contentenc.FileHeader
+	// IV for block 0
+	block0IV []byte
+	// Content encryption helper
+	contentEnc *contentenc.ContentEnc
+}
+
+var inodeTable syncmap.Map
+
+// newFile receives a ciphered path "relPath" and its corresponding
+// decrypted path "pRelPath", opens it and returns a reverseFile
+// object. The backing file descriptor is always read-only.
+func (rfs *ReverseFS) newFile(relPath string, pRelPath string) (*reverseFile, fuse.Status) {
+	if rfs.isExcludedPlain(pRelPath) {
+		// Excluded paths should have been filtered out beforehand. Better safe
+		// than sorry.
+		tlog.Warn.Printf("BUG: newFile: received excluded path %q. This should not happen.", relPath)
+		return nil, fuse.ENOENT
+	}
+	dir := filepath.Dir(pRelPath)
+	dirfd, err := syscallcompat.OpenDirNofollow(rfs.args.Cipherdir, dir)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	fd, err := syscallcompat.Openat(dirfd, filepath.Base(pRelPath), syscall.O_RDONLY|syscall.O_NOFOLLOW, 0)
+	syscall.Close(dirfd)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	var st syscall.Stat_t
+	err = syscall.Fstat(fd, &st)
+	if err != nil {
+		tlog.Warn.Printf("newFile: Fstat error: %v", err)
+		syscall.Close(fd)
+		return nil, fuse.ToStatus(err)
+	}
+	// Reject access if the file descriptor does not refer to a regular file.
+	var a fuse.Attr
+	a.FromStat(&st)
+	if !a.IsRegular() {
+		tlog.Warn.Printf("ino%d: newFile: not a regular file", st.Ino)
+		syscall.Close(fd)
+		return nil, fuse.ToStatus(syscall.EACCES)
+	}
+	// See if we have that inode number already in the table
+	// (even if Nlink has dropped to 1)
+	var derivedIVs pathiv.FileIVs
+	v, found := inodeTable.Load(st.Ino)
+	if found {
+		tlog.Debug.Printf("ino%d: newFile: found in the inode table", st.Ino)
+		derivedIVs = v.(pathiv.FileIVs)
+	} else {
+		derivedIVs = pathiv.DeriveFile(relPath)
+		// Nlink > 1 means there is more than one path to this file.
+		// Store the derived values so we always return the same data,
+		// regardless of the path that is used to access the file.
+		// This means that the first path wins.
+		if st.Nlink > 1 {
+			v, found = inodeTable.LoadOrStore(st.Ino, derivedIVs)
+			if found {
+				// Another thread has stored a different value before we could.
+				derivedIVs = v.(pathiv.FileIVs)
+			} else {
+				tlog.Debug.Printf("ino%d: newFile: Nlink=%d, stored in the inode table", st.Ino, st.Nlink)
+			}
+		}
+	}
+	header := contentenc.FileHeader{
+		Version: contentenc.CurrentVersion,
+		ID:      derivedIVs.ID,
+	}
+	return &reverseFile{
+		File:       nodefs.NewDefaultFile(),
+		fd:         os.NewFile(uintptr(fd), pRelPath),
+		header:     header,
+		block0IV:   derivedIVs.Block0IV,
+		contentEnc: rfs.contentEnc,
+	}, fuse.OK
+}
+
+// GetAttr - FUSE call
+// Triggered by fstat() from userspace
+func (rf *reverseFile) GetAttr(*fuse.Attr) fuse.Status {
+	tlog.Debug.Printf("reverseFile.GetAttr fd=%d\n", rf.fd.Fd())
+	// The kernel should fall back to stat()
+	return fuse.ENOSYS
+}
+
+// encryptBlocks - encrypt "plaintext" into a number of ciphertext blocks.
+// "plaintext" must already be block-aligned.
+func (rf *reverseFile) encryptBlocks(plaintext []byte, firstBlockNo uint64, fileID []byte, block0IV []byte) []byte {
+	inBuf := bytes.NewBuffer(plaintext)
+	var outBuf bytes.Buffer
+	bs := int(rf.contentEnc.PlainBS())
+	for blockNo := firstBlockNo; inBuf.Len() > 0; blockNo++ {
+		inBlock := inBuf.Next(bs)
+		iv := pathiv.BlockIV(block0IV, blockNo)
+		outBlock := rf.contentEnc.EncryptBlockNonce(inBlock, blockNo, fileID, iv)
+		outBuf.Write(outBlock)
+	}
+	return outBuf.Bytes()
+}
+
+// readBackingFile: read from the backing plaintext file, encrypt it, return the
+// ciphertext.
+// "off" ... ciphertext offset (must be >= HEADER_LEN)
+// "length" ... ciphertext length
+func (rf *reverseFile) readBackingFile(off uint64, length uint64) (out []byte, err error) {
+	blocks := rf.contentEnc.ExplodeCipherRange(off, length)
+
+	// Read the backing plaintext in one go
+	alignedOffset, alignedLength := contentenc.JointPlaintextRange(blocks)
+	plaintext := make([]byte, int(alignedLength))
+	n, err := rf.fd.ReadAt(plaintext, int64(alignedOffset))
+	if err != nil && err != io.EOF {
+		tlog.Warn.Printf("readBackingFile: ReadAt: %s", err.Error())
+		return nil, err
+	}
+	// Truncate buffer down to actually read bytes
+	plaintext = plaintext[0:n]
+
+	// Encrypt blocks
+	ciphertext := rf.encryptBlocks(plaintext, blocks[0].BlockNo, rf.header.ID, rf.block0IV)
+
+	// Crop down to the relevant part
+	lenHave := len(ciphertext)
+	skip := blocks[0].Skip
+	endWant := int(skip + length)
+	if lenHave > endWant {
+		out = ciphertext[skip:endWant]
+	} else if lenHave > int(skip) {
+		out = ciphertext[skip:lenHave]
+	} // else: out stays empty, file was smaller than the requested offset
+
+	return out, nil
+}
+
+// Read - FUSE call
+func (rf *reverseFile) Read(buf []byte, ioff int64) (resultData fuse.ReadResult, status fuse.Status) {
+	length := uint64(len(buf))
+	off := uint64(ioff)
+	var out bytes.Buffer
+	var header []byte
+
+	// Synthesize file header
+	if off < contentenc.HeaderLen {
+		header = rf.header.Pack()
+		// Truncate to requested part
+		end := int(off) + len(buf)
+		if end > len(header) {
+			end = len(header)
+		}
+		header = header[off:end]
+		// Write into output buffer and adjust offsets
+		out.Write(header)
+		hLen := uint64(len(header))
+		off += hLen
+		length -= hLen
+	}
+
+	// Read actual file data
+	if length > 0 {
+		fileData, err := rf.readBackingFile(off, length)
+		if err != nil {
+			return nil, fuse.ToStatus(err)
+		}
+		if len(fileData) == 0 {
+			// If we could not read any actual data, we also don't want to
+			// return the file header. An empty file stays empty in encrypted
+			// form.
+			return nil, fuse.OK
+		}
+		out.Write(fileData)
+	}
+
+	return fuse.ReadResultData(out.Bytes()), fuse.OK
+}
+
+// Release - FUSE call, close file
+func (rf *reverseFile) Release() {
+	rf.fd.Close()
+}
diff --git a/internal/fusefrontend_reverse_v1api/rfs.go b/internal/fusefrontend_reverse_v1api/rfs.go
new file mode 100644
index 0000000..9f7d1f6
--- /dev/null
+++ b/internal/fusefrontend_reverse_v1api/rfs.go
@@ -0,0 +1,472 @@
+package fusefrontend_reverse
+
+import (
+	"fmt"
+	"path/filepath"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/hanwen/go-fuse/v2/fuse"
+	"github.com/hanwen/go-fuse/v2/fuse/nodefs"
+	"github.com/hanwen/go-fuse/v2/fuse/pathfs"
+
+	"github.com/rfjakob/gocryptfs/internal/configfile"
+	"github.com/rfjakob/gocryptfs/internal/contentenc"
+	"github.com/rfjakob/gocryptfs/internal/cryptocore"
+	"github.com/rfjakob/gocryptfs/internal/fusefrontend"
+	"github.com/rfjakob/gocryptfs/internal/inomap"
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+	"github.com/rfjakob/gocryptfs/internal/pathiv"
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+
+	"github.com/sabhiram/go-gitignore"
+)
+
+// ReverseFS implements the pathfs.FileSystem interface and provides an
+// encrypted view of a plaintext directory.
+type ReverseFS struct {
+	// Embed pathfs.defaultFileSystem for a ENOSYS implementation of all methods
+	pathfs.FileSystem
+	// pathfs.loopbackFileSystem, see go-fuse/fuse/pathfs/loopback.go
+	loopbackfs pathfs.FileSystem
+	// Stores configuration arguments
+	args fusefrontend.Args
+	// Filename encryption helper
+	nameTransform nametransform.NameTransformer
+	// Content encryption helper
+	contentEnc *contentenc.ContentEnc
+	// Tests whether a path is excluded (hiden) from the user. Used by -exclude.
+	excluder ignore.IgnoreParser
+	// inoMap translates inode numbers from different devices to unique inode
+	// numbers.
+	inoMap *inomap.InoMap
+}
+
+var _ pathfs.FileSystem = &ReverseFS{}
+
+// NewFS returns an encrypted FUSE overlay filesystem.
+// In this case (reverse mode) the backing directory is plain-text and
+// ReverseFS provides an encrypted view.
+func NewFS(args fusefrontend.Args, c *contentenc.ContentEnc, n nametransform.NameTransformer) *ReverseFS {
+	initLongnameCache()
+	fs := &ReverseFS{
+		// pathfs.defaultFileSystem returns ENOSYS for all operations
+		FileSystem:    pathfs.NewDefaultFileSystem(),
+		loopbackfs:    pathfs.NewLoopbackFileSystem(args.Cipherdir),
+		args:          args,
+		nameTransform: n,
+		contentEnc:    c,
+		inoMap:        inomap.New(),
+	}
+	fs.prepareExcluder(args)
+	return fs
+}
+
+// relDir is identical to filepath.Dir excepts that it returns "" when
+// filepath.Dir would return ".".
+// In the FUSE API, the root directory is called "", and we actually want that.
+func relDir(path string) string {
+	dir := filepath.Dir(path)
+	if dir == "." {
+		return ""
+	}
+	return dir
+}
+
+// getFileInfo returns information on a ciphertext path "relPath":
+// - ftype: file type (as returned by getFileType)
+// - excluded: if the path is excluded
+// - pPath: if it's not a special file, the decrypted path
+// - err: non nil if any error happens
+func (rfs *ReverseFS) getFileInfo(relPath string) (ftype fileType, excluded bool, pPath string, err error) {
+	ftype = rfs.getFileType(relPath)
+	if ftype == typeConfig {
+		excluded, pPath, err = false, "", nil
+		return
+	}
+	if ftype == typeDiriv {
+		parentDir := nametransform.Dir(relPath)
+		_, excluded, _, err = rfs.getFileInfo(parentDir)
+		pPath = ""
+		return
+	}
+	if ftype == typeName {
+		parentDir := nametransform.Dir(relPath)
+		var parentExcluded bool
+		_, parentExcluded, _, err = rfs.getFileInfo(parentDir)
+		if parentExcluded || err != nil {
+			excluded, pPath = parentExcluded, ""
+			return
+		}
+		relPath = nametransform.RemoveLongNameSuffix(relPath)
+	}
+	pPath, err = rfs.decryptPath(relPath)
+	excluded = err == nil && rfs.isExcludedPlain(pPath)
+	return
+}
+
+type fileType int
+
+// Values returned by getFileType
+const (
+	// A regular file/directory/symlink
+	typeRegular fileType = iota
+	// A DirIV (gocryptfs.diriv) file
+	typeDiriv
+	// A gocryptfs.longname.*.name file for a file with a long name
+	typeName
+	// The config file gocryptfs.conf
+	typeConfig
+)
+
+// getFileType returns the type of file (one of the fileType constants above).
+func (rfs *ReverseFS) getFileType(cPath string) fileType {
+	if !rfs.args.PlaintextNames {
+		cName := filepath.Base(cPath)
+		// Is it a gocryptfs.diriv file?
+		if cName == nametransform.DirIVFilename {
+			return typeDiriv
+		}
+		// Is it a gocryptfs.longname.*.name file?
+		if t := nametransform.NameType(cName); t == nametransform.LongNameFilename {
+			return typeName
+		}
+	}
+	if rfs.isTranslatedConfig(cPath) {
+		return typeConfig
+	}
+	return typeRegular
+}
+
+// isTranslatedConfig returns true if the default config file name is in use
+// and the ciphertext path is "gocryptfs.conf".
+// "gocryptfs.conf" then maps to ".gocryptfs.reverse.conf" in the plaintext
+// directory.
+func (rfs *ReverseFS) isTranslatedConfig(relPath string) bool {
+	if rfs.args.ConfigCustom {
+		return false
+	}
+	if relPath == configfile.ConfDefaultName {
+		return true
+	}
+	return false
+}
+
+// GetAttr - FUSE call
+// "relPath" is the relative ciphertext path
+func (rfs *ReverseFS) GetAttr(relPath string, context *fuse.Context) (*fuse.Attr, fuse.Status) {
+	ftype, excluded, pPath, err := rfs.getFileInfo(relPath)
+	if excluded {
+		return nil, fuse.ENOENT
+	}
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	// Handle "gocryptfs.conf"
+	if ftype == typeConfig {
+		absConfPath, _ := rfs.abs(configfile.ConfReverseName, nil)
+		var st syscall.Stat_t
+		err = syscall.Lstat(absConfPath, &st)
+		if err != nil {
+			return nil, fuse.ToStatus(err)
+		}
+		rfs.inoMap.TranslateStat(&st)
+		var a fuse.Attr
+		a.FromStat(&st)
+		if rfs.args.ForceOwner != nil {
+			a.Owner = *rfs.args.ForceOwner
+		}
+		return &a, fuse.OK
+	}
+	// Handle virtual files (gocryptfs.diriv, *.name)
+	var f nodefs.File
+	var status fuse.Status
+	virtual := false
+	if ftype == typeDiriv {
+		virtual = true
+		f, status = rfs.newDirIVFile(relPath)
+	}
+	if ftype == typeName {
+		virtual = true
+		f, status = rfs.newNameFile(relPath)
+	}
+	if virtual {
+		if !status.Ok() {
+			tlog.Warn.Printf("GetAttr %q: newXFile failed: %v\n", relPath, status)
+			return nil, status
+		}
+		var a fuse.Attr
+		status = f.GetAttr(&a)
+		if rfs.args.ForceOwner != nil {
+			a.Owner = *rfs.args.ForceOwner
+		}
+		return &a, status
+	}
+	// Normal file / directory
+	dirfd, name, err := rfs.openBackingDir(pPath)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	// Stat the backing file/dir using Fstatat
+	var st syscall.Stat_t
+	{
+		var st2 unix.Stat_t
+		err = syscallcompat.Fstatat(dirfd, name, &st2, unix.AT_SYMLINK_NOFOLLOW)
+		syscall.Close(dirfd)
+		if err != nil {
+			return nil, fuse.ToStatus(err)
+		}
+		st = syscallcompat.Unix2syscall(st2)
+	}
+	rfs.inoMap.TranslateStat(&st)
+	var a fuse.Attr
+	a.FromStat(&st)
+	// Calculate encrypted file size
+	if a.IsRegular() {
+		a.Size = rfs.contentEnc.PlainSizeToCipherSize(a.Size)
+	} else if a.IsSymlink() {
+		var linkTarget string
+		var readlinkStatus fuse.Status
+
+		linkTarget, readlinkStatus = rfs.Readlink(relPath, context)
+		if !readlinkStatus.Ok() {
+			return nil, readlinkStatus
+		}
+
+		a.Size = uint64(len(linkTarget))
+	}
+	if rfs.args.ForceOwner != nil {
+		a.Owner = *rfs.args.ForceOwner
+	}
+	return &a, fuse.OK
+}
+
+// Access - FUSE call
+func (rfs *ReverseFS) Access(relPath string, mode uint32, context *fuse.Context) fuse.Status {
+	ftype, excluded, pPath, err := rfs.getFileInfo(relPath)
+	if excluded {
+		return fuse.ENOENT
+	}
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	if ftype != typeRegular {
+		// access(2) R_OK flag for checking if the file is readable, always 4 as defined in POSIX.
+		ROK := uint32(0x4)
+		// Virtual files can always be read and never written
+		if mode == ROK || mode == 0 {
+			return fuse.OK
+		}
+		return fuse.EPERM
+	}
+	dirfd, name, err := rfs.openBackingDir(pPath)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	err = syscallcompat.Faccessat(dirfd, name, mode)
+	syscall.Close(dirfd)
+	return fuse.ToStatus(err)
+}
+
+// Open - FUSE call
+func (rfs *ReverseFS) Open(relPath string, flags uint32, context *fuse.Context) (fuseFile nodefs.File, status fuse.Status) {
+	ftype, excluded, pPath, err := rfs.getFileInfo(relPath)
+	if excluded {
+		return nil, fuse.ENOENT
+	}
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	if ftype == typeConfig {
+		return rfs.loopbackfs.Open(configfile.ConfReverseName, flags, context)
+	}
+	if ftype == typeDiriv {
+		return rfs.newDirIVFile(relPath)
+	}
+	if ftype == typeName {
+		return rfs.newNameFile(relPath)
+	}
+	return rfs.newFile(relPath, pPath)
+}
+
+func (rfs *ReverseFS) openDirPlaintextnames(relPath string, entries []fuse.DirEntry) ([]fuse.DirEntry, fuse.Status) {
+	if relPath != "" || rfs.args.ConfigCustom {
+		return entries, fuse.OK
+	}
+	// We are in the root dir and the default config file name
+	// ".gocryptfs.reverse.conf" is used. We map it to "gocryptfs.conf".
+	dupe := -1
+	status := fuse.OK
+	for i := range entries {
+		if entries[i].Name == configfile.ConfReverseName {
+			entries[i].Name = configfile.ConfDefaultName
+		} else if entries[i].Name == configfile.ConfDefaultName {
+			dupe = i
+		}
+	}
+	if dupe >= 0 {
+		// Warn the user loudly: The gocryptfs.conf_NAME_COLLISION file will
+		// throw ENOENT errors that are hard to miss.
+		tlog.Warn.Printf("The file %q is mapped to %q and shadows another file. Please rename %q in directory %q.",
+			configfile.ConfReverseName, configfile.ConfDefaultName, configfile.ConfDefaultName, rfs.args.Cipherdir)
+		entries[dupe].Name = "gocryptfs.conf_NAME_COLLISION_" + fmt.Sprintf("%d", cryptocore.RandUint64())
+	}
+	return entries, status
+}
+
+// OpenDir - FUSE readdir call
+func (rfs *ReverseFS) OpenDir(cipherPath string, context *fuse.Context) ([]fuse.DirEntry, fuse.Status) {
+	ftype, excluded, relPath, err := rfs.getFileInfo(cipherPath)
+	if excluded {
+		return nil, fuse.ENOENT
+	}
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	if ftype != typeRegular {
+		return nil, fuse.ENOTDIR
+	}
+	// Read plaintext dir
+	dirfd, err := syscallcompat.OpenDirNofollow(rfs.args.Cipherdir, filepath.Dir(relPath))
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	fd, err := syscallcompat.Openat(dirfd, filepath.Base(relPath), syscall.O_RDONLY|syscall.O_DIRECTORY|syscall.O_NOFOLLOW, 0)
+	syscall.Close(dirfd)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	entries, err := syscallcompat.Getdents(fd)
+	syscall.Close(fd)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	if rfs.args.PlaintextNames {
+		var status fuse.Status
+		entries, status = rfs.openDirPlaintextnames(cipherPath, entries)
+		if !status.Ok() {
+			return nil, status
+		}
+		entries = rfs.excludeDirEntries(relPath, entries)
+		return entries, fuse.OK
+	}
+	// Filter out excluded entries
+	entries = rfs.excludeDirEntries(relPath, entries)
+	// 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
+	virtualFiles[0] = fuse.DirEntry{
+		Mode: virtualFileMode,
+		Name: nametransform.DirIVFilename,
+	}
+	// Actually used entries
+	nVirtual := 1
+
+	// Encrypt names
+	dirIV := pathiv.Derive(cipherPath, pathiv.PurposeDirIV)
+	for i := range entries {
+		var cName string
+		// ".gocryptfs.reverse.conf" in the root directory is mapped to "gocryptfs.conf"
+		if cipherPath == "" && entries[i].Name == configfile.ConfReverseName &&
+			!rfs.args.ConfigCustom {
+			cName = configfile.ConfDefaultName
+		} else {
+			cName = rfs.nameTransform.EncryptName(entries[i].Name, dirIV)
+			if len(cName) > unix.NAME_MAX {
+				cName = rfs.nameTransform.HashLongName(cName)
+				dotNameFile := fuse.DirEntry{
+					Mode: virtualFileMode,
+					Name: cName + nametransform.LongNameSuffix,
+				}
+				virtualFiles[nVirtual] = dotNameFile
+				nVirtual++
+			}
+		}
+		entries[i].Name = cName
+	}
+	// Add virtual files
+	entries = append(entries, virtualFiles[:nVirtual]...)
+	return entries, fuse.OK
+}
+
+// excludeDirEntries filters out directory entries that are "-exclude"d.
+// pDir is the relative plaintext path to the directory these entries are
+// from. The entries should be plaintext files.
+func (rfs *ReverseFS) excludeDirEntries(pDir string, entries []fuse.DirEntry) (filtered []fuse.DirEntry) {
+	if rfs.excluder == nil {
+		return entries
+	}
+	filtered = make([]fuse.DirEntry, 0, len(entries))
+	for _, entry := range entries {
+		// filepath.Join handles the case of pDir="" correctly:
+		// Join("", "foo") -> "foo". This does not: pDir + "/" + name"
+		p := filepath.Join(pDir, entry.Name)
+		if rfs.isExcludedPlain(p) {
+			// Skip file
+			continue
+		}
+		filtered = append(filtered, entry)
+	}
+	return filtered
+}
+
+// StatFs - FUSE call. Returns information about the filesystem (free space
+// etc).
+// Securing statfs against symlink races seems to be more trouble than
+// it's worth, so we just ignore the path and always return info about the
+// backing storage root dir.
+func (rfs *ReverseFS) StatFs(relPath string) *fuse.StatfsOut {
+	_, excluded, _, err := rfs.getFileInfo(relPath)
+	if excluded || err != nil {
+		return nil
+	}
+	var s syscall.Statfs_t
+	err = syscall.Statfs(rfs.args.Cipherdir, &s)
+	if err != nil {
+		return nil
+	}
+	out := &fuse.StatfsOut{}
+	out.FromStatfsT(&s)
+	return out
+}
+
+// Readlink - FUSE call
+func (rfs *ReverseFS) Readlink(relPath string, context *fuse.Context) (string, fuse.Status) {
+	ftype, excluded, pPath, err := rfs.getFileInfo(relPath)
+	if excluded {
+		return "", fuse.ENOENT
+	}
+	if err != nil {
+		return "", fuse.ToStatus(err)
+	}
+	if ftype != typeRegular {
+		return "", fuse.EINVAL
+	}
+	dirfd, name, err := rfs.openBackingDir(pPath)
+	if err != nil {
+		return "", fuse.ToStatus(err)
+	}
+	// read the link target using Readlinkat
+	plainTarget, err := syscallcompat.Readlinkat(dirfd, name)
+	syscall.Close(dirfd)
+	if err != nil {
+		return "", fuse.ToStatus(err)
+	}
+	if rfs.args.PlaintextNames {
+		return plainTarget, fuse.OK
+	}
+	nonce := pathiv.Derive(relPath, pathiv.PurposeSymlinkIV)
+	// Symlinks are encrypted like file contents and base64-encoded
+	cBinTarget := rfs.contentEnc.EncryptBlockNonce([]byte(plainTarget), 0, nil, nonce)
+	cTarget := rfs.nameTransform.B64EncodeToString(cBinTarget)
+	// The kernel will reject a symlink target above 4096 chars and return
+	// and I/O error to the user. Better emit the proper error ourselves.
+	if len(cTarget) > syscallcompat.PATH_MAX {
+		return "", fuse.Status(syscall.ENAMETOOLONG)
+	}
+	return cTarget, fuse.OK
+}
diff --git a/internal/fusefrontend_reverse_v1api/rfs_test.go b/internal/fusefrontend_reverse_v1api/rfs_test.go
new file mode 100644
index 0000000..eccaab9
--- /dev/null
+++ b/internal/fusefrontend_reverse_v1api/rfs_test.go
@@ -0,0 +1,124 @@
+package fusefrontend_reverse
+
+import (
+	"testing"
+
+	"github.com/rfjakob/gocryptfs/internal/configfile"
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+)
+
+func TestShouldDetectDirIV(t *testing.T) {
+	var rfs ReverseFS
+	ftype := rfs.getFileType("some/path/" + nametransform.DirIVFilename)
+	if ftype != typeDiriv {
+		t.Errorf("Expecting %d, got %d\n", typeDiriv, ftype)
+	}
+}
+
+func TestShouldDetectNameFile(t *testing.T) {
+	var rfs ReverseFS
+	ftype := rfs.getFileType("dir1/dir2/gocryptfs.longname.URrM8kgxTKYMgCk4hKk7RO9Lcfr30XQof4L_5bD9Iro=" + nametransform.LongNameSuffix)
+	if ftype != typeName {
+		t.Errorf("Expecting %d, got %d\n", typeName, ftype)
+	}
+}
+
+func TestShouldDetectConfigFile(t *testing.T) {
+	var rfs ReverseFS
+	ftype := rfs.getFileType(configfile.ConfDefaultName)
+	if ftype != typeConfig {
+		t.Errorf("Expecting %d, got %d\n", typeConfig, ftype)
+	}
+}
+
+func TestShouldDetectRegularFile(t *testing.T) {
+	var rfs ReverseFS
+	ftype := rfs.getFileType("documents/text_file.txt")
+	if ftype != typeRegular {
+		t.Errorf("Expecting %d, got %d\n", typeRegular, ftype)
+	}
+}
+
+// Note: For path exclusion, see also the integration tests in
+// tests/reverse/exclude_test.go
+func TestShouldNotCallIgnoreParserForTranslatedConfig(t *testing.T) {
+	rfs, ignorerMock := createRFSWithMocks()
+
+	ftype, excluded, _, err := rfs.getFileInfo(configfile.ConfDefaultName)
+	if err != nil {
+		t.Errorf("Unexpected error %q\n", err)
+	}
+	if ftype != typeConfig {
+		t.Errorf("Wrong file type, expecting %d, got %d\n", typeConfig, ftype)
+	}
+	if excluded {
+		t.Error("Should not exclude translated config")
+	}
+	if ignorerMock.calledWith != "" {
+		t.Error("Should not call IgnoreParser for translated config")
+	}
+}
+
+func TestShouldCheckIfParentIsExcludedForDirIV(t *testing.T) {
+	rfs, ignorerMock := createRFSWithMocks()
+	path := "dir"
+	ignorerMock.toExclude = "mockdecrypt_dir"
+	dirIV := path + "/" + nametransform.DirIVFilename
+
+	ftype, excluded, _, err := rfs.getFileInfo(dirIV)
+	if err != nil {
+		t.Errorf("Unexpected error %q\n", err)
+	}
+	if ftype != typeDiriv {
+		t.Errorf("Wrong file type, expecting %d, got %d\n", typeDiriv, ftype)
+	}
+	if !excluded {
+		t.Error("Should have excluded DirIV based on parent")
+	}
+	if ignorerMock.calledWith != "mockdecrypt_dir" {
+		t.Errorf("Should have checked parent dir, checked %q", ignorerMock.calledWith)
+	}
+}
+
+func TestShouldCheckIfParentIsExcludedForLongName(t *testing.T) {
+	rfs, ignorerMock := createRFSWithMocks()
+	path := "parent"
+	ignorerMock.toExclude = "mockdecrypt_parent"
+	dirIV := path + "/" + "gocryptfs.longname.fake.name"
+
+	ftype, excluded, _, err := rfs.getFileInfo(dirIV)
+	if err != nil {
+		t.Errorf("Unexpected error %q\n", err)
+	}
+	if ftype != typeName {
+		t.Errorf("Wrong file type, expecting %d, got %d\n", typeName, ftype)
+	}
+	if !excluded {
+		t.Error("Should have excluded LongName based on parent")
+	}
+	if ignorerMock.calledWith != "mockdecrypt_parent" {
+		t.Errorf("Should have checked parent dir, checked %q", ignorerMock.calledWith)
+	}
+}
+
+func TestShouldDecryptPathAndReturnTrueForExcludedPath(t *testing.T) {
+	rfs, ignorerMock := createRFSWithMocks()
+	ignorerMock.toExclude = "mockdecrypt_file.txt"
+
+	ftype, excluded, pPath, err := rfs.getFileInfo("file.txt")
+	if err != nil {
+		t.Errorf("Unexpected error %q\n", err)
+	}
+	if ftype != typeRegular {
+		t.Errorf("Wrong file type, expecting %d, got %d\n", typeRegular, ftype)
+	}
+	if !excluded {
+		t.Error("Should have excluded")
+	}
+	if pPath != "mockdecrypt_file.txt" {
+		t.Errorf("Wrong pPath returned, got %q\n", pPath)
+	}
+	if ignorerMock.calledWith != "mockdecrypt_file.txt" {
+		t.Error("Didn't call IgnoreParser with decrypted path")
+	}
+}
diff --git a/internal/fusefrontend_reverse_v1api/rpath.go b/internal/fusefrontend_reverse_v1api/rpath.go
new file mode 100644
index 0000000..2da8379
--- /dev/null
+++ b/internal/fusefrontend_reverse_v1api/rpath.go
@@ -0,0 +1,113 @@
+package fusefrontend_reverse
+
+import (
+	"encoding/base64"
+	"path/filepath"
+	"strings"
+	"syscall"
+
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+	"github.com/rfjakob/gocryptfs/internal/pathiv"
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+// abs basically returns storage dir + "/" + relPath.
+// It takes an error parameter so it can directly wrap decryptPath like this:
+// a, err := rfs.abs(rfs.decryptPath(relPath))
+// abs never generates an error on its own. In other words, abs(p, nil) never
+// fails.
+func (rfs *ReverseFS) abs(relPath string, err error) (string, error) {
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(rfs.args.Cipherdir, relPath), nil
+}
+
+// rDecryptName decrypts the ciphertext name "cName", given the dirIV of the
+// directory "cName" lies in. The relative plaintext path to the directory
+// "pDir" is used if a "gocryptfs.longname.XYZ.name" must be resolved.
+func (rfs *ReverseFS) rDecryptName(cName string, dirIV []byte, pDir string) (pName string, err error) {
+	nameType := nametransform.NameType(cName)
+	if nameType == nametransform.LongNameNone {
+		pName, err = rfs.nameTransform.DecryptName(cName, dirIV)
+		if err != nil {
+			// We get lots of decrypt requests for names like ".Trash" that
+			// are invalid base64. Convert them to ENOENT so the correct
+			// error gets returned to the user.
+			if _, ok := err.(base64.CorruptInputError); ok {
+				return "", syscall.ENOENT
+			}
+			// Stat attempts on the link target of encrypted symlinks.
+			// These are always valid base64 but the length is not a
+			// multiple of 16.
+			if err == syscall.EBADMSG {
+				return "", syscall.ENOENT
+			}
+			return "", err
+		}
+	} else if nameType == nametransform.LongNameContent {
+		pName, err = rfs.findLongnameParent(pDir, dirIV, cName)
+		if err != nil {
+			return "", err
+		}
+	} else {
+		// It makes no sense to decrypt a ".name" file. This is a virtual file
+		// that has no representation in the plaintext filesystem. ".name"
+		// files should have already been handled in virtualfile.go.
+		tlog.Warn.Printf("rDecryptName: cannot decrypt virtual file %q", cName)
+		return "", syscall.EINVAL
+	}
+	return pName, nil
+}
+
+// decryptPath decrypts a relative ciphertext path to a relative plaintext
+// path.
+func (rfs *ReverseFS) decryptPath(relPath string) (string, error) {
+	if rfs.args.PlaintextNames || relPath == "" {
+		return relPath, nil
+	}
+	// Check if the parent dir is in the cache
+	cDir := nametransform.Dir(relPath)
+	dirIV, pDir := rPathCache.lookup(cDir)
+	if dirIV != nil {
+		cName := filepath.Base(relPath)
+		pName, err := rfs.rDecryptName(cName, dirIV, pDir)
+		if err != nil {
+			return "", err
+		}
+		return filepath.Join(pDir, pName), nil
+	}
+	parts := strings.Split(relPath, "/")
+	var transformedParts []string
+	for i := range parts {
+		// Start at the top and recurse
+		currentCipherDir := filepath.Join(parts[:i]...)
+		currentPlainDir := filepath.Join(transformedParts[:i]...)
+		dirIV = pathiv.Derive(currentCipherDir, pathiv.PurposeDirIV)
+		transformedPart, err := rfs.rDecryptName(parts[i], dirIV, currentPlainDir)
+		if err != nil {
+			return "", err
+		}
+		transformedParts = append(transformedParts, transformedPart)
+	}
+	pRelPath := filepath.Join(transformedParts...)
+	rPathCache.store(cDir, dirIV, nametransform.Dir(pRelPath))
+	return pRelPath, nil
+}
+
+// openBackingDir receives an already decrypted relative path
+// "pRelPath", opens the directory that contains the target file/dir
+// and returns the fd to the directory and the decrypted name of the
+// target file. The fd/name pair is intended for use with fchownat and
+// friends.
+func (rfs *ReverseFS) openBackingDir(pRelPath string) (dirfd int, pName string, err error) {
+	// Open directory, safe against symlink races
+	pDir := filepath.Dir(pRelPath)
+	dirfd, err = syscallcompat.OpenDirNofollow(rfs.args.Cipherdir, pDir)
+	if err != nil {
+		return -1, "", err
+	}
+	pName = filepath.Base(pRelPath)
+	return dirfd, pName, nil
+}
diff --git a/internal/fusefrontend_reverse_v1api/rpath_cache.go b/internal/fusefrontend_reverse_v1api/rpath_cache.go
new file mode 100644
index 0000000..221f578
--- /dev/null
+++ b/internal/fusefrontend_reverse_v1api/rpath_cache.go
@@ -0,0 +1,45 @@
+package fusefrontend_reverse
+
+import (
+	"sync"
+)
+
+// rPathCacheContainer is a simple one entry path cache. Because the dirIV
+// is generated deterministically from the directory path, there is no need
+// to ever invalidate entries.
+type rPathCacheContainer struct {
+	sync.Mutex
+	// Relative ciphertext path to the directory
+	cPath string
+	// Relative plaintext path
+	pPath string
+	// Directory IV of the directory
+	dirIV []byte
+}
+
+// lookup relative ciphertext path "cPath". Returns dirIV, relative
+// plaintext path.
+func (c *rPathCacheContainer) lookup(cPath string) ([]byte, string) {
+	c.Lock()
+	defer c.Unlock()
+	if cPath == c.cPath {
+		// hit
+		return c.dirIV, c.pPath
+	}
+	// miss
+	return nil, ""
+}
+
+// store - write entry for the directory at relative ciphertext path "cPath"
+// into the cache.
+// "dirIV" = directory IV of the directory, "pPath" = relative plaintext path
+func (c *rPathCacheContainer) store(cPath string, dirIV []byte, pPath string) {
+	c.Lock()
+	defer c.Unlock()
+	c.cPath = cPath
+	c.dirIV = dirIV
+	c.pPath = pPath
+}
+
+// rPathCache: see rPathCacheContainer above for a detailed description
+var rPathCache rPathCacheContainer
diff --git a/internal/fusefrontend_reverse_v1api/virtualfile.go b/internal/fusefrontend_reverse_v1api/virtualfile.go
new file mode 100644
index 0000000..f258e7f
--- /dev/null
+++ b/internal/fusefrontend_reverse_v1api/virtualfile.go
@@ -0,0 +1,110 @@
+package fusefrontend_reverse
+
+import (
+	"log"
+	"path/filepath"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/hanwen/go-fuse/v2/fuse"
+	"github.com/hanwen/go-fuse/v2/fuse/nodefs"
+
+	"github.com/rfjakob/gocryptfs/internal/inomap"
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+	"github.com/rfjakob/gocryptfs/internal/pathiv"
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+const (
+	// virtualFileMode is the mode to use for virtual files (gocryptfs.diriv and
+	// *.name). They are always readable, as stated in func Access
+	virtualFileMode = syscall.S_IFREG | 0444
+	// We use inomap's `Tag` feature to generate unique inode numbers for
+	// virtual files. These are the tags we use.
+	inoTagDirIV    = 1
+	inoTagNameFile = 2
+)
+
+func (rfs *ReverseFS) newDirIVFile(cRelPath string) (nodefs.File, fuse.Status) {
+	cDir := nametransform.Dir(cRelPath)
+	dir, err := rfs.decryptPath(cDir)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	iv := pathiv.Derive(cDir, pathiv.PurposeDirIV)
+	return rfs.newVirtualFile(iv, rfs.args.Cipherdir, dir, inoTagDirIV)
+}
+
+type virtualFile struct {
+	// Embed nodefs.defaultFile for a ENOSYS implementation of all methods
+	nodefs.File
+	// pointer to parent filesystem
+	rfs *ReverseFS
+	// file content
+	content []byte
+	// backing directory
+	cipherdir string
+	// path to a parent file (relative to cipherdir)
+	parentFile string
+	// inomap `Tag`.
+	// Depending on the file type, either `inoTagDirIV` or `inoTagNameFile`.
+	inoTag uint8
+}
+
+// newVirtualFile creates a new in-memory file that does not have a representation
+// on disk. "content" is the file content. Timestamps and file owner are copied
+// from "parentFile" (plaintext path relative to "cipherdir").
+// For a "gocryptfs.diriv" file, you would use the parent directory as
+// "parentFile".
+func (rfs *ReverseFS) newVirtualFile(content []byte, cipherdir string, parentFile string, inoTag uint8) (nodefs.File, fuse.Status) {
+	if inoTag == 0 {
+		log.Panicf("BUG: inoTag for virtual file is zero - this will cause ino collisions!")
+	}
+	return &virtualFile{
+		File:       nodefs.NewDefaultFile(),
+		rfs:        rfs,
+		content:    content,
+		cipherdir:  cipherdir,
+		parentFile: parentFile,
+		inoTag:     inoTag,
+	}, fuse.OK
+}
+
+// Read - FUSE call
+func (f *virtualFile) Read(buf []byte, off int64) (resultData fuse.ReadResult, status fuse.Status) {
+	if off >= int64(len(f.content)) {
+		return nil, fuse.OK
+	}
+	end := int(off) + len(buf)
+	if end > len(f.content) {
+		end = len(f.content)
+	}
+	return fuse.ReadResultData(f.content[off:end]), fuse.OK
+}
+
+// GetAttr - FUSE call
+func (f *virtualFile) GetAttr(a *fuse.Attr) fuse.Status {
+	dir := filepath.Dir(f.parentFile)
+	dirfd, err := syscallcompat.OpenDirNofollow(f.cipherdir, dir)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	defer syscall.Close(dirfd)
+	name := filepath.Base(f.parentFile)
+	var st2 unix.Stat_t
+	err = syscallcompat.Fstatat(dirfd, name, &st2, unix.AT_SYMLINK_NOFOLLOW)
+	if err != nil {
+		tlog.Debug.Printf("GetAttr: Fstatat %q: %v\n", f.parentFile, err)
+		return fuse.ToStatus(err)
+	}
+	st := syscallcompat.Unix2syscall(st2)
+	q := inomap.NewQIno(uint64(st.Dev), f.inoTag, uint64(st.Ino))
+	st.Ino = f.rfs.inoMap.Translate(q)
+	st.Size = int64(len(f.content))
+	st.Mode = virtualFileMode
+	st.Nlink = 1
+	a.FromStat(&st)
+	return fuse.OK
+}