From 6d4f1a6888cafd218cb97bd11de6a7553d9bc8f1 Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher
Date: Sun, 9 Aug 2020 22:11:46 +0200
Subject: v2api/reverse: implement Read

---
 internal/fusefrontend_reverse/file.go           |  70 ++++++++++++++
 internal/fusefrontend_reverse/file_api_check.go |  23 +++++
 internal/fusefrontend_reverse/file_helpers.go   |  62 +++++++++++++
 internal/fusefrontend_reverse/node.go           |  86 +++++++++++++++--
 internal/fusefrontend_reverse/node_api_check.go |   6 +-
 internal/fusefrontend_reverse/node_helpers.go   |  33 ++++++-
 internal/fusefrontend_reverse/virtualconf.go    |  55 +++++++++++
 internal/fusefrontend_reverse/virtualfile.go    | 115 -----------------------
 internal/fusefrontend_reverse/virtualnode.go    | 117 ++++++++++++++++++++++++
 9 files changed, 435 insertions(+), 132 deletions(-)
 create mode 100644 internal/fusefrontend_reverse/file.go
 create mode 100644 internal/fusefrontend_reverse/file_api_check.go
 create mode 100644 internal/fusefrontend_reverse/file_helpers.go
 create mode 100644 internal/fusefrontend_reverse/virtualconf.go
 delete mode 100644 internal/fusefrontend_reverse/virtualfile.go
 create mode 100644 internal/fusefrontend_reverse/virtualnode.go

diff --git a/internal/fusefrontend_reverse/file.go b/internal/fusefrontend_reverse/file.go
new file mode 100644
index 0000000..55f5f80
--- /dev/null
+++ b/internal/fusefrontend_reverse/file.go
@@ -0,0 +1,70 @@
+package fusefrontend_reverse
+
+import (
+	"bytes"
+	"context"
+	"os"
+	"syscall"
+
+	"github.com/hanwen/go-fuse/v2/fs"
+	"github.com/hanwen/go-fuse/v2/fuse"
+
+	"github.com/rfjakob/gocryptfs/internal/contentenc"
+)
+
+type File struct {
+	// 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
+}
+
+// Read - FUSE call
+func (f *File) Read(ctx context.Context, buf []byte, ioff int64) (resultData fuse.ReadResult, errno syscall.Errno) {
+	length := uint64(len(buf))
+	off := uint64(ioff)
+	out := bytes.NewBuffer(buf[:0])
+	var header []byte
+
+	// Synthesize file header
+	if off < contentenc.HeaderLen {
+		header = f.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 := f.readBackingFile(off, length)
+		if err != nil {
+			return nil, fs.ToErrno(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, 0
+		}
+		out.Write(fileData)
+	}
+
+	return fuse.ReadResultData(out.Bytes()), 0
+}
+
+// Release - FUSE call, close file
+func (f *File) Release(context.Context) syscall.Errno {
+	return fs.ToErrno(f.fd.Close())
+}
diff --git a/internal/fusefrontend_reverse/file_api_check.go b/internal/fusefrontend_reverse/file_api_check.go
new file mode 100644
index 0000000..6dd1771
--- /dev/null
+++ b/internal/fusefrontend_reverse/file_api_check.go
@@ -0,0 +1,23 @@
+package fusefrontend_reverse
+
+import (
+	"github.com/hanwen/go-fuse/v2/fs"
+)
+
+// Check that we have implemented the fs.File* interfaces
+var _ = (fs.FileReader)((*File)(nil))
+var _ = (fs.FileReleaser)((*File)(nil))
+
+/* TODO
+var _ = (fs.FileGetattrer)((*File2)(nil))
+var _ = (fs.FileSetattrer)((*File2)(nil))
+var _ = (fs.FileWriter)((*File2)(nil))
+var _ = (fs.FileFsyncer)((*File2)(nil))
+var _ = (fs.FileFlusher)((*File2)(nil))
+var _ = (fs.FileAllocater)((*File2)(nil))
+var _ = (fs.FileLseeker)((*File2)(nil))
+var _ = (fs.FileHandle)((*File2)(nil))
+var _ = (fs.FileGetlker)((*File2)(nil))
+var _ = (fs.FileSetlker)((*File2)(nil))
+var _ = (fs.FileSetlkwer)((*File2)(nil))
+*/
diff --git a/internal/fusefrontend_reverse/file_helpers.go b/internal/fusefrontend_reverse/file_helpers.go
new file mode 100644
index 0000000..f024e69
--- /dev/null
+++ b/internal/fusefrontend_reverse/file_helpers.go
@@ -0,0 +1,62 @@
+package fusefrontend_reverse
+
+import (
+	"bytes"
+	"io"
+	"sync"
+
+	"github.com/rfjakob/gocryptfs/internal/contentenc"
+	"github.com/rfjakob/gocryptfs/internal/pathiv"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+var inodeTable sync.Map
+
+// encryptBlocks - encrypt "plaintext" into a number of ciphertext blocks.
+// "plaintext" must already be block-aligned.
+func (rf *File) 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 (f *File) readBackingFile(off uint64, length uint64) (out []byte, err error) {
+	blocks := f.contentEnc.ExplodeCipherRange(off, length)
+
+	// Read the backing plaintext in one go
+	alignedOffset, alignedLength := contentenc.JointPlaintextRange(blocks)
+	plaintext := make([]byte, int(alignedLength))
+	n, err := f.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 := f.encryptBlocks(plaintext, blocks[0].BlockNo, f.header.ID, f.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
+}
diff --git a/internal/fusefrontend_reverse/node.go b/internal/fusefrontend_reverse/node.go
index 884a97e..deaf953 100644
--- a/internal/fusefrontend_reverse/node.go
+++ b/internal/fusefrontend_reverse/node.go
@@ -2,6 +2,8 @@ package fusefrontend_reverse
 
 import (
 	"context"
+	"fmt"
+	"os"
 	"path/filepath"
 	"syscall"
 
@@ -10,8 +12,10 @@ import (
 	"github.com/hanwen/go-fuse/v2/fs"
 	"github.com/hanwen/go-fuse/v2/fuse"
 
-	"github.com/rfjakob/gocryptfs/internal/configfile"
+	"github.com/rfjakob/gocryptfs/internal/contentenc"
+	"github.com/rfjakob/gocryptfs/internal/pathiv"
 	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
 )
 
 // Node is a file or directory in the filesystem tree
@@ -33,15 +37,7 @@ func (n *Node) Lookup(ctx context.Context, cName string, out *fuse.EntryOut) (ch
 		return n.lookupLongnameName(ctx, cName, out)
 	} else if t == typeConfig {
 		// gocryptfs.conf
-		var err error
-		pName = configfile.ConfReverseName
-		rn := n.rootNode()
-		dirfd, err = syscallcompat.OpenDirNofollow(rn.args.Cipherdir, "")
-		if err != nil {
-			errno = fs.ToErrno(err)
-			return
-		}
-		defer syscall.Close(dirfd)
+		return n.lookupConf(ctx, out)
 	} else if t == typeReal {
 		// real file
 		dirfd, pName, errno = n.prepareAtSyscall(cName)
@@ -112,3 +108,73 @@ func (n *Node) Readlink(ctx context.Context) (out []byte, errno syscall.Errno) {
 	cName := filepath.Base(n.Path())
 	return n.readlink(dirfd, cName, pName)
 }
+
+// Open - FUSE call. Open already-existing file.
+//
+// Symlink-safe through Openat().
+func (n *Node) Open(ctx context.Context, flags uint32) (fh fs.FileHandle, fuseFlags uint32, errno syscall.Errno) {
+	dirfd, pName, errno := n.prepareAtSyscall("")
+	if errno != 0 {
+		return
+	}
+	defer syscall.Close(dirfd)
+
+	fd, err := syscallcompat.Openat(dirfd, pName, syscall.O_RDONLY|syscall.O_NOFOLLOW, 0)
+	if err != nil {
+		errno = fs.ToErrno(err)
+		return
+	}
+
+	// Reject access if the file descriptor does not refer to a regular file.
+	var st syscall.Stat_t
+	err = syscall.Fstat(fd, &st)
+	if err != nil {
+		tlog.Warn.Printf("Open: Fstat error: %v", err)
+		syscall.Close(fd)
+		errno = fs.ToErrno(err)
+		return
+	}
+	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)
+		errno = syscall.EACCES
+		return
+	}
+	// 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 {
+		p := n.Path()
+		derivedIVs = pathiv.DeriveFile(p)
+		// 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,
+	}
+	fh = &File{
+		fd:         os.NewFile(uintptr(fd), fmt.Sprintf("fd%d", fd)),
+		header:     header,
+		block0IV:   derivedIVs.Block0IV,
+		contentEnc: n.rootNode().contentEnc,
+	}
+	return
+}
diff --git a/internal/fusefrontend_reverse/node_api_check.go b/internal/fusefrontend_reverse/node_api_check.go
index e926fc3..875c9b9 100644
--- a/internal/fusefrontend_reverse/node_api_check.go
+++ b/internal/fusefrontend_reverse/node_api_check.go
@@ -9,11 +9,10 @@ var _ = (fs.NodeGetattrer)((*Node)(nil))
 var _ = (fs.NodeLookuper)((*Node)(nil))
 var _ = (fs.NodeReaddirer)((*Node)(nil))
 var _ = (fs.NodeReadlinker)((*Node)(nil))
-
-/* TODO
 var _ = (fs.NodeOpener)((*Node)(nil))
+
+/*
 var _ = (fs.NodeStatfser)((*Node)(nil))
-var _ = (fs.NodeMknoder)((*Node)(nil))
 var _ = (fs.NodeGetxattrer)((*Node)(nil))
 var _ = (fs.NodeListxattrer)((*Node)(nil))
 */
@@ -23,6 +22,7 @@ var _ = (fs.NodeOpendirer)((*Node)(nil))
 */
 
 /* Will not implement these - reverse mode is read-only!
+var _ = (fs.NodeMknoder)((*Node)(nil))
 var _ = (fs.NodeCreater)((*Node)(nil))
 var _ = (fs.NodeMkdirer)((*Node)(nil))
 var _ = (fs.NodeRmdirer)((*Node)(nil))
diff --git a/internal/fusefrontend_reverse/node_helpers.go b/internal/fusefrontend_reverse/node_helpers.go
index 7669a17..fd0abfc 100644
--- a/internal/fusefrontend_reverse/node_helpers.go
+++ b/internal/fusefrontend_reverse/node_helpers.go
@@ -10,6 +10,7 @@ import (
 	"github.com/hanwen/go-fuse/v2/fs"
 	"github.com/hanwen/go-fuse/v2/fuse"
 
+	"github.com/rfjakob/gocryptfs/internal/configfile"
 	"github.com/rfjakob/gocryptfs/internal/pathiv"
 	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
 )
@@ -115,8 +116,8 @@ func (n *Node) lookupLongnameName(ctx context.Context, nameFile string, out *fus
 		errno = fs.ToErrno(err)
 		return
 	}
-	var vf *virtualFile
-	vf, errno = n.newVirtualFile([]byte(cFullname), st, inoTagNameFile)
+	var vf *VirtualMemNode
+	vf, errno = n.newVirtualMemNode([]byte(cFullname), st, inoTagNameFile)
 	if errno != 0 {
 		return nil, errno
 	}
@@ -141,8 +142,8 @@ func (n *Node) lookupDiriv(ctx context.Context, out *fuse.EntryOut) (ch *fs.Inod
 		return
 	}
 	content := pathiv.Derive(n.Path(), pathiv.PurposeDirIV)
-	var vf *virtualFile
-	vf, errno = n.newVirtualFile(content, st, inoTagDirIV)
+	var vf *VirtualMemNode
+	vf, errno = n.newVirtualMemNode(content, st, inoTagDirIV)
 	if errno != 0 {
 		return nil, errno
 	}
@@ -153,6 +154,30 @@ func (n *Node) lookupDiriv(ctx context.Context, out *fuse.EntryOut) (ch *fs.Inod
 	return
 }
 
+// lookupConf returns a new Inode for the gocryptfs.conf file
+func (n *Node) lookupConf(ctx context.Context, out *fuse.EntryOut) (ch *fs.Inode, errno syscall.Errno) {
+	rn := n.rootNode()
+	p := filepath.Join(rn.args.Cipherdir, configfile.ConfReverseName)
+	var st syscall.Stat_t
+	err := syscall.Stat(p, &st)
+	if err != nil {
+		errno = fs.ToErrno(err)
+		return
+	}
+	// Get unique inode number
+	rn.inoMap.TranslateStat(&st)
+	out.Attr.FromStat(&st)
+	// Create child node
+	id := fs.StableAttr{
+		Mode: uint32(st.Mode),
+		Gen:  1,
+		Ino:  st.Ino,
+	}
+	node := &VirtualConfNode{path: p}
+	ch = n.NewInode(ctx, node, id)
+	return
+}
+
 // readlink reads and encrypts a symlink. Used by Readlink, Getattr, Lookup.
 func (n *Node) readlink(dirfd int, cName string, pName string) (out []byte, errno syscall.Errno) {
 	plainTarget, err := syscallcompat.Readlinkat(dirfd, pName)
diff --git a/internal/fusefrontend_reverse/virtualconf.go b/internal/fusefrontend_reverse/virtualconf.go
new file mode 100644
index 0000000..8620f6d
--- /dev/null
+++ b/internal/fusefrontend_reverse/virtualconf.go
@@ -0,0 +1,55 @@
+package fusefrontend_reverse
+
+import (
+	"context"
+	"sync"
+	"syscall"
+
+	"github.com/hanwen/go-fuse/v2/fs"
+	"github.com/hanwen/go-fuse/v2/fuse"
+)
+
+var _ = (fs.NodeOpener)((*VirtualConfNode)(nil))
+
+type VirtualConfNode struct {
+	fs.Inode
+
+	path string
+}
+
+func (n *VirtualConfNode) Open(ctx context.Context, flags uint32) (fh fs.FileHandle, fuseFlags uint32, errno syscall.Errno) {
+	fd, err := syscall.Open(n.path, syscall.O_RDONLY, 0)
+	if err != nil {
+		errno = fs.ToErrno(err)
+		return
+	}
+	fh = &VirtualConfFile{fd: fd}
+	return
+}
+
+// Check that we have implemented the fs.File* interfaces
+var _ = (fs.FileReader)((*VirtualConfFile)(nil))
+var _ = (fs.FileReleaser)((*VirtualConfFile)(nil))
+
+type VirtualConfFile struct {
+	mu sync.Mutex
+	fd int
+}
+
+func (f *VirtualConfFile) Read(ctx context.Context, buf []byte, off int64) (res fuse.ReadResult, errno syscall.Errno) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	res = fuse.ReadResultFd(uintptr(f.fd), off, len(buf))
+	return
+}
+
+func (f *VirtualConfFile) Release(ctx context.Context) syscall.Errno {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	if f.fd != -1 {
+		err := syscall.Close(f.fd)
+		f.fd = -1
+		return fs.ToErrno(err)
+	}
+	return syscall.EBADF
+}
diff --git a/internal/fusefrontend_reverse/virtualfile.go b/internal/fusefrontend_reverse/virtualfile.go
deleted file mode 100644
index a7f6913..0000000
--- a/internal/fusefrontend_reverse/virtualfile.go
+++ /dev/null
@@ -1,115 +0,0 @@
-package fusefrontend_reverse
-
-import (
-	"context"
-	"log"
-	"syscall"
-
-	"github.com/hanwen/go-fuse/v2/fs"
-	"github.com/hanwen/go-fuse/v2/fuse"
-
-	"github.com/rfjakob/gocryptfs/internal/configfile"
-	"github.com/rfjakob/gocryptfs/internal/inomap"
-	"github.com/rfjakob/gocryptfs/internal/nametransform"
-)
-
-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
-)
-
-type fileType int
-
-// Values returned by lookupFileType
-const (
-	// A real file/directory/symlink in the backing plaintext directory
-	typeReal 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
-)
-
-// lookupFileType returns the type of child file name
-// (one of the fileType constants above). Called from Lookup().
-func (n *Node) lookupFileType(cName string) fileType {
-	rn := n.rootNode()
-	// In -plaintextname mode, neither diriv nor longname files exist.
-	if !rn.args.PlaintextNames {
-		// 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
-		}
-	}
-	// gocryptfs.conf in the root directory. This is passed through to
-	// .gocryptfs.reverse.conf in the backing plaintext directory.
-	if n.isRoot() && !rn.args.ConfigCustom && cName == configfile.ConfDefaultName {
-		return typeConfig
-	}
-	return typeReal
-}
-
-type virtualFile struct {
-	fs.Inode
-
-	// file content
-	content []byte
-	// attributes for Getattr()
-	attr fuse.Attr
-}
-
-// 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" (file descriptor).
-// For a "gocryptfs.diriv" file, you would use the parent directory as
-// "parentFile".
-func (n *Node) newVirtualFile(content []byte, parentStat *syscall.Stat_t, inoTag uint8) (vf *virtualFile, errno syscall.Errno) {
-	if inoTag == 0 {
-		log.Panicf("BUG: inoTag for virtual file is zero - this will cause ino collisions!")
-	}
-
-	// Adjust inode number and size
-	rn := n.rootNode()
-	st := parentStat
-	q := inomap.NewQIno(uint64(st.Dev), inoTag, uint64(st.Ino))
-	st.Ino = rn.inoMap.Translate(q)
-	st.Size = int64(len(content))
-	st.Mode = virtualFileMode
-	st.Nlink = 1
-	var a fuse.Attr
-	a.FromStat(st)
-
-	vf = &virtualFile{content: content, attr: a}
-	return
-}
-
-// Open - FUSE call
-func (f *virtualFile) Open(ctx context.Context, flags uint32) (fh fs.FileHandle, fuseFlags uint32, errno syscall.Errno) {
-	return nil, fuse.FOPEN_KEEP_CACHE, 0
-}
-
-// GetAttr - FUSE call
-func (f *virtualFile) Getattr(ctx context.Context, fh fs.FileHandle, out *fuse.AttrOut) syscall.Errno {
-	out.Attr = f.attr
-	return 0
-}
-
-// Read - FUSE call
-func (f *virtualFile) Read(ctx context.Context, fh fs.FileHandle, dest []byte, off int64) (fuse.ReadResult, syscall.Errno) {
-	end := int(off) + len(dest)
-	if end > len(f.content) {
-		end = len(f.content)
-	}
-	return fuse.ReadResultData(f.content[off:end]), 0
-}
diff --git a/internal/fusefrontend_reverse/virtualnode.go b/internal/fusefrontend_reverse/virtualnode.go
new file mode 100644
index 0000000..2ee9548
--- /dev/null
+++ b/internal/fusefrontend_reverse/virtualnode.go
@@ -0,0 +1,117 @@
+package fusefrontend_reverse
+
+import (
+	"context"
+	"log"
+	"syscall"
+
+	"github.com/hanwen/go-fuse/v2/fs"
+	"github.com/hanwen/go-fuse/v2/fuse"
+
+	"github.com/rfjakob/gocryptfs/internal/configfile"
+	"github.com/rfjakob/gocryptfs/internal/inomap"
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+)
+
+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
+)
+
+type fileType int
+
+// Values returned by lookupFileType
+const (
+	// A real file/directory/symlink in the backing plaintext directory
+	typeReal 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
+)
+
+// lookupFileType returns the type of child file name
+// (one of the fileType constants above). Called from Lookup().
+func (n *Node) lookupFileType(cName string) fileType {
+	rn := n.rootNode()
+	// In -plaintextname mode, neither diriv nor longname files exist.
+	if !rn.args.PlaintextNames {
+		// 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
+		}
+	}
+	// gocryptfs.conf in the root directory. This is passed through to
+	// .gocryptfs.reverse.conf in the backing plaintext directory.
+	if n.isRoot() && !rn.args.ConfigCustom && cName == configfile.ConfDefaultName {
+		return typeConfig
+	}
+	return typeReal
+}
+
+// VirtualMemNode is an in-memory node that does not have a representation
+// on disk.
+type VirtualMemNode struct {
+	fs.Inode
+
+	// file content
+	content []byte
+	// attributes for Getattr()
+	attr fuse.Attr
+}
+
+// newVirtualMemNode 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" (file descriptor).
+// For a "gocryptfs.diriv" file, you would use the parent directory as
+// "parentFile".
+func (n *Node) newVirtualMemNode(content []byte, parentStat *syscall.Stat_t, inoTag uint8) (vf *VirtualMemNode, errno syscall.Errno) {
+	if inoTag == 0 {
+		log.Panicf("BUG: inoTag for virtual file is zero - this will cause ino collisions!")
+	}
+
+	// Adjust inode number and size
+	rn := n.rootNode()
+	st := parentStat
+	q := inomap.NewQIno(uint64(st.Dev), inoTag, uint64(st.Ino))
+	st.Ino = rn.inoMap.Translate(q)
+	st.Size = int64(len(content))
+	st.Mode = virtualFileMode
+	st.Nlink = 1
+	var a fuse.Attr
+	a.FromStat(st)
+
+	vf = &VirtualMemNode{content: content, attr: a}
+	return
+}
+
+// Open - FUSE call
+func (f *VirtualMemNode) Open(ctx context.Context, flags uint32) (fh fs.FileHandle, fuseFlags uint32, errno syscall.Errno) {
+	return nil, fuse.FOPEN_KEEP_CACHE, 0
+}
+
+// GetAttr - FUSE call
+func (f *VirtualMemNode) Getattr(ctx context.Context, fh fs.FileHandle, out *fuse.AttrOut) syscall.Errno {
+	out.Attr = f.attr
+	return 0
+}
+
+// Read - FUSE call
+func (f *VirtualMemNode) Read(ctx context.Context, fh fs.FileHandle, dest []byte, off int64) (fuse.ReadResult, syscall.Errno) {
+	end := int(off) + len(dest)
+	if end > len(f.content) {
+		end = len(f.content)
+	}
+	return fuse.ReadResultData(f.content[off:end]), 0
+}
-- 
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