fusefrontend: get the file ID from the open files table

This fixes the problem that a truncate can reset the file
ID without the other open FDs noticing it.

internal/fusefrontend/file.go

@@ -40,11 +40,11 @@ type file struct {
 	contentEnc *contentenc.ContentEnc
 	// Device and inode number uniquely identify the backing file
 	devIno DevInoStruct
-	// File header
-	header *contentenc.FileHeader
+	// Entry in the open file map
+	fileTableEntry *openFileEntryT
 	// go-fuse nodefs.loopbackFile
 	loopbackFile nodefs.File
-	// Store what the last byte was written
+	// Store where the last byte was written
 	lastWrittenOffset int64
 	// The opCount is used to judge whether "lastWrittenOffset" is still
 	// guaranteed to be correct.
@@ -60,14 +60,15 @@ func NewFile(fd *os.File, writeOnly bool, contentEnc *contentenc.ContentEnc) (no
 		return nil, fuse.ToStatus(err)
 	}
 	di := DevInoFromStat(&st)
-	wlock.register(di)
+	t := openFileMap.register(di)
 
 	return &file{
-		fd:           fd,
-		writeOnly:    writeOnly,
-		contentEnc:   contentEnc,
-		devIno:       di,
-		loopbackFile: nodefs.NewLoopbackFile(fd),
+		fd:             fd,
+		writeOnly:      writeOnly,
+		contentEnc:     contentEnc,
+		devIno:         di,
+		fileTableEntry: t,
+		loopbackFile:   nodefs.NewLoopbackFile(fd),
 	}, fuse.OK
 }
 
@@ -84,44 +85,39 @@ func (f *file) InnerFile() nodefs.File {
 func (f *file) SetInode(n *nodefs.Inode) {
 }
 
-// readHeader - load the file header from disk
-//
-// Returns io.EOF if the file is empty
-func (f *file) readHeader() error {
+// readFileID loads the file header from disk and extracts the file ID.
+// Returns io.EOF if the file is empty.
+func (f *file) readFileID() ([]byte, error) {
 	buf := make([]byte, contentenc.HeaderLen)
 	_, err := f.fd.ReadAt(buf, 0)
 	if err != nil {
-		return err
+		return nil, err
 	}
 	h, err := contentenc.ParseHeader(buf)
 	if err != nil {
-		return err
+		return nil, err
 	}
-	f.header = h
-
-	return nil
+	return h.ID, nil
 }
 
-// createHeader - create a new random header and write it to disk
-func (f *file) createHeader() error {
+// createHeader creates a new random header and writes it to disk.
+// Returns the new file ID.
+// The caller must hold fileIDLock.Lock().
+func (f *file) createHeader() (fileID []byte, err error) {
 	h := contentenc.RandomHeader()
 	buf := h.Pack()
-
 	// Prevent partially written (=corrupt) header by preallocating the space beforehand
-	err := syscallcompat.EnospcPrealloc(int(f.fd.Fd()), 0, contentenc.HeaderLen)
+	err = syscallcompat.EnospcPrealloc(int(f.fd.Fd()), 0, contentenc.HeaderLen)
 	if err != nil {
 		tlog.Warn.Printf("ino%d: createHeader: prealloc failed: %s\n", f.devIno.ino, err.Error())
-		return err
+		return nil, err
 	}
-
 	// Actually write header
 	_, err = f.fd.WriteAt(buf, 0)
 	if err != nil {
-		return err
+		return nil, err
 	}
-	f.header = h
-
-	return nil
+	return h.ID, err
 }
 
 func (f *file) String() string {
@@ -137,25 +133,39 @@ func (f *file) String() string {
 // Called by Read() for normal reading,
 // by Write() and Truncate() for Read-Modify-Write
 func (f *file) doRead(off uint64, length uint64) ([]byte, fuse.Status) {
-
-	// Read file header
-	if f.header == nil {
-		err := f.readHeader()
+	// Make sure we have the file ID.
+	f.fileTableEntry.IDLock.RLock()
+	if f.fileTableEntry.ID == nil {
+		f.fileTableEntry.IDLock.RUnlock()
+		// Yes, somebody else may take the lock before we can. This will get
+		// the header read twice, but causes no harm otherwise.
+		f.fileTableEntry.IDLock.Lock()
+		tmpID, err := f.readFileID()
 		if err == io.EOF {
+			f.fileTableEntry.IDLock.Unlock()
 			return nil, fuse.OK
 		}
 		if err != nil {
+			f.fileTableEntry.IDLock.Unlock()
 			return nil, fuse.ToStatus(err)
 		}
+		f.fileTableEntry.ID = tmpID
+		// Downgrade the lock.
+		f.fileTableEntry.IDLock.Unlock()
+		// The file ID may change in here. This does no harm because we
+		// re-read it after the RLock().
+		f.fileTableEntry.IDLock.RLock()
 	}
-
+	fileID := f.fileTableEntry.ID
 	// Read the backing ciphertext in one go
 	blocks := f.contentEnc.ExplodePlainRange(off, length)
 	alignedOffset, alignedLength := blocks[0].JointCiphertextRange(blocks)
 	skip := blocks[0].Skip
 	tlog.Debug.Printf("JointCiphertextRange(%d, %d) -> %d, %d, %d", off, length, alignedOffset, alignedLength, skip)
 	ciphertext := make([]byte, int(alignedLength))
 	n, err := f.fd.ReadAt(ciphertext, int64(alignedOffset))
+	// We don't care if the file ID changes after we have read the data. Drop the lock.
+	f.fileTableEntry.IDLock.RUnlock()
 	if err != nil && err != io.EOF {
 		tlog.Warn.Printf("read: ReadAt: %s", err.Error())
 		return nil, fuse.ToStatus(err)
@@ -167,7 +177,7 @@ func (f *file) doRead(off uint64, length uint64) ([]byte, fuse.Status) {
 	tlog.Debug.Printf("ReadAt offset=%d bytes (%d blocks), want=%d, got=%d", alignedOffset, firstBlockNo, alignedLength, n)
 
 	// Decrypt it
-	plaintext, err := f.contentEnc.DecryptBlocks(ciphertext, firstBlockNo, f.header.ID)
+	plaintext, err := f.contentEnc.DecryptBlocks(ciphertext, firstBlockNo, fileID)
 	if err != nil {
 		curruptBlockNo := firstBlockNo + f.contentEnc.PlainOffToBlockNo(uint64(len(plaintext)))
 		tlog.Warn.Printf("ino%d: doRead: corrupt block #%d: %v", f.devIno.ino, curruptBlockNo, err)
@@ -223,18 +233,28 @@ func (f *file) Read(buf []byte, off int64) (resultData fuse.ReadResult, code fus
 //
 // Empty writes do nothing and are allowed.
 func (f *file) doWrite(data []byte, off int64) (uint32, fuse.Status) {
-
 	// Read header from disk, create a new one if the file is empty
-	if f.header == nil {
-		err := f.readHeader()
+	f.fileTableEntry.IDLock.RLock()
+	if f.fileTableEntry.ID == nil {
+		f.fileTableEntry.IDLock.RUnlock()
+		// Somebody else may write the header here, but this would do no harm.
+		f.fileTableEntry.IDLock.Lock()
+		tmpID, err := f.readFileID()
 		if err == io.EOF {
-			err = f.createHeader()
-
+			tmpID, err = f.createHeader()
 		}
 		if err != nil {
+			f.fileTableEntry.IDLock.Unlock()
 			return 0, fuse.ToStatus(err)
 		}
+		f.fileTableEntry.ID = tmpID
+		f.fileTableEntry.IDLock.Unlock()
+		// The file ID may change in here. This does no harm because we
+		// re-read it after the RLock().
+		f.fileTableEntry.IDLock.RLock()
 	}
+	fileID := f.fileTableEntry.ID
+	defer f.fileTableEntry.IDLock.RUnlock()
 
 	var written uint32
 	status := fuse.OK
@@ -261,7 +281,7 @@ func (f *file) doWrite(data []byte, off int64) (uint32, fuse.Status) {
 
 		// Encrypt
 		blockOffset := b.BlockCipherOff()
-		blockData = f.contentEnc.EncryptBlock(blockData, b.BlockNo, f.header.ID)
+		blockData = f.contentEnc.EncryptBlock(blockData, b.BlockNo, fileID)
 		tlog.Debug.Printf("ino%d: Writing %d bytes to block #%d",
 			f.devIno.ino, uint64(len(blockData))-f.contentEnc.BlockOverhead(), b.BlockNo)
 
@@ -292,7 +312,7 @@ func (f *file) doWrite(data []byte, off int64) (uint32, fuse.Status) {
 // Stat() call is very expensive.
 // The caller must "wlock.lock(f.devIno.ino)" otherwise this check would be racy.
 func (f *file) isConsecutiveWrite(off int64) bool {
-	opCount := atomic.LoadUint64(&wlock.opCount)
+	opCount := atomic.LoadUint64(&openFileMap.opCount)
 	return opCount == f.lastOpCount+1 && off == f.lastWrittenOffset+1
 }
 
@@ -309,8 +329,8 @@ func (f *file) Write(data []byte, off int64) (uint32, fuse.Status) {
 		tlog.Warn.Printf("ino%d fh%d: Write on released file", f.devIno.ino, f.intFd())
 		return 0, fuse.EBADF
 	}
-	wlock.lock(f.devIno)
-	defer wlock.unlock(f.devIno)
+	f.fileTableEntry.writeLock.Lock()
+	defer f.fileTableEntry.writeLock.Unlock()
 	tlog.Debug.Printf("ino%d: FUSE Write: offset=%d length=%d", f.devIno.ino, off, len(data))
 	// If the write creates a file hole, we have to zero-pad the last block.
 	// But if the write directly follows an earlier write, it cannot create a
@@ -323,7 +343,7 @@ func (f *file) Write(data []byte, off int64) (uint32, fuse.Status) {
 	}
 	n, status := f.doWrite(data, off)
 	if status.Ok() {
-		f.lastOpCount = atomic.LoadUint64(&wlock.opCount)
+		f.lastOpCount = atomic.LoadUint64(&openFileMap.opCount)
 		f.lastWrittenOffset = off + int64(len(data)) - 1
 	}
 	return n, status
@@ -339,7 +359,7 @@ func (f *file) Release() {
 	f.released = true
 	f.fdLock.Unlock()
 
-	wlock.unregister(f.devIno)
+	openFileMap.unregister(f.devIno)
 }
 
 // Flush - FUSE call

internal/fusefrontend/file_allocate_truncate.go

@@ -50,8 +50,8 @@ func (f *file) Allocate(off uint64, sz uint64, mode uint32) fuse.Status {
 	if f.released {
 		return fuse.EBADF
 	}
-	wlock.lock(f.devIno)
-	defer wlock.unlock(f.devIno)
+	f.fileTableEntry.writeLock.Lock()
+	defer f.fileTableEntry.writeLock.Unlock()
 
 	blocks := f.contentEnc.ExplodePlainRange(off, sz)
 	firstBlock := blocks[0]
@@ -100,8 +100,8 @@ func (f *file) Truncate(newSize uint64) fuse.Status {
 		tlog.Warn.Printf("ino%d fh%d: Truncate on released file", f.devIno.ino, f.intFd())
 		return fuse.EBADF
 	}
-	wlock.lock(f.devIno)
-	defer wlock.unlock(f.devIno)
+	f.fileTableEntry.writeLock.Lock()
+	defer f.fileTableEntry.writeLock.Unlock()
 	var err error
 	// Common case first: Truncate to zero
 	if newSize == 0 {
@@ -111,7 +111,9 @@ func (f *file) Truncate(newSize uint64) fuse.Status {
 			return fuse.ToStatus(err)
 		}
 		// Truncate to zero kills the file header
-		f.header = nil
+		f.fileTableEntry.IDLock.Lock()
+		f.fileTableEntry.ID = nil
+		f.fileTableEntry.IDLock.Unlock()
 		return fuse.OK
 	}
 	// We need the old file size to determine if we are growing or shrinking
@@ -184,7 +186,9 @@ func (f *file) truncateGrowFile(oldPlainSz uint64, newPlainSz uint64) fuse.Statu
 	var err error
 	// File was empty, create new header
 	if oldPlainSz == 0 {
-		err = f.createHeader()
+		f.fileTableEntry.IDLock.Lock()
+		_, err = f.createHeader()
+		f.fileTableEntry.IDLock.Unlock()
 		if err != nil {
 			return fuse.ToStatus(err)
 		}

internal/fusefrontend/write_lock.go

@@ -22,81 +22,79 @@ func DevInoFromStat(st *syscall.Stat_t) DevInoStruct {
 }
 
 func init() {
-	wlock.inodeLocks = make(map[DevInoStruct]*refCntMutex)
+	openFileMap.entries = make(map[DevInoStruct]*openFileEntryT)
 }
 
 // wlock - serializes write accesses to each file (identified by inode number)
 // Writing partial blocks means we have to do read-modify-write cycles. We
 // really don't want concurrent writes there.
 // Concurrent full-block writes could actually be allowed, but are not to
 // keep the locking simple.
-var wlock wlockMap
+var openFileMap openFileMapT
 
 // wlockMap - usage:
 // 1) register
 // 2) lock ... unlock ...
 // 3) unregister
-type wlockMap struct {
-	// opCount counts lock() calls. As every operation that modifies a file should
+type openFileMapT struct {
+	// opCount counts writeLock.Lock() calls. As every operation that modifies a file should
 	// call it, this effectively serves as a write-operation counter.
 	// The variable is accessed without holding any locks so atomic operations
 	// must be used. It must be the first element of the struct to guarantee
 	// 64-bit alignment.
 	opCount uint64
 	// Protects map access
 	sync.Mutex
-	inodeLocks map[DevInoStruct]*refCntMutex
+	entries map[DevInoStruct]*openFileEntryT
 }
 
-// refCntMutex - mutex with reference count
-type refCntMutex struct {
-	// Write lock for this inode
+type opCountMutex struct {
 	sync.Mutex
+	// Points to the opCount variable of the parent openFileMapT
+	opCount *uint64
+}
+
+func (o *opCountMutex) Lock() {
+	o.Mutex.Lock()
+	atomic.AddUint64(o.opCount, 1)
+}
+
+// refCntMutex - mutex with reference count
+type openFileEntryT struct {
 	// Reference count
 	refCnt int
+	// Write lock for this inode
+	writeLock *opCountMutex
+	// ID is the file ID in the file header.
+	ID     []byte
+	IDLock sync.RWMutex
 }
 
 // register creates an entry for "ino", or incrementes the reference count
 // if the entry already exists.
-func (w *wlockMap) register(di DevInoStruct) {
+func (w *openFileMapT) register(di DevInoStruct) *openFileEntryT {
 	w.Lock()
 	defer w.Unlock()
 
-	r := w.inodeLocks[di]
+	r := w.entries[di]
 	if r == nil {
-		r = &refCntMutex{}
-		w.inodeLocks[di] = r
+		o := opCountMutex{opCount: &w.opCount}
+		r = &openFileEntryT{writeLock: &o}
+		w.entries[di] = r
 	}
 	r.refCnt++
+	return r
 }
 
 // unregister decrements the reference count for "di" and deletes the entry if
 // the reference count has reached 0.
-func (w *wlockMap) unregister(di DevInoStruct) {
+func (w *openFileMapT) unregister(di DevInoStruct) {
 	w.Lock()
 	defer w.Unlock()
 
-	r := w.inodeLocks[di]
+	r := w.entries[di]
 	r.refCnt--
 	if r.refCnt == 0 {
-		delete(w.inodeLocks, di)
+		delete(w.entries, di)
 	}
 }
-
-// lock retrieves the entry for "di" and locks it.
-func (w *wlockMap) lock(di DevInoStruct) {
-	atomic.AddUint64(&w.opCount, 1)
-	w.Lock()
-	r := w.inodeLocks[di]
-	w.Unlock()
-	// this can take a long time - execute outside the wlockMap lock
-	r.Lock()
-}
-
-// unlock retrieves the entry for "di" and unlocks it.
-func (w *wlockMap) unlock(di DevInoStruct) {
-	w.Lock()
-	r := w.inodeLocks[di]
-	w.Unlock()
-	r.Unlock()
-}