X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/67bd03fc4c2b3fbb25613c76a9470b53ebaa832a..8b43f32b2c11d45f951bf4ff1bffab03d391ff41:/sdk/go/arvados/fs_collection.go

diff --git a/sdk/go/arvados/fs_collection.go b/sdk/go/arvados/fs_collection.go
index e4511895ff..b3e6aa96e4 100644
--- a/sdk/go/arvados/fs_collection.go
+++ b/sdk/go/arvados/fs_collection.go
@@ -5,6 +5,7 @@
 package arvados
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -18,12 +19,10 @@ import (
 	"time"
 )
 
-var maxBlockSize = 1 << 26
-
-type keepClient interface {
-	ReadAt(locator string, p []byte, off int) (int, error)
-	PutB(p []byte) (string, int, error)
-}
+var (
+	maxBlockSize      = 1 << 26
+	concurrentWriters = 4 // max goroutines writing to Keep in background and during flush()
+)
 
 // A CollectionFileSystem is a FileSystem that can be serialized as a
 // manifest and stored as a collection.
@@ -35,64 +34,164 @@ type CollectionFileSystem interface {
 	// Prefix (normally ".") is a top level directory, effectively
 	// prepended to all paths in the returned manifest.
 	MarshalManifest(prefix string) (string, error)
+
+	// Total data bytes in all files.
+	Size() int64
+
+	// Memory consumed by buffered file data.
+	memorySize() int64
+}
+
+type collectionFileSystem struct {
+	fileSystem
+	uuid string
 }
 
 // FileSystem returns a CollectionFileSystem for the collection.
-func (c *Collection) FileSystem(client *Client, kc keepClient) (CollectionFileSystem, error) {
+func (c *Collection) FileSystem(client apiClient, kc keepClient) (CollectionFileSystem, error) {
 	var modTime time.Time
 	if c.ModifiedAt == nil {
 		modTime = time.Now()
 	} else {
 		modTime = *c.ModifiedAt
 	}
-	dn := &dirnode{
-		client: client,
-		kc:     kc,
+	fs := &collectionFileSystem{
+		uuid: c.UUID,
+		fileSystem: fileSystem{
+			fsBackend: keepBackend{apiClient: client, keepClient: kc},
+			thr:       newThrottle(concurrentWriters),
+		},
+	}
+	root := &dirnode{
+		fs: fs,
 		treenode: treenode{
 			fileinfo: fileinfo{
 				name:    ".",
 				mode:    os.ModeDir | 0755,
 				modTime: modTime,
 			},
-			parent: nil,
 			inodes: make(map[string]inode),
 		},
 	}
-	dn.parent = dn
-	fs := &collectionFileSystem{fileSystem: fileSystem{inode: dn}}
-	if err := dn.loadManifest(c.ManifestText); err != nil {
+	root.SetParent(root, ".")
+	if err := root.loadManifest(c.ManifestText); err != nil {
 		return nil, err
 	}
+	backdateTree(root, modTime)
+	fs.root = root
 	return fs, nil
 }
 
-type collectionFileSystem struct {
-	fileSystem
+func backdateTree(n inode, modTime time.Time) {
+	switch n := n.(type) {
+	case *filenode:
+		n.fileinfo.modTime = modTime
+	case *dirnode:
+		n.fileinfo.modTime = modTime
+		for _, n := range n.inodes {
+			backdateTree(n, modTime)
+		}
+	}
 }
 
-func (fs collectionFileSystem) Child(name string, replace func(inode) inode) inode {
-	if name == ".arvados#collection" {
-		return &getternode{Getter: func() ([]byte, error) {
-			var coll Collection
-			var err error
-			coll.ManifestText, err = fs.MarshalManifest(".")
-			if err != nil {
-				return nil, err
-			}
-			data, err := json.Marshal(&coll)
-			if err == nil {
-				data = append(data, 10)
+func (fs *collectionFileSystem) newNode(name string, perm os.FileMode, modTime time.Time) (node inode, err error) {
+	if name == "" || name == "." || name == ".." {
+		return nil, ErrInvalidArgument
+	}
+	if perm.IsDir() {
+		return &dirnode{
+			fs: fs,
+			treenode: treenode{
+				fileinfo: fileinfo{
+					name:    name,
+					mode:    perm | os.ModeDir,
+					modTime: modTime,
+				},
+				inodes: make(map[string]inode),
+			},
+		}, nil
+	} else {
+		return &filenode{
+			fs: fs,
+			fileinfo: fileinfo{
+				name:    name,
+				mode:    perm & ^os.ModeDir,
+				modTime: modTime,
+			},
+		}, nil
+	}
+}
+
+func (fs *collectionFileSystem) Sync() error {
+	if fs.uuid == "" {
+		return nil
+	}
+	txt, err := fs.MarshalManifest(".")
+	if err != nil {
+		return fmt.Errorf("sync failed: %s", err)
+	}
+	coll := &Collection{
+		UUID:         fs.uuid,
+		ManifestText: txt,
+	}
+	err = fs.RequestAndDecode(nil, "PUT", "arvados/v1/collections/"+fs.uuid, nil, map[string]interface{}{
+		"collection": map[string]string{
+			"manifest_text": coll.ManifestText,
+		},
+		"select": []string{"uuid"},
+	})
+	if err != nil {
+		return fmt.Errorf("sync failed: update %s: %s", fs.uuid, err)
+	}
+	return nil
+}
+
+func (fs *collectionFileSystem) Flush(path string, shortBlocks bool) error {
+	node, err := rlookup(fs.fileSystem.root, path)
+	if err != nil {
+		return err
+	}
+	dn, ok := node.(*dirnode)
+	if !ok {
+		return ErrNotADirectory
+	}
+	dn.Lock()
+	defer dn.Unlock()
+	names := dn.sortedNames()
+	if path != "" {
+		// Caller only wants to flush the specified dir,
+		// non-recursively.  Drop subdirs from the list of
+		// names.
+		var filenames []string
+		for _, name := range names {
+			if _, ok := dn.inodes[name].(*filenode); ok {
+				filenames = append(filenames, name)
 			}
-			return data, err
-		}}
+		}
+		names = filenames
+	}
+	for _, name := range names {
+		child := dn.inodes[name]
+		child.Lock()
+		defer child.Unlock()
 	}
-	return fs.fileSystem.Child(name, replace)
+	return dn.flush(context.TODO(), names, flushOpts{sync: false, shortBlocks: shortBlocks})
 }
 
-func (fs collectionFileSystem) MarshalManifest(prefix string) (string, error) {
-	fs.fileSystem.inode.Lock()
-	defer fs.fileSystem.inode.Unlock()
-	return fs.fileSystem.inode.(*dirnode).marshalManifest(prefix)
+func (fs *collectionFileSystem) memorySize() int64 {
+	fs.fileSystem.root.Lock()
+	defer fs.fileSystem.root.Unlock()
+	return fs.fileSystem.root.(*dirnode).memorySize()
+}
+
+func (fs *collectionFileSystem) MarshalManifest(prefix string) (string, error) {
+	fs.fileSystem.root.Lock()
+	defer fs.fileSystem.root.Unlock()
+	return fs.fileSystem.root.(*dirnode).marshalManifest(context.TODO(), prefix)
+}
+
+func (fs *collectionFileSystem) Size() int64 {
+	return fs.fileSystem.root.(*dirnode).TreeSize()
 }
 
 // filenodePtr is an offset into a file that is (usually) efficient to
@@ -170,8 +269,9 @@ func (fn *filenode) seek(startPtr filenodePtr) (ptr filenodePtr) {
 
 // filenode implements inode.
 type filenode struct {
+	parent   inode
+	fs       FileSystem
 	fileinfo fileinfo
-	parent   *dirnode
 	segments []segment
 	// number of times `segments` has changed in a
 	// way that might invalidate a filenodePtr
@@ -187,12 +287,23 @@ func (fn *filenode) appendSegment(e segment) {
 	fn.fileinfo.size += int64(e.Len())
 }
 
+func (fn *filenode) SetParent(p inode, name string) {
+	fn.Lock()
+	defer fn.Unlock()
+	fn.parent = p
+	fn.fileinfo.name = name
+}
+
 func (fn *filenode) Parent() inode {
 	fn.RLock()
 	defer fn.RUnlock()
 	return fn.parent
 }
 
+func (fn *filenode) FS() FileSystem {
+	return fn.fs
+}
+
 // Read reads file data from a single segment, starting at startPtr,
 // into p. startPtr is assumed not to be up-to-date. Caller must have
 // RLock or Lock.
@@ -430,150 +541,407 @@ func (fn *filenode) Write(p []byte, startPtr filenodePtr) (n int, ptr filenodePt
 // Write some data out to disk to reduce memory use. Caller must have
 // write lock.
 func (fn *filenode) pruneMemSegments() {
-	// TODO: async (don't hold Lock() while waiting for Keep)
-	// TODO: share code with (*dirnode)sync()
+	// TODO: share code with (*dirnode)flush()
 	// TODO: pack/flush small blocks too, when fragmented
 	for idx, seg := range fn.segments {
 		seg, ok := seg.(*memSegment)
-		if !ok || seg.Len() < maxBlockSize {
-			continue
-		}
-		locator, _, err := fn.parent.kc.PutB(seg.buf)
-		if err != nil {
-			// TODO: stall (or return errors from)
-			// subsequent writes until flushing
-			// starts to succeed
+		if !ok || seg.Len() < maxBlockSize || seg.flushing != nil {
 			continue
 		}
-		fn.memsize -= int64(seg.Len())
-		fn.segments[idx] = storedSegment{
-			kc:      fn.parent.kc,
-			locator: locator,
-			size:    seg.Len(),
-			offset:  0,
-			length:  seg.Len(),
+		// Setting seg.flushing guarantees seg.buf will not be
+		// modified in place: WriteAt and Truncate will
+		// allocate a new buf instead, if necessary.
+		idx, buf := idx, seg.buf
+		done := make(chan struct{})
+		seg.flushing = done
+		// If lots of background writes are already in
+		// progress, block here until one finishes, rather
+		// than pile up an unlimited number of buffered writes
+		// and network flush operations.
+		fn.fs.throttle().Acquire()
+		go func() {
+			defer close(done)
+			locator, _, err := fn.FS().PutB(buf)
+			fn.fs.throttle().Release()
+			fn.Lock()
+			defer fn.Unlock()
+			if seg.flushing != done {
+				// A new seg.buf has been allocated.
+				return
+			}
+			seg.flushing = nil
+			if err != nil {
+				// TODO: stall (or return errors from)
+				// subsequent writes until flushing
+				// starts to succeed.
+				return
+			}
+			if len(fn.segments) <= idx || fn.segments[idx] != seg || len(seg.buf) != len(buf) {
+				// Segment has been dropped/moved/resized.
+				return
+			}
+			fn.memsize -= int64(len(buf))
+			fn.segments[idx] = storedSegment{
+				kc:      fn.FS(),
+				locator: locator,
+				size:    len(buf),
+				offset:  0,
+				length:  len(buf),
+			}
+		}()
+	}
+}
+
+// Block until all pending pruneMemSegments/flush work is
+// finished. Caller must NOT have lock.
+func (fn *filenode) waitPrune() {
+	var pending []<-chan struct{}
+	fn.Lock()
+	for _, seg := range fn.segments {
+		if seg, ok := seg.(*memSegment); ok && seg.flushing != nil {
+			pending = append(pending, seg.flushing)
 		}
 	}
+	fn.Unlock()
+	for _, p := range pending {
+		<-p
+	}
 }
 
 type dirnode struct {
+	fs *collectionFileSystem
 	treenode
-	client *Client
-	kc     keepClient
 }
 
-// sync flushes in-memory data (for all files in the tree rooted at
-// dn) to persistent storage. Caller must hold dn.Lock().
-func (dn *dirnode) sync() error {
-	type shortBlock struct {
-		fn  *filenode
-		idx int
+func (dn *dirnode) FS() FileSystem {
+	return dn.fs
+}
+
+func (dn *dirnode) Child(name string, replace func(inode) (inode, error)) (inode, error) {
+	if dn == dn.fs.rootnode() && name == ".arvados#collection" {
+		gn := &getternode{Getter: func() ([]byte, error) {
+			var coll Collection
+			var err error
+			coll.ManifestText, err = dn.fs.MarshalManifest(".")
+			if err != nil {
+				return nil, err
+			}
+			data, err := json.Marshal(&coll)
+			if err == nil {
+				data = append(data, '\n')
+			}
+			return data, err
+		}}
+		gn.SetParent(dn, name)
+		return gn, nil
 	}
-	var pending []shortBlock
-	var pendingLen int
+	return dn.treenode.Child(name, replace)
+}
+
+type fnSegmentRef struct {
+	fn  *filenode
+	idx int
+}
 
-	flush := func(sbs []shortBlock) error {
-		if len(sbs) == 0 {
+// commitBlock concatenates the data from the given filenode segments
+// (which must be *memSegments), writes the data out to Keep as a
+// single block, and replaces the filenodes' *memSegments with
+// storedSegments that reference the relevant portions of the new
+// block.
+//
+// bufsize is the total data size in refs. It is used to preallocate
+// the correct amount of memory when len(refs)>1.
+//
+// If sync is false, commitBlock returns right away, after starting a
+// goroutine to do the writes, reacquire the filenodes' locks, and
+// swap out the *memSegments. Some filenodes' segments might get
+// modified/rearranged in the meantime, in which case commitBlock
+// won't replace them.
+//
+// Caller must have write lock.
+func (dn *dirnode) commitBlock(ctx context.Context, refs []fnSegmentRef, bufsize int, sync bool) error {
+	if len(refs) == 0 {
+		return nil
+	}
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+	done := make(chan struct{})
+	var block []byte
+	segs := make([]*memSegment, 0, len(refs))
+	offsets := make([]int, 0, len(refs)) // location of segment's data within block
+	for _, ref := range refs {
+		seg := ref.fn.segments[ref.idx].(*memSegment)
+		if seg.flushing != nil && !sync {
+			// Let the other flushing goroutine finish. If
+			// it fails, we'll try again next time.
 			return nil
+		} else {
+			// In sync mode, we proceed regardless of
+			// whether another flush is in progress: It
+			// can't finish before we do, because we hold
+			// fn's lock until we finish our own writes.
+		}
+		seg.flushing = done
+		offsets = append(offsets, len(block))
+		if len(refs) == 1 {
+			block = seg.buf
+		} else if block == nil {
+			block = append(make([]byte, 0, bufsize), seg.buf...)
+		} else {
+			block = append(block, seg.buf...)
 		}
-		block := make([]byte, 0, maxBlockSize)
-		for _, sb := range sbs {
-			block = append(block, sb.fn.segments[sb.idx].(*memSegment).buf...)
+		segs = append(segs, seg)
+	}
+	dn.fs.throttle().Acquire()
+	errs := make(chan error, 1)
+	go func() {
+		defer close(done)
+		defer close(errs)
+		locked := map[*filenode]bool{}
+		locator, _, err := dn.fs.PutB(block)
+		dn.fs.throttle().Release()
+		{
+			if !sync {
+				for _, name := range dn.sortedNames() {
+					if fn, ok := dn.inodes[name].(*filenode); ok {
+						fn.Lock()
+						defer fn.Unlock()
+						locked[fn] = true
+					}
+				}
+			}
+			defer func() {
+				for _, seg := range segs {
+					if seg.flushing == done {
+						seg.flushing = nil
+					}
+				}
+			}()
 		}
-		locator, _, err := dn.kc.PutB(block)
 		if err != nil {
-			return err
+			errs <- err
+			return
 		}
-		off := 0
-		for _, sb := range sbs {
-			data := sb.fn.segments[sb.idx].(*memSegment).buf
-			sb.fn.segments[sb.idx] = storedSegment{
-				kc:      dn.kc,
+		for idx, ref := range refs {
+			if !sync {
+				// In async mode, fn's lock was
+				// released while we were waiting for
+				// PutB(); lots of things might have
+				// changed.
+				if len(ref.fn.segments) <= ref.idx {
+					// file segments have
+					// rearranged or changed in
+					// some way
+					continue
+				} else if seg, ok := ref.fn.segments[ref.idx].(*memSegment); !ok || seg != segs[idx] {
+					// segment has been replaced
+					continue
+				} else if seg.flushing != done {
+					// seg.buf has been replaced
+					continue
+				} else if !locked[ref.fn] {
+					// file was renamed, moved, or
+					// deleted since we called
+					// PutB
+					continue
+				}
+			}
+			data := ref.fn.segments[ref.idx].(*memSegment).buf
+			ref.fn.segments[ref.idx] = storedSegment{
+				kc:      dn.fs,
 				locator: locator,
 				size:    len(block),
-				offset:  off,
+				offset:  offsets[idx],
 				length:  len(data),
 			}
-			off += len(data)
-			sb.fn.memsize -= int64(len(data))
+			ref.fn.memsize -= int64(len(data))
 		}
+	}()
+	if sync {
+		return <-errs
+	} else {
 		return nil
 	}
+}
 
-	names := make([]string, 0, len(dn.inodes))
-	for name := range dn.inodes {
-		names = append(names, name)
+type flushOpts struct {
+	sync        bool
+	shortBlocks bool
+}
+
+// flush in-memory data and remote-cluster block references (for the
+// children with the given names, which must be children of dn) to
+// local-cluster persistent storage.
+//
+// Caller must have write lock on dn and the named children.
+//
+// If any children are dirs, they will be flushed recursively.
+func (dn *dirnode) flush(ctx context.Context, names []string, opts flushOpts) error {
+	cg := newContextGroup(ctx)
+	defer cg.Cancel()
+
+	goCommit := func(refs []fnSegmentRef, bufsize int) {
+		cg.Go(func() error {
+			return dn.commitBlock(cg.Context(), refs, bufsize, opts.sync)
+		})
 	}
-	sort.Strings(names)
 
+	var pending []fnSegmentRef
+	var pendingLen int = 0
+	localLocator := map[string]string{}
 	for _, name := range names {
-		fn, ok := dn.inodes[name].(*filenode)
-		if !ok {
-			continue
-		}
-		fn.Lock()
-		defer fn.Unlock()
-		for idx, seg := range fn.segments {
-			seg, ok := seg.(*memSegment)
-			if !ok {
-				continue
+		switch node := dn.inodes[name].(type) {
+		case *dirnode:
+			grandchildNames := node.sortedNames()
+			for _, grandchildName := range grandchildNames {
+				grandchild := node.inodes[grandchildName]
+				grandchild.Lock()
+				defer grandchild.Unlock()
 			}
-			if seg.Len() > maxBlockSize/2 {
-				if err := flush([]shortBlock{{fn, idx}}); err != nil {
-					return err
+			cg.Go(func() error { return node.flush(cg.Context(), grandchildNames, opts) })
+		case *filenode:
+			for idx, seg := range node.segments {
+				switch seg := seg.(type) {
+				case storedSegment:
+					loc, ok := localLocator[seg.locator]
+					if !ok {
+						var err error
+						loc, err = dn.fs.LocalLocator(seg.locator)
+						if err != nil {
+							return err
+						}
+						localLocator[seg.locator] = loc
+					}
+					seg.locator = loc
+					node.segments[idx] = seg
+				case *memSegment:
+					if seg.Len() > maxBlockSize/2 {
+						goCommit([]fnSegmentRef{{node, idx}}, seg.Len())
+						continue
+					}
+					if pendingLen+seg.Len() > maxBlockSize {
+						goCommit(pending, pendingLen)
+						pending = nil
+						pendingLen = 0
+					}
+					pending = append(pending, fnSegmentRef{node, idx})
+					pendingLen += seg.Len()
+				default:
+					panic(fmt.Sprintf("can't sync segment type %T", seg))
 				}
-				continue
 			}
-			if pendingLen+seg.Len() > maxBlockSize {
-				if err := flush(pending); err != nil {
-					return err
+		}
+	}
+	if opts.shortBlocks {
+		goCommit(pending, pendingLen)
+	}
+	return cg.Wait()
+}
+
+// caller must have write lock.
+func (dn *dirnode) memorySize() (size int64) {
+	for _, name := range dn.sortedNames() {
+		node := dn.inodes[name]
+		node.Lock()
+		defer node.Unlock()
+		switch node := node.(type) {
+		case *dirnode:
+			size += node.memorySize()
+		case *filenode:
+			for _, seg := range node.segments {
+				switch seg := seg.(type) {
+				case *memSegment:
+					size += int64(seg.Len())
 				}
-				pending = nil
-				pendingLen = 0
 			}
-			pending = append(pending, shortBlock{fn, idx})
-			pendingLen += seg.Len()
 		}
 	}
-	return flush(pending)
+	return
 }
 
-// caller must have read lock.
-func (dn *dirnode) marshalManifest(prefix string) (string, error) {
-	var streamLen int64
-	type filepart struct {
-		name   string
-		offset int64
-		length int64
+// caller must have write lock.
+func (dn *dirnode) sortedNames() []string {
+	names := make([]string, 0, len(dn.inodes))
+	for name := range dn.inodes {
+		names = append(names, name)
 	}
-	var fileparts []filepart
-	var subdirs string
-	var blocks []string
+	sort.Strings(names)
+	return names
+}
 
-	if err := dn.sync(); err != nil {
-		return "", err
+// caller must have write lock.
+func (dn *dirnode) marshalManifest(ctx context.Context, prefix string) (string, error) {
+	cg := newContextGroup(ctx)
+	defer cg.Cancel()
+
+	if len(dn.inodes) == 0 {
+		if prefix == "." {
+			return "", nil
+		}
+		// Express the existence of an empty directory by
+		// adding an empty file named `\056`, which (unlike
+		// the more obvious spelling `.`) is accepted by the
+		// API's manifest validator.
+		return manifestEscape(prefix) + " d41d8cd98f00b204e9800998ecf8427e+0 0:0:\\056\n", nil
 	}
 
-	names := make([]string, 0, len(dn.inodes))
-	for name, node := range dn.inodes {
-		names = append(names, name)
-		node.Lock()
-		defer node.Unlock()
+	names := dn.sortedNames()
+
+	// Wait for children to finish any pending write operations
+	// before locking them.
+	for _, name := range names {
+		node := dn.inodes[name]
+		if fn, ok := node.(*filenode); ok {
+			fn.waitPrune()
+		}
 	}
-	sort.Strings(names)
 
+	var dirnames []string
+	var filenames []string
 	for _, name := range names {
-		switch node := dn.inodes[name].(type) {
+		node := dn.inodes[name]
+		node.Lock()
+		defer node.Unlock()
+		switch node := node.(type) {
 		case *dirnode:
-			subdir, err := node.marshalManifest(prefix + "/" + name)
-			if err != nil {
-				return "", err
-			}
-			subdirs = subdirs + subdir
+			dirnames = append(dirnames, name)
 		case *filenode:
+			filenames = append(filenames, name)
+		default:
+			panic(fmt.Sprintf("can't marshal inode type %T", node))
+		}
+	}
+
+	subdirs := make([]string, len(dirnames))
+	rootdir := ""
+	for i, name := range dirnames {
+		i, name := i, name
+		cg.Go(func() error {
+			txt, err := dn.inodes[name].(*dirnode).marshalManifest(cg.Context(), prefix+"/"+name)
+			subdirs[i] = txt
+			return err
+		})
+	}
+
+	cg.Go(func() error {
+		var streamLen int64
+		type filepart struct {
+			name   string
+			offset int64
+			length int64
+		}
+
+		var fileparts []filepart
+		var blocks []string
+		if err := dn.flush(cg.Context(), filenames, flushOpts{sync: true, shortBlocks: true}); err != nil {
+			return err
+		}
+		for _, name := range filenames {
+			node := dn.inodes[name].(*filenode)
 			if len(node.segments) == 0 {
 				fileparts = append(fileparts, filepart{name: name})
-				break
+				continue
 			}
 			for _, seg := range node.segments {
 				switch seg := seg.(type) {
@@ -599,24 +967,25 @@ func (dn *dirnode) marshalManifest(prefix string) (string, error) {
 				default:
 					// This can't happen: we
 					// haven't unlocked since
-					// calling sync().
+					// calling flush(sync=true).
 					panic(fmt.Sprintf("can't marshal segment type %T", seg))
 				}
 			}
-		default:
-			panic(fmt.Sprintf("can't marshal inode type %T", node))
 		}
-	}
-	var filetokens []string
-	for _, s := range fileparts {
-		filetokens = append(filetokens, fmt.Sprintf("%d:%d:%s", s.offset, s.length, manifestEscape(s.name)))
-	}
-	if len(filetokens) == 0 {
-		return subdirs, nil
-	} else if len(blocks) == 0 {
-		blocks = []string{"d41d8cd98f00b204e9800998ecf8427e+0"}
-	}
-	return manifestEscape(prefix) + " " + strings.Join(blocks, " ") + " " + strings.Join(filetokens, " ") + "\n" + subdirs, nil
+		var filetokens []string
+		for _, s := range fileparts {
+			filetokens = append(filetokens, fmt.Sprintf("%d:%d:%s", s.offset, s.length, manifestEscape(s.name)))
+		}
+		if len(filetokens) == 0 {
+			return nil
+		} else if len(blocks) == 0 {
+			blocks = []string{"d41d8cd98f00b204e9800998ecf8427e+0"}
+		}
+		rootdir = manifestEscape(prefix) + " " + strings.Join(blocks, " ") + " " + strings.Join(filetokens, " ") + "\n"
+		return nil
+	})
+	err := cg.Wait()
+	return rootdir + strings.Join(subdirs, ""), err
 }
 
 func (dn *dirnode) loadManifest(txt string) error {
@@ -677,8 +1046,14 @@ func (dn *dirnode) loadManifest(txt string) error {
 			}
 			name := dirname + "/" + manifestUnescape(toks[2])
 			fnode, err := dn.createFileAndParents(name)
-			if err != nil {
-				return fmt.Errorf("line %d: cannot use path %q: %s", lineno, name, err)
+			if fnode == nil && err == nil && length == 0 {
+				// Special case: an empty file used as
+				// a marker to preserve an otherwise
+				// empty directory in a manifest.
+				continue
+			}
+			if err != nil || (fnode == nil && length != 0) {
+				return fmt.Errorf("line %d: cannot use path %q with length %d: %s", lineno, name, length, err)
 			}
 			// Map the stream offset/range coordinates to
 			// block/offset/range coordinates and add
@@ -709,7 +1084,7 @@ func (dn *dirnode) loadManifest(txt string) error {
 					blkLen = int(offset + length - pos - int64(blkOff))
 				}
 				fnode.appendSegment(storedSegment{
-					kc:      dn.kc,
+					kc:      dn.fs,
 					locator: seg.locator,
 					size:    seg.size,
 					offset:  blkOff,
@@ -736,15 +1111,14 @@ func (dn *dirnode) loadManifest(txt string) error {
 	return nil
 }
 
-// only safe to call from loadManifest -- no locking
+// only safe to call from loadManifest -- no locking.
+//
+// If path is a "parent directory exists" marker (the last path
+// component is "."), the returned values are both nil.
 func (dn *dirnode) createFileAndParents(path string) (fn *filenode, err error) {
-	node := dn
+	var node inode = dn
 	names := strings.Split(path, "/")
 	basename := names[len(names)-1]
-	if basename == "" || basename == "." || basename == ".." {
-		err = fmt.Errorf("invalid filename")
-		return
-	}
 	for _, name := range names[:len(names)-1] {
 		switch name {
 		case "", ".":
@@ -754,108 +1128,69 @@ func (dn *dirnode) createFileAndParents(path string) (fn *filenode, err error) {
 				// can't be sure parent will be a *dirnode
 				return nil, ErrInvalidArgument
 			}
-			node = node.Parent().(*dirnode)
+			node = node.Parent()
 			continue
 		}
-		node.Child(name, func(child inode) inode {
-			switch child.(type) {
-			case nil:
-				node, err = dn.newDirnode(node, name, 0755|os.ModeDir, node.Parent().FileInfo().ModTime())
-				child = node
-			case *dirnode:
-				node = child.(*dirnode)
-			case *filenode:
-				err = ErrFileExists
-			default:
-				err = ErrInvalidOperation
+		node, err = node.Child(name, func(child inode) (inode, error) {
+			if child == nil {
+				child, err := node.FS().newNode(name, 0755|os.ModeDir, node.Parent().FileInfo().ModTime())
+				if err != nil {
+					return nil, err
+				}
+				child.SetParent(node, name)
+				return child, nil
+			} else if !child.IsDir() {
+				return child, ErrFileExists
+			} else {
+				return child, nil
 			}
-			return child
 		})
 		if err != nil {
 			return
 		}
 	}
-	node.Child(basename, func(child inode) inode {
+	if basename == "." {
+		return
+	} else if !permittedName(basename) {
+		err = fmt.Errorf("invalid file part %q in path %q", basename, path)
+		return
+	}
+	_, err = node.Child(basename, func(child inode) (inode, error) {
 		switch child := child.(type) {
 		case nil:
-			fn, err = dn.newFilenode(node, basename, 0755, node.FileInfo().ModTime())
-			return fn
+			child, err = node.FS().newNode(basename, 0755, node.FileInfo().ModTime())
+			if err != nil {
+				return nil, err
+			}
+			child.SetParent(node, basename)
+			fn = child.(*filenode)
+			return child, nil
 		case *filenode:
 			fn = child
-			return child
+			return child, nil
 		case *dirnode:
-			err = ErrIsDirectory
-			return child
+			return child, ErrIsDirectory
 		default:
-			err = ErrInvalidOperation
-			return child
+			return child, ErrInvalidArgument
 		}
 	})
 	return
 }
 
-// rlookup (recursive lookup) returns the inode for the file/directory
-// with the given name (which may contain "/" separators). If no such
-// file/directory exists, the returned node is nil.
-func rlookup(start inode, path string) (node inode) {
-	node = start
-	for _, name := range strings.Split(path, "/") {
-		if node == nil {
-			break
-		}
-		if node.IsDir() {
-			if name == "." || name == "" {
-				continue
-			}
-			if name == ".." {
-				node = node.Parent()
-				continue
-			}
+func (dn *dirnode) TreeSize() (bytes int64) {
+	dn.RLock()
+	defer dn.RUnlock()
+	for _, i := range dn.inodes {
+		switch i := i.(type) {
+		case *filenode:
+			bytes += i.Size()
+		case *dirnode:
+			bytes += i.TreeSize()
 		}
-		node = func() inode {
-			node.RLock()
-			defer node.RUnlock()
-			return node.Child(name, nil)
-		}()
 	}
 	return
 }
 
-// Caller must have lock, and must have already ensured
-// Children(name,nil) is nil.
-func (dn *dirnode) newDirnode(parent *dirnode, name string, perm os.FileMode, modTime time.Time) (node *dirnode, err error) {
-	if name == "" || name == "." || name == ".." {
-		return nil, ErrInvalidArgument
-	}
-	return &dirnode{
-		client: dn.client,
-		kc:     dn.kc,
-		treenode: treenode{
-			parent: parent,
-			fileinfo: fileinfo{
-				name:    name,
-				mode:    perm | os.ModeDir,
-				modTime: modTime,
-			},
-			inodes: make(map[string]inode),
-		},
-	}, nil
-}
-
-func (dn *dirnode) newFilenode(parent *dirnode, name string, perm os.FileMode, modTime time.Time) (node *filenode, err error) {
-	if name == "" || name == "." || name == ".." {
-		return nil, ErrInvalidArgument
-	}
-	return &filenode{
-		parent: parent,
-		fileinfo: fileinfo{
-			name:    name,
-			mode:    perm & ^os.ModeDir,
-			modTime: modTime,
-		},
-	}, nil
-}
-
 type segment interface {
 	io.ReaderAt
 	Len() int
@@ -866,6 +1201,11 @@ type segment interface {
 
 type memSegment struct {
 	buf []byte
+	// If flushing is not nil, then a) buf is being shared by a
+	// pruneMemSegments goroutine, and must be copied on write;
+	// and b) the flushing channel will close when the goroutine
+	// finishes, whether it succeeds or not.
+	flushing <-chan struct{}
 }
 
 func (me *memSegment) Len() int {
@@ -882,28 +1222,31 @@ func (me *memSegment) Slice(off, length int) segment {
 }
 
 func (me *memSegment) Truncate(n int) {
-	if n > cap(me.buf) {
+	if n > cap(me.buf) || (me.flushing != nil && n > len(me.buf)) {
 		newsize := 1024
 		for newsize < n {
 			newsize = newsize << 2
 		}
 		newbuf := make([]byte, n, newsize)
 		copy(newbuf, me.buf)
-		me.buf = newbuf
+		me.buf, me.flushing = newbuf, nil
 	} else {
-		// Zero unused part when shrinking, in case we grow
-		// and start using it again later.
-		for i := n; i < len(me.buf); i++ {
+		// reclaim existing capacity, and zero reclaimed part
+		oldlen := len(me.buf)
+		me.buf = me.buf[:n]
+		for i := oldlen; i < n; i++ {
 			me.buf[i] = 0
 		}
 	}
-	me.buf = me.buf[:n]
 }
 
 func (me *memSegment) WriteAt(p []byte, off int) {
 	if off+len(p) > len(me.buf) {
 		panic("overflowed segment")
 	}
+	if me.flushing != nil {
+		me.buf, me.flushing = append([]byte(nil), me.buf...), nil
+	}
 	copy(me.buf[off:], p)
 }
 
@@ -920,7 +1263,7 @@ func (me *memSegment) ReadAt(p []byte, off int64) (n int, err error) {
 }
 
 type storedSegment struct {
-	kc      keepClient
+	kc      fsBackend
 	locator string
 	size    int // size of stored block (also encoded in locator)
 	offset  int // position of segment within the stored block