Merge branch 'main' into 18842-arv-mount-disk-config
[arvados.git] / sdk / go / arvados / fs_collection.go
index 0233826a7281e9aa95f5dbb9f74e93ddb1bfd473..354658a257dba00d54f9d98f9f7c1328e84b7ae2 100644 (file)
@@ -5,6 +5,7 @@
 package arvados
 
 import (
+       "bytes"
        "context"
        "encoding/json"
        "fmt"
@@ -42,7 +43,21 @@ type CollectionFileSystem interface {
 
 type collectionFileSystem struct {
        fileSystem
-       uuid string
+       uuid           string
+       savedPDH       atomic.Value
+       replicas       int
+       storageClasses []string
+       // guessSignatureTTL tracks a lower bound for the server's
+       // configured BlobSigningTTL. The guess is initially zero, and
+       // increases when we come across a signature with an expiry
+       // time further in the future than the previous guess.
+       //
+       // When the guessed TTL is much smaller than the real TTL,
+       // preemptive signature refresh is delayed or missed entirely,
+       // which is OK.
+       guessSignatureTTL time.Duration
+       holdCheckChanges  time.Time
+       lockCheckChanges  sync.Mutex
 }
 
 // FileSystem returns a CollectionFileSystem for the collection.
@@ -52,12 +67,17 @@ func (c *Collection) FileSystem(client apiClient, kc keepClient) (CollectionFile
                modTime = time.Now()
        }
        fs := &collectionFileSystem{
-               uuid: c.UUID,
+               uuid:           c.UUID,
+               storageClasses: c.StorageClassesDesired,
                fileSystem: fileSystem{
                        fsBackend: keepBackend{apiClient: client, keepClient: kc},
                        thr:       newThrottle(concurrentWriters),
                },
        }
+       fs.savedPDH.Store(c.PortableDataHash)
+       if r := c.ReplicationDesired; r != nil {
+               fs.replicas = *r
+       }
        root := &dirnode{
                fs: fs,
                treenode: treenode{
@@ -65,6 +85,7 @@ func (c *Collection) FileSystem(client apiClient, kc keepClient) (CollectionFile
                                name:    ".",
                                mode:    os.ModeDir | 0755,
                                modTime: modTime,
+                               sys:     func() interface{} { return c },
                        },
                        inodes: make(map[string]inode),
                },
@@ -78,16 +99,112 @@ func (c *Collection) FileSystem(client apiClient, kc keepClient) (CollectionFile
        return fs, nil
 }
 
-func backdateTree(n inode, modTime time.Time) {
+// caller must have lock (or guarantee no concurrent accesses somehow)
+func eachNode(n inode, ffunc func(*filenode), dfunc func(*dirnode)) {
        switch n := n.(type) {
        case *filenode:
-               n.fileinfo.modTime = modTime
+               if ffunc != nil {
+                       ffunc(n)
+               }
        case *dirnode:
-               n.fileinfo.modTime = modTime
+               if dfunc != nil {
+                       dfunc(n)
+               }
                for _, n := range n.inodes {
-                       backdateTree(n, modTime)
+                       eachNode(n, ffunc, dfunc)
+               }
+       }
+}
+
+// caller must have lock (or guarantee no concurrent accesses somehow)
+func backdateTree(n inode, modTime time.Time) {
+       eachNode(n, func(fn *filenode) {
+               fn.fileinfo.modTime = modTime
+       }, func(dn *dirnode) {
+               dn.fileinfo.modTime = modTime
+       })
+}
+
+// Approximate portion of signature TTL remaining, usually between 0
+// and 1, or negative if some signatures have expired.
+func (fs *collectionFileSystem) signatureTimeLeft() (float64, time.Duration) {
+       var (
+               now      = time.Now()
+               earliest = now.Add(time.Hour * 24 * 7 * 365)
+               latest   time.Time
+       )
+       fs.fileSystem.root.RLock()
+       eachNode(fs.root, func(fn *filenode) {
+               fn.Lock()
+               defer fn.Unlock()
+               for _, seg := range fn.segments {
+                       seg, ok := seg.(storedSegment)
+                       if !ok {
+                               continue
+                       }
+                       expiryTime, err := signatureExpiryTime(seg.locator)
+                       if err != nil {
+                               continue
+                       }
+                       if expiryTime.Before(earliest) {
+                               earliest = expiryTime
+                       }
+                       if expiryTime.After(latest) {
+                               latest = expiryTime
+                       }
+               }
+       }, nil)
+       fs.fileSystem.root.RUnlock()
+
+       if latest.IsZero() {
+               // No signatures == 100% of TTL remaining.
+               return 1, 1
+       }
+
+       ttl := latest.Sub(now)
+       fs.fileSystem.root.Lock()
+       {
+               if ttl > fs.guessSignatureTTL {
+                       // ttl is closer to the real TTL than
+                       // guessSignatureTTL.
+                       fs.guessSignatureTTL = ttl
+               } else {
+                       // Use the previous best guess to compute the
+                       // portion remaining (below, after unlocking
+                       // mutex).
+                       ttl = fs.guessSignatureTTL
                }
        }
+       fs.fileSystem.root.Unlock()
+
+       return earliest.Sub(now).Seconds() / ttl.Seconds(), ttl
+}
+
+func (fs *collectionFileSystem) updateSignatures(newmanifest string) {
+       newLoc := map[string]string{}
+       for _, tok := range regexp.MustCompile(`\S+`).FindAllString(newmanifest, -1) {
+               if mBlkRe.MatchString(tok) {
+                       newLoc[stripAllHints(tok)] = tok
+               }
+       }
+       fs.fileSystem.root.Lock()
+       defer fs.fileSystem.root.Unlock()
+       eachNode(fs.root, func(fn *filenode) {
+               fn.Lock()
+               defer fn.Unlock()
+               for idx, seg := range fn.segments {
+                       seg, ok := seg.(storedSegment)
+                       if !ok {
+                               continue
+                       }
+                       loc, ok := newLoc[stripAllHints(seg.locator)]
+                       if !ok {
+                               continue
+                       }
+                       seg.locator = loc
+                       fn.segments[idx] = seg
+               }
+       }, nil)
 }
 
 func (fs *collectionFileSystem) newNode(name string, perm os.FileMode, modTime time.Time) (node inode, err error) {
@@ -173,27 +290,149 @@ func (fs *collectionFileSystem) Truncate(int64) error {
        return ErrInvalidOperation
 }
 
+// Check for and incorporate upstream changes. If force==false, this
+// is a no-op except once every ttl/100 or so.
+//
+// Return value is true if new content was loaded from upstream and
+// any unsaved local changes have been discarded.
+func (fs *collectionFileSystem) checkChangesOnServer(force bool) (bool, error) {
+       if fs.uuid == "" && fs.savedPDH.Load() == "" {
+               return false, nil
+       }
+
+       fs.lockCheckChanges.Lock()
+       if !force && fs.holdCheckChanges.After(time.Now()) {
+               fs.lockCheckChanges.Unlock()
+               return false, nil
+       }
+       remain, ttl := fs.signatureTimeLeft()
+       if remain > 0.01 {
+               fs.holdCheckChanges = time.Now().Add(ttl / 100)
+       }
+       fs.lockCheckChanges.Unlock()
+
+       if !force && remain >= 0.5 {
+               // plenty of time left on current signatures
+               return false, nil
+       }
+
+       getparams := map[string]interface{}{"select": []string{"portable_data_hash", "manifest_text"}}
+       if fs.uuid != "" {
+               var coll Collection
+               err := fs.RequestAndDecode(&coll, "GET", "arvados/v1/collections/"+fs.uuid, nil, getparams)
+               if err != nil {
+                       return false, err
+               }
+               if coll.PortableDataHash != fs.savedPDH.Load().(string) {
+                       // collection has changed upstream since we
+                       // last loaded or saved. Refresh local data,
+                       // losing any unsaved local changes.
+                       newfs, err := coll.FileSystem(fs.fileSystem.fsBackend, fs.fileSystem.fsBackend)
+                       if err != nil {
+                               return false, err
+                       }
+                       snap, err := Snapshot(newfs, "/")
+                       if err != nil {
+                               return false, err
+                       }
+                       err = Splice(fs, "/", snap)
+                       if err != nil {
+                               return false, err
+                       }
+                       fs.savedPDH.Store(coll.PortableDataHash)
+                       return true, nil
+               }
+               fs.updateSignatures(coll.ManifestText)
+               return false, nil
+       }
+       if pdh := fs.savedPDH.Load().(string); pdh != "" {
+               var coll Collection
+               err := fs.RequestAndDecode(&coll, "GET", "arvados/v1/collections/"+pdh, nil, getparams)
+               if err != nil {
+                       return false, err
+               }
+               fs.updateSignatures(coll.ManifestText)
+       }
+       return false, nil
+}
+
+// Refresh signature on a single locator, if necessary. Assume caller
+// has lock. If an update is needed, and there are any storedSegments
+// whose signatures can be updated, start a background task to update
+// them asynchronously when the caller releases locks.
+func (fs *collectionFileSystem) refreshSignature(locator string) string {
+       exp, err := signatureExpiryTime(locator)
+       if err != nil || exp.Sub(time.Now()) > time.Minute {
+               // Synchronous update is not needed. Start an
+               // asynchronous update if needed.
+               go fs.checkChangesOnServer(false)
+               return locator
+       }
+       var manifests string
+       for _, id := range []string{fs.uuid, fs.savedPDH.Load().(string)} {
+               if id == "" {
+                       continue
+               }
+               var coll Collection
+               err := fs.RequestAndDecode(&coll, "GET", "arvados/v1/collections/"+id, nil, map[string]interface{}{"select": []string{"portable_data_hash", "manifest_text"}})
+               if err != nil {
+                       continue
+               }
+               manifests += coll.ManifestText
+       }
+       hash := stripAllHints(locator)
+       for _, tok := range regexp.MustCompile(`\S+`).FindAllString(manifests, -1) {
+               if mBlkRe.MatchString(tok) {
+                       if stripAllHints(tok) == hash {
+                               locator = tok
+                               break
+                       }
+               }
+       }
+       go fs.updateSignatures(manifests)
+       return locator
+}
+
 func (fs *collectionFileSystem) Sync() error {
-       if fs.uuid == "" {
+       refreshed, err := fs.checkChangesOnServer(true)
+       if err != nil {
+               return err
+       }
+       if refreshed || fs.uuid == "" {
                return nil
        }
        txt, err := fs.MarshalManifest(".")
        if err != nil {
                return fmt.Errorf("sync failed: %s", err)
        }
-       coll := &Collection{
+       if PortableDataHash(txt) == fs.savedPDH.Load() {
+               // No local changes since last save or initial load.
+               return nil
+       }
+       coll := Collection{
                UUID:         fs.uuid,
                ManifestText: txt,
        }
-       err = fs.RequestAndDecode(nil, "PUT", "arvados/v1/collections/"+fs.uuid, nil, map[string]interface{}{
+
+       selectFields := []string{"uuid", "portable_data_hash"}
+       fs.lockCheckChanges.Lock()
+       remain, _ := fs.signatureTimeLeft()
+       fs.lockCheckChanges.Unlock()
+       if remain < 0.5 {
+               selectFields = append(selectFields, "manifest_text")
+       }
+
+       err = fs.RequestAndDecode(&coll, "PUT", "arvados/v1/collections/"+fs.uuid, nil, map[string]interface{}{
                "collection": map[string]string{
                        "manifest_text": coll.ManifestText,
                },
-               "select": []string{"uuid"},
+               "select": selectFields,
        })
        if err != nil {
-               return fmt.Errorf("sync failed: update %s: %s", fs.uuid, err)
+               return fmt.Errorf("sync failed: update %s: %w", fs.uuid, err)
        }
+       fs.updateSignatures(coll.ManifestText)
+       fs.savedPDH.Store(coll.PortableDataHash)
        return nil
 }
 
@@ -230,8 +469,6 @@ func (fs *collectionFileSystem) Flush(path string, shortBlocks bool) error {
 }
 
 func (fs *collectionFileSystem) MemorySize() int64 {
-       fs.fileSystem.root.Lock()
-       defer fs.fileSystem.root.Unlock()
        return fs.fileSystem.root.(*dirnode).MemorySize()
 }
 
@@ -245,6 +482,14 @@ func (fs *collectionFileSystem) Size() int64 {
        return fs.fileSystem.root.(*dirnode).TreeSize()
 }
 
+func (fs *collectionFileSystem) Snapshot() (inode, error) {
+       return fs.fileSystem.root.Snapshot()
+}
+
+func (fs *collectionFileSystem) Splice(r inode) error {
+       return fs.fileSystem.root.Splice(r)
+}
+
 // filenodePtr is an offset into a file that is (usually) efficient to
 // seek to. Specifically, if filenode.repacked==filenodePtr.repacked
 // then
@@ -268,9 +513,9 @@ type filenodePtr struct {
 //
 // After seeking:
 //
-//     ptr.segmentIdx == len(filenode.segments) // i.e., at EOF
-//     ||
-//     filenode.segments[ptr.segmentIdx].Len() > ptr.segmentOff
+//     ptr.segmentIdx == len(filenode.segments) // i.e., at EOF
+//     ||
+//     filenode.segments[ptr.segmentIdx].Len() > ptr.segmentOff
 func (fn *filenode) seek(startPtr filenodePtr) (ptr filenodePtr) {
        ptr = startPtr
        if ptr.off < 0 {
@@ -321,7 +566,7 @@ func (fn *filenode) seek(startPtr filenodePtr) (ptr filenodePtr) {
 // filenode implements inode.
 type filenode struct {
        parent   inode
-       fs       FileSystem
+       fs       *collectionFileSystem
        fileinfo fileinfo
        segments []segment
        // number of times `segments` has changed in a
@@ -355,6 +600,16 @@ func (fn *filenode) FS() FileSystem {
        return fn.fs
 }
 
+func (fn *filenode) MemorySize() (size int64) {
+       fn.RLock()
+       defer fn.RUnlock()
+       size = 64
+       for _, seg := range fn.segments {
+               size += seg.memorySize()
+       }
+       return
+}
+
 // 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.
@@ -368,6 +623,10 @@ func (fn *filenode) Read(p []byte, startPtr filenodePtr) (n int, ptr filenodePtr
                err = io.EOF
                return
        }
+       if ss, ok := fn.segments[ptr.segmentIdx].(storedSegment); ok {
+               ss.locator = fn.fs.refreshSignature(ss.locator)
+               fn.segments[ptr.segmentIdx] = ss
+       }
        n, err = fn.segments[ptr.segmentIdx].ReadAt(p, int64(ptr.segmentOff))
        if n > 0 {
                ptr.off += int64(n)
@@ -610,7 +869,11 @@ func (fn *filenode) pruneMemSegments() {
                fn.fs.throttle().Acquire()
                go func() {
                        defer close(done)
-                       locator, _, err := fn.FS().PutB(buf)
+                       resp, err := fn.FS().BlockWrite(context.Background(), BlockWriteOptions{
+                               Data:           buf,
+                               Replicas:       fn.fs.replicas,
+                               StorageClasses: fn.fs.storageClasses,
+                       })
                        fn.fs.throttle().Release()
                        fn.Lock()
                        defer fn.Unlock()
@@ -631,7 +894,7 @@ func (fn *filenode) pruneMemSegments() {
                        fn.memsize -= int64(len(buf))
                        fn.segments[idx] = storedSegment{
                                kc:      fn.FS(),
-                               locator: locator,
+                               locator: resp.Locator,
                                size:    len(buf),
                                offset:  0,
                                length:  len(buf),
@@ -656,6 +919,47 @@ func (fn *filenode) waitPrune() {
        }
 }
 
+func (fn *filenode) Snapshot() (inode, error) {
+       fn.RLock()
+       defer fn.RUnlock()
+       segments := make([]segment, 0, len(fn.segments))
+       for _, seg := range fn.segments {
+               segments = append(segments, seg.Slice(0, seg.Len()))
+       }
+       return &filenode{
+               fileinfo: fn.fileinfo,
+               segments: segments,
+       }, nil
+}
+
+func (fn *filenode) Splice(repl inode) error {
+       repl, err := repl.Snapshot()
+       if err != nil {
+               return err
+       }
+       fn.parent.Lock()
+       defer fn.parent.Unlock()
+       fn.Lock()
+       defer fn.Unlock()
+       _, err = fn.parent.Child(fn.fileinfo.name, func(inode) (inode, error) { return repl, nil })
+       if err != nil {
+               return err
+       }
+       switch repl := repl.(type) {
+       case *dirnode:
+               repl.parent = fn.parent
+               repl.fileinfo.name = fn.fileinfo.name
+               repl.setTreeFS(fn.fs)
+       case *filenode:
+               repl.parent = fn.parent
+               repl.fileinfo.name = fn.fileinfo.name
+               repl.fs = fn.fs
+       default:
+               return fmt.Errorf("cannot splice snapshot containing %T: %w", repl, ErrInvalidArgument)
+       }
+       return nil
+}
+
 type dirnode struct {
        fs *collectionFileSystem
        treenode
@@ -674,6 +978,7 @@ func (dn *dirnode) Child(name string, replace func(inode) (inode, error)) (inode
                        if err != nil {
                                return nil, err
                        }
+                       coll.UUID = dn.fs.uuid
                        data, err := json.Marshal(&coll)
                        if err == nil {
                                data = append(data, '\n')
@@ -747,7 +1052,11 @@ func (dn *dirnode) commitBlock(ctx context.Context, refs []fnSegmentRef, bufsize
        go func() {
                defer close(done)
                defer close(errs)
-               locator, _, err := dn.fs.PutB(block)
+               resp, err := dn.fs.BlockWrite(context.Background(), BlockWriteOptions{
+                       Data:           block,
+                       Replicas:       dn.fs.replicas,
+                       StorageClasses: dn.fs.storageClasses,
+               })
                dn.fs.throttle().Release()
                if err != nil {
                        errs <- err
@@ -779,7 +1088,7 @@ func (dn *dirnode) commitBlock(ctx context.Context, refs []fnSegmentRef, bufsize
                        data := ref.fn.segments[ref.idx].(*memSegment).buf
                        ref.fn.segments[ref.idx] = storedSegment{
                                kc:      dn.fs,
-                               locator: locator,
+                               locator: resp.Locator,
                                size:    blocksize,
                                offset:  offsets[idx],
                                length:  len(data),
@@ -875,23 +1184,16 @@ func (dn *dirnode) flush(ctx context.Context, names []string, opts flushOpts) er
        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())
-                               }
-                       }
-               }
+       dn.RLock()
+       todo := make([]inode, 0, len(dn.inodes))
+       for _, node := range dn.inodes {
+               todo = append(todo, node)
+       }
+       dn.RUnlock()
+       size = 64
+       for _, node := range todo {
+               size += node.MemorySize()
        }
        return
 }
@@ -1025,38 +1327,64 @@ func (dn *dirnode) marshalManifest(ctx context.Context, prefix string) (string,
 }
 
 func (dn *dirnode) loadManifest(txt string) error {
-       var dirname string
-       streams := strings.Split(txt, "\n")
-       if streams[len(streams)-1] != "" {
+       streams := bytes.Split([]byte(txt), []byte{'\n'})
+       if len(streams[len(streams)-1]) != 0 {
                return fmt.Errorf("line %d: no trailing newline", len(streams))
        }
        streams = streams[:len(streams)-1]
        segments := []storedSegment{}
+       // To reduce allocs, we reuse a single "pathparts" slice
+       // (pre-split on "/" separators) for the duration of this
+       // func.
+       var pathparts []string
+       // To reduce allocs, we reuse a single "toks" slice of 3 byte
+       // slices.
+       var toks = make([][]byte, 3)
+       // Similar to bytes.SplitN(token, []byte{c}, 3), but splits
+       // into the toks slice rather than allocating a new one, and
+       // returns the number of toks (1, 2, or 3).
+       splitToToks := func(src []byte, c rune) int {
+               c1 := bytes.IndexRune(src, c)
+               if c1 < 0 {
+                       toks[0] = src
+                       return 1
+               }
+               toks[0], src = src[:c1], src[c1+1:]
+               c2 := bytes.IndexRune(src, c)
+               if c2 < 0 {
+                       toks[1] = src
+                       return 2
+               }
+               toks[1], toks[2] = src[:c2], src[c2+1:]
+               return 3
+       }
        for i, stream := range streams {
                lineno := i + 1
                var anyFileTokens bool
                var pos int64
                var segIdx int
                segments = segments[:0]
-               for i, token := range strings.Split(stream, " ") {
+               pathparts = nil
+               streamparts := 0
+               for i, token := range bytes.Split(stream, []byte{' '}) {
                        if i == 0 {
-                               dirname = manifestUnescape(token)
+                               pathparts = strings.Split(manifestUnescape(string(token)), "/")
+                               streamparts = len(pathparts)
                                continue
                        }
-                       if !strings.Contains(token, ":") {
+                       if !bytes.ContainsRune(token, ':') {
                                if anyFileTokens {
                                        return fmt.Errorf("line %d: bad file segment %q", lineno, token)
                                }
-                               toks := strings.SplitN(token, "+", 3)
-                               if len(toks) < 2 {
+                               if splitToToks(token, '+') < 2 {
                                        return fmt.Errorf("line %d: bad locator %q", lineno, token)
                                }
-                               length, err := strconv.ParseInt(toks[1], 10, 32)
+                               length, err := strconv.ParseInt(string(toks[1]), 10, 32)
                                if err != nil || length < 0 {
                                        return fmt.Errorf("line %d: bad locator %q", lineno, token)
                                }
                                segments = append(segments, storedSegment{
-                                       locator: token,
+                                       locator: string(token),
                                        size:    int(length),
                                        offset:  0,
                                        length:  int(length),
@@ -1065,23 +1393,26 @@ func (dn *dirnode) loadManifest(txt string) error {
                        } else if len(segments) == 0 {
                                return fmt.Errorf("line %d: bad locator %q", lineno, token)
                        }
-
-                       toks := strings.SplitN(token, ":", 3)
-                       if len(toks) != 3 {
+                       if splitToToks(token, ':') != 3 {
                                return fmt.Errorf("line %d: bad file segment %q", lineno, token)
                        }
                        anyFileTokens = true
 
-                       offset, err := strconv.ParseInt(toks[0], 10, 64)
+                       offset, err := strconv.ParseInt(string(toks[0]), 10, 64)
                        if err != nil || offset < 0 {
                                return fmt.Errorf("line %d: bad file segment %q", lineno, token)
                        }
-                       length, err := strconv.ParseInt(toks[1], 10, 64)
+                       length, err := strconv.ParseInt(string(toks[1]), 10, 64)
                        if err != nil || length < 0 {
                                return fmt.Errorf("line %d: bad file segment %q", lineno, token)
                        }
-                       name := dirname + "/" + manifestUnescape(toks[2])
-                       fnode, err := dn.createFileAndParents(name)
+                       if !bytes.ContainsAny(toks[2], `\/`) {
+                               // optimization for a common case
+                               pathparts = append(pathparts[:streamparts], string(toks[2]))
+                       } else {
+                               pathparts = append(pathparts[:streamparts], strings.Split(manifestUnescape(string(toks[2])), "/")...)
+                       }
+                       fnode, err := dn.createFileAndParents(pathparts)
                        if fnode == nil && err == nil && length == 0 {
                                // Special case: an empty file used as
                                // a marker to preserve an otherwise
@@ -1089,7 +1420,7 @@ func (dn *dirnode) loadManifest(txt string) error {
                                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)
+                               return fmt.Errorf("line %d: cannot use name %q with length %d: %s", lineno, toks[2], length, err)
                        }
                        // Map the stream offset/range coordinates to
                        // block/offset/range coordinates and add
@@ -1140,7 +1471,7 @@ func (dn *dirnode) loadManifest(txt string) error {
                        return fmt.Errorf("line %d: no file segments", lineno)
                } else if len(segments) == 0 {
                        return fmt.Errorf("line %d: no locators", lineno)
-               } else if dirname == "" {
+               } else if streamparts == 0 {
                        return fmt.Errorf("line %d: no stream name", lineno)
                }
        }
@@ -1151,9 +1482,11 @@ func (dn *dirnode) loadManifest(txt string) error {
 //
 // 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) {
+//
+// Newly added nodes have modtime==0. Caller is responsible for fixing
+// them with backdateTree.
+func (dn *dirnode) createFileAndParents(names []string) (fn *filenode, err error) {
        var node inode = dn
-       names := strings.Split(path, "/")
        basename := names[len(names)-1]
        for _, name := range names[:len(names)-1] {
                switch name {
@@ -1167,9 +1500,12 @@ func (dn *dirnode) createFileAndParents(path string) (fn *filenode, err error) {
                        node = node.Parent()
                        continue
                }
+               node.Lock()
+               unlock := node.Unlock
                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())
+                               // note modtime will be fixed later in backdateTree()
+                               child, err := node.FS().newNode(name, 0755|os.ModeDir, time.Time{})
                                if err != nil {
                                        return nil, err
                                }
@@ -1181,6 +1517,7 @@ func (dn *dirnode) createFileAndParents(path string) (fn *filenode, err error) {
                                return child, nil
                        }
                })
+               unlock()
                if err != nil {
                        return
                }
@@ -1188,13 +1525,15 @@ func (dn *dirnode) createFileAndParents(path string) (fn *filenode, err error) {
        if basename == "." {
                return
        } else if !permittedName(basename) {
-               err = fmt.Errorf("invalid file part %q in path %q", basename, path)
+               err = fmt.Errorf("invalid file part %q in path %q", basename, names)
                return
        }
+       node.Lock()
+       defer node.Unlock()
        _, err = node.Child(basename, func(child inode) (inode, error) {
                switch child := child.(type) {
                case nil:
-                       child, err = node.FS().newNode(basename, 0755, node.FileInfo().ModTime())
+                       child, err = node.FS().newNode(basename, 0755, time.Time{})
                        if err != nil {
                                return nil, err
                        }
@@ -1227,12 +1566,93 @@ func (dn *dirnode) TreeSize() (bytes int64) {
        return
 }
 
+func (dn *dirnode) Snapshot() (inode, error) {
+       return dn.snapshot()
+}
+
+func (dn *dirnode) snapshot() (*dirnode, error) {
+       dn.RLock()
+       defer dn.RUnlock()
+       snap := &dirnode{
+               treenode: treenode{
+                       inodes:   make(map[string]inode, len(dn.inodes)),
+                       fileinfo: dn.fileinfo,
+               },
+       }
+       for name, child := range dn.inodes {
+               dupchild, err := child.Snapshot()
+               if err != nil {
+                       return nil, err
+               }
+               snap.inodes[name] = dupchild
+               dupchild.SetParent(snap, name)
+       }
+       return snap, nil
+}
+
+func (dn *dirnode) Splice(repl inode) error {
+       repl, err := repl.Snapshot()
+       if err != nil {
+               return fmt.Errorf("cannot copy snapshot: %w", err)
+       }
+       switch repl := repl.(type) {
+       default:
+               return fmt.Errorf("cannot splice snapshot containing %T: %w", repl, ErrInvalidArgument)
+       case *dirnode:
+               dn.Lock()
+               defer dn.Unlock()
+               dn.inodes = repl.inodes
+               dn.setTreeFS(dn.fs)
+       case *filenode:
+               dn.parent.Lock()
+               defer dn.parent.Unlock()
+               removing, err := dn.parent.Child(dn.fileinfo.name, nil)
+               if err != nil {
+                       return fmt.Errorf("cannot use Splice to replace a top-level directory with a file: %w", ErrInvalidOperation)
+               } else if removing != dn {
+                       // If ../thisdirname is not this dirnode, it
+                       // must be an inode that wraps a dirnode, like
+                       // a collectionFileSystem or deferrednode.
+                       if deferred, ok := removing.(*deferrednode); ok {
+                               // More useful to report the type of
+                               // the wrapped node rather than just
+                               // *deferrednode. (We know the real
+                               // inode is already loaded because dn
+                               // is inside it.)
+                               removing = deferred.realinode()
+                       }
+                       return fmt.Errorf("cannot use Splice to attach a file at top level of %T: %w", removing, ErrInvalidOperation)
+               }
+               dn.Lock()
+               defer dn.Unlock()
+               _, err = dn.parent.Child(dn.fileinfo.name, func(inode) (inode, error) { return repl, nil })
+               if err != nil {
+                       return fmt.Errorf("error replacing filenode: dn.parent.Child(): %w", err)
+               }
+               repl.fs = dn.fs
+       }
+       return nil
+}
+
+func (dn *dirnode) setTreeFS(fs *collectionFileSystem) {
+       dn.fs = fs
+       for _, child := range dn.inodes {
+               switch child := child.(type) {
+               case *dirnode:
+                       child.setTreeFS(fs)
+               case *filenode:
+                       child.fs = fs
+               }
+       }
+}
+
 type segment interface {
        io.ReaderAt
        Len() int
        // Return a new segment with a subsection of the data from this
        // one. length<0 means length=Len()-off.
        Slice(off int, length int) segment
+       memorySize() int64
 }
 
 type memSegment struct {
@@ -1311,6 +1731,10 @@ func (me *memSegment) ReadAt(p []byte, off int64) (n int, err error) {
        return
 }
 
+func (me *memSegment) memorySize() int64 {
+       return 64 + int64(len(me.buf))
+}
+
 type storedSegment struct {
        kc      fsBackend
        locator string
@@ -1348,6 +1772,10 @@ func (se storedSegment) ReadAt(p []byte, off int64) (n int, err error) {
        return se.kc.ReadAt(se.locator, p, int(off)+se.offset)
 }
 
+func (se storedSegment) memorySize() int64 {
+       return 64 + int64(len(se.locator))
+}
+
 func canonicalName(name string) string {
        name = path.Clean("/" + name)
        if name == "/" || name == "./" {