Fix quadratic file reading in restic mount

internal/fuse/file.go

@@ -3,6 +3,8 @@
 package fuse
 
 import (
+	"sort"
+
 	"github.com/restic/restic/internal/errors"
 	"github.com/restic/restic/internal/restic"
 
@@ -18,21 +20,26 @@ const blockSize = 512
 
 // Statically ensure that *file implements the given interface
 var _ = fs.HandleReader(&file{})
-var _ = fs.HandleReleaser(&file{})
 
 type file struct {
 	root  *Root
 	node  *restic.Node
 	inode uint64
 
-	sizes []int
+	// cumsize[i] holds the cumulative size of blobs[:i].
-	blobs [][]byte
+	cumsize []uint64
+
+	// Cached blob and its index in the blobs of node.
+	cached struct {
+		blob  []byte
+		index int
+	}
 }
 
 func newFile(ctx context.Context, root *Root, inode uint64, node *restic.Node) (fusefile *file, err error) {
 	debug.Log("create new file for %v with %d blobs", node.Name, len(node.Content))
 	var bytes uint64
-	sizes := make([]int, len(node.Content))
+	cumsize := make([]uint64, 1+len(node.Content))
 	for i, id := range node.Content {
 		size, ok := root.blobSizeCache.Lookup(id)
 		if !ok {
@@ -43,8 +50,8 @@ func newFile(ctx context.Context, root *Root, inode uint64, node *restic.Node) (
 			}
 		}
 
-		sizes[i] = int(size)
 		bytes += uint64(size)
+		cumsize[i+1] = bytes
 	}
 
 	if bytes != node.Size {
@@ -56,8 +63,8 @@ func newFile(ctx context.Context, root *Root, inode uint64, node *restic.Node) (
 		inode: inode,
 		root:  root,
 		node:  node,
-		sizes: sizes,
+
-		blobs: make([][]byte, len(node.Content)),
+		cumsize: cumsize,
 	}, nil
 }
 
@@ -84,13 +91,8 @@ func (f *file) Attr(ctx context.Context, a *fuse.Attr) error {
 
 func (f *file) getBlobAt(ctx context.Context, i int) (blob []byte, err error) {
 	debug.Log("getBlobAt(%v, %v)", f.node.Name, i)
-	if f.blobs[i] != nil {
+	if i == f.cached.index && f.cached.blob != nil {
-		return f.blobs[i], nil
+		return f.cached.blob, nil
-	}
-
-	// release earlier blobs
-	for j := 0; j < i; j++ {
-		f.blobs[j] = nil
 	}
 
 	blob, err = f.root.repo.LoadBlob(ctx, restic.DataBlob, f.node.Content[i], nil)
@@ -98,16 +100,16 @@ func (f *file) getBlobAt(ctx context.Context, i int) (blob []byte, err error) {
 		debug.Log("LoadBlob(%v, %v) failed: %v", f.node.Name, f.node.Content[i], err)
 		return nil, err
 	}
-	f.blobs[i] = blob
+	f.cached.blob, f.cached.index = blob, i
 
 	return blob, nil
 }
 
 func (f *file) Read(ctx context.Context, req *fuse.ReadRequest, resp *fuse.ReadResponse) error {
 	debug.Log("Read(%v, %v, %v), file size %v", f.node.Name, req.Size, req.Offset, f.node.Size)
-	offset := req.Offset
+	offset := uint64(req.Offset)
 
-	if uint64(offset) > f.node.Size {
+	if offset > f.node.Size {
 		debug.Log("Read(%v): offset is greater than file size: %v > %v",
 			f.node.Name, req.Offset, f.node.Size)
 
@@ -123,16 +125,15 @@ func (f *file) Read(ctx context.Context, req *fuse.ReadRequest, resp *fuse.ReadR
 	}
 
 	// Skip blobs before the offset
-	startContent := 0
+	startContent := -1 + sort.Search(len(f.cumsize), func(i int) bool {
-	for offset > int64(f.sizes[startContent]) {
+		return f.cumsize[i] > offset
-		offset -= int64(f.sizes[startContent])
+	})
-		startContent++
+	offset -= f.cumsize[startContent]
-	}
 
 	dst := resp.Data[0:req.Size]
 	readBytes := 0
 	remainingBytes := req.Size
-	for i := startContent; remainingBytes > 0 && i < len(f.sizes); i++ {
+	for i := startContent; remainingBytes > 0 && i < len(f.cumsize)-1; i++ {
 		blob, err := f.getBlobAt(ctx, i)
 		if err != nil {
 			return err
@@ -154,13 +155,6 @@ func (f *file) Read(ctx context.Context, req *fuse.ReadRequest, resp *fuse.ReadR
 	return nil
 }
 
-func (f *file) Release(ctx context.Context, req *fuse.ReleaseRequest) error {
-	for i := range f.blobs {
-		f.blobs[i] = nil
-	}
-	return nil
-}
-
 func (f *file) Listxattr(ctx context.Context, req *fuse.ListxattrRequest, resp *fuse.ListxattrResponse) error {
 	debug.Log("Listxattr(%v, %v)", f.node.Name, req.Size)
 	for _, attr := range f.node.ExtendedAttributes {

internal/fuse/fuse_test.go

@@ -146,8 +146,6 @@ func TestFuseFile(t *testing.T) {
 			t.Errorf("test %d failed, wrong data returned (offset %v, length %v)", i, offset, length)
 		}
 	}
-
-	rtest.OK(t, f.Release(ctx, nil))
 }
 
 // Test top-level directories for their UID and GID.