diff --git a/fs/march.go b/fs/march.go
new file mode 100644
index 000000000..3bfd702c0
--- /dev/null
+++ b/fs/march.go
@@ -0,0 +1,317 @@
+package fs
+
+import (
+	"sync"
+
+	"golang.org/x/net/context"
+)
+
+// march traverses two Fs simultaneously, calling walker for each match
+type march struct {
+	// parameters
+	ctx      context.Context
+	fdst     Fs
+	fsrc     Fs
+	dir      string
+	callback marcher
+	// internal state
+	srcListDir listDirFn // function to call to list a directory in the src
+	dstListDir listDirFn // function to call to list a directory in the dst
+}
+
+// marcher is called on each match
+type marcher interface {
+	// SrcOnly is called for a DirEntry found only in the source
+	SrcOnly(src DirEntry) (recurse bool)
+	// DstOnly is called for a DirEntry found only in the destination
+	DstOnly(dst DirEntry) (recurse bool)
+	// Match is called for a DirEntry found both in the source and destination
+	Match(dst, src DirEntry) (recurse bool)
+}
+
+// newMarch sets up a march over fsrc, and fdst calling back callback for each match
+func newMarch(ctx context.Context, fdst, fsrc Fs, dir string, callback marcher) *march {
+	m := &march{
+		ctx:      ctx,
+		fdst:     fdst,
+		fsrc:     fsrc,
+		dir:      dir,
+		callback: callback,
+	}
+	m.srcListDir = m.makeListDir(fsrc, false)
+	m.dstListDir = m.makeListDir(fdst, Config.Filter.DeleteExcluded)
+	return m
+}
+
+// list a directory into entries, err
+type listDirFn func(dir string) (entries DirEntries, err error)
+
+// makeListDir makes a listing function for the given fs and includeAll flags
+func (m *march) makeListDir(f Fs, includeAll bool) listDirFn {
+	if !Config.UseListR || f.Features().ListR == nil {
+		return func(dir string) (entries DirEntries, err error) {
+			return ListDirSorted(f, includeAll, dir)
+		}
+	}
+	var (
+		mu      sync.Mutex
+		started bool
+		dirs    DirTree
+		dirsErr error
+	)
+	return func(dir string) (entries DirEntries, err error) {
+		mu.Lock()
+		defer mu.Unlock()
+		if !started {
+			dirs, dirsErr = NewDirTree(f, m.dir, includeAll, Config.MaxDepth)
+			started = true
+		}
+		if dirsErr != nil {
+			return nil, dirsErr
+		}
+		entries, ok := dirs[dir]
+		if !ok {
+			err = ErrorDirNotFound
+		} else {
+			delete(dirs, dir)
+		}
+		return entries, err
+	}
+}
+
+// listDirJob describe a directory listing that needs to be done
+type listDirJob struct {
+	srcRemote string
+	dstRemote string
+	srcDepth  int
+	dstDepth  int
+	noSrc     bool
+	noDst     bool
+}
+
+// run starts the matching process off
+func (m *march) run() {
+	srcDepth := Config.MaxDepth
+	if srcDepth < 0 {
+		srcDepth = MaxLevel
+	}
+	dstDepth := srcDepth
+	if Config.Filter.DeleteExcluded {
+		dstDepth = MaxLevel
+	}
+
+	// Start some directory listing go routines
+	var wg sync.WaitGroup         // sync closing of go routines
+	var traversing sync.WaitGroup // running directory traversals
+	in := make(chan listDirJob, Config.Checkers)
+	for i := 0; i < Config.Checkers; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for {
+				select {
+				case <-m.ctx.Done():
+					return
+				case job, ok := <-in:
+					if !ok {
+						return
+					}
+					jobs := m.processJob(job)
+					if len(jobs) > 0 {
+						traversing.Add(len(jobs))
+						go func() {
+							// Now we have traversed this directory, send these
+							// jobs off for traversal in the background
+							for _, newJob := range jobs {
+								in <- newJob
+							}
+						}()
+					}
+					traversing.Done()
+				}
+			}
+		}()
+	}
+
+	// Start the process
+	traversing.Add(1)
+	in <- listDirJob{
+		srcRemote: m.dir,
+		srcDepth:  srcDepth - 1,
+		dstRemote: m.dir,
+		dstDepth:  dstDepth - 1,
+	}
+	traversing.Wait()
+	close(in)
+	wg.Wait()
+}
+
+// Check to see if the context has been cancelled
+func (m *march) aborting() bool {
+	select {
+	case <-m.ctx.Done():
+		return true
+	default:
+	}
+	return false
+}
+
+type matchPair struct {
+	src, dst DirEntry
+}
+
+// Process the two sorted listings, matching up the items in the two
+// sorted slices
+//
+// Into srcOnly go Entries which only exist in the srcList
+// Into dstOnly go Entries which only exist in the dstList
+// Into matches go matchPair's of src and dst which have the same name
+//
+// This checks for duplicates and checks the list is sorted.
+func matchListings(srcList, dstList DirEntries) (srcOnly DirEntries, dstOnly DirEntries, matches []matchPair) {
+	for iSrc, iDst := 0, 0; ; iSrc, iDst = iSrc+1, iDst+1 {
+		var src, dst DirEntry
+		var srcRemote, dstRemote string
+		if iSrc < len(srcList) {
+			src = srcList[iSrc]
+			srcRemote = src.Remote()
+		}
+		if iDst < len(dstList) {
+			dst = dstList[iDst]
+			dstRemote = dst.Remote()
+		}
+		if src == nil && dst == nil {
+			break
+		}
+		if src != nil && iSrc > 0 {
+			prev := srcList[iSrc-1].Remote()
+			if srcRemote == prev {
+				Logf(src, "Duplicate %s found in source - ignoring", DirEntryType(src))
+				src = nil // ignore the src
+			} else if srcRemote < prev {
+				Errorf(src, "Out of order listing in source")
+				src = nil // ignore the src
+			}
+		}
+		if dst != nil && iDst > 0 {
+			prev := dstList[iDst-1].Remote()
+			if dstRemote == prev {
+				Logf(dst, "Duplicate %s found in destination - ignoring", DirEntryType(dst))
+				dst = nil // ignore the dst
+			} else if dstRemote < prev {
+				Errorf(dst, "Out of order listing in destination")
+				dst = nil // ignore the dst
+			}
+		}
+		if src != nil && dst != nil {
+			if srcRemote < dstRemote {
+				dst = nil
+				iDst-- // retry the dst
+			} else if srcRemote > dstRemote {
+				src = nil
+				iSrc-- // retry the src
+			}
+		}
+		// Debugf(nil, "src = %v, dst = %v", src, dst)
+		switch {
+		case src == nil && dst == nil:
+			// do nothing
+		case src == nil:
+			dstOnly = append(dstOnly, dst)
+		case dst == nil:
+			srcOnly = append(srcOnly, src)
+		default:
+			matches = append(matches, matchPair{src: src, dst: dst})
+		}
+	}
+	return
+}
+
+// processJob processes a listDirJob listing the source and
+// destination directories, comparing them and returning a slice of
+// more jobs
+//
+// returns errors using processError
+func (m *march) processJob(job listDirJob) (jobs []listDirJob) {
+	var (
+		srcList, dstList       DirEntries
+		srcListErr, dstListErr error
+		wg                     sync.WaitGroup
+	)
+
+	// List the src and dst directories
+	if !job.noSrc {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			srcList, srcListErr = m.srcListDir(job.srcRemote)
+		}()
+	}
+	if !job.noDst {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			dstList, dstListErr = m.dstListDir(job.dstRemote)
+		}()
+	}
+
+	// Wait for listings to complete and report errors
+	wg.Wait()
+	if srcListErr != nil {
+		Errorf(job.srcRemote, "error reading source directory: %v", srcListErr)
+		Stats.Error()
+		return nil
+	}
+	if dstListErr == ErrorDirNotFound {
+		// Copy the stuff anyway
+	} else if dstListErr != nil {
+		Errorf(job.dstRemote, "error reading destination directory: %v", dstListErr)
+		Stats.Error()
+		return nil
+	}
+
+	// Work out what to do and do it
+	srcOnly, dstOnly, matches := matchListings(srcList, dstList)
+	for _, src := range srcOnly {
+		if m.aborting() {
+			return nil
+		}
+		recurse := m.callback.SrcOnly(src)
+		if recurse && job.srcDepth > 0 {
+			jobs = append(jobs, listDirJob{
+				srcRemote: src.Remote(),
+				srcDepth:  job.srcDepth - 1,
+				noDst:     true,
+			})
+		}
+
+	}
+	for _, dst := range dstOnly {
+		if m.aborting() {
+			return nil
+		}
+		recurse := m.callback.DstOnly(dst)
+		if recurse && job.dstDepth > 0 {
+			jobs = append(jobs, listDirJob{
+				dstRemote: dst.Remote(),
+				dstDepth:  job.dstDepth - 1,
+				noSrc:     true,
+			})
+		}
+	}
+	for _, match := range matches {
+		if m.aborting() {
+			return nil
+		}
+		recurse := m.callback.Match(match.dst, match.src)
+		if recurse && job.srcDepth > 0 && job.dstDepth > 0 {
+			jobs = append(jobs, listDirJob{
+				srcRemote: match.src.Remote(),
+				dstRemote: match.dst.Remote(),
+				srcDepth:  job.srcDepth - 1,
+				dstDepth:  job.dstDepth - 1,
+			})
+		}
+	}
+	return jobs
+}
diff --git a/fs/sync_internal_test.go b/fs/march_test.go
similarity index 98%
rename from fs/sync_internal_test.go
rename to fs/march_test.go
index 2f8cf86d2..c5df0192b 100644
--- a/fs/sync_internal_test.go
+++ b/fs/march_test.go
@@ -1,4 +1,4 @@
-// Internal tests for sync/copy/move
+// Internal tests for march
 
 package fs
 
diff --git a/fs/sync.go b/fs/sync.go
index ff1a85ef4..c0d73fe71 100644
--- a/fs/sync.go
+++ b/fs/sync.go
@@ -3,6 +3,7 @@
 package fs
 
 import (
+	"context"
 	"fmt"
 	"sort"
 	"sync"
@@ -52,8 +53,6 @@ type syncCopyMove struct {
 	renameCheck    []Object            // accumulate files to check for rename here
 	backupDir      Fs                  // place to store overwrites/deletes
 	suffix         string              // suffix to add to files placed in backupDir
-	srcListDir     listDirFn           // function to call to list a directory in the src
-	dstListDir     listDirFn           // function to call to list a directory in the dst
 }
 
 func newSyncCopyMove(fdst, fsrc Fs, deleteMode DeleteMode, DoMove bool) (*syncCopyMove, error) {
@@ -122,47 +121,9 @@ func newSyncCopyMove(fdst, fsrc Fs, deleteMode DeleteMode, DoMove bool) (*syncCo
 		}
 		s.suffix = Config.Suffix
 	}
-	s.srcListDir = s.makeListDir(fsrc, false)
-	s.dstListDir = s.makeListDir(fdst, Config.Filter.DeleteExcluded)
 	return s, nil
 }
 
-// list a directory into entries, err
-type listDirFn func(dir string) (entries DirEntries, err error)
-
-// makeListDir makes a listing function for the given fs and includeAll flags
-func (s *syncCopyMove) makeListDir(f Fs, includeAll bool) listDirFn {
-	if !Config.UseListR || f.Features().ListR == nil {
-		return func(dir string) (entries DirEntries, err error) {
-			return ListDirSorted(f, includeAll, dir)
-		}
-	}
-	var (
-		mu      sync.Mutex
-		started bool
-		dirs    DirTree
-		dirsErr error
-	)
-	return func(dir string) (entries DirEntries, err error) {
-		mu.Lock()
-		defer mu.Unlock()
-		if !started {
-			dirs, dirsErr = NewDirTree(f, s.dir, includeAll, Config.MaxDepth)
-			started = true
-		}
-		if dirsErr != nil {
-			return nil, dirsErr
-		}
-		entries, ok := dirs[dir]
-		if !ok {
-			err = ErrorDirNotFound
-		} else {
-			delete(dirs, dir)
-		}
-		return entries, err
-	}
-}
-
 // Check to see if have set the abort flag
 func (s *syncCopyMove) aborting() bool {
 	select {
@@ -667,15 +628,6 @@ func (s *syncCopyMove) tryRename(src Object) bool {
 	return true
 }
 
-// listDirJob describe a directory listing that needs to be done
-type listDirJob struct {
-	remote   string
-	srcDepth int
-	dstDepth int
-	noSrc    bool
-	noDst    bool
-}
-
 // Syncs fsrc into fdst
 //
 // If Delete is true then it deletes any files in fdst that aren't in fsrc
@@ -684,15 +636,6 @@ type listDirJob struct {
 //
 // dir is the start directory, "" for root
 func (s *syncCopyMove) run() error {
-	srcDepth := Config.MaxDepth
-	if srcDepth < 0 {
-		srcDepth = MaxLevel
-	}
-	dstDepth := srcDepth
-	if Config.Filter.DeleteExcluded {
-		dstDepth = MaxLevel
-	}
-
 	if Same(s.fdst, s.fsrc) {
 		Errorf(s.fdst, "Nothing to do as source and destination are the same")
 		return nil
@@ -705,53 +648,11 @@ func (s *syncCopyMove) run() error {
 	s.startDeleters()
 	s.dstFiles = make(map[string]Object)
 
-	// Start some directory listing go routines
-	var wg sync.WaitGroup         // sync closing of go routines
-	var traversing sync.WaitGroup // running directory traversals
-	in := make(chan listDirJob, Config.Checkers)
 	s.startTrackRenames()
-	for i := 0; i < Config.Checkers; i++ {
-		wg.Add(1)
-		go func() {
-			defer wg.Done()
-			for {
-				if s.aborting() {
-					return
-				}
-				select {
-				case job, ok := <-in:
-					if !ok {
-						return
-					}
-					jobs := s.processJob(job)
-					if len(jobs) > 0 {
-						traversing.Add(len(jobs))
-						go func() {
-							// Now we have traversed this directory, send these
-							// jobs off for traversal in the background
-							for _, newJob := range jobs {
-								in <- newJob
-							}
-						}()
-					}
-					traversing.Done()
-				case <-s.abort:
-					return
-				}
-			}
-		}()
-	}
 
-	// Start the process
-	traversing.Add(1)
-	in <- listDirJob{
-		remote:   s.dir,
-		srcDepth: srcDepth - 1,
-		dstDepth: dstDepth - 1,
-	}
-	traversing.Wait()
-	close(in)
-	wg.Wait()
+	ctx := context.Background()
+	m := newMarch(ctx, s.fdst, s.fsrc, s.dir, s)
+	m.run()
 
 	s.stopTrackRenames()
 	if s.trackRenames {
@@ -789,10 +690,10 @@ func (s *syncCopyMove) run() error {
 	return s.currentError()
 }
 
-// Have an object which is in the destination only
-func (s *syncCopyMove) dstOnly(dst DirEntry, job listDirJob, jobs *[]listDirJob) {
+// DstOnly have an object which is in the destination only
+func (s *syncCopyMove) DstOnly(dst DirEntry) (recurse bool) {
 	if s.deleteMode == DeleteModeOff {
-		return
+		return false
 	}
 	switch x := dst.(type) {
 	case Object:
@@ -809,29 +710,24 @@ func (s *syncCopyMove) dstOnly(dst DirEntry, job listDirJob, jobs *[]listDirJob)
 		}
 	case Directory:
 		// Do the same thing to the entire contents of the directory
-		if job.dstDepth > 0 {
-			*jobs = append(*jobs, listDirJob{
-				remote:   dst.Remote(),
-				dstDepth: job.dstDepth - 1,
-				noSrc:    true,
-			})
-		}
 		// Record directory as it is potentially empty and needs deleting
 		if s.fdst.Features().CanHaveEmptyDirectories {
 			s.dstEmptyDirsMu.Lock()
 			s.dstEmptyDirs = append(s.dstEmptyDirs, dst)
 			s.dstEmptyDirsMu.Unlock()
 		}
+		return true
 	default:
 		panic("Bad object in DirEntries")
 
 	}
+	return false
 }
 
-// Have an object which is in the source only
-func (s *syncCopyMove) srcOnly(src DirEntry, job listDirJob, jobs *[]listDirJob) {
+// SrcOnly have an object which is in the source only
+func (s *syncCopyMove) SrcOnly(src DirEntry) (recurse bool) {
 	if s.deleteMode == DeleteModeOnly {
-		return
+		return false
 	}
 	switch x := src.(type) {
 	case Object:
@@ -844,24 +740,19 @@ func (s *syncCopyMove) srcOnly(src DirEntry, job listDirJob, jobs *[]listDirJob)
 		}
 	case Directory:
 		// Do the same thing to the entire contents of the directory
-		if job.srcDepth > 0 {
-			*jobs = append(*jobs, listDirJob{
-				remote:   src.Remote(),
-				srcDepth: job.srcDepth - 1,
-				noDst:    true,
-			})
-		}
+		return true
 	default:
 		panic("Bad object in DirEntries")
 	}
+	return false
 }
 
-// Given a src and a dst, transfer the src to dst
-func (s *syncCopyMove) transfer(dst, src DirEntry, job listDirJob, jobs *[]listDirJob) {
+// Match is called when src and dst are present, so sync src to dst
+func (s *syncCopyMove) Match(dst, src DirEntry) (recurse bool) {
 	switch srcX := src.(type) {
 	case Object:
 		if s.deleteMode == DeleteModeOnly {
-			return
+			return false
 		}
 		dstX, ok := dst.(Object)
 		if ok {
@@ -876,157 +767,16 @@ func (s *syncCopyMove) transfer(dst, src DirEntry, job listDirJob, jobs *[]listD
 		// Do the same thing to the entire contents of the directory
 		_, ok := dst.(Directory)
 		if ok {
-			if job.srcDepth > 0 && job.dstDepth > 0 {
-				*jobs = append(*jobs, listDirJob{
-					remote:   src.Remote(),
-					srcDepth: job.srcDepth - 1,
-					dstDepth: job.dstDepth - 1,
-				})
-			}
-		} else {
-			// FIXME src is dir, dst is file
-			err := errors.New("can't overwrite file with directory")
-			Errorf(dst, "%v", err)
-			s.processError(err)
+			return true
 		}
+		// FIXME src is dir, dst is file
+		err := errors.New("can't overwrite file with directory")
+		Errorf(dst, "%v", err)
+		s.processError(err)
 	default:
 		panic("Bad object in DirEntries")
 	}
-}
-
-type matchPair struct {
-	src, dst DirEntry
-}
-
-// Process the two sorted listings, matching up the items in the two
-// sorted slices
-//
-// Into srcOnly go Entries which only exist in the srcList
-// Into dstOnly go Entries which only exist in the dstList
-// Into matches go matchPair's of src and dst which have the same name
-//
-// This checks for duplicates and checks the list is sorted.
-func matchListings(srcList, dstList DirEntries) (srcOnly DirEntries, dstOnly DirEntries, matches []matchPair) {
-	for iSrc, iDst := 0, 0; ; iSrc, iDst = iSrc+1, iDst+1 {
-		var src, dst DirEntry
-		var srcRemote, dstRemote string
-		if iSrc < len(srcList) {
-			src = srcList[iSrc]
-			srcRemote = src.Remote()
-		}
-		if iDst < len(dstList) {
-			dst = dstList[iDst]
-			dstRemote = dst.Remote()
-		}
-		if src == nil && dst == nil {
-			break
-		}
-		if src != nil && iSrc > 0 {
-			prev := srcList[iSrc-1].Remote()
-			if srcRemote == prev {
-				Logf(src, "Duplicate %s found in source - ignoring", DirEntryType(src))
-				src = nil // ignore the src
-			} else if srcRemote < prev {
-				Errorf(src, "Out of order listing in source")
-				src = nil // ignore the src
-			}
-		}
-		if dst != nil && iDst > 0 {
-			prev := dstList[iDst-1].Remote()
-			if dstRemote == prev {
-				Logf(dst, "Duplicate %s found in destination - ignoring", DirEntryType(dst))
-				dst = nil // ignore the dst
-			} else if dstRemote < prev {
-				Errorf(dst, "Out of order listing in destination")
-				dst = nil // ignore the dst
-			}
-		}
-		if src != nil && dst != nil {
-			if srcRemote < dstRemote {
-				dst = nil
-				iDst-- // retry the dst
-			} else if srcRemote > dstRemote {
-				src = nil
-				iSrc-- // retry the src
-			}
-		}
-		// Debugf(nil, "src = %v, dst = %v", src, dst)
-		switch {
-		case src == nil && dst == nil:
-			// do nothing
-		case src == nil:
-			dstOnly = append(dstOnly, dst)
-		case dst == nil:
-			srcOnly = append(srcOnly, src)
-		default:
-			matches = append(matches, matchPair{src: src, dst: dst})
-		}
-	}
-	return
-}
-
-// processJob processes a listDirJob listing the source and
-// destination directories, comparing them and returning a slice of
-// more jobs
-//
-// returns errors using processError
-func (s *syncCopyMove) processJob(job listDirJob) (jobs []listDirJob) {
-	var (
-		srcList, dstList       DirEntries
-		srcListErr, dstListErr error
-		wg                     sync.WaitGroup
-	)
-
-	// List the src and dst directories
-	if !job.noSrc {
-		wg.Add(1)
-		go func() {
-			defer wg.Done()
-			srcList, srcListErr = s.srcListDir(job.remote)
-		}()
-	}
-	if !job.noDst {
-		wg.Add(1)
-		go func() {
-			defer wg.Done()
-			dstList, dstListErr = s.dstListDir(job.remote)
-		}()
-	}
-
-	// Wait for listings to complete and report errors
-	wg.Wait()
-	if srcListErr != nil {
-		s.processError(errors.Wrapf(srcListErr, "error reading source directory %q", job.remote))
-		return nil
-	}
-	if dstListErr == ErrorDirNotFound {
-		// Copy the stuff anyway
-	} else if dstListErr != nil {
-		s.processError(errors.Wrapf(dstListErr, "error reading destination directory %q", job.remote))
-		return nil
-	}
-
-	// Work out what to do and do it
-	srcOnly, dstOnly, matches := matchListings(srcList, dstList)
-	for _, src := range srcOnly {
-		if s.aborting() {
-			return nil
-		}
-		s.srcOnly(src, job, &jobs)
-	}
-	for _, dst := range dstOnly {
-		if s.aborting() {
-			return nil
-		}
-		s.dstOnly(dst, job, &jobs)
-	}
-	for _, match := range matches {
-		if s.aborting() {
-			return nil
-		}
-		s.transfer(match.dst, match.src, job, &jobs)
-	}
-	return jobs
+	return false
 }
 
 // Syncs fsrc into fdst