Reject files excluded by name before calling lstat to improve scan speed

Adds a SelectByName method to the archive and scanner which only require
the filename as input, and can thus be run before calling lstat on the
file. Can speed up scanning significantly if a lot of filename excludes
are used.

cmd/restic/cmd_backup.go

@@ -186,18 +186,9 @@ func (opts BackupOptions) Check(gopts GlobalOptions, args []string) error {
 	return nil
 }
 
-// collectRejectFuncs returns a list of all functions which may reject data
-// from being saved in a snapshot
-func collectRejectFuncs(opts BackupOptions, repo *repository.Repository, targets []string) (fs []RejectFunc, err error) {
-	// allowed devices
-	if opts.ExcludeOtherFS && !opts.Stdin {
-		f, err := rejectByDevice(targets)
-		if err != nil {
-			return nil, err
-		}
-		fs = append(fs, f)
-	}
-
+// collectRejectByNameFuncs returns a list of all functions which may reject data
+// from being saved in a snapshot based on path only
+func collectRejectByNameFuncs(opts BackupOptions, repo *repository.Repository, targets []string) (fs []RejectByNameFunc, err error) {
 	// exclude restic cache
 	if repo.Cache != nil {
 		f, err := rejectResticCache(repo)
@@ -237,6 +228,21 @@ func collectRejectFuncs(opts BackupOptions, repo *repository.Repository, targets
 	return fs, nil
 }
 
+// collectRejectFuncs returns a list of all functions which may reject data
+// from being saved in a snapshot based on path and file info
+func collectRejectFuncs(opts BackupOptions, repo *repository.Repository, targets []string) (fs []RejectFunc, err error) {
+	// allowed devices
+	if opts.ExcludeOtherFS && !opts.Stdin {
+		f, err := rejectByDevice(targets)
+		if err != nil {
+			return nil, err
+		}
+		fs = append(fs, f)
+	}
+
+	return fs, nil
+}
+
 // readExcludePatternsFromFiles reads all exclude files and returns the list of
 // exclude patterns. For each line, leading and trailing white space is removed
 // and comment lines are ignored. For each remaining pattern, environment
@@ -393,7 +399,13 @@ func runBackup(opts BackupOptions, gopts GlobalOptions, term *termstatus.Termina
 		return err
 	}
 
-	// rejectFuncs collect functions that can reject items from the backup
+	// rejectByNameFuncs collect functions that can reject items from the backup based on path only
+	rejectByNameFuncs, err := collectRejectByNameFuncs(opts, repo, targets)
+	if err != nil {
+		return err
+	}
+
+	// rejectFuncs collect functions that can reject items from the backup based on path and file info
 	rejectFuncs, err := collectRejectFuncs(opts, repo, targets)
 	if err != nil {
 		return err
@@ -414,6 +426,15 @@ func runBackup(opts BackupOptions, gopts GlobalOptions, term *termstatus.Termina
 		p.V("using parent snapshot %v\n", parentSnapshotID.Str())
 	}
 
+	selectByNameFilter := func(item string) bool {
+		for _, reject := range rejectByNameFuncs {
+			if reject(item) {
+				return false
+			}
+		}
+		return true
+	}
+
 	selectFilter := func(item string, fi os.FileInfo) bool {
 		for _, reject := range rejectFuncs {
 			if reject(item, fi) {
@@ -436,6 +457,7 @@ func runBackup(opts BackupOptions, gopts GlobalOptions, term *termstatus.Termina
 	}
 
 	sc := archiver.NewScanner(targetFS)
+	sc.SelectByName = selectByNameFilter
 	sc.Select = selectFilter
 	sc.Error = p.ScannerError
 	sc.Result = p.ReportTotal
@@ -444,6 +466,7 @@ func runBackup(opts BackupOptions, gopts GlobalOptions, term *termstatus.Termina
 	t.Go(func() error { return sc.Scan(t.Context(gopts.ctx), targets) })
 
 	arch := archiver.New(repo, targetFS, archiver.Options{})
+	arch.SelectByName = selectByNameFilter
 	arch.Select = selectFilter
 	arch.WithAtime = opts.WithAtime
 	arch.Error = p.Error

cmd/restic/exclude.go

@@ -60,15 +60,20 @@ func (rc *rejectionCache) Store(dir string, rejected bool) {
 	rc.m[dir] = rejected
 }
 
+// RejectByNameFunc is a function that takes a filename of a
+// file that would be included in the backup. The function returns true if it
+// should be excluded (rejected) from the backup.
+type RejectByNameFunc func(path string) bool
+
 // RejectFunc is a function that takes a filename and os.FileInfo of a
 // file that would be included in the backup. The function returns true if it
 // should be excluded (rejected) from the backup.
 type RejectFunc func(path string, fi os.FileInfo) bool
 
-// rejectByPattern returns a RejectFunc which rejects files that match
+// rejectByPattern returns a RejectByNameFunc which rejects files that match
 // one of the patterns.
-func rejectByPattern(patterns []string) RejectFunc {
-	return func(item string, fi os.FileInfo) bool {
+func rejectByPattern(patterns []string) RejectByNameFunc {
+	return func(item string) bool {
 		matched, _, err := filter.List(patterns, item)
 		if err != nil {
 			Warnf("error for exclude pattern: %v", err)
@@ -83,14 +88,14 @@ func rejectByPattern(patterns []string) RejectFunc {
 	}
 }
 
-// rejectIfPresent returns a RejectFunc which itself returns whether a path
-// should be excluded. The RejectFunc considers a file to be excluded when
+// rejectIfPresent returns a RejectByNameFunc which itself returns whether a path
+// should be excluded. The RejectByNameFunc considers a file to be excluded when
 // it resides in a directory with an exclusion file, that is specified by
 // excludeFileSpec in the form "filename[:content]". The returned error is
 // non-nil if the filename component of excludeFileSpec is empty. If rc is
-// non-nil, it is going to be used in the RejectFunc to expedite the evaluation
+// non-nil, it is going to be used in the RejectByNameFunc to expedite the evaluation
 // of a directory based on previous visits.
-func rejectIfPresent(excludeFileSpec string) (RejectFunc, error) {
+func rejectIfPresent(excludeFileSpec string) (RejectByNameFunc, error) {
 	if excludeFileSpec == "" {
 		return nil, errors.New("name for exclusion tagfile is empty")
 	}
@@ -107,7 +112,7 @@ func rejectIfPresent(excludeFileSpec string) (RejectFunc, error) {
 	}
 	debug.Log("using %q as exclusion tagfile", tf)
 	rc := &rejectionCache{}
-	fn := func(filename string, _ os.FileInfo) bool {
+	fn := func(filename string) bool {
 		return isExcludedByFile(filename, tf, tc, rc)
 	}
 	return fn, nil
@@ -252,11 +257,11 @@ func rejectByDevice(samples []string) (RejectFunc, error) {
 	}, nil
 }
 
-// rejectResticCache returns a RejectFunc that rejects the restic cache
+// rejectResticCache returns a RejectByNameFunc that rejects the restic cache
 // directory (if set).
-func rejectResticCache(repo *repository.Repository) (RejectFunc, error) {
+func rejectResticCache(repo *repository.Repository) (RejectByNameFunc, error) {
 	if repo.Cache == nil {
-		return func(string, os.FileInfo) bool {
+		return func(string) bool {
 			return false
 		}, nil
 	}
@@ -266,7 +271,7 @@ func rejectResticCache(repo *repository.Repository) (RejectFunc, error) {
 		return nil, errors.New("cacheBase is empty string")
 	}
 
-	return func(item string, _ os.FileInfo) bool {
+	return func(item string) bool {
 		if fs.HasPathPrefix(cacheBase, item) {
 			debug.Log("rejecting restic cache directory %v", item)
 			return true

cmd/restic/exclude_test.go

@@ -27,7 +27,7 @@ func TestRejectByPattern(t *testing.T) {
 	for _, tc := range tests {
 		t.Run("", func(t *testing.T) {
 			reject := rejectByPattern(patterns)
-			res := reject(tc.filename, nil)
+			res := reject(tc.filename)
 			if res != tc.reject {
 				t.Fatalf("wrong result for filename %v: want %v, got %v",
 					tc.filename, tc.reject, res)
@@ -140,8 +140,8 @@ func TestMultipleIsExcludedByFile(t *testing.T) {
 		if err != nil {
 			return err
 		}
-		excludedByFoo := fooExclude(p, fi)
-		excludedByBar := barExclude(p, fi)
+		excludedByFoo := fooExclude(p)
+		excludedByBar := barExclude(p)
 		excluded := excludedByFoo || excludedByBar
 		// the log message helps debugging in case the test fails
 		t.Logf("%q: %v || %v = %v", p, excludedByFoo, excludedByBar, excluded)

internal/archiver/archiver.go

@@ -16,6 +16,10 @@ import (
 	tomb "gopkg.in/tomb.v2"
 )
 
+// SelectByNameFunc returns true for all items that should be included (files and
+// dirs). If false is returned, files are ignored and dirs are not even walked.
+type SelectByNameFunc func(item string) bool
+
 // SelectFunc returns true for all items that should be included (files and
 // dirs). If false is returned, files are ignored and dirs are not even walked.
 type SelectFunc func(item string, fi os.FileInfo) bool
@@ -44,6 +48,7 @@ func (s *ItemStats) Add(other ItemStats) {
 // Archiver saves a directory structure to the repo.
 type Archiver struct {
 	Repo         restic.Repository
+	SelectByName SelectByNameFunc
 	Select       SelectFunc
 	FS           fs.FS
 	Options      Options
@@ -120,7 +125,8 @@ func (o Options) ApplyDefaults() Options {
 func New(repo restic.Repository, fs fs.FS, opts Options) *Archiver {
 	arch := &Archiver{
 		Repo:         repo,
-		Select:  func(string, os.FileInfo) bool { return true },
+		SelectByName: func(item string) bool { return true },
+		Select:       func(item string, fi os.FileInfo) bool { return true },
 		FS:           fs,
 		Options:      opts.ApplyDefaults(),
 
@@ -297,7 +303,7 @@ func (fn *FutureNode) wait(ctx context.Context) {
 // excluded, this function returns a nil node and error, with excluded set to
 // true.
 //
-// Errors and completion is needs to be handled by the caller.
+// Errors and completion needs to be handled by the caller.
 //
 // snPath is the path within the current snapshot.
 func (arch *Archiver) Save(ctx context.Context, snPath, target string, previous *restic.Node) (fn FutureNode, excluded bool, err error) {
@@ -316,6 +322,13 @@ func (arch *Archiver) Save(ctx context.Context, snPath, target string, previous
 
 	fn.absTarget = abstarget
 
+	// exclude files by path before running Lstat to reduce number of lstat calls
+	if !arch.SelectByName(abstarget) {
+		debug.Log("%v is excluded by path", target)
+		return FutureNode{}, true, nil
+	}
+
+	// get file info and run remaining select functions that require file information
 	fi, err := arch.FS.Lstat(target)
 	if !arch.Select(abstarget, fi) {
 		debug.Log("%v is excluded", target)

internal/archiver/scanner.go

@@ -13,6 +13,7 @@ import (
 // items should be included. Error is called when an error occurs.
 type Scanner struct {
 	FS           fs.FS
+	SelectByName SelectByNameFunc
 	Select       SelectFunc
 	Error        ErrorFunc
 	Result       func(item string, s ScanStats)
@@ -22,12 +23,9 @@ type Scanner struct {
 func NewScanner(fs fs.FS) *Scanner {
 	return &Scanner{
 		FS:           fs,
-		Select: func(item string, fi os.FileInfo) bool {
-			return true
-		},
-		Error: func(item string, fi os.FileInfo, err error) error {
-			return err
-		},
+		SelectByName: func(item string) bool { return true },
+		Select:       func(item string, fi os.FileInfo) bool { return true },
+		Error:        func(item string, fi os.FileInfo, err error) error { return err },
 		Result:       func(item string, s ScanStats) {},
 	}
 }
@@ -70,17 +68,18 @@ func (s *Scanner) scan(ctx context.Context, stats ScanStats, target string) (Sca
 		return stats, ctx.Err()
 	}
 
-	fi, err := s.FS.Lstat(target)
-	if err != nil {
-		// ignore error if the target is to be excluded anyway
-		if !s.Select(target, nil) {
+	// exclude files by path before running stat to reduce number of lstat calls
+	if !s.SelectByName(target) {
 		return stats, nil
 	}
 
-		// else return filtered error
+	// get file information
+	fi, err := s.FS.Lstat(target)
+	if err != nil {
 		return stats, s.Error(target, fi, err)
 	}
 
+	// run remaining select functions that require file information
 	if !s.Select(target, fi) {
 		return stats, nil
 	}