all: Convert folders to use filesystem abstraction

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4228
2017-08-19 14:36:56 +00:00
parent ab8c2fb5c7
commit 3d8b4a42b7
78 changed files with 2588 additions and 1665 deletions
--- a/lib/fs/basicfs.go
+++ b/lib/fs/basicfs.go
@@ -9,30 +9,156 @@ package fs
 import (
 	"errors"
 	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
 	"time"
+
+	"github.com/calmh/du"
+)
+
+var (
+	ErrInvalidFilename = errors.New("filename is invalid")
+	ErrNotRelative     = errors.New("not a relative path")
 )

 // The BasicFilesystem implements all aspects by delegating to package os.
+// All paths are relative to the root and cannot (should not) escape the root directory.
 type BasicFilesystem struct {
+	root string
 }

-func NewBasicFilesystem() *BasicFilesystem {
-	return new(BasicFilesystem)
+func newBasicFilesystem(root string) *BasicFilesystem {
+	// The reason it's done like this:
+	// C:          ->  C:\            ->  C:\        (issue that this is trying to fix)
+	// C:\somedir  ->  C:\somedir\    ->  C:\somedir
+	// C:\somedir\ ->  C:\somedir\\   ->  C:\somedir
+	// This way in the tests, we get away without OS specific separators
+	// in the test configs.
+	root = filepath.Dir(root + string(filepath.Separator))
+
+	// Attempt tilde expansion; leave unchanged in case of error
+	if path, err := ExpandTilde(root); err == nil {
+		root = path
+	}
+
+	// Attempt absolutification; leave unchanged in case of error
+	if !filepath.IsAbs(root) {
+		// Abs() looks like a fairly expensive syscall on Windows, while
+		// IsAbs() is a whole bunch of string mangling. I think IsAbs() may be
+		// somewhat faster in the general case, hence the outer if...
+		if path, err := filepath.Abs(root); err == nil {
+			root = path
+		}
+	}
+
+	// Attempt to enable long filename support on Windows. We may still not
+	// have an absolute path here if the previous steps failed.
+	if runtime.GOOS == "windows" {
+		if filepath.IsAbs(root) && !strings.HasPrefix(root, `\\`) {
+			root = `\\?\` + root
+		}
+		// If we're not on Windows, we want the path to end with a slash to
+		// penetrate symlinks. On Windows, paths must not end with a slash.
+	} else if root[len(root)-1] != filepath.Separator {
+		root = root + string(filepath.Separator)
+	}
+
+	return &BasicFilesystem{
+		root: root,
+	}
+}
+
+// rooted expands the relative path to the full path that is then used with os
+// package. If the relative path somehow causes the final path to escape the root
+// directoy, this returns an error, to prevent accessing files that are not in the
+// shared directory.
+func (f *BasicFilesystem) rooted(rel string) (string, error) {
+	// The root must not be empty.
+	if f.root == "" {
+		return "", ErrInvalidFilename
+	}
+
+	pathSep := string(PathSeparator)
+
+	// The expected prefix for the resulting path is the root, with a path
+	// separator at the end.
+	expectedPrefix := filepath.FromSlash(f.root)
+	if !strings.HasSuffix(expectedPrefix, pathSep) {
+		expectedPrefix += pathSep
+	}
+
+	// The relative path should be clean from internal dotdots and similar
+	// funkyness.
+	rel = filepath.FromSlash(rel)
+	if filepath.Clean(rel) != rel {
+		return "", ErrInvalidFilename
+	}
+
+	// It is not acceptable to attempt to traverse upwards.
+	switch rel {
+	case "..", pathSep:
+		return "", ErrNotRelative
+	}
+	if strings.HasPrefix(rel, ".."+pathSep) {
+		return "", ErrNotRelative
+	}
+
+	if strings.HasPrefix(rel, pathSep+pathSep) {
+		// The relative path may pretend to be an absolute path within the
+		// root, but the double path separator on Windows implies something
+		// else. It would get cleaned by the Join below, but it's out of
+		// spec anyway.
+		return "", ErrNotRelative
+	}
+
+	// The supposedly correct path is the one filepath.Join will return, as
+	// it does cleaning and so on. Check that one first to make sure no
+	// obvious escape attempts have been made.
+	joined := filepath.Join(f.root, rel)
+	if rel == "." && !strings.HasSuffix(joined, pathSep) {
+		joined += pathSep
+	}
+	if !strings.HasPrefix(joined, expectedPrefix) {
+		return "", ErrNotRelative
+	}
+
+	return joined, nil
+}
+
+func (f *BasicFilesystem) unrooted(path string) string {
+	return strings.TrimPrefix(strings.TrimPrefix(path, f.root), string(PathSeparator))
 }

 func (f *BasicFilesystem) Chmod(name string, mode FileMode) error {
+	name, err := f.rooted(name)
+	if err != nil {
+		return err
+	}
 	return os.Chmod(name, os.FileMode(mode))
 }

 func (f *BasicFilesystem) Chtimes(name string, atime time.Time, mtime time.Time) error {
+	name, err := f.rooted(name)
+	if err != nil {
+		return err
+	}
 	return os.Chtimes(name, atime, mtime)
 }

 func (f *BasicFilesystem) Mkdir(name string, perm FileMode) error {
+	name, err := f.rooted(name)
+	if err != nil {
+		return err
+	}
 	return os.Mkdir(name, os.FileMode(perm))
 }

 func (f *BasicFilesystem) Lstat(name string) (FileInfo, error) {
+	name, err := f.rooted(name)
+	if err != nil {
+		return nil, err
+	}
 	fi, err := underlyingLstat(name)
 	if err != nil {
 		return nil, err
@@ -41,14 +167,38 @@ func (f *BasicFilesystem) Lstat(name string) (FileInfo, error) {
 }

 func (f *BasicFilesystem) Remove(name string) error {
+	name, err := f.rooted(name)
+	if err != nil {
+		return err
+	}
 	return os.Remove(name)
 }

+func (f *BasicFilesystem) RemoveAll(name string) error {
+	name, err := f.rooted(name)
+	if err != nil {
+		return err
+	}
+	return os.RemoveAll(name)
+}
+
 func (f *BasicFilesystem) Rename(oldpath, newpath string) error {
+	oldpath, err := f.rooted(oldpath)
+	if err != nil {
+		return err
+	}
+	newpath, err = f.rooted(newpath)
+	if err != nil {
+		return err
+	}
 	return os.Rename(oldpath, newpath)
 }

 func (f *BasicFilesystem) Stat(name string) (FileInfo, error) {
+	name, err := f.rooted(name)
+	if err != nil {
+		return nil, err
+	}
 	fi, err := os.Stat(name)
 	if err != nil {
 		return nil, err
@@ -57,7 +207,11 @@ func (f *BasicFilesystem) Stat(name string) (FileInfo, error) {
 }

 func (f *BasicFilesystem) DirNames(name string) ([]string, error) {
-	fd, err := os.OpenFile(name, os.O_RDONLY, 0777)
+	name, err := f.rooted(name)
+	if err != nil {
+		return nil, err
+	}
+	fd, err := os.OpenFile(name, OptReadOnly, 0777)
 	if err != nil {
 		return nil, err
 	}
@@ -72,19 +226,39 @@ func (f *BasicFilesystem) DirNames(name string) ([]string, error) {
 }

 func (f *BasicFilesystem) Open(name string) (File, error) {
-	fd, err := os.Open(name)
+	rootedName, err := f.rooted(name)
 	if err != nil {
 		return nil, err
 	}
-	return fsFile{fd}, err
+	fd, err := os.Open(rootedName)
+	if err != nil {
+		return nil, err
+	}
+	return fsFile{fd, name}, err
+}
+
+func (f *BasicFilesystem) OpenFile(name string, flags int, mode FileMode) (File, error) {
+	rootedName, err := f.rooted(name)
+	if err != nil {
+		return nil, err
+	}
+	fd, err := os.OpenFile(rootedName, flags, os.FileMode(mode))
+	if err != nil {
+		return nil, err
+	}
+	return fsFile{fd, name}, err
 }

 func (f *BasicFilesystem) Create(name string) (File, error) {
-	fd, err := os.Create(name)
+	rootedName, err := f.rooted(name)
 	if err != nil {
 		return nil, err
 	}
-	return fsFile{fd}, err
+	fd, err := os.Create(rootedName)
+	if err != nil {
+		return nil, err
+	}
+	return fsFile{fd, name}, err
 }

 func (f *BasicFilesystem) Walk(root string, walkFn WalkFunc) error {
@@ -92,9 +266,47 @@ func (f *BasicFilesystem) Walk(root string, walkFn WalkFunc) error {
 	return errors.New("not implemented")
 }

+func (f *BasicFilesystem) Glob(pattern string) ([]string, error) {
+	pattern, err := f.rooted(pattern)
+	if err != nil {
+		return nil, err
+	}
+	files, err := filepath.Glob(pattern)
+	unrooted := make([]string, len(files))
+	for i := range files {
+		unrooted[i] = f.unrooted(files[i])
+	}
+	return unrooted, err
+}
+
+func (f *BasicFilesystem) Usage(name string) (Usage, error) {
+	name, err := f.rooted(name)
+	if err != nil {
+		return Usage{}, err
+	}
+	u, err := du.Get(name)
+	return Usage{
+		Free:  u.FreeBytes,
+		Total: u.TotalBytes,
+	}, err
+}
+
+func (f *BasicFilesystem) Type() FilesystemType {
+	return FilesystemTypeBasic
+}
+
+func (f *BasicFilesystem) URI() string {
+	return strings.TrimPrefix(f.root, `\\?\`)
+}
+
 // fsFile implements the fs.File interface on top of an os.File
 type fsFile struct {
 	*os.File
+	name string
+}
+
+func (f fsFile) Name() string {
+	return f.name
 }

 func (f fsFile) Stat() (FileInfo, error) {
@@ -105,6 +317,17 @@ func (f fsFile) Stat() (FileInfo, error) {
 	return fsFileInfo{info}, nil
 }

+func (f fsFile) Sync() error {
+	err := f.File.Sync()
+	// On Windows, fsyncing a directory returns a "handle is invalid"
+	// So we swallow that and let things go through in order not to have to add
+	// a separate way of syncing directories versus files.
+	if err != nil && (runtime.GOOS != "windows" || !strings.Contains(err.Error(), "handle is invalid")) {
+		return err
+	}
+	return nil
+}
+
 // fsFileInfo implements the fs.FileInfo interface on top of an os.FileInfo.
 type fsFileInfo struct {
 	os.FileInfo
--- a/lib/fs/basicfs_symlink_unix.go
+++ b/lib/fs/basicfs_symlink_unix.go
@@ -1,29 +0,0 @@
-// Copyright (C) 2016 The Syncthing Authors.
-//
-// This Source Code Form is subject to the terms of the Mozilla Public
-// License, v. 2.0. If a copy of the MPL was not distributed with this file,
-// You can obtain one at https://mozilla.org/MPL/2.0/.
-
-// +build !windows
-
-package fs
-
-import "os"
-
-var symlinksSupported = true
-
-func DisableSymlinks() {
-	symlinksSupported = false
-}
-
-func (BasicFilesystem) SymlinksSupported() bool {
-	return symlinksSupported
-}
-
-func (BasicFilesystem) CreateSymlink(name, target string) error {
-	return os.Symlink(target, name)
-}
-
-func (BasicFilesystem) ReadSymlink(path string) (string, error) {
-	return os.Readlink(path)
-}
--- a/lib/fs/basicfs_symlink_windows.go
+++ b/lib/fs/basicfs_symlink_windows.go
@@ -1,27 +0,0 @@
-// Copyright (C) 2014 The Syncthing Authors.
-//
-// This Source Code Form is subject to the terms of the Mozilla Public
-// License, v. 2.0. If a copy of the MPL was not distributed with this file,
-// You can obtain one at https://mozilla.org/MPL/2.0/.
-
-// +build windows
-
-package fs
-
-import "errors"
-
-var errNotSupported = errors.New("symlinks not supported")
-
-func DisableSymlinks() {}
-
-func (BasicFilesystem) SymlinksSupported() bool {
-	return false
-}
-
-func (BasicFilesystem) ReadSymlink(path string) (string, error) {
-	return "", errNotSupported
-}
-
-func (BasicFilesystem) CreateSymlink(path, target string) error {
-	return errNotSupported
-}
--- a/lib/fs/basicfs_test.go
+++ b/lib/fs/basicfs_test.go
@@ -0,0 +1,486 @@
+// Copyright (C) 2017 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package fs
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"runtime"
+	"sort"
+	"strings"
+	"testing"
+	"time"
+)
+
+func setup(t *testing.T) (Filesystem, string) {
+	dir, err := ioutil.TempDir("", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	return newBasicFilesystem(dir), dir
+}
+
+func TestChmodFile(t *testing.T) {
+	fs, dir := setup(t)
+	path := filepath.Join(dir, "file")
+	defer os.RemoveAll(dir)
+
+	defer os.Chmod(path, 0666)
+
+	fd, err := os.Create(path)
+	if err != nil {
+		t.Error(err)
+	}
+	fd.Close()
+
+	if err := os.Chmod(path, 0666); err != nil {
+		t.Error(err)
+	}
+
+	if stat, err := os.Stat(path); err != nil || stat.Mode()&os.ModePerm != 0666 {
+		t.Errorf("wrong perm: %t %#o", err == nil, stat.Mode()&os.ModePerm)
+	}
+
+	if err := fs.Chmod("file", 0444); err != nil {
+		t.Error(err)
+	}
+
+	if stat, err := os.Stat(path); err != nil || stat.Mode()&os.ModePerm != 0444 {
+		t.Errorf("wrong perm: %t %#o", err == nil, stat.Mode()&os.ModePerm)
+	}
+}
+
+func TestChmodDir(t *testing.T) {
+	fs, dir := setup(t)
+	path := filepath.Join(dir, "dir")
+	defer os.RemoveAll(dir)
+
+	mode := os.FileMode(0755)
+	if runtime.GOOS == "windows" {
+		mode = os.FileMode(0777)
+	}
+
+	defer os.Chmod(path, mode)
+
+	if err := os.Mkdir(path, mode); err != nil {
+		t.Error(err)
+	}
+
+	if stat, err := os.Stat(path); err != nil || stat.Mode()&os.ModePerm != mode {
+		t.Errorf("wrong perm: %t %#o", err == nil, stat.Mode()&os.ModePerm)
+	}
+
+	if err := fs.Chmod("dir", 0555); err != nil {
+		t.Error(err)
+	}
+
+	if stat, err := os.Stat(path); err != nil || stat.Mode()&os.ModePerm != 0555 {
+		t.Errorf("wrong perm: %t %#o", err == nil, stat.Mode()&os.ModePerm)
+	}
+}
+
+func TestChtimes(t *testing.T) {
+	fs, dir := setup(t)
+	path := filepath.Join(dir, "file")
+	defer os.RemoveAll(dir)
+	fd, err := os.Create(path)
+	if err != nil {
+		t.Error(err)
+	}
+	fd.Close()
+
+	mtime := time.Now().Add(-time.Hour)
+
+	fs.Chtimes("file", mtime, mtime)
+
+	stat, err := os.Stat(path)
+	if err != nil {
+		t.Error(err)
+	}
+
+	diff := stat.ModTime().Sub(mtime)
+	if diff > 3*time.Second || diff < -3*time.Second {
+		t.Errorf("%s != %s", stat.Mode(), mtime)
+	}
+}
+
+func TestCreate(t *testing.T) {
+	fs, dir := setup(t)
+	path := filepath.Join(dir, "file")
+	defer os.RemoveAll(dir)
+
+	if _, err := os.Stat(path); err == nil {
+		t.Errorf("exists?")
+	}
+
+	fd, err := fs.Create("file")
+	if err != nil {
+		t.Error(err)
+	}
+	fd.Close()
+
+	if _, err := os.Stat(path); err != nil {
+		t.Error(err)
+	}
+}
+
+func TestCreateSymlink(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("windows not supported")
+	}
+
+	fs, dir := setup(t)
+	path := filepath.Join(dir, "file")
+	defer os.RemoveAll(dir)
+
+	if err := fs.CreateSymlink("blah", "file"); err != nil {
+		t.Error(err)
+	}
+
+	if target, err := os.Readlink(path); err != nil || target != "blah" {
+		t.Error("target", target, "err", err)
+	}
+
+	if err := os.Remove(path); err != nil {
+		t.Error(err)
+	}
+
+	if err := fs.CreateSymlink(filepath.Join("..", "blah"), "file"); err != nil {
+		t.Error(err)
+	}
+
+	if target, err := os.Readlink(path); err != nil || target != filepath.Join("..", "blah") {
+		t.Error("target", target, "err", err)
+	}
+}
+
+func TestDirNames(t *testing.T) {
+	fs, dir := setup(t)
+	defer os.RemoveAll(dir)
+
+	// Case differences
+	testCases := []string{
+		"a",
+		"bC",
+	}
+	sort.Strings(testCases)
+
+	for _, sub := range testCases {
+		if err := os.Mkdir(filepath.Join(dir, sub), 0777); err != nil {
+			t.Error(err)
+		}
+	}
+
+	if dirs, err := fs.DirNames("."); err != nil || len(dirs) != len(testCases) {
+		t.Errorf("%s %s %s", err, dirs, testCases)
+	} else {
+		sort.Strings(dirs)
+		for i := range dirs {
+			if dirs[i] != testCases[i] {
+				t.Errorf("%s != %s", dirs[i], testCases[i])
+			}
+		}
+	}
+}
+
+func TestNames(t *testing.T) {
+	// Tests that all names are without the root directory.
+	fs, dir := setup(t)
+	defer os.RemoveAll(dir)
+
+	expected := "file"
+	fd, err := fs.Create(expected)
+	if err != nil {
+		t.Error(err)
+	}
+	defer fd.Close()
+
+	if fd.Name() != expected {
+		t.Errorf("incorrect %s != %s", fd.Name(), expected)
+	}
+	if stat, err := fd.Stat(); err != nil || stat.Name() != expected {
+		t.Errorf("incorrect %s != %s (%v)", stat.Name(), expected, err)
+	}
+
+	if err := fs.Mkdir("dir", 0777); err != nil {
+		t.Error(err)
+	}
+
+	expected = filepath.Join("dir", "file")
+	fd, err = fs.Create(expected)
+	if err != nil {
+		t.Error(err)
+	}
+	defer fd.Close()
+
+	if fd.Name() != expected {
+		t.Errorf("incorrect %s != %s", fd.Name(), expected)
+	}
+
+	// os.fd.Stat() returns just base, so do we.
+	if stat, err := fd.Stat(); err != nil || stat.Name() != filepath.Base(expected) {
+		t.Errorf("incorrect %s != %s (%v)", stat.Name(), filepath.Base(expected), err)
+	}
+}
+
+func TestGlob(t *testing.T) {
+	// Tests that all names are without the root directory.
+	fs, dir := setup(t)
+	defer os.RemoveAll(dir)
+
+	for _, dirToCreate := range []string{
+		filepath.Join("a", "test", "b"),
+		filepath.Join("a", "best", "b"),
+		filepath.Join("a", "best", "c"),
+	} {
+		if err := fs.MkdirAll(dirToCreate, 0777); err != nil {
+			t.Error(err)
+		}
+	}
+
+	testCases := []struct {
+		pattern string
+		matches []string
+	}{
+		{
+			filepath.Join("a", "?est", "?"),
+			[]string{
+				filepath.Join("a", "test", "b"),
+				filepath.Join("a", "best", "b"),
+				filepath.Join("a", "best", "c"),
+			},
+		},
+		{
+			filepath.Join("a", "?est", "b"),
+			[]string{
+				filepath.Join("a", "test", "b"),
+				filepath.Join("a", "best", "b"),
+			},
+		},
+		{
+			filepath.Join("a", "best", "?"),
+			[]string{
+				filepath.Join("a", "best", "b"),
+				filepath.Join("a", "best", "c"),
+			},
+		},
+	}
+
+	for _, testCase := range testCases {
+		results, err := fs.Glob(testCase.pattern)
+		sort.Strings(results)
+		sort.Strings(testCase.matches)
+		if err != nil {
+			t.Error(err)
+		}
+		if len(results) != len(testCase.matches) {
+			t.Errorf("result count mismatch")
+		}
+		for i := range testCase.matches {
+			if results[i] != testCase.matches[i] {
+				t.Errorf("%s != %s", results[i], testCase.matches[i])
+			}
+		}
+	}
+}
+
+func TestUsage(t *testing.T) {
+	fs, dir := setup(t)
+	defer os.RemoveAll(dir)
+	usage, err := fs.Usage(".")
+	if err != nil {
+		if runtime.GOOS == "netbsd" || runtime.GOOS == "openbsd" || runtime.GOOS == "solaris" {
+			t.Skip()
+		}
+		t.Errorf("Unexpected error: %s", err)
+	}
+	if usage.Free < 1 {
+		t.Error("Disk is full?", usage.Free)
+	}
+}
+
+func TestWindowsPaths(t *testing.T) {
+	if runtime.GOOS != "windows" {
+		t.Skip("Not useful on non-Windows")
+		return
+	}
+
+	testCases := []struct {
+		input        string
+		expectedRoot string
+		expectedURI  string
+	}{
+		{`e:\`, `\\?\e:\`, `e:\`},
+		{`\\?\e:\`, `\\?\e:\`, `e:\`},
+		{`\\192.0.2.22\network\share`, `\\192.0.2.22\network\share`, `\\192.0.2.22\network\share`},
+	}
+
+	for _, testCase := range testCases {
+		fs := newBasicFilesystem(testCase.input)
+		if fs.root != testCase.expectedRoot {
+			t.Errorf("root %q != %q", fs.root, testCase.expectedRoot)
+		}
+		if fs.URI() != testCase.expectedURI {
+			t.Errorf("uri %q != %q", fs.URI(), testCase.expectedURI)
+		}
+	}
+
+	fs := newBasicFilesystem(`relative\path`)
+	if fs.root == `relative\path` || !strings.HasPrefix(fs.root, "\\\\?\\") {
+		t.Errorf("%q == %q, expected absolutification", fs.root, `relative\path`)
+	}
+}
+
+func TestRooted(t *testing.T) {
+	type testcase struct {
+		root   string
+		rel    string
+		joined string
+		ok     bool
+	}
+	cases := []testcase{
+		// Valid cases
+		{"foo", "bar", "foo/bar", true},
+		{"foo", "/bar", "foo/bar", true},
+		{"foo/", "bar", "foo/bar", true},
+		{"foo/", "/bar", "foo/bar", true},
+		{"baz/foo", "bar", "baz/foo/bar", true},
+		{"baz/foo", "/bar", "baz/foo/bar", true},
+		{"baz/foo/", "bar", "baz/foo/bar", true},
+		{"baz/foo/", "/bar", "baz/foo/bar", true},
+		{"foo", "bar/baz", "foo/bar/baz", true},
+		{"foo", "/bar/baz", "foo/bar/baz", true},
+		{"foo/", "bar/baz", "foo/bar/baz", true},
+		{"foo/", "/bar/baz", "foo/bar/baz", true},
+		{"baz/foo", "bar/baz", "baz/foo/bar/baz", true},
+		{"baz/foo", "/bar/baz", "baz/foo/bar/baz", true},
+		{"baz/foo/", "bar/baz", "baz/foo/bar/baz", true},
+		{"baz/foo/", "/bar/baz", "baz/foo/bar/baz", true},
+
+		// Not escape attempts, but oddly formatted relative paths. Disallowed.
+		{"foo", "./bar", "", false},
+		{"baz/foo", "./bar", "", false},
+		{"foo", "./bar/baz", "", false},
+		{"baz/foo", "./bar/baz", "", false},
+		{"baz/foo", "bar/../baz", "", false},
+		{"baz/foo", "/bar/../baz", "", false},
+		{"baz/foo", "./bar/../baz", "", false},
+		{"baz/foo", "bar/../baz", "", false},
+		{"baz/foo", "/bar/../baz", "", false},
+		{"baz/foo", "./bar/../baz", "", false},
+
+		// Results in an allowed path, but does it by probing. Disallowed.
+		{"foo", "../foo", "", false},
+		{"foo", "../foo/bar", "", false},
+		{"baz/foo", "../foo/bar", "", false},
+		{"baz/foo", "../../baz/foo/bar", "", false},
+		{"baz/foo", "bar/../../foo/bar", "", false},
+		{"baz/foo", "bar/../../../baz/foo/bar", "", false},
+
+		// Escape attempts.
+		{"foo", "", "", false},
+		{"foo", "/", "", false},
+		{"foo", "..", "", false},
+		{"foo", "/..", "", false},
+		{"foo", "../", "", false},
+		{"foo", "../bar", "", false},
+		{"foo", "../foobar", "", false},
+		{"foo/", "../bar", "", false},
+		{"foo/", "../foobar", "", false},
+		{"baz/foo", "../bar", "", false},
+		{"baz/foo", "../foobar", "", false},
+		{"baz/foo/", "../bar", "", false},
+		{"baz/foo/", "../foobar", "", false},
+		{"baz/foo/", "bar/../../quux/baz", "", false},
+
+		// Empty root is a misconfiguration.
+		{"", "/foo", "", false},
+		{"", "foo", "", false},
+		{"", ".", "", false},
+		{"", "..", "", false},
+		{"", "/", "", false},
+		{"", "", "", false},
+
+		// Root=/ is valid, and things should be verified as usual.
+		{"/", "foo", "/foo", true},
+		{"/", "/foo", "/foo", true},
+		{"/", "../foo", "", false},
+		{"/", "..", "", false},
+		{"/", "/", "", false},
+		{"/", "", "", false},
+
+		// special case for filesystems to be able to MkdirAll('.') for example
+		{"/", ".", "/", true},
+	}
+
+	if runtime.GOOS == "windows" {
+		extraCases := []testcase{
+			{`c:\`, `foo`, `c:\foo`, true},
+			{`\\?\c:\`, `foo`, `\\?\c:\foo`, true},
+			{`c:\`, `\foo`, `c:\foo`, true},
+			{`\\?\c:\`, `\foo`, `\\?\c:\foo`, true},
+			{`c:\`, `\\foo`, ``, false},
+			{`c:\`, ``, ``, false},
+			{`c:\`, `\`, ``, false},
+			{`\\?\c:\`, `\\foo`, ``, false},
+			{`\\?\c:\`, ``, ``, false},
+			{`\\?\c:\`, `\`, ``, false},
+
+			// makes no sense, but will be treated simply as a bad filename
+			{`c:\foo`, `d:\bar`, `c:\foo\d:\bar`, true},
+
+			// special case for filesystems to be able to MkdirAll('.') for example
+			{`c:\`, `.`, `c:\`, true},
+			{`\\?\c:\`, `.`, `\\?\c:\`, true},
+		}
+
+		for _, tc := range cases {
+			// Add case where root is backslashed, rel is forward slashed
+			extraCases = append(extraCases, testcase{
+				root:   filepath.FromSlash(tc.root),
+				rel:    tc.rel,
+				joined: tc.joined,
+				ok:     tc.ok,
+			})
+			// and the opposite
+			extraCases = append(extraCases, testcase{
+				root:   tc.root,
+				rel:    filepath.FromSlash(tc.rel),
+				joined: tc.joined,
+				ok:     tc.ok,
+			})
+			// and both backslashed
+			extraCases = append(extraCases, testcase{
+				root:   filepath.FromSlash(tc.root),
+				rel:    filepath.FromSlash(tc.rel),
+				joined: tc.joined,
+				ok:     tc.ok,
+			})
+		}
+
+		cases = append(cases, extraCases...)
+	}
+
+	for _, tc := range cases {
+		fs := BasicFilesystem{root: tc.root}
+		res, err := fs.rooted(tc.rel)
+		if tc.ok {
+			if err != nil {
+				t.Errorf("Unexpected error for rooted(%q, %q): %v", tc.root, tc.rel, err)
+				continue
+			}
+			exp := filepath.FromSlash(tc.joined)
+			if res != exp {
+				t.Errorf("Unexpected result for rooted(%q, %q): %q != expected %q", tc.root, tc.rel, res, exp)
+			}
+		} else if err == nil {
+			t.Errorf("Unexpected pass for rooted(%q, %q) => %q", tc.root, tc.rel, res)
+			continue
+		}
+	}
+}
--- a/lib/fs/basicfs_unix.go
+++ b/lib/fs/basicfs_unix.go
@@ -0,0 +1,57 @@
+// Copyright (C) 2016 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+// +build !windows
+
+package fs
+
+import "os"
+
+func (BasicFilesystem) SymlinksSupported() bool {
+	return true
+}
+
+func (f *BasicFilesystem) CreateSymlink(target, name string) error {
+	name, err := f.rooted(name)
+	if err != nil {
+		return err
+	}
+	return os.Symlink(target, name)
+}
+
+func (f *BasicFilesystem) ReadSymlink(name string) (string, error) {
+	name, err := f.rooted(name)
+	if err != nil {
+		return "", err
+	}
+	return os.Readlink(name)
+}
+
+func (f *BasicFilesystem) MkdirAll(name string, perm FileMode) error {
+	name, err := f.rooted(name)
+	if err != nil {
+		return err
+	}
+	return os.MkdirAll(name, os.FileMode(perm))
+}
+
+// Unhide is a noop on unix, as unhiding files requires renaming them.
+// We still check that the relative path does not try to escape the root
+func (f *BasicFilesystem) Unhide(name string) error {
+	_, err := f.rooted(name)
+	return err
+}
+
+// Hide is a noop on unix, as hiding files requires renaming them.
+// We still check that the relative path does not try to escape the root
+func (f *BasicFilesystem) Hide(name string) error {
+	_, err := f.rooted(name)
+	return err
+}
+
+func (f *BasicFilesystem) Roots() ([]string, error) {
+	return []string{"/"}, nil
+}
--- a/lib/fs/basicfs_windows.go
+++ b/lib/fs/basicfs_windows.go
@@ -0,0 +1,165 @@
+// Copyright (C) 2014 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+// +build windows
+
+package fs
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"syscall"
+	"unsafe"
+)
+
+var errNotSupported = errors.New("symlinks not supported")
+
+func (BasicFilesystem) SymlinksSupported() bool {
+	return false
+}
+
+func (BasicFilesystem) ReadSymlink(path string) (string, error) {
+	return "", errNotSupported
+}
+
+func (BasicFilesystem) CreateSymlink(path, target string) error {
+	return errNotSupported
+}
+
+// MkdirAll creates a directory named path, along with any necessary parents,
+// and returns nil, or else returns an error.
+// The permission bits perm are used for all directories that MkdirAll creates.
+// If path is already a directory, MkdirAll does nothing and returns nil.
+func (f *BasicFilesystem) MkdirAll(path string, perm FileMode) error {
+	path, err := f.rooted(path)
+	if err != nil {
+		return err
+	}
+
+	return f.mkdirAll(path, os.FileMode(perm))
+}
+
+// Required due to https://github.com/golang/go/issues/10900
+func (f *BasicFilesystem) mkdirAll(path string, perm os.FileMode) error {
+	// Fast path: if we can tell whether path is a directory or file, stop with success or error.
+	dir, err := os.Stat(path)
+	if err == nil {
+		if dir.IsDir() {
+			return nil
+		}
+		return &os.PathError{
+			Op:   "mkdir",
+			Path: path,
+			Err:  syscall.ENOTDIR,
+		}
+	}
+
+	// Slow path: make sure parent exists and then call Mkdir for path.
+	i := len(path)
+	for i > 0 && IsPathSeparator(path[i-1]) { // Skip trailing path separator.
+		i--
+	}
+
+	j := i
+	for j > 0 && !IsPathSeparator(path[j-1]) { // Scan backward over element.
+		j--
+	}
+
+	if j > 1 {
+		// Create parent
+		parent := path[0 : j-1]
+		if parent != filepath.VolumeName(parent) {
+			err = os.MkdirAll(parent, perm)
+			if err != nil {
+				return err
+			}
+		}
+	}
+
+	// Parent now exists; invoke Mkdir and use its result.
+	err = os.Mkdir(path, perm)
+	if err != nil {
+		// Handle arguments like "foo/." by
+		// double-checking that directory doesn't exist.
+		dir, err1 := os.Lstat(path)
+		if err1 == nil && dir.IsDir() {
+			return nil
+		}
+		return err
+	}
+	return nil
+}
+
+func (f *BasicFilesystem) Unhide(name string) error {
+	name, err := f.rooted(name)
+	if err != nil {
+		return err
+	}
+	p, err := syscall.UTF16PtrFromString(name)
+	if err != nil {
+		return err
+	}
+
+	attrs, err := syscall.GetFileAttributes(p)
+	if err != nil {
+		return err
+	}
+
+	attrs &^= syscall.FILE_ATTRIBUTE_HIDDEN
+	return syscall.SetFileAttributes(p, attrs)
+}
+
+func (f *BasicFilesystem) Hide(name string) error {
+	name, err := f.rooted(name)
+	if err != nil {
+		return err
+	}
+	p, err := syscall.UTF16PtrFromString(name)
+	if err != nil {
+		return err
+	}
+
+	attrs, err := syscall.GetFileAttributes(p)
+	if err != nil {
+		return err
+	}
+
+	attrs |= syscall.FILE_ATTRIBUTE_HIDDEN
+	return syscall.SetFileAttributes(p, attrs)
+}
+
+func (f *BasicFilesystem) Roots() ([]string, error) {
+	kernel32, err := syscall.LoadDLL("kernel32.dll")
+	if err != nil {
+		return nil, err
+	}
+	getLogicalDriveStringsHandle, err := kernel32.FindProc("GetLogicalDriveStringsA")
+	if err != nil {
+		return nil, err
+	}
+
+	buffer := [1024]byte{}
+	bufferSize := uint32(len(buffer))
+
+	hr, _, _ := getLogicalDriveStringsHandle.Call(uintptr(unsafe.Pointer(&bufferSize)), uintptr(unsafe.Pointer(&buffer)))
+	if hr == 0 {
+		return nil, fmt.Errorf("Syscall failed")
+	}
+
+	var drives []string
+	parts := bytes.Split(buffer[:], []byte{0})
+	for _, part := range parts {
+		if len(part) == 0 {
+			break
+		}
+		drives = append(drives, string(part))
+	}
+
+	return drives, nil
+}
--- a/lib/fs/debug.go
+++ b/lib/fs/debug.go
@@ -0,0 +1,22 @@
+// Copyright (C) 2015 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package fs
+
+import (
+	"os"
+	"strings"
+
+	"github.com/syncthing/syncthing/lib/logger"
+)
+
+var (
+	l = logger.DefaultLogger.NewFacility("filesystem", "Filesystem access")
+)
+
+func init() {
+	l.SetDebug("filesystem", strings.Contains(os.Getenv("STTRACE"), "filesystem") || os.Getenv("STTRACE") == "all")
+}
--- a/lib/fs/errorfs.go
+++ b/lib/fs/errorfs.go
@@ -0,0 +1,41 @@
+// Copyright (C) 2016 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package fs
+
+import "time"
+
+type errorFilesystem struct {
+	err    error
+	fsType FilesystemType
+	uri    string
+}
+
+func (fs *errorFilesystem) Chmod(name string, mode FileMode) error                      { return fs.err }
+func (fs *errorFilesystem) Chtimes(name string, atime time.Time, mtime time.Time) error { return fs.err }
+func (fs *errorFilesystem) Create(name string) (File, error)                            { return nil, fs.err }
+func (fs *errorFilesystem) CreateSymlink(name, target string) error                     { return fs.err }
+func (fs *errorFilesystem) DirNames(name string) ([]string, error)                      { return nil, fs.err }
+func (fs *errorFilesystem) Lstat(name string) (FileInfo, error)                         { return nil, fs.err }
+func (fs *errorFilesystem) Mkdir(name string, perm FileMode) error                      { return fs.err }
+func (fs *errorFilesystem) MkdirAll(name string, perm FileMode) error                   { return fs.err }
+func (fs *errorFilesystem) Open(name string) (File, error)                              { return nil, fs.err }
+func (fs *errorFilesystem) OpenFile(string, int, FileMode) (File, error)                { return nil, fs.err }
+func (fs *errorFilesystem) ReadSymlink(name string) (string, error)                     { return "", fs.err }
+func (fs *errorFilesystem) Remove(name string) error                                    { return fs.err }
+func (fs *errorFilesystem) RemoveAll(name string) error                                 { return fs.err }
+func (fs *errorFilesystem) Rename(oldname, newname string) error                        { return fs.err }
+func (fs *errorFilesystem) Stat(name string) (FileInfo, error)                          { return nil, fs.err }
+func (fs *errorFilesystem) SymlinksSupported() bool                                     { return false }
+func (fs *errorFilesystem) Walk(root string, walkFn WalkFunc) error                     { return fs.err }
+func (fs *errorFilesystem) Unhide(name string) error                                    { return fs.err }
+func (fs *errorFilesystem) Hide(name string) error                                      { return fs.err }
+func (fs *errorFilesystem) Glob(pattern string) ([]string, error)                       { return nil, fs.err }
+func (fs *errorFilesystem) SyncDir(name string) error                                   { return fs.err }
+func (fs *errorFilesystem) Roots() ([]string, error)                                    { return nil, fs.err }
+func (fs *errorFilesystem) Usage(name string) (Usage, error)                            { return Usage{}, fs.err }
+func (fs *errorFilesystem) Type() FilesystemType                                        { return fs.fsType }
+func (fs *errorFilesystem) URI() string                                                 { return fs.uri }
--- a/lib/fs/filesystem.go
+++ b/lib/fs/filesystem.go
@@ -7,6 +7,7 @@
 package fs

 import (
+	"errors"
 	"io"
 	"os"
 	"path/filepath"
@@ -22,23 +23,38 @@ type Filesystem interface {
 	DirNames(name string) ([]string, error)
 	Lstat(name string) (FileInfo, error)
 	Mkdir(name string, perm FileMode) error
+	MkdirAll(name string, perm FileMode) error
 	Open(name string) (File, error)
+	OpenFile(name string, flags int, mode FileMode) (File, error)
 	ReadSymlink(name string) (string, error)
 	Remove(name string) error
+	RemoveAll(name string) error
 	Rename(oldname, newname string) error
 	Stat(name string) (FileInfo, error)
 	SymlinksSupported() bool
 	Walk(root string, walkFn WalkFunc) error
+	Hide(name string) error
+	Unhide(name string) error
+	Glob(pattern string) ([]string, error)
+	Roots() ([]string, error)
+	Usage(name string) (Usage, error)
+	Type() FilesystemType
+	URI() string
 }

 // The File interface abstracts access to a regular file, being a somewhat
 // smaller interface than os.File
 type File interface {
-	io.Reader
-	io.WriterAt
 	io.Closer
+	io.Reader
+	io.ReaderAt
+	io.Seeker
+	io.Writer
+	io.WriterAt
+	Name() string
 	Truncate(size int64) error
 	Stat() (FileInfo, error)
+	Sync() error
 }

 // The FileInfo interface is almost the same as os.FileInfo, but with the
@@ -59,12 +75,27 @@ type FileInfo interface {
 // FileMode is similar to os.FileMode
 type FileMode uint32

-// ModePerm is the equivalent of os.ModePerm
-const ModePerm = FileMode(os.ModePerm)
+// Usage represents filesystem space usage
+type Usage struct {
+	Free  int64
+	Total int64
+}

-// DefaultFilesystem is the fallback to use when nothing explicitly has
-// been passed.
-var DefaultFilesystem Filesystem = NewWalkFilesystem(NewBasicFilesystem())
+// Equivalents from os package.
+
+const ModePerm = FileMode(os.ModePerm)
+const ModeSetgid = FileMode(os.ModeSetgid)
+const ModeSetuid = FileMode(os.ModeSetuid)
+const ModeSticky = FileMode(os.ModeSticky)
+const PathSeparator = os.PathSeparator
+const OptAppend = os.O_APPEND
+const OptCreate = os.O_CREATE
+const OptExclusive = os.O_EXCL
+const OptReadOnly = os.O_RDONLY
+const OptReadWrite = os.O_RDWR
+const OptSync = os.O_SYNC
+const OptTruncate = os.O_TRUNC
+const OptWriteOnly = os.O_WRONLY

 // SkipDir is used as a return value from WalkFuncs to indicate that
 // the directory named in the call is to be skipped. It is not returned
@@ -76,3 +107,29 @@ var IsExist = os.IsExist

 // IsNotExist is the equivalent of os.IsNotExist
 var IsNotExist = os.IsNotExist
+
+// IsPermission is the equivalent of os.IsPermission
+var IsPermission = os.IsPermission
+
+// IsPathSeparator is the equivalent of os.IsPathSeparator
+var IsPathSeparator = os.IsPathSeparator
+
+func NewFilesystem(fsType FilesystemType, uri string) Filesystem {
+	var fs Filesystem
+	switch fsType {
+	case FilesystemTypeBasic:
+		fs = NewWalkFilesystem(newBasicFilesystem(uri))
+	default:
+		l.Debugln("Unknown filesystem", fsType, uri)
+		fs = &errorFilesystem{
+			fsType: fsType,
+			uri:    uri,
+			err:    errors.New("filesystem with type " + fsType.String() + " does not exist."),
+		}
+	}
+
+	if l.ShouldDebug("filesystem") {
+		fs = &logFilesystem{fs}
+	}
+	return fs
+}
--- a/lib/fs/logfs.go
+++ b/lib/fs/logfs.go
@@ -0,0 +1,158 @@
+// Copyright (C) 2016 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package fs
+
+import (
+	"fmt"
+	"path/filepath"
+	"runtime"
+	"time"
+)
+
+type logFilesystem struct {
+	Filesystem
+}
+
+func getCaller() string {
+	_, file, line, ok := runtime.Caller(2)
+	if !ok {
+		return "unknown"
+	}
+	return fmt.Sprintf("%s:%d", filepath.Base(file), line)
+}
+
+func (fs *logFilesystem) Chmod(name string, mode FileMode) error {
+	err := fs.Filesystem.Chmod(name, mode)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "Chmod", name, mode, err)
+	return err
+}
+
+func (fs *logFilesystem) Chtimes(name string, atime time.Time, mtime time.Time) error {
+	err := fs.Filesystem.Chtimes(name, atime, mtime)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "Chtimes", name, atime, mtime, err)
+	return err
+}
+
+func (fs *logFilesystem) Create(name string) (File, error) {
+	file, err := fs.Filesystem.Create(name)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "Create", name, file, err)
+	return file, err
+}
+
+func (fs *logFilesystem) CreateSymlink(name, target string) error {
+	err := fs.Filesystem.CreateSymlink(name, target)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "CreateSymlink", name, target, err)
+	return err
+}
+
+func (fs *logFilesystem) DirNames(name string) ([]string, error) {
+	names, err := fs.Filesystem.DirNames(name)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "DirNames", name, names, err)
+	return names, err
+}
+
+func (fs *logFilesystem) Lstat(name string) (FileInfo, error) {
+	info, err := fs.Filesystem.Lstat(name)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "Lstat", name, info, err)
+	return info, err
+}
+
+func (fs *logFilesystem) Mkdir(name string, perm FileMode) error {
+	err := fs.Filesystem.Mkdir(name, perm)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "Mkdir", name, perm, err)
+	return err
+}
+
+func (fs *logFilesystem) MkdirAll(name string, perm FileMode) error {
+	err := fs.Filesystem.MkdirAll(name, perm)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "MkdirAll", name, perm, err)
+	return err
+}
+
+func (fs *logFilesystem) Open(name string) (File, error) {
+	file, err := fs.Filesystem.Open(name)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "Open", name, file, err)
+	return file, err
+}
+
+func (fs *logFilesystem) OpenFile(name string, flags int, mode FileMode) (File, error) {
+	file, err := fs.Filesystem.OpenFile(name, flags, mode)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "OpenFile", name, flags, mode, file, err)
+	return file, err
+}
+
+func (fs *logFilesystem) ReadSymlink(name string) (string, error) {
+	target, err := fs.Filesystem.ReadSymlink(name)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "ReadSymlink", name, target, err)
+	return target, err
+}
+
+func (fs *logFilesystem) Remove(name string) error {
+	err := fs.Filesystem.Remove(name)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "Remove", name, err)
+	return err
+}
+
+func (fs *logFilesystem) RemoveAll(name string) error {
+	err := fs.Filesystem.RemoveAll(name)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "RemoveAll", name, err)
+	return err
+}
+
+func (fs *logFilesystem) Rename(oldname, newname string) error {
+	err := fs.Filesystem.Rename(oldname, newname)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "Rename", oldname, newname, err)
+	return err
+}
+
+func (fs *logFilesystem) Stat(name string) (FileInfo, error) {
+	info, err := fs.Filesystem.Stat(name)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "Stat", name, info, err)
+	return info, err
+}
+
+func (fs *logFilesystem) SymlinksSupported() bool {
+	supported := fs.Filesystem.SymlinksSupported()
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "SymlinksSupported", supported)
+	return supported
+}
+
+func (fs *logFilesystem) Walk(root string, walkFn WalkFunc) error {
+	err := fs.Filesystem.Walk(root, walkFn)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "Walk", root, walkFn, err)
+	return err
+}
+
+func (fs *logFilesystem) Unhide(name string) error {
+	err := fs.Filesystem.Unhide(name)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "Unhide", name, err)
+	return err
+}
+
+func (fs *logFilesystem) Hide(name string) error {
+	err := fs.Filesystem.Hide(name)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "Hide", name, err)
+	return err
+}
+
+func (fs *logFilesystem) Glob(name string) ([]string, error) {
+	names, err := fs.Filesystem.Glob(name)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "Glob", name, names, err)
+	return names, err
+}
+
+func (fs *logFilesystem) Roots() ([]string, error) {
+	roots, err := fs.Filesystem.Roots()
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "Roots", roots, err)
+	return roots, err
+}
+
+func (fs *logFilesystem) Usage(name string) (Usage, error) {
+	usage, err := fs.Filesystem.Usage(name)
+	l.Debugln(getCaller(), fs.Type(), fs.URI(), "Usage", name, usage, err)
+	return usage, err
+}
--- a/lib/fs/mtimefs.go
+++ b/lib/fs/mtimefs.go
@@ -6,12 +6,7 @@

 package fs

-import (
-	"os"
-	"time"
-
-	"github.com/syncthing/syncthing/lib/osutil"
-)
+import "time"

 // The database is where we store the virtual mtimes
 type database interface {
@@ -20,36 +15,34 @@ type database interface {
 	Delete(key string)
 }

-// variable so that we can mock it for testing
-var osChtimes = os.Chtimes
-
 // The MtimeFS is a filesystem with nanosecond mtime precision, regardless
 // of what shenanigans the underlying filesystem gets up to. A nil MtimeFS
 // just does the underlying operations with no additions.
 type MtimeFS struct {
 	Filesystem
-	db database
+	chtimes func(string, time.Time, time.Time) error
+	db      database
 }

 func NewMtimeFS(underlying Filesystem, db database) *MtimeFS {
 	return &MtimeFS{
 		Filesystem: underlying,
+		chtimes:    underlying.Chtimes, // for mocking it out in the tests
 		db:         db,
 	}
 }

 func (f *MtimeFS) Chtimes(name string, atime, mtime time.Time) error {
 	if f == nil {
-		return osChtimes(name, atime, mtime)
+		return f.chtimes(name, atime, mtime)
 	}

 	// Do a normal Chtimes call, don't care if it succeeds or not.
-	osChtimes(name, atime, mtime)
+	f.chtimes(name, atime, mtime)

 	// Stat the file to see what happened. Here we *do* return an error,
-	// because it might be "does not exist" or similar. osutil.Lstat is the
-	// souped up version to account for Android breakage.
-	info, err := osutil.Lstat(name)
+	// because it might be "does not exist" or similar.
+	info, err := f.Filesystem.Lstat(name)
 	if err != nil {
 		return err
 	}
--- a/lib/fs/mtimefs_test.go
+++ b/lib/fs/mtimefs_test.go
@@ -25,22 +25,22 @@ func TestMtimeFS(t *testing.T) {
 	// a random time with nanosecond precision
 	testTime := time.Unix(1234567890, 123456789)

-	mtimefs := NewMtimeFS(DefaultFilesystem, make(mapStore))
+	mtimefs := NewMtimeFS(newBasicFilesystem("."), make(mapStore))

 	// Do one Chtimes call that will go through to the normal filesystem
-	osChtimes = os.Chtimes
+	mtimefs.chtimes = os.Chtimes
 	if err := mtimefs.Chtimes("testdata/exists0", testTime, testTime); err != nil {
 		t.Error("Should not have failed:", err)
 	}

 	// Do one call that gets an error back from the underlying Chtimes
-	osChtimes = failChtimes
+	mtimefs.chtimes = failChtimes
 	if err := mtimefs.Chtimes("testdata/exists1", testTime, testTime); err != nil {
 		t.Error("Should not have failed:", err)
 	}

 	// Do one call that gets struck by an exceptionally evil Chtimes
-	osChtimes = evilChtimes
+	mtimefs.chtimes = evilChtimes
 	if err := mtimefs.Chtimes("testdata/exists2", testTime, testTime); err != nil {
 		t.Error("Should not have failed:", err)
 	}
--- a/lib/fs/types.go
+++ b/lib/fs/types.go
@@ -0,0 +1,36 @@
+// Copyright (C) 2016 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package fs
+
+type FilesystemType int
+
+const (
+	FilesystemTypeBasic FilesystemType = iota // default is basic
+)
+
+func (t FilesystemType) String() string {
+	switch t {
+	case FilesystemTypeBasic:
+		return "basic"
+	default:
+		return "unknown"
+	}
+}
+
+func (t FilesystemType) MarshalText() ([]byte, error) {
+	return []byte(t.String()), nil
+}
+
+func (t *FilesystemType) UnmarshalText(bs []byte) error {
+	switch string(bs) {
+	case "basic":
+		*t = FilesystemTypeBasic
+	default:
+		*t = FilesystemTypeBasic
+	}
+	return nil
+}
--- a/lib/fs/util.go
+++ b/lib/fs/util.go
@@ -0,0 +1,55 @@
+// Copyright (C) 2016 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package fs
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+)
+
+var errNoHome = errors.New("no home directory found - set $HOME (or the platform equivalent)")
+
+func ExpandTilde(path string) (string, error) {
+	if path == "~" {
+		return getHomeDir()
+	}
+
+	path = filepath.FromSlash(path)
+	if !strings.HasPrefix(path, fmt.Sprintf("~%c", PathSeparator)) {
+		return path, nil
+	}
+
+	home, err := getHomeDir()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(home, path[2:]), nil
+}
+
+func getHomeDir() (string, error) {
+	var home string
+
+	switch runtime.GOOS {
+	case "windows":
+		home = filepath.Join(os.Getenv("HomeDrive"), os.Getenv("HomePath"))
+		if home == "" {
+			home = os.Getenv("UserProfile")
+		}
+	default:
+		home = os.Getenv("HOME")
+	}
+
+	if home == "" {
+		return "", errNoHome
+	}
+
+	return home, nil
+}
--- a/lib/fs/walkfs.go
+++ b/lib/fs/walkfs.go
@@ -28,16 +28,16 @@ import "path/filepath"
 // Walk skips the remaining files in the containing directory.
 type WalkFunc func(path string, info FileInfo, err error) error

-type WalkFilesystem struct {
+type walkFilesystem struct {
 	Filesystem
 }

-func NewWalkFilesystem(next Filesystem) *WalkFilesystem {
-	return &WalkFilesystem{next}
+func NewWalkFilesystem(next Filesystem) Filesystem {
+	return &walkFilesystem{next}
 }

 // walk recursively descends path, calling walkFn.
-func (f *WalkFilesystem) walk(path string, info FileInfo, walkFn WalkFunc) error {
+func (f *walkFilesystem) walk(path string, info FileInfo, walkFn WalkFunc) error {
 	err := walkFn(path, info, nil)
 	if err != nil {
 		if info.IsDir() && err == SkipDir {
@@ -80,7 +80,7 @@ func (f *WalkFilesystem) walk(path string, info FileInfo, walkFn WalkFunc) error
 // order, which makes the output deterministic but means that for very
 // large directories Walk can be inefficient.
 // Walk does not follow symbolic links.
-func (f *WalkFilesystem) Walk(root string, walkFn WalkFunc) error {
+func (f *walkFilesystem) Walk(root string, walkFn WalkFunc) error {
 	info, err := f.Lstat(root)
 	if err != nil {
 		return walkFn(root, nil, err)