syncthing/lib/fs/mtimefs.go

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// 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 http://mozilla.org/MPL/2.0/.
package fs
import (
"os"
"time"
"github.com/syncthing/syncthing/lib/osutil"
)
// The database is where we store the virtual mtimes
type database interface {
Bytes(key string) (data []byte, ok bool)
PutBytes(key string, data []byte)
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.
type MtimeFS struct {
db database
}
func NewMtimeFS(db database) *MtimeFS {
return &MtimeFS{
db: db,
}
}
func (f *MtimeFS) Chtimes(name string, atime, mtime time.Time) error {
// Do a normal Chtimes call, don't care if it succeeds or not.
osChtimes(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)
if err != nil {
return err
}
f.save(name, info.ModTime(), mtime)
return nil
}
func (f *MtimeFS) Lstat(name string) (os.FileInfo, error) {
info, err := osutil.Lstat(name)
if err != nil {
return nil, err
}
real, virtual := f.load(name)
if real == info.ModTime() {
info = mtimeFileInfo{
FileInfo: info,
mtime: virtual,
}
}
return info, nil
}
// "real" is the on disk timestamp
// "virtual" is what want the timestamp to be
func (f *MtimeFS) save(name string, real, virtual time.Time) {
if real.Equal(virtual) {
// If the virtual time and the real on disk time are equal we don't
// need to store anything.
f.db.Delete(name)
return
}
mtime := dbMtime{
real: real,
virtual: virtual,
}
bs, _ := mtime.Marshal() // Can't fail
f.db.PutBytes(name, bs)
}
func (f *MtimeFS) load(name string) (real, virtual time.Time) {
data, exists := f.db.Bytes(name)
if !exists {
return
}
var mtime dbMtime
if err := mtime.Unmarshal(data); err != nil {
return
}
return mtime.real, mtime.virtual
}
// The mtimeFileInfo is an os.FileInfo that lies about the ModTime().
type mtimeFileInfo struct {
os.FileInfo
mtime time.Time
}
func (m mtimeFileInfo) ModTime() time.Time {
return m.mtime
}
// The dbMtime is our database representation
type dbMtime struct {
real time.Time
virtual time.Time
}
func (t *dbMtime) Marshal() ([]byte, error) {
bs0, _ := t.real.MarshalBinary()
bs1, _ := t.virtual.MarshalBinary()
return append(bs0, bs1...), nil
}
func (t *dbMtime) Unmarshal(bs []byte) error {
if err := t.real.UnmarshalBinary(bs[:len(bs)/2]); err != nil {
return err
}
if err := t.virtual.UnmarshalBinary(bs[len(bs)/2:]); err != nil {
return err
}
return nil
}