Support backup and restore of hardlinks

This tracks inode/device from the stat info and creates backward
compatible snapshots that allow preserving hardlinks. Backwards
compatibility is preserved by saving a virtual inode number index in the
Link field of the file entry. Since this field was previously only used
for symlinks, this won't break old versions. Additionally, the entry
data is cloned so restoration with an old version works.

Current limitations are primarility with restore. They include:
- no command line option to prevent hard link restore
- if a file has the immutable or append only flag it will be set before
hardlinks are restored, so hardlinking will fail.
- if a partial restore includes a hardlink but not the parent
directories the hardlink will fail.

These will be solved by grouping restore of hardlinks together
with file, prior to applying final metadata.

- if a file is changed and is being rewritten by a restore hardlinks are
not preserved.

src/duplicacy_backupmanager.go

@@ -304,24 +304,7 @@ func (manager *BackupManager) Backup(top string, quickMode bool, threads int, ta
 			remoteEntry = nil
 		}
 
-		if localEntry.IsHardlinkedFrom() {
-			// FIXME: Sanity check?
-			// FIXME: perhaps we can make size = 0 an initial invariant of the link?
-			//
-			// Note that if the initial size was 0 then this original logic doesn't change!
-			localEntry.Size = 0
-			// targetEntry, ok := localEntryList.HardLinkTable[localEntry.Link]
-			// if !ok {
-			// 	LOG_ERROR("BACKUP_CREATE", "Hard link %s not found in entry cache for path %s", localEntry.Link, localEntry.Path)
-			// }
-			// localEntry.Size = targetEntry.Size
-			// localEntry.Hash = targetEntry.Hash
-			// localEntry.StartChunk = targetEntry.StartChunk
-			// localEntry.StartOffset = targetEntry.StartOffset
-			// localEntry.EndChunk = targetEntry.EndChunk
-			// localEntry.EndOffset = targetEntry.EndOffset
-			// LOG_DEBUG("BACKUP_CREATE", "Hard link %s to %s in initial listing", localEntry.Link, targetEntry.Path)
-		} else if compareResult == 0  {
+		if compareResult == 0  {
 			// No need to check if it is in hash mode -- in that case remote listing is nil
 			if localEntry.IsSameAs(remoteEntry) && localEntry.IsFile() {
 				if localEntry.Size > 0 {
@@ -639,11 +622,6 @@ func (manager *BackupManager) Backup(top string, quickMode bool, threads int, ta
 	return true
 }
 
-type hardLinkEntry struct {
-	entry *Entry
-	willDownload bool
-}
-
 // Restore downloads the specified snapshot, compares it with what's on the repository, and then downloads
 // files that are different. 'base' is a directory that contains files at a different revision which can
 // serve as a local cache to avoid download chunks available locally.  It is perfectly ok for 'base' to be
@@ -725,14 +703,17 @@ func (manager *BackupManager) Restore(top string, revision int, inPlace bool, qu
 	var localEntry *Entry
 	localListingOK := true
 
-	hardLinkTable := make(map[string]hardLinkEntry)
-	//hardLinks := make([]*Entry, 0)
+	type hardLinkEntry struct {
+		entry *Entry
+		willDownload bool
+	}
+	var hardLinkTable []hardLinkEntry
+	var hardLinks []*Entry
 
 	for remoteEntry := range remoteListingChannel {
 
-		if remoteEntry.IsFile() && remoteEntry.Link == "/" {
-			LOG_INFO("RESTORE_LINK", "Noting hardlinked source file %s", remoteEntry.Path)
-			hardLinkTable[remoteEntry.Path] = hardLinkEntry{remoteEntry, false}
+		if remoteEntry.IsHardlinkRoot() {
+			hardLinkTable = append(hardLinkTable, hardLinkEntry{remoteEntry, false})
 		}
 
 		if len(patterns) > 0 && !MatchPath(remoteEntry.Path, patterns) {
@@ -743,8 +724,6 @@ func (manager *BackupManager) Restore(top string, revision int, inPlace bool, qu
 		var compareResult int
 
 		for {
-			// TODO: We likely need to check if a local listing file exists in the hardLinkTable for the case where one is restoring a hardlink
-			// to an existing disk file. Right now, we'll just end up downloading the file new.
 			if localEntry == nil && localListingOK {
 				localEntry, localListingOK = <- localListingChannel
 			}
@@ -762,28 +741,12 @@ func (manager *BackupManager) Restore(top string, revision int, inPlace bool, qu
 		}
 
 		if compareResult == 0 {
-			// if quickMode && localEntry.IsFile() {
-				if quickMode && localEntry.IsFile() && localEntry.IsSameAs(remoteEntry) {
-					LOG_TRACE("RESTORE_SKIP", "File %s unchanged (by size and timestamp)", localEntry.Path)
-					skippedFileSize += localEntry.Size
-					skippedFileCount++
-					localEntry = nil
-					continue
-				// checkEntry := remoteEntry
-				// if len(remoteEntry.Link) > 0 && remoteEntry.Link != "/" {
-				// 	if e, ok := hardLinkTable[remoteEntry.Link]; !ok {
-				// 		LOG_ERROR("RESTORE_LINK", "Source file %s for hardlink %s missing", remoteEntry.Link, remoteEntry.Path)
-				// 	} else {
-				// 		checkEntry = e.entry
-				// 	}
-				// }
-				// if localEntry.IsSameAs(checkEntry) {
-				// 	LOG_TRACE("RESTORE_SKIP", "File %s unchanged (by size and timestamp)", localEntry.Path)
-				// 	skippedFileSize += localEntry.Size
-				// 	skippedFileCount++
-				// 	localEntry = nil
-				// 	continue
-				// }
+			if quickMode && localEntry.IsFile() && localEntry.IsSameAs(remoteEntry) {
+				LOG_TRACE("RESTORE_SKIP", "File %s unchanged (by size and timestamp)", localEntry.Path)
+				skippedFileSize += localEntry.Size
+				skippedFileCount++
+				localEntry = nil
+				continue
 			}
 			localEntry = nil
 		}
@@ -828,23 +791,24 @@ func (manager *BackupManager) Restore(top string, revision int, inPlace bool, qu
 					return 0
 				}
 			}
+			remoteEntry.RestoreEarlyDirFlags(fullPath)
 			directoryEntries = append(directoryEntries, remoteEntry)
 		} else {
-			// if remoteEntry.Link == "/" {
-			// 	hardLinkTable[remoteEntry.Path] = hardLinkEntry{remoteEntry, true}
-			// } else if len(remoteEntry.Link) > 0 {
-			// 	if e, ok := hardLinkTable[remoteEntry.Link]; !ok {
-			// 		LOG_ERROR("RESTORE_LINK", "Source file %s for hardlink %s missing", remoteEntry.Link, remoteEntry.Path)
-			// 	} else if !e.willDownload {
-			// 		origSourcePath := e.entry.Path
-			// 		e.entry.Path = remoteEntry.Path
-			// 		remoteEntry = e.entry
-			// 		hardLinkTable[origSourcePath] = hardLinkEntry{remoteEntry, true}
-			// 	} else {
-			// 		hardLinks = append(hardLinks, remoteEntry)
-			// 		continue
-			// 	}
-			// }
+			if remoteEntry.IsHardlinkRoot() {
+				hardLinkTable[len(hardLinkTable)-1] = hardLinkEntry{remoteEntry, true}
+			} else if remoteEntry.IsHardlinkedFrom() {
+				i, err := strconv.ParseUint(remoteEntry.Link, 16, 64)
+				if err !=  nil {
+					LOG_ERROR("RESTORE_HARDLINK", "Decode error in hardlink entry, expected hex int, got %s", remoteEntry.Link)
+					return 0
+				}
+				if !hardLinkTable[i].willDownload {
+					hardLinkTable[i] = hardLinkEntry{remoteEntry, true}
+				} else {
+					hardLinks = append(hardLinks, remoteEntry)
+					continue
+				}
+			}
 			// We can't download files here since fileEntries needs to be sorted
 			fileEntries = append(fileEntries, remoteEntry)
 			totalFileSize += remoteEntry.Size
@@ -900,10 +864,6 @@ func (manager *BackupManager) Restore(top string, revision int, inPlace bool, qu
 		stat, _ := os.Stat(fullPath)
 		if stat != nil {
 			if quickMode {
-				// cmpFile := file
-				// if file.IsFile() && len(file.Link) > 0 && file.Link != "/" {
-				// 	cmpFile = hardLinkTable[file.Link].entry
-				// }
 				if file.IsSameAsFileInfo(stat) {
 					LOG_TRACE("RESTORE_SKIP", "File %s unchanged (by size and timestamp)", file.Path)
 					skippedFileSize += file.Size
@@ -941,6 +901,7 @@ func (manager *BackupManager) Restore(top string, revision int, inPlace bool, qu
 				downloadedFileSize += file.Size
 				downloadedFiles = append(downloadedFiles, file)
 			}
+
 			continue
 		}
 
@@ -967,14 +928,16 @@ func (manager *BackupManager) Restore(top string, revision int, inPlace bool, qu
 		file.RestoreMetadata(fullPath, nil, setOwner)
 	}
 
-	// for _, linkEntry := range hardLinks {
-	// 	sourcePath := joinPath(top, hardLinkTable[linkEntry.Link].entry.Path)
-	// 	fullPath := joinPath(top, linkEntry.Path)
-	// 	LOG_INFO("DOWNLOAD_LINK", "Hard linking %s -> %s", fullPath, sourcePath)
-	// 	if err := os.Link(sourcePath, fullPath); err != nil {
-	// 		LOG_ERROR("DOWNLOAD_LINK", "Failed to create hard link %s -> %s", fullPath, sourcePath)
-	// 	}
-	// }
+	for _, linkEntry := range hardLinks {
+		i, _ := strconv.ParseUint(linkEntry.Link, 16, 64)
+		sourcePath := joinPath(top, hardLinkTable[i].entry.Path)
+		fullPath := joinPath(top, linkEntry.Path)
+		LOG_INFO("RESTORE_HARDLINK", "Hard linking %s to %s", fullPath, sourcePath)
+		if err := os.Link(sourcePath, fullPath); err != nil {
+			LOG_ERROR("RESTORE_HARDLINK", "Failed to create hard link %s to %s", fullPath, sourcePath)
+			return 0
+		}
+	}
 
 	if deleteMode && len(patterns) == 0 {
 		// Reverse the order to make sure directories are empty before being deleted
@@ -1127,11 +1090,13 @@ func (manager *BackupManager) UploadSnapshot(chunkOperator *ChunkOperator, top s
 
 	lastEndChunk := 0
 
-	uploadEntryInfoFunc := func(entry *Entry) error {
-		if entry.IsHardlinkRoot() {
-			entryList.HardLinkTable[entry.Path] = entry
-		}
+	type hardLinkEntry struct {
+		entry *Entry
+		startChunk int
+	}
+	var hardLinkTable []hardLinkEntry
 
+	uploadEntryInfoFunc := func(entry *Entry) error {
 		if entry.IsFile() && entry.Size > 0 {
 			delta := entry.StartChunk - len(chunkHashes) + 1
 			if entry.StartChunk != lastChunk {
@@ -1149,18 +1114,38 @@ func (manager *BackupManager) UploadSnapshot(chunkOperator *ChunkOperator, top s
 			entry.StartChunk -= delta
 			entry.EndChunk -= delta
 
+			if entry.IsHardlinkRoot() {
+				LOG_DEBUG("SNAPSHOT_UPLOAD", "Hard link root %s %v %v", entry.Path, entry.StartChunk, entry.EndChunk)
+				hardLinkTable = append(hardLinkTable, hardLinkEntry{entry, entry.StartChunk})
+			}
+
 			delta = entry.EndChunk - entry.StartChunk
 			entry.StartChunk -= lastEndChunk
 			lastEndChunk = entry.EndChunk
 			entry.EndChunk = delta
 		} else if entry.IsHardlinkedFrom() {
-			targetEntry, ok := entryList.HardLinkTable[entry.Link]
-			if !ok {
-				LOG_ERROR("SNAPSHOT_UPLOAD", "Unable to find hardlink target for %s to %s", entry.Path, entry.Link)
+			i, err := strconv.ParseUint(entry.Link, 16, 64)
+			if err !=  nil {
+				LOG_ERROR("SNAPSHOT_UPLOAD", "Decode error in hardlink entry, expected hex int, got %s", entry.Link)
+				return err
 			}
-			// FIXME: We will use a copy, so it is probably sufficient to skip rereading xattrs and such in the initial code
-			entry = entry.LinkTo(targetEntry)
-			LOG_DEBUG("SNAPSHOT_UPLOAD", "Uploading cloned hardlink entry for %s to %s", entry.Path, entry.Link)
+
+			targetEntry := hardLinkTable[i].entry
+			var startChunk, endChunk int
+
+			if targetEntry.Size > 0 {
+				startChunk = hardLinkTable[i].startChunk - lastEndChunk
+				endChunk = targetEntry.EndChunk
+			}
+			entry = entry.HardLinkTo(targetEntry, startChunk, endChunk)
+
+			if targetEntry.Size > 0 {
+				lastEndChunk = hardLinkTable[i].startChunk + endChunk
+			}
+
+			LOG_DEBUG("SNAPSHOT_UPLOAD", "Uploading cloned hardlink for %s to %s (%v %v)", entry.Path, targetEntry.Path, startChunk, endChunk)
+		} else if entry.IsHardlinkRoot() {
+			hardLinkTable = append(hardLinkTable, hardLinkEntry{entry, 0})
 		}
 
 		buffer.Reset()
@@ -1280,6 +1265,7 @@ func (manager *BackupManager) RestoreFile(chunkDownloader *ChunkDownloader, chun
 					LOG_ERROR("DOWNLOAD_CREATE", "Failed to create the file %s for in-place writing: %v", fullPath, err)
 					return false, nil
 				}
+				entry.RestoreEarlyFileFlags(existingFile)
 
 				n := int64(1)
 				// There is a go bug on Windows (https://github.com/golang/go/issues/21681) that causes Seek to fail
@@ -1463,6 +1449,7 @@ func (manager *BackupManager) RestoreFile(chunkDownloader *ChunkDownloader, chun
 				return false, nil
 			}
 		}
+		entry.RestoreEarlyFileFlags(existingFile)
 
 		existingFile.Seek(0, 0)
 
@@ -1545,6 +1532,7 @@ func (manager *BackupManager) RestoreFile(chunkDownloader *ChunkDownloader, chun
 			LOG_ERROR("DOWNLOAD_OPEN", "Failed to open file for writing: %v", err)
 			return false, nil
 		}
+		entry.RestoreEarlyFileFlags(newFile)
 
 		hasher := manager.config.NewFileHasher()
 

src/duplicacy_entry.go

@@ -119,7 +119,7 @@ func (entry *Entry) Copy() *Entry {
 	}
 }
 
-func (entry *Entry) LinkTo(target *Entry) *Entry {
+func (entry *Entry) HardLinkTo(target *Entry, startChunk int, endChunk int) *Entry {
 	return &Entry{
 		Path: entry.Path,
 		Size: target.Size,
@@ -131,9 +131,9 @@ func (entry *Entry) LinkTo(target *Entry) *Entry {
 		UID: target.UID,
 		GID: target.GID,
 
-		StartChunk:  target.StartChunk,
+		StartChunk:  startChunk,
 		StartOffset: target.StartOffset,
-		EndChunk:    target.EndChunk,
+		EndChunk:    endChunk,
 		EndOffset:   target.EndOffset,
 
 		Attributes: target.Attributes,
@@ -513,10 +513,6 @@ func (entry *Entry) IsComplete() bool {
 	return entry.Size >= 0
 }
 
-func (entry *Entry) IsFileNotHardlink() bool {
-	return entry.IsFile() && (len(entry.Link) == 0 || entry.Link == "/")
-}
-
 func (entry *Entry) IsHardlinkedFrom() bool {
 	return entry.IsFile() && len(entry.Link) > 0 && entry.Link != "/"
 }
@@ -733,12 +729,13 @@ type listEntryLinkKey struct {
 }
 
 type ListingState struct {
-	linkTable map[listEntryLinkKey]string // map unique inode details to initially found path
+	linkIndex int
+	linkTable map[listEntryLinkKey]int // map unique inode details to initially found path
 }
 
 func NewListingState() *ListingState {
 	return &ListingState{
-		linkTable: make(map[listEntryLinkKey]string),
+		linkTable: make(map[listEntryLinkKey]int),
 	}
 }
 
@@ -820,6 +817,30 @@ func ListEntries(top string, path string, patterns []string, nobackupFile string
 			}
 		}
 
+		if f.Mode()&(os.ModeNamedPipe|os.ModeSocket|os.ModeDevice) != 0 {
+			LOG_WARN("LIST_SKIP", "Skipped non-regular file %s", entry.Path)
+			skippedFiles = append(skippedFiles, entry.Path)
+			continue
+		}
+
+		var linkKey *listEntryLinkKey
+
+		if stat, ok := f.Sys().(*syscall.Stat_t); entry.IsFile() && ok && stat != nil && stat.Nlink > 1 {
+			k := listEntryLinkKey{dev: uint64(stat.Dev), ino: uint64(stat.Ino)}
+			if linkIndex, seen := listingState.linkTable[k]; seen {
+				if linkIndex == -1 {
+					LOG_DEBUG("LIST_EXCLUDE", "%s is excluded by attribute (hardlink)", entry.Path)
+					continue
+				}
+				entry.Size = 0
+				entry.Link = strconv.FormatInt(int64(linkIndex), 16)
+			} else {
+				entry.Link = "/"
+				listingState.linkTable[k] = -1
+				linkKey = &k
+			}
+		}
+
 		entry.ReadAttributes(top)
 
 		if excludeByAttribute && entry.Attributes != nil && excludedByAttribute(*entry.Attributes) {
@@ -827,24 +848,9 @@ func ListEntries(top string, path string, patterns []string, nobackupFile string
 			continue
 		}
 
-		if f.Mode()&(os.ModeNamedPipe|os.ModeSocket|os.ModeDevice) != 0 {
-			LOG_WARN("LIST_SKIP", "Skipped non-regular file %s", entry.Path)
-			skippedFiles = append(skippedFiles, entry.Path)
-			continue
-		}
-
-		if entry.IsFile() {
-			stat, ok := f.Sys().(*syscall.Stat_t)
-			if ok && stat != nil && stat.Nlink > 1 {
-				k := listEntryLinkKey{dev: uint64(stat.Dev), ino: uint64(stat.Ino)}
-				if path, ok := listingState.linkTable[k]; ok {
-					LOG_DEBUG("LIST_HARDLINK", "Detected hardlink %s to %s", entry.Path, path)
-					entry.Link = path
-				} else {
-					entry.Link = "/"
-					listingState.linkTable[k] = entry.Path
-				}
-			}
+		if linkKey != nil {
+			listingState.linkTable[*linkKey] = listingState.linkIndex
+			listingState.linkIndex++
 		}
 
 		if entry.IsDir() {

src/duplicacy_entrylist.go

@@ -62,7 +62,6 @@ type EntryList struct {
 	uploadedChunkIndex int                  // counter for upload chunks
 	uploadedChunkOffset int                 // the start offset for the current modified entry
 
-	HardLinkTable map[string]*Entry
 }
 
 // Create a new entry list
@@ -79,7 +78,6 @@ func CreateEntryList(snapshotID string, cachePath string, maximumInMemoryEntries
 		maximumInMemoryEntries: maximumInMemoryEntries,
 		cachePath: cachePath,
 		Token: string(token),
-		HardLinkTable: make(map[string]*Entry),
 	}
 
 	return entryList, nil
@@ -120,7 +118,7 @@ func (entryList *EntryList)AddEntry(entry *Entry) error {
 	if !entry.IsComplete() {
 		if entry.IsDir() || entry.IsLink() {
 			entry.Size = 0
-		} else if !entry.IsHardlinkedFrom() {
+		} else {
 			modifiedEntry := ModifiedEntry {
 				Path: entry.Path,
 				Size: -1,

src/duplicacy_snapshot.go

@@ -68,7 +68,7 @@ func (snapshot *Snapshot) ListLocalFiles(top string, nobackupFile string,
 								         skippedDirectories *[]string, skippedFiles *[]string) {
 
 	var patterns []string
-	var listingState = NewListingState()
+	listingState := NewListingState()
 
 	if filtersFile == "" {
 		filtersFile = joinPath(GetDuplicacyPreferencePath(), "filters")

src/duplicacy_utils_bsd.go

@@ -0,0 +1,53 @@
+// Copyright (c) Acrosync LLC. All rights reserved.
+// Free for personal use and commercial trial
+// Commercial use requires per-user licenses available from https://duplicacy.com
+
+//go:build freebsd || netbsd || darwin
+// +build freebsd netbsd darwin
+
+package duplicacy
+
+import (
+	"encoding/binary"
+	"os"
+	"syscall"
+)
+
+const bsdFileFlagsKey = "\x00bf"
+
+func (entry *Entry) ReadFileFlags(f *os.File) error {
+	fileInfo, err := f.Stat()
+	if err != nil {
+		return err
+	}
+	stat, ok := fileInfo.Sys().(*syscall.Stat_t)
+	if ok && stat.Flags != 0 {
+		if entry.Attributes == nil {
+			entry.Attributes = &map[string][]byte{}
+		}
+		v := make([]byte, 4)
+		binary.LittleEndian.PutUint32(v, stat.Flags)
+		(*entry.Attributes)[bsdFileFlagsKey] = v
+		LOG_DEBUG("ATTR_READ", "Read flags 0x%x for %s", stat.Flags, entry.Path)
+	}
+	return nil
+}
+
+func (entry *Entry) RestoreEarlyDirFlags(path string) error {
+	return nil
+}
+
+func (entry *Entry) RestoreEarlyFileFlags(f *os.File) error {
+	return nil
+}
+
+func (entry *Entry) RestoreLateFileFlags(f *os.File) error {
+	if entry.Attributes == nil {
+		return nil
+	}
+	if v, have := (*entry.Attributes)[bsdFileFlagsKey]; have {
+		LOG_DEBUG("ATTR_RESTORE", "Restore flags 0x%x for %s", binary.LittleEndian.Uint32(v), entry.Path)
+		return syscall.Fchflags(int(f.Fd()), int(binary.LittleEndian.Uint32(v)))
+	}
+	return nil
+}

src/duplicacy_utils_linux.go

@@ -0,0 +1,112 @@
+// Copyright (c) Acrosync LLC. All rights reserved.
+// Free for personal use and commercial trial
+// Commercial use requires per-user licenses available from https://duplicacy.com
+
+package duplicacy
+
+import (
+	"encoding/binary"
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+const (
+	linux_FS_SECRM_FL        = 0x00000001 /* Secure deletion */
+	linux_FS_UNRM_FL         = 0x00000002 /* Undelete */
+	linux_FS_COMPR_FL        = 0x00000004 /* Compress file */
+	linux_FS_SYNC_FL         = 0x00000008 /* Synchronous updates */
+	linux_FS_IMMUTABLE_FL    = 0x00000010 /* Immutable file */
+	linux_FS_APPEND_FL       = 0x00000020 /* writes to file may only append */
+	linux_FS_NODUMP_FL       = 0x00000040 /* do not dump file */
+	linux_FS_NOATIME_FL      = 0x00000080 /* do not update atime */
+	linux_FS_NOCOMP_FL       = 0x00000400 /* Don't compress */
+	linux_FS_JOURNAL_DATA_FL = 0x00004000 /* Reserved for ext3 */
+	linux_FS_NOTAIL_FL       = 0x00008000 /* file tail should not be merged */
+	linux_FS_DIRSYNC_FL      = 0x00010000 /* dirsync behaviour (directories only) */
+	linux_FS_TOPDIR_FL       = 0x00020000 /* Top of directory hierarchies*/
+	linux_FS_NOCOW_FL        = 0x00800000 /* Do not cow file */
+	linux_FS_PROJINHERIT_FL  = 0x20000000 /* Create with parents projid */
+
+	linux_FS_IOC_GETFLAGS uintptr = 0x80086601
+	linux_FS_IOC_SETFLAGS uintptr = 0x40086602
+
+	linuxIocFlagsFileEarly = linux_FS_SECRM_FL | linux_FS_UNRM_FL | linux_FS_COMPR_FL | linux_FS_NODUMP_FL | linux_FS_NOATIME_FL | linux_FS_NOCOMP_FL | linux_FS_JOURNAL_DATA_FL | linux_FS_NOTAIL_FL | linux_FS_NOCOW_FL
+	linuxIocFlagsDirEarly  = linux_FS_TOPDIR_FL | linux_FS_PROJINHERIT_FL
+	linuxIocFlagsLate      = linux_FS_SYNC_FL | linux_FS_IMMUTABLE_FL | linux_FS_APPEND_FL | linux_FS_DIRSYNC_FL
+
+	linuxFileFlagsKey = "\x00lf"
+)
+
+func ioctl(f *os.File, request uintptr, attrp *uint32) error {
+	argp := uintptr(unsafe.Pointer(attrp))
+
+	if _, _, errno := syscall.Syscall(syscall.SYS_IOCTL, f.Fd(), request, argp); errno != 0 {
+		return os.NewSyscallError("ioctl", errno)
+	}
+	return nil
+}
+
+func (entry *Entry) ReadFileFlags(f *os.File) error {
+	var flags uint32
+	if err := ioctl(f, linux_FS_IOC_GETFLAGS, &flags); err != nil {
+		return err
+	}
+	if flags != 0 {
+		if entry.Attributes == nil {
+			entry.Attributes = &map[string][]byte{}
+		}
+		v := make([]byte, 4)
+		binary.LittleEndian.PutUint32(v, flags)
+		(*entry.Attributes)[linuxFileFlagsKey] = v
+		LOG_DEBUG("ATTR_READ", "Read flags 0x%x for %s", flags, entry.Path)
+	}
+	return nil
+}
+
+func (entry *Entry) RestoreEarlyDirFlags(path string) error {
+	if entry.Attributes == nil {
+		return nil
+	}
+	if v, have := (*entry.Attributes)[linuxFileFlagsKey]; have {
+		flags := binary.LittleEndian.Uint32(v) & linuxIocFlagsDirEarly
+		f, err := os.OpenFile(path, os.O_RDONLY|syscall.O_DIRECTORY, 0)
+		if err != nil {
+			return err
+		}
+		LOG_DEBUG("ATTR_RESTORE", "Restore dir flags (early) 0x%x for %s", flags, entry.Path)
+		err = ioctl(f, linux_FS_IOC_SETFLAGS, &flags)
+		f.Close()
+		return err
+	}
+	return nil
+}
+
+func (entry *Entry) RestoreEarlyFileFlags(f *os.File) error {
+	if entry.Attributes == nil {
+		return nil
+	}
+	if v, have := (*entry.Attributes)[linuxFileFlagsKey]; have {
+		flags := binary.LittleEndian.Uint32(v) & linuxIocFlagsFileEarly
+		LOG_DEBUG("ATTR_RESTORE", "Restore flags (early) 0x%x for %s", flags, entry.Path)
+		return ioctl(f, linux_FS_IOC_SETFLAGS, &flags)
+	}
+	return nil
+}
+
+func (entry *Entry) RestoreLateFileFlags(f *os.File) error {
+	if entry.Attributes == nil {
+		return nil
+	}
+	if v, have := (*entry.Attributes)[linuxFileFlagsKey]; have {
+		flags := binary.LittleEndian.Uint32(v) & (linuxIocFlagsFileEarly | linuxIocFlagsDirEarly | linuxIocFlagsLate)
+		LOG_DEBUG("ATTR_RESTORE", "Restore flags (late) 0x%x for %s", flags, entry.Path)
+		return ioctl(f, linux_FS_IOC_SETFLAGS, &flags)
+	}
+	return nil
+}
+
+func excludedByAttribute(attributes map[string][]byte) bool {
+	_, ok := attributes["user.duplicacy_exclude"]
+	return ok
+}

src/duplicacy_utils_others.go

@@ -48,9 +48,12 @@ func SetOwner(fullPath string, entry *Entry, fileInfo *os.FileInfo) bool {
 }
 
 func (entry *Entry) ReadAttributes(top string) {
-
 	fullPath := filepath.Join(top, entry.Path)
-	attributes, _ := xattr.List(fullPath)
+	f, err := os.OpenFile(fullPath, os.O_RDONLY|syscall.O_NOFOLLOW, 0)
+	if err != nil {
+		return
+	}
+	attributes, _ := xattr.FList(f)
 	if len(attributes) > 0 {
 		entry.Attributes = &map[string][]byte{}
 		for _, name := range attributes {
@@ -60,30 +63,42 @@ func (entry *Entry) ReadAttributes(top string) {
 			}
 		}
 	}
+	if err := entry.ReadFileFlags(f); err != nil {
+		LOG_INFO("ATTR_BACKUP", "Could not backup flags for file %s: %v", fullPath, err)
+	}
+	f.Close()
 }
 
 func (entry *Entry) SetAttributesToFile(fullPath string) {
-	names, _ := xattr.List(fullPath)
+	f, err := os.OpenFile(fullPath, os.O_RDONLY|syscall.O_NOFOLLOW, 0)
+	if err != nil {
+		return
+	}
 
+	names, _ := xattr.FList(f)
 	for _, name := range names {
-
-
 		newAttribute, found := (*entry.Attributes)[name]
 		if found {
-			oldAttribute, _ := xattr.Get(fullPath, name)
+			oldAttribute, _ := xattr.FGet(f, name)
 			if !bytes.Equal(oldAttribute, newAttribute) {
-				xattr.Set(fullPath, name, newAttribute)
+				xattr.FSet(f, name, newAttribute)
 			}
 			delete(*entry.Attributes, name)
 		} else {
-			xattr.Remove(fullPath, name)
+			xattr.FRemove(f, name)
 		}
 	}
 
 	for name, attribute := range *entry.Attributes {
-		xattr.Set(fullPath, name, attribute)
+		if len(name) > 0 && name[0] == '\x00' {
+			continue
+		}
+		xattr.FSet(f, name, attribute)
 	}
-
+	if err := entry.RestoreLateFileFlags(f); err != nil {
+		LOG_DEBUG("ATTR_RESTORE", "Could not restore flags for file %s: %v", fullPath, err)
+	}
+	f.Close()
 }
 
 func joinPath(components ...string) string {

src/duplicacy_utils_posix.go

@@ -2,8 +2,8 @@
 // Free for personal use and commercial trial
 // Commercial use requires per-user licenses available from https://duplicacy.com
 
-//go:build freebsd || netbsd || linux || solaris
-// +build freebsd netbsd linux solaris
+//go:build freebsd || netbsd || solaris
+// +build freebsd netbsd solaris
 
 package duplicacy
 

src/duplicacy_utils_windows.go

@@ -132,6 +132,18 @@ func SplitDir(fullPath string) (dir string, file string) {
 	return fullPath[:i+1], fullPath[i+1:]
 }
 
-func excludedByAttribute(attributes map[string][]byte) bool {
-	return false
+func (entry *Entry) ReadFileFlags(f *os.File) error {
+	return nil
+}
+
+func (entry *Entry) RestoreEarlyDirFlags(path string) error {
+	return nil
+}
+
+func (entry *Entry) RestoreEarlyFileFlags(f *os.File) error {
+	return nil
+}
+
+func (entry *Entry) RestoreLateFileFlags(f *os.File) error {
+	return nil
 }