node/Linux: Implement setting timestamps for symlinks

node.go

@@ -146,14 +146,12 @@ func (node Node) restoreMetadata(path string) error {
 		return errors.Annotate(err, "Lchown")
 	}
 
-	if node.Type == "symlink" {
+	if node.Type != "symlink" {
-		return nil
-	}
-
 		err = os.Chmod(path, node.Mode)
 		if err != nil {
 			return errors.Annotate(err, "Chmod")
 		}
+	}
 
 	if node.Type != "dir" {
 		err = node.RestoreTimestamps(path)
@@ -166,12 +164,20 @@ func (node Node) restoreMetadata(path string) error {
 }
 
 func (node Node) RestoreTimestamps(path string) error {
-	var utimes = []syscall.Timespec{
+	var utimes = [...]syscall.Timespec{
 		syscall.NsecToTimespec(node.AccessTime.UnixNano()),
 		syscall.NsecToTimespec(node.ModTime.UnixNano()),
 	}
 
-	if err := syscall.UtimesNano(path, utimes); err != nil {
+	if node.Type == "symlink" {
+		if err := node.restoreSymlinkTimestamps(path, utimes); err != nil {
+			return errors.Annotate(err, "UtimesNano")
+		}
+
+		return nil
+	}
+
+	if err := syscall.UtimesNano(path, utimes[:]); err != nil {
 		return errors.Annotate(err, "UtimesNano")
 	}
 

node_darwin.go

@@ -18,3 +18,7 @@ func (node *Node) fillTimes(stat *syscall.Stat_t) {
 	node.ChangeTime = time.Unix(stat.Ctimespec.Unix())
 	node.AccessTime = time.Unix(stat.Atimespec.Unix())
 }
+
+func (node Node) restoreSymlinkTimestamps(path string, utimes [2]syscall.Timespec) error {
+	return nil
+}

node_freebsd.go

@@ -18,3 +18,7 @@ func (node *Node) fillTimes(stat *syscall.Stat_t) {
 func changeTime(stat *syscall.Stat_t) time.Time {
 	return time.Unix(stat.Ctimespec.Unix())
 }
+
+func (node Node) restoreSymlinkTimestamps(path string, utimes [2]syscall.Timespec) error {
+	return nil
+}

node_linux.go

@@ -2,8 +2,10 @@ package restic
 
 import (
 	"os"
+	"path/filepath"
 	"syscall"
 	"time"
+	"unsafe"
 )
 
 func (node *Node) OpenForReading() (*os.File, error) {
@@ -22,3 +24,36 @@ func (node *Node) fillTimes(stat *syscall.Stat_t) {
 func changeTime(stat *syscall.Stat_t) time.Time {
 	return time.Unix(stat.Ctim.Unix())
 }
+
+func (node Node) restoreSymlinkTimestamps(path string, utimes [2]syscall.Timespec) error {
+	dir, err := os.Open(filepath.Dir(path))
+	defer dir.Close()
+	if err != nil {
+		return err
+	}
+
+	return utimesNanoAt(int(dir.Fd()), filepath.Base(path), utimes, AT_SYMLINK_NOFOLLOW)
+}
+
+// very lowlevel below
+
+const AT_SYMLINK_NOFOLLOW = 0x100
+
+func utimensat(dirfd int, path string, times *[2]syscall.Timespec, flags int) (err error) {
+	var _p0 *byte
+	_p0, err = syscall.BytePtrFromString(path)
+	if err != nil {
+		return
+	}
+	_, _, e1 := syscall.Syscall6(syscall.SYS_UTIMENSAT, uintptr(dirfd), uintptr(unsafe.Pointer(_p0)), uintptr(unsafe.Pointer(times)), uintptr(flags), 0, 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}
+
+//sys	utimensat(dirfd int, path string, times *[2]Timespec, flags int) (err error)
+
+func utimesNanoAt(dirfd int, path string, ts [2]syscall.Timespec, flags int) (err error) {
+	return utimensat(dirfd, path, (*[2]syscall.Timespec)(unsafe.Pointer(&ts[0])), flags)
+}

node_openbsd.go

@@ -22,3 +22,7 @@ func (node *Node) fillTimes(stat *syscall.Stat_t) {
 func changeTime(stat *syscall.Stat_t) time.Time {
 	return time.Unix(stat.Ctim.Unix())
 }
+
+func (node Node) restoreSymlinkTimestamps(path string, utimes [2]syscall.Timespec) error {
+	return nil
+}