fusefrontend: support RENAME_WHITEOUT, RENAME_EXCHANGE

Both new internal test and xfstests generic/013 are happy.

https://github.com/rfjakob/gocryptfs/issues/641

internal/fusefrontend/node.go

@@ -391,23 +391,17 @@ func (n *Node) Symlink(ctx context.Context, target, name string, out *fuse.Entry
 	return inode, 0
 }
 
-// xfstests generic/013 now also exercises RENAME_EXCHANGE and RENAME_WHITEOUT,
-// uncovering lots of problems with longnames
-//
-// Reject those flags with syscall.EINVAL.
 // If we can handle the flags, this function returns 0.
 func rejectRenameFlags(flags uint32) syscall.Errno {
-	// Normal rename, we can handle that
-	if flags == 0 {
+	switch flags {
+	case 0, syscallcompat.RENAME_NOREPLACE, syscallcompat.RENAME_EXCHANGE, syscallcompat.RENAME_WHITEOUT:
 		return 0
-	}
-	// We also can handle RENAME_NOREPLACE
-	if flags == syscallcompat.RENAME_NOREPLACE {
+	case syscallcompat.RENAME_NOREPLACE | syscallcompat.RENAME_WHITEOUT:
 		return 0
+	default:
+		tlog.Warn.Printf("rejectRenameFlags: unknown flag combination 0x%x", flags)
+		return syscall.EINVAL
 	}
-	// We cannot handle RENAME_EXCHANGE and RENAME_WHITEOUT yet.
-	// Needs extra code for .name files.
-	return syscall.EINVAL
 }
 
 // Rename - FUSE call.
@@ -472,6 +466,11 @@ func (n *Node) Rename(ctx context.Context, name string, newParent fs.InodeEmbedd
 		}
 		return fs.ToErrno(err)
 	}
+	if flags&syscallcompat.RENAME_EXCHANGE != 0 || flags&syscallcompat.RENAME_WHITEOUT != 0 {
+		// These flags mean that there is now a new file at cName and we
+		// should NOT delete its longname file.
+		return 0
+	}
 	if nametransform.IsLongContent(cName) {
 		nametransform.DeleteLongNameAt(dirfd, cName)
 	}

internal/syscallcompat/sys_darwin.go

@@ -21,8 +21,10 @@ const (
 	// O_PATH is only defined on Linux
 	O_PATH = 0
 
-	// RENAME_NOREPLACE is only defined on Linux
+	// Only defined on Linux
 	RENAME_NOREPLACE = 0
+	RENAME_WHITEOUT  = 0
+	RENAME_EXCHANGE  = 0
 
 	// KAUTH_UID_NONE and KAUTH_GID_NONE are special values to
 	// revert permissions to the process credentials.

internal/syscallcompat/sys_linux.go

@@ -28,8 +28,10 @@ const (
 	// O_PATH is only defined on Linux
 	O_PATH = unix.O_PATH
 
-	// RENAME_NOREPLACE is only defined on Linux
+	// Only defined on Linux
 	RENAME_NOREPLACE = unix.RENAME_NOREPLACE
+	RENAME_WHITEOUT  = unix.RENAME_WHITEOUT
+	RENAME_EXCHANGE  = unix.RENAME_EXCHANGE
 )
 
 var preallocWarn sync.Once