fusefrontend: move openBackingDir into its own file

This function is in all fastpaths, will get a cache, and needs
its own file.
renamed:    internal/fusefrontend/names.go -> internal/fusefrontend/openbackingdir.go
renamed:    internal/fusefrontend/names_test.go -> internal/fusefrontend/openbackingdir_test.go

1 files changed, 19 insertions, 0 deletions

diff --git a/internal/fusefrontend/fs.go b/internal/fusefrontend/fs.go
index 5c52a19..5adade6 100644
--- a/internal/fusefrontend/fs.go
+++ b/internal/fusefrontend/fs.go
@@ -16,6 +16,7 @@ import (
 	"github.com/hanwen/go-fuse/fuse/nodefs"
 	"github.com/hanwen/go-fuse/fuse/pathfs"
 
+	"github.com/rfjakob/gocryptfs/internal/configfile"
 	"github.com/rfjakob/gocryptfs/internal/contentenc"
 	"github.com/rfjakob/gocryptfs/internal/nametransform"
 	"github.com/rfjakob/gocryptfs/internal/serialize_reads"
@@ -661,3 +662,21 @@ func (fs *FS) reportMitigatedCorruption(item string) {
 		return
 	}
 }
+
+// isFiltered - check if plaintext "path" should be forbidden
+//
+// Prevents name clashes with internal files when file names are not encrypted
+func (fs *FS) isFiltered(path string) bool {
+	if !fs.args.PlaintextNames {
+		return false
+	}
+	// gocryptfs.conf in the root directory is forbidden
+	if path == configfile.ConfDefaultName {
+		tlog.Info.Printf("The name /%s is reserved when -plaintextnames is used\n",
+			configfile.ConfDefaultName)
+		return true
+	}
+	// Note: gocryptfs.diriv is NOT forbidden because diriv and plaintextnames
+	// are exclusive
+	return false
+}