main: add "-sharedstorage" flag

At the moment, it does two things:

1. Disable stat() caching so changes to the backing storage show up
   immediately.
2. Disable hard link tracking, as the inode numbers on the backing
   storage are not stable when files are deleted and re-created behind
   our back. This would otherwise produce strange "file does not exist"
   and other errors.

Mitigates https://github.com/rfjakob/gocryptfs/issues/156

1 files changed, 19 insertions, 6 deletions

diff --git a/mount.go b/mount.go
index 007cc46..c3fda80 100644
--- a/mount.go
+++ b/mount.go
@@ -230,6 +230,12 @@ func initFuseFrontend(masterkey []byte, args *argContainer, confFile *configfile
 	var ctlSockBackend ctlsock.Interface
 	// pathFsOpts are passed into go-fuse/pathfs
 	pathFsOpts := &pathfs.PathNodeFsOptions{ClientInodes: true}
+	if args.sharedstorage {
+		// shared storage mode disables hard link tracking as the backing inode
+		// numbers may change behind our back:
+		// https://github.com/rfjakob/gocryptfs/issues/156
+		pathFsOpts.ClientInodes = false
+	}
 	if args.reverse {
 		// The dance with the intermediate variables is because we need to
 		// cast the FS into pathfs.FileSystem *and* ctlsock.Interface. This
@@ -257,12 +263,19 @@ func initFuseFrontend(masterkey []byte, args *argContainer, confFile *configfile
 		go ctlsock.Serve(args._ctlsockFd, ctlSockBackend)
 	}
 	pathFs := pathfs.NewPathNodeFs(finalFs, pathFsOpts)
-	fuseOpts := &nodefs.Options{
-		// These options are to be compatible with libfuse defaults,
-		// making benchmarking easier.
-		NegativeTimeout: time.Second,
-		AttrTimeout:     time.Second,
-		EntryTimeout:    time.Second,
+	var fuseOpts *nodefs.Options
+	if args.sharedstorage {
+		// sharedstorage mode sets all cache timeouts to zero so changes to the
+		// backing shared storage show up immediately.
+		fuseOpts = &nodefs.Options{}
+	} else {
+		fuseOpts = &nodefs.Options{
+			// These options are to be compatible with libfuse defaults,
+			// making benchmarking easier.
+			NegativeTimeout: time.Second,
+			AttrTimeout:     time.Second,
+			EntryTimeout:    time.Second,
+		}
 	}
 	conn := nodefs.NewFileSystemConnector(pathFs.Root(), fuseOpts)
 	mOpts := fuse.MountOptions{