v2api: -sharestorage: disable hard link tracking & add tests

Hard link tracking was not correctly disabled
since the migration to the go-fuse v2 api.

Add a test to ensure it stays off.

Fixes https://github.com/rfjakob/gocryptfs/issues/525

4 files changed, 24 insertions, 3 deletions

diff --git a/internal/fusefrontend/args.go b/internal/fusefrontend/args.go
index 5eb6bff..ae1c30c 100644
--- a/internal/fusefrontend/args.go
+++ b/internal/fusefrontend/args.go
@@ -46,4 +46,7 @@ type Args struct {
 	Suid bool
 	// Enable the FUSE kernel_cache option
 	KernelCache bool
+	// SharedStorage disables caching & hard link tracking,
+	// enabled via cli flag "-sharedstorage"
+	SharedStorage bool
 }
diff --git a/internal/fusefrontend/node_helpers.go b/internal/fusefrontend/node_helpers.go
index ad92043..f99e6df 100644
--- a/internal/fusefrontend/node_helpers.go
+++ b/internal/fusefrontend/node_helpers.go
@@ -102,8 +102,9 @@ func (n *Node) prepareAtSyscall(child string) (dirfd int, cName string, errno sy
 // newChild attaches a new child inode to n.
 // The passed-in `st` will be modified to get a unique inode number.
 func (n *Node) newChild(ctx context.Context, st *syscall.Stat_t, out *fuse.EntryOut) *fs.Inode {
-	// Get unique inode number
 	rn := n.rootNode()
+	// Get stable inode number based on underlying (device,ino) pair
+	// (or set to zero in case of `-sharestorage`)
 	rn.inoMap.TranslateStat(st)
 	out.Attr.FromStat(st)
 	// Create child node
diff --git a/internal/fusefrontend/root_node.go b/internal/fusefrontend/root_node.go
index e03e250..bdefafa 100644
--- a/internal/fusefrontend/root_node.go
+++ b/internal/fusefrontend/root_node.go
@@ -50,7 +50,7 @@ type RootNode struct {
 	IsIdle uint32
 	// inoMap translates inode numbers from different devices to unique inode
 	// numbers.
-	inoMap *inomap.InoMap
+	inoMap inomap.TranslateStater
 }
 
 func NewRootNode(args Args, c *contentenc.ContentEnc, n nametransform.NameTransformer) *RootNode {
@@ -60,12 +60,18 @@ func NewRootNode(args Args, c *contentenc.ContentEnc, n nametransform.NameTransf
 	if len(args.Exclude) > 0 {
 		tlog.Warn.Printf("Forward mode does not support -exclude")
 	}
-	return &RootNode{
+	rn := &RootNode{
 		args:          args,
 		nameTransform: n,
 		contentEnc:    c,
 		inoMap:        inomap.New(),
 	}
+	// In `-sharedstorage` mode we always set the inode number to zero.
+	// This makes go-fuse generate a new inode number for each lookup.
+	if args.SharedStorage {
+		rn.inoMap = &inomap.TranslateStatZero{}
+	}
+	return rn
 }
 
 // mangleOpenFlags is used by Create() and Open() to convert the open flags the user
diff --git a/internal/inomap/inomap.go b/internal/inomap/inomap.go
index 82d50b0..0977a46 100644
--- a/internal/inomap/inomap.go
+++ b/internal/inomap/inomap.go
@@ -104,3 +104,14 @@ func (m *InoMap) TranslateStat(st *syscall.Stat_t) {
 	in := QInoFromStat(st)
 	st.Ino = m.Translate(in)
 }
+
+type TranslateStater interface {
+	TranslateStat(st *syscall.Stat_t)
+}
+
+// TranslateStatZero always sets st.Ino to zero. Used for `-sharedstorage`.
+type TranslateStatZero struct{}
+
+func (z TranslateStatZero) TranslateStat(st *syscall.Stat_t) {
+	st.Ino = 0
+}