From 5547228a17c07e5fbd1c543218e4a1e25cbd2a25 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Anders=20F=20Bj=C3=B6rklund?= <anders.f.bjorklund@gmail.com>
Date: Fri, 14 Mar 2025 17:58:45 +0100
Subject: [PATCH] Add support for mount export for fuse-nfs
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It wants to list the exported file systems, for mount.

But currently the nullauth ignores the dirpath anyway.

Signed-off-by: Anders F Björklund <anders.f.bjorklund@gmail.com>
---
 handler.go                 |  3 +++
 helpers/nullauthhandler.go |  5 +++++
 mount.go                   | 16 ++++++++++++++++
 mountinterface.go          | 13 +++++++++++++
 4 files changed, 37 insertions(+)

diff --git a/handler.go b/handler.go
index 13a0eaf..8fafd03 100644
--- a/handler.go
+++ b/handler.go
@@ -20,6 +20,9 @@ type Handler interface {
 
 	// Optional methods - generic helpers or trivial implementations can be sufficient depending on use case.
 
+	// List of all exported file systems.
+	Export(context.Context) []Export
+
 	// Fill in information about a file system's free space.
 	FSStat(context.Context, billy.Filesystem, *FSStat) error
 
diff --git a/helpers/nullauthhandler.go b/helpers/nullauthhandler.go
index f7571b1..0094512 100644
--- a/helpers/nullauthhandler.go
+++ b/helpers/nullauthhandler.go
@@ -34,6 +34,11 @@ func (h *NullAuthHandler) Change(fs billy.Filesystem) billy.Change {
 	return nil
 }
 
+// List of all exported file systems.
+func (h *NullAuthHandler) Export(context.Context) []nfs.Export {
+	return []nfs.Export{{Dir: []byte("/mount")}}
+}
+
 // FSStat provides information about a filesystem.
 func (h *NullAuthHandler) FSStat(ctx context.Context, f billy.Filesystem, s *nfs.FSStat) error {
 	return nil
diff --git a/mount.go b/mount.go
index e95d098..55e7445 100644
--- a/mount.go
+++ b/mount.go
@@ -15,6 +15,7 @@ func init() {
 	_ = RegisterMessageHandler(mountServiceID, uint32(MountProcNull), onMountNull)
 	_ = RegisterMessageHandler(mountServiceID, uint32(MountProcMount), onMount)
 	_ = RegisterMessageHandler(mountServiceID, uint32(MountProcUmnt), onUMount)
+	_ = RegisterMessageHandler(mountServiceID, uint32(MountProcExport), onMountExport)
 }
 
 func onMountNull(ctx context.Context, w *response, userHandle Handler) error {
@@ -56,3 +57,18 @@ func onUMount(ctx context.Context, w *response, userHandle Handler) error {
 
 	return w.writeHeader(ResponseCodeSuccess)
 }
+
+func onMountExport(ctx context.Context, w *response, userHandle Handler) error {
+	exports := userHandle.Export(ctx)
+
+	if err := w.writeHeader(ResponseCodeSuccess); err != nil {
+		return err
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+
+	if err := xdr.Write(writer, exports); err != nil {
+		return err
+	}
+	return w.Write(writer.Bytes())
+}
diff --git a/mountinterface.go b/mountinterface.go
index 1dc39ee..01559c0 100644
--- a/mountinterface.go
+++ b/mountinterface.go
@@ -88,3 +88,16 @@ type MountResponse struct {
 	FileHandle
 	AuthFlavors []int
 }
+
+// Group contains a group node, with information about the allowed access group.
+type Group struct {
+	Name []byte
+	Next []Group
+}
+
+// Export contains an export node, with information about an exported filesystem.
+type Export struct {
+	Dir     []byte
+	Groups  []Group
+	Next    []Export
+}