Report filesystem-specific mount options.

PiperOrigin-RevId: 362406813

3 files changed, 20 insertions, 2 deletions

diff --git a/pkg/sentry/vfs/anonfs.go b/pkg/sentry/vfs/anonfs.go
index 7ad0eaf86..3caf417ca 100644
--- a/pkg/sentry/vfs/anonfs.go
+++ b/pkg/sentry/vfs/anonfs.go
@@ -291,6 +291,11 @@ func (fs *anonFilesystem) PrependPath(ctx context.Context, vfsroot, vd VirtualDe
 	return PrependPathSyntheticError{}
 }
 
+// MountOptions implements FilesystemImpl.MountOptions.
+func (fs *anonFilesystem) MountOptions() string {
+	return ""
+}
+
 // IncRef implements DentryImpl.IncRef.
 func (d *anonDentry) IncRef() {
 	// no-op
diff --git a/pkg/sentry/vfs/filesystem.go b/pkg/sentry/vfs/filesystem.go
index 2c4b81e78..059939010 100644
--- a/pkg/sentry/vfs/filesystem.go
+++ b/pkg/sentry/vfs/filesystem.go
@@ -502,6 +502,15 @@ type FilesystemImpl interface {
 	//
 	// Preconditions: vd.Mount().Filesystem().Impl() == this FilesystemImpl.
 	PrependPath(ctx context.Context, vfsroot, vd VirtualDentry, b *fspath.Builder) error
+
+	// MountOptions returns mount options for the current filesystem. This
+	// should only return options specific to the filesystem (i.e. don't return
+	// "ro", "rw", etc). Options should be returned as a comma-separated string,
+	// similar to the input to the 5th argument to mount.
+	//
+	// If the implementation has no filesystem-specific options, it should
+	// return the empty string.
+	MountOptions() string
 }
 
 // PrependPathAtVFSRootError is returned by implementations of
diff --git a/pkg/sentry/vfs/mount.go b/pkg/sentry/vfs/mount.go
index bac9eb905..922f9e697 100644
--- a/pkg/sentry/vfs/mount.go
+++ b/pkg/sentry/vfs/mount.go
@@ -959,13 +959,17 @@ func manglePath(p string) string {
 // superBlockOpts returns the super block options string for the the mount at
 // the given path.
 func superBlockOpts(mountPath string, mnt *Mount) string {
-	// gVisor doesn't (yet) have a concept of super block options, so we
-	// use the ro/rw bit from the mount flag.
+	// Compose super block options by combining global mount flags with
+	// FS-specific mount options.
 	opts := "rw"
 	if mnt.ReadOnly() {
 		opts = "ro"
 	}
 
+	if mopts := mnt.fs.Impl().MountOptions(); mopts != "" {
+		opts += "," + mopts
+	}
+
 	// NOTE(b/147673608): If the mount is a cgroup, we also need to include
 	// the cgroup name in the options. For now we just read that from the
 	// path.