Re: [PATCH v6 02/40] fs: add id translation helpers

+	struct user_namespace *s_user_ns = sb->s_user_ns;
+	if (!kuid_has_mapping(s_user_ns,
+		kuid_from_mnt(mnt_userns, current_fsuid())))
+		return false;
+	if (!kgid_has_mapping(s_user_ns,
+		kgid_from_mnt(mnt_userns, current_fsgid())))
+		return false;
+	return true;

Please don't use one tab indents for conditional continuations, as
that looks really weird.  Always use two tabs or align to the
opening brace.

Otherwise these helpers looks really useful.