On Wed, Sep 28, 2022 at 06:11:17PM -0700, Jakub Kicinski wrote:

+Answer requests
+---------------
+
+Older families do not reply to all of the commands, especially NEW / ADD
+commands. User only gets information whether the operation succeeded or
+not via the ACK. Try to find useful data to return. Once the command is
+added whether it replies with a full message or only an ACK is uAPI and
+cannot be changed. It's better to err on the side of replying.
+
+Specifically NEW and ADD commands should reply with information identifying
+the created object such as the allocated object's ID.
+
+Having to rely on ``NLM_F_ECHO`` is a hack, not a valid design.
+
+NLM_F_ECHO
+----------
+
+Make sure to pass the request info to genl_notify() to allow ``NLM_F_ECHO``
+to take effect.

Do you mean that netlink commands should properly handle NLM_F_ECHO,
although they should also design their API so that users don't need it?