Hi Lin,

(1) will get AF_MCTP with nla_type(...) call, and (2) will then
passing `af` to `mctp_set_link_af`, which will expect the
`NLA_F_NESTED` flag.

You could set that flag? It's not exclusive with the attribute type.
From netlink.h:

  /*
   * nla_type (16 bits)
   * +---+---+-------------------------------+
   * | N | O | Attribute Type                |
   * +---+---+-------------------------------+
   * N := Carries nested attributes
   * O := Payload stored in network byte order
   *
   * Note: The N and O flag are mutually exclusive.
   */

Which is what we do with existing userspace:

  https://github.com/CodeConstruct/mctp/blob/6aa4b052d/src/mctp.c#L569C1-L569C1

Cheers,


Jeremy