netdev - Re: [PATCH net-next v1] net: mctp: use deprecated parser in mctp_set_link

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Message-ID: <e5e0640094a4e594eda8c3f8a54eca6728e58510.camel@codeconstruct.com.au>
Date: Thu, 04 Jan 2024 14:43:38 +0800
From: Jeremy Kerr <jk@...econstruct.com.au>
To: Lin Ma <linma@....edu.cn>, Jakub Kicinski <kuba@...nel.org>
Cc: matt@...econstruct.com.au, davem@...emloft.net, edumazet@...gle.com, 
	pabeni@...hat.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v1] net: mctp: use deprecated parser in
 mctp_set_link_af

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