netdev - Netlink messages without NLM_F

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Message-ID: <20170607161901.GD1127@mtr-leonro.local>
Date:   Wed, 7 Jun 2017 19:19:01 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Kaike Wan <kaike.wan@...el.com>, John Fleck <john.fleck@...el.com>,
        Ira Weiny <ira.weiny@...el.com>
Cc:     Thomas Graf <tgraf@...g.ch>, Doug Ledford <dledford@...hat.com>,
        Jiri Pirko <jiri@...lanox.com>,
        RDMA mailing list <linux-rdma@...r.kernel.org>,
        linux-netdev <netdev@...r.kernel.org>,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Subject: Netlink messages without NLM_F_REQUEST flag

Hi Kaike,

In the commit bc10ed7d3d19 ("IB/core: Add rdma netlink helper functions"),
part of larger series [1], you introduced ibnl_rcv_reply_skb(), which is very
similar to netlink_rcv_skb() with one major change.

The netlink messages without NLM_F_REQUEST flag are handled by ibnl_rcv_reply_skb(),
while netlink_rcv_skb() doesn't. The comment introduced in commit d35b685640ae
"[NETLINK]: Ignore !NLM_F_REQUEST messages directly in netlink_run_queue()")
says that "Only requests are handled by the kernel".

It makes me wonder if it is expected behavior for ibnl_rcv_reply_skb()
to handle !NLM_F_REQUEST messages and do we really need it? What are the scenarios?
In my use case, which is for sure different from yours, I'm always setting NLM_F_REQUEST
while communicating with kernel.

Thanks

[1] http://www.spinics.net/lists/linux-rdma/msg28153.html

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