netdev - Re: Netlink messages without NLM_F

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Message-ID: <CALq1K=Jj_jJ5_OAiiws-es37tFEsLeLJeSvnU+bfwd0KLkGM3Q@mail.gmail.com>
Date:   Wed, 7 Jun 2017 19:43:44 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     Leon Romanovsky <leon@...nel.org>, Kaike Wan <kaike.wan@...el.com>,
        John Fleck <john.fleck@...el.com>,
        Ira Weiny <ira.weiny@...el.com>, 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>
Subject: Re: Netlink messages without NLM_F_REQUEST flag

On Wed, Jun 7, 2017 at 7:37 PM, Jason Gunthorpe
<jgunthorpe@...idianresearch.com> wrote:
> On Wed, Jun 07, 2017 at 07:19:01PM +0300, Leon Romanovsky wrote:
>> 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.
>
> If I recall the user space SA code issues REQUESTS from the kernel to
> userspace, so userspace returns with the response format. This is
> abnormal for netlink hence the special function.

In netlink semantics, kernel side is supposed to send netlink
notification message and userspace is supposed to send REQUEST.

>
> Jason