netdev - Re: Netlink messages without NLM_F

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Message-ID: <20170607183511.GA10225@obsidianresearch.com>
Date:   Wed, 7 Jun 2017 12:35:11 -0600
From:   Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     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 07, 2017 at 09:18:10PM +0300, Leon Romanovsky wrote:

> > AFAIK, that is different, that is acking and retriggering a single shot
> > notification, not completing a kernel initiated handshake.
> 
> It is acking that message from user was received by kernel and now
> processing.

But isn't what is cared about here - the SA thing needs to send a
request to user space and collect a reply, it runs the protocol
backwards from normal.

It is not a notification because the request actually needs a reply,
and ACK's don't help because the reply has content.

It does not use the NOTIFICATION/REQUEST/REPLY sequence because it
does not care about reliability of delivering the REQUEST to user
space.

Jason