netdev - Re: [RFC v1] nvme-tcp: enable linger socket option on shutdown

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Message-ID: <20210914084613.75qykjxweh66mdpx@carbon>
Date:   Tue, 14 Sep 2021 10:46:13 +0200
From:   Daniel Wagner <dwagner@...e.de>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [RFC v1] nvme-tcp: enable linger socket option on shutdown

On Mon, Sep 06, 2021 at 08:58:20AM +0100, Christoph Hellwig wrote:
> On Fri, Sep 03, 2021 at 02:17:57PM +0200, Daniel Wagner wrote:
> > When the no linger is set, the networking stack sends FIN followed by
> > RST immediately when shutting down the socket. By enabling linger when
> > shutting down we have a proper shutdown sequence on the wire.
> > 
> > Signed-off-by: Daniel Wagner <dwagner@...e.de>
> > ---
> > The current shutdown sequence on the wire is a bit harsh and
> > doesn't let the remote host to react. I suppose we should
> > introduce a short (how long?) linger pause when shutting down
> > the connection. Thoughs?
> 
> Why?  I'm not really a TCP expert, but why is this different from
> say iSCSI or NBD?

I am also no TCP expert. Adding netdev to Cc.

During testing the nvme-tcp subsystem by one of our partners we observed
this. Maybe this is perfectly fine. Just as I said it looks a bit weird
that a proper shutdown of the connection a RST is send out right after
the FIN.

No idea how iSCSI or NBD handles this. I'll check.