linux-kernel - Re: [Nbd] [PATCH][V3] nbd: add multi-connection support

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Message-ID: <20161006135529.zrdkxycu7ajvhhmv@grep.be>
Date:   Thu, 6 Oct 2016 15:55:29 +0200
From:   Wouter Verhelst <w@...r.be>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     "nbd-general@...ts.sourceforge.net" 
        <nbd-general@...ts.sourceforge.net>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        Jens Axboe <axboe@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Josef Bacik <jbacik@...com>, Kernel Team <Kernel-team@...com>
Subject: Re: [Nbd] [PATCH][V3] nbd: add multi-connection support

On Thu, Oct 06, 2016 at 06:16:30AM -0700, Christoph Hellwig wrote:
> On Thu, Oct 06, 2016 at 03:09:49PM +0200, Wouter Verhelst wrote:
> > Okay, I've updated the proto.md file then, to clarify that in the case
> > of multiple connections, a client MUST NOT send a flush request until it
> > has seen the replies to the write requests that it cares about. That
> > should be enough for now.
> 
> How do you guarantee that nothing has been reordered or even lost even for
> a single connection?

In the case of a single connection, we already stated that the flush
covers the write requests for which a reply has already been sent out by
the time the flush reply is sent out. On a single connection, there is
no way an implementation can comply with the old requirement but not the
new one.

We do not guarantee any ordering beyond that; and lost requests would be
a bug in the server.

-- 
< ron> I mean, the main *practical* problem with C++, is there's like a dozen
       people in the world who think they really understand all of its rules,
       and pretty much all of them are just lying to themselves too.
 -- #debian-devel, OFTC, 2016-02-12