linux-kernel - Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements

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Date:   Thu, 15 Sep 2016 04:39:18 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Alex Bligh <alex@...x.org.uk>
Cc:     Wouter Verhelst <w@...r.be>, Josef Bacik <jbacik@...com>,
        linux-block@...r.kernel.org, Markus Pargmann <mpa@...gutronix.de>,
        kernel-team@...com,
        "nbd-general@...ts.sourceforge.net" 
        <nbd-general@...ts.sourceforge.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Eric Blake <eblake@...hat.com>
Subject: Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements

On Thu, Sep 15, 2016 at 12:09:28PM +0100, Alex Bligh wrote:
> A more general point is that with multiple queues requests
> may be processed in a different order even by those servers that
> currently process the requests in strict order, or in something
> similar to strict order. The server is permitted by the spec
> (save as mandated by NBD_CMD_FLUSH and NBD_CMD_FLAG_FUA) to
> process commands out of order anyway, but I suspect this has
> to date been little tested.

The Linux kernel does not assume any synchroniztion between block I/O
commands.  So any sort of synchronization a protocol does is complete
overkill for us.