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

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Message-ID: <20160915122008.GB1155@infradead.org>
Date:   Thu, 15 Sep 2016 05:20:08 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Wouter Verhelst <w@...r.be>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Alex Bligh <alex@...x.org.uk>,
        "nbd-general@...ts.sourceforge.net" 
        <nbd-general@...ts.sourceforge.net>, linux-block@...r.kernel.org,
        Josef Bacik <jbacik@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Markus Pargmann <mpa@...gutronix.de>, kernel-team@...com
Subject: Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements

On Thu, Sep 15, 2016 at 02:01:59PM +0200, Wouter Verhelst wrote:
> Yes. There was some discussion on that part, and we decided that setting
> the flag doesn't hurt, but the spec also clarifies that using it on READ
> does nothing, semantically.
>
> 
> The problem is that there are clients in the wild which do set it on
> READ, so it's just a matter of "be liberal in what you accept".

Note that FUA on READ in SCSI and NVMe does have a meaning - it
requires you to bypass any sort of cache on the target.  I think it's an
wrong defintion because it mandates implementation details that aren't
observable by the initiator, but it's still the spec wording and nbd
diverges from it.  That's not nessecarily a bad thing, but a caveat to
look out for.