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

On 15 Sep 2016, at 12:40, Christoph Hellwig [off-list ref] wrote:
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On Thu, Sep 15, 2016 at 01:29:36PM +0200, Wouter Verhelst wrote:

quoted

Yes, and that is why I was asking about this. If the write barriers
are expected to be shared across connections, we have a problem. If,
however, they are not, then it doesn't matter that the commands may =

be

quoted

processed out of order.

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There is no such thing as a write barrier in the Linux kernel.  We'd
much prefer protocols not to introduce any pointless synchronization
if we can avoid it.

I suspect the issue is terminological.

Essentially NBD does supports FLUSH/FUA like this:

=
https://www.kernel.org/doc/Documentation/block/writeback_cache_control.txt=


IE supports the same FLUSH/FUA primitives as other block drivers (AIUI).

Link to protocol (per last email) here:

=
https://github.com/yoe/nbd/blob/master/doc/proto.md#ordering-of-messages-a=
nd-writes

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Alex Bligh