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

Christoph,

On 15 Sep 2016, at 12:38, Christoph Hellwig [off-list ref] wrote:
=20
On Thu, Sep 15, 2016 at 12:49:35PM +0200, Wouter Verhelst wrote:

quoted

A while back, we spent quite some time defining the semantics of the
various commands in the face of the NBD_CMD_FLUSH and =

NBD_CMD_FLAG_FUA

quoted

write barriers. At the time, we decided that it would be unreasonable
to expect servers to make these write barriers effective across
different connections.

=20
Do you have a nbd protocol specification?  treating a flush or fua
as any sort of barrier is incredibly stupid.  Is it really documented
that way, and if yes, why?

Sure, it's at:

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

and that link takes you to the specific section.

The treatment of FLUSH and FUA is meant to mirror exactly the
linux block layer (or rather how the linux block layer was a few
years ago). I even asked on LKML to verify a few points.

--=20
Alex Bligh