Re: [Qemu-devel] [PATCH v4 04/11] nbd: Improve server handling of bogus commands

[Paolo Bonzini]

On 13/06/2016 23:41, Alex Bligh wrote:
> That's one of the reasons that there is a proposal to add
> STRUCTURED_READ to the spec (although I still haven't had time to
> implement that for qemu), so that we have a newer approach that allows
> for proper error handling without ambiguity on whether bogus bytes must
> be sent on a failed read.  But you'd have to convince me that ALL
> existing NBD server and client implementations expect to handle a read
> error without read payload, otherwise, I will stick with the notion that
> the current spec wording is correct, and that read errors CANNOT be
> gracefully recovered from unless BOTH sides transfer (possibly bogus)
> bytes along with the error message, and which is why BOTH sides of the
> protocol are warned that read errors usually result in a disconnection
> rather than clean continuation, without the addition of STRUCTURED_READ.

I suspect that there are exactly two client implementations, namely
Linux and QEMU's, and both do the right thing.

What servers do doesn't matter, if all the clients agree.

Paolo