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

[Paolo Bonzini]

On 15/06/2016 12:27, Alex Bligh wrote:
> 
> On 15 Jun 2016, at 10:18, Paolo Bonzini <address@hidden> wrote:
> 
>>> So what should those servers do (like 2 of mine) which don't buffer
>>> the entire read, if they get an error having already sent some data?
>>
>> They have sent an error code of zero, and it turned out to be wrong.  So
>> the only thing they can do safely is disconnect.
> 
> Right, but that is not what Wouter's change says:
> 
> +    If an error occurs, the server SHOULD set the appropriate error code
> +    in the error field. The server MAY then initiate a hard disconnect.
> +    If it chooses not to, it MUST NOT send any payload for this request.
> 
> I read this as either
> 
> a) the server can issue a hard disconnect without sending any reply; or
> 
> b) it must send the reply header with no payload
> 
> It also seems to permit not setting the error code (it's only a 'SHOULD'),
> not disconnecting (it's a MAY), then not sending any payload, which is a
> nonsense.

Right.

> Perhaps this should read "If an error occurs, the server MUST either initiate
> a hard disconnect before the entire payload has been sent or
> set the appropriate code in the error field and send the response header
> without any payload." if we want to go down this route.

Yes, I agree.

I do believe we want to go down this route.  I think we agree that
partial buffering may always require the server to disconnect after an
error.  Therefore I don't see any benefit at all in sending a payload
after an error message.

Paolo