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

[Alex Bligh]

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.

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.


-- 
Alex Bligh