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Re: [Qemu-devel] [Nbd] [PATCHv8] Improve documentation for TLS

From: Alex Bligh
Subject: Re: [Qemu-devel] [Nbd] [PATCHv8] Improve documentation for TLS
Date: Mon, 11 Apr 2016 21:34:44 +0100


On 11 Apr 2016, at 21:14, Eric Blake <address@hidden> wrote:
> Current qemu NBD server implementation does NOT send a reply to
> NBD_OPT_ABORT, but immediately closes the connection. I don't know if
> that is a bug in qemu (especially given the discussion on NBD_CMD_DISC),
> but it is an independent issue from TLS documentation, so may be better
> discussed on that thread.

Ha, neither does mine, despite my reading of the protocol being
that it should.

Reference nbd-server.c doesn't either.

> Likewise, current qemu NBD client implementation does NOT send
> NBD_OPT_ABORT at all, so it's hard to say whether waiting around for a
> reply is worthwhile.


nbd-client.c only appears to send it after asking for a list,
and not in any error conditions.

>> Obviously NBD_OPT_ABORT and aborting the connection needs
>> more clearing up, but I'm loathe to do it in the TLS patch.
>> In order not to make things worse, how about:
>>> There is no requirement for the client or server to complete a
>>> negotiation if it does not wish to do so. Either end may simply
>>> close the TCP connection (though see below re prior use
> Not sure if the use of "re" is ideal (are you abbreviating for "regarding")?

OK will fix that if Wouter likes the words.

>>> of NBD_OPT_ABORT). Under certain circumstances either
>>> the client or the server may be required by this document to close
>>> the TCP connection. In each case, this is referred to as 'terminate
>>> the session'.
>>> If the client wishes to terminate the session in the negotiation
>>> phase, and is not doing so because it is required to do so
>>> by this document, it SHOULD send NBD_OPT_ABORT first if the protocol
>>> permits. There are instances where this is impossible, such as after
>>> an NBD_OPT_EXPORTNAME has been issued, or on an unsuccessful
>>> negotiation of TLS.  For instance, if the client does not find an
>>> export it is looking for, it may simply send an NBD_OPT_ABORT
>>> and close the TCP connection.
> Otherwise, this seems reasonable, other than the fact that qemu needs
> patches to actually start sending NBD_OPT_ABORT where possible.

I'd suggest waiting for a definitive answer on whether it's meant
to have a reply.

Alex Bligh

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