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Re: [Nbd] [PATCH v4] doc: Propose STRUCTURED_REPLY extension



On 04/01/2016 02:57 AM, Wouter Verhelst wrote:
> Did a few minor changes, though:
> 
> On Thu, Mar 31, 2016 at 11:29:48PM -0600, Eric Blake wrote:
>> -S: 32 bits, 0x67446698, magic (`NBD_REPLY_MAGIC`)  
>> -S: 32 bits, error  
>> +S: 32 bits, 0x67446698, magic (`NBD_SIMPLE_REPLY_MAGIC`)  
> 
> Added a reference to the old name, for clarity.
> 
> [...]
>> +- bit 6, `NBD_FLAG_SEND_DF`; defined by the `STRUCTURED_REPLY` extension;
>> +  see below.
> 
> This is now bit 7 (we're already halfway through our available flags! time
> flies...)

Well, if (when?) we get to 15, one possible solution is fairly
straightforward: the server advertises a handshake flag, and the client
replies with the counterpart flag, and then both sides know to send 64
bits instead of 16 bits for all places that send a transmission flag.
It may make documentation of NBD_REP_SERVER (as used by NBD_OPT_GO) a
bit trickier, in that the length returned in the option reply is
dependent on what handshake flags were negotiated.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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