[Sheepdog] [PATCH v3] sheep: change snapshot/clone flow

[Christoph Hellwig]

On Fri, Apr 20, 2012 at 12:55:33PM -0700, MORITA Kazutaka wrote:
> At Fri, 20 Apr 2012 15:15:38 -0400,
> Christoph Hellwig wrote:
> > 
> > On Fri, Apr 20, 2012 at 09:25:52AM +0000, Huxinwei wrote:
> > > What if the old code from qemu connects to the latest sheepdog with basic data structure changed ?
> > > Will it destroy our precious data ?
> > > 
> > > Btw: It seems that we don't have version defined for client-server communication. Is that right ?
> > 
> > Seems like it doesn't exist, but really should.  But even with
> 
> SD_PROTO_VER is the protocol version number between client and server.
> It is checked when the VDI is opened.

I know that part, but it doesn't really help to negotiate optional
protocol features between client and gateway. For that the client would
have to send a bitmap of supported features to the gateway, and the
gateway would respond with which bits it supports.  Similar to how e.g.
the virtio feature negotiation works.