Re: [Xen-devel] xen-vbd interface (segment size expansion) - FreeBSD host have it.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Aug 20, 2012 at 06:56:02PM +0000, Justin Gibbs wrote:
> Ronghui,
> 
> It has been a while since I've actively worked on the blkif stuff.  ...
> 
> That said, I'm happy to help in whatever ways I can to help get the blkif 
> interface sorted out.  I see several steps that should be taken:
> 
> 1) Fix the Xen and QEMU builds so that QEMU keeps its own copy of the Xen 
> interface version.  This will allow interfaces to rev safely and in a 
> coordinated fashion (i.e. update interface in Xen, then add support for the 
> new interface in QEMU upstream).
> 
> 2) Complete support in drivers for the existing blkif interface so that you 
> get maximum performance against systems using the existing multi-page 
> extensions.
> 
> 3) Do something to allow for larger and more numerous requests.
> 
> On point 3, my approach was to try to perturb the existing protocol as little 
> as possible in the hopes that other implementations could quickly be enhanced 
> to support the feature.  However, there is a lot of ugliness in the existing 
> blkif interface.  I can certainly understand the desires of some to just 
> replace blkif with a blkif2.
> 
> What are your current plans in this area?  How can I be of assistance?

Hey Justin and Ronghui,

Note: I've expanded the email thread to include xen-devel.

I was wondering how the protocol you developed works when it comes
to migration to a host that does not support the new features?

Specifically how do deal with a guest which tries to replay in progress I/Os
that do not fit within the old-segment size (11)?

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