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Re: [Xen-devel] blkback feature announcement

On Mon, Dec 07, 2015 at 01:42:09PM +0100, Roger Pau Monné wrote:
> El 07/12/15 a les 13.00, Jan Beulich ha escrit:
> > Hello,

Ccing Bob.
> > 
> > is there a particular reason why "max-ring-page-order" gets written in
> > xen_blkbk_probe(), but e.g. "feature-max-indirect-segments" and
> > "feature-persistent" get written only in connect(), despite both having
> > constant values (and hence the node value effectively being known as
> > soon as the device exists)?
> No, AFAIK there's no specific reason.
> > Or in more general terms: Shouldn't it be well defined at what time
> > a frontend can rely on certain nodes to be available for inspection?
> > And in doing so, I'd expect the determination to be done such that
> > widest flexibility is provided towards the actual implementation, i.e.
> > nodes should be written as early as possible. (Of course this applies
> > to other frontend/backend pairs too.)
> I agree. Regarding blkback the nodes about persistent grants, indirect
> descriptors and the ring page order should be written in
> xen_blkbk_probe, while the specific information about this virtual disk
> (sectors, sector size...) should be written before switching to the
> connected state (ie: after hotplug scripts have run).
> Roger.

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