Re: [Xen-devel] blkback feature announcement

[Roger Pau Monnà <roger.pau@xxxxxxxxxx>]

El 07/12/15 a les 13.00, Jan Beulich ha escrit:
> Hello,
> 
> 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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