From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= <roger.pau@citrix.com>
Subject: Re: blkback feature announcement
Date: Mon, 7 Dec 2015 13:42:09 +0100
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To: Jan Beulich <JBeulich@suse.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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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.