From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: blkback feature announcement
Date: Mon, 7 Dec 2015 09:54:07 -0500
Message-ID: <20151207145406.GF22814@char.us.oracle.com>
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To: Roger Pau =?iso-8859-1?Q?Monn=E9?= <roger.pau@citrix.com>, bob.liu@oracle.com
Cc: xen-devel <xen-devel@lists.xenproject.org>, Jan Beulich <JBeulich@suse.com>
List-Id: xen-devel@lists.xenproject.org

On Mon, Dec 07, 2015 at 01:42:09PM +0100, Roger Pau Monn=E9 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.
> =