Re: [Xen-devel] Xen 4.4 development update

[Thanos Makatos <thanos.makatos@xxxxxxxxxx>]

> -----Original Message-----
> From: George Dunlap [mailto:george.dunlap@xxxxxxxxxxxxx]
> Sent: 19 August 2013 13:54
> To: Pasi Kärkkäinen
> Cc: Wei Liu; Ian Jackson; Jan Beulich; xen-devel@xxxxxxxxxxxxx; Thanos
> Makatos
> Subject: Re: [Xen-devel] Xen 4.4 development update
> 
> On 19/08/13 13:08, Pasi Kärkkäinen wrote:
> > On Mon, Aug 19, 2013 at 12:38:16PM +0100, George Dunlap wrote:
> >> * However, blktap is unmaintained.  Unless someone steps up to add
> >> the functionality (which is not recommended as it would probably te
> >> a waste of effort), it will continue to require a modprobe. On newer
> >> systems, without blktap, the modprobe will be harmless.  So for
> >> blktap, the modprobe will have to remain for the forseeable future.
> >>
> > What I've been wondering.. XenServer is shipping with and using
> blktap,
> > so there must be someone maintaining blktap at Citrix?
> > I also understand blktap is on the way out and will be replaced with
> qdisc in the future..
> 
> As I understand it, XenServer is using a private fork of blktap2, with
> significant changes.  Since blktap2 as a whole can't be upstreamed into

That's right, the so-called blktap2.5 that lives in github 
(https://github.com/xapi-project/blktap).

> the mainline kernel, I think the feeling was that there wasn't any
> point
> in trying to upstream the local changes to the "classic" kernel.
> Blktap3 was meant to be the mainline-friendly version of blktap, but as
> you say, work on it has halted and the plan at the moment, I'm told is
> to look into qdisk, since it uses a similar technology, but gives
> access
> to work from other communities as well (Ceph, for example).

blktap3 work hasn't been halted, only the upstream process has. On the 
contrary, we're still developing blktap3 (currently on 
https://github.com/tmakatos/blktap/tree/blktap3 but that's temporary) and our 
plan is to have it working for XenServer rather soon.

I don't see any technical difficulties in Xen using blktap3, pretty much in the 
same way it does with qemu.

> 
> Thanos, correct me if I've made a mistake somewhere...
> 
>   -George


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