Re: [Xen-devel] Xen 4.3 development update

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-09-26 at 18:15 +0100, Matt Wilson wrote:
> On Wed, Sep 26, 2012 at 11:25:54AM +0100, Thanos Makatos wrote:
> > > -----Original Message-----
> > > From: George Dunlap [mailto:george.dunlap@xxxxxxxxxxxxx]
> > > Sent: 26 September 2012 10:37
> > > To: Matt Wilson
> > > Cc: Jan Beulich; xen-devel@xxxxxxxxxxxxx; Thanos Makatos
> > > Subject: Re: [Xen-devel] Xen 4.3 development update
> > > 
> > > On 21/09/12 04:18, Matt Wilson wrote:
> > > > On Thu, Sep 20, 2012 at 08:03:11AM +0100, Jan Beulich wrote:
> > > >>> On 19.09.12 at 18:58, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> > > wrote:
> > > >>> * Persistent grants
> > > >>>    owner: @citrix
> > > >>>    status: ?
> > > >> Isn't that a guest side only thing (i.e. not really to be tracked
> > > >> here)? Or does that mean migrating active grants?
> > > > I'd assume that the device would be renegotiated during migration,
> > > and
> > > > that new grants would be established during the re-connect sequence.
> > > >
> > > > One question I have is how persistent grants intersect with blktap3.
> > > > Will a persistent grant-capable blktap3 implementation be in scope
> > > for
> > > > 4.3?
> > > Thanos is working on blktap3 -- Thanos, can you comment?
> > 
> > Supporting this in 4.3 is not top priority; however I'll do it if I
> > have time.
> 
> I brought this up in response to Jan's question as to if persistent
> grants should be on the 4.3 release plan. With the introduction of
> blktap3, we have a separate implementation of the protocol in a Xen
> component. One worry I have about blktap3 is that it will lag behind
> the in-kernel blkback implementation.

We already have multiple block backend implementations (blktap1,
blktap2, qdisk, non-Linux dom0s), so I don't think that is a new
concern.

If anything blktap3 improves things by making blktap1 + 2 obsolete, plus
it comes with an active maintainer!

I think getting a working blktap3 implementation of the basic blk
protocol for 4.3 is a big enough chunk of work in its own right, it's
more than enough to fill someone's time for one release cycle IMHO.

So, I don't think implementing extensions (persistent grants, multipage
rings etc) need to be a requirement for blktap3 in 4.3, there's always
4.4 and beyond. Of course if someone wants to contribute patches I'm
sure Thanos would be very pleased ;-)

Ian.


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