Re: [Xen-devel] [PATCH v3 COLOPre 19/26] libxc/migration: Specification update for DIRTY_BITMAP records

[Yang Hongyang <yanghy@xxxxxxxxxxxxxx>]

On 06/30/2015 06:24 PM, Ian Campbell wrote:
> On Thu, 2015-06-25 at 14:25 +0800, Yang Hongyang wrote:
> > Used by secondary to send it's dirty bitmap to primary under COLO.
> This is the backchannel, right?
Right.

> It seems to me that this ought to be described more clearly as a
> separate stream in the opposite direction, rather than looking like just
> another record in the forward channel.
Agreed, I'm not sure if having this back channel record is eligible,
Andy, thoughts?

> Does the back channel not also need some sort of negotiation phase where
> we check both ends are compatible (i.e. like the forward channel's
> header). This might be easier than with the forward channel since you
> might assert that the versions must match exactly for COLO to be
> possible, that might not be true of some potential future user of the
> backchannel though.
The negotiation record for COLO is introduced in the following patch
on libxl side. But that might be diffrent form what you said here, we
don't have a version check currently, if the 2 side doesn't match, for
example one has colo feature enabled and the other end do not, the
migration will simply fail.

> .
--
Thanks,
Yang.

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