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Re: [libvirt] [PATCHv4 01/18] blockjob: add qemu capabilities related to block jobs



On Tue, Apr 10, 2012 at 01:17:44PM -0400, Laine Stump wrote:
> On 04/09/2012 11:52 PM, Eric Blake wrote:
> > The new block copy storage migration sequence requires both the
> > 'drive-mirror' action in 'transaction' (present if the 'drive-mirror'
> > standalone monitor command also exists) and the 'drive-reopen' monitor
> > command (it would be nice if that were also part of a 'transaction',
> > but the initial qemu implementation has it standalone only).
> >
> > Furthermore, qemu 1.1 will be adding 'block_job_cancel' as an
> > asynchronous command, but an earlier implementation (that supported
> > only the qed file format) existed which was synchronous only.  If
> > 'drive-mirror' is added in time, then we can safely use 'drive-mirror'
> > as the witness of whether 'block_job_cancel' is synchronous or
> > asynchronous.
> >
> > As of this[1] qemu email, both commands have been proposed but not yet
> > incorporated into the tree; in fact, the implementation I tested with
> > has changed to match this[2] email that suggested a mandatory
> > 'full':'bool' argument rather than 'mode':'no-backing-file'.  So there
> > is a risk that qemu 1.1 will have yet another subtly different
> > implementation.
> > [1]https://lists.gnu.org/archive/html/qemu-devel/2012-03/msg01524.html
> > [2]https://lists.gnu.org/archive/html/qemu-devel/2012-04/msg00886.html
> 
> 
> None of this gives me warm fuzzies :-/

Based on previous experience, my suggestion is that we do *not* merge
any of this new libvirt API work, until the QEMU stuff has actually
been accepted into their git master. The previous block streaming
stuff is a nice history lesson in what happens when we merge stuff
in libvirt before QEMU has agreed their final design :-(

Daniel
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