Re: [Xen-devel] [PATCH v3 COLOPre 11/26] tools/libxl: introduce a new API libxl__domain_restore() to load qemu state

[Yang Hongyang <yanghy@xxxxxxxxxxxxxx>]

On 06/30/2015 12:38 AM, Ian Campbell wrote:
> On Thu, 2015-06-25 at 14:25 +0800, Yang Hongyang wrote:
> > Secondary vm is running in colo mode. So we will do
> > the following things again and again:
> > 1. suspend both primay vm and secondary vm
> > 2. sync the state
> > 3. resume both primary vm and secondary vm
> > We will send qemu's state each time in step2, and
> > slave's qemu should read it each time before resuming
> > secondary vm. Introduce a new API libxl__domain_restore()
> > to do it. This API should be called before resuming
> > secondary vm.
> I think before this patch the state was passed to qemu as a parameter
> when it was launched, is that correct? If so then that would be worth
> mentioning for completeness.
Inaccurate I think. What you said before is the normal migration, in that
case, yes, the state was passed to qemu as a parameter. With COLO, the
first step is live migration, so the state is still passed to qemu as a
parameter when the live migration ended. The new introduced API only used
when we need to restore the DM state after a checkpoint, at this point,
guest QEMU already started, we can not pass the state as a parameter like
we do on first boot, so we introduce this API to restore the state after
QEMU has started.

> > Signed-off-by: Yang Hongyang <yanghy@xxxxxxxxxxxxxx>
> > Signed-off-by: Wen Congyang <wency@xxxxxxxxxxxxxx>
> > Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>
> > ---
> >   tools/libxl/libxl_dom_save.c | 49 ++++++++++++++++++++++++++++++++++++++++++++
> >   tools/libxl/libxl_internal.h |  3 +++
> >   tools/libxl/libxl_qmp.c      | 10 +++++++++
> >   3 files changed, 62 insertions(+)
> >
> > diff --git a/tools/libxl/libxl_dom_save.c b/tools/libxl/libxl_dom_save.c
> > index 8fe1625..0ad2894 100644
> > --- a/tools/libxl/libxl_dom_save.c
> > +++ b/tools/libxl/libxl_dom_save.c
> > @@ -639,6 +639,55 @@ int libxl__toolstack_restore(uint32_t domid, const uint8_t 
> > *buf,
> >       }
> >       return 0;
> >   }
> > +
> > +static int libxl__domain_restore_device_model(libxl__gc *gc, uint32_t domid);
> > +
> > +int libxl__domain_restore(libxl__gc *gc, uint32_t domid)
> We don't have any libxl__domain_save counterpart, but we do have
> libxl__domain_save_device_model, so I wonder if the upcoming callers
> ought to just call that direct? Especially given that this function
> isn't any kind of generic domain restore, but has rather specific
> functionality (in particular it fails for PV guests).
Maybe we just introduce libxl__domain_restore_device_model() and call
this when needed, discard the new libxl__domain_restore() API, what do
you think?

> .
--
Thanks,
Yang.

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