Re: [Xen-devel] [PATCH v7 08/18] tools/libxl: introduce libxl__domain_restore_device_model to load qemu state

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Feb 04, 2016 at 09:41:54AM +0000, Wei Liu wrote:
> On Thu, Feb 04, 2016 at 01:24:41PM +0800, Wen Congyang wrote:
> > On 02/04/2016 03:40 AM, Wei Liu wrote:
> > > On Fri, Jan 29, 2016 at 01:27:24PM +0800, Wen Congyang wrote:
> > >> In normal migration, the qemu state is passed to qemu as a parameter.
> > >> With COLO, secondary vm is running. So we will do the following steps
> > >> at every checkpoint:
> > >> 1. suspend both primary vm and secondary vm
> > >> 2. sync the state
> > >> 3. resume both primary vm and secondary vm
> > >> Primary will send qemu's state in step2, and secondary's qemu should
> > >> read it and restore the state before it is resumed. We can not pass
> > >> the state to qemu as a parameter because secondary QEMU already started
> > >> at this point, so we introduce libxl__domain_restore_device_model() to
> > >> do it. This API MUST be called before resuming secondary vm.
> > >>
> > >> Signed-off-by: Yang Hongyang <hongyang.yang@xxxxxxxxxxxx>
> > >> Signed-off-by: Wen Congyang <wency@xxxxxxxxxxxxxx>
> > >> Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>
> > >> ---
> > >>  tools/libxl/libxl_dom_save.c | 20 ++++++++++++++++++++
> > >>  tools/libxl/libxl_internal.h |  4 ++++
> > >>  tools/libxl/libxl_qmp.c      | 10 ++++++++++
> > >>  3 files changed, 34 insertions(+)
> > >>
> > >> diff --git a/tools/libxl/libxl_dom_save.c b/tools/libxl/libxl_dom_save.c
> > >> index cd2e7de..7383d2d 100644
> > >> --- a/tools/libxl/libxl_dom_save.c
> > >> +++ b/tools/libxl/libxl_dom_save.c
> > >> @@ -518,6 +518,26 @@ int 
> > >> libxl__restore_emulator_xenstore_data(libxl__domain_create_state *dcs,
> > >>      return rc;
> > >>  }
> > >>  
> > >> +int libxl__domain_restore_device_model(libxl__gc *gc, uint32_t domid,
> > >> +                                       const char *restore_file)
> > >> +{
> > >> +    int rc;
> > >> +
> > >> +    switch (libxl__device_model_version_running(gc, domid)) {
> > >> +    case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL:
> > >> +        /* Will never be supported. */
> > >> +        rc = ERROR_INVAL;
> > >> +        break;
> > > 
> > > I'm not entirely sure if this statement would be true. The function name
> > > is generic enough to indicate this case should be supported.
> > > 
> > > However, this function is not used anywhere in this series, so I don't
> > > know whether my comment makes sense.
> > > 
> > > One way of moving forward is to stick this patch to COLO series itself.
> > > Let's skip this in this prerequisite series.
> > 
> > OK, I will put it in the COLO series itself.
> > This API is used for COLO, and COLO requries the newest qemu with block 
> > replication.
> > The block replication is still in the way. The tranditional qemu doesn't 
> > support
> > block replication and it is hard to backport it.
> > 
> 
> OK. I'm asking you to support qemu-trad in COLO -- definitely not.
         ^ NOT

(Not enough caffeine in the morning, sorry.)

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