Re: [Xen-devel] [PATCH v4 --for 4.6 COLOPre 14/25] tools/libxl: introduce libxl__domain_restore_device_model to load qemu state

[Yang Hongyang <yanghy@xxxxxxxxxxxxxx>]

On 07/15/2015 08:45 PM, Ian Campbell wrote:
> On Wed, 2015-07-15 at 15:45 +0800, Yang Hongyang wrote:
> > In normal migration, the qemu state was 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 primay vm and secondary vm
> "primary"
>
> > 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 should be called before resuming secondary vm.
> >
> > 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 | 29 +++++++++++++++++++++++++++++
> >   tools/libxl/libxl_internal.h |  3 +++
> >   tools/libxl/libxl_qmp.c      | 10 ++++++++++
> >   3 files changed, 42 insertions(+)
> >
> > diff --git a/tools/libxl/libxl_dom_save.c b/tools/libxl/libxl_dom_save.c
> > index f89f5d4..0926b71 100644
> > --- a/tools/libxl/libxl_dom_save.c
> > +++ b/tools/libxl/libxl_dom_save.c
> > @@ -675,6 +675,35 @@ out:
> >       return ret;
> >   }
> >
> > +int libxl__domain_restore_device_model(libxl__gc *gc, uint32_t domid)
> > +{
> > +    char *state_file;
> > +    int rc;
> > +
> > +    switch (libxl__device_model_version_running(gc, domid)) {
> > +    case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL:
> > +        /* not supported now */
> > +        rc = ERROR_INVAL;
> > +        break;
> > +    case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN:
> > +        /*
> > +         * This function may be called too many times for the same gc,
> > +         * so we use NOGC, and free the memory before return to avoid
> > +         * OOM.
> > +         */
> It occurs to me that domid shouldn't change for the duration of a COLO
> run, right?
right!

> Thus I think the path can be allocated once at start of day and not per
> iteration, and can be stored in suspend_state (or similar) and passed in
> here. Hence no complexity like a nested ao is needed.
Good idea, thank you!

> > +        state_file = libxl__sprintf(NOGC,
> > +                                    XC_DEVICE_MODEL_RESTORE_FILE".%d",
> > +                                    domid);
> > +        rc = libxl__qmp_restore(gc, domid, state_file);
> > +        free(state_file);
> > +        break;
> > +    default:
> > +        rc = ERROR_INVAL;
> > +    }
> > +
> > +    return rc;
> > +}
> > +
> >   /*
> >    * Local variables:
> >    * mode: C
> > diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
> > index 0eb5f41..fb777c1 100644
> > --- a/tools/libxl/libxl_internal.h
> > +++ b/tools/libxl/libxl_internal.h
> > @@ -1074,6 +1074,7 @@ _hidden int libxl__domain_rename(libxl__gc *gc, uint32_t 
> > domid,
> >
> >   _hidden int libxl__toolstack_restore(uint32_t domid, const uint8_t *buf,
> >                                        uint32_t size, void *data);
> > +_hidden int libxl__domain_restore_device_model(libxl__gc *gc, uint32_t domid);
> >   _hidden int libxl__domain_resume_device_model(libxl__gc *gc, uint32_t domid);
> >
> >   _hidden const char *libxl__userdata_path(libxl__gc *gc, uint32_t domid,
> > @@ -1702,6 +1703,8 @@ _hidden int libxl__qmp_stop(libxl__gc *gc, int domid);
> >   _hidden int libxl__qmp_resume(libxl__gc *gc, int domid);
> >   /* Save current QEMU state into fd. */
> >   _hidden int libxl__qmp_save(libxl__gc *gc, int domid, const char *filename);
> > +/* Load current QEMU state from fd. */
> > +_hidden int libxl__qmp_restore(libxl__gc *gc, int domid, const char *filename);
> >   /* Set dirty bitmap logging status */
> >   _hidden int libxl__qmp_set_global_dirty_log(libxl__gc *gc, int domid, bool 
> > enable);
> >   _hidden int libxl__qmp_insert_cdrom(libxl__gc *gc, int domid, const 
> > libxl_device_disk *disk);
> > diff --git a/tools/libxl/libxl_qmp.c b/tools/libxl/libxl_qmp.c
> > index 6484f5e..080cb9f 100644
> > --- a/tools/libxl/libxl_qmp.c
> > +++ b/tools/libxl/libxl_qmp.c
> > @@ -904,6 +904,16 @@ int libxl__qmp_save(libxl__gc *gc, int domid, const char 
> > *filename)
> >                              NULL, NULL);
> >   }
> >
> > +int libxl__qmp_restore(libxl__gc *gc, int domid, const char *state_file)
> > +{
> > +    libxl__json_object *args = NULL;
> > +
> > +    qmp_parameters_add_string(gc, &args, "filename", state_file);
> > +
> > +    return qmp_run_command(gc, domid, "xen-load-devices-state", args,
> > +                           NULL, NULL);
> > +}
> > +
> >   static int qmp_change(libxl__gc *gc, libxl__qmp_handler *qmp,
> >                         char *device, char *target, char *arg)
> >   {
>
> .
--
Thanks,
Yang.

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