Re: [Qemu-devel] [QEMU PATCH v5 2/6] migration: spapr_drc: defined VMStateDescription struct

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Oct 05, 2016 at 12:38:53PM +0100, Dr. David Alan Gilbert wrote:
> * Jianjun Duan (duanj@linux.vnet.ibm.com) wrote:
> > To manage hotplug/unplug of dynamic resources such as PCI cards,
> > memory, and CPU on sPAPR guests, a firmware abstraction known as
> > a Dynamic Resource Connector (DRC) is used to assign a particular
> > dynamic resource to the guest, and provide an interface for the
> > guest to manage configuration/removal of the resource associated
> > with it.
> > 
> > To migrate the hotplugged resources in migration, the
> > associated DRC state need be migrated. To migrate the DRC state,
> > we defined the VMStateDescription struct for spapr_drc to enable
> > the transmission of spapr_drc state in migration.
> > 
> > Not all the elements in the DRC state are migrated. Only those
> > ones modifiable or needed by guest actions or device add/remove
> > operation are migrated. From the perspective of device
> > hotplugging, if we hotplug a device on the source, we need to
> > "coldplug" it on the target. The states across two hosts for the
> > same device are not the same. Ideally we want the states be same
> > after migration so that the device would function as hotplugged
> > on the target. For example we can unplug it. The minimum DRC
> > state we need to transfer should cover all the pieces changed by
> > hotplugging. Out of the elements of the DRC state, isolation_state,
> > allocation_sate, and configured are involved in the DR state
> > transition diagram from PAPR+ 2.7, 13.4. configured and signalled
> > are needed in attaching and detaching devices. indicator_state
> > provides users with hardware state information. These 6 elements
> > are migrated.
> > 
> > detach_cb in the DRC state is a function pointer that cannot be
> > migrated. We set it right after DRC state is migrated so that
> > a migrated hot-unplug event could finish its work.
> 
> Be careful with that; it'll get tricky if you have a bunch of different
> possible callbacks.   If you want to explicitly migrate it then you'd
> have to have an enum of different functions that could be called rather
> than storing the pointer explicitly.

Quite.  Looking at the code, I'm quite baffled as to how detach_cb and
detach_cb_opaque get populated in the first place anyway.  All the
assignments I can see seem to be assigning the same variable to itself
(loaded in the caller, passed to another function, stored back to the
same place in the callee).

> 
> > The instance_id is used to identify objects in migration. We set
> > instance_id of DRC using the unique index so that it is the same
> > across migration.
> > 
> > Signed-off-by: Jianjun Duan <duanj@linux.vnet.ibm.com>
> 
> I think this is OK from a migration point of view; I'll leave
> it to someone else to check the Power side of things.
> 
> > ---
> >  hw/ppc/spapr_drc.c         | 69 ++++++++++++++++++++++++++++++++++++++++++++++
> >  hw/ppc/spapr_pci.c         | 22 +++++++++++++++
> >  include/hw/ppc/spapr_drc.h |  9 ++++++
> >  3 files changed, 100 insertions(+)
> > 
> > diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
> > index 6e54fd4..369ec02 100644
> > --- a/hw/ppc/spapr_drc.c
> > +++ b/hw/ppc/spapr_drc.c
> > @@ -615,6 +615,71 @@ static void spapr_dr_connector_instance_init(Object *obj)
> >                          NULL, NULL, NULL, NULL);
> >  }
> >  
> > +static bool spapr_drc_needed(void *opaque)
> > +{
> > +    sPAPRDRConnector *drc = (sPAPRDRConnector *)opaque;
> > +    sPAPRDRConnectorClass *drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
> > +    bool rc = false;
> > +    sPAPRDREntitySense value;
> > +
> > +    drck->entity_sense(drc, &value);
> > +    /* If no dev is plugged in there is no need to migrate the DRC state */
> > +    if (value != SPAPR_DR_ENTITY_SENSE_PRESENT) {
> > +        return false;
> > +    }
> > +    /*
> > +     * If there is dev plugged in, we need to migrate the DRC state when
> > +     * it is different from cold-plugged state
> > +     */
> > +    switch(drc->type) {
> > +    /* for PCI type */
> > +    case SPAPR_DR_CONNECTOR_TYPE_PCI:
> > +        rc = !((drc->isolation_state == SPAPR_DR_ISOLATION_STATE_UNISOLATED) &&
> > +               (drc->allocation_state == SPAPR_DR_ALLOCATION_STATE_USABLE) &&
> > +               drc->configured && drc->signalled && !drc->awaiting_release);
> > +        break;
> > +    /* for LMB type */
> > +    case SPAPR_DR_CONNECTOR_TYPE_LMB:
> > +        rc = !((drc->isolation_state == SPAPR_DR_ISOLATION_STATE_ISOLATED) &&
> > +               (drc->allocation_state == SPAPR_DR_ALLOCATION_STATE_UNUSABLE) &&
> > +               drc->configured && drc->signalled && !drc->awaiting_release);
> > +        break;
> > +    default:
> > +        ;
> > +    }
> > +
> > +    return rc;
> > +}
> > +
> > +/* detach_cb needs be set since it is not migrated */
> > +static void postmigrate_set_detach_cb(sPAPRDRConnector *drc,
> > +                                      spapr_drc_detach_cb *detach_cb)
> > +{
> > +    drc->detach_cb = detach_cb;
> > +}
> > +
> > +/* return the unique drc index as instance_id for qom interfaces*/
> > +static int get_instance_id(DeviceState *dev)
> > +{
> > +    return (int)get_index(SPAPR_DR_CONNECTOR(OBJECT(dev)));
> > +}
> > +
> > +static const VMStateDescription vmstate_spapr_drc = {
> > +    .name = "spapr_drc",
> > +    .version_id = 1,
> > +    .minimum_version_id = 1,
> > +    .needed = spapr_drc_needed,
> > +    .fields  = (VMStateField []) {
> > +        VMSTATE_UINT32(isolation_state, sPAPRDRConnector),
> > +        VMSTATE_UINT32(allocation_state, sPAPRDRConnector),
> > +        VMSTATE_UINT32(indicator_state, sPAPRDRConnector),
> > +        VMSTATE_BOOL(configured, sPAPRDRConnector),
> > +        VMSTATE_BOOL(awaiting_release, sPAPRDRConnector),
> > +        VMSTATE_BOOL(signalled, sPAPRDRConnector),
> > +        VMSTATE_END_OF_LIST()
> > +    }
> > +};
> > +
> >  static void spapr_dr_connector_class_init(ObjectClass *k, void *data)
> >  {
> >      DeviceClass *dk = DEVICE_CLASS(k);
> > @@ -623,6 +688,8 @@ static void spapr_dr_connector_class_init(ObjectClass *k, void *data)
> >      dk->reset = reset;
> >      dk->realize = realize;
> >      dk->unrealize = unrealize;
> > +    dk->vmsd = &vmstate_spapr_drc;
> > +    dk->dev_get_instance_id = get_instance_id;
> >      drck->set_isolation_state = set_isolation_state;
> >      drck->set_indicator_state = set_indicator_state;
> >      drck->set_allocation_state = set_allocation_state;
> > @@ -636,6 +703,8 @@ static void spapr_dr_connector_class_init(ObjectClass *k, void *data)
> >      drck->detach = detach;
> >      drck->release_pending = release_pending;
> >      drck->set_signalled = set_signalled;
> > +    drck->postmigrate_set_detach_cb = postmigrate_set_detach_cb;
> > +
> >      /*
> >       * Reason: it crashes FIXME find and document the real reason
> >       */
> > diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
> > index 4f00865..080471c 100644
> > --- a/hw/ppc/spapr_pci.c
> > +++ b/hw/ppc/spapr_pci.c
> > @@ -1594,11 +1594,33 @@ static void spapr_pci_pre_save(void *opaque)
> >      }
> >  }
> >  
> > +/*
> > + * detach_cb in the DRC state is a function pointer that cannot be
> > + * migrated. We set it right after migration so that a migrated
> > + * hot-unplug event could finish its work.
> > + */
> > +static void spapr_pci_set_detach_cb(PCIBus *bus, PCIDevice *pdev,
> > +                                 void *opaque)
> > +{
> > +    sPAPRPHBState *sphb = opaque;
> > +    sPAPRDRConnector *drc = spapr_phb_get_pci_drc(sphb, pdev);
> > +    sPAPRDRConnectorClass *drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
> > +    drck->postmigrate_set_detach_cb(drc, spapr_phb_remove_pci_device_cb);
> > +}
> > +
> >  static int spapr_pci_post_load(void *opaque, int version_id)
> >  {
> >      sPAPRPHBState *sphb = opaque;
> >      gpointer key, value;
> >      int i;
> > +    PCIBus *bus = PCI_HOST_BRIDGE(sphb)->bus;
> > +    unsigned int bus_no = 0;
> > +
> > +    /* Set detach_cb for the drc unconditionally after migration */
> > +    if (bus) {
> > +        pci_for_each_device(bus, pci_bus_num(bus), spapr_pci_set_detach_cb,
> > +                            &bus_no);
> > +    }
> >  
> >      for (i = 0; i < sphb->msi_devs_num; ++i) {
> >          key = g_memdup(&sphb->msi_devs[i].key,
> > diff --git a/include/hw/ppc/spapr_drc.h b/include/hw/ppc/spapr_drc.h
> > index fa531d5..17589c8 100644
> > --- a/include/hw/ppc/spapr_drc.h
> > +++ b/include/hw/ppc/spapr_drc.h
> > @@ -192,6 +192,15 @@ typedef struct sPAPRDRConnectorClass {
> >                     void *detach_cb_opaque, Error **errp);
> >      bool (*release_pending)(sPAPRDRConnector *drc);
> >      void (*set_signalled)(sPAPRDRConnector *drc);
> > +
> > +    /*
> > +     * QEMU interface for setting detach_cb after migration.
> > +     * detach_cb in the DRC state is a function pointer that cannot be
> > +     * migrated. We set it right after migration so that a migrated
> > +     * hot-unplug event could finish its work.
> > +     */
> > +    void (*postmigrate_set_detach_cb)(sPAPRDRConnector *drc,
> > +                                      spapr_drc_detach_cb *detach_cb);
> >  } sPAPRDRConnectorClass;
> >  
> >  sPAPRDRConnector *spapr_dr_connector_new(Object *owner,

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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