Re: [Qemu-devel] [QEMU RFC PATCH v3 1/6] Migration: Defined VMStateDescription struct for spapr_drc

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

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On Thu, Jun 02, 2016 at 05:28:45PM -0700, Jianjun Duan wrote:
> 
> 
> On 06/01/2016 09:07 PM, David Gibson wrote:
> > On Tue, May 31, 2016 at 11:02:39AM -0700, Jianjun Duan 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.
> >>
> >> Signed-off-by: Jianjun Duan <duanj@linux.vnet.ibm.com>
> > 
> > So, the thing which concerns me about this patch is that it exposes
> > the DRCs as real objects in the migration stream, which will make it
> > difficult to ever remove them in the future.
> > 
> > Particularly for LMBs having full QOM objects for every individual DRC
> > is kind of clunky, and I'd already considered replacing them instead
> > with a QOM interface implementing a whole array of DRCs as part of the
> > "owning" object (machine or PHB).
> > 
> > The internal structure of the VMSD looks ok to me, but the
> > complication is the automatic "addressing" of it as a separate
> > object.  If we could manually take that over, allowing us to direct
> > the same VMSD data at elements in a simpler DRC array later, that
> > would be preferable.
> 
> We can address this concern by setting the unique instance_id for each
> drc. The instance_id can be used to match the drcs from source and
> target.

Ah, yes, that sounds like it should work.  And we already have a DRC
id value we can use for the purpose.

> > 
> > 
> >> ---
> >>  hw/ppc/spapr_drc.c         | 61 ++++++++++++++++++++++++++++++++++++++++++++++
> >>  hw/ppc/spapr_pci.c         | 22 +++++++++++++++++
> >>  include/hw/ppc/spapr_drc.h |  9 +++++++
> >>  3 files changed, 92 insertions(+)
> >>
> >> diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
> >> index 94c875d..1fb5e23 100644
> >> --- a/hw/ppc/spapr_drc.c
> >> +++ b/hw/ppc/spapr_drc.c
> >> @@ -617,6 +617,65 @@ 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;
> >> +}
> >> +
> >> +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);
> >> @@ -625,6 +684,7 @@ 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;
> >>      drck->set_isolation_state = set_isolation_state;
> >>      drck->set_indicator_state = set_indicator_state;
> >>      drck->set_allocation_state = set_allocation_state;
> >> @@ -638,6 +698,7 @@ 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 856aec7..c68da08 100644
> >> --- a/hw/ppc/spapr_pci.c
> >> +++ b/hw/ppc/spapr_pci.c
> >> @@ -1562,11 +1562,33 @@ 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 fa21ba0..a68433b 100644
> >> --- a/include/hw/ppc/spapr_drc.h
> >> +++ b/include/hw/ppc/spapr_drc.h
> >> @@ -190,6 +190,15 @@ 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,
> > 
> Thanks,
> Jianjun
> 

-- 
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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