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Re: [libvirt] qemu: hotplug virtio_scsi over lsilogic when sicsi controller is not present?



On Tue, Jul 11, 2017 at 03:47:55PM -0400, Liang Yan wrote:
Hi,

We hit some problems when we attached some lun devices in our vm, turns
out that libvirt created lsilogic scsi controller automatically for
these scsi devices, however these device works well under virtio_scsi
controller.

the current code logic is check lsilogic first, if qemu could not
support it, then check virtio_scsi, however is it better to check
virtio_scsi earlier? since it is supported better in qemu level?


It is not in older QEMUs which we need to stay compatible with.

I am wondering which solution is better?
1. simple switch sequence and check virtio_scsi first


We can't do that.  We have to keep parsing older XMLs (that did not have
the model in them) the same way as we were before so that we keep stable
guest ABI.

2. add extra option for "virsh attach-disk" to choose specific
controller type


Or you can first attach the controller and then attach-device with the
xml that specifies that particular controller.  attach-disk is a
syntactic sugar for attach-device IIRC.

Thanks,
Liang


====================================
Code part is like below

qemu_hotplug.c  qemuDomainFindOrCreateSCSIDiskController

   /* No SCSI controller present, for backward compatibility we
    * now hotplug a controller */
   if (VIR_ALLOC(cont) < 0)
       return NULL;
   cont->type = VIR_DOMAIN_CONTROLLER_TYPE_SCSI;
   cont->idx = controller;
   cont->model = -1;

   VIR_INFO("No SCSI controller present, hotplugging one");
   if (qemuDomainAttachControllerDevice(driver,



qemu_domain_address.c  qemuDomainSetSCSIControllerModel

       if (qemuDomainIsPSeries(def)) {
           *model = VIR_DOMAIN_CONTROLLER_MODEL_SCSI_IBMVSCSI;
       } else if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_SCSI_LSI)) {
           *model = VIR_DOMAIN_CONTROLLER_MODEL_SCSI_LSILOGIC;
       } else if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_VIRTIO_SCSI)) {
           *model = VIR_DOMAIN_CONTROLLER_MODEL_SCSI_VIRTIO_SCSI;
       } else {
           virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                          _("Unable to determine model for scsi
controller"));
           return -1;


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