Re: [Qemu-devel] [PATCH v3] xen: implement unplug protocol in xen_platform

[Stefano Stabellini]

On Thu, 30 Jun 2011, Kevin Wolf wrote:
> > +static int pci_piix3_xen_ide_unplug(DeviceState *dev)
> > +{
> > +    PCIDevice *pci_dev;
> > +    PCIIDEState *pci_ide;
> > +    DriveInfo *di;
> > +    int i = 0;
> > +
> > +    pci_dev = DO_UPCAST(PCIDevice, qdev, dev);
> > +    pci_ide = DO_UPCAST(PCIIDEState, dev, pci_dev);
> > +
> > +    for (; i < 3; i++) {
> > +        di = drive_get_by_index(IF_IDE, i);
> > +        if (di != NULL && di->bdrv != NULL && !di->bdrv->removable) {
> > +            DeviceState *ds = bdrv_get_attached(di->bdrv);
> > +            if (ds) {
> > +                bdrv_detach(di->bdrv, ds);
> > +            }
> > +            bdrv_close(di->bdrv);
> > +            pci_ide->bus[di->bus].ifs[di->unit].bs = NULL;
> 
> Have you tested if this is enough if the guest tries to continue using
> the device? I don't know of any case where it's not sufficient, just
> trying to make sure that it's really true in practice.

The purpose of this is to "hide" the disk from the guest. The unplug is
supposed to happen *before* the guest enumerates the IDE disks; it is
responsibility of the guest to make sure of it.
I tested it with Linux PV on HVM drivers, and Linux doesn't see the
emulated disk after the unplug, as it should be.


> > +            drive_put_ref(di);
> > +        }
> > +    }
> > +    qdev_reset_all(&(pci_ide->dev.qdev));
> > +    return 0;
> > +}
> > +
> > +PCIDevice *pci_piix3_xen_ide_init(PCIBus *bus, DriveInfo **hd_table, int 
> > devfn)
> > +{
> > +    PCIDevice *dev;
> > +
> > +    dev = pci_create_simple(bus, devfn, "piix3-ide-xen");
> > +    dev->qdev.info->unplug = pci_piix3_xen_ide_unplug;
> 
> Can't this be moved into the PCIDeviceInfo now that we have a separate
> one for Xen?
 
No because it would be overridden by the default pci unplug function,
that is not what we want in this case.