[libvirt] [PATCH 3/5] qemu: add usb-bot support from disks points of view

[Gerd Hoffmann]

  Hi,

> > > How does this work if we start off a guest with 3 disks
> > > attached to the usb-bot SCSI controller. Then hot-unplug
> > > the 2nd disk.
> > 
> > You can't hotplug individual luns anyway.
> 
> How does hotplug/unplug work in the context of usb-bot ?
> 
> AFAIK we need to be able to run
> 
>   device_add usb_bot
>   drive_add file...
>   device_add scsi-hd
> 
> And the reverse, to unplug it, if we're to have feature parity with
> usb-storage.

Hot-unplug is easy.  You can remove the usb-bot device which will also
remove all child devices.

Hot-plug doesn't work at the moment, and I don't see any obvious way to
fix that properly :-(

We need some way to hotplug a *group* of devices (usb-bot + all
children) as usb-bot itself is hotpluggable but the individual scsi
devices connected to it are not.

I could allow hotplug on usb-bot as workaround, then you can do

  stop
  device_add usb_bot
  device_add scsi-{hd,cd,whatever}
  cont

but that would be more a gross hack than a solution ...

cheers,
  Gerd