[Xen-devel] [PATCH 0/3][RFC] PV Passthrough PCI Device Hotplug Support

[Yosuke Iwamatsu <y-iwamatsu@xxxxxxxxxxxxx>]

Hi all,

This patch set adds passthrough PCI device hotplug support for PV
driver domains.

I began working on this some little time ago and developed independently
of the HVM PCI device hotplug code. Now that HVM PCI device hotplug was
checked in, some modifications are needed to apply this patch to
current xen-unstable.

Please see below for detailed descriptions.
Comments are welcome.

[Usage]
To hot add a new PCI device '0000:00:1d.0',
  xm pci-attach <PV domain> 0000:00:1d.0
To hot remove a PCI device '0000:00:1d.0',
  xm pci-detach <PV domain> 0000:00:1d.0

[Implementation details]

- Interface changes
  New xenbus states "Reconfiguring" and "Reconfigured" are introduced.

- Xenstore changes
  Substates(state-#) and virtual pci slots(vdev-#) entries are added
  for pciback driver. For example, when PCI devices 00:1d.0 and 00:1d.1
  are connected, xenstore-ls will show information like this.
    pci = ""
     3 = ""
      0 = ""
       ...
       state = "4"
       dev-0 = "0000:00:1d.00"
       vdev-0 = "0000:00:00.00"
       state-0 = "3"
       dev-1 = "0000:00:1d.1"
       vdev-1 = "0000:00:00.01"
       state-1 = "3"
       ...

- Attach sequence
  1) User executes xm pci-attach.
  2) If there's no pcidev, Xend create new one.
     Otherwise, Xend does following things:
     2a) write new dev-# entry on xenstore
     2b) write new state-# entry and set it as "Initialising"
     2c) enable io resources
     2d) switch pciback state from "Connected" to "Reconfiguring"
  3) pcifront detects backend change and switch its state from
     "Connected" to "Reconfiguring".
  4) pciback detects frontend change and:
     4a) scan xenstore and find the device being attached
     4b) export the device, write vdev-# entry on xenstore and change
         state-# to "Initialized"
     4c) switch its state from "Reconfiguring" to "Reconfigured"
  5) pcifront detects backend change and:
     5a) rescan the pcibus for the attached device and enable it.
     5b) switch its state from "Reconfiguring" to "Connected"
  6) pciback detects pcifront change and switch its state from
     "Reconfigured" to "Connected".

- Detach sequence
  1) User executes xm pci-detach.
  2) If the specified device exists, Xend does following things:
     2a) change the device's substate(state-#) to "Closing"
     2b) switch pciback state from "Connected" to "Reconfiguring"
  3) pcifront detects backend change and:
     3a) scan xenstore and find the device being detached
         (the virtual pci slot can be identified by vdev-# entry)
     3b) remove the device
     3c) switch its state from "Connected" to "Reconfiguring"
  4) pciback detects frontend change and:
     4a) scan xenstore and find the device being detached
     4b) remove the device
     4c) switch its state from "Reconfiguring" to "Reconfigured"
  5) pcifront detects backend change and switch its state from
     "Reconfiguring" to "Connected".
  6) pciback detects pcifront change and switch its state from
     "Reconfigured" to "Connected".
  7) Xend, who has been watching on the xenbus state, detects backend
     change and:
     7a) cleanup xenstore entries
     7b) disable io resources
     7c) if there's no device left, destroy pcidev

- Limitations
  Hotplug currently only works when pciback is compiled with
  CONFIG_XEN_PCIDEV_BACKEND_VPCI or CONFIG_XEN_PCIDEV_BACKEND_SLOT.

Thanks,
-------------------
Yosuke Iwamatsu
        NEC Corporation


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