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3. In scheduler layer, add a filter to find proper host which contains the usb devices and create VM in this host.

4. The schema of flavor which contains USB device information may like this: {"usb_devices":[{"id": 5}]}

5. How to distinguish USB device is important because user wants to specify which USB device to which VM.

I consider it as follows:

1. The identifier of a USB device which are supported by libvirt are vendor id, product id, bus and device. Bellow is a example:

<vendor id='0x136b'/>
<product id='0x0003'/>
<address bus='2' device='3'/>

</hostdev>

Different USB devices may have the same vendor id and product id, so they are not appropriate to distinguish devices.

The bus+device maybe a good choice to distinguish devices, but I have made some tests and found that the device id will change every time reboot host or detach/reattach USB device from/to host.

I have tested vsphere and saw some documents, they in fact pass-through physical port of a host to VM, if user insert a USB device to this port, guest os will automatic discovery the new devices.

I think libvirt doesn't support this function by now.

So I think bus+device maybe the best choice.

5. Use which usb controller is also an important thing to consider. I have made some tests with libvirt-1.2.0-1.el6.x86_64 and qemu-kvm-1.6.2-00001.x86_64 in centos 6.5. The test results are:

               xp(sp3)		    win7		    centos6.5
               uhci	ehci	uhci	ehci	uhci	ehci

create vm OK NOK NOK OK OK OK detach usb OK OK OK OK atach usb OK OK OK OK start vm OK OK OK OK restart OK OK OK OK suspend/resume OK OK OK OK

xp(sp3)+ehci: Device is in abnormal status. After shutdown VM the device will not be normally released to hypervisor. Is the guest os problem?

win7+uhci: Device is in abnormal status. After shutdown VM the device will be normally released to hypervisor. A related bug about it in https://bugs.launchpad.net/qemu/+bug/685096

So I think the default uhci controller can not meet the requirements. I suggest two options:

Option 1: Create a default ehci USB controller in libvirt driver, all usb devices use this default controller. Guest os should support ehci controller by installing driver or they will not been supported by this function.

Option 2: User can specify USB controller type when specify USB device, then system create USB controller(ehci, xhci) for USB device.

I suggest option 2 because although it is more complex to implement but it is more flexible for future extension.

6. Restriction on max supported USB devices: I think a VM with 2 USB devices will cover 99% use scenarios. So it is not necessary to consider USB hub or some other mechanisms to extend more ports for more USB device. Every kind of USB controller has only one.

REST API impact

API for query USB device information of a hypervisor

V2 API specification:

GET v2/{tenant_id}/os-hypervisors/{hypervisor_hostname}

V3 API specification:

GET v3/os-hypervisors/{hypervisor_hostname}

The response JSON contains the variable "usb_device_stats" {"hypervisor":{"usb_device_stats":[{"id": 1,"compute_node_id": 1, "address": "usb_2_3", "product_id": "1520","vendor_id": "8086", "bus_id": "2", "device_id": "3","port_id": "", "status":"available", "extra_info": """instance_uuid":""}]}}

Security impact

None

Notifications impact

None

Other end user impact

I have implemented a demo and made some tests:

1. If migrate(live-migration, with shared storage or not) a VM with USB device from host A to host B, because the destination host doesn't have USB device the migration may be failed.

2. Currently I want to use <address bus='2' device='3'/> to exclusively identify a physical USB device of a host. But I found that every time reboot host or detach/re-attach USB device from/to host the device id will change.

For this problem I suggest to refer to pci-passthrough:

(1) System change the 'invalid' device's status to 'deleted', and create a new device record in DB.

(2) If user starts VM with 'invalid' device, the libvirt driver will automatically ignore the 'invalid' device when construct xml. So VM will start normally but user can not see USB device in guest os.

(3) If user wants to use USB device again, him can create a new flavor with this 'new' USB device and resize VM with the new flavor.

3. System has restriction on max supported USB device number because a single USB controller has restricted port numbers.For example a uhci controller has 2 ports so only supports two USB devices.

4. Have restriction on mas supported USB devices.

5. Currently I only plan to provide this function in KVM so not consider too much for xen.

Performance Impact

None

Other deployer impact

None

Developer impact

I have implemented a demo and made some tests:

1. This new function doesn't affect other server actions including start, stop, reboot, pause/unpause, suspend/resume, rebuild.

2. We need to add some processes of USB devices in resize function, like resize VM from flavor A with USB device A to flavor B with USB device B.

Implementation

==

Assignee(s)

Primary assignee:

 <Jing Yuan>

Work Items

Step 1: Implement function of discover usb device in libvirt driver.

Step 2: Implement function of periodically update USB device information from nova-compute to DB.

Step 3: Implement function of query USB devices of hypervisor.

Step 4: Implement function of create VM with USB device.

Step 5: Make changes to other functions which are affected by this new function.

Dependencies

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None

Testing

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It is necessary to add tempest for this new function.

Documentation Impact

========

It is necessary to add doc for how to use this new function.

References

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None

Main Page/cobbler

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