Nova/USB device&USB controller
< Nova
Contents
USB device and USB controller Features
Background
Currently, nova has already supported function of pci-passthrough, but dosen't support usb-passthrough. I think usb-passthrough is also a important and necessary function especially in private cloud.
User scenarios
1. When a user transfer money online, him may need a usb-key provided by bank for authentication.
2. When a user run a ERP software, him may need a usb-key provided by software provider for authentication.
3. When a user want to copy data to a removable media for business trip him may want a usb data disk.
Technical verification
1. Test case
Attach different number of usb devices to different type of usb controllers.
2. Xml definition
(1)Sample of usb controller: <controller type='usb' index='2' model='piix3-uhci'/> <controller type='usb' index='1' model='ehci'/>
(2)Sample of pass-through usb devices
<hostdev mode='subsystem' type='usb'>
< source>
<vendor id='0x136b'/>
<product id='0x0003'/>
<address bus='2' device='2'/>
</source>
<address type='usb' bus='1' port='1'/>
</hostdev>
(3)Sample of emulated usb disks
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'/>
< source file='/home/vms/usb/sdb.qcow2'/>
<target dev='sdb' bus='usb'/>
<address type='usb' bus='1' port='1'/>
</disk>
3. The test results
(1)Usb controllers have a maximum port restriction. Uhci controller support maxmum of 2 while ehci controller support maxmum of 6. (2)If create vm without usb controller, qemu will default create a piix3-usb-uhci controller but not creating other type's controllers by default. (3)If create vm with usb device but no usb controller, the usb device will default be attached to the default uhci controller, but speed may mismatch. (4)There are two ways for supporting more usb devices. 1. Add cascaded hubs and connect usb devices to them. 2.Create more controllers and connect usb devices to different controllers. (5)When create vm with a pair of usb hub and ehci controller, the vm crashed. Qemu thrown a error(why?)
Proposed solution
1. Use cases
Case 1: (1)Admin/User request to create a flavor with usb controllers(key arguments: type, quantity). (2)System create a flavor. (3)Admin/User request to create a vm with flavor created above. (4)System first validate usb arguments specified in flavor, if valid then create a vm with usb controllers.
Case 2: (1)Admin/User request to create a flavor with usb devices(key arguments: unique identifiers of devices). (2)System create a flavor. (3)Admin/User request to create a vm with flavor created above. (4)System first validate if usb devices are exist, available, and in the same host, if valid then create a vm with usb devices in the host. The usb devices will be attached to the default uhci controller created by qemu .
Case 3: (1)Admin/User request to create a flavor with usb controllers(key argument: type, quantity) and usb devices(key arguments: identifiers and usb controller type). (2)System create a flavor. (3)Admin/User request to create a vm with flavor created above. (4)Admin/User first validate if usb devices are exist, available,in the same host, and matching with controllers(type, free port and so on), if valid then create a vm with usb devices and usb controllers in the host. The usb devices will be attached to the controllers by type.
2. System requirements and things should be considered for usb controller(An optional Implementation):
(1)System support creating flavor with usb controller.
Add a property to extra_specs of flavor. The scheme may like {"usb_controllers":[{"type":"piix3-uhci", "count": 1},{"type":"ehci", "count": 1}]}
(2)System support constructing usb controller xml in libvirt driver and config.
(3)System support managing usb controller index/port<--->usb device's relationship so that we can attach usb device to unique usb controller port.
The usb controller schema may like
{
"usb_controller_requests":
[
{
"type": "piix3-uhci",
"count": 2,
"usb_controllers":
[
{
"index": 1,
"ports":
[
{
"port": 1,
"usb_device": "dev_pci"
}
]
}
]
}
]
}
(4)System support saving usb controller information in DB so that the next starting of vm will create usb controllers.
3. System requirements and things should be considered for usb device(An optional Implementation):
(1)System support automatically discovering usb devices and save them to DB.
The main process can refer to pci-passthrough:
<1>Using white-list and lsusb command to retrieve available usb devices of a host.
<2>Adding auto-update process to synchronize
Add a table like usb_devices in DB for saving usb devices.
(2)System support creating vm with usb devices.
(3)System support detaching usb devices when shutting down a vm with usb devices.
(4)System support detaching usb devices when suspending a vm with usb devices, and re-attaching usb devices when resuming the vm.
(5)System support detaching usb devices when terminating a vm with usb devices.
(6)System support detaching usb devices before making snapshot of a vm and re-attaching usb devices after making snapshot. System also support the protection of usb device when using snapshot to resume a vm. (7)System support reporting error when migrating vm with usb device.
A datatable usb_devices may been needed for storing usb devices information like pci_devices.
How to uniquely identify a usb device? One choose is node id + device id(address or label or dev_id) which stored in usb_devices.
key arguments: identifiers that can find the device, like in which host, bus number and device number and so on
<2>In extra_specs of flavor add a property for usb devices: eg {'devices':[{'node_id':'1', 'dev_id':'pci_0000_00_03_0', 'usbcontroller_type':'piix3-uhci'},{{'node_id':'1', 'dev_id':'pci_0000_00_03_1', 'usbcontroller_type':'ehci'}]}
{'usb_controllers':[{'type':'piix3-uhci', 'index':'1', 'address':{'type':'pci','domain':'0x0000', 'bus':'0x00', 'slot':'0x01', 'function':'0x2'}, ports':[{'port':‘0’, 'status':'available', 'usb_device':}, {'port':‘1’, 'status':'used', 'usb_device':'dev1'}]}]}
Detailed things:
<3>Add UsbDeviceFilter for locating the correct node.
<4>Add algorithm in libvirt driver for choosing usb controller.
And so on.
