USB emulation
QEMU can emulate a PCI UHCI, OHCI, EHCI or XHCI USB controller. You can plug virtual USB devices or real host USB devices (only works with certain host operating systems). QEMU will automatically create and connect virtual USB hubs as necessary to connect multiple USB devices.
USB controllers
XHCI controller support
QEMU has XHCI host adapter support. The XHCI hardware design is much more virtualization-friendly when compared to EHCI and UHCI, thus XHCI emulation uses less resources (especially CPU). So if your guest supports XHCI (which should be the case for any operating system released around 2010 or later) we recommend using it:
qemu -device qemu-xhci
XHCI supports USB 1.1, USB 2.0 and USB 3.0 devices, so this is the only controller you need. With only a single USB controller (and therefore only a single USB bus) present in the system there is no need to use the bus= parameter when adding USB devices.
EHCI controller support
The QEMU EHCI Adapter supports USB 2.0 devices. It can be used either standalone or with companion controllers (UHCI, OHCI) for USB 1.1 devices. The companion controller setup is more convenient to use because it provides a single USB bus supporting both USB 2.0 and USB 1.1 devices. See next section for details.
When running EHCI in standalone mode you can add UHCI or OHCI controllers for USB 1.1 devices too. Each controller creates its own bus though, so there are two completely separate USB buses: One USB 1.1 bus driven by the UHCI controller and one USB 2.0 bus driven by the EHCI controller. Devices must be attached to the correct controller manually.
The easiest way to add a UHCI controller to a pc
machine is the
-usb
switch. QEMU will create the UHCI controller as function of
the PIIX3 chipset. The USB 1.1 bus will carry the name usb-bus.0
.
You can use the standard -device
switch to add a EHCI controller to
your virtual machine. It is strongly recommended to specify an ID for
the controller so the USB 2.0 bus gets an individual name, for example
-device usb-ehci,id=ehci
. This will give you a USB 2.0 bus named
ehci.0
.
When adding USB devices using the -device
switch you can specify the
bus they should be attached to. Here is a complete example:
qemu-system-x86_64 -M pc ${otheroptions} \ -drive if=none,id=usbstick,format=raw,file=/path/to/image \ -usb \ -device usb-ehci,id=ehci \ -device usb-tablet,bus=usb-bus.0 \ -device usb-storage,bus=ehci.0,drive=usbstick
This attaches a USB tablet to the UHCI adapter and a USB mass storage device to the EHCI adapter.
Companion controller support
The UHCI and OHCI controllers can attach to a USB bus created by EHCI
as companion controllers. This is done by specifying the masterbus
and firstport
properties. masterbus
specifies the bus name the
controller should attach to. firstport
specifies the first port the
controller should attach to, which is needed as usually one EHCI
controller with six ports has three UHCI companion controllers with
two ports each.
There is a config file in docs which will do all this for you, which you can use like this:
qemu-system-x86_64 -readconfig docs/config/ich9-ehci-uhci.cfg
Then use bus=ehci.0
to assign your USB devices to that bus.
Using the -usb
switch for q35
machines will create a similar
USB controller configuration.
Connecting USB devices
USB devices can be connected with the -device usb-...
command line
option or the device_add
monitor command. Available devices are:
usb-mouse
Virtual Mouse. This will override the PS/2 mouse emulation when activated.
usb-tablet
Pointer device that uses absolute coordinates (like a touchscreen). This means QEMU is able to report the mouse position without having to grab the mouse. Also overrides the PS/2 mouse emulation when activated.
usb-storage,drive=drive_id
Mass storage device backed by drive_id (see the Disk Images chapter in the System Emulation Users Guide). This is the classic bulk-only transport protocol used by 99% of USB sticks. This example shows it connected to an XHCI USB controller and with a drive backed by a raw format disk image:
qemu-system-x86_64 [...] \ -drive if=none,id=stick,format=raw,file=/path/to/file.img \ -device nec-usb-xhci,id=xhci \ -device usb-storage,bus=xhci.0,drive=stick
usb-uas
USB attached SCSI device. This does not create a SCSI disk, so you need to explicitly create a
scsi-hd
orscsi-cd
device on the command line, as well as using the-drive
option to specify what those disks are backed by. Oneusb-uas
device can handle multiple logical units (disks). This example creates three logical units: two disks and one cdrom drive:qemu-system-x86_64 [...] \ -drive if=none,id=uas-disk1,format=raw,file=/path/to/file1.img \ -drive if=none,id=uas-disk2,format=raw,file=/path/to/file2.img \ -drive if=none,id=uas-cdrom,media=cdrom,format=raw,file=/path/to/image.iso \ -device nec-usb-xhci,id=xhci \ -device usb-uas,id=uas,bus=xhci.0 \ -device scsi-hd,bus=uas.0,scsi-id=0,lun=0,drive=uas-disk1 \ -device scsi-hd,bus=uas.0,scsi-id=0,lun=1,drive=uas-disk2 \ -device scsi-cd,bus=uas.0,scsi-id=0,lun=5,drive=uas-cdrom
usb-bot
Bulk-only transport storage device. This presents the guest with the same USB bulk-only transport protocol interface as
usb-storage
, but the QEMU command line option works likeusb-uas
and does not automatically create SCSI disks for you.usb-bot
supports up to 16 LUNs. Unlikeusb-uas
, the LUN numbers must be continuous, i.e. for three devices you must use 0+1+2. The 0+1+5 numbering from theusb-uas
example above won’t work withusb-bot
.usb-mtp,rootdir=dir
Media transfer protocol device, using dir as root of the file tree that is presented to the guest.
usb-host,hostbus=bus,hostaddr=addr
Pass through the host device identified by bus and addr
usb-host,vendorid=vendor,productid=product
Pass through the host device identified by vendor and product ID
usb-wacom-tablet
Virtual Wacom PenPartner tablet. This device is similar to the
tablet
above but it can be used with the tslib library because in addition to touch coordinates it reports touch pressure.usb-kbd
Standard USB keyboard. Will override the PS/2 keyboard (if present).
usb-serial,chardev=id
Serial converter. This emulates an FTDI FT232BM chip connected to host character device id.
usb-braille,chardev=id
Braille device. This emulates a Baum Braille device USB port. id has to specify a character device defined with
-chardev …,id=id
. One will normally use BrlAPI to display the braille output on a BRLTTY-supported device withqemu-system-x86_64 [...] -chardev braille,id=brl -device usb-braille,chardev=brl
or alternatively, use the following equivalent shortcut:
qemu-system-x86_64 [...] -usbdevice braille
usb-net[,netdev=id]
Network adapter that supports CDC ethernet and RNDIS protocols. id specifies a netdev defined with
-netdev …,id=id
. For instance, user-mode networking can be used withqemu-system-x86_64 [...] -netdev user,id=net0 -device usb-net,netdev=net0
usb-ccid
Smartcard reader device
usb-audio
USB audio device
u2f-{emulated,passthru}
Universal Second Factor device
canokey
An Open-source Secure Key implementing FIDO2, OpenPGP, PIV and more. For more information, see CanoKey QEMU.
Physical port addressing
For all the above USB devices, by default QEMU will plug the device
into the next available port on the specified USB bus, or onto
some available USB bus if you didn’t specify one explicitly.
If you need to, you can also specify the physical port where
the device will show up in the guest. This can be done using the
port
property. UHCI has two root ports (1,2). EHCI has six root
ports (1-6), and the emulated (1.1) USB hub has eight ports.
Plugging a tablet into UHCI port 1 works like this:
-device usb-tablet,bus=usb-bus.0,port=1
Plugging a hub into UHCI port 2 works like this:
-device usb-hub,bus=usb-bus.0,port=2
Plugging a virtual USB stick into port 4 of the hub just plugged works this way:
-device usb-storage,bus=usb-bus.0,port=2.4,drive=...
In the monitor, the device_add` command also accepts a ``port
property specification. If you want to unplug devices too you should
specify some unique id which you can use to refer to the device.
You can then use device_del
to unplug the device later.
For example:
(qemu) device_add usb-tablet,bus=usb-bus.0,port=1,id=my-tablet
(qemu) device_del my-tablet
Hotplugging USB storage
The usb-bot
and usb-uas
devices can be hotplugged. In the hotplug
case they are added with attached = false
so the guest will not see
the device until the attached
property is explicitly set to true.
That allows you to attach one or more scsi devices before making the
device visible to the guest. The workflow looks like this:
device-add usb-bot,id=foo
device-add scsi-{hd,cd},bus=foo.0,lun=0
optionally add more devices (luns 1 … 15)
scripts/qmp/qom-set foo.attached = true
Using host USB devices on a Linux host
WARNING: this is an experimental feature. QEMU will slow down when using it. USB devices requiring real time streaming (i.e. USB Video Cameras) are not supported yet.
If you use an early Linux 2.4 kernel, verify that no Linux driver is actually using the USB device. A simple way to do that is simply to disable the corresponding kernel module by renaming it from
mydriver.o
tomydriver.o.disabled
.Verify that
/proc/bus/usb
is working (most Linux distributions should enable it by default). You should see something like that:ls /proc/bus/usb 001 devices drivers
Since only root can access to the USB devices directly, you can either launch QEMU as root or change the permissions of the USB devices you want to use. For testing, the following suffices:
chown -R myuid /proc/bus/usb
Launch QEMU and do in the monitor:
info usbhost Device 1.2, speed 480 Mb/s Class 00: USB device 1234:5678, USB DISK
You should see the list of the devices you can use (Never try to use hubs, it won’t work).
Add the device in QEMU by using:
device_add usb-host,vendorid=0x1234,productid=0x5678
Normally the guest OS should report that a new USB device is plugged. You can use the option
-device usb-host,...
to do the same.Now you can try to use the host USB device in QEMU.
When relaunching QEMU, you may have to unplug and plug again the USB device to make it work again (this is a bug).
usb-host
properties for specifying the host device
The example above uses the vendorid
and productid
to
specify which host device to pass through, but this is not
the only way to specify the host device. usb-host
supports
the following properties:
hostbus=<nr>
Specifies the bus number the device must be attached to
hostaddr=<nr>
Specifies the device address the device got assigned by the guest os
hostport=<str>
Specifies the physical port the device is attached to
vendorid=<hexnr>
Specifies the vendor ID of the device
productid=<hexnr>
Specifies the product ID of the device.
In theory you can combine all these properties as you like. In practice only a few combinations are useful:
vendorid
andproductid
– match for a specific device, pass it to the guest when it shows up somewhere in the host.hostbus
andhostport
– match for a specific physical port in the host, any device which is plugged in there gets passed to the guest.hostbus
andhostaddr
– most useful for ad-hoc pass through as the hostaddr isn’t stable. The next time you plug the device into the host it will get a new hostaddr.
Note that on the host USB 1.1 devices are handled by UHCI/OHCI and USB 2.0 by EHCI. That means different USB devices plugged into the very same physical port on the host may show up on different host buses depending on the speed. Supposing that devices plugged into a given physical port appear as bus 1 + port 1 for 2.0 devices and bus 3 + port 1 for 1.1 devices, you can pass through any device plugged into that port and also assign it to the correct USB bus in QEMU like this:
qemu-system-x86_64 -M pc [...] \ -usb \ -device usb-ehci,id=ehci \ -device usb-host,bus=usb-bus.0,hostbus=3,hostport=1 \ -device usb-host,bus=ehci.0,hostbus=1,hostport=1
usb-host
properties for reset behavior
The guest-reset
and guest-reset-all
properties control
whenever the guest is allowed to reset the physical usb device on the
host. There are three cases:
guest-reset=false
The guest is not allowed to reset the (physical) usb device.
guest-reset=true,guest-resets-all=false
The guest is allowed to reset the device when it is not yet initialized (aka no usb bus address assigned). Usually this results in one guest reset being allowed. This is the default behavior.
guest-reset=true,guest-resets-all=true
The guest is allowed to reset the device as it pleases.
The reason for this existing are broken usb devices. In theory one should be able to reset (and re-initialize) usb devices at any time. In practice that may result in shitty usb device firmware crashing and the device not responding any more until you power-cycle (aka un-plug and re-plug) it.
What works best pretty much depends on the behavior of the specific usb device at hand, so it’s a trial-and-error game. If the default doesn’t work, try another option and see whenever the situation improves.
record usb transfers
All usb devices have support for recording the usb traffic. This can
be enabled using the pcap=<file>
property, for example:
-device usb-mouse,pcap=mouse.pcap
The pcap files are compatible with the linux kernels usbmon. Many
tools, including wireshark
, can decode and inspect these trace
files.