vdev virtio-console

Synopsis:

vdev virtio-console options

Options:

delayed seconds|forever

If specified, delay opening the device in the host until it is first referenced by the guest.

If the device isn't found in the host, continue trying for the number of seconds specified by seconds before timing out (e.g., delayed 5). If seconds is set to 0 (e.g., delayed 0), try only once to find the device on the host. If the argument is set to “forever” (e.g., delayed forever), never time out (i.e., keep trying to find the device on the host).

hostdev [<|>]host_device_name

Use the host_device_name as the source and/or destination of characters to the device.

Use < (input) or > (output) to specify if the host device specified by host_device_name provides input or receives output, as you would in a shell.

intr intr

Signal intr for device interrupts. Not required when the vdev appears as a PCI device.

legacy

Provide the VirtIO legacy interface (0.9.5) rather than the 1.0 standard version.

loc addr

Set the base address of the device registers to addr. Not required if the vdev appears as a PCI device.

sched priority

Use the priority specified by priority for pulses indicating that input is available on the host device.

For a list of options available to all vdevs, see “Common vdev options” at the beginning of this chapter.

Description:

ARM and x86. Normally the device appears as a PCI device, but if you specify the loc and intr options, the guest will see it as a memory mapped I/O device at the specified location.

The virtio-console vdev can be very useful on systems where console interaction to a guest is slow over a regular console or serial terminal. The virtio-console vdev is a buffering driver; most often it is used when a guest is interacting with the host over an emulated UART. For example, many embedded ARM boards will use the PL011 serial port as a terminal for output from Linux kernel. Using virtio-console to buffer PL011 reduces emulation overhead.

The virtio-console vdev requires:

• A device to run on. For example, for ARM systems, the virtio-console vdev is usually used for buffering the PL011 serial device.

  The PL011 is slow and will have slow output because there are many interactions with the virtualized serial port. By using the virtio-console vdev on top of the PL011 device, the console interaction is very fast both on input and output due to the virtio-console vdev's larger and more efficient buffering.

• A virtual driver running in the guest. Both Linux and QNX guests need a virtio driver to be running. For example, in a Linux guest, configure the guest to include the virtio-console kernel module, and specify console=hvc0 in the cmdline option in the qvm configuration for the VM.