qemu guest automation

Question

I've not been able to find any documentation stating the existence of an API that can be used to automate things inside of a qemu guest.

For example, I would like to launch a process inside of the guest machine from the host machine. Libvirt does not appear to contain such functionality.

Answer 1

[Note: Automation without using any virtualization API. From my blog post.]

Step 1:

By default, QEMU uses SDL to display the VGA output. So, the first step is make this interaction with QEMU through standard I/O. QEMU provides an option for this.

From QEMU docs:

-nographic Normally, QEMU uses SDL to display the VGA output. With this option, you can totally disable graphical output so that QEMU is a simple command line application. The emulated serial port is redirected on the console. Therefore, you can still use QEMU to debug a Linux kernel with a serial console.

So, all you have to do is invoke QEMU with -nographic.

qemu -nographic -hda guest.disk

Step 2:

Now that you can interact with your guest (or QEMU process) through command line, you have to automate this interaction. The obvious way to do this in python is start the QEMU process (with -nographic) with subprocess module and then communicate with that process. But to my surprise, this just didn’t work out for me. So, I looked for some other way.

Later, I found out that the most awesome tool for this kind of jobs is Expect. It is an automation tool for interactive applications written in TCL.

This guide should help you in getting started with Expect. Here is the script to run a guest with QEMU using Expect.

#!/usr/bin/expect -f

#starts guest vm, run benchmarks, poweroff
set timeout -1

#Assign a variable to the log file
set log     [lindex $argv 0]

#Start the guest VM
spawn qemu -nographic -hda guest.disk

#Login process
expect "login: "
#Enter username
send "user\r"

#Enter Password
expect "Password: "
send "user\r"

#Do whatever you want to do with in the guest VM. ( Run a process and write result to log )

#poweroff the Guest VM
expect "# "
send "shutdown -h now\r"

Answer 2

The QEMU Monitor can interact with guest systems to a limited extent using it's own console. This includes reading registers, controlling the mouse/keyboard, and getting screen dumps. There is a QEMU Monitor Protocol (QMP) that let's you pass JSON commands to and read values from the guest system.

Answer 3

PyQemu can theoretically do this. I've used it in the past, although it looks like a stale project now. It provides a python agent (the equivalent of VMWare guest tools) to run on the guest, communicating with the host via serial port. You can get proxies to python modules running in the context of the VM, and any communication with them is marshaled over the serial port. In the following example, AutoIt is being used to automate Notepad:

machine = PyQemu.GetProxy("win2k")

# Wrap the machine object in another proxy representing the 'os'
# module running inside the VM.
os = PyQemu.vm.Module(machine,"os")

# NOTE: This is running on the VM!
os.system("notepad")

# Get an IDispatch object representing the autoit ActiveX control
autoit = PyQemu.vm.Dispatch(machine,"AutoItX3.Control")

# See if a window is active on the VM
state = autoit.WinActive("Untitled -")

Caveat: Due to using the serial port it is far from quick (regardless of serial speed settings), so perhaps best to transfer any bulk data by other means, e.g. Virtual FAT disk image.