[Qemu-devel] Problems with saving a vm in the qemu monitor

[Keith Stevens]

Hi all,

I'm a teaching assistant for an operating systems class and we've been using an ancient version of qemu to do some of our lab assignments (v0.9.something).  We've been relying on a qcow2 qemu image that we created a while back.  Recently, I've been trying to get the labs working with the latest version of qemu and have run into a few problems.

First, i found that our old qcow2 image does not work with qemu v0.12.5.  I get an error saying that SaveVM 2 version is obsolete.  To get around this, i decided to simply rebuild the image file, but i ran into a really strange problem: whenever i reload the qcow2 image and try to run some commands, a lot of white space gets printed to the screen instead of the expected output.  After running several commands, qemu starts printing text from the boot process to stdout in qemu.

I've tried creating the image with qemu versions 0.10.6 and 0.11.1 and the process works correctly with no unusual behavior.  Would anyone happen to know why version 0.12.5 would create this odd behavior?

To help diagnose the problem, i run these commands to create the image:

qemu-img create -f qcow2 cs111snap.qcow2 512M

mv cs111snap.qcow2 /usr/local/share/qemu

qemu -m 128 -hda /usr/local/share/qemu/cs111snap.qcow2 -cdrom     /usr/local/share/qemu/cs111.iso -tftp /tmp/cs111_keith16400 -redir tcp:2222::22

 

I give live nousb acpi=off as boot options

once booted, i run the following in qemu

  sudo -i

  passwd (set to something simple)

  mknod /dev/fd0 b 2 0

Outside of qemu i then run 

  scp -p -P2222 -o"UserKnownHostsFile false" go-in-qemu address@hidden:/root/go

  to copy over a setup script that we have

Then in qemu again i run

ifconfig eth0 down; clear; echo "If using ./run-qemu, simply press Enter to load your code."; echo; history -c

and end with ". go" and unentered command

I then save the image by hitting ctrl+alt+2, typing "savevm osp" and then "quit"

I reload the image with the following command

qemu -m 128 -hda /usr/local/share/qemu/cs111snap.qcow2 -cdrom /usr/local/share/qemu/cs111.iso -loadvm osp -tftp /tmp/cs111_keith16100 -redir tcp:2222::22

After running this last command, qemu loads up and has "

If using ./run-qemu, simply press Enter to load your code.

> . go

printed to the screen.  After i hit enter, a lot of white space gets printed, instead of some echo output that i expect from the go script.  Note that this happens regardless of what is in the go script (I've tried it with just a simple echo statement).

I should note that cs111.iso is a copy of Debian.

Again, this whole process works correctly with older versions of qemu, but not with version 0.12.5.

if anyone has any insights to the problem, I would greatly appreciate any suggestions

Thanks!

--Keith