Changing the ISO image in a virtual CDROM drive while KVM-Qemu is running

If you run KVM with enabled monitor management console, you can do some pretty powerful internal stuff while the KVM guest is running.

In order to have a KVM-Qemu management console, you should start KVM with something like:

-monitor telnet:127.0.0.1:3010,server,nowait,ipv4

See the official documentation of Qemu for more details and also the man page of qemu-kvm (unofficial mirror).

Once you have it set up, you can then telnet to the management console and review the available commands:

famzah@famzahpc:~$ telnet localhost 3010
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.

QEMU 0.11.0 monitor - type 'help' for more information
(qemu) help

Changing the ISO image of a virtual CDROM drive is quite easy:

  • First review what the current status of the drives is:
    (qemu) info block
    virtio0: type=hd removable=0 file=/dev/sdb-vol/win7 ro=0 drv=host_device encrypted=0
    ide0-cd0: type=cdrom removable=1 locked=0 file=/shared/win7-eval.iso ro=0 drv=raw encrypted=0
    ide1-cd0: type=cdrom removable=1 locked=0 [not inserted]
    
  • Then change the mounted ISO image in the CDROM drive on the fly:
    (qemu) change ide1-cd0 /shared/win-virtio-drivers.iso
    
  • Double-check that the changes took effect. KVM-Qemu will not issue an error message in case something went wrong (duh!):
    (qemu) info block
    virtio0: type=hd removable=0 file=/dev/sdb-vol/win7 ro=0 drv=host_device encrypted=0
    ide0-cd0: type=cdrom removable=1 locked=0 file=/shared/win7-eval.iso ro=0 drv=raw encrypted=0
    ide1-cd0: type=cdrom removable=1 locked=0 file=/shared/win-virtio-drivers.iso ro=1 drv=raw encrypted=0
    

Use the “help” command to review the other powerful commands which you can use to tune and debug your running KVM guest (“info”, “migrate” and “system_reset” seem like interesting candidates).

KVM-Qemu Virtio storage and network drivers for 32-bit/64-bit Windows 7, Windows Vista, Windows XP and Windows 2000

…bundled as ISO images, so that you can easily mount and use them in a KVM guest.

UPDATE: It seems that Fedora started to provide the latest drivers bundled as an ISO. Check the official Windows VirtIO Drivers page for links.


Download locations follow:

These are static ISO images, and I’ve built them by downloading the ZIP sources dated 24.09.2009 from the official WindowsGuestDrivers KVM page and then converting them to ISO image files by using K3b.

Note that Virtio provides noticeably faster disk and network access.

Please review the official page of Virtio for sample KVM command line arguments which set up Virtio storage and network devices. You may notice that there is an (undocumented) parameter “boot=on” specified for the “-drive” option. This “boot=on” parameter is vital for the “-drive” option, or else Windows 7 won’t like your drive and won’t install on it.

Note about Virtio storage drives and the Windows 7 installer
I was able to install Windows 7 right from the start by using a Virtio storage drive within the KVM guest. At first the Windows installer didn’t see the Virtio disk at all but there is an option to install additional storage drivers. I installed the Virtio Windows drivers from the above ISO images, the Windows installer detected the Virtio storage disk properly and everything went quite smooth afterwards.


Resources:

Debian rootfs installation customized for Bifferboard

Update: There are (more up-to-date) automated scripts which you can use for the below actions:

  1. You need to checkout the whole Bifferboard SVN repository.
  2. The scripts are located in the directory “/debian/rootfs“. Execute them from the checked out repository on your local computer.

First you have to mount a medium on which we are going to install the Debian system. Generally, you have two options:

  • Using a USB Flash drive:


    ## MAKE SURE THAT YOU UPDATE THIS
    $ export ROOTDEV=/dev/sdc1
    $ sudo mkfs.ext3 $ROOTDEV
    $ sudo tune2fs -c 0 -i 0 $ROOTDEV
    $ export MNTPOINT=/mnt/diskimage
    $ sudo mount $ROOTDEV $MNTPOINT

  • Using a Qemu image:


    $ export MNTPOINT=/mnt/diskimage
    $ export IMGFILE=hd0.img
    $ sudo mount -o loop,offset=32256 "$IMGFILE" $MNTPOINT

Once we have the medium mounted at $MNTPOINT, we can proceed with installing Debian there and configuring it for Bifferboard:

$ export DBS_OS_VERSION=lenny
## replace "bg." with your local archive, or just omit it
$ export DBS_LOCAL_ARCHIVE=bg.
$ sudo debootstrap --arch i386 ${DBS_OS_VERSION} $MNTPOINT/ http://ftp.${DBS_LOCAL_ARCHIVE}debian.org/debian
## ... go grab a pizza or something ... this will take a while
$ sudo cp /etc/resolv.conf $MNTPOINT/etc/
$ sudo mount proc $MNTPOINT/proc -t proc
$ sudo chroot $MNTPOINT
##
## We are now in the "chroot" environment as root
##
/# apt-get -qq update && apt-get install wget
/# cd /root && wget http://bifferboard.svn.sourceforge.net/viewvc/bifferboard/debian/rootfs/include/debootstrap-postconfig.sh
/root# chmod +x debootstrap-postconfig.sh && ./debootstrap-postconfig.sh
/root# passwd root
/root# exit
##
## Back to our machine
##
$ sudo umount $MNTPOINT/proc
$ sudo umount $MNTPOINT


Now you have a minimum Debian installation customized for Bifferboard in the following way:

  • Custom kernel for Bifferboard installed by a .deb package.
  • Ethernet interface configured as DHCP client.
  • Temporary directories /tmp and /var/tmp mounted on a RAM-disk.
  • All APT sources “main contrib non-free” enabled.
  • Serial console on ttyS0 (115200 8N1).
  • RTC (real-time clock) kernel modules blacklisted – the Bifferboard has no RTC.
  • IPv6 disabled – takes a lot of resources and we won’t use it anyway, for now.

I may add any further customizations if needed. You can always review the debootstrap-postconfig.sh script for details on what is being configured.

You can use this image/disk as a rootfs which you can boot directly on Bifferboard or try in Qemu. Note that you have to install our Debian kernel on Bifferboard prior to booting this rootfs.


Used resources:

Create a Qemu image file which you can mount in both Linux and Qemu

The idea is to be able to easily manage a Qemu image outside of Qemu, natively on Linux. This can help you to alter the files on the Qemu image easily on Linux and then test the modified Qemu image on a Qemu virtual machine.

You can download an empty, formatted with Ext3 Qemu raw image at the following URL address:


There is nothing special about how you can achieve this yourself:

  • Create an empty Qemu image file.
  • Run an installation CD of Debian (or any other Linux) under Qemu and use the empty image as an available hard disk.
  • Partition and format the Qemu hard disk (resp. the Qemu image file) using the Linux installer.
  • Interrupt the Linux installer, stop Qemu, mount the Qemu image on Linux and clean it up.

You can achieve the above using the following commands:

# make sure to update the .iso URL if needed
$ wget http://cdimage.debian.org/debian-cd/5.0.3/i386/iso-cd/debian-503-i386-netinst.iso
$ qemu-img create hd0.img 2G
$ qemu -hda hd0.img -cdrom debian-503-i386-netinst.iso -boot d
# continue with the installation to the point where you can set up the partitions
# set up a primary partition using the entire disk space, do not set up a swap partition; save changes to disk and continue
# interrupt the installation (for example from the second console by executing "halt"), stop the virtual machine, we will not need it any further
$ sudo mkdir -p /mnt/diskimage
$ sudo mount -o loop,offset=32256 hd0.img /mnt/diskimage
$ sudo rm -r /mnt/diskimage/*
$ sudo mkdir -m 0700 '/mnt/diskimage/lost+found'
$ sudo umount /mnt/diskimage

Now we have an empty Qemu image which we can mount in both Linux and Qemu.

Here is an example on how to mount this image in Qemu:

qemu -usb -usbdevice disk:hd0.img

Do not use the image simultaneously as Linux mount and Qemu hard disk.


Used resources:

Qemu .deb package for the RDC Bifferboard hardware

Following the instructions found at these articles, I build a .deb package for Qemu which is suitable for the RDC processor which is used by Bifferboard. The instructions and patches can be found at the official Qemu Wiki page of Bifferboard.

There is nothing special I’ve done here, just packaged the qemu binary, so that you can easily try the “qemu-rdc” binary. The download link follows:

Here are some simple instructions on how to test your own “bzImage” kernel build:

#
# Installation instructions for the .deb package and for the Qemu setup
#
famzah@FURNA:~$ wget http://www.famzah.net/download/bifferboard/qemu-rdc_0.10.5-1_i386.deb
famzah@FURNA:~$ sudo dpkg -i qemu-rdc_0.10.5-1_i386.deb
famzah@FURNA:~$ mkdir test-kernel
famzah@FURNA:~$ cd test-kernel/
famzah@FURNA:~/test-kernel$ svn co https://bifferboard.svn.sourceforge.net/svnroot/bifferboard/qemu/
famzah@FURNA:~/test-kernel$ cd qemu/run
famzah@FURNA:~/test-kernel/qemu/run$ vi run-qemu.sh # at the last line, change "qemu" with "qemu-rdc"

#
# You can now test your kernel/rootfs build. For example:
#
famzah@FURNA:~/test-kernel/qemu/run$ cp /home/famzah/biffer/qemu/custom_bzImage ./bzImage
famzah@FURNA:~/test-kernel/qemu/run$ QEMU_BIN=qemu-rdc ./run-qemu.sh

If you want to attach a USB mass-storage device and try your rootfs build there, please follow the instructions at the official Qemu Wiki page of Bifferboard on which parameters to add to “qemu-rdc” in “run-qemu.sh”.

You can exit the emulator by pressing CTRL+a and “x”. You will get some help info by pressing CTRL+a and “?”. See the man or documentation pages of “qemu” for more information.

In a few days I’ll post an article and a .deb package for a kernel 2.6.30.5 build with (almost) all possible modules, suitable for running a native i386 Debian rootfs installation on Bifferboard.

P.S. Today I got my serial USB RS232 @ 3.3V cable and can now start with some real tests :D