QEmu

Dec 16, 2013

3 min read

May 31, 2023 18:15 EEST

Installing QEmu

I use QEmu to have a emulated environment to test Xenomai applications without crashing the main system.

We need to enable sdl for qemu to have all display output available, edit /etc/portage/package.use:

app-emulation/qemu-softmmu sdl

To install QEmu on Gentoo we need at first gcc 3.x:

emerge =gcc-3.4.6*
gcc-config i686-pc-linux-gnu-3.4.6
source /etc/profile
emerge app-emulation/qemu
gcc-config i686-pc-linux-gnu-4.1.1
source /etc/profile

Prepare Linux for Qemu

Do as root:

echo 1024 > /proc/sys/dev/rtc/max-user-freq

Compile kernel with tun support.

CONFIG_TUN=m
CONFIG_BRIDGE=m

Install everything for bridging:

emerge net-misc/bridge-utils
emerge sys-apps/usermode-utilities
modprobe tun
modprobe bridge

Note: If you get an error message about unresolved symbols, reboot easily the system then everything should work.

Configure for bridge device now in /etc/conf.d/net:

bridge_add_eth0="br0"
config_eth0=( "null" )
config_br0=( "192.168.0.151/24" )
brctl_br0=( "setfd 0" "sethello 0" "stp off" )
routes_br0=( "default gw 192.168.0.251" )

Add the tun device to your startup config:

cd /etc/init.d
ln -s net.lo net.br0
rc-update add net.br0 default

/etc/init.d/net.eth0 stop
/etc/init.d/net.br0 start
ifconfig br0
ifconfig eth0

Configure Qemu to use a network interface edit /etc/qemu-ifup

#!/bin/sh
#
# ____Address: 192.168.0.1 (guest01)
# ____Netmask: 255.255.255.0
# ___Wildcard: 0.0.0.255
# ____Gateway: 192.168.0.251
#

if test $(sudo /sbin/ifconfig | grep -c $1) -gt 0; then
        sudo /sbin/brctl delif br0 $1
        sudo ifconfig $1 down
fi

sudo /sbin/ifconfig $1 0.0.0.0 promisc up
sudo /sbin/brctl addif br0 $1
chmod +x /etc/qemu-ifup

Create a persistant tun interface:

tunctl -u root -t tap0

Booting OS in Qemu

We want to boot via network so we create first the needed structure in out tftp server.

Take the file pxelinux.0 from isolinux and copy it to the tftp root directory.
create a directory pxelinux.cfg
create the file pxelinux.cfg/default, see below for more details
copy kernel to zimage

The structure of the directory is:

tftpboot/
|-- pxelinux.0
|-- pxelinux.cfg
|   |-- default
|   `-- zimage
`-- zimage

The file default has the following input:

DEFAULT qemu
PROMPT 1
TIMEOUT 10

LABEL qemu
  KERNEL zimage
  APPEND vga=0x314 install=nfs://192.168.0.151/qemu

LABEL local
  LOCALBOOT 0

Now configure your dhcp server:

# settings for booting our qemu image
allow booting;
allow bootp;
next-server 192.168.0.251;
filename "pxelinux.0";
mkdir qemu
cd !$
qemu-img create disk.img 4G
qemu -localtime -hda disk.img -boot d -m 256

You should see now some output. If you get the error message

Could not initialize SDL - exiting

Be sure that $DISPLAY is set and execute on the xserver xhost + to allow all hosts to connect to your xserver.

Now download pxe iso from http://rom-o-matic.net/ .

Choose as nic: ns8390:rtl8029 – [[0x10ec,0x8029]]
Select ISO bootable image for without legacy floppy emulation
Click Get ROM

Now we can boot via network with:

qemu -cdrom eb-5.4.2-ns8390.iso -boot d -net tap -net nic,macaddr=52:54:00:12:34:56

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