Buildroot for KVM Guest
Here is a set of configuration files to quickly build a minimal KVM-based hypervisor guest with Buildroot. It attempts to use mostly VirtIO paravirtualization to maximize performance. This includes virtual console, virtual network and virtualized filesystem with the 9P protocol.
These files are based on version 2016.11 of Buildroot, gotten from https://buildroot.org/downloads/buildroot-2016.11.tar.bz2
Main Buildroot configuration file, should be stored as "configs/kvm_guest_defconfig" in the Buildroot structure:
BR2_x86_64=y
BR2_x86_core2=y
BR2_TOOLCHAIN_BUILDROOT_GLIBC=y
BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_4_4=y
BR2_TOOLCHAIN_BUILDROOT_CXX=y
BR2_TARGET_GENERIC_HOSTNAME="kvm-guest"
BR2_TARGET_GENERIC_ISSUE="Welcome to Virtualized KVM Guest"
BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_EUDEV=y
BR2_TARGET_GENERIC_GETTY_PORT="hvc0"
BR2_TARGET_GENERIC_GETTY_BAUDRATE_115200=y
BR2_LINUX_KERNEL=y
BR2_LINUX_KERNEL_CUSTOM_VERSION=y
BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="4.4.38"
BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="board/kvm_guest/linux-4.4.config"
BR2_LINUX_KERNEL_INSTALL_TARGET=y
BR2_TARGET_ROOTFS_EXT2=y
BR2_TARGET_ROOTFS_EXT2_4=y
# BR2_TARGET_ROOTFS_TAR is not set
Linux kernel configuration, should be stored as "board/kvm_guest/linux-4.4.config":
CONFIG_SYSVIPC=y
CONFIG_NO_HZ_IDLE=y
CONFIG_HIGH_RES_TIMERS=y
CONFIG_VIRT_CPU_ACCOUNTING_GEN=y
CONFIG_NAMESPACES=y
CONFIG_KALLSYMS_ALL=y
CONFIG_EMBEDDED=y
CONFIG_MODULES=y
CONFIG_MODULE_UNLOAD=y
CONFIG_SMP=y
CONFIG_HYPERVISOR_GUEST=y
CONFIG_SCHED_SMT=y
CONFIG_NUMA=y
CONFIG_IA32_EMULATION=y
CONFIG_NET=y
CONFIG_PACKET=y
CONFIG_UNIX=y
CONFIG_INET=y
CONFIG_NET_9P=y
CONFIG_NET_9P_VIRTIO=y
CONFIG_DEVTMPFS=y
CONFIG_DEVTMPFS_MOUNT=y
CONFIG_VIRTIO_BLK=y
CONFIG_NETDEVICES=y
CONFIG_VIRTIO_NET=y
CONFIG_VT_HW_CONSOLE_BINDING=y
CONFIG_SERIAL_8250=y
CONFIG_SERIAL_8250_CONSOLE=y
CONFIG_VIRTIO_CONSOLE=y
CONFIG_HW_RANDOM=y
CONFIG_HW_RANDOM_VIRTIO=y
CONFIG_VIRT_DRIVERS=y
CONFIG_VIRTIO_PCI=y
CONFIG_VIRTIO_BALLOON=y
CONFIG_VIRTIO_INPUT=y
CONFIG_VIRTIO_MMIO=y
CONFIG_VIRTIO_MMIO_CMDLINE_DEVICES=y
CONFIG_EXT2_FS=y
CONFIG_EXT3_FS=y
CONFIG_TMPFS=y
CONFIG_TMPFS_POSIX_ACL=y
CONFIG_9P_FS=y
CONFIG_9P_FS_POSIX_ACL=y
CONFIG_DEBUG_FS=y
CONFIG_STACKTRACE=y
Once the files are in place, the build can be performed with:
make kvm_guest_defconfig
make
Here is a helper script to unpack the root filesystem and launch the whole thing under QEMU:
#!/bin/sh
if [ `id -u` != "0" ]; then
echo "Must be root!"
exit 1
fi
cd `dirname "$0"`
if [ ! -d /tmp/kvm_guest ]; then
mkdir -p /tmp/kvm_guest
mkdir -p /tmp/kvm_guest_loop
mount -o loop output/images/rootfs.ext4 /tmp/kvm_guest_loop
cp -a /tmp/kvm_guest_loop/* /tmp/kvm_guest
umount /tmp/kvm_guest_loop
rmdir /tmp/kvm_guest_loop
fi
qemu-system-x86_64 \
-enable-kvm \
-cpu host \
-m 128 \
-kernel output/images/bzImage \
-serial none \
-display none \
-monitor none \
-chardev stdio,id=char0 \
-device virtio-serial \
-device virtconsole,chardev=char0 \
-fsdev local,id=fs0,path=/tmp/kvm_guest,security_model=none \
-device virtio-9p-pci,fsdev=fs0,mount_tag=/dev/root \
-net nic,macaddr=00:00:de:ad:be:ef,model=virtio,vlan=1 \
-net tap,ifname=tap0,vlan=1,script=no,downscript=no \
-append "root=/dev/root rw rootfstype=9p rootflags=trans=virtio console=hvc0"