Debian-Gastsysteme mit QEMU-ARM und libvirt virtualisieren

shell
qemu-system-arm -M virt -m 1024 \
  -kernel vmlinuz-3.16.0-4-armmp-lpae \
  -initrd initrd.img-3.16.0-4-armmp-lpae \
  -append 'root=/dev/vda2' \
  -drive if=none,file=hda.qcow2,format=qcow2,id=hd \
  -device virtio-blk-device,drive=hd \
  -netdev user,id=mynet \
  -device virtio-net-device,netdev=mynet \
  -nographic

platform-a003c00.virtio_mmio platform-a003e00.virtio_mmio

<domain type='qemu' id='38'>
 <name>usain</name>
 <uuid>3bf6e58f-e513-47b4-9b64-e00b32d9d9f4</uuid>
 <memory unit='KiB'>3145728</memory>
 <currentMemory unit='KiB'>3145728</currentMemory>
 <vcpu placement='static'>3</vcpu>
 <resource>
 <partition>/machine</partition>
 </resource>
 <os>
 <type arch='armv7l' machine='virt-3.1'>hvm</type>
 <kernel>/var/lib/libvirt/boot/usain/vmlinuz</kernel>
 <initrd>/var/lib/libvirt/boot/usain/initrd.img</initrd>
 <cmdline>root=UUID=7a7f1855-2536-4342-a481-4853a125560f</cmdline>
 <boot dev='hd'/>
 </os>
 <features>
 <gic version='2'/>
 </features>
 <clock offset='utc'/>
 <on_poweroff>destroy</on_poweroff>
 <on_reboot>restart</on_reboot>
 <on_crash>restart</on_crash>
 <devices>
 <emulator>/usr/bin/qemu-system-arm</emulator>
 <disk type='block' device='disk'>
 <driver name='qemu' type='raw'/>
 <source dev='/dev/lvm-uhura/usain-boot'/>
 <backingStore/>
 <target dev='vda' bus='virtio'/>
 <alias name='virtio-disk0'/>
 <address type='virtio-mmio'/>
 </disk>
 <disk type='block' device='disk'>
 <driver name='qemu' type='raw'/>
 <source dev='/dev/lvm-uhura/usain-root'/>
 <backingStore/>
 <target dev='vdb' bus='virtio'/>
 <alias name='virtio-disk1'/>
 <address type='virtio-mmio'/>
 </disk>
 <controller type='pci' index='0' model='pcie-root'>
 <alias name='pcie.0'/>
 </controller>
 <interface type='bridge'>
 <mac address='52:54:00:79:39:16'/>
 <source bridge='br-virt'/>
 <target dev='vnet0'/>
 <model type='virtio'/>
 <alias name='net0'/>
 <address type='virtio-mmio'/>
 </interface>
 <serial type='pty'>
 <source path='/dev/pts/1'/>
 <target type='system-serial' port='0'>
 <model name='pl011'/>
 </target>
 <alias name='serial0'/>
 </serial>
 <console type='pty' tty='/dev/pts/1'>
 <source path='/dev/pts/1'/>
 <target type='serial' port='0'/>
 <alias name='serial0'/>
 </console>
 </devices>
 <seclabel type='dynamic' model='apparmor' relabel='yes'>
 <label>libvirt-3bf6e58f-e513-47b4-9b64-e00b32d9d9f4</label>
 <imagelabel>libvirt-3bf6e58f-e513-47b4-9b64-e00b32d9d9f4</imagelabel>
 </seclabel>
 <seclabel type='dynamic' model='dac' relabel='yes'>
 <label>+64055:+64055</label>
 <imagelabel>+64055:+64055</imagelabel>
 </seclabel>
</domain>

set -eu

GUEST="$1"
ACTION="$2"
PHASE="$3"

BOOT_IMAGE_BASE_PATH=/var/lib/libvirt/boot

_is_mounted() {
    grep -qwF "$1" /proc/mounts
}

_is_host_running() {
    # calling virsh domstate here will cause the process to hang so we use ps instead
    ps --no-headers -u libvirt-qemu -o cmd | grep -q -- "-name guest=$1"
}

_get_boot_volume() {
    local guest="$1"
    local configured_volume
    local dm_path

    # looks for a volume whose name ends with "-boot"
    configured_volume="$(
        xmllint --xpath 'string(/domain/devices/disk[@type="block"]/source[substring(@dev, string-length(@dev) - string-length("-boot") + 1) = "-boot"]/@dev)' \
            "/etc/libvirt/qemu/$guest.xml"
    )"

    # the configured volume might contain any path that refers to a volume but /proc/mounts
    # will contain paths from /dev/mapper so we need to find the path of the actual devices
    # and then find the corresponding symlink in /dev/mapper
    dm_path="$(realpath "$configured_volume")"
    find /dev/mapper -type l | while read -r mapper_path; do
        if [ "$(readlink -f "$mapper_path")" = "$dm_path" ]; then
            echo "$mapper_path"
            break
        fi
    done
}

update_guest_kernel_and_initrd() {
    # ARM hosts cannot be booted like any x64_64 host.
    # Instead we need libvirt to boot the kernel directly along with the guest’s generated initrd.
    # We update the kernel and initrd on every guest startup, so that a system update will behave
    # as expected on the next reboot.
    local guest="$1"
    local boot_image_path="$BOOT_IMAGE_BASE_PATH/$guest"
    local boot_volume
    local tmp_mount_path
    boot_volume="${2:-$(_get_boot_volume "$guest")}"

    if [ ! -z "$boot_volume" ]; then
        echo "Boot volume for guest $guest not found." >&2
        return 1
    fi

    if [ ! -e "$boot_volume" ]; then
        echo "Boot volume for guest $guest does not exist in '$boot_volume'. Cannot extract kernel and initrd." >&2
        return 1
    fi

    if _is_host_running "$guest"; then
        # this should not happen, but maybe someone is calling this script manually
        echo "Guest $guest is not shut down. Refusing to mount volumes." >&2
        return 1
    fi

    if _is_mounted "$boot_volume"; then
        echo "Boot volume '$boot_volume' is already mounted in the system. Mounting the volume twice may cause data loss." >&2
        return 1
    fi

    mkdir -p --mode 750 "$boot_image_path"
    chgrp libvirt-qemu "$boot_image_path"
    tmp_mount_path="$(mktemp -d)"
    trap "umount '$tmp_mount_path'; rmdir '$tmp_mount_path'" EXIT
    mount -o ro "$boot_volume" "$tmp_mount_path"
    cp "$tmp_mount_path/vmlinuz" "$tmp_mount_path/initrd.img" "$boot_image_path/"
}

if [ "$ACTION" = prepare ] && [ "$PHASE" = begin ]; then
    # kernel and initrd of guests that use ARM emulation should be updated before being started
    if grep -qwF /usr/bin/qemu-system-arm "/etc/libvirt/qemu/$GUEST.xml"; then
        update_guest_kernel_and_initrd "$GUEST"
    fi
fi