If like me you care about your data stored on your laptop, you certainly use a fully encrypted (excepted /boot) configuration based on lvm.

In my case I also like to create, build, fix packages locally with our tool osc. I’ve plenty of power, beefy ssd, so I dedicate a logical lvm for building cleanly package with qemu-kvm configuration, like obs does

Prepare the kvm building system

As root you create 2 lvm volume with lvcreate, one will be the build root, the other one will be the additional swap

In ~/.oscrc I enable the following parameters

build-type = kvm
build-device = /dev/mapper/vg0-lvobsbuild
build-swap = /dev/mapper/vg1-lvobsswap
build-memory = 4096
build-vmdisk-rootsize = 16000
build-vmdisk-swapsize = 4000
build-vmdisk-filesystem = ext4

You just have to adjust the Memory quantity and the device to what you create for your own environment.

Building with qemu-kvm

Once the preparation is done you could try to build a package

Skipping verification of package signatures due to secure VM build
Writing build configuration
Running build
No initrd that provides virtio support found. virtio accelleration disabled.
Run the following command as root to enable virtio:
 "env" "rootfstype=ext4" "mkinitrd" "-d" "/dev/null" "-m" "ext3 ext4 btrfs reiserfs binfmt_misc virtio_pci virtio_blk" "-k" "/boot/vmlinuz" "-i" "/boot/initrd-3.13.6-1.g4727218-desktop-virtio"
VM_IMAGE: /dev/mapper/vg0-lvobsbuild, VM_SWAP: /dev/mapper/vg1-lvobsswap
Creating ext4 filesystem on /dev/mapper/vg0-lvobsbuild
tune2fs 1.42.8 (20-Jun-2013)
Setting maximal mount count to -1
mkswap /dev/mapper/vg1-lvobsswap
Setting up swapspace version 1, size = 4194300 KiB
no label, UUID=935f0e2d-52d7-4013-8a7f-7d48c813a482
logging output to /tmp/obsbuild/.build.log...

As you can see, it warn you that you could create a -virtio initrd to use virtio acceleration (who contribute a patch for the typo

But the command line is not completely correct in our case. It need the -d to be filled with the lvm buildroot to work as expected. If you successfully create the initrd-virtio you still will face a number of trouble, due to the way mkinitrd work.

Defeating the errors

You remember that we have a fully encrypted volume group, and as a clever tool mkinitrd will feed the initrd with all the tools needed to boot your system.

But that mean it will forget the lv buildroot we ask, and will put unnecessary tools and options.

Typical errors with a non optimized -virtio initrd

[    3s] /usr/bin/qemu-kvm -no-reboot -nographic -vga none -net none -cpu host -kernel /boot/vmlinuz -initrd /boot/initrd-3.13.6-1.g4727218-desktop -append root=/dev/sda panic=1 quiet no-kvmclock nmi_watchdog=0 rw elevator=noop console=ttyS0 init=/.build/build -m 4096 -hda /dev/mapper/vg0-lvobsbuild -drive file=/dev/mapper/vg1-lvobsswap,if=ide,index=1,cache=none -smp 8
[    9s] FATAL: Error inserting nvidia (/lib/modules/3.13.6-1.g4727218-desktop/updates/nvidia.ko): No such device
[    9s]   WARNING: Failed to connect to lvmetad: No such file or directory. Falling back to internal scanning.
[    9s]   Volume group "vg0" not found
[    9s]   WARNING: Failed to connect to lvmetad: No such file or directory. Falling back to internal scanning.
[    9s]   Volume group "vg0" not found
[    9s] *** Note: only US keyboard layout is supported.
[    9s] *** Please ensure that the password is typed correctly.
[   41s] Waiting for device /dev/disk/by-id/ata-Corsair_Force_GT_blah-part2 to appear: ..............................Unlocking cr_sda2 (/dev/disk/by-id/ata-Corsair_Force_GT_blah-part2)
[   41s] Device /dev/disk/by-id/ata-Corsair_Force_GT_blah-part2 doesn't exist or access denied.
[   41s] Trying manual resume from /dev/vg0/lvswap
[   41s] resume device /dev/vg0/lvswap not found (ignoring)
[   41s] Trying manual resume from /dev/vg0/lvswap
[   41s] resume device /dev/vg0/lvswap not found (ignoring)
[   73s] Waiting for device /dev/sda to appear: ..............................Could not find /dev/sda.
[   73s] Want me to fall back to /dev/vg0/lvsuse? (Y/n)

Rescue you have as root to kill all build process.

for P in $(ps auxw| grep build | grep -v grep | awk {'print $2'} );do kill $P;done

Find a solution

We want an optimized -virtio initrd, which filter all the lvm and crypting tools we don’t need. Also there’s no need to encumber it with graphic blob.
Then I create a small script I’ve called patch-initrd-virtio (source below) which exactly do that work anytime I’ve a kernel change.
As it need to be run by root only, I normally place it in /root/bin/

patch-initrd-virtio sources

#!/usr/bin/env bash

# WTF License 1.0 
# Author Bruno Friedmann tigerfoot (at) opensuse.org

# Usage : this script will create an optimized virtio initrd without
# lvm, crypt, gfx tool
# by using the actual /boot/initrd symlink you have.
# Edit the 2 devices you target to use 
# 
DEVBUILD='/dev/vg0/lvobsbuild'
DEVSWAP='/dev/vg1/lvobsswap'

nokms(){
sed -i '/^NO_KMS_IN_INITRD/s/no/yes/' /etc/sysconfig/kernel
}

kms(){
sed -i '/^NO_KMS_IN_INITRD/s/yes/no/' /etc/sysconfig/kernel
}

echo "cleanup /tmp"
rm -fr /tmp/initrd*

# Patch the virtio initrd
if [ -z "$1" ];then
export VER=`uname -r`
else
export VER="$1"
fi
export INITRD="/boot/initrd-$VER-virtio"
echo "Setting nokms"
nokms

echo "Building -virtio initrd ..."
"env" "rootfstype=ext4,resume=$DEVSWAP,rootdev=$DEVBUILD,udevtimeout=2,udev_timeout=2,nosplash,noluks" "mkinitrd" "-B" "-d" "$DEVBUILD" "-m" "ext4 btrfs binfmt_misc virtio_pci virtio_blk" "-k" "/boot/vmlinuz-$VER" "-i" "$INITRD"

ls -l $INITRD

echo "Setting kms"
kms

# copy the *.virtio initrd to /tmp
cp -vfa $INITRD /tmp/initrd-virtio.gz

# ungzip it gzip -d initrd
cd /tmp
mkdir initrd.build
gzip -d initrd-virtio.gz

cd initrd.build

# uncpio cpio -id < ../initrd
cpio -id  ../initrd
rm -fv ../initrd-virtio
echo "rebuilding initrd ..."
find . | cpio --create --format='newc' > ../initrd-virtio
cd ../
echo "Compressing initrd ..."
# Install pigz if you want to save half an hour of your life.
if [ -x /usr/bin/pigz ];then
 pigz -9v initrd-virtio
else
 gzip -9v initrd-virtio
fi
# copy to /boot
cp -v initrd-virtio.gz $INITRD
echo "Done ..."

Usage of patch-initrd-virtio

Here’s the result of a run

cleanup /tmp
Setting nokms
Building -virtio initrd ...

Kernel image:   /boot/vmlinuz-3.13.6-1.g4727218-desktop
Initrd image:   /boot/initrd-3.13.6-1.g4727218-desktop-virtio
Root device:    /dev/vg0/lvobsbuild (mounted on / as ext4)
Resume device:  /dev/vg0/lvswap
enabling LUKS support for /dev/disk/by-id/ata-Corsair_Force_GT_blah-part2 (cr_sda2)
Microcode: Adding Intel microcode 06-2a-07
Kernel Modules: thermal_sys thermal processor fan libcrc32c xor raid6_pq btrfs binfmt_misc virtio virtio_ring virtio_pci virtio_blk dm-mod dm-crypt dm-log dm-region-hash dm-mirror dm-snapshot scsi_dh scsi_dh_hp_sw scsi_dh_alua scsi_dh_rdac scsi_dh_emc xhci-hcd hid-logitech-dj hid-holtek-kbd hid-lenovo-tpkbd hid-ortek hid-roccat hid-roccat-common hid-roccat-arvo hid-roccat-isku hid-samsung ohci-pci linear arc4 sha256_generic cryptd crct10dif-pclmul crc32-pclmul crc32c-intel ghash-clmulni-intel aes-x86_64 glue_helper gf128mul lrw ablk_helper aesni-intel
Features:       acpi dm intel_microcode block usb lvm2 luks btrfs resume.userspace resume.kernel
Did not refresh the bootloader. You might need to refresh it manually.
-rw------- 1 root root 29338540 Mar 15 18:18 /boot/initrd-3.13.6-1.g4727218-desktop-virtio
Setting kms
‘/boot/initrd-3.13.6-1.g4727218-desktop-virtio’ -> ‘/tmp/initrd-virtio.gz’
160249 blocks
removed ‘./boot/71-luks.sh’
removed ‘./config/luks.sh’
removed ‘../initrd-virtio’
rebuilding initrd ...
160239 blocks
Compressing initrd ...
initrd-virtio to initrd-virtio.gz
‘initrd-virtio.gz’ -> ‘/boot/initrd-3.13.6-1.g4727218-desktop-virtio’
Done ...

Finally start a build with -virtio activated

So with our new optimized initrd-virtio we can restart a fully qemu-kvm build with osc build –clean

Skipping verification of package signatures due to secure VM build
Writing build configuration
Running build
VM_IMAGE: /dev/mapper/vg0-lvobsbuild, VM_SWAP: /dev/mapper/vg1-lvobsswap
Creating ext4 filesystem on /dev/mapper/vg0-lvobsbuild
tune2fs 1.42.8 (20-Jun-2013)
Setting maximal mount count to -1
mkswap /dev/mapper/vg1-lvobsswap
mkswap: /dev/mapper/vg1-lvobsswap: warning: wiping old swap signature.
Setting up swapspace version 1, size = 4194300 KiB
no label, UUID=c19c873b-2b6c-4200-9575-a60adc581204
logging output to /tmp/obsbuild/.build.log...
[    0s] Using BUILD_ROOT=/tmp/obsbuild/.mount
[    0s] Using BUILD_ARCH=x86_64:i686:i586:i486:i386
[    0s] Doing kvm build in /dev/mapper/vg0-lvobsbuild
[    0s] 
[    0s] 
[    0s] c-3po.labaroche.ioda.net started "build postgresql-plr.spec" at Sat Mar 15 17:27:18 UTC 2014.
[    0s] 
[    0s] 
[    0s] processing specfile /home/bruno/openSUSE/obs/home:bruno_friedmann:branches:openSUSE:12.3:Update/postgresql-plr.openSUSE_12.3_Update/postgresql-plr.spec ...
[    0s] running changelog2spec --target rpm --file /home/bruno/openSUSE/obs/home:bruno_friedmann:branches:openSUSE:12.3:Update/postgresql-plr.openSUSE_12.3_Update/postgresql-plr.spec
[    0s] init_buildsystem --configdir /usr/lib/build/configs --cachedir /var/cache/build --prepare --clean --rpmlist /tmp/rpmlist.Vy31Li /home/bruno/openSUSE/obs/home:bruno_friedmann:branches:openSUSE:12.3:Update/postgresql-plr.openSUSE_12.3_Update/postgresql-plr.spec ...
[    1s] cycle: pam -> permissions -> coreutils
[    1s]   breaking dependency permissions -> coreutils
[    1s] [1/29] preinstalling filesystem...

Hope this give you the taste of building!