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CAS in virtual environment

CAS kernel tracing module can be used in virtual environment. Following guide will enable to use etrace in QEMU KVM.

Please be aware that most of following commands will require elevated permissions to run properly.

TLDR

Check tools/virtual_environment/img_build.sh script. Run it in empty directory to create the QEMU image in one shot. To know exactly what happens during image creation please follow the guide.

Requirements

Installing required packages on host system

sudo apt install libguestfs-tools qemu-utils qemu-system-x86

User permissions for kvm and libvirt groups

During image creation process user may be prompted to add himself to kvm and libvirt group with following message.

libguestfs: warning: current user is not a member of the KVM group (group ID ###). This user cannot access /dev/kvm, so libguestfs may run very slowly. It is recommended that you 'chmod 0666 /dev/kvm' or add the current user to the KVM group (you might need to log out and log in again).

Run following commands to prevent this warning.

sudo adduser `id -un` kvm
sudo adduser `id -un` libvirt

Kernel image (Ubuntu OS only)

Ubuntu OS have restrict policy in case of access kernel image by users. By default user cannot read kernel images in /boot/ directory. To use commands in this guide without elevated privileges copy currently running kernel image to work directory.

cat /proc/cmdline
BOOT_IMAGE=/vmlinuz-5.15.0-46-generic root=/dev/mapper/vg01-root ro quiet splash
cd ${WORKDIR}
sudo cp /boot/vmlinuz-5.15.0-46-generic .
export SUPERMIN_KERNEL=${WORKDIR}/vmlinuz-5.15.0-46-generic

Exporting SUPERMIN_KERNEL variable will prevent virt-tools from copying kernel file from /boot/ - and crashing on Ubuntu OS.

Download image

Following guide will use Ubuntu Cloud Image as root filesystem.

export IMG_BASE=base_system.img

curl -s -o "${IMG_BASE}" "https://cloud-images.ubuntu.com/minimal/releases/focal/release/ubuntu-20.04-minimal-cloudimg-amd64.img"

Expand image partition size

To build CAS tracer and cas libraries there are some requirements that must be installed in guest system. Unfortunately Ubuntu Cloud Image (and some other) have limited space on root partition.

Partition list can be checked using following command

$ virt-list-partitions --long --human --format=qcow2 ${IMG_BASE} 

/dev/sda1  ext4      2.1G
/dev/sda14 unknown   4.0M
/dev/sda15 vfat    106.0M

To expand root partition size (let's say to ~20GB) following commands must be processed

export IMG_RESIZED=system_resized.img

$ qemu-img create -f qcow2 ${IMG_RESIZED} 20G

$ virt-resize --format=qcow2 --expand /dev/sda1 ${IMG_BASE} ${IMG_RESIZED}

NOTE: Check if partition layout changed. Changed partition order will most likely cause error when booting image in QEMU.

Look for something like this in virt-resize log:

[  22.3] Expanding /dev/sda1 (now /dev/sda3) using the ‘resize2fs’ method

It's clear that root /dev/sda1 partition name changed to /dev/sda3.

To fix possible booting problems we must reinstall grub - use CHANGED partition name (eg /dev/sda3) as mount source.

EXPANDED_PARTITION=/dev/sda3

virt-customize -a ${IMG_RESIZED} \
      --run-command "mkdir -p /mnt && mount ${EXPANDED_PARTITION} /mnt && mount --bind /dev /mnt/dev && mount --bind /proc /mnt/proc && mount --bind /sys /mnt/sys && chroot /mnt && grub-install /dev/sda"

After that, booting should be fixed.

Customize image

There is handy tool to customize images called virt-customize. Note, that each run of virt-customize creates qemu instance that inject some changes into image, then quits and commit changes.

From this point is highly recommend to work on copy of resized image, because in case of some error in virt-customize you won't have to resize image from begining.

export IMG_WORK=cas_tracer_env.img
cp ${IMG_RESIZED} ${IMG_WORK}

Note -smp ${PROC} -m ${MEM} parameters in following commands - it is good to speedup virt-customize by adding some cores and memory (by default it uses single core and ~700M RAM)

It is highly recommend to set some resonable values to $PROC and $MEM - for example 80% of system resources.

export MEM=$(free --mega | grep "Mem:" | awk '{printf "%.0f",($2 * 0.8)}')
export PROC=$(nproc | awk '{printf "%.0f",($1 * 0.8)}')

Set root password (example)

It is required to set root user password - or create new user for using VM. Following example sets pass as root password.

virt-customize -a ${IMG_WORK} -smp ${PROC} -m ${MEM} \
   --root-password password:pass

Install packages required by CAS

Following packages are required for building CAS tracer, library and use scripts from examples directory.

virt-customize -a ${IMG_WORK} -smp ${PROC} -m ${MEM} \
   --install "build-essential,linux-headers-generic,git,cmake,llvm,clang,clang-10,libclang-dev,python3-dev,gcc-9-plugin-dev,rsync,clang-11,flex,bison"

Build CAS

virt-customize -a ${IMG_WORK} -smp ${PROC} -m ${MEM} \
   --mkdir /opt/ \
   --run-command 'git clone https://github.com/Samsung/CAS.git /opt/cas/' \
   --run-command 'cd /opt/cas/tracer/ && make -C /lib/modules/$(ls /lib/modules/ | grep kvm)/build M=$PWD && make -C /lib/modules/$(ls /lib/modules/ | grep kvm)/build M=$PWD modules_install' \
   --run-command 'cd /opt/cas/bas/ && cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ .. && make && make install' \
   --run-command 'cd /opt/cas/ && ./etrace_install.sh' \
   --firstboot-command "depmod -a"

(Optional) Enable network and ssh

virt-customize -a ${IMG_WORK} -smp ${PROC} -m ${MEM} \
   --run-command "sed -i 's/GRUB_CMDLINE_LINUX=/GRUB_CMDLINE_LINUX=\"net.ifnames=0 biosdevname=0\"/g' /etc/default/grub" \
   --run-command "update-grub" \
   --run-command "echo '
network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      dhcp4: true
      optional: true
' > /etc/netplan/01-netcfg.yaml" \
   --firstboot-command "netplan apply" \
   --firstboot-command "dpkg-reconfigure openssh-server"

Preparing source image

This step is not mandatory, User may use virtio mounts access host sources from guest. But in some cases (eg mmpaing while building AOSP) it may be required to use mounted image with sources.

Following example will describe how to create image with sources.

virt-make-fs --format=qcow2 --size=+30G ~/source_dir/ src.img

This will build image with sources and additionally 30GB free space.

It is good to have some qcow2 overlay serving as mutable storage. In case of any errors while compiling it will not harm source src.img.

qemu-img create -f qcow2 -b src.img -F qcow2 work.qcow2

Running KVM

After building root image and preparing some sources it's finall time to run VM. It is up to user how to run VM using raw command or tools like virsh. Following command is example how user may run it in current terminal (useful for remote execution).

qemu-system-x86_64 --enable-kvm -nographic -cpu host -smp ${PROC} -m ${MEM} -drive file=${IMG_WORK} -drive file=work.qcow2 -device virtio-net,netdev=vmnic -netdev user,id=vmnic

After VM boot login with previously set root password (or another user if created). To mount source image run

mkdir /mnt/sources/
mount /dev/sdb /mnt/sources

(Optional) SMP configuration

To properly passthrough CPU configuration to virtual machine provide topology in -smp parameter.

PROC=$(nproc)
SOCKETS=$(lscpu -J | jq -r '.lscpu[]| select(.field=="Socket(s):").data')
CORES=$(lscpu -J | jq -r '.lscpu[]| select(.field=="Core(s) per socket:").data')
TPERCORE=$(lscpu -J | jq -r '.lscpu[]| select(.field=="Thread(s) per core:").data')

-smp ${PROC},cores=${CORES},threads=${TPERCORE},sockets=${SOCKETS}

To mount the provided source image inside the QEMU run the following:

mkdir /mnt/src/
mount /dev/sdb /mnt/src/