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  • URL: git://git.kernel.org/pub/scm/linux/kernel/git/vireshk/linux.git

  • Branch: virtio/msg-v1

  • Commit: 1e5e683a3d1aa8b584f279edd144b4b1d5aad45c

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The only difference is that it is adding buildroot path for the guest.

Custom QEMU for system model

This QEMU has support for I2C needed below.

Build as:

Code Block
git clone https://github.com/vireshk/qemu
mkdir -p build/qemu
mkdir -p build/qemu-install
cd build/qemu
../../qemu/configure \
    --target-list="aarch64-softmmu" \
    --prefix="$(cd ../qemu-install; pwd)" \
    --enable-fdt --enable-slirp --enable-strip \
    --disable-docs \
    --disable-gtk --disable-opengl --disable-sdl \
    --disable-dbus-display --disable-virglrenderer \
    --disable-vte --disable-brlapi \
    --disable-alsa --disable-jack --disable-oss --disable-pa
  make -j10
  make install

Testing

The following steps lets one test I2C vhost-device on Xen.

Putting the pieces together:

Now that we have built everything we need, we need to assemble the pieces. We will be using a Debian 12 arm64 root filesystem and adding or components to it.

There are many was to add the content to the disk but here we will use guestfish.

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Build host kernel at the branch tip commit

Run make ARCH=arm64 defconfig to get a basic .config setup, then make -j$(nproc) ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- to build the Host kernel. Disabling graphics driver by overriding CONFIG_DRM=n in the .config file might make your build faster.

Copy the host kernel image somewhere else before building the guest image. It is located at arch/arm64/boot/Image.

Building the guest kernel with buildroot

We will provide a small busybox-based rootfs to the guest kernel as an initramfs image by using the buildroot project. First, acquire buildbox by either downloading a tarball from its website or by cloning it locally:

Code Block
git clone https://gitlab.com/buildroot.org/buildroot.git

Follow the steps:

Code Block
make menuconfig

  • Target Options → Target Architecture → select aarch64 little endian

  • Target Options → Target Architecture Variant → select cortex-a57 CPU

  • Filesystem images → select cpio the root filesystem (for use as an initial RAM filesystem)

  • we will leave every other value at their default, so select exit, which will prompt you to save the .config file.

Code Block
make

will download all required tarballs and build the .cpio image in output/images/rootfs.cpio

View file
name.config
View file
namerootfs.cpio

Build guest kernel at the tip’s previous commit

Do a git checkout HEAD^ to go back to the previous commit. The build will be the same except now we will add a rootfs at the guest kernel so that we can run it in Xen with ease.

Run make ARCH=arm64 defconfig to get a basic .config setup again. Open the file in an editor, locate the line with the variable CONFIG_INITRAMFS_SOURCE and change its value to the location of the rootfs cpio file. Repeat build. Copy arch/arm64/boot/Image somewhere else for convenience. This file will need go into the emulated host along with the vhost binaries we compiled.

Custom QEMU for system model

This build of QEMU is necessary to use the I2C device with the argument -device ds1338,address=0x20 as described later in the document.

Build as:

Code Block
git clone https://github.com/vireshk/qemu
mkdir -p build/qemu
mkdir -p build/qemu-install
cd build/qemu
../../qemu/configure \
    --target-list="aarch64-softmmu" \
    --prefix="$(cd ../qemu-install; pwd)" \
    --enable-fdt --enable-slirp --enable-strip \
    --disable-docs \
    --disable-gtk --disable-opengl --disable-sdl \
    --disable-dbus-display --disable-virglrenderer \
    --disable-vte --disable-brlapi \
    --disable-alsa --disable-jack --disable-oss --disable-pa
  make -j10
  make install

Testing

The following steps lets one test I2C vhost-device on Xen.

Putting the pieces together:

Now that we have built everything we need, we need to assemble the pieces. We will be using a Debian 12 arm64 root filesystem and adding or components to it.

There are many was to add the content to the disk but here we will use guestfish.

Code Block
mkdir -p build/disk
(cd build/disk; wget https://cloud.debian.org/images/cloud/bookworm/latest/debian-12-nocloud-arm64.qcow2)
cp build/disk/debian-12-nocloud-arm64.qcow2 build/disk.qcow2
MODULES_TAR=$(ls -1 build/linux-install/modules-*.tar.gz)
DEB=$(cd xen/dist; ls -1 xen-*.deb)
guestfish --rw -a build/disk.qcow2 <<EOF
run
mount /dev/sda1 /
tar-in $MODULES_TAR / compress:gzip
upload build/vhost-device-i2c /root/vhost-device-i2c
upload build/xen-vhost-frontend /root/xen-vhost-frontend
upload xen/dist/$DEB /root/$DEB
upload guestKernelImage /root/guestKernelImage
upload domu.conf /root/domu.conf
EOF

If guestfish is not available, as a last resort you can scp the files while QEMU is running with scp -P 8022 file root@localhost:/root/. To get an ssh login use ssh -p root@loclahost (Capitol P for scp and lowercase p for ssh.). The Debian nocloud image recommended at the next step has the default credentials root and no password. You will need to install an OpenSSH server apt update && apt install -y openssh-server then enable it by:

  • edit /etc/ssh/sshd_config and un-comment the lines:

  • Code Block
    Port 22
AddressFamily any
ListenAddress 0.0.0.0
ListenAddress ::

HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key

PermitRootLogin yes
PasswordAuthentication yes
PermitEmptyPasswords yes

  • service ssh restart

Run Xen via Qemu on X86 machine:

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First start the I2C backend in the background.

Code Block
vhost-device-i2c -s /root/i2c.sock -c 1 -l "90c0000.i2c:32" &

This tells the I2C backend to hook up to /root/i2c.sock0 socket and wait for the master to start transacting.

...

Then start xen-vhost-frontend in the background, by providing path of the socket to the master side. This by default will create grant-mapping for the memory regions (buffers mapped on the fly).

Code Block
xen-vhost-frontend --socket-path /root/ &

Now that all the preparations are done, lets start the guest.

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