Initial Process Echo Application

This example Echo application is intended to be run as the initial process (PID 1) on Linux.

The application listen for bytes on the first Virtio Console port and echoes the exact same contents back over the same port.

To test this application as intended, it must be copied onto an initial RAM disk (initramfs). The easiest way to execute the initial RAM disk is to use QEMU's direct Linux boot feature.

Since the initial RAM disk does not contain a dynamic linker or any other dependencies the application must be built as a statically linked binary.

Testing Steps

Note: these steps assume that the commands will be executed from the project root.

Build the application as a statically linked binary:

cargo build --release --target=x86_64-unknown-linux-musl \
    --package=oak_echo_linux_init

Create the initial RAM disk:

# Create a temporary directory containing the initial workload.
export RAMDIR=$(mktemp -d)
cp --archive target/x86_64-unknown-linux-musl/release/oak_echo_linux_init \
    ${RAMDIR}/init
# Create a compressed CPIO archive.
( cd ${RAMDIR}; find . -print0 \
    | cpio --null --create --format=newc ) \
    | gzip \
    > bin/initramfs

Build the Stage 0 Firmware image:

( cd stage0_bin; cargo build --release; )
objcopy --output-format binary stage0_bin/target/x86_64-unknown-none/release/oak_stage0_bin \
    bin/stage0.bin

Sets up two named pipes (/tmp/comms.in and /tmp/comms.out) on the host for communication with the Virtio Console device on the guest:

mkfifo /tmp/comms.in /tmp/comms.out

Execute the initial RAM disk with QEMU:

Note: this assumes that an appropiate uncompressed Linux kernel ELF binary has been copied to bin/vmlinux. The Linux Kernel must be built with ACPI, ACPI Plug-and-Play, Virtio MMIO, and Virtio Console support, as this is needed for the /dev/hvc0 device to become available.

qemu-system-x86_64 -cpu host -enable-kvm -machine "microvm" -m 1G \
    -nographic -nodefaults -no-reboot -serial stdio \
    -chardev "pipe,id=comms,path=/tmp/comms" \
    -device "virtio-serial-device,max_ports=1" \
    -device "virtconsole,chardev=comms" \
    -bios "bin/stage0.bin" \
    -fw_cfg "name=opt/stage0/elf_kernel,file=bin/vmlinux" \
    -fw_cfg "name=opt/stage0/initramfs,file=bin/initramfs" \
    -fw_cfg "name=opt/stage0/cmdline,string=console=ttyS0 quiet"

While the VM is running, listen for bytes on the output pipe in a separate terminal:

cat /tmp/comms.out

In another separate terminal send content to the application via the input pipe:

echo "Test Message 1" > /tmp/comms.in
echo "Test Message 2" > /tmp/comms.in
echo "Test Message 3" > /tmp/comms.in