busybear-linux is a tiny RISC-V Linux root filesystem image that targets the virt machine in riscv-qemu. As the name suggests, busybear-linux is a riscv-linux root image comprised of busybox and dropbear.

The root image is intended to demonstrate virtio-net and virtio-block in riscv-qemu and features a dropbear ssh server which allows out-of-the-box ssh access to a RISC-V virtual machine.

See the releases for pre-built kernel and filesystem images.

The busybear build system has been written by and is copyright (C) 2017 by Michael J. Clark [email protected]. Enhancements to the build system have been contributed by and are copyright (C) 2017 by Karsten Merker [email protected].

The busybear build system is provided under the following license ("MIT license"):

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

• riscv-gnu-toolchain (RISC-V Linux toolchain)
• busybox (downloaded automatically)
• dropbear (downloaded automatically)
• sudo, curl, openssl and rsync

• ntpd for time configuration
• klog for kernel logging
• syslog for system logging
• dropbear for ssh access
• busybox with almost everything enabled

• conf contains the linux image build configuration
  • conf/linux.config contains the linux-kernel configuration
  • conf/busybox.config contains the busybox configuration
  • conf/busybear.config contains the image build configuration
    • ROOT_PASSWORD=busybear
    • IMAGE_FILE=busybear.bin
• etc contains the linux guest system configuration
  • etc/network/interfaces (guest 192.168.100.2, router 192.168.100.1)
  • etc/resolv.conf (nameserver 8.8.8.8, nameserver 8.8.4.4)
  • etc/ntp.conf (server 0.pool.ntp.org, server 1.pool.ntp.org)
  • etc/passwd, etc/shadow, etc/group and etc/hosts

The default config assumes bridged networking with 192.168.100.1 on the host and 192.168.100.2 in the guest.

The build process downloads busybox and dropbear, compiles them and prepares a root filesystem image to the file busybear.bin. The build script needs to be run in Linux, even if preparing a root filesystem image for macOS.

git clone --recursive https://github.com/michaeljclark/busybear-linux.git
cd busybear-linux
make

git clone https://github.com/riscv/riscv-qemu.git
cd riscv-qemu
./configure --target-list=riscv64-softmmu,riscv32-softmmu
make

Note: busybear-linux builds linux kernel automatically

git clone https://github.com/riscv/riscv-linux.git
cd riscv-linux
git checkout riscv-linux-4.14
cp ../busybear-linux/conf/linux.config .config
make ARCH=riscv olddefconfig
make ARCH=riscv vmlinux

Note: busybear-linux builds bbl automatically

git clone https://github.com/riscv/riscv-pk.git
cd riscv-pk
mkdir build
cd build
../configure \
    --enable-logo \
    --host=riscv64-unknown-elf \
    --with-payload=../../riscv-linux/vmlinux
make

busybear requires the riscv-qemu virt board with virtio-block and virtio-net devices.

The following command starts busybear-linux:

./scripts/run-qemu.sh

which runs executes this command:

sudo qemu-system-riscv64 -nographic -machine virt \
  -kernel bbl -append "root=/dev/vda ro console=ttyS0" \
  -drive file=busybear.bin,format=raw,id=hd0 \
  -device virtio-blk-device,drive=hd0 \
  -netdev type=tap,script=scripts/ifup.sh,downscript=scripts/ifdown.sh,id=net0 \
  -device virtio-net-device,netdev=net0

After booting the virtual machine you should be able to ssh into it.

$ ssh [email protected]
The authenticity of host '192.168.100.2 (192.168.100.2)' can't be established.
ECDSA key fingerprint is 3f:4b:69:59:01:c8:b2:9c:fb:52:a5:d4:21:c9:3c:1b.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.100.2' (ECDSA) to the list of known hosts.
[email protected]'s password: 
    ____                   ____                     __    _                 
   / __ )__  _________  __/ __ )___  ____ ______   / /   (_)___  __  ___  __
  / __  / / / / ___/ / / / __  / _ \/ __ `/ ___/  / /   / / __ \/ / / / |/_/
 / /_/ / /_/ (__  ) /_/ / /_/ /  __/ /_/ / /     / /___/ / / / / /_/ />  <  
/_____/\__,_/____/\__, /_____/\___/\__,_/_/     /_____/_/_/ /_/\__,_/_/|_|  
                 /____/                                                     
root@ucbvax:~# uname -a
Linux ucbvax 4.14.0-00030-gc2d852cb2f3d #56 Thu Dec 14 10:12:10 NZDT 2017 riscv64 GNU/Linux
root@ucbvax:~# cat /proc/interrupts 
           CPU0       
  1:        107  riscv,plic0,c000000  10  ttyS0
  7:        115  riscv,plic0,c000000   7  virtio1
  8:        135  riscv,plic0,c000000   8  virtio0
root@ucbvax:~# 

Note: the disk image is stateful and needs to be shutdown cleanly.

root@ucbvax:~# halt

/etc/network/interfaces

iface br0 inet static
  bridge_ports eth0
  address 192.168.100.1
  netmask 255.255.255.0
  network 192.168.100.0
  broadcast 192.168.100.255

#!/bin/sh

brctl addif br0 $1
ifconfig $1 up

#!/bin/sh

ifconfig $1 down
brctl delif br0 $1

These steps show how to setup tuntap bridged networking on macOS:

Note: the tuntap driver installation requires authorization in the macOS Security and Privacy section of System Preferences.

brew tap caskroom/cask
brew install caskroom/cask/tuntap

sudo ifconfig bridge1 create
sudo ifconfig bridge1 192.168.100.1/24

#!/bin/sh
ifconfig bridge1 addm $1

#!/bin/sh
ifconfig bridge1 deletem $1

nat on en0 from { 192.168.100.0/24 } to any -> (en0)
pass from {lo0, 192.168.100.0/24} to any keep state

sudo sysctl -w net.inet.ip.forwarding=1
sudo pfctl -e
sudo pfctl -F all
sudo pfctl -f pfctl.rules