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title: Tailscale on the DevTerm R-01
tags: devterm riscv linux tailscale
date: 2023-01-25
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Intro

Recently I assembled a ClockworkPi DevTerm R-01, a cyberdeck-like
terminal with a RISC-V compute module. While the retro-future design
of the DevTerm really appealed to me, and I’ve also been wanting to
work with RISC-V for a while to learn a new architecture making the
R-01 a perfect esoteric project platform.

 [ClockworkPi DevTerm R-01]: https://www.clockworkpi.com/product-page/devterm-kit-r01
 [RISC-V]: https://en.wikipedia.org/wiki/RISC-V

[DevTermR01]

 [DevTermR01]: /assets/images/posts/devtermtailscale/devterm-r01.png

ClockworkPi DevTerm R-01
After trying out a few things like DOSBox, Surf, and ScummVM, I found
the Allwinner D1 RISC-V chip wasn’t powerful enough to do much other
than some basic window management, Interactive Fiction, and browsing
gopher:// with Bombadillo. However I still wanted to use it as a
terminal to access other systems, which lead me to attempting to
install Tailscale to leverage the mesh VPN and other features.

 [DOSBox]: https://www.dosbox.com/
 [Surf]: https://git.suckless.org/surf/
 [ScummVM]: https://www.scummvm.org/
 [Allwinner D1]: https://linux-sunxi.org/D1
 [Interactive Fiction]: http://www.infocom-if.org/downloads/downloads.html
 [Bombadillo]: https://bombadillo.colorfield.space/
 [Tailscale]: https://tailscale.com

Installing tailscale was un-eventful, as it’s had RISC-V support for a
while, and following the install guide did what was expected. The
problem is tailscaled fails due to the required tun kernel module
missing in the 5.4.61 kernel running on the DevTerm.

 [RISC-V support]: https://github.com/tailscale/tailscale/issues/2119

   Jan 26 02:25:17 localhost systemd[1]: Started Tailscale node agent.
   Jan 26 02:25:17 localhost tailscaled[1074605]: wgengine.NewUserspaceEngine(tun "tailscale0") ...
   Jan 26 02:25:17 localhost tailscaled[1074605]: Linux kernel version: 5.4.61
   Jan 26 02:25:17 localhost tailscaled[1074605]: is CONFIG_TUN enabled in your kernel? `modprobe tun` failed with: modprobe: FATAL: Module tun not found in directory /lib/modules/5.4.61
   Jan 26 02:25:19 localhost tailscaled[1074605]: tun module not loaded nor found on disk
   Jan 26 02:25:19 localhost tailscaled[1074605]: wgengine.NewUserspaceEngine(tun "tailscale0") error: tstun.New("tailscale0"): CreateTUN("tailscale0") failed; /dev/net/tun does not exist
   Jan 26 02:25:19 localhost tailscaled[1074605]: flushing log.
   Jan 26 02:25:19 localhost tailscaled[1074605]: logger closing down

Building a TUN/TAP Kernel Module

The first step was finding if the R-01 kernel source was available so
re-build the exact kernel version and include the tun module by
setting CONFIG_TUN=m. Looking around the ClockworkPi website, Discord,
and Github I eventually found the How to Compile Kernel documentation.
This had links to the original source and the toolchain.

 [How to Compile Kernel]: https://github.com/clockworkpi/DevTerm/wiki/Create-DevTerm-R01-OS-image-from-scratch#how-to-compile-kernel

Since the R-01 isn’t exactly fast, cross-building this on a x86 system
was required. My personal Debian server is a bit of mess when it comes
to package pinning, so I created a new 8 CPU, 8GiB memory virtual
machine in qemu and install Ubuntu 22.04 “Jammy Jellyfish” since
that’s what the R-01 is running and what ClockworkPi has in it’s
documentation.

 [Ubuntu 22.04 “Jammy Jellyfish”]: https://www.releases.ubuntu.com/jammy/

Installing Required Packages

After setting up the VM, install required packages for cross-building
the kernel,

   sudo apt-get install gcc-11-riscv64-linux-gnu binutils-riscv64-linux-gnu qemu-user-static build-essential git wget curl vim libncurses-dev flex automake autoconf bison libssl-dev

Cloning ClockworkPi Kernel Source

Clone the kernel source into ~/git,

 [kernel source]: https://github.com/cuu/last_linux-5.4

   mkdir ~/git
   git clone https://github.com/cuu/last_linux-5.4.git

Setting Up Build Toolchain

Download the ClockworkPi toolchain from
https://github.com/cuu/toolchain-thead-glibc, which is a README
pointing to a Mega link. While it’s a bit concerning coming from Mega,
since it’s a tarball and running in a VM it’s not that risky. There’s
also a section on installing the official RISC-V toolchain which is
another option, but requires additional building.

Untar in home directory,

   cd ~
   tar -xvzf riscv64-glibc-gcc-thead_20200702.tar.gz

Existing Kernel Config from DevTerm

Copy the running kernel config in /proc/config.gz on the DevTerm to
the VM. The config.gz contains the configuration for how the running
5.4.61 kernel was configured and is loaded to set everything the exact
same way when building the new kernel.

   cd ~/git/last_linux-5.4
   scp cpi@devterm:/proc/config.gz .
   gunzip config.gz
   mv config .config

Enabling CONFIG_TUN

There are two ways to enable the TUN/TAP module,

-   Edit .config and set CONFIG_TUN=m

or

-   Interactively run menuconfig and set it in
   Device Drivers -> Network device support -> Universal TUN/TAP device driver support

   export PATH=~/riscv64-glibc-gcc-thead_20200702/bin/:$PATH
   make LOCALVERSION= CROSS_COMPILE=riscv64-unknown-linux-gnu- ARCH=riscv menuconfig

Building the Kernel

Build the kernel using the provided m.sh script, but first edit it to
include the PATH for the toolchain and LOCALVERSION=. If LOCALVERSION=
isn’t set then the kernel version will include a + at the end and
modules will not load due to a version mis-match,

   export PATH=~/riscv64-glibc-gcc-thead_20200702/bin/:$PATH
   make LOCALVERSION= CROSS_COMPILE=riscv64-unknown-linux-gnu- ARCH=riscv
   make LOCALVERSION= CROSS_COMPILE=riscv64-unknown-linux-gnu- ARCH=riscv INSTALL_MOD_PATH=test/rootfs/ modules_install
   make LOCALVERSION= CROSS_COMPILE=riscv64-unknown-linux-gnu- ARCH=riscv INSTALL_PATH=test/boot/ zinstall
   mkdir -p test/boot/
   cp arch/riscv/boot/dts/sunxi/board.dtb test/boot/

Run ./m.sh and wait a few minutes while it builds.

When successful, the new kernel and modules are in test/boot/

Setting up New Modules on DevTerm

Create a tarball of the new modules and copy them to the DevTerm,

   cd ~/git/last_linux-5.4/test/rootfs/lib/modules
   tar -cvzf 5.4.61.modules.tar.gz 5.4.61/
   scp 5.4.61.modules.tar.gz cpi@devterm:~

On the DevTerm, backup original modules directory,

   cd /lib/modules
   sudo mv 5.4.61 5.4.61.orig

and untar the new modules directory,

   cd /lib/modules
   sudo tar -xvzf ~/5.4.61.modules.tar.gz

Loading the TUN/TAP Module

Load the new TUN/TAP Module,

   sudo modprobe tun

If successfull dmesg will show,

   tun: Universal TUN/TAP device driver, 1.6

Setting up Tailscale

Now that the TUN/TAP module is loaded, start tailscaled and finish
setting up Tailscale,

   sudo service tailscaled start
   sudo tailscale up

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