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TTY Resizer for SimpleCom

TTY Resizer would resize specified console when SimpleCom sends resize request.

How to build

Requirements

Linux kernel v6.0 or later

v6.4 or later is required when you run TTY Resizer on AArch64 Linux.

Fedora

  • make
  • clang
  • libbpf-devel
  • bpftool
  • kernel-devel

Ubuntu

  • make
  • clang
  • libbpf-dev
  • linux-tools-common

On distros which does not provide vmlinux.h like Ubuntu, you have to generate it via bpftool btf dump.

bpftool btf dump file /sys/kernel/btf/vmlinux format c > vmlinux.h

Note

Linux kernel from Raspberry Pi disables CONFIG_DEBUG_INFO_BTF by default. This configuration is mandatory to generate vmlinux.h . So you have to build and deploy the kernel which enables CONFIG_DEBUG_INFO_BTF, and also bpftool for it by yourself. See document by Raspberry Pi for details.

Build

make

You can specify following parameters:

  • KERNEL_DEVEL_ROOT: Include path should be added (for kernel headers)
  • BPFTOOL: Path to bpftool

Install

sudo make install

make install will install following files:

  • /usr/local/sbin/tty-resizer
  • /usr/lib/systemd/system/tty-resizer.service

How it works

sudo tty-resizer [-v] /dev/<TTY device>

Add -v if you want to see the log from libbpf.

Install systemd unit file

Specify TTY device file to tty-resizer.service (/dev/ttyGS0 is set by default), then run systemd enable in below:

sudo systemctl enable tty-resizer

If you want to change the device, run following commands:

sudo systemctl daemon-reaload
sudo systemctl restart tty-resizer

Send command

Send following format command to TTY console:

[0x12][Row];[Col]t

Both Row and Col are unsigned short.

When 0x12 (DC2) is received in tty-resizer, subsequent chars are captured in tty-resizer, and they will not propagate to real TTY. t is terminator, then capture mode in tty-resizer is finished, and subsequent chars are propagated to real TTY, and TIOCSWINSZ ioctl would be issued to the specified TTY. c means "cancel" for tty-resizer, then capture mode will be finished, and happens nothing.

0-9 and ;, t, c is valid chars on capture mode. Capture mode will be aborted when other char is received - it would be treated as c.

Known issue

TTY Resizer might not work fine with full-screen application like Vim. Noisy chars (for Vim) might be input, and TTY Resizer might not be able to set resized console size while that app is running.