commit	0860239744c1ec759d020d366498b80f029401d3	[log] [tgz]
author	Tim Van Patten <timvp@google.com>	Tue Aug 22 15:50:10 2023
committer	Chromeos LUCI <chromeos-scoped@luci-project-accounts.iam.gserviceaccount.com>	Fri Sep 01 17:11:48 2023
tree	61b22eada74ffcb2cf7150dc04d8f325a2972eaf
parent	50536661c7bba31321eb0bec514a587a849a1018 [diff]

tree: 61b22eada74ffcb2cf7150dc04d8f325a2972eaf

README.md

frecon: the Freon Console

This is a terminal emulator that replaces the kernel Virtual Terminal (VT) console. It uses the Kernel Mode Setting (KMS) support in the kernel. It is similar to the kmscon project: https://www.freedesktop.org/wiki/Software/kmscon

A new project was created (rather than re-using kmscon) because:

We show a boot splash animation during early boot.
Dynamic VT initialization.
Integration with CrOS dev mode checks.
A D-Bus IPC protocol for Chrome to control startup/shutdown.
VT switching negotiation with Chrome.
We don't need all the seat logic that kmscon includes.

However, it‘s not as bad as it sounds! We haven’t re-implemented our own terminal emulator -- we use the same library that kmscon does: libtsm. That's the much more tricky part too.

For even more details, check out the design doc in this repo.

Command line options

--clear=color Specify clear color for splash screen terminal. The color is 32-bit integer in a framebuffer format (ARGB) in any format supported by strtoul.
--daemon Daemonize frecon.
--enable-gfx Enable image and box drawing OSC escape codes.
--enable-vts Enable additional terminals in addition to splash screen.
--enable-vt1 Enable switching to VT1 (aka splash screen) and keep a terminal on it after finishing splash animation.
--frame-interval=N Specify default time (in milliseconds) between frames of splash screen animation.
--loop-start=N Specify frame to start splash animation loop. This option also enables the animation loop.
--loop-count=N Specify number of splash animation loop repetitions. Default of 0 repeats forever. Looping has to be enabled using --loop-start.
--loop-interval=N Specify default time (in milliseconds) between frames of loop animation.
--loop-offset=x,y Specify default offset to centered image in loop.
--no-login When additional terminals are enabled do not display login prompt on them. Can be used by scripts to display debugging information and logs on additional terminals.
--num-vts=N Specify number of enabled VTs. The default is 4, the maximum is 12.
--offset=x,y Specify absolute location of the splash image on screen.
--pre-create-vts Normally VTs are create on demand the the user switches to a VT. In some cases it may be necessary to pre-create them at startup, for instance to write a log or debug output for them while they are not active so it can be examined later. This option allows for that. This option also ensures daemon parent waits for daemon child to finish initalization so consoles are created by the time daemon parent exits.
--print-resolution Print detected screen resolution and exit. Deprecated.
--scale=N Set default scale for splash screen images. The scale is a positive integer number. Default scale is 1. 0 has a special meaning - using scale 1 for screens with horizontal resolution lower and equal than 1920 and 2 otherwise. Scale affects image/box size and offset.
--splash-only Exit immediately after finishing splash animation. Otherwise frecon will wait for DBUS signal (LoginScreenVisible) from Chrome before exiting when extra terminals are not enabled.
--image=/path/to/image.png
--image-hires=/path/to/image.png or any image file name specified after options Add image to splash screen animation. --image and --image-hires are added conditionally depending whether horizontal or vertical screen resolution is above 1920. This allows frecon to make runtime decision which set of images to use instead running frecon first with --print-resolution option and making this decision in a script that invokes frecon. Free form image file name in the command line are added unconditionally.
--wait-drop-master Wait to call drmDropMaster until prompted by the caller with the escape code: drmdropmaster:.

Imaging escape codes

Frecon implements rudimentary functionality to display images and draw single color boxes on the terminal screen using OSC (Operating System Command) based terminal escape codes.

The OSC sequences always start with ESC+] (\033]) and end with either the String Terminator (ST) sequence (\033\\) or a BEL (\a) character.

Two escapes are implemented, all escape parameters can be specified in any order.

image:file=/full/path/to/file.png;location=x,y;offset=x,y;scale=s

box:size=w,h;color=c;location=x,y;offset=x,y;scale=s

location is the absolute location on screen.
offset is an image offset starting with image centered on screen.
color is a 32-bit number in the same format as --clear command line argument, it defaults to 0.
size is two integer numbers.
scale is integer scaling factor applied to image size or box size.

Examples:

printf "\033]image:file=/usr/share/chromeos-assets/images_100_percent/boot_splash_frame18.png\a" > /dev/pts/1
printf "\033]box:color=0xFFFFFFFF;size=100,100\a" > /dev/pts/1

Input escape code

An escape code can be used to enable/disable keyboard input processing on a terminal. The setting is stored per terminal and applies to input “within” terminal. Switching between terminals, scrolling, backlight control etc remains operational.

input:onoff

where onoff is one of: on,1,true or off,0,false

Examples:

printf "\033]input:on\a" > /run/frecon/vt0
printf "\033]input:off\a" > /run/frecon/vt1

SwitchVT escape code

An escape code that can be used to switch currently active terminal. switchvt:termnum

where termnum is an integer from 0 to num-vts-1

Example:

printf "\033]switchvt:1\a" > /run/frecon/current

Files

Frecon creates the following files and links in /run/frecon directory:

/run/frecon/pid which contains pid for frecon daemon process (only when --daemon is specified on command line).
for every VT it creates, a link from /run/frecon/vt%u to /dev/pts/X where %u is terminal number from 0 to num-vts - 1 so the user can determine which VT uses which pts since pts number assignment is not deterministic.
/run/frecon/current is a symlink to currently active terminal (/run/frecon/vtX). It can be used to discover which terminal is currently active or to write text to currently active terminal.

Example Usage

For the sake of an example let's assume you wish to switch between vt1 -> vt0(normal screen) -> vt1 we can do so using the following steps:

start off by linking /run/frecon/current to /run/frecon/vt1
use exit code to actually switch to vt1 i.e. ‘printf “\033]switchvt:1\a” > /run/frecon/current’
switch to vt0 now by using the following command ‘printf “\033]switchvt:0\a” > /run/frecon/current’
repeat steps 1 and 2 since switching to vt0 breaks the link

DRM Drop Master

An escape code can be used to tell frecon to drop DRM master. This is useful when frecon is invoked with --wait-drop-master.

Example:

printf "\033]drmdropmaster\a" > /run/frecon/current