burrow-pi-img/README.md

# FRCVision-pi-gen

_Tool used to create the FRCVision Raspbian image_


## Dependencies

pi-gen runs on Debian based operating systems. Currently it is only supported on
either Debian Stretch or Ubuntu Xenial and is known to have issues building on
earlier releases of these systems.

To install the required dependencies for pi-gen you should run:

```bash
apt-get install quilt parted realpath qemu-user-static debootstrap zerofree pxz zip \
dosfstools bsdtar libcap2-bin grep rsync xz-utils file git curl \
xxd build-essential cmake python3 ant sudo openjdk-8-jdk openjdk-11-jdk
```

Or better, use build-docker.sh instead of build.sh, as the Docker image will
install the required tools as part of the Docker image build.

The file `depends` contains a list of tools needed.  The format of this
package is `<tool>[:<debian-package>]`.


## Config

Upon execution, `build.sh` will source the file `config` in the current
working directory.  This bash shell fragment is intended to set needed
environment variables.

The following environment variables are supported:

 * `IMG_NAME` **required** (Default: `'FRCVision'`)

   The name of the image to build with the current stage directories.  Setting
   `IMG_NAME=FRCVision` is logical for an unmodified
   wpilibsuite/FRCVision-pi-gen build, but you should use something else for a
   customized version.  Export files in stages may add suffixes to `IMG_NAME`.

 * `APT_PROXY` (Default: unset)

   If you require the use of an apt proxy, set it here.  This proxy setting
   will not be included in the image, making it safe to use an `apt-cacher` or
   similar package for development.

   If you have Docker installed, you can set up a local apt caching proxy to
   like speed up subsequent builds like this:

       docker-compose up -d
       echo 'APT_PROXY=http://172.17.0.1:3142' >> config

 * `BASE_DIR`  (Default: location of `build.sh`)

   **CAUTION**: Currently, changing this value will probably break build.sh

   Top-level directory for `pi-gen`.  Contains stage directories, build
   scripts, and by default both work and deployment directories.

 * `WORK_DIR`  (Default: `"$BASE_DIR/work"`)

   Directory in which `pi-gen` builds the target system.  This value can be
   changed if you have a suitably large, fast storage location for stages to
   be built and cached.  Note, `WORK_DIR` stores a complete copy of the target
   system for each build stage, amounting to tens of gigabytes in the case of
   Raspbian.
   
   **CAUTION**: If your working directory is on an NTFS partition you probably won't be able to build. Make sure this is a proper Linux filesystem.

 * `DEPLOY_DIR`  (Default: `"$BASE_DIR/deploy"`)

   Output directory for target system images and NOOBS bundles.

 * `USE_QEMU` (Default: `"0"`)

   Setting to '1' enables the QEMU mode - creating an image that can be mounted via QEMU for an emulated
   environment. These images include "-qemu" in the image file name.

 * `FIRST_USER_NAME` (Default: "pi" )

   Username for the first user

 * `FIRST_USER_PASS` (Default: "raspberry")

   Password for the first user

 * `WPA_ESSID`, `WPA_PASSWORD` and `WPA_COUNTRY` (Default: unset)

   If these are set, they are use to configure `wpa_supplicant.conf`, so that the raspberry pi can automatically connect to a wifi network on first boot.

 * `ENABLE_SSH` (Default: `1`)

   Setting to `1` will enable ssh server for remote log in. Note that if you are using a common password such as the defaults there is a high risk of attackers taking over you RaspberryPi.

A simple example for building FRCVision:

```bash
IMG_NAME='FRCVision'
```

The config file can also be specified on the command line as an argument the `build.sh` or `build-docker.sh` scripts.

```
./build -c myconfig
```

This is parsed after `config` so can be used to override values set there.

## How the build process works

The following process is followed to build images:

 * Loop through all of the stage directories in alphanumeric order

 * Move on to the next directory if this stage directory contains a file called
   "SKIP"

 * Run the script ```prerun.sh``` which is generally just used to copy the build
   directory between stages.

 * In each stage directory loop through each subdirectory and then run each of the
   install scripts it contains, again in alphanumeric order. These need to be named
   with a two digit padded number at the beginning.
   There are a number of different files and directories which can be used to
   control different parts of the build process:

     - **00-run.sh** - A unix shell script. Needs to be made executable for it to run.

     - **00-run-chroot.sh** - A unix shell script which will be run in the chroot
       of the image build directory. Needs to be made executable for it to run.

     - **00-debconf** - Contents of this file are passed to debconf-set-selections
       to configure things like locale, etc.

     - **00-packages** - A list of packages to install. Can have more than one, space
       separated, per line.

     - **00-packages-nr** - As 00-packages, except these will be installed using
       the ```--no-install-recommends -y``` parameters to apt-get.

     - **00-patches** - A directory containing patch files to be applied, using quilt.
       If a file named 'EDIT' is present in the directory, the build process will
       be interrupted with a bash session, allowing an opportunity to create/revise
       the patches.

  * If the stage directory contains files called "EXPORT_NOOBS" or "EXPORT_IMAGE" then
    add this stage to a list of images to generate

  * Generate the images for any stages that have specified them

It is recommended to examine build.sh for finer details.


## Docker Build

```bash
vi config         # Edit your config file. See above.
./build-docker.sh
```

If everything goes well, your finished image will be in the `deploy/` folder.
You can then remove the build container with `docker rm -v pigen_work`

If something breaks along the line, you can edit the corresponding scripts, and
continue:

```bash
CONTINUE=1 ./build-docker.sh
```

After successful build, the build container is by default removed. This may be undesired when making incremental changes to a customized build. To prevent the build script from remove the container add

```bash
PRESERVE_CONTAINER=1 ./build-docker.sh
```

There is a possibility that even when running from a docker container, the
installation of `qemu-user-static` will silently fail when building the image
because `binfmt-support` _must be enabled on the underlying kernel_. An easy
fix is to ensure `binfmt-support` is installed on the host machine before
starting the `./build-docker.sh` script (or using your own docker build
solution).


## Stage Anatomy

### FRCVision Raspbian Stage Overview

The build of FRCVision Raspbian is divided up into several stages for logical
clarity and modularity.  This causes some initial complexity, but it simplifies
maintenance and allows for more easy customization.

 - **Stage 0** - bootstrap.  The primary purpose of this stage is to create a
   usable filesystem.  This is accomplished largely through the use of
   `debootstrap`, which creates a minimal filesystem suitable for use as a
   base.tgz on Debian systems.  This stage also configures apt settings and
   installs `raspberrypi-bootloader` which is missed by debootstrap.  The
   minimal core is installed but not configured, and the system will not quite
   boot yet.

 - **Stage 1** - truly minimal system.  This stage makes the system bootable by
   installing system files like `/etc/fstab`, configures the bootloader, makes
   the network operable, and installs packages like raspi-config.  At this
   stage the system should boot to a local console from which you have the
   means to perform basic tasks needed to configure and install the system.
   This is as minimal as a system can possibly get, and its arguably not
   really usable yet in a traditional sense yet.  Still, if you want minimal,
   this is minimal and the rest you could reasonably do yourself as sysadmin.

 - **Stage 2** - basic system.  It installs some optimized memory functions,
   sets timezone and charmap defaults, installs fake-hwclock and ntp, wifi and
   bluetooth support, dphys-swapfile, and other basics for managing the
   hardware.  It also creates necessary groups and gives the pi user access to
   sudo and the standard console hardware permission groups.  It also does most
   of the configuration for a read-only filesystem.

   There are a few tools that may not make a whole lot of sense here for
   development purposes on a minimal system such as basic Python and OpenJDK
   packages as well as the `build-essential` package.  They are lumped right
   in with more essential packages presently, though they need not be with
   pi-gen.

 - **Stage 3** - OpenCV and WPILib system.  Here's where you get the full
   WPILib libraries for both Java and C++, as well as the required OpenCV
   dependencies.  The RobotPy NetworkTables and CameraServer libraries are
   also built and installed here.

 - **Stage 4** - The official FRCVision image.  Adds multi camera builtin
   application and services, the FRCVision web dashboard, and example vision
   programs.  This is the stage that builds and installs all of the things that
   make FRCVision friendly to new users.

### Stage specification

If you wish to build up to a specified stage (such as building up to stage 2
for a lite system), place an empty file named `SKIP` in each of the `./stage`
directories you wish not to include.

Then add an empty file named `SKIP_IMAGES` to `./stage4`.

If you wish to build further configurations upon (for example) the basic
system, you can also delete the contents of `./stage3` and `./stage4` and
replace with your own contents in the same format.


## Skipping stages to speed up development

If you're working on a specific stage the recommended development process is as
follows:

 * Add a file called SKIP_IMAGES into the directories containing EXPORT_* files
   (currently stage4)
 * Add SKIP files to the stages you don't want to build. For example, if you're
   basing your image on the WPILib image you would add this to stage 4.
 * Run build.sh to build all stages, or if you're using Docker, run ```env PRESERVE_CONTAINER=1 ./build-docker.sh```
 * Add SKIP files to the earlier successfully built stages
 * Modify the last stage
 * Rebuild just the last stage using ```sudo CLEAN=1 ./build.sh```, or if
   you're using Docker, using ```env CONTINUE=1 PRESERVE_CONTAINER=1 ./build-docker.sh```
 * Once you're happy with the image you can remove the SKIP_IMAGES files and
   export your image to test

# Troubleshooting

## `binfmt_misc`

Linux is able execute binaries from other architectures, meaning that it should be
possible to make use of `pi-gen` on an x86_64 system, even though it will be running
ARM binaries. This requires support from the [`binfmt_misc`](https://en.wikipedia.org/wiki/Binfmt_misc)
kernel module.

You may see the following error:

```
update-binfmts: warning: Couldn't load the binfmt_misc module.
```

To resolve this, ensure that the following files are available (install them if necessary):

```
/lib/modules/$(uname -r)/kernel/fs/binfmt_misc.ko
/usr/bin/qemu-arm-static
```

You may also need to load the module by hand - run `modprobe binfmt_misc`.