I had more trouble with this than I expected and I said to @bucknalla I’d put some notes down.
There’s no criticism here. I knew what I was getting into would be fiddly just because of the nature of Docker, modules and Linux kernels. That said, while I remember, some of this might be useful feedback for the team from a customer who has been through it.
Annoyingly Pimoroni have a nice install script but it expects Raspbian and does various things with raspi-config and config.txt so I had to do my own thing. C’est la vie.
So the bulk of the Enviro+ Docker template was quite easy, just tracking down dependencies. I have my container running in privileged mode which although non-ideal from a security perspective is good enough for me (PRs always gratefully accepted of course!)
I ran into trouble with the MEMS microphone on the Enviro+ as it wasn’t being detected as a card. I ended up going all over the place trying to work out exactly what this was, and how to support it.
Long story short I had to add a driver which isn’t present in BalenaOS. This means I then had to build that driver for the kernel running on my BalenaOS device, in this case balenaOS 2.54.2+rev1
Now my first port of call via Google was this set of instructions from the Resin.io days
I like this as I understand it and it’s pretty straightforward but for whatever reason I couldn’t get it working. The files for my BalenaOS couldn’t be found for some reason. I assume that things have changed since this was written and if so it would be worth putting a note in deprecating it? Or maybe I just didn’t understand what I was doing wrong!
So then I moved onto the more recent example here
So this is a great effort to help - thanks for that!
I found it really hard to work out what was going on, partly as I was using this within a DockerFile and going around and around the houses trying to figure out what was going wrong.
A couple of things that would help
- this is for out of tree modules only. I suspect a lot of people just want an in-tree module added so it would really help to have a simple parameterised script that builds an existing in-tree module
- the searching for the kernel tarball and the kernel modules tarball is quite obscure. It would be really helpful to have a blog description of how this is working to find the right files
- we have to set the BalenaOS version (and potentially the Linux kernel version). it would help if this was an ENV variable we could just use against a specific device (not sure how doable this is if Apps can have Devices with different BalenaOS versions though?)
- the way the get_and_build() function works by going through twice in sequence is clever but really obscure. It would make the process a lot clearer to break out the pulling of module tarball, the pulling of kernel tarball and the building of the in tree or out of tree module
- it also takes quite a while when you are testing so if these processes could be seperated it allows the search + pull to be cached to make it easier to test the building
- it would be great to get rid of the dependency on aws. something like the github URLs for artifacts feels much simpler where you just pull github.com/owner/project/version_of_artifact type of thing
- when I finally did get to look at the kernel source file I assumed it would be a full buildable kernel (i.e. including .c files) but it seems only to have includes and such which meant I couldn’t build the in-tree module I wanted. I might have gotten this wrong as it seem a bit odd.
The ability to add in custom in and out of tree modules feels relevant as I am sure some users need this like me and I really don’t want to have to go to the trouble of setting up a full Yocto+Balena environment to build my own custom host OS image.
So those are my thoughts. Offered in the spirit of support and feedback! If I think of anything else I’ll add it in 
Cheers, Alex