Would like expanded releng docs for building OS images

[rmustacc]

If you're getting started from the perspective of I normally build an OS image, but not in Omicron context, and have an urgent need to turn that into one that does, I think expanding the docs to cover some of the expected pre-reqs and which parts of the other Omicron dev docs are required might be useful. From reading the current docs one might assume that it'd be reasonable to just clone omicron and run cargo xtask releng --helios-local --helios-dir ~/src/path/to/helios. There are a few additional things I've found that need to be set up, which I expect are true regardless of what one is doing:

• Creating required ZFS datasets
• Having downloaded dendrite bits (cargo xtask download dendrite-openapi)

From the --help and current docs it's not clear if I should have already built the illumos bits (I did) or not. I'm assuming it wants me to at this point in the process, but I'm also not sure how it would pick debug vs. non-debug.

[rmustacc]

In rereading a bit, there's a bit of contradictory advice around the install_builder_prerequisites.sh, but that doesn't work on shared hosts where you actually already have the builder preqeqs installed, but just don't have the downloads. Maybe in addition, we can pull in that bit into this logic and verification? The system clearly knew enough to know I didn't have it, but prompted me each time to go grab it.

[iliana]

If you're getting started from the perspective of I normally build an OS image, but not in Omicron context, and have an urgent need to turn that into one that does, I think expanding the docs to cover some of the expected pre-reqs and which parts of the other Omicron dev docs are required might be useful.

This is for building a custom Helios but using the Omicron build system (and thus having sled-agent and all of the other global zone packages present)? Or building an OS image without any Omicron bits? (both?)

[rmustacc]

This is about building a correct OS (or recovery) image for the product that includes sled-agent, dendrite, etc., but assuming I have built a custom set of stlouis bits, i.e. cargo xtask releng --helios-local --helios-dir ~/src/path/to/helios. If I want to build an OS image without omicron bits we have some docs and can do that out of the helios repo no problem.