General Device Building Overview [Was, Re: Looking for general device building overview]

Fri Sep 9 11:45:18 UTC 2016

Thanks Steve!

This will be very helpful to me - a clear and simple "lay of the land".

I'll try to put this information to use shortly.

Cheers, Mike

On Fri, Sep 9, 2016 at 2:04 AM, Steve Langasek <steve.langasek at canonical.com
> wrote:

> Hi Mike,
>
> On Thu, Sep 08, 2016 at 06:16:58PM -0400, MikeB wrote:
> > I feel like I am stumbling around in the dark as I'm learning about
> getting
> > Ubuntu-Core running on new devices.  I'm discovering things in a
> bottom-up
> > direction and I think I'm not seeing some basic concepts that Canonical
> > engineers take for granted.  I've trolled through the Ubuntu sites and
> > mailing lists trying to get good overview and understanding about
> subjects
> > but have come up empty or, at best, sparse.  Learning about concepts
> > through a mailing list "keyhole" is very difficult.
> >
> > I think I'm way off on my knowledge about the following.
> >
> > * Assertions/Model Assertions - I see them mentioned, but have no idea
> what
> > they are.
> > * Gadgets - Again hear and see them a lot, but no clue what they are.
> How
> > can I create and use one for my target platforms.
> > * ubuntu-image - No idea of its status or how to use it.
> > * ubuntu-device-flash - Using it now from a recipe but don't know much
> else
> > about it.  Is it obsolete?
>
> > Any pointers to good overviews or documentation would be appreciated.
>
> > Regards, Mike
>
> These are some wonderfully timely questions, that I'm happy to help answer
> for you!  This should also help with the problems of your other post, about
> the image you've built with ubuntu-device-flash not letting snapd run.
>
> To answer the last question first: up until this week, ubuntu-device-flash
> has been The Way to make ubuntu-core images.  However, we've known for some
> time that this needed to be replaced, and this in-progress replacement is
> called ubuntu-image.
>
> We haven't been writing much about the status of ubuntu-image here because
> it's been pre-alpha, and would likely only add to people's frustrations
> around image building. ;)  But the images released this week were all made
> using ubuntu-image, which is a good indicator that it's now ready to be
> shared more widely.
>
> ubuntu-image is now available as a snap.  For the moment, it's only on the
> edge channel and requires devmode, so it can be installed as:
>
>   sudo snap install --channel=edge --devmode ubuntu-image
>
> You can also find the source repository for ubuntu-image at:
>
>   https://github.com/CanonicalLtd/ubuntu-image/
>
> Now, ubuntu-image has a number of commandline options, most of which are
> only of interest if you're working on ubuntu-image itself (we will clean up
> the --help output soon).  The basic usage is just:
>
>   UBUNTU_IMAGE_SKIP_COPY_UNVERIFIED_MODEL=1 \
>       ubuntu-image -c edge my-model.assertion -o my_output.img
>
> So, what is a model assertion?  Others can speak more authoritatively than
> I
> can about the definition of a model assertion, but the summary is that this
> is a text document declaring what should go into your image.  Instead of
> specifying the gadget, kernel, and os snaps as commandline arguments to
> ubuntu-device-flash, you declare these in the model assertion, which can
> then be signed and referenced by the store and snapd.
>
> If you are making your own image, you will need your own model assertion.
>
> You can find some practical examples here:
>
>   http://people.canonical.com/~vorlon/amd64-generic-model.assertion
>   http://people.canonical.com/~vorlon/pi2-model.assertion
>
> These are 90% of the way to what was used in producing this week's images,
> which should be enough to get you going for your own local builds.  Note
> that current snapd requires model assertions to be signed, so the above
> include a signature - but the signature is not valid (and obviously won't
> be
> valid when you make your changes), thus the need for setting
> UBUNTU_IMAGE_SKIP_COPY_UNVERIFIED_MODEL=1.
>
> And the main thing you're going to want to permute in your model assertion,
> vs. one of our reference assertions, are the snaps that you're using.
> You're already using a custom kernel snap; you will also want a custom
> gadget snap.
>
> A gadget snap is a snap that details how the kernel and os snap should be
> combined into an image for a given device.  This includes partition
> layouts,
> what bootloader snappy uses (grub or uboot), and how to integrate with the
> firmware.
>
> The backbone of a gadget snap is the meta/gadget.yaml.  You can find
> documentation of this yaml file here:
>
>   https://github.com/CanonicalLtd/ubuntu-image/
> blob/master/docs/gadget-yaml.rst
>
> And you can find the source for the reference gadget snaps at:
>
>   https://code.launchpad.net/~snappy-dev/snappy-hub/snappy-systems/
>
>
> And since ubuntu-image is calling 'snap prepare-image' under the hood to
> create your ubuntu-core root filesystem, this will also take care of all
> the
> problems with /var/lib/snapd/seed in your other mail!
>
> Hope that helps,
> --
> Steve Langasek                   Give me a lever long enough and a Free OS
> Debian Developer                   to set it on, and I can move the world.
> Ubuntu Developer                                    http://www.debian.org/
> slangasek at ubuntu.com                                     vorlon at debian.org
>
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