Documentation on the images structure/how to debug invalid builds?

[Steve Langasek]

Hi Seb,

On Tue, Jun 09, 2015 at 08:31:10PM +0200, Sebastien Bacher wrote:
> The desktop team continues looking at getting a desktop-next image based
> on snappy going, we managed to get the a first successful build on i386
> today (amd64 fails in what looks like the copy of signed boot bits, that
> needs extra debugging)
> https://launchpad.net/~ubuntu-cdimage/+livefs/ubuntu/wily/ubuntu-desktop-next/+build/29166

> The build is giving us a device and a rootfs tarball, we are having some
> difficulties combining those into a working image though, some help
> would be welcome...

> I've some question:

> - is there any documentation describing what the device and rootfs
> tarballs should contain? that would be useful to valid if the bits
> available at the url mentioned before are valid

> - is there some documentation describing what a "built" image is looking
> like? (like partitions schemes/types, what they should contain to be a
> valid boot medium, etc)

> - what's the right way to build an image from those tarball? I've tried
> to build goget-ubuntu-touch with the changes from
> https://code.launchpad.net/~canonical-ci-engineering/goget-ubuntu-touch/local_image/+merge/260531
> then used
> "u-d-f core rolling --channel edge
> --device-part=livecd.ubuntu-desktop-next.device.tar.gz
> --image-part=livecd.ubuntu-desktop-next.rootfs.tar.gz -o wily.img""

This change only adds support for feeding an image part from a local file;
it still expects the image part in question to be in the format provided by
the system-image server.  This is not the same format as the output of a
Launchpad livefs build - those images must be post-processed to match the
format used by system-image.  (In theory launchpad could generate them in
the same format; no one has bothered to implement this because
post-processing would still be required in order to change the compression
format and generate deltas.)

I saw mention on IRC today of setting up auto-importing these images onto a
system-image channel.  Is there a reason this isn't the answer you're
looking for in this case?  I can see that ideally it should be easier to
substitute a locally-generated rootfs for testing, but for the case of the
desktop image, it seems to me that we should be getting this set up
officially ASAP.

-- 
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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