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

[Sebastien Bacher]

Hey everyone,

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""

that gives an img but it seems invalid, trying to but it in kvm returns
a "not a bootable disk" error, trying to use a local kernel/initrd
(suggested by mvo) doesn't work either, it complains about missing fstab
and other issues...

- should the grub configuration be part of the device tarball or
generated by the image builder?
(unsure if having a device tarball there is needed/right, ubuntu-core
build doesn't have one)


Having some advice/help on figuring out the answer to those questions
would be welcome ;-)

Thanks,
Sebastien Bacher