[OE-core] Wic and "live" images

[Ian Geiser]

Greetings, I am trying to learn "wic" and have been confused as how to create a "live" style image.  I am following "http://www.yoctoproject.org/docs/1.5.2/dev-manual/dev-manual.html#creating-partitioned-images" but am getting confused on the target to use to create the a file system that has a single squashfs file containing my root file system.  

My desired partition layout is as follows:
      40MiB                 40MiB               300MiB
+--------------------+-----------------+-----------------------------+
|      BOOT (esp)    |    DATA (fat)   |          ROOT (live)        |  
+--------------------+-----------------+-----------------------------+

BOOT - efi boot partition with kernel and initramfs
DATA - generic fat filesystem to hold configuration files
ROOT - an ext4 filesystem that contains a single os.img, which is a squashfs file.

I have ROOT and DATA figured out but I am at a loss as how to generate the os.img file and copy it into ROOT.  If I generate the os.img file with bitbake and then use the "-r" option to manually supply a directory structure it works, but I would rather have it done from a wks file for automation reasons.

Any hints?

Thanks!