I have a semi related question. I see that the OLPC project uses buildroot to create a root filesystem. I've done the same for a few projects. I'm wondering though, how they convert the filesystem to a disk image. I went over the docs on the wiki and used google, and I don't know how they get a disk image from the filesystems it creates.
I think you are a bit confused with what OLPC buildrom does. Note thats 'buildrom' not 'buildroot'. OLPC buildrom is based on buildroot but has been customized for our use by Jordan Crouse of AMD.
The output of buildrom is a 1 MiB ROM image called 'linuxbios.rom' that is ready to be programmed into the onboard flash. It contains linuxbios, EC, VSA code and linux kernel payload.
The qemu images are created by Redhat in a totally separate build process and other than the fact that linuxbios.rom is included in the images have little to do with buildrom.