Hi,

If you're following the changes in git a bit more closely you might have
noticed some changes about image creation since the last release. This is
something that deserves a few words of explanation.

The mechanisms to create images that we've had so far have a lot of
shortcomings and I wanted something new for a long time. What I've
committed over the last weeks is far from finished, but I thinks it's a
good start.

So what's wrong with the old mechanism:
- It's not really integrated with the build process, but rather attached at
  the end. As a result dependencies don't work correctly.
- The way things work with the one working directory makes it almost
  impossible to fill an image with anything other than the rootfs.
- With the way these rules live in rules/post, overwriting them in a BSP is
  not really possible. Even adding new ones is not really nice.
- Kconfig is not good at describing the complex possibilities for creating
  images. As a result we have lot's of options most people don't need and
  still can't do everything we want.

So how do the new style images work:
First there is a new package type "image-<pkg>". Like host- or cross-
packages it has a special meaning:
- It has one target, IMAGE_<PKG>_IMAGE that is built with 'ptxdist images'
  when selected.
- It depends on any packages listed in MAGE_<PKG>_PKGS and all files in
  MAGE_<PKG>_FILES.

It's not yet used for any package, but there are the first templates. The
image-tgz template extracts all packages and creates a .tgz from this. With
$(PTX_PACKAGES_INSTALL) as packages list we get the root.tgz we currently
have. But it's now also possible to extract a different set of packages,
e.g. for a rescue system, etc. I have plans to use collectionconfigs for
this, but this is not yet implemented.

The next piece of the puzzle is a tool called genimage. It's basically a
wrapper for all the tools needed to create images. It uses libconfuse for
its config files. The idea is to do all the complex stuff in these config
files and add the basic variables from the platformconfig.
e.g. for an ext2 image we only define the type (ext2/ext3/ext4) and the
size in the platformconfig. If you need special genext2fs or tune2fs
options, the genimage config file can be overwritten in the BSP.
The content for the image is defined by setting MAGE_<PKG>_FILES to a
tarball. The mechanism described above can be used to create it.
The template image-genimage can be used to define such images.

I've attached the files for root.tgz and root.ext2 as an example:
platforms/image-root-tgz.in
rules/image-root-tgz.make
platforms/image-root-ext.in
rules/image-root-ext.make
config/images/ext.config

I've not yet committed these because I'm not sure if I want to immediately
replace the old rules, or have them side by side for some time. So this is
something for after the next release.

Please give it a try and tell me what you think.

Regards,
Michael

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