[U-Boot] SWUpdate - U-Boot environment library dependency

[Andreas Reichel <andreas.reichel.ext@siemens.com>]

Hi all,

as Stefano Babic was so friendly and pointed out a few things already,
we come the following problematic points:

For SWupdate to access U-Boot's environment, it uses code from U-Boot.
Before 2015, fw_env.c was copied - hence out of version control,
afterwards and since then, a lib.a produced by U-Boot has been used
and renamed to libubootenv.a to link against.

However, this approach creates several difficulties:

* Distros like Debian cannot provide a devel package for SWUpdate like
  u-boot-dev, since U-Boot has its default environment code compiled
  board-dependently and Debian needed it board-independent.
  If a board-independent libubootenv.a was provided without
  a specific default environment, the first update process would destroy
  the U-Boot environment if it had had bad CRC before.
  (Thanks Stefano for this good point).

* If we have a board with U-Boot already preinstalled and want to
  compile SWUpdate for it, we need the sources of this very U-Boot to
  get the propper lib. For example in a debian-like build system we had to
  compile U-Boot again, although it is already installed since we lack
  a dev package.

* U-Boot does not provide any default means to install a development
  library. Thus anything we modify on-top might break with the next
  version.

First proposal by Stefano and me would be to somehow split the default
environment from the library to have a board-independent component and
board specific data that is passed to U-Boot and SWUpdate somehow.

Goal is to factor out U-Boot environment support for other software like
SWUpdate and not patching and hacking like its the case with recipes as in
openembedded atm.

Thanks,
Andreas

-- 
Andreas Reichel
Dipl.-Phys. (Univ.)
Software Consultant

Andreas.Reichel at tngtech.com, +49-174-3180074
TNG Technology Consulting GmbH, Betastr. 13a, 85774 Unterfoehring
Geschaeftsfuehrer: Henrik Klagges, Dr. Robert Dahlke, Gerhard Mueller
Sitz: Unterfoehring * Amtsgericht Muenchen * HRB 135082