[Yum] creating build order from rpm spec files

[Alfred Landrum]

>When I worked on this problem before I found that circular build deps
>and not-quite-specified-enough build deps  - especially when pkgs
>changed names or changed where the provider lived were very common and
>wrought havoc over any ordering I tried to do.
This utility is part of a prototype for a internal build system here at
Riverbed; since most of the code we build is developed in-house, we'll
have more options for handling circular deps when they come up - like
talking to the handful of development teams about changing their deps -
than a distro would.  Since we also build packages from the outside world,
though, we will have to handle them.  We'll identify some (hopefully
small) set of binary rpms that are needed to seed a base repository, and
then use that to pull from as needed.  From what I understand, that's how
Koji works as well.

>It worked for small sets of pkgs - but if I passed in something like a
>big stack of gnome pkgs it returned unreliable results.
Yeah - when I first started working on this, I grabbed a handful of
specfiles (m4, texinfo, and a few others) and was quite surprised at the
circular dependencies I found, even on what I thought would have been
small, standalone packages.  It's been an education reading about the
Fedora build process, especially that the mass rebuilds usually happen w/o
any dependency order.