[gentoo-portage-dev] prefix portage chaining

[Markus Duft]

Hey guys :)

Just wanted to stop by and get some opinions on a patch i wrote for the
prefix branch.

i'll try and explain what i want in the first place: i'm porting things
to native windows. since windows isn't too cooperative, i'm unable to
merge most things (and with other things, i simply don't want to), and
thus i need to take those things from somewhere else (more or less the
complete @system). I _am_ able to build all those things for interix
(which is the host system in the windows case). So what i want is a
setup of two prefix instances with a certain relation to each other: the
native windows prefix should be able to recognize installed packages
from the other instance, and resolve dependencies by eventually using
the other .../var/db/...

This could be (and is) quite usefull for all other platforms too. For
exmaple i could use prefix chaining on a linux box. I could create a
prefix containing a base system, and then for testing of
i-don't-know-whatever, i could create another small prefix inheriting
all installed packages from the other one. this way new prefixes can
stay very slim, but still the "parent" prefix is not altered on merges.

one issue not handled by the current patch is, that prefixes can have
different CHOST/ARCH/... (which is the case with x86-interix and
x86-winnt for example).

another thing is, that i plan to add some output in the merge list,
telling the user, which packages have been readonly-resolved from
another portage instance. right now the dependency is treated as if it
didn't exist.

all together, i'm pretty sure i did the one or the other forbidden thing
in my patch, but that's why i'm asking the guys-who-know :) it was hard
enough to read the portage source and get where i am, so i'm happy with
the result ;)

Waiting for comments, suggestions, etc.

Thanks in advance,
Cheers, Markus