[gentoo-alt] branched prefix chaining

[Viktor Griph]

Hi,

I've just started playing with the prefix-chaining abilities, and I
find it quite useful. However what is the reason for not allowing
multiple read only prefixes in a chained prefix? I'm currently working
with a setup where the policy is that each application should be
installed in it's own prefix, which means that if there should be only
one log chain of prefixes it would possible get very long, whereas if
it were branching it could be kept at a relatively low depth.

I'm tempted to try to change this myself, but before I do I'd like to
get some input on why it was made the way it is. A few things I've
noticed about the chaining prefixes as they are now:
1) the prefixes are linked in with no particular order in portage, but
follows the chain in /etc/profile. I'm not sure if the portage order
makes any difference as I've very little experience with this yet, but
I think that those prefixes should be included in order as well.

My idea on how branching prefixes could be done is similar to how the
chaining prefixes work now, but with a little extra logic required to
not include the same prefix more than once.
I think that changing the current inclusion to a breath first tree
traversal with marking of already visited prefixes should work for the
portage tree. When it comes to the environment I really don't see why
it is made from /etc/profile recursively currently. Wouldn't it make
more sence to have env-update simply source the profile.env of the
parent prefix, and poin it with the env.d at the current level, and
possible include a utility for recursively doing env-update in several
prefix-chains if needed. At least that's the way I think would work
the best when it comes to multiple readonly prefixes. Is there any
reason why this wouldn't work? (Other than the fact that this would be
a depth first inclusion instead of a breath first inclusion as I
suggested for portage, if the order matters.)


Viktor Griph