Gentoo Archives: gentoo-dev

From: Ciaran McCreesh <ciaran.mccreesh@××××××××××.com>
To: gentoo-dev@l.g.o
Subject: Re: [gentoo-dev] The fun of being a PDEPEND
Date: Thu, 11 Aug 2011 05:41:05
In Reply to: [gentoo-dev] The fun of being a PDEPEND by Fabio Erculiani
1 On Wed, 10 Aug 2011 23:14:22 +0200
2 Fabio Erculiani <lxnay@g.o> wrote:
3 > I've intermittently spent my last two days trying to figure out a
4 > weird bug on Entropy dependency resolution algorithm (which is
5 > actually just a simple topological sorting out of a digraph)
7 You can't use a naive topological sort to do dependency resolution.
8 RDEPEND-RDEPEND cycles are legal and common.
10 > Entropy always tried to strictly follow PMS (bugs apart). Given the
11 > same document, about PDEPEND it says something like this: there is no
12 > guarantee that a PDEPEND gets installed at a certain, specified point
13 > during the schedule, if not specifically listed as RDEPEND by some
14 > package.
15 > The problem here is that Portage enforces the same rule by trying to
16 > schedule the PDEPEND "as soon as possible", which leads ebuild writers
17 > to think to have gotten the deps order right.
18 > In simple words, it doesn't seem that Portage itself follows PMS or
19 > PMS is detailed enough.
21 Portage *tries*. There's no guarantee that it will succeed. If you need
22 a particular ordering, you can't use PDEPEND. If something's there only
23 because of a PDEPEND, there are absolutely no guarantees whatsoever as
24 to when it will get resolved; PDEPEND imposes absolutely no reliable
25 conditions upon ordering. Any ebuild assuming otherwise should be fixed.
27 Purely as a quality of implementation issue, scheduling a PDEPEND
28 reasonably soon after (or even before) the package requiring it may be
29 a good idea, simply because users may get confused if when they try to
30 install a bunch of things and one of those things gets installed long
31 before related packages. But you can't rely upon that happening.
33 (Incidentally, one could also argue that package manglers should always
34 try to come up with the most perverse legal ordering possible for any
35 situation. That way bugs will be identified much more quickly. Part of
36 the problem with Portage is that it has so many tricks and so little
37 error checking that broken things quite often appear to work.)
39 --
40 Ciaran McCreesh


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Subject Author
Re: [gentoo-dev] The fun of being a PDEPEND Fabio Erculiani <lxnay@g.o>