Gentoo Archives: gentoo-dev

From: Ciaran McCreesh <ciaran.mccreesh@×××××××××××××.uk>
To: gentoo-dev@l.g.o
Subject: [gentoo-dev] Phase invariancy and exclusivity requirements
Date: Fri, 09 Nov 2007 22:43:18
1 What specifically are the phase invariancy and exclusivity requirements
2 for ebuilds? Currently PMS doesn't have anything to say about this;
3 clearly it needs to, since existing ebuilds fairly obviously do have
4 invariancy and exclusivity requirements.
6 Note that we're only discussing package manager related things here. If
7 the user manually upgrades libc / switches compiler / whatever whilst a
8 package manager is busy, there's nothing we can do.
10 Is the following set sufficient? Is the following set the least
11 restrictive correct solution?
13 * No syncing whilst anything else is going on.
15 * Variancy is any package manager action that modifies ROOT in a way
16 that isn't merely a simple addition of something that doesn't alter
17 other packages. This includes any non-default pkg_(pre|post)(inst|rm),
18 merging to ROOT and unmerging from ROOT.
20 * As an exception, changes to DISTDIR do not count as variancy. [1]
22 * pkg_setup does not introduce variancy. [2]
24 * Any pkg_ function that is not the default must be run exclusively. [3]
26 * No variancy may be introduced at any point between a package's
27 pkg_setup run up to the point that it is merged, except for any
28 variancy introduced by that package.
30 * There must be no variancy between a package's pkg_setup and a
31 package's pkg_postinst, except for any variancy introduced by that
32 package.
34 [1]: This allows background fetching. It means DISTDIR can be added to
35 by other processes at any point. It doesn't mean that a package's ${A}
36 can be nuked randomly.
38 [2]: Because otherwise a failed install would result in a damaged
39 system, and an install would temporarily damage a system until
40 complete. Adding a user isn't variancy by our definition, since when
41 combined with the exclusivity requirements it doesn't alter any part of
42 other packages.
44 [3]: Weird stuff happens if, for example, two package's pkg_postinsts
45 are run at the same time, since ebuilds do no ROOT locking. I'm fairly
46 sure the exclusivity needs to be shared amongst all pkg_ phases (think
47 package one doing a useradd fred in pkg_setup and package two doing it
48 in pkg_postinst).
50 --
51 Ciaran McCreesh


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Re: [gentoo-dev] Phase invariancy and exclusivity requirements Ciaran McCreesh <ciaran.mccreesh@×××××××××××××.uk>