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1 g2boojum 1.1 GLEP: 9
2     Title: Gentoo Package Update System
3 g2boojum 1.3 Version: $Revision: 1.2 $
4     Last-Modified: $Date: 2003/07/25 22:32:20 $
5 g2boojum 1.1 Author: John J. Whitney <jjw@linuxmail.org>
6 g2boojum 1.3 Status: deferred
7 g2boojum 1.1 Type: Standards Track
8     Content-Type: text/x-rst
9     Created: 19-Jul-2003
10     Post-History: 25-Jul-2003
13     Abstract
14     ========
16     This document proposes an official package updating system for Gentoo Linux.
17     The Deltup project has been developed for this purpose. [#DELTUP]_
19     As packages grow larger the amount of redundant data keeps increasing. Updating
20     existing tarballs by patching is the natural way to handle source updates.
22     Motivation
23     ==========
25     This system will reduce mirror loads (potentially mirror size as well) and
26     significantly speed up downloads, making Gentoo much more attractive for users
27     with low-bandwidth connections.
29     Server Implementation
30     =====================
32     I propose that the patches be put onto the Gentoo Mirrors and stored in a new
33     directory called "patchfiles" which could be placed beside "distfiles".
35     It would be advantageous to have a list of available patches within the portage
36     tree so that it can be updated during "emerge sync". A file named "dtu.list"
37     can be created and placed in $PORTDIR/profiles.
39     If a machine can be set up to generate patches it should contain a local mirror
40     of distfiles which it can monitor for added packages. When a package is added
41     to distfiles the machine can try to determine the previous tarball so a patch
42     can be made and placed in the patchfiles dir. In addition, special-case patches
43     can be added manually.
45     The dtu.list file will be maintained by a special script. Whenever patches
46     are added or removed to the patchfiles dir, the script will make necessary
47     additions/removals in dtu.list. This will be done with minimal changes in the
48     file so it can be synchronized efficiently.
50     Client Implementation
51     =====================
53     The system will be optional for users and can be enabled by making portage
54     invoke efetch through the FETCHCOMMAND environment variable [#TINYHOWTO]_.
56     When a package fetch is requested, the efetch/fetchcommand scripts (part of
57     Deltup) will scan the dtu.list file for updates and try downloading and applying
58     them if they exist, or fall back to a full package download if they don't or if
59     the patching process fails.
61     Rationale
62     =========
63     The most controversial feature has been the addition of dtu.list to the portage
64     tree, so in this section I will list the reasons I support it.
66     - Flexibility. Without it, there must be a standard naming scheme which we
67     would be stuck with once the system is in place. Changing the system would
68     require serious compatibility breaks. With the dtu.list file we can change
69     the naming scheme easily without problems, or even have several different
70     naming schemes.
72     - Features. Without patch information detecting different upgrade paths would
73     be impossible. Split package patching would also be impossible. If the info
74     is available we can use it to find the quickest upgrade path, like jumping
75     from a .0 release, or even disable certain patches if there are problems with
76     them.
78     - It would be impossible to know which packages to upgrade from in some cases,
79     including renamed packages.
81     - Knowing which patches are available will eliminate the overhead of attempting
82     to download patches which don't exist.
84     The dtu.list file will contain several hundred kilobytes of data. That has
85     caused some concern over how efficiently it can be rsynced. To address these
86     concerns the file's format will be plaintext and care has been taken to
87     minimize the number of changes as removals/additions are made.
89     Backwards Compatibility
90     =======================
92     There are no backwards compatibility issues since Deltup can generate correct
93     package MD5sums.
96     Conclusion
97     ==========
99     I suggest we start with a scaled-down implementation and provide more as the
100     demand increases. All of the necesary code is already written and working in
101     non-official tests.
103     References
104     ==========
106     .. [#DELTUP] http://sourceforge.net/projects/deltup
107     .. [#PATCHES] ftp://sunsite.dk/projects/deltup/patchfiles
108     .. [#TINYHOWTO] Tiny Deltup HOWTO
109     (http://www.thedoh.com/linux/HOWTO/deltup)
111     Copyright
112     =========
114     This document has been placed in the public domain.

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