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1 GLEP: 21
2 Title: User-defined Package Sets
3 Version: $Revision: 1.1 $
4 Last-Modified: $Date: 2004/03/06 23:19:05 $
5 Author: Tal Peer <coredumb@gentoo.org>
6 Status: Draft
7 Type: Standards Track
8 Discussed-To: gentoo-portage-dev@lists.gentoo.org
9 Content-Type: text/x-rst
10 Created: 22-Feb-2004
11 Post-History: 6-Mar-2004
12
13
14 Abstract
15 ========
16
17 In Portage, package sets (formerly known as 'classes' or 'targets')
18 are mere groups of packages, grouped together to allow easier updating
19 and handling of them. Currently it is impossible to define sets further
20 than the two default ones: "system" and "world".
21
22 Motivation
23 ==========
24
25 Over the months, quite a few requests for user-defined sets were
26 made by users and developers, either by posting bugs, messages to
27 mailing lists or on IRC. Usually the response is that this is an
28 awesome idea, but no one ever took the time to actually define it
29 properly and implement it.
30
31 This document offers a specification for the implementation of
32 user-defined sets using configuration files similar to the current
33 world/system sets use.
34
35 Specification
36 =============
37
38 The proposed implementation uses a one file per set approach, meaning
39 each package set is defined in a single file. All set definition files
40 will reside in a directory ``/etc/portage/sets/`` and each set's name
41 will be its file name. Therefore, if one defines a set in
42 /etc/portage/sets/foo-set, the set name will be 'foo-set'. Usual
43 package naming rules [#NAME-RULES]_ also apply to sets.
44
45 As it is impossible to create two or more files with identical names
46 in the same directory, a theoretic conflict between two different sets
47 sharing the same name is impossible. However, users may define a
48 package set whose name conflicts with one more or packages (for ambiguity
49 resolution, see below).
50
51 Syntax for the package list file is the same as the world file syntax,
52 as described in the Portage manpage [#PORTAGE-MANPAGE]_, with one
53 addition: sets may not be 'inherited' by other sets, only packages may
54 be listed. There is no limitation to the number of packages in a set
55 or to the number of sets a package may belong to.
56
57 Using User-defined Sets With Emerge
58 --------------------------------------
59
60 The user-defined sets will be available either directly or using
61 the --package-set option, As in::
62
63 # Basically the same:
64 emerge foo-set
65 emerge --package-set foo-set
66
67 The --package-set option is introduced to bypass ambiguities, as
68 illustrated in the next example::
69
70 emerge foo # Where foo is both a set and a one or more
71 # existing packages. This will cause emerge to show
72 # the ambiguity, ask us to be more
73 # specific, and stop.
74
75 emerge --package-set foo # So we specify that what we actually
76 # meant was the package set.
77
78 emerge cat-bar/foo # Or we specify the exact package name.
79
80 When running emerge with the --pretend option, sets will be
81 expanded to the packages they are comprised off in the output, as with
82 the current system-defined sets.
83
84 Only one set may be passed to portage at time, and sets can not
85 be mixed with ordinary packages. Thus, the following snippets are
86 all invalid and will result in an error (assuming ``foo-set`` and
87 ``bar-set`` are defined as sets)::
88
89 emerge foo-set glibc
90 emerge bar-set system
91 emerge world foo-set gcc
92
93 Compatibility With Other Portage Features
94 -----------------------------------------
95
96 * Dependencies:
97 Package sets (both system-defined and user-defined) may not be
98 depended on by ordinary packages and eclasses.
99
100 * package.mask:
101 Masking a package set through the ``package.mask`` file is forbidden.
102 In order to 'mask' a package set, one should move it away from the
103 sets directory.
104
105 * package.use:
106 USE flags may not be defined for sets in the ``package.use`` file.
107
108 Implementation
109 ==============
110
111 The implementation of the package sets concept in Portage should be
112 mostly done in portage.py, and only the interface parts should be
113 added to emerge itself, to keep the separation between interface and
114 logic.
115
116 The amount of work needed for implementation is not trivial, but not
117 huge either.
118
119 Rationale
120 =========
121
122 The one file per set approach makes it easy to list the sets which are
123 defined on a system by just listing the ``/etc/portage/sets``
124 directory contents. Additionally, it makes the set lookup process more
125 efficient as it only requires to check if a file exists.
126
127 I chose the --package-set option over the --set option for explicitly
128 telling portage to emerge a set mostly because --set implies setting
129 an environment variable, or such.
130
131 Allowing sets' USE flags to be manipulated through the ``package.use``
132 file would have done more harm than good, for several reasons:
133
134 - If a USE flag is turned on (i.e. 'foo') for a set and the same USE
135 flag is turned off (i.e. '-foo'), for a package which is part of
136 the set, it is unclear which setting should take precedence.
137
138 - Similarly, if a USE flag is turned on for a set and the same USE flag
139 is turned off for a set that is a subset of the original set, it is
140 unclear which setting should take precedence.
141
142 - If a USE flag is defined (either off or on) for a set and a package
143 that belongs in the set is to be emerged, it is unclear whether the
144 USE flag should be defined when emerging the package in question.
145
146 Therefore, I have decided it would be better to disallow setting USE
147 flags for sets.
148
149 Backwards Compatibility
150 =======================
151
152 Backwards compatibility with the current situation, in which only two
153 system-defined sets exist can be kept in one of two ways:
154
155 1. Leaving the situation as is - the 'world' and 'system' sets are
156 hard-coded in Portage.
157 2. Distributing default 'system' and 'world' files under the
158 ``/etc/portage/sets/`` directory.
159
160 Other than that, there are no other backwards compatibility concerns
161 involved.
162
163 References
164 ==========
165
166 .. [#NAME-RULES] Gentoo Linux Development Policy - Ebuild Policy
167 (http://www.gentoo.org/doc/en/policy.xml#doc_chap3)
168
169 .. [#PORTAGE-MANPAGE]
170 http://www.gentoo.org/cgi-bin/viewcvs.cgi/portage/man/portage.5?root=gentoo-src
171
172 Copyright
173 =========
174
175 This document has been placed in the public domain.

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