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12 <title>GLEP 37 -- Virtuals Deprecation</title>
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31 <tr class="field"><th class="field-name">GLEP:</th><td class="field-body">37</td>
32 </tr>
33 <tr class="field"><th class="field-name">Title:</th><td class="field-body">Virtuals Deprecation</td>
34 </tr>
35 <tr class="field"><th class="field-name">Version:</th><td class="field-body">1.1</td>
36 </tr>
37 <tr class="field"><th class="field-name">Last-Modified:</th><td class="field-body"><a class="reference" href="http://www.gentoo.org/cgi-bin/viewcvs/xml/htdocs/proj/en/glep/glep-0037.txt?cvsroot=gentoo">2005/04/30 22:35:58</a></td>
38 </tr>
39 <tr class="field"><th class="field-name">Author:</th><td class="field-body">Jason Stubbs &lt;jstubbs&#32;&#97;t&#32;gentoo.org&gt;</td>
40 </tr>
41 <tr class="field"><th class="field-name">Status:</th><td class="field-body">Draft</td>
42 </tr>
43 <tr class="field"><th class="field-name">Type:</th><td class="field-body">Standards Track</td>
44 </tr>
45 <tr class="field"><th class="field-name">Content-Type:</th><td class="field-body"><a class="reference" href="glep-0012.html">text/x-rst</a></td>
46 </tr>
47 <tr class="field"><th class="field-name">Created:</th><td class="field-body">30-April-2005</td>
48 </tr>
49 <tr class="field"><th class="field-name">Post-History:</th><td class="field-body">30-April-2005</td>
50 </tr>
51 </tbody>
52 </table>
53 <hr />
54 <div class="contents topic" id="contents">
55 <p class="topic-title first"><a name="contents">Contents</a></p>
56 <ul class="simple">
57 <li><a class="reference" href="#credits" id="id2" name="id2">Credits</a></li>
58 <li><a class="reference" href="#abstract" id="id3" name="id3">Abstract</a></li>
59 <li><a class="reference" href="#motivation" id="id4" name="id4">Motivation</a></li>
60 <li><a class="reference" href="#specification" id="id5" name="id5">Specification</a><ul>
61 <li><a class="reference" href="#consistency" id="id6" name="id6">Consistency</a></li>
62 <li><a class="reference" href="#overrides" id="id7" name="id7">Overrides</a></li>
63 </ul>
64 </li>
65 <li><a class="reference" href="#rationale" id="id8" name="id8">Rationale</a></li>
66 <li><a class="reference" href="#backwards-compatibility" id="id9" name="id9">Backwards Compatibility</a></li>
67 <li><a class="reference" href="#copyright" id="id10" name="id10">Copyright</a></li>
68 </ul>
69 </div>
70 <div class="section" id="credits">
71 <h1><a class="toc-backref" href="#id2" name="credits">Credits</a></h1>
72 <p>Most ideas in this GLEP came out of discussion with Thomas de Grenier de
73 Latour. Ciaran McCreesh, Brian Harring and Stephen Bennett have also provided
74 help in fleshing out the idea.</p>
75 </div>
76 <div class="section" id="abstract">
77 <h1><a class="toc-backref" href="#id3" name="abstract">Abstract</a></h1>
78 <p>This GLEP covers the pitfalls of the current virtuals system, the benefits of
79 using regular ebuilds to serve the purpose of virtuals and what needs to be
80 supported to make it viable.</p>
81 </div>
82 <div class="section" id="motivation">
83 <h1><a class="toc-backref" href="#id4" name="motivation">Motivation</a></h1>
84 <p>The current virtuals system is decentralized; that is there is no way to find
85 information about a specific virtual other than to scan all packages for what
86 they provide. There is also no way to tell whether an atom is a virtual or
87 not - yes, the &quot;virtual/&quot; prefix could have been used but it isn't which has
88 led to its abuse.</p>
89 <p>What this means is that portage must scan all installed packages for the
90 virtuals they provide, that profiles must provide a default for every single
91 virtual that portage might encounter and that every single atom that portage
92 processes must be checked against the list of virtuals. Needless to say that
93 this causes quite a performance decrease.</p>
94 <p>The current virtuals system also has some other major shortcomings. The most
95 well known case is virtual/jdk and kaffe. Kaffe-1.1.4 implements the Java 1.4
96 API but can not satisfy a package that requires &gt;=virtual/jdk-1.4 because
97 kaffe's versioning scheme differs. (ED: Need to add some more here. ;)</p>
98 </div>
99 <div class="section" id="specification">
100 <h1><a class="toc-backref" href="#id5" name="specification">Specification</a></h1>
101 <p>This GLEP recommends that virtuals become no different to regular packages.
102 Specifically, the standard virtual would include the DESCRIPTION, KEYWORDS,
103 IUSE and RDEPEND metadata. An example would be something like this:</p>
104 <pre class="literal-block">
105 DESCRIPTION=&quot;Java Development Kit 1.4&quot;
106 KEYWORDS=&quot;amd64 hppa ia64 ppc ppc64 sparc x86&quot;
107 RDEPEND=&quot;|| (
108 =dev-java/blackdown-jdk-1.4\*
109 =dev-java/ibm-jdk-bin-1.4*
110 =dev-java/jrockit-jdk-bin-1.4*
111 =dev-java/kaffe-1.1.4*
112 =dev-java/sun-jdk-1.4*
113 )&quot;
114 IUSE=&quot;&quot;
115 </pre>
116 <p>However, there are some issues that have been brought up with doing this.</p>
117 <div class="section" id="consistency">
118 <h2><a class="toc-backref" href="#id6" name="consistency">Consistency</a></h2>
119 <p>Presently, it is very easy to remove packages even if others are dependent
120 on them, which can lead to broken emerges when packages rely on indirect
121 dependencies. For example, if kdelibs is merged bringing in qt and then
122 qt is unmerged, attempting to merge kdebase will likely fail. This becomes
123 a much bigger problem with virtuals as packages because the dependencies
124 are always indirect.</p>
125 <p>The resolution for this issue will be to add full dependency tracking and
126 verification to portage. The details of how it will be done are outside the
127 scope of this GLEP, but essentially this means that portage will need to be
128 forced to unmerge a package that is depended on by another and will also be
129 able to scan and fix any broken dependencies.</p>
130 </div>
131 <div class="section" id="overrides">
132 <h2><a class="toc-backref" href="#id7" name="overrides">Overrides</a></h2>
133 <p>Profiles currently specify the default provider of each virtual and users are
134 able to override these defaults using /etc/portage/profile/virtuals. If
135 virtuals are replaced by regular packages and thus able to have arbitrarily
136 complex DEPENDs, the current method of overriding default virtuals can not
137 be extended to support this.</p>
138 <p>Before looking at a solution, lets look at how the current system works. When
139 portage initializes, it searches installed packages for available virtuals.
140 It then searches profiles and user overrides and adds them to the available
141 providers list and/or changes the order of the providers so that overrides are
142 listed earlier. Portage then expands any virtual atom it finds into an OR
143 list using the order decided upon at initialization.</p>
144 <p>To keep this behaviour available, this GLEP proposes a new file named
145 package.prefer. In its basic form, this is just a list of package names
146 ordered by preference. Portage would use it by reordering the atoms of any
147 OR list it processes to fit the order given by package.prefer. For example,
148 if package.prefer contained &quot;dev-java/kaffe&quot; then:</p>
149 <pre class="literal-block">
150 || (
151 dev-java/blackdown-jdk
152 dev-java/sun-jdk
153 dev-java/kaffe
154 )
155 </pre>
156 <p>would be processed as:</p>
157 <pre class="literal-block">
158 || (
159 dev-java/kaffe
160 dev-java/blackdown-jdk
161 dev-java/sun-jdk
162 )
163 </pre>
164 <p>In its basic form, package.prefer already covers profile and user overrides.
165 However, this GLEP proposes that any type of atom be usable. This will be
166 accomplished by checking for intersections of the atoms in the OR list and
167 atoms in the preferred list. When an intersection is found, both atoms
168 would be specified in a sublist, which would then be treated as a ranged dep.
169 For example, if package.prefer contained &quot;&lt;=dev-java/sun-jdk-1.4&quot; then:</p>
170 <pre class="literal-block">
171 || (
172 &gt;=dev-java/blackdown-jdk-1.3
173 &gt;=dev-java/sun-jdk-1.3
174 )
175 </pre>
176 <p>would be processed as:</p>
177 <pre class="literal-block">
178 || (
179 (
180 &lt;=dev-java/sun-jdk-1.4
181 &gt;=dev-java/sun-jdk-1.3
182 )
183 &gt;=dev-java/blackdown-jdk-1.3
184 &gt;=dev-java/sun-jdk-1.3
185 )
186 </pre>
187 <p>Ranged deps are outside of the scope of this GLEP.</p>
188 </div>
189 </div>
190 <div class="section" id="rationale">
191 <h1><a class="toc-backref" href="#id8" name="rationale">Rationale</a></h1>
192 <p>The number one advantage is that it offers more power to both the user and
193 the developer. Flexibility of virtuals is far greater in this scheme and
194 fulfills requirements that exist already. It also means that the maintainers
195 of profiles will not need to list a default for every virtual. The user
196 benefits by being able to easily gather a list of providers of a virtual as
197 well as their control being extended to allow selection where there is a
198 choice within any package.</p>
199 <p>Portage code also benefits from this scheme as virtuals will no longer
200 require special handling or dual implementations of essentially the same
201 feature, for example USE-based PROVIDEs. This scheme is also much easier to
202 optimize which will benefit the processing of all packages. It also means
203 that any additions to the DEPEND vocabulary become available for use in the
204 definitions of virtuals.</p>
205 </div>
206 <div class="section" id="backwards-compatibility">
207 <h1><a class="toc-backref" href="#id9" name="backwards-compatibility">Backwards Compatibility</a></h1>
208 <p>Compatibility will begin by making treat unknown virtuals like
209 regular packages. When the tree is stripped of PROVIDEs and &quot;virtuals&quot;
210 override files, the only virtuals that these portages will use are those that
211 the user has specified and those gleaned from installed packages. Any
212 unknown virtual will be treated like a regular package and looked for in the
213 tree.</p>
214 <p>The next major version of portage (2.1.0) will support consistency
215 checking. The only remaining issue is that of user overrides. The old
216 method will work even with new style virtuals. The only catch is that
217 complex virtuals - that is virtuals that will install more than one package -
218 may not be overridable satisfactorally.</p>
219 <p>Dropping of support of current style virtuals is planned for the following
220 major version of portage (2.2.0). When the time comes to release it, scripts
221 will be written to create packages from the existing virtuals system as well
222 as to create appropriate package.prefer overrides within the profiles.</p>
223 </div>
224 <div class="section" id="copyright">
225 <h1><a class="toc-backref" href="#id10" name="copyright">Copyright</a></h1>
226 <p>This document has been placed in the public domain.</p>
227 </div>
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