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Sat Feb 11 21:43:14 2006 UTC (12 years, 11 months ago) by grobian
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Many pieces rewritten, reworded and explained in more detail.
- clarified 'safeness' of CHOST variable
- note on USE-expansion variables and use of variables separate +
- defined semantics env-map file interpreter
- defined requirements for env-map file expressiveness

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27     <div class="document">
28     <table class="rfc2822 field-list" frame="void" rules="none">
29     <col class="field-name" />
30     <col class="field-body" />
31     <tbody valign="top">
32     <tr class="field"><th class="field-name">GLEP:</th><td class="field-body">47</td>
33     </tr>
34     <tr class="field"><th class="field-name">Title:</th><td class="field-body">Creating 'safe' environment variables</td>
35     </tr>
36 grobian 1.2 <tr class="field"><th class="field-name">Version:</th><td class="field-body">1.1</td>
37 grobian 1.1 </tr>
38 grobian 1.2 <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-0047.txt?cvsroot=gentoo">2006/02/09 21:42:57</a></td>
39 grobian 1.1 </tr>
40 grobian 1.2 <tr class="field"><th class="field-name">Author:</th><td class="field-body">Diego Pettenò, Fabian Groffen</td>
41 grobian 1.1 </tr>
42 grobian 1.2 <tr class="field"><th class="field-name">Status:</th><td class="field-body">Draft</td>
43 grobian 1.1 </tr>
44 grobian 1.2 <tr class="field"><th class="field-name">Type:</th><td class="field-body">Standards Track</td>
45 grobian 1.1 </tr>
46     <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>
47     </tr>
48     <tr class="field"><th class="field-name">Created:</th><td class="field-body">14-Oct-2005</td>
49     </tr>
50 grobian 1.2 <tr class="field"><th class="field-name">Post-History:</th><td class="field-body">09-Feb-2006</td>
51 grobian 1.1 </tr>
52     </tbody>
53     </table>
54     <hr />
55     <div class="contents topic" id="contents">
56     <p class="topic-title first"><a name="contents">Contents</a></p>
57     <ul class="simple">
58 grobian 1.2 <li><a class="reference" href="#credits" id="id5" name="id5">Credits</a></li>
59     <li><a class="reference" href="#abstract" id="id6" name="id6">Abstract</a></li>
60     <li><a class="reference" href="#motivation" id="id7" name="id7">Motivation</a></li>
61     <li><a class="reference" href="#rationale" id="id8" name="id8">Rationale</a></li>
62     <li><a class="reference" href="#backwards-compatibility" id="id9" name="id9">Backwards Compatibility</a></li>
63     <li><a class="reference" href="#specification" id="id10" name="id10">Specification</a><ul>
64     <li><a class="reference" href="#variable-assignment" id="id11" name="id11">Variable Assignment</a></li>
65 grobian 1.1 </ul>
66     </li>
67 grobian 1.2 <li><a class="reference" href="#references" id="id12" name="id12">References</a></li>
68     <li><a class="reference" href="#copyright" id="id13" name="id13">Copyright</a></li>
69 grobian 1.1 </ul>
70     </div>
71     <div class="section" id="credits">
72 grobian 1.2 <h1><a class="toc-backref" href="#id5" name="credits">Credits</a></h1>
73 grobian 1.1 <p>The text of this GLEP is a result of a discussion and input of the
74     following persons, in no particular order: Mike Frysinger, Diego
75     Pettenò, Fabian Groffen and Finn Thain.</p>
76     </div>
77     <div class="section" id="abstract">
78 grobian 1.2 <h1><a class="toc-backref" href="#id6" name="abstract">Abstract</a></h1>
79 grobian 1.1 <p>In order for ebuilds and eclasses to be able to make host specific
80     decisions, it is necessary to have a number of environmental variables
81     which allow for such decisions. This GLEP introduces some measures that
82     need to be made to make these decisions 'safe', by making sure the
83     variables the decisions are based on are 'safe'. A small overlap with
84 grobian 1.2 GLEP 22 <a class="footnote-reference" href="#id3" id="id1" name="id1">[1]</a> is being handled in this GLEP where the use of 2-tuple
85 grobian 1.1 keywords are being kept instead of 4-tuple keywords. Additionally, the
86     <tt class="literal"><span class="pre">ELIBC</span></tt>, <tt class="literal"><span class="pre">KERNEL</span></tt> and <tt class="literal"><span class="pre">ARCH</span></tt> get auto filled starting from
87     <tt class="literal"><span class="pre">CHOST</span></tt> and the 2-tuple keyword, instead of solely from they 4-tuple
88     keyword as proposed in GLEP 22.</p>
89     <p>The destiny of the <tt class="literal"><span class="pre">USERLAND</span></tt> variable is out of the scope of this
90     GLEP. Depending on its presence in the tree, it may be decided to set
91     this variable the same way we propose to set <tt class="literal"><span class="pre">ELIBC</span></tt>, <tt class="literal"><span class="pre">KERNEL</span></tt> and
92     <tt class="literal"><span class="pre">ARCH</span></tt>, or alternatively, e.g. via the profiles.</p>
93     </div>
94     <div class="section" id="motivation">
95 grobian 1.2 <h1><a class="toc-backref" href="#id7" name="motivation">Motivation</a></h1>
96 grobian 1.1 <p>The Gentoo/Alt project is in an emerging state to get ready to serve a
97     plethora of 'alternative' configurations such as FreeBSD, NetBSD,
98     DragonflyBSD, GNU/kFreeBSD, Mac OS X, (Open)Darwin, (Open)Solaris and so
99     on. As such, the project is in need for a better grip on the actual
100     host being built on. This information on the host environment is
101     necessary to make proper (automated) decisions on settings that are
102 grobian 1.2 highly dependant on the build environment, such as platform or C-library
103     implementation.</p>
104 grobian 1.1 </div>
105     <div class="section" id="rationale">
106 grobian 1.2 <h1><a class="toc-backref" href="#id8" name="rationale">Rationale</a></h1>
107 grobian 1.1 <p>Gentoo's unique Portage system allows easy installation of applications
108     from source packages. Compiling sources is prone to many environmental
109     settings and availability of certain tools. Only recently the Gentoo
110     for FreeBSD project has started, as second Gentoo project that operates
111     on a foreign host operating system using foreign (non-GNU) C-libraries
112     and userland utilities. Such projects suffer from the current implicit
113     assumption made within Gentoo Portage's ebuilds that there is a single
114     type of operating system, C-libraries and system utilities. In order to
115     enable ebuilds -- and also eclasses -- to be aware of these
116     environmental differences, information regarding it should be supplied.
117     Since decisions based on this information can be vital, it is of high
118     importance that this information can be trusted and the values can be
119     considered 'safe' and correct.</p>
120     </div>
121     <div class="section" id="backwards-compatibility">
122 grobian 1.2 <h1><a class="toc-backref" href="#id9" name="backwards-compatibility">Backwards Compatibility</a></h1>
123 grobian 1.1 <p>The proposed keywording scheme in this GLEP is fully compatible with the
124     current situation of the portage tree, this in contrast to GLEP 22. The
125     variables provided by GLEP 22 can't be extracted from the new keyword,
126     but since GLEP 22-style keywords aren't in the tree at the moment, that
127     is not a problem. The same information can be extracted from the CHOST
128     variable, if necessary. No modifications to ebuilds will have to be
129     made.</p>
130     </div>
131     <div class="section" id="specification">
132 grobian 1.2 <h1><a class="toc-backref" href="#id10" name="specification">Specification</a></h1>
133     <p>Unlike GLEP 22 the currently used keyword scheme is not changed.
134     Instead of proposing a 4-tuple <a class="footnote-reference" href="#id4" id="id2" name="id2">[2]</a> keyword, a 2-tuple keyword is chosen
135     for archs that require them. Archs for which a 1-tuple keyword
136     suffices, can keep that keyword. Since this doesn't change anything to
137     the current situation in the tree, it is considered to be a big
138     advantage over the 4-tuple keyword from GLEP 22. This GLEP is an
139 grobian 1.1 official specification of the syntax of the keyword.</p>
140     <p>Keywords will consist out of two parts separated by a hyphen ('-'). The
141     left hand part of the keyword 2-tuple is the architecture, such as
142     ppc64, sparc and x86. The right hand part indicates the operating
143     system or distribution, such as linux, macos, darwin, obsd, etc. If the
144     right hand part is omitted, it implies the operating system/distribution
145 grobian 1.2 type is Gentoo GNU/Linux. In such case the hyphen is also omitted.
146     Examples of such keywords are ppc-darwin and x86. This is fully
147     compatible with the current use of keywords in the tree.</p>
148 grobian 1.1 <p>The variables <tt class="literal"><span class="pre">ELIBC</span></tt>, <tt class="literal"><span class="pre">KERNEL</span></tt> and <tt class="literal"><span class="pre">ARCH</span></tt> are currently set in
149     the profiles when other than their defaults for a GNU/Linux system.
150     They can as such easily be overridden and defined by the user. To
151     prevent this from happening, the variables should be auto filled by
152 grobian 1.2 Portage itself, based on the <tt class="literal"><span class="pre">CHOST</span></tt> variable. While the <tt class="literal"><span class="pre">CHOST</span></tt>
153     variable can be as easy as the others set by the user, it still is
154     assumed to be 'safe'. This assumption is grounded in the fact that the
155     variable itself is being used in various other places with the same
156     intention, and that an invalid <tt class="literal"><span class="pre">CHOST</span></tt> will cause major malfunctioning
157     of the system. A user that changes the <tt class="literal"><span class="pre">CHOST</span></tt> into something that is
158     not valid for the system, is already warned that this might render the
159     system unusable. Concluding, the 'safeness' of the <tt class="literal"><span class="pre">CHOST</span></tt> variable
160     is based on externally assumed 'safeness', which's discussion falls
161     outside this GLEP.</p>
162     <p>Current USE-expansion of the variables is being maintained, as this
163     results in full backward compatibility. Since the variables themself
164     don't change in what they represent, but only how they are being
165     assigned, there should be no problem in maintaining them. Using
166     USE-expansion, conditional code can be written down in ebuilds, which is
167     not different from any existing methods at all:</p>
168     <pre class="literal-block">
169     ...
170     RDEPEND=&quot;elibc_FreeBSD? ( sys-libs/com_err )&quot;
171     ...
172     src_compile() {
173     ...
174     use elibc_FreeBSD &amp;&amp; myconf=&quot;${myconf} -Dlibc=/usr/lib/libc.a&quot;
175     ...
176     }
177     </pre>
178     <p>Alternatively, the variables <tt class="literal"><span class="pre">ELIBC</span></tt>, <tt class="literal"><span class="pre">KERNEL</span></tt> and <tt class="literal"><span class="pre">ARCH</span></tt>
179     are available in the ebuild evironment and they can be used instead of
180     invoking <tt class="literal"><span class="pre">xxx_Xxxx</span></tt> or in switch statements where they are actually
181     necessary.</p>
182 grobian 1.1 <p>A map file can be used to have the various <tt class="literal"><span class="pre">CHOST</span></tt> values being
183     translated to the correct values for the four variables. This change is
184     invisible for ebuilds and eclasses, but allows to rely on these
185     variables as they are based on a 'safe' value -- the <tt class="literal"><span class="pre">CHOST</span></tt> variable.
186     Ebuilds should not be sensitive to the keyword value, but use the
187     aforementioned four variables instead. They allow specific tests for
188     properties. If this is undesirable, the full <tt class="literal"><span class="pre">CHOST</span></tt> variable can be
189     used to match a complete operating system.</p>
190 grobian 1.2 <div class="section" id="variable-assignment">
191     <h2><a class="toc-backref" href="#id11" name="variable-assignment">Variable Assignment</a></h2>
192 grobian 1.1 <p>The <tt class="literal"><span class="pre">ELIBC</span></tt>, <tt class="literal"><span class="pre">KERNEL</span></tt>, <tt class="literal"><span class="pre">ARCH</span></tt> variables are filled from a profile
193     file. The file can be overlaid, such that the following entries in the
194     map file (on the left of the arrow) will result in the assigned
195     variables on the right hand side of the arrow:</p>
196     <pre class="literal-block">
197     *-*-linux-* -&gt; KERNEL=&quot;linux&quot;
198     *-*-*-gnu -&gt; ELIBC=&quot;glibc&quot;
199     *-*-kfreebsd-gnu -&gt; KERNEL=&quot;FreeBSD&quot; ELIBC=&quot;glibc&quot;
200     *-*-freebsd* -&gt; KERNEL=&quot;FreeBSD&quot; ELIBC=&quot;FreeBSD&quot;
201     *-*-darwin* -&gt; KERNEL=&quot;Darwin&quot; ELIBC=&quot;Darwin&quot;
202     *-*-netbsd* -&gt; KERNEL=&quot;NetBSD&quot; ELIBC=&quot;NetBSD&quot;
203     *-*-solaris* -&gt; KERNEL=&quot;Solaris&quot; ELIBC=&quot;Solaris&quot;
204     </pre>
205 grobian 1.2 <p>A way to achieve this is proposed by Mike Frysinger, which
206 grobian 1.1 suggests to have a env-map file, for instance filled with:</p>
207     <pre class="literal-block">
208     % cat env-map
209     *-linux-* KERNEL=linux
210     *-gnu ELIBC=glibc
211     x86_64-* ARCH=amd64
212     </pre>
213     <p>then the following bash script can be used to set the four variables to
214     their correct values:</p>
215     <pre class="literal-block">
216     % cat readmap
217     #!/bin/bash
219     CBUILD=${CBUILD:-${CHOST=${CHOST:-$1}}}
220     [[ -z ${CHOST} ]] &amp;&amp; echo need chost
222     unset KERNEL ELIBC ARCH
224     while read LINE ; do
225     set -- ${LINE}
226     targ=$1
227     shift
228     [[ ${CBUILD} == ${targ} ]] &amp;&amp; eval $&#64;
229     done &lt; env-map
232     </pre>
233     <p>Given the example env-map file, this script would result in:</p>
234     <pre class="literal-block">
235     % ./readmap x86_64-pc-linux-gnu
236     ARCH=amd64 KERNEL=linux ELIBC=glibc
237     </pre>
238 grobian 1.2 <p>The entries in the <tt class="literal"><span class="pre">env-map</span></tt> file will be evaluated in a forward
239     linear full scan. A side-effect of this exhaustive search is that the
240     variables can be re-assigned if multiple entries match the given
241     <tt class="literal"><span class="pre">CHOST</span></tt>. Because of this, the order of the entries does matter.
242     Because the <tt class="literal"><span class="pre">env-map</span></tt> file size is assumed not to exceed the block
243     size of the file system, the performance penalty of a full scan versus
244     'first-hit-stop technique' is assumed to be minimal.</p>
245     <p>It should be noted, however, that the above bash script is a proof of
246     concept implementation. Since Portage is largerly written in Python, it
247     will be more efficient to write an equivalent of this code in Python
248     also. Coding wise, this is considered to be a non-issue, but the format
249     of the <tt class="literal"><span class="pre">env-map</span></tt> file, and especially its wildcard characters, might
250     not be the best match with Python. For this purpose, the format
251     specification of the <tt class="literal"><span class="pre">env-map</span></tt> file is deferred to the Python
252     implementation, and only the requirements are given here.</p>
253     <p>The <tt class="literal"><span class="pre">env-map</span></tt> file should be capable of encoding a <tt class="literal"><span class="pre">key</span></tt>, <tt class="literal"><span class="pre">value</span></tt>
254     pair, where <tt class="literal"><span class="pre">key</span></tt> is a (regular) expression that matches a
255     chost-string, and <tt class="literal"><span class="pre">value</span></tt> contains at least one, distinct variable
256     assignment for the variables <tt class="literal"><span class="pre">ARCH</span></tt>, <tt class="literal"><span class="pre">KERNEL</span></tt> and <tt class="literal"><span class="pre">ELIBC</span></tt>. The
257     interpreter of the <tt class="literal"><span class="pre">env-map</span></tt> file must scan the file linearly and
258     continue trying to match the <tt class="literal"><span class="pre">key</span></tt>s and assign variables if
259     appropriate until the end of file.</p>
260     <p>Since Portage will use the <tt class="literal"><span class="pre">env-map</span></tt> file, the location of the file is
261     beyond the scope of this GLEP and up to the Portage implementors.</p>
262 grobian 1.1 </div>
263     </div>
264     <div class="section" id="references">
265 grobian 1.2 <h1><a class="toc-backref" href="#id12" name="references">References</a></h1>
266     <table class="footnote" frame="void" id="id3" rules="none">
267 grobian 1.1 <colgroup><col class="label" /><col /></colgroup>
268     <tbody valign="top">
269 grobian 1.2 <tr><td class="label"><a class="fn-backref" href="#id1" name="id3">[1]</a></td><td>GLEP 22, New &quot;keyword&quot; system to incorporate various
270 grobian 1.1 userlands/kernels/archs, Goodyear,
271     (<a class="reference" href="http://glep.gentoo.org/glep-0022.html">http://glep.gentoo.org/glep-0022.html</a>)</td></tr>
272     </tbody>
273     </table>
274 grobian 1.2 <table class="footnote" frame="void" id="id4" rules="none">
275 grobian 1.1 <colgroup><col class="label" /><col /></colgroup>
276     <tbody valign="top">
277 grobian 1.2 <tr><td class="label"><a class="fn-backref" href="#id2" name="id4">[2]</a></td><td>For the purpose of readability, we will refer to 1, 2 and
278 grobian 1.1 4-tuples, even though tuple in itself suggest a field consisting of
279     two values. For clarity: a 1-tuple describes a single value field,
280 grobian 1.2 while a 4-tuple describes a field consisting out of four values.</td></tr>
281 grobian 1.1 </tbody>
282     </table>
283     </div>
284     <div class="section" id="copyright">
285 grobian 1.2 <h1><a class="toc-backref" href="#id13" name="copyright">Copyright</a></h1>
286 grobian 1.1 <p>This document has been placed in the public domain.</p>
287     </div>
288     </div>
290     <hr class="footer" />
291     <div class="footer">
292     <a class="reference" href="glep-0047.txt">View document source</a>.
293 grobian 1.2 Generated on: 2006-02-11 21:38 UTC.
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