Difference between pages "Package:Eselect (OpenGL)" and "New EAPI specification"

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{{Ebuild
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This page explains the need for a new EAPI specification and the guidelines for it.
|Summary=A Gentoo/Funtoo utility that allows the active OpenGL implementation on a system to be switched between a variety of installed options.
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|CatPkg=app-admin/eselect-opengl
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|Maintainer=
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}}
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== Introduction ==
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Eselect (OpenGL) (also called <tt>eselect-opengl</tt>) is a module for [[Package:Eselect|Eselect]] that allows the OpenGL implementation on a Funtoo Linux or Gentoo Linux system to be switched between a variety of installed OpenGL implementations. It functions by creating an <tt>env.d</tt> file at <tt>/etc/env.d/03opengl</tt> which contains OpenGL settings, as well as managing symbolic links to OpenGL libraries and headers.
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== Current specification ==
  
=== Sample env.d File ===
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The ebuild format is currently covered by the [https://wiki.gentoo.org/wiki/Project:PMS Package Manager Specification]. This is an Exherbo-originated project that is maintained in Gentoo-Exherbo cooperation. Sadly, the current spec shows a number of issues.
  
A sample <tt>env.d</tt> file for a multilib system with xorg-x11 OpenGL implementation may look like this:
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Most notably, the current organization and wording often proves cumbersome for developers. It is easy to mis-understand some of the sections of the specification. Sometimes it is necessary to read multiple (non-cross-referenced) sections to understand the actual status.
  
{{file|name=/etc/env.d/03opengl|desc=An example env.d file for eselect-opengl|body=
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The specification often misses rationale, historical or implementation notes. It also has been changed retroactively a few times without a proper behavior change note.
# Configuration file for eselect
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# This file has been automatically generated.
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LDPATH="/usr/lib32/opengl/xorg-x11/lib:/usr/lib64/opengl/xorg-x11/lib"
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OPENGL_PROFILE="xorg-x11"
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}}
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== Implementation ==
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The specification offers only limited description of ebuild, profile and repository format. It lacks any details on multi-repository systems, installed package database (vardb), md5-cache. The Manifest files are specified only via reference to [https://wiki.gentoo.org/wiki/GLEP:44 GLEP-44] which also doesn't cover most recent changes in Manifest format.
 
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Eselect-opengl is implemented as a single bash-based [[Package:Eselect|Eselect]] module approximately 10K in size, installed at <tt>/usr/share/eselect/modules/opengl.eselect</tt>. One interfaces with this module via the main <tt>eselect</tt> command:
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<console>
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# ##i##eselect opengl help
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Manage the OpenGL implementation used by your system
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Usage: eselect opengl <action> <options>
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##g##Standard actions:
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  help                      Display help text
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  usage                    Display usage information
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  version                  Display version information
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##g##Extra actions:
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  list                      List the available OpenGL implementations.
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  set <target>              Select the OpenGL implementation.
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    <target>                  The profile to activate
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    --use-old                If an implementation is already set, use that one instead
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    --prefix=<val>            Set the source prefix (default: /usr)
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    --dst-prefix=<val>        Set the destination prefix (default: /usr)
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    --ignore-missing          Ignore missing files when setting a new implementation
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  show                      Print the current OpenGL implementation.
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</console>
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== What is Switched ==
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Using <tt>eselect opengl set</tt> causes the following symbolic links to be updated to point to the files corresponding to the OpenGL implementation that you chose:
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* ''Libraries'' (32-bit and 64-bit):
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** <tt>/usr/lib(64)/libGL.so.*</tt>
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** <tt>/usr/lib(64)/libEGL.so.*</tt>
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** <tt>/usr/lib/(32|64|)/libGLESv1.so.*</tt>
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** <tt>/usr/lib/(32|64|)/libGLESv2.so.*</tt>
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* ''C Headers'':
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** <tt>/usr/include/GL/*</tt>
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** <tt>/usr/include/EGL/*</tt>
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** <tt>/usr/include/KHR/*</tt>
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* <tt>/usr/lib(64|)/xorg/modules/extensions/libglx.so</tt>
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The symbolic links point to an installed OpenGL implementation, stored inside <tt>/usr/lib(32|64|)/opengl/(implementation-name)</tt>. These files are structured as follows:
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* <tt>/usr/lib/opengl/(implementation-name)/lib</tt>
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* <tt>/usr/lib/opengl/(implementation-name)/include/(GL|EGL|KHR)</tt>
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* <tt>/usr/lib/opengl/(implementation-name)/extensions/libglx.so</tt>
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On multilib systems, ebuilds that provide an OpenGL implementation install 32-bit libraries in <tt>/usr/lib32/opengl/(implementation name)/lib</tt> and 64-bit libraries in <tt>/usr/lib64/opengl/(implementation name)/lib</tt>.
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== Criticisms ==
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=== Violation of Build Consistency ===
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As documented in {{Bug|FL-1309}}, sometimes packages fail to merge when the "wrong" eselect opengl implementation is selected. This violates Portage's ability to consistently build a package from source, assuming all its dependencies are satisfied. This could be classified as a design bug -- eselect-opengl is functioning as intended, but its underlying theory of operation is not correct.
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== eselect-opengl-1.3* experiment ==
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=== Introduction ===
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As a result of {{Bug|FL-1309}}, an experimental solution was implemented in eselect-opengl-1.3*. With this version, all packages are built unconditionally against xorg-x11 OpenGL implementation and the other implementations are used only in runtime.
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The rationale for this design change is that:
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# There should be a consistent and repeatable build/linking process for all OpenGL applications.
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# AMD and NVIDIA implementations of OpenGL are designed to be more of a "drop-in" runtime replacement for xorg-x11, rather than a standalone replacement for xorg-x11, and thus appear to exhibit more build-time bugs.
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=== Implementation ===
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The new version of eselect-opengl switched two files:
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* an env.d file <tt>000opengl</tt> specifying <tt>LDPATH</tt> for the run-time implementation override,
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* an xorg.conf.d file overriding the ModulePath for custom glx xorg modules.
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The env.d file has the same contents as the original one, except that the name was changed to ensure that the additional linker paths are added before the system paths where xorg-x11 libraries are installed.
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The xorg.conf.d sets ModulePaths for non-xorg module replacements (such as the nvidia glx module), if necessary.
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=== Issues ===
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The widespread testing of eselect-opengl-1.3* has proven some issues with the new design:
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# xorg-server is unable to handle multiple occurences of <tt>Files</tt> section gracefully. Therefore, eselect-opengl's generated xorg.conf.d file collides with many user-defined configurations.
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# There are rumors of arm mali's prioprietary OpenGL implementations requiring applications to be built against its own GLES headers.
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{{EbuildFooter}}
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Revision as of 11:34, January 18, 2015

This page explains the need for a new EAPI specification and the guidelines for it.

Current specification

The ebuild format is currently covered by the Package Manager Specification. This is an Exherbo-originated project that is maintained in Gentoo-Exherbo cooperation. Sadly, the current spec shows a number of issues.

Most notably, the current organization and wording often proves cumbersome for developers. It is easy to mis-understand some of the sections of the specification. Sometimes it is necessary to read multiple (non-cross-referenced) sections to understand the actual status.

The specification often misses rationale, historical or implementation notes. It also has been changed retroactively a few times without a proper behavior change note.

The specification offers only limited description of ebuild, profile and repository format. It lacks any details on multi-repository systems, installed package database (vardb), md5-cache. The Manifest files are specified only via reference to GLEP-44 which also doesn't cover most recent changes in Manifest format.