PackagingDrafts/ArchSpecificRequires

From FedoraProject

< PackagingDrafts(Difference between revisions)
Jump to: navigation, search
(Add the "when not to use it" section.)
m (Make this more succinct but still informative)
Line 2: Line 2:
  
 
== Rationale ==
 
== Rationale ==
rpm/yum treat a dependency (Requires) on &ldquo;foo&rdquo; as satisfiable by any available foo, regardless of architecture. The consequence of this is that on multilib systems, when the architecture of a dependency has not been specified (even though it is important), yum can install the wrong architecture build of the dependency&mdash;resulting in, most likely, a nonfunctional installation.  This can happen when, for some reason, the correct architecture is not available to yum or (somewhat more importantly) the opposite arch. than the one desired is already installed.
+
<code>rpm</code> and <code>yum</code> treat a dependency on a package (<code>Requires: foo</code>) as being fulfilled by any available package <code>foo</code>, regardless of arch. On multilib systems such as x86_64 there are often two packages with the same name, one for each of the multilib arches.  When yum is asked to satisfy a dependency for that package name it could pull in the package for the wrong arch.  This is most often encountered when the package for the opposite arch is already installed.
  
 
== Making Requires Arch-Specific ==
 
== Making Requires Arch-Specific ==

Revision as of 17:10, 12 May 2010

Warning (medium size).png
This page is a draft only
It is still under construction and content may change. Do not rely on the information on this page.

Contents

Rationale

rpm and yum treat a dependency on a package (Requires: foo) as being fulfilled by any available package foo, regardless of arch. On multilib systems such as x86_64 there are often two packages with the same name, one for each of the multilib arches. When yum is asked to satisfy a dependency for that package name it could pull in the package for the wrong arch. This is most often encountered when the package for the opposite arch is already installed.

Making Requires Arch-Specific

Explicit requires must be made arch-specific by appending the macro %{?_isa} to the package name. For instance,

Requires: foo

becomes

Requires: foo%{?_isa}

...full documentation can be seen at The rpm Wiki page, on Arch requires.

When To Do It

If a dependency really can be satisfied by a build for any architecture, clearly there's no reason to make the dependency architecture-specific. But it does matter in these scenarios:

  • A library in the dependency is dlopen'd.
  • A non-noarch -devel package depends on another -devel package.
  • A non-noarch subpackage's dependency on its main package (Eg. libfoo-devel depends on libfoo).

So, unless you have a very good reason to not make an explicit dependency architecture specific (and if so, be sure to document it in the spec file with a comment), you MUST do it.

When NOT To Do It

Making a general requirement more specific rarely produces significant problems. However there is at least one scenario where you should never use arch. specific requires:

  • A package has a Build-Requires on a specific arch. library (because rpmbuild evaluates the %{_isa} at .src.rpm buildtime, and not at .src.rpm => .arch.rpm build time).