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ref-manual: Added new section on general migration points.

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Fixes [YOCTO #4958]

Added a new section to start the Migration chapter.  This
section will hold general migration issues that are not tied
to a specific release.

(From yocto-docs rev: e78ae7c64ae5fa7e7a5b1f804fb40b5690a4e899)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark
2014-06-16 21:11:02 +03:00
committed by Richard Purdie
parent 7dd70a879d
commit 99caeda1a1
1 changed files with 64 additions and 0 deletions
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documentation/ref-manual/migration.xml
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@@ -11,6 +11,70 @@
release notes for a given release.
</para>
<section id='general-migration-considerations'>
<title>General Migration Considerations</title>
<para>
Some considerations are not tied to a specific Yocto Project
release.
This section presents information you should consider when
migrating to any new Yocto Project release.
<itemizedlist>
<listitem><para><emphasis>Dealing with Customized Recipes</emphasis>:
Issues could arise if you take older recipes that contain
customizations and simply copy them forward expecting them
to work after you migrate to new Yocto Project metadata.
For example, suppose you have a recipe in your layer that is
a customized version of a core recipe copied from the earlier
release, rather than through the use of an append file.
When you migrate to a newer version of Yocto Project, the
metadata (e.g. perhaps an include file used by the recipe)
could have changed in a way that would break the build.
Say, for example, a function is removed from an include file
and the customized recipe tries to call that function.
</para>
<para>You could "forward-port" all your customizations in your
recipe so that everything works for the new release.
However, this is not the optimal solution as you would have
to repeat this process with each new release if changes
occur that give rise to problems.</para>
<para>The better solution (where practical) is to use append
files (<filename>*.bbappend</filename>) to capture any
customizations you want to make to a recipe.
Doing so, isolates your changes from the main recipe making
them much more manageable.
However, sometimes it is not practical to use an append
file.
A good example of this is when introducing a newer or older
version of a recipe in another layer.</para>
</listitem>
<listitem><para><emphasis>Updating Append Files</emphasis>:
Since append files generally only contain your customizations,
they often do not need to be adjusted for new releases.
However, if the <filename>.bbappend</filename> file is
specific to a particular version of the recipe (i.e. its
name does not use the % wildcard) and the version of the
recipe to which it is appending has changed, then you will
at a minimum need to rename the append file to match the
name of the recipe file.
A mismatch between an append file and its corresponding
recipe file (<filename>.bb</filename>) will
trigger an error during parsing.</para>
<para>Depending on the type of customization the append file
applies, other incompatibilities might occur when you
upgrade.
For example, if your append file applies a patch and the
recipe to which it is appending is updated to a newer
version, the patch might no longer apply.
If this is the case and assuming the patch is still needed,
you must modify the patch file so that it does apply.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='moving-to-the-yocto-project-1.3-release'>
<title>Moving to the Yocto Project 1.3 Release</title>