dev-manual: First pass at poky-tiny section.
(From yocto-docs rev: fbf31831e9cf3fc088c12a2867fa56e2004d624b) 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
Richard Purdie
parent
9f1b358400
commit
ac15c28151
|
|
@ -2013,7 +2013,7 @@
|
|||
</para>
|
||||
</section>
|
||||
|
||||
<section id="creating-your-own-distribution">
|
||||
<section id='creating-your-own-distribution'>
|
||||
<title>Creating Your Own Distribution</title>
|
||||
|
||||
<para>
|
||||
|
|
@ -2127,6 +2127,154 @@
|
|||
</para>
|
||||
</section>
|
||||
|
||||
<section id='building-a-tiny-system'>
|
||||
<title>Building a Tiny System</title>
|
||||
|
||||
<literallayout class='monospaced'>
|
||||
* Introduction that tells what, why, and benefits
|
||||
* Overview of the process
|
||||
* Cutting back on the kernel size
|
||||
* Cutting back on the filesystem (libc and busybox)
|
||||
</literallayout>
|
||||
|
||||
<para>
|
||||
Very small distributions have some significant advantages such
|
||||
requiring less on-die memory (cheaper), better performance through
|
||||
efficient cache usage, lower power requirements due to less
|
||||
memory, faster boot times, and reduced development overhead.
|
||||
Some real-world examples where a very small distribution gives
|
||||
you distinct advantages are digital cameras, medical devices,
|
||||
small headless systems, and partitioned flash.
|
||||
You can use the Yocto Project to create very small distribution.
|
||||
</para>
|
||||
|
||||
<para>
|
||||
This section presents information that shows you how you can
|
||||
trim your distribution to even smaller sizes than the
|
||||
8 Mbytes <filename>poky-tiny</filename> distribution that
|
||||
can be built out-of-the-box using the Yocto Project.
|
||||
</para>
|
||||
|
||||
<section id='tiny-system-overview'>
|
||||
<title>Overview</title>
|
||||
|
||||
<para>
|
||||
The following list presents the overall steps you need to
|
||||
consider and perform to create very small systems that
|
||||
have a kernel and root filesystem under 4 Mbytes, boot to the
|
||||
shell in under two seconds, maintain <filename>ipv4</filename>
|
||||
functionality, and avoid an initial RAM disk:
|
||||
<itemizedlist>
|
||||
<listitem><para>Determine your goals and guiding
|
||||
principles.</para></listitem>
|
||||
<listitem><para>Know what you are starting with.
|
||||
</para></listitem>
|
||||
<listitem><para>Trim the root filesystem.
|
||||
</para></listitem>
|
||||
<listitem><para>Trim the kernel</para></listitem>
|
||||
</itemizedlist>
|
||||
</para>
|
||||
</section>
|
||||
|
||||
<section id='goals-and-guiding-principles'>
|
||||
<title>Goals and Guiding Principles</title>
|
||||
|
||||
<para>
|
||||
Before you can reach your destination, you need to know
|
||||
where you are going.
|
||||
Here is an example list that you can use as a guide when
|
||||
creating very small distributions:
|
||||
<itemizedlist>
|
||||
<listitem><para>Determine how much space you need
|
||||
(e.g. a kernel that is 1 Mbyte or less and
|
||||
a root filesystem that is 3 Mbytes or less).
|
||||
</para></listitem>
|
||||
<listitem><para>Find the areas that are currently
|
||||
taking 90% of the space and concentrate on that
|
||||
for trimming.
|
||||
</para></listitem>
|
||||
<listitem><para>Do not create any difficult "hacks"
|
||||
to achieve your goals.</para></listitem>
|
||||
<listitem><para>Leverage of the device-specific
|
||||
options.</para></listitem>
|
||||
<listitem><para>Do your work in a separate layer
|
||||
to keep changes isolated.
|
||||
For information on how to create layers, see
|
||||
the "<link linkend='understanding-and-creating-layers'>Understanding and Creating Layers</link>" section.
|
||||
</para></listitem>
|
||||
</itemizedlist>
|
||||
</para>
|
||||
</section>
|
||||
|
||||
<section id='know-what-you-are-starting-with'>
|
||||
<title>Know What You Are Starting With</title>
|
||||
|
||||
<para>
|
||||
You will need to have an image from which you can
|
||||
work.
|
||||
The Yocto Project ships with the ability to create a
|
||||
<filename>poky-tiny</filename> distribution.
|
||||
This distribution consists of a small, sub-8 Mbyte kernel
|
||||
that works with two shipped Board Support Packages (BSPs):
|
||||
Fish River Island 2 and QEMU.
|
||||
You can use this distribution as a starting point and trim
|
||||
down from there.
|
||||
If you need to build out the <filename>poky-tiny</filename>
|
||||
distribution, see the
|
||||
"<link linkend='creating-your-own-distribution'>Creating Your Own Distribution</link>"
|
||||
section.
|
||||
</para>
|
||||
|
||||
<para>
|
||||
Understanding some memory concepts will help you reduce the
|
||||
system size.
|
||||
Memory consists of static, dynamic, and temporary memory.
|
||||
Static memory is the TEXT, DATA, and BSS sections.
|
||||
Dynamic memory contains memory that is allocate at runtime,
|
||||
stacks, hashtables, and so forth.
|
||||
Temporary memory is decompression and
|
||||
<filename>__init__</filename>
|
||||
</para>
|
||||
|
||||
<para>
|
||||
To help you see where you currently are with kernel and root
|
||||
filesystem sizes, you can use some tools found in the
|
||||
<link linkend='source-directory'>Source Directory</link> in
|
||||
the <filename>scripts</filename> directory:
|
||||
<itemizedlist>
|
||||
<listitem><para><filename>ksize.py</filename>: Reports
|
||||
the size of the kernel files.</para></listitem>
|
||||
<listitem><para><filename>dirsize.py</filename>: Reports
|
||||
the size of the root filesystem.</para></listitem>
|
||||
</itemizedlist>
|
||||
This next tool and command helps you organized configuration
|
||||
fragments and view file dependencies in a human-readable form:
|
||||
<itemizedlist>
|
||||
<listitem><para><filename>merge_config.sh</filename>:
|
||||
Merges individual configuration fragments.
|
||||
For more information on configuration fragments, see
|
||||
the
|
||||
"<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#generating-configuration-files'>Generating Configuration Files</ulink>"
|
||||
section of the Yocto Project Linux Kernel Development
|
||||
Manual and the "<link linkend='creating-config-fragments'>Creating Configuration Fragments</link>"
|
||||
section in this manual.</para></listitem>
|
||||
<listitem><para><filename>bitbake -u depexp -g core-image-*</filename>:
|
||||
Using the BitBake command with these options brings up
|
||||
a Dependency Explorer from which you can view file
|
||||
dependencies.
|
||||
Understanding these dependencies allows you to make
|
||||
sane decisions when cutting out various pieces of the
|
||||
kernel and root filesystem.</para></listitem>
|
||||
</itemizedlist>
|
||||
</para>
|
||||
</section>
|
||||
|
||||
<section id='trim-the-root-filesystem'>
|
||||
<title>Trim the Root Filesystem</title>
|
||||
|
||||
</section>
|
||||
</section>
|
||||
|
||||
<section id='working-with-packages'>
|
||||
<title>Working with Packages</title>
|
||||
|
||||
|
|
|
|||
Loading…
Reference in New Issue