mirrors/poky
1
0
Fork 0
mirror of https://git.yoctoproject.org/poky synced 2026-05-31 12:49:46 +00:00
Code Issues Projects Releases Wiki Activity

dev-manual, ref-manual: Created new section on initramfs

Browse Source 
Fixes [YOCTO #7096]

We did not document how to create an initramfs image to be included
with a kernel build.  Various variables sort of inferred the
knowledge.  I created a new section in the "Common Tasks" section
of the dev-manual that describes how to create an initramfs image.

Also, I updated the kernel.bbclass reference section to point back
to the new "how-to" section.

Finally, I also created a bunch of cross-reference links from various
related variables back to the new "how-to" section.

(From yocto-docs rev: 289dfbd5d24241e42446a043104eecd6dca76f13)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark
2016-12-29 10:26:15 -08:00
committed by Richard Purdie
parent d229fded3e
commit ecaab75be6
3 changed files with 124 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files
documentation/dev-manual/dev-manual-common-tasks.xml
+73
View File
@@ -5475,6 +5475,79 @@
</section>
</section>
<section id='building-an-initramfs-image'>
<title>Building an Initial RAM Filesystem (initramfs) Image</title>
<para>
initramfs is the successor of Initial RAM Disk (initrd).
It is a "copy in and out" (cpio) archive of the initial file system
that gets loaded into memory during the Linux startup process.
Because Linux uses the contents of the archive during
initialization, the initramfs needs to contain all of the device
drivers and tools needed to mount the final root filesystem.
</para>
<para>
To build an initramfs image and bundle it into the kernel, set the
following variables:
<literallayout class='monospaced'>
INITRAMFS_IMAGE_BUNDLE = "1"
INITRAMFS_IMAGE = "<replaceable>image_recipe_name</replaceable>"
</literallayout>
Setting the
<ulink url='&YOCTO_DOCS_REF_URL;#var-INITRAMFS_IMAGE_BUNDLE'><filename>INITRAMFS_IMAGE_BUNDLE</filename></ulink>
flag causes the initramfs created by the recipe
and defined by
<ulink url='&YOCTO_DOCS_REF_URL;#var-INITRAMFS_IMAGE'><filename>INITRAMFS_IMAGE</filename></ulink>
to be unpacked into the <filename>${B}/usr/</filename> directory.
The unpacked initramfs is then passed to the kernel's
<filename>Makefile</filename> using the
<ulink url='&YOCTO_DOCS_REF_URL;#var-CONFIG_INITRAMFS_SOURCE'><filename>CONFIG_INITRAMFS_SOURCE</filename></ulink>
variable, allowing initramfs to be built in to the kernel
normally.
<note>
The preferred method is to use the
<filename>INITRAMFS_IMAGE</filename> variable rather than the
<filename>INITRAMFS_TASK</filename> variable.
Setting <filename>INITRAMFS_TASK</filename> is supported for
backward compatibility.
However, use of this variable has circular dependency
problems.
See the
<ulink url='&YOCTO_DOCS_REF_URL;#var-INITRAMFS_IMAGE_BUNDLE'><filename>INITRAMFS_IMAGE_BUNDLE</filename></ulink>
variable for additional information on these dependency
problems.
</note>
</para>
<para>
The recipe that <filename>INITRAMFS_IMAGE</filename>
points to must produce a <filename>.cpio.gz</filename>,
<filename>.cpio.tar</filename>, <filename>.cpio.lz4</filename>,
<filename>.cpio.lzma</filename>, or
<filename>.cpio.xz</filename> file.
You can ensure you produce one of these <filename>.cpio.*</filename>
files by setting the
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></ulink>
variable in your configuration file to one or more of the above
file types.
<note>
If you add items to the initramfs image by way of its recipe,
you should use
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_INSTALL'><filename>PACKAGE_INSTALL</filename></ulink>
rather than
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></ulink>.
<filename>PACKAGE_INSTALL</filename> gives more direct control
of what is added to the image as compared to the defaults you
might not necessarily want that are set by the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-image'><filename>image</filename></ulink>
or
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-core-image'><filename>core-image</filename></ulink>
classes.
</note>
</para>
</section>
<section id='configuring-the-kernel'>
<title>Configuring the Kernel</title>