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documentation/poky-ref-manual/ref-variables.xml: updates to rootfs variables

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I made another pass over the variables that affect the root filesystem
size generation.  The changes are based on review feedback from both
Saul and Joshua.

(From yocto-docs rev: ccd569d7e464a219a1a3ff9b063e431ba3c946de)

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
2012-01-17 10:04:32 -06:00
committed by Richard Purdie
parent 4c6c766baa
commit 2df457033b
1 changed files with 32 additions and 8 deletions
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40
documentation/poky-ref-manual/ref-variables.xml
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@@ -513,11 +513,21 @@
<glossentry id='var-IMAGE_OVERHEAD_FACTOR'><glossterm>IMAGE_OVERHEAD_FACTOR</glossterm>
<glossdef>
<para>
Defines a multiplier that the build system might apply to the initial image
size to create free disk space in the image as overhead.
Defines a multiplier that the build system applies to the initial image
size for cases when the multiplier times the returned disk usage value
for the image is greater than the sum of
<filename><link linkend='var-IMAGE_ROOTFS_SIZE'>IMAGE_ROOTFS_SIZE</link></filename>
and
<filename><link linkend='var-IMAGE_ROOTFS_EXTRA_SPACE'>IMAGE_ROOTFS_EXTRA_SPACE</link></filename>.
The result of the multiplier applied to the initial image size creates
free disk space in the image as overhead.
By default, the build process uses a multiplier of 1.3 for this variable.
This default value results in 30% free disk space added to the image when this
method is used to determine the final generated image size.
method is used to determine the final generated image size.
You should be aware that post install scripts and the package management
system uses disk space inside this overhead area.
Consequently, the multiplier does not produce an image with
all the theoretical free disk space.
See <filename><link linkend='var-IMAGE_ROOTFS_SIZE'>IMAGE_ROOTFS_SIZE</link></filename>
for information on how the build system determines the overall image size.
</para>
@@ -576,17 +586,31 @@
Programatically, the build system determines the final size of the
generated image as follows:
<literallayout class='monospaced'>
if (du * overhead) &lt; IMAGE_ROOTFS_SIZE:
IMAGE_ROOTFS_SIZE = IMAGE_ROOTFS_SIZE + xspace
if (image-du * overhead) &lt; rootfs-size:
internal-rootfs-size = rootfs-size + xspace
else:
IMAGE_ROOTFS_SIZE = (du * overhead) + xspace
internal-rootfs-size = (image-du * overhead) + xspace
where:
image-du = Returned value of the du command on
the image.
overhead = IMAGE_OVERHEAD_FACTOR
rootfs-size = IMAGE_ROOTFS_SIZE
internal-rootfs-size = Initial root filesystem
size before any modifications.
xspace = IMAGE_ROOTFS_EXTRA_SPACE
</literallayout>
In the above example, <filename>overhead</filename> is defined by the
<!-- In the above example, <filename>overhead</filename> is defined by the
<filename><link linkend='var-IMAGE_OVERHEAD_FACTOR'>IMAGE_OVERHEAD_FACTOR</link></filename>
variable, <filename>xspace</filename> is defined by the
<filename><link linkend='var-IMAGE_ROOTFS_EXTRA_SPACE'>IMAGE_ROOTFS_EXTRA_SPACE</link></filename>
variable, and <filename>du</filename> is the results of the disk usage command
on the initially generated image.
on the initially generated image. -->
</para>
</glossdef>
</glossentry>