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dev-manual: New section on choosing a device manager added.

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This patch was modified to fit in with the style of the book.

(From yocto-docs rev: 7c6c7ac573f92bfc844977e0d7a97ca4aac9bc70)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Pascal Bach
2015-01-16 16:01:06 -08:00
committed by Richard Purdie
parent a23e76dbce
commit da47cb736b
1 changed files with 108 additions and 1 deletions
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documentation/dev-manual/dev-manual-common-tasks.xml
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@@ -946,7 +946,7 @@
Furthermore, you must use <filename>_append</filename> instead Furthermore, you must use <filename>_append</filename> instead
of the <filename>+=</filename> operator if you want to avoid of the <filename>+=</filename> operator if you want to avoid
ordering issues. ordering issues.
The reason for this is because doing so unconditionally appends The reason for this is because doing so un>+conditionally appends
to the variable and avoids ordering problems due to the to the variable and avoids ordering problems due to the
variable being set in image recipes and variable being set in image recipes and
<filename>.bbclass</filename> files with operators like <filename>.bbclass</filename> files with operators like
@@ -7587,6 +7587,113 @@
</section> </section>
</section> </section>
<section id="selecting-dev-manager">
<title>Selecting a Device Manager</title>
<para>
The Yocto Project provides multiple ways to manage the device
manager (<filename>/dev</filename>):
<itemizedlist>
<listitem><para><emphasis>Persistent and Pre-Populated<filename>/dev</filename>:</emphasis>
For this case, the <filename>/dev</filename> directory
is persistent and the required device nodes are created
during the build.
</para></listitem>
<listitem><para><emphasis>Use <filename>devtmps</filename> with a Device Manager:</emphasis>
For this case, the <filename>/dev</filename> directory
is provided by the kernel as an in-memory file system and
is automatically populated by the kernel at runtime.
Additional configuration of device nodes is done in user
space by a device manager like
<filename>udev</filename> or
<filename>busybox-mdev</filename>.
</para></listitem>
</itemizedlist>
</para>
<section id="static-dev-management">
<title>Using Persistent and Pre-Populated<filename>/dev</filename></title>
<para>
To use the static method for device population, you need to
set the
<ulink url='&YOCTO_DOCS_REF_URL;#var-USE_DEVFS'><filename>USE_DEVFS</filename></ulink>
variable to "0" as follows:
<literallayout class='monospaced'>
USE_DEVFS = "0"
</literallayout>
</para>
<para>
The content of the resulting <filename>/dev</filename>
directory is defined in a Device Table file.
The
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_DEVICE_TABLES'><filename>IMAGE_DEVICE_TABLES</filename></ulink>
variable defines the Device Table to use and should be set
in the machine or distro configuration file.
Alternatively, you can set this variable in your
<filename>local.conf</filename> configuration file.
</para>
<para>
If you do not define the
<filename>IMAGE_DEVICE_TABLES</filename> variable, the default
<filename>device_table-minimal.txt</filename> is used:
<literallayout class='monospaced'>
IMAGE_DEVICE_TABLES = "device_table-mymachine.txt"
</literallayout>
</para>
<para>
The population is handled by the <filename>makedevs</filename>
utility during image creation:
</para>
</section>
<section id="devtmps-dev-management">
<title>Using <filename>devtmpfs</filename> and a Device Manager</title>
<para>
To use the dynamic method for device population, you need to
use (or be sure to set) the
<ulink url='&YOCTO_DOCS_REF_URL;#var-USE_DEVFS'><filename>USE_DEVFS</filename></ulink>
variable to "1", which is the default:
<literallayout class='monospaced'>
USE_DEVFS = "1"
</literallayout>
With this setting, the resulting <filename>/dev</filename>
is populated by the kernel using <filename>devtmpfs</filename>.
Make sure the corresponding kernel configuration variable
<filename>CONFIG_DEVTMPFS</filename> is set when building
you build a linux kernel.
</para>
<para>
All devices created by <filename>devtmpfs</filename> will be
owned by <filename>root</filename> and have permissions
<filename>0600</filename>.
</para>
<para>
To have more control over the device nodes, you can use a
device manager like <filename>udev</filename> or
<filename>busybox-mdev</filename>.
You choose the device manager by defining the
<filename>VIRTUAL-RUNTIME_dev_manager</filename> variable
in your machine or distro configuration file.
Alternatively, you can set this variable in your
<filename>local.conf</filename> configuration file:
<literallayout class='monospaced'>
VIRTUAL-RUNTIME_dev_manager = "udev"
# Some alternative values
# VIRTUAL-RUNTIME_dev_manager = "busybox-mdev"
# VIRTUAL-RUNTIME_dev_manager = "systemd"
</literallayout>
</para>
</section>
</section>
<section id="platdev-appdev-srcrev"> <section id="platdev-appdev-srcrev">
<title>Using an External SCM</title> <title>Using an External SCM</title>