Signed-off-by: Pascal Bach <pascal.b...@siemens.com>
---
.../dev-manual/dev-manual-common-tasks.xml | 104 ++++++++++++++++++++
1 file changed, 104 insertions(+)
diff --git a/documentation/dev-manual/dev-manual-common-tasks.xml
b/documentation/dev-manual/dev-manual-common-tasks.xml
index 17d725b..9072586 100644
--- a/documentation/dev-manual/dev-manual-common-tasks.xml
+++ b/documentation/dev-manual/dev-manual-common-tasks.xml
@@ -7582,6 +7582,110 @@ Gateways via their Web Interfaces</ulink>"</emphasis>
</section>
</section>
+ <section id="selecting-dev-manager">
+ <title>Selecting a Device Manager</title>
+
+ <para>
+ Yocto provides multiple ways to manage <filename>/dev</filename>
+ <itemizedlist>
+ <listitem><para>
+ <emphasis>Persistent and pre populated
<filename>/dev</filename>:</emphasis>
+ in this case the <filename>/dev</filename> directory is
persistent
+ and the required device nodes are created at build time.
+ </para></listitem>
+
+ <listitem><para>
+ <emphasis>Use <filename>devtmps</filename> with a device
manager:</emphasis>
+ in 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>Use Persistent and pre-populated
<filename>/dev</filename></title>
+
+ <para>
+ To use the static method for device population the variable
+ <ulink
url='&YOCTO_DOCS_REF_URL;#var-USE_DEVFS'><filename>USE_DEVFS</filename></ulink>
+ needs to be set to 0.
+
+ <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 device table to use is
defined by the variable
+ <ulink
url='&YOCTO_DOCS_REF_URL;#var-IMAGE_DEVICE_TABLES'><filename>IMAGE_DEVICE_TABLES</filename></ulink>
and should be set
+ in the <ulink
url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>,
+ <ulink
url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
+ or <filename>local.conf</filename> configuration file.
+ </para>
+
+ <para>
+ If nothing is defined the default
<filename>device_table-minimal.txt</filename> is used.
+ </para>
+
+ <para>
+ The population is handled by the <filename>makedevs</filename>
utility
+ during image creation.
+
+ <literallayout class='monospaced'>
+ IMAGE_DEVICE_TABLES = "device_table-mymachine.txt"
+ </literallayout>
+
+ </para>
+ </section>
+
+ <section id="devtmps-dev-management">
+ <title>Use <filename>devtmpfs</filename> and a device
manager</title>
+
+ <para>
+ To use the dynamic method for device population the variable
+ <ulink
url='&YOCTO_DOCS_REF_URL;#var-USE_DEVFS'><filename>USE_DEVFS</filename></ulink>
+ needs to be set to 1. This is the default.
+
+ <literallayout class='monospaced'>
+ USE_DEVFS = "1"
+ </literallayout>
+
+ This way 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 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>.
+
+ To have more control over the device nodes a device manager
like
+ <filename>udev</filename> or <filename>busybox-mdev</filename>
+ can be used.
+
+ The device manager to use is defined by the variable
+ <filename>VIRTUAL-RUNTIME_dev_manager</filename> and should be
set
+ in the <ulink
url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>,
+ <ulink
url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
+ or <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">
<title>Using an External SCM</title>
--
1.7.10.4
--
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