Re: [yocto-docs][PATCH 2/2] dev-manual: Add section about /dev population

["Rifenbark, Scott M" <scott.m.rifenbark@intel.com>]

Pascal, 

I have applied this patch with some editing.  Also, applied the patch that added the USE_DEVFS variable to the ref-manual.

Thanks,
Scott

>-----Original Message-----
>From: yocto-bounces@yoctoproject.org [mailto:yocto-
>bounces@yoctoproject.org] On Behalf Of Pascal Bach
>Sent: Wednesday, January 07, 2015 6:58 AM
>To: yocto@yoctoproject.org
>Subject: [yocto] [yocto-docs][PATCH 2/2] dev-manual: Add section about
>/dev population
>
>Signed-off-by: Pascal Bach <pascal.bach@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></ul
>ink> 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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