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Tweaked some of the educational text regarding udev.

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git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@7510 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689
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Archaic 2006-04-13 20:17:52 +00:00
parent d2c332bc21
commit a0d96d25cf
2 changed files with 23 additions and 28 deletions
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7
chapter06/kernfs.xml
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@ -31,10 +31,9 @@
device nodes, in particular the <filename
class="devicefile">console</filename> and <filename
class="devicefile">null</filename> devices. The device nodes will be created
on the hard disk so that they are available before <command>udev</command>
has been started, and additionally when Linux is started in single user mode
(hence the restrictive permissions on <filename
class="devicefile">console</filename>). Create the devices by running the
on the hard disk so that they are available before <command>udevd</command>
has been started, and additionally when Linux is started with
<parameter>init=/bin/bash</parameter>. Create the devices by running the
following commands:</para>
<screen><userinput>mknod -m 600 $LFS/dev/console c 5 1

44
chapter07/udev.xml
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@ -95,24 +95,24 @@
<title>Udev Bootscript</title>
<para>The <command>S10udev</command> initscript takes care of creating
device nodes when Linux is booted. The script starts by unsetting the
hotplug event handler from the default of <command>/sbin/hotplug</command>
This is done because, instead of the kernel calling out to an external
binary, <command>udevd</command> will listen on a netlink socket for
hotplug events that the kernel raises. The bootscript copies any static
device nodes when Linux is booted. The script unsets the uevent handler
from the default of <command>/sbin/hotplug</command>. This is done
because the kernel no longer needs to call out to an external binary.
Instead <command>udevd</command> will listen on a netlink socket for
uevents that the kernel raises. Next, the bootscript copies any static
device nodes that exist in <filename
class="directory">/lib/udev/devices</filename> to <filename
class="directory">/dev</filename>. This is necessary because some devices,
directories and symlinks are needed before the dynamic device handling
directories, and symlinks are needed before the dynamic device handling
processes are available during the early stages of booting a system.
Creating static device nodes in
<filename class="directory">/lib/udev/devices</filename> also provides
an easy workaround for devices that are not supported by the dynamic
device handling infrastructure. The bootscript then starts the Udev
daemon, <command>udevd</command>, which will act on any hotplug events it
receives. Finally, the bootscript &quot;coldplugs&quot; any devices that
have already been registered with the kernel by forcing them to raise
hotplug events which <command>udevd</command> will then handle.</para>
Creating static device nodes in <filename
class="directory">/lib/udev/devices</filename> also provides an easy
workaround for devices that are not supported by the dynamic device
handling infrastructure. The bootscript then starts the Udev daemon,
<command>udevd</command>, which will act on any uevents it receives.
Finally, the bootscript forces the kernel to replay uevents for any
devices that have already been registered and then waits for
<command>udevd</command> to handle them.</para>
</sect3>
@ -177,7 +177,7 @@
<para>When you plug in a device, such as a Universal Serial Bus (USB) MP3
player, the kernel recognizes that the device is now connected and
generates a hotplug event. This hotplug event is then handled by
generates a uevent. This uevent is then handled by
<command>udevd</command> as described above.</para>
</sect3>
@ -197,10 +197,8 @@
bus driver properly exports the necessary aliases to <systemitem
class="filesystem">sysfs</systemitem>. In other cases, one should
arrange module loading by other means. With Linux-&linux-version;, Udev is
known to load properly-written drivers for PCI, USB, SCSI, SERIO and
FireWire devices.</para>
<!-- After linux-2.6.16, add INPUT and IDE to the list above -->
known to load properly-written drivers for INPUT, IDE, PCI, USB, SCSI,
SERIO and FireWire devices.</para>
<para>To determine if the device driver you require has the necessary
support for Udev, run <command>modinfo</command> with the module name as
@ -217,10 +215,8 @@
<para>If there is no <filename>modalias</filename> file in the relevant
directory under <filename class="directory">/sys/bus</filename>, this
means that the kernel developers have not yet added modalias support to
this bus type. With Linux-&linux-version;, this is the case with ISA and
IDE busses. Expect this issue to be fixed in later kernel versions.</para>
<!-- Remove IDE from the list above after Linux-2.6.16 -->
this bus type. With Linux-&linux-version;, this is the case with ISA
busses. Expect this issue to be fixed in later kernel versions.</para>
<para>Udev is not intended to load <quote>wrapper</quote> drivers such as
<emphasis>snd-pcm-oss</emphasis> and non-hardware drivers such as
@ -269,7 +265,7 @@
<title>Udev creates a device incorrectly, or makes a wrong symlink</title>
<para>This usually happens if a rule unexpectedly matches a device. For
example, a poorly-writen rule can match by both a SCSI disk (as desired)
example, a poorly-writen rule can match both a SCSI disk (as desired)
and the corresponding SCSI generic device (incorrectly) by vendor.
Increase the logging verbosity of Udev, find the offending rule by
examining the logs and make it more specific.</para>