diff options
Diffstat (limited to 'chapter07/udev.xml')
| -rw-r--r-- | chapter07/udev.xml | 42 |
1 files changed, 30 insertions, 12 deletions
diff --git a/chapter07/udev.xml b/chapter07/udev.xml index ba8b851e0..7d4bcc495 100644 --- a/chapter07/udev.xml +++ b/chapter07/udev.xml @@ -88,6 +88,7 @@ registered with <systemitem class="filesystem">sysfs</systemitem> are available to userspace processes and to <command>udevd</command> for device node creation.</para> + </sect3> <sect3> @@ -112,6 +113,7 @@ receives. Finally, the bootscript "coldplugs" 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> + </sect3> <sect3> @@ -134,6 +136,7 @@ <emphasis>root:root</emphasis>. Documentation on the syntax of the Udev rules configuration files are available in <filename>/usr/share/doc/udev-&udev-version;/index.html</filename></para> + </sect3> <sect3> @@ -166,6 +169,7 @@ <para>The kernel itself is also able to load modules for network protocols, filesystems and NLS support on demand.</para> + </sect3> <sect3> @@ -175,6 +179,7 @@ player, the kernel recognizes that the device is now connected and generates a hotplug event. This hotplug event is then handled by <command>udevd</command> as described above.</para> + </sect3> </sect2> @@ -187,6 +192,7 @@ <sect3> <title>A kernel module is not loaded automatically</title> + <para>Udev will only load a module if it has a bus-specific alias and the bus driver properly exports the necessary aliases to <systemitem class="filesystem">sysfs</systemitem>. In other cases, one should @@ -201,7 +207,7 @@ the argument. Now try locating the device directory under <filename class="directory">/sys/bus</filename> and check whether there is a <filename>modalias</filename> file there.</para> - + <para>If the <filename>modalias</filename> file exists in <systemitem class="filesystem">sysfs</systemitem>, the driver supports the device and can talk to it directly, but doesn't have the alias, it is a bug in the @@ -213,12 +219,13 @@ 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 --> <para>Udev is not intended to load <quote>wrapper</quote> drivers such as <emphasis>snd-pcm-oss</emphasis> and non-hardware drivers such as <emphasis>loop</emphasis> at all.</para> + </sect3> <sect3> @@ -232,14 +239,16 @@ <command>modprobe</command> to load the wrapper after Udev loads the wrapped module. To do this, add an <quote>install</quote> line in <filename>/etc/modprobe.conf</filename>. For example:</para> -<screen role="nodump">install snd-pcm modprobe -i snd-pcm ; modprobe \ - snd-pcm-oss ; true</screen> - + +<screen role="nodump"><literal>install snd-pcm modprobe -i snd-pcm ; modprobe \ + snd-pcm-oss ; true</literal></screen> + <para>If the module in question is not a wrapper and is useful by itself, configure the <command>S05modules</command> bootscript to load this module on system boot. To do this, add the module name to the <filename>/etc/sysconfig/modules</filename> file on a separate line. This works for wrapper modules too, but is suboptimal in that case.</para> + </sect3> <sect3> @@ -248,10 +257,12 @@ <para>Either don't build the module, or blacklist it in <filename>/etc/modprobe.conf</filename> file as done with the <emphasis>forte</emphasis> module in the example below:</para> -<screen role="nodump">blacklist forte</screen> + +<screen role="nodump"><literal>blacklist forte</literal></screen> <para>Blacklisted modules can still be loaded manually with the explicit <command>modprobe</command> command.</para> + </sect3> <sect3> @@ -262,26 +273,30 @@ 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> + </sect3> <sect3> <title>Udev rule works unreliably</title> + <para>This may be another manifestation of the previous problem. If not, and your rule uses <systemitem class="filesystem">sysfs</systemitem> attributes, it may be a kernel timing issue, to be fixed in later kernels. For now, you can work around it by creating a rule that waits for the used <systemitem class="filesystem">sysfs</systemitem> attribute and appending it to the <filename>/etc/udev/rules.d/10-wait_for_sysfs.rules</filename> - file. Please notify the LFS Development list if you do so and it helps. - </para> + file. Please notify the LFS Development list if you do so and it + helps.</para> + </sect3> - + <sect3> <title>Udev does not create a device</title> + <para>Further text assumes that the driver is built statically into the kernel or already loaded as a module, and that you have already checked that Udev doesn't create a misnamed device.</para> - + <para>Udev has no information needed to create a device node if a kernel driver does not export its data to <systemitem class="filesystem">sysfs</systemitem>. @@ -293,10 +308,12 @@ vendor). The static device node will be copied to <filename class="directory">/dev</filename> by the <command>S10udev</command> bootscript.</para> + </sect3> - + <sect3> <title>Device naming order changes randomly after rebooting</title> + <para>This is due to the fact that Udev, by design, handles uevents and loads modules in parallel, and thus in an unpredictable order. This will never be <quote>fixed</quote>. You should not rely upon the kernel device @@ -305,8 +322,9 @@ serial number or the output of various *_id utilities installed by Udev. See also the network interface renaming example in <xref linkend="ch-scripts-network"/>.</para> + </sect3> - + </sect2> <sect2> |