[Clfs-commits] [Cross-LFS]Cross-LFS Book branch, sysvinit, updated. clfs-2.1.0-1114-gbbf3c21
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commit bbf3c21d061696848b42748780677b3252b2b38e
Author: Chris Staub <chris at beaker67.com>
Date: Wed May 28 03:57:40 2014 -0400
More updates to udev explanation page
Conflicts:
BOOK/system-config/common/eudev.xml
diff --git a/BOOK/system-config/common/eudev.xml b/BOOK/system-config/common/eudev.xml
index 3c3d9b3..be1e5d5 100644
--- a/BOOK/system-config/common/eudev.xml
+++ b/BOOK/system-config/common/eudev.xml
@@ -28,12 +28,12 @@
<para>Linux systems in general traditionally use a static device creation
method, whereby a great many device nodes are created under <filename
- class="directory">/dev</filename> (sometimes literally thousands of nodes),
- regardless of whether the corresponding hardware devices actually exist.
- This is typically done via a <command>MAKEDEV</command> script, which
- contains a number of calls to the <command>mknod</command> program with the
- relevant major and minor device numbers for every possible device that
- might exist in the world.</para>
+ class="directory">/dev</filename> (sometimes literally thousands of
+ nodes), regardless of whether the corresponding hardware devices actually
+ exist. This is typically done via a <command>MAKEDEV</command> script,
+ which contains a number of calls to the <command>mknod</command> program
+ with the relevant major and minor device numbers for every possible
+ device that might exist in the world.</para>
</sect3>
@@ -41,11 +41,12 @@
<title>Devfs</title>
<para>In February 2000, a new filesystem called <systemitem
- class="filesystem">devfs</systemitem> was merged into the 2.3.46 kernel
- and was made available during the 2.4 series of stable kernels. Although
- it was present in the kernel source itself, this method of creating devices
- dynamically never received overwhelming support from the core kernel
- developers.</para>
+ class="filesystem">devfs</systemitem>, which dynamically created device
+ nodes as devices were found by the kernel, was merged into the
+ 2.3.46 kernel and was made available during the 2.4 series of stable
+ kernels. Although it was present in the kernel source itself, this method
+ of creating devices dynamically never received overwhelming support from
+ the core kernel developers.</para>
<para>The main problem with the approach adopted by <systemitem
class="filesystem">devfs</systemitem> was the way it handled device
@@ -55,8 +56,8 @@
should be up to a system administrator, not imposed on them by any
particular developer(s). The <systemitem
class="filesystem">devfs</systemitem> file system also suffered from race
- conditions that were inherent in its design and could not be fixed without a
- substantial revision to the kernel. It was marked deprecated with the
+ conditions that were inherent in its design and could not be fixed without
+ a substantial revision to the kernel. It was marked deprecated with the
release of the 2.6 kernel series, and was removed entirely as of version
2.6.18.</para>
@@ -77,72 +78,85 @@
class="filesystem">sysfs</systemitem> filesystem is mounted (on <filename
class="directory">/sys</filename>), data which the built-in drivers
registered with <systemitem class="filesystem">sysfs</systemitem> are
- available to userspace processes. With this
- userspace-visible representation, the possibility of seeing a userspace
- replacement for <systemitem class="filesystem">devfs</systemitem> became
- much more realistic.</para>
+ available to userspace processes. With this userspace-visible
+ representation, the possibility of seeing a userspace replacement for
+ <systemitem class="filesystem">devfs</systemitem> became much more
+ realistic.</para>
</sect3>
<sect3>
<title>Udev Implementation</title>
-<!-- <title>Device Node Creation</title> -->
-
- <para>When Udev was introduced, the <command>udevd</command> daemon made
- calls to mknod() to create device nodes in
- <filename class="directory">/dev</filename> dynamically, based on the
+ <para>Shortly after the introduction of
+ <systemitem class="filesystem">sysfs</systemitem>, work began on a
+ program called Udev to advantage of it. The <command>udev</command>
+ daemon made calls to <function>mknod()</function> to create device nodes
+ in <filename class="directory">/dev</filename> dynamically, based on the
information from <systemitem class="filesystem">sysfs</systemitem>, in
<filename class="directory">/sys</filename>. For example,
<filename>/sys/class/tty/vcs/dev</filename> contains the string
- <quote>7:0</quote>. This string was used by <command>udevd</command>
+ <quote>7:0</quote>. This string was used by <command>udev</command>
to create a device node with major number <emphasis>7</emphasis> and
- minor number <emphasis>0</emphasis>. Using the Udev method
- only those devices which are detected by the kernel would get device
- nodes created for them. Because these device nodes were created each time
- the system boots, they were stored on a
- <systemitem class="filesystem">tmpfs</systemitem> file system (a virtual
- file system that resides entirely in system memory). Device nodes do not
- require much space, so the memory that is used is negligible.</para>
+ minor number <emphasis>0</emphasis>.</para>
<para>Linux kernel version 2.6.32 introduced a new virtual file system
- called <systemitem class="filesystem">devtmpfs</systemitem>, a
- replacement for <systemitem class="filesystem">devfs</systemitem>.
- With this approach, a
- <systemitem class="filesystem">devtmpfs</systemitem> file system is
- mounted on <filename class="directory">/dev/</filename> when the system
- is booted, and all needed device nodes are created on this virtual
- file system. As of version 176, Udev no longer creates device nodes
- itself, instead relying on
+ called <systemitem class="filesystem">devtmpfs</systemitem>, an improved
+ replacement for <systemitem class="filesystem">devfs</systemitem>. This
+ allows device nodes to once again be dynamically created by the kernel,
+ without many of the problems of
+ <systemitem class="filesystem">devfs</systemitem>. As of version 176,
+ Udev no longer creates device nodes itself, instead relying on
<systemitem class="filesystem">devtmpfs</systemitem> to do so.</para>
- <para>Udev also sets appropriate ownership and permissions
- for the device nodes, and creates extra symlinks as needed (such as
- <filename class="symlink">/dev/cdrom</filename>). The ownership and
- permissions of the nodes under the
- <filename class="directory">/dev</filename> directory are
- determined by rules specified in the files within the <filename
- class="directory">/etc/udev/rules.d/</filename> directory. These are
- numbered in a similar fashion to the CLFS-Bootscripts package. If
- <command>udevd</command> can't find a rule for the device it is creating,
- it will default permissions to <emphasis>660</emphasis> and ownership to
- <emphasis>root:root</emphasis>.</para>
-
</sect3>
<sect3>
<title>Systemd and Eudev</title>
- <para>In May 2012, Udev's source was merged with systemd, an alternate
- <command>init</command> implementation. Some time later, several Gentoo
- developers took the Udev code from systemd and created a fork called
- Eudev.</para>
-
+ <para>In 2010, development began on systemd, an alternate
+ <command>init</command> implementation. Starting with Udev 183, Udev's
+ source tree was merged with systemd. Several Gentoo
+ developers who disagreed with this merge announced a project fork
+ called Eudev in December 2012, created by extracting the
+ Udev code from systemd. One of the goals of Eudev is to allow for
+ easier installation and usage of <command>udevd</command> without
+ the need for the rest of systemd.</para>
</sect3>
</sect2>
<sect2>
+ <title>Device Node Creation</title>
+
+ <para>By default, device nodes created by the kernel in a
+ <systemitem class="filesystem">devtmpfs</systemitem> are owned by
+ <emphasis>root:root</emphasis> and have <emphasis>600</emphasis>
+ permissions. <command>udevd</command> can modify ownership and permissions
+ of the nodes under the <filename class="directory">/dev</filename>
+ directory, and can also create additional symlinks, based on rules
+ specified in the files within the
+ <filename class="directory">/etc/udev/rules.d</filename>,
+ <filename class="directory">/lib/udev/rules.d</filename>,
+ and <filename class="directory">/run/udev/rules.d</filename> directories.
+ The names for these files start with a number, to indicate the order in
+ which they are run, and they have a <filename>.rules</filename>
+ extension (<command>udevd</command> will ignore files with any other
+ extension). All of the rules files from these directories are combined into
+ a single list, sorted by filename, and run in that order. In the event of
+ a conflict, where a rules file with the same name exists in two or more of
+ these directories, the rules in <filename class="directory">/etc</filename>
+ take the highest priority, followed by rules files in
+ <filename class="directory">/run</filename>, and finally
+ <filename class="directory">/lib</filename>. Any device for which a rule
+ cannot be found will just be ignored by <command>udevd</command>
+ and be left at the defaults defined by the kernel, as described above. For
+ more details about writing Udev rules, see
+ <ulink url="/usr/share/doc/systemd-&systemd-version;/udev.html" />.</para>
+
+ </sect2>
+
+ <sect2>
<title>Module Loading</title>
<para>Device drivers compiled as modules may have aliases built into them.
@@ -176,16 +190,6 @@
</sect2>
<sect2>
- <title>Handling Hotpluggable/Dynamic Devices</title>
-
- <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 uevent. This uevent is then handled by
- <command>udevd</command> as described above.</para>
-
- </sect2>
-
- <sect2>
<title>Problems with Loading Modules and Creating Devices</title>
<para>There are a few possible problems when it comes to automatically
@@ -234,8 +238,8 @@
enhances the functionality of <emphasis>snd-pcm</emphasis> by making the
sound cards available to OSS applications), configure
<command>modprobe</command> to load the wrapper after Eudev loads the
- wrapped module. To do this, add an <quote>install</quote> line in
- <filename>/etc/modprobe.conf</filename>. For example:</para>
+ wrapped module. To do this, add an <quote>install</quote> line to a file
+ in <filename>/etc/modprobe.d</filename>. For example:</para>
<screen role="nodump"><literal>install snd-pcm /sbin/modprobe -i snd-pcm ; \
/sbin/modprobe snd-pcm-oss ; true</literal></screen>
@@ -252,7 +256,7 @@
<title>Eudev loads some unwanted module</title>
<para>Either don't build the module, or blacklist it in
- <filename>/etc/modprobe.conf</filename> file as done with the
+ <filename>/etc/modprobe.d</filename> file as done with the
<emphasis>forte</emphasis> module in the example below:</para>
<screen role="nodump"><literal>blacklist forte</literal></screen>
@@ -263,7 +267,7 @@
</sect3>
<sect3>
- <title>Eudev creates a device incorrectly, or makes a wrong symlink</title>
+ <title>Eudev makes a wrong symlink</title>
<para>This usually happens if a rule unexpectedly matches a device. For
example, a poorly-writen rule can match both a SCSI disk (as desired)
commit f53e20f5394018d60cd959a6bba425903314d743
Author: Chris Staub <chris at beaker67.com>
Date: Wed May 28 03:57:13 2014 -0400
Updated date
diff --git a/BOOK/general.ent b/BOOK/general.ent
index feb68e5..7219a5b 100644
--- a/BOOK/general.ent
+++ b/BOOK/general.ent
@@ -2,7 +2,7 @@
<!ENTITY month "05"> <!-- Use two digits -->
<!ENTITY month_name "May">
-<!ENTITY day "25"> <!-- Use two digits -->
+<!ENTITY day "28"> <!-- Use two digits -->
<!ENTITY year "2014"> <!-- Use four digits -->
<!ENTITY releasedate "&month_name; &day;, &year;">
-----------------------------------------------------------------------
Summary of changes:
BOOK/general.ent | 2 +-
BOOK/system-config/common/eudev.xml | 142 ++++++++++++++++++-----------------
2 files changed, 74 insertions(+), 70 deletions(-)
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