lfs-book-i18n/zh_CN/chapter09/udev.po

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#. type: Content of: <sect1><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:11
msgid "Overview of Device and Module Handling"
msgstr ""

#. type: Content of: <sect1><indexterm><primary>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:14
msgid "Udev"
msgstr ""

#. type: Content of: <sect1><indexterm><secondary>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:15
msgid "usage"
msgstr ""

#. type: Content of: <sect1><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:18
msgid ""
"In <xref linkend=\"chapter-building-system\"/>, we installed the udev "
"package when <phrase revision=\"sysv\">eudev</phrase> <phrase "
"revision=\"systemd\">systemd</phrase> was built. Before we go into the "
"details regarding how this works, a brief history of previous methods of "
"handling devices is in order."
msgstr ""

#. type: Content of: <sect1><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:24
msgid ""
"Linux systems in general traditionally used a static device creation method, "
"whereby a great many device nodes were created under <filename "
"class=\"directory\">/dev</filename> (sometimes literally thousands of "
"nodes), regardless of whether the corresponding hardware devices actually "
"existed. This was 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."
msgstr ""

#. type: Content of: <sect1><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:33
msgid ""
"Using the udev method, only those devices which are detected by the kernel "
"get device nodes created for them. Because these device nodes will be "
"created each time the system boots, they will be stored on a <systemitem "
"class=\"filesystem\">devtmpfs</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."
msgstr ""

#. type: Content of: <sect1><sect2><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:41
msgid "History"
msgstr ""

#. type: Content of: <sect1><sect2><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:43
msgid ""
"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."
msgstr ""

#. type: Content of: <sect1><sect2><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:50
msgid ""
"The main problem with the approach adopted by <systemitem "
"class=\"filesystem\">devfs</systemitem> was the way it handled device "
"detection, creation, and naming. The latter issue, that of device node "
"naming, was perhaps the most critical. It is generally accepted that if "
"device names are allowed to be configurable, then the device naming policy "
"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 as deprecated for a long "
"period &ndash; due to a lack of maintenance &ndash; and was finally removed "
"from the kernel in June, 2006."
msgstr ""

#. type: Content of: <sect1><sect2><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:63
msgid ""
"With the development of the unstable 2.5 kernel tree, later released as the "
"2.6 series of stable kernels, a new virtual filesystem called <systemitem "
"class=\"filesystem\">sysfs</systemitem> came to be. The job of <systemitem "
"class=\"filesystem\">sysfs</systemitem> is to export a view of the system's "
"hardware configuration to userspace processes. With this userspace-visible "
"representation, the possibility of developing a userspace replacement for "
"<systemitem class=\"filesystem\">devfs</systemitem> became much more "
"realistic."
msgstr ""

#. type: Content of: <sect1><sect2><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:75
msgid "Udev Implementation"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:78
msgid "Sysfs"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:80
msgid ""
"The <systemitem class=\"filesystem\">sysfs</systemitem> filesystem was "
"mentioned briefly above. One may wonder how <systemitem "
"class=\"filesystem\">sysfs</systemitem> knows about the devices present on a "
"system and what device numbers should be used for them. Drivers that have "
"been compiled into the kernel directly register their objects with a "
"<systemitem class=\"filesystem\">sysfs</systemitem> (devtmpfs internally)  "
"as they are detected by the kernel. For drivers compiled as modules, this "
"registration will happen when the module is loaded. Once the <systemitem "
"class=\"filesystem\">sysfs</systemitem> filesystem is mounted (on /sys), "
"data which the drivers register with <systemitem "
"class=\"filesystem\">sysfs</systemitem> are available to userspace processes "
"and to udevd for processing (including modifications to device nodes)."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:97
msgid "Device Node Creation"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:99
msgid ""
"Device files are created by the kernel by the <systemitem "
"class=\"filesystem\">devtmpfs</systemitem> filesystem.  Any driver that "
"wishes to register a device node will go through the <systemitem "
"class=\"filesystem\">devtmpfs</systemitem> (via the driver core) to do it.  "
"When a <systemitem class=\"filesystem\">devtmpfs</systemitem> instance is "
"mounted on <filename class=\"directory\">/dev</filename>, the device node "
"will initially be created with a fixed name, permissions, and owner."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:108
msgid ""
"A short time later, the kernel will send a uevent to <command> "
"udevd</command>.  Based on the 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, <command> "
"udevd</command> will create additional symlinks to the device node, or "
"change its permissions, owner, or group, or modify the internal "
"<command>udevd</command> database entry (name) for that object."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:117
msgid ""
"The rules in these three directories are numbered and all three directories "
"are merged together. If <command>udevd</command> can't find a rule for the "
"device it is creating, it will leave the permissions and ownership at "
"whatever <systemitem class=\"filesystem\">devtmpfs</systemitem> used "
"initially."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:124
msgid "Module Loading"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:126
msgid ""
"Device drivers compiled as modules may have aliases built into them.  "
"Aliases are visible in the output of the <command>modinfo</command> program "
"and are usually related to the bus-specific identifiers of devices supported "
"by a module. For example, the <emphasis>snd-fm801</emphasis> driver supports "
"PCI devices with vendor ID 0x1319 and device ID 0x0801, and has an alias of "
"<quote>pci:v00001319d00000801sv*sd*bc04sc01i*</quote>.  For most devices, "
"the bus driver exports the alias of the driver that would handle the device "
"via <systemitem class=\"filesystem\">sysfs</systemitem>. E.g., the "
"<filename>/sys/bus/pci/devices/0000:00:0d.0/modalias</filename> file might "
"contain the string "
"<quote>pci:v00001319d00000801sv00001319sd00001319bc04sc01i00</quote>.  The "
"default rules provided with udev will cause <command>udevd</command> to call "
"out to <command>/sbin/modprobe</command> with the contents of the "
"<envar>MODALIAS</envar> uevent environment variable (which should be the "
"same as the contents of the <filename>modalias</filename> file in sysfs), "
"thus loading all modules whose aliases match this string after wildcard "
"expansion."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:145
msgid ""
"In this example, this means that, in addition to "
"<emphasis>snd-fm801</emphasis>, the obsolete (and unwanted)  "
"<emphasis>forte</emphasis> driver will be loaded if it is available. See "
"below for ways in which the loading of unwanted drivers can be prevented."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:151
msgid ""
"The kernel itself is also able to load modules for network protocols, "
"filesystems, and NLS support on demand."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:157
msgid "Handling Hotpluggable/Dynamic Devices"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:159
msgid ""
"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."
msgstr ""

#. type: Content of: <sect1><sect2><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:169
msgid "Problems with Loading Modules and Creating Devices"
msgstr ""

#. type: Content of: <sect1><sect2><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:171
msgid ""
"There are a few possible problems when it comes to automatically creating "
"device nodes."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:175
msgid "A kernel module is not loaded automatically"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:177
msgid ""
"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 arrange "
"module loading by other means. With Linux-&linux-version;, udev is known to "
"load properly-written drivers for INPUT, IDE, PCI, USB, SCSI, SERIO, and "
"FireWire devices."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:184
msgid ""
"To determine if the device driver you require has the necessary support for "
"udev, run <command>modinfo</command> with the module name as 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."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:190
msgid ""
"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 "
"driver. Load the driver without the help from udev and expect the issue to "
"be fixed later."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:196
msgid ""
"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 busses. Expect this issue "
"to be fixed in later kernel versions."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:202
msgid ""
"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."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:209
msgid ""
"A kernel module is not loaded automatically, and udev is not intended to "
"load it"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:212
msgid ""
"If the <quote>wrapper</quote> module only enhances the functionality "
"provided by some other module (e.g., <emphasis>snd-pcm-oss</emphasis> "
"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 udev loads the wrapped "
"module. To do this, add a <quote>softdep</quote> line to the corresponding "
"<filename>/etc/modprobe.d/<replaceable>&lt;filename&gt;</replaceable>.conf</filename> "
"file. For example:"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><screen>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:222
#, no-wrap
msgid "<literal>softdep snd-pcm post: snd-pcm-oss</literal>"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:224
msgid ""
"Note that the <quote>softdep</quote> command also allows "
"<literal>pre:</literal> dependencies, or a mixture of both "
"<literal>pre:</literal> and <literal>post:</literal> dependencies.  See the "
"<filename>modprobe.d(5)</filename> manual page for more information on "
"<quote>softdep</quote> syntax and capabilities."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:230
msgid ""
"If the module in question is not a wrapper and is useful by itself, "
"configure the <command>modules</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."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:239
msgid "Udev loads some unwanted module"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:241
msgid ""
"Either don't build the module, or blacklist it in a "
"<filename>/etc/modprobe.d/blacklist.conf</filename> file as done with the "
"<emphasis>forte</emphasis> module in the example below:"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><screen>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:245
#, no-wrap
msgid "<literal>blacklist forte</literal>"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:247
msgid ""
"Blacklisted modules can still be loaded manually with the explicit "
"<command>modprobe</command> command."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:253
msgid "Udev creates a device incorrectly, or makes a wrong symlink"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:255
msgid ""
"This usually happens if a rule unexpectedly matches a device. For example, a "
"poorly-written rule can match both a SCSI disk (as desired)  and the "
"corresponding SCSI generic device (incorrectly) by vendor.  Find the "
"offending rule and make it more specific, with the help of the "
"<command>udevadm info</command> command."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:264
msgid "Udev rule works unreliably"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:266
msgid ""
"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 (create "
"this file if it does not exist). Please notify the LFS Development list if "
"you do so and it helps."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:278
msgid "Udev does not create a device"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:280
msgid ""
"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."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:284
msgid ""
"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>. This is most common with third "
"party drivers from outside the kernel tree. Create a static device node in "
"<filename>/lib/udev/devices</filename> with the appropriate major/minor "
"numbers (see the file <filename>devices.txt</filename> inside the kernel "
"documentation or the documentation provided by the third party driver "
"vendor). The static device node will be copied to <filename "
"class=\"directory\">/dev</filename> by <command>udev</command>."
msgstr ""

#. type: Content of: <sect1><sect2><sect3><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:298
msgid "Device naming order changes randomly after rebooting"
msgstr ""

#. type: Content of: <sect1><sect2><sect3><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:300
msgid ""
"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 names being "
"stable. Instead, create your own rules that make symlinks with stable names "
"based on some stable attributes of the device, such as a serial number or "
"the output of various *_id utilities installed by udev.  See <xref "
"linkend=\"ch-config-symlinks\"/> and <xref linkend=\"ch-config-network\"/> "
"for examples."
msgstr ""

#. type: Content of: <sect1><sect2><title>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:314
msgid "Useful Reading"
msgstr ""

#. type: Content of: <sect1><sect2><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:316
msgid "Additional helpful documentation is available at the following sites:"
msgstr ""

#. type: Content of: <sect1><sect2><itemizedlist><listitem><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:322
msgid ""
"A Userspace Implementation of <systemitem "
"class=\"filesystem\">devfs</systemitem> <ulink "
"url=\"http://www.kroah.com/linux/talks/ols_2003_udev_paper/Reprint-Kroah-Hartman-OLS2003.pdf\"/>"
msgstr ""

#. type: Content of: <sect1><sect2><itemizedlist><listitem><para>
#: /home/xry111/svn-repos/LFS-BOOK/chapter09/udev.xml:327
msgid ""
"The <systemitem class=\"filesystem\">sysfs</systemitem> Filesystem <ulink "
"url=\"http://www.kernel.org/pub/linux/kernel/people/mochel/doc/papers/ols-2005/mochel.pdf\"/>"
msgstr ""