21 strings / 972 words

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Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
In <xref linkend="chapter-building-system"/>, we installed the udev daemon when <phrase revision="sysv">udev</phrase> <phrase revision="systemd">systemd</phrase> was built. Before we go into the details regarding how udev works, a brief history of previous methods of handling devices is in order.
在<xref linkend="chapter-building-system"/>中，我们在构建 <phrase revision="sysv">eudev</phrase> <phrase revision="systemd">systemd</phrase> 时安装了 Udev 软件包。在我们详细讨论它的工作原理之前，首先按时间顺序简要介绍历史上曾经使用过的设备管理方式。
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
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 contained 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.
传统的 Linux 系统通常使用静态地创建设备，即在 <filename class="directory">/dev</filename> 下创建大量设备节点 (有时有数千个节点)，无论对应的硬件设备是否真的存在。一般通过 <command>MAKEDEV</command> 脚本完成这一工作，它包含以相关的主设备号和次设备号，为世界上可能存在的每个设备建立节点的大量 <command>mknod</command> 命令。
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
Using the udev method, device nodes are only created for those devices which are detected by the kernel. These device nodes are created each time the system boots; they are stored in 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.
使用 Udev，则只有那些被内核检测到的设备才会获得为它们创建的设备节点。由于这些设备节点在每次引导系统时都会重新创建，它们被储存在 <systemitem class="filesystem">devtmpfs</systemitem> 文件系统中 (一个虚拟文件系统，完全驻留在系统内存)。设备节点不需要太多空间，它们使用的系统内存可以忽略不计。
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
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 configurable, the device naming policy should be chosen by system administrators, and not imposed on them by the developer(s). The <systemitem class="filesystem">devfs</systemitem> file system also suffered from race conditions that were inherent in its design; these could not be fixed without a substantial revision of the kernel. <systemitem class="filesystem">devfs</systemitem> was marked as deprecated for a long time, and was finally removed from the kernel in June, 2006.
<systemitem class="filesystem">devfs</systemitem> 实现机制的主要问题是它处理设备的检测、创建和命名的方式，其中最致命的或许最后一项，即设备节点命名方式。通常认为，如果设备名称是可配置的，那么设备命名策略应该由系统管理员，而不是某个 (某些)特定开发者决定。<systemitem class="filesystem">devfs</systemitem> 还受到其设计中固有的竞争条件的严重影响，在不对内核进行大量修改的前提下无法修复这一问题。由于缺乏维护，它早已被标记为过时特性，最终在 2006 年 6 月被从内核中移除。
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
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 provide information about the system's hardware configuration to userspace processes. With this userspace-visible representation, it became possible to develop a userspace replacement for <systemitem class="filesystem">devfs</systemitem>.
在不稳定的 2.5 系列内核开发过程中，加入了一个新的虚拟文件系统，称为 <systemitem class="filesystem">sysfs</systemitem>，并在 2.6 系列稳定内核中发布。<systemitem class="filesystem">sysfs</systemitem> 的工作是将系统硬件配置信息导出给用户空间进程，有了这个用户空间可见的配置描述，就可能开发一种 <systemitem class="filesystem">devfs</systemitem> 的用户空间替代品。
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
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 register their objects in <systemitem class="filesystem">sysfs</systemitem> (devtmpfs internally) as they are detected by the kernel. For drivers compiled as modules, registration happens when the module is loaded. Once the <systemitem class="filesystem">sysfs</systemitem> filesystem is mounted (on <filename class="directory">/sys</filename>), data which the drivers have registered with <systemitem class="filesystem">sysfs</systemitem> are available to userspace processes and to udevd for processing (including modifications to device nodes).
前面已经简要提到了 <systemitem class="filesystem">sysfs</systemitem> 文件系统。有些读者可能好奇，<systemitem class="filesystem">sysfs</systemitem> 是如何知道系统中存在哪些设备，以及应该为它们使用什么设备号的。答案是，那些编译到内核中的驱动程序在它们的对象被内核检测到时，直接将它们注册到 <systemitem class="filesystem">sysfs</systemitem> (内部的 devtmpfs)。对于那些被编译为模块的驱动程序，注册过程在模块加载时进行。只要 <systemitem class="filesystem">sysfs</systemitem> 文件系统被挂载好 (位于 /sys)，用户空间程序即可使用驱动程序注册在 <systemitem class="filesystem">sysfs</systemitem> 中的数据，Udev 就能够使用这些数据对设备进行处理 (包括修改设备节点)。
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
Device files are created by the kernel in the <systemitem class="filesystem">devtmpfs</systemitem> file system. Any driver that wishes to register a device node will use 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 exposed to userspace with a fixed name, permissions, and owner.
内核通过 <systemitem class="filesystem">devtmpfs</systemitem> 直接创建设备文件，任何希望注册设备节点的驱动程序都要通过 <systemitem class="filesystem">devtmpfs</systemitem> (经过驱动程序核心) 实现。当一个 <systemitem class="filesystem">devtmpfs</systemitem> 实例被挂载到 <filename class="directory">/dev</filename> 时，设备节点将被以固定的名称、访问权限和所有者首次创建。
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
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">/usr/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.
很快，内核会向 <command>udevd</command> 发送一个 uevent。根据 <filename class="directory">/etc/udev/rules.d</filename>，<filename class="directory">/lib/udev/rules.d</filename>，以及 <filename class="directory">/run/udev/rules.d</filename> 目录中文件指定的规则，<command>udevd</command> 将为设备节点创建额外的符号链接，修改其访问权限，所有者，或属组，或者修改该对象的 <command>udevd</command> 数据库条目 (名称)。
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
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 <literal>pci:v00001319d00000801sv*sd*bc04sc01i*</literal>. 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 <literal>pci:v00001319d00000801sv00001319sd00001319bc04sc01i00</literal>. 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.
编译为内核模块的设备驱动程序可能有内建的别名。别名可以通过 <command>modinfo</command> 程序查询，它通常和该模块支持的设备的总线相关标识符有关。例如，<emphasis>snd-fm801</emphasis> 驱动程序支持厂商 ID 为 0x1319，设备 ID 为 0x0801 的 PCI 设备，其别名为<quote>pci:v00001319d00000801sv*sd*bc04sc01l*</quote>。对于多数设备，总线驱动程序会通过 <systemitem class="filesystem">sysfs</systemitem> 导出应该处理该设备的驱动程序别名，例如 <filename>/sys/bus/pci/devices/0000:00:0d.0/modalias</filename> 文件应该包含字符串<quote>pci:v00001319d00000801sv00001319sd00001319bc04sc01i00</quote>。Udev 附带的默认规则会导致 <command>udevd</command> 调用 <command>/sbin/modprobe</command> 时传递 <envar>MODALIAS</envar> uevent 环境变量 (它的值应该和 sysfs 中<filename>modalias</filename> 文件的内容相同)，从而加载那些在通配符扩展后别名与这个字符串匹配的模块。
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
A Kernel Module Is Not Loaded Automatically
内核模块没有自动加载
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
A Kernel Module Is Not Loaded Automatically, and Udev Is Not Intended to Load It
内核模块没有自动加载，且 Udev 不尝试加载它
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
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 <ulink role='man' url='&man;modprobe.d.5'>modprobe.d(5)</ulink> manual page for more information on <quote>softdep</quote> syntax and capabilities.
注意<quote>softdep</quote>命令也允许 <literal>pre:</literal> 依赖项，或混合使用 <literal>pre:</literal> 和 <literal>post:</literal> 依赖项。参阅 <filename>modprobe.d(5)</filename> man 手册页面，了解更多关于<quote>softdep</quote>语法和功能的信息。
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
Udev Loads Some Unwanted Module
Udev 加载了不希望的模块
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
Udev Creates a Device Incorrectly, or Makes the Wrong Symlink
Udev 创建了错误的设备或错误的符号链接
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
Udev Rule Works Unreliably
Udev 规则工作不可靠
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
Udev Does Not Create a Device
Udev 没有创建设备
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
First, be certain that the driver is built into the kernel or already loaded as a module, and that udev isn't creating a misnamed device.
以下内容假设驱动程序已经被编译到内核中，或作为模块被加载，而且您已经检查过并确认 Udev 没有创建命名错误的设备。
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
If a kernel driver does not export its data to <systemitem class="filesystem">sysfs</systemitem>, udev lacks the information needed to create a device node. This is most likely to happen with third party drivers from outside the kernel tree. Create a static device node in <filename>/usr/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>.
如果驱动程序没有将它的信息导出到 <systemitem class="filesystem">sysfs</systemitem>，Udev 就无法获得创建设备节点必需的信息。这种问题往往出现在内核源代码树以外的第三方驱动程序中。这时，需要在 <filename>/lib/udev/devices</filename> 中使用正确的主设备号和次设备号，创建一个静态设备节点 (参考内核文档中的 <filename>devices.txt</filename> 或第三方驱动厂商提供的文档)，该静态设备节点将被复制到 <filename class="directory">/dev</filename>，<command>udev</command> 会自动完成复制。
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
Device Naming Order Changes Randomly After Rebooting
重启后设备命名顺序随机变化
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
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.
这是由于 Udev 从设计上就是并行加载模块的，因此无法预测加载顺序。这个问题永远也不会被 <quote>修复</quote>。您不应该指望内核提供稳定的设备命名，而是应该创建您自己的规则，以根据设备的一些稳定属性，例如设备序列号或 Udev 安装的一些 *_id 工具的输出，来创建具有稳定名称的符号链接。可以参考<xref linkend="ch-config-symlinks"/>和<xref linkend="ch-config-network"/>中的例子。
Linux From Scratch 12.3/chapter09_udev — Chinese (Simplified Han script)
The <systemitem class="filesystem">sysfs</systemitem> Filesystem <ulink url="https://www.kernel.org/pub/linux/kernel/people/mochel/doc/papers/ols-2005/mochel.pdf"/>
The <systemitem class="filesystem">sysfs</systemitem> Filesystem <ulink url="http://www.kernel.org/pub/linux/kernel/people/mochel/doc/papers/ols-2005/mochel.pdf"/>