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86 lines
4.1 KiB
XML
86 lines
4.1 KiB
XML
<sect1 id="ch-system-MAKEDEV" xreflabel="Make_devices">
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<title>Creating devices with Make_devices-&makedev-version;</title>
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<?dbhtml filename="makedevices.html" dir="chapter06"?>
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<para>The Make_devices package contains a script for creating device
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nodes.</para>
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<screen>&buildtime; &makedev-time;
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&diskspace; &makedev-compsize;</screen>
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&aa-makedev-down;
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&aa-makedev-dep;
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<sect2><title> </title><para> </para></sect2>
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<sect2>
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<title>Making devices</title>
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<para>Note that unpacking the
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<filename>make_devices-&makedev-version;.bz2</filename> file doesn't
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create a directory for you to <command>cd</command> into, as the file
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contains only a shell script.</para>
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<para>Install the <filename>make_devices</filename> script:</para>
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<screen><userinput>bzcat make_devices-&makedev-version;.bz2 > /dev/make_devices
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chmod 754 /dev/make_devices</userinput></screen>
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<para>Device nodes are special files: things that can generate or receive data.
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They usually correspond to physical pieces of hardware. Device nodes can be
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created by issuing commands of the form: <command>mknod -m mode name type major
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minor</command>. In such a command, <emphasis>mode</emphasis> is the usual
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octal read/write/execute permissions triplet, and <emphasis>name</emphasis> is
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the name of the device file to be created. It may seem surprising, but the
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device name is actually arbitrary, except that most programs rely on devices
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such as <filename>/dev/null</filename> having their usual names. The remaining
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three parameters tell the kernel what device the node
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actually refers to. The <emphasis>type</emphasis> is a letter, either b or c,
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indicating whether the device is accessed in blocks (such as a hard disk) or
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character by character (such as the console). And <emphasis>major</emphasis>
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and <emphasis>minor</emphasis> are numbers, together forming a code that
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identifies the device to the kernel. A list of the currently assigned device
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numbers for Linux can be found in the file <filename>devices.txt</filename> in
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the <filename class="directory">Documentation</filename> subdirectory of the
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kernel sources.</para>
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<para>Note that the same major/minor combination is usually assigned to both a
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block and a character device. These are, however, completely unrelated devices
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that cannot be interchanged. A device is identified by the type/major/minor
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triple, not just the major/minor pair, so when creating a device node it is
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important to choose the correct <emphasis>type</emphasis> of device.</para>
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<para>Because looking up the type/major/minor triples and using
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<command>mknod</command> manually is tedious and error-prone, the
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<filename>make_devices</filename> script has been created. It contains a whole
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series of <command>mknod</command> commands, one for each device, complete with
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recommended name, permissions and group assignment. It has been set up so that
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only a minimal set of commonly used devices is enabled and the other lines are
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commented out. You should open <filename>make_devices</filename> in an editor
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and customize it to your needs. This takes some time, but is very simple. When
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you are satisfied, run the script to create the device files:</para>
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<screen><userinput>cd /dev
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./make_devices</userinput></screen>
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<para>If you had success with mounting the devpts file system earlier in <xref
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linkend="ch-system-proc"/>, you can continue with the next section. If you were
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unable to mount devpts, you will have to create a few static ptyXX and ttyXX
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device nodes instead. To do this, open <filename>make_devices</filename> in
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your editor, go to the section "Pseudo-TTY masters" and enable a few ptyXX
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devices -- a handful are enough to enable the test suites to run, but if you
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plan to run a kernel without devpts support you will probably need many more
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(every xterm, ssh connection, telnet connection, and the like, uses one of
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these pseudo terminals). In the immediately following section "Pseudo-TTY
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slaves", enable the corresponding ttyXX devices. When you are done, rerun
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<command>./make_devices</command> from inside <filename>/dev</filename> to
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have it create the new devices.</para>
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</sect2>
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&aa-makedev-shortdesc;
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&aa-makedev-desc;
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</sect1>
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