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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html><head> <title></title> <link rel="stylesheet" media="screen" type="text/css" href="./style.css" /> <link rel="stylesheet" media="screen" type="text/css" href="./design.css" /> <link rel="stylesheet" media="print" type="text/css" href="./print.css" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /></head><body><a href=start.html>start</a></br><h3><a name="a_basic_char_device_driver" id="a_basic_char_device_driver">A Basic Char Device Driver</a></h3><div class="level3"><p>The following code represents a most basic device driver. This code can be compiled to run on the host or the target systems. It is broken up into sections to help understand it.</p><p>Includes and defines:</p><pre class="code c"> <span class="co1">// </span> <span class="co1">// Basic Character mode driver </span> <span class="co1">// </span> <span class="co2">#include <linux/module.h> </span> <span class="co2">#include <linux/kernel.h> </span> <span class="co2">#include <linux/init.h> </span> <span class="co2">#include <linux/fs.h> </span> <span class="co2">#define SCMD_DEV "scmd_basic" </span> <span class="kw4">static</span> <span class="kw4">int</span> scmd_major=<span class="nu0">250</span>; <span class="coMULTI">/* * for dynamic major allocation static int scmd_major=0; */</span> </pre><p>The <strong>fops</strong> table</p><pre class="code c"> <span class="kw4">struct</span> file_operations scmd_driver_fops = <span class="br0">{</span> <span class="kw2">NULL</span>, <span class="coMULTI">/* nothing more, fill with NULLs */</span> <span class="br0">}</span>; </pre><p>This is the code that registers the module as a device driver:</p><pre class="code c"> <span class="kw4">static</span> <span class="kw4">int</span> __init scmd_init<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span><span class="br0">{</span> <span class="kw4">int</span> ret; <span class="co1">//SET_MODULE_OWNER(&scmd_driver_fops); //not now in 2.6 kernels</span> ret = register_chrdev<span class="br0">(</span>scmd_major, SCMD_DEV, &scmd_driver_fops<span class="br0">)</span>; printk<span class="br0">(</span><span class="st0">" Driver scmd_basic registered .. ret %d <span class="es0">\n</span>"</span>,ret<span class="br0">)</span>; <span class="kw1">if</span> <span class="br0">(</span> ret > <span class="nu0">0</span> <span class="br0">)</span> <span class="br0">{</span> scmd_major = ret; ret = <span class="nu0">0</span>; <span class="br0">}</span> <span class="kw1">return</span> ret; <span class="br0">}</span></pre><p>Here is the cleanup code to remove the device driver:</p><pre class="code c"> <span class="kw4">static</span> <span class="kw4">void</span> __exit scmd_exit<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span> <span class="br0">{</span> <span class="kw4">int</span> ret; ret = unregister_chrdev <span class="br0">(</span>scmd_major, SCMD_DEV<span class="br0">)</span>; printk<span class="br0">(</span><span class="st0">" Driver scmd_basic unregistered .. ret %d <span class="es0">\n</span>"</span>,ret<span class="br0">)</span>; <span class="br0">}</span></pre><p> This is the way the module entry and exit fuinctions are defined:</p><pre class="code c"> module_init<span class="br0">(</span>scmd_init<span class="br0">)</span>; module_exit<span class="br0">(</span>scmd_exit<span class="br0">)</span>; </pre><p> Although this device driver does not have any actual <strong>Device Driver</strong> code it does perform the proper kernel functions to get to the point where the driver code can be added. </p></div></body></html>⌨️ 快捷键说明
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