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<a name='TOP'><h2><a href='../mains.html'>root</a>/<a href='../files/104.html'>kernel</a>/printk.c</h2>
<i><font color='green'>/* [<][>]<a href='#L30'>[^]</a>[v][top]<a href='#BOTTOM'>[bottom]</a><a href='../mains.html'>[index]</a><a href='../help.html'>[help]</a> */</font></i>
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<h2>DEFINITIONS</h2>
This source file includes following definitions.
<ol>
<li><a href='#L30' title='Defined at 30.'>printk</a>
</ol>
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<pre>
<a name='L1'><i><font color='green'>/*</font></i>
<a name='L2'><i><font color='green'>* linux/kernel/printk.c</font></i>
<a name='L3'><i><font color='green'>*</font></i>
<a name='L4'><i><font color='green'>* (C) 1991 Linus Torvalds</font></i>
<a name='L5'><i><font color='green'>*/</font></i>
<a name='L6'>
<a name='L7'><i><font color='green'>/*</font></i>
<a name='L8'><i><font color='green'>* When in kernel-mode, we cannot use printf, as fs is liable to</font></i>
<a name='L9'><i><font color='green'>* point to 'interesting' things. Make a printf with fs-saving, and</font></i>
<a name='L10'><i><font color='green'>* all is well.</font></i>
<a name='L11'><i><font color='green'>*/</font></i>
<a name='L12'><i><font color='green'>/*</font></i>
<a name='L13'><i><font color='green'>* 当处于内核模式时，我们不能使用printf，因为寄存器fs 指向其它不感兴趣的地方。</font></i>
<a name='L14'><i><font color='green'>* 自己编制一个printf 并在使用前保存fs，一切就解决了。</font></i>
<a name='L15'><i><font color='green'>*/</font></i>
<a name='L16'><font color='darkred'>#include</font> <<a href='40.html'>stdarg.h</a>> <i><font color='green'>// 标准参数头文件。以宏的形式定义变量参数列表。主要说明了-个</font></i>
<a name='L17'><i><font color='green'>// 类型(va_list)和三个宏(va_start, va_arg 和va_end)，用于</font></i>
<a name='L18'><i><font color='green'>// vsprintf、vprintf、vfprintf 函数。</font></i>
<a name='L19'><font color='darkred'>#include</font> <<a href='41.html'>stddef.h</a>> <i><font color='green'>// 标准定义头文件。定义了NULL, offsetof(TYPE, MEMBER)。</font></i>
<a name='L20'>
<a name='L21'><font color='darkred'>#include</font> <<a href='34.html'>linux/kernel.h</a>> <i><font color='green'>// 内核头文件。含有一些内核常用函数的原形定义。</font></i>
<a name='L22'>
<a name='L23'><b>static</b> <b>char</b> <a href='../D/716.html' title='Multiple defined in 16 places.'>buf</a>[1024];
<a name='L24'>
<a name='L25'><i><font color='green'>// 下面该函数vsprintf()在linux/kernel/vsprintf.c 中92 行开始。</font></i>
<a name='L26'><b>extern</b> <b>int</b> <a href='../S/78.html#L137' title='Defined at 137 in kernel/vsprintf.c.'>vsprintf</a> (<b>char</b> *buf, <b>const</b> <b>char</b> *fmt, va_list args);
<a name='L27'>
<a name='L28'><i><font color='green'>// 内核使用的显示函数。</font></i>
<a name='L29'><b>int</b>
<a name='L30'><a href='../R/554.html' title='Multiple refered from 73 places.'>printk</a> (<b>const</b> <b>char</b> *fmt, ...)
<a name='L31'><font color='red'>{</font>
<a name='L32'> <a href='../S/40.html#L4' title='Defined at 4 in include/stdarg.h.'>va_list</a> args; <i><font color='green'>// va_list 实际上是一个字符指针类型。</font></i>
<a name='L33'> <b>int</b> <a href='../D/839.html' title='Multiple defined in 4 places.'>i</a>;
<a name='L34'>
<a name='L35'> <a href='../D/1107.html' title='Multiple defined in 2 places.'>va_start</a> (args, fmt); <i><font color='green'>// 参数处理开始函数。在（include/stdarg.h,13）</font></i>
<a name='L36'> <a href='../D/839.html' title='Multiple defined in 4 places.'>i</a> = <a href='../S/78.html#L137' title='Defined at 137 in kernel/vsprintf.c.'>vsprintf</a> (<a href='../D/716.html' title='Multiple defined in 16 places.'>buf</a>, fmt, args); <i><font color='green'>// 使用格式串fmt 将参数列表args 输出到buf 中。</font></i>
<a name='L37'><i><font color='green'>// 返回值i 等于输出字符串的长度。</font></i>
<a name='L38'> <a href='../S/40.html#L32' title='Defined at 32 in include/stdarg.h.'>va_end</a> (args); <i><font color='green'>// 参数处理结束函数。</font></i>
<a name='L39'> <b>__asm__</b> ("push %%fs\n\t" <i><font color='green'>// 保存fs。</font></i>
<a name='L40'> "push %%ds\n\t" "pop %%fs\n\t" <i><font color='green'>// 令fs = ds。</font></i>
<a name='L41'> "pushl %0\n\t" <i><font color='green'>// 将字符串长度压入堆栈(这三个入栈是调用参数)。</font></i>
<a name='L42'> "pushl $_buf\n\t" <i><font color='green'>// 将buf 的地址压入堆栈。</font></i>
<a name='L43'> "pushl $0\n\t" <i><font color='green'>// 将数值0 压入堆栈。是通道号channel。</font></i>
<a name='L44'> "call _tty_write\n\t" <i><font color='green'>// 调用tty_write 函数。(kernel/chr_drv/tty_io.c,290)。</font></i>
<a name='L45'> "addl $8,%%esp\n\t" <i><font color='green'>// 跳过（丢弃）两个入栈参数(buf,channel)。</font></i>
<a name='L46'> "popl %0\n\t" <i><font color='green'>// 弹出字符串长度值，作为返回值。</font></i>
<a name='L47'> "pop %%fs" <i><font color='green'>// 恢复原fs 寄存器。</font></i>
<a name='L48'>::"r" (<a href='../D/839.html' title='Multiple defined in 4 places.'>i</a>):"ax", "cx", "dx"); <i><font color='green'>// 通知编译器，寄存器ax,cx,dx 值可能已经改变。</font></i>
<a name='L49'> <b>return</b> <a href='../D/839.html' title='Multiple defined in 4 places.'>i</a>; <i><font color='green'>// 返回字符串长度。</font></i>
<a name='L50'><font color='red'>}</font>
</pre>
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