📄 linux设备驱动程序学习（3-补）-linux中的循环缓冲区 - linux设备驱动程序 - tekkaman ninja.htm
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style="COLOR: #000000"><FONT face=新宋体><SPAN
style="COLOR: #0000ff">unsigned</SPAN> <SPAN
style="COLOR: #0000ff">int</SPAN> kfifo_put<SPAN
style="COLOR: #0000cc">(</SPAN><SPAN
style="COLOR: #0000ff">struct</SPAN> kfifo <SPAN
style="COLOR: #0000cc">*</SPAN>fifo<SPAN
style="COLOR: #0000cc">,</SPAN><SPAN
style="COLOR: #0000ff">unsigned</SPAN> <SPAN
style="COLOR: #0000ff">char</SPAN> <SPAN
style="COLOR: #0000cc">*</SPAN>buffer<SPAN
style="COLOR: #0000cc">,</SPAN> <SPAN
style="COLOR: #0000ff">unsigned</SPAN> <SPAN
style="COLOR: #0000ff">int</SPAN> len<SPAN
style="COLOR: #0000cc">);</SPAN><BR><SPAN
style="COLOR: #0000ff">unsigned</SPAN> <SPAN
style="COLOR: #0000ff">int</SPAN>
__kfifo_put<SPAN
style="COLOR: #0000cc">(</SPAN><SPAN
style="COLOR: #0000ff">struct</SPAN> kfifo <SPAN
style="COLOR: #0000cc">*</SPAN>fifo<SPAN
style="COLOR: #0000cc">,</SPAN><SPAN
style="COLOR: #0000ff">unsigned</SPAN> <SPAN
style="COLOR: #0000ff">char</SPAN> <SPAN
style="COLOR: #0000cc">*</SPAN>buffer<SPAN
style="COLOR: #0000cc">,</SPAN> <SPAN
style="COLOR: #0000ff">unsigned</SPAN> <SPAN
style="COLOR: #0000ff">int</SPAN> len<SPAN
style="COLOR: #0000cc">)</SPAN><SPAN
style="COLOR: #0000cc">;</SPAN></FONT></SPAN></CODE></P></TD></TR></TBODY></TABLE></P>
<P><FONT face=新宋体>fifo：要写入数据的缓冲区结构体指针；</FONT></P>
<P><FONT
face=新宋体>buffer：要写入的数据指针，指向内核空间。如需要用户空间数据，之前要用copy_from_user复制数据到内核空间；</FONT></P>
<P><FONT face=新宋体>len：要写入的数据大小；</FONT></P>
<P><FONT face=新宋体><FONT color=#0000ff>返回值</FONT>
为写入缓冲区的数据字节数。</FONT></P>
<P><FONT face=新宋体>（3）从缓冲区里读出数据</FONT>
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style="MARGIN: 5px; LINE-HEIGHT: 150%"><CODE><SPAN
style="COLOR: #000000"><FONT face=新宋体><SPAN
style="COLOR: #0000ff">unsigned</SPAN> <SPAN
style="COLOR: #0000ff">int</SPAN> kfifo_get<SPAN
style="COLOR: #0000cc">(</SPAN><SPAN
style="COLOR: #0000ff">struct</SPAN> kfifo <SPAN
style="COLOR: #0000cc">*</SPAN>fifo<SPAN
style="COLOR: #0000cc">,</SPAN> <SPAN
style="COLOR: #0000ff">unsigned</SPAN> <SPAN
style="COLOR: #0000ff">char</SPAN> <SPAN
style="COLOR: #0000cc">*</SPAN>buffer<SPAN
style="COLOR: #0000cc">,</SPAN> <SPAN
style="COLOR: #0000ff">unsigned</SPAN> <SPAN
style="COLOR: #0000ff">int</SPAN> len<SPAN
style="COLOR: #0000cc">)</SPAN><SPAN
style="COLOR: #0000cc">;</SPAN><BR><SPAN
style="COLOR: #0000ff">unsigned</SPAN> <SPAN
style="COLOR: #0000ff">int</SPAN>
__kfifo_get<SPAN
style="COLOR: #0000cc">(</SPAN><SPAN
style="COLOR: #0000ff">struct</SPAN> kfifo <SPAN
style="COLOR: #0000cc">*</SPAN>fifo<SPAN
style="COLOR: #0000cc">,</SPAN> <SPAN
style="COLOR: #0000ff">unsigned</SPAN> <SPAN
style="COLOR: #0000ff">char</SPAN> <SPAN
style="COLOR: #0000cc">*</SPAN>buffer<SPAN
style="COLOR: #0000cc">,</SPAN> <SPAN
style="COLOR: #0000ff">unsigned</SPAN> <SPAN
style="COLOR: #0000ff">int</SPAN> len<SPAN
style="COLOR: #0000cc">)</SPAN><SPAN
style="COLOR: #0000cc">;</SPAN></FONT></SPAN></CODE></P></TD></TR></TBODY></TABLE></P>
<P>参数定义和<FONT face=新宋体>kfifo_put类似。</FONT></P>
<P><FONT face=新宋体><FONT color=#0000ff>返回值</FONT>
为从缓冲区读出的数据字节数。</FONT></P>
<P><FONT face=新宋体>（4）得到缓冲区已有的数据字节数</FONT>
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<P
style="MARGIN: 5px; LINE-HEIGHT: 150%"><CODE><SPAN
style="COLOR: #000000"><FONT face=新宋体><SPAN
style="COLOR: #0000ff">unsigned</SPAN> <SPAN
style="COLOR: #0000ff">int</SPAN> kfifo_len<SPAN
style="COLOR: #0000cc">(</SPAN><SPAN
style="COLOR: #0000ff">struct</SPAN> kfifo <SPAN
style="COLOR: #0000cc">*</SPAN>fifo<SPAN
style="COLOR: #0000cc">)</SPAN><SPAN
style="COLOR: #0000cc">;</SPAN><BR><SPAN
style="COLOR: #0000ff">unsigned</SPAN> <SPAN
style="COLOR: #0000ff">int</SPAN>
__kfifo_len<SPAN
style="COLOR: #0000cc">(</SPAN><SPAN
style="COLOR: #0000ff">struct</SPAN> kfifo <SPAN
style="COLOR: #0000cc">*</SPAN>fifo<SPAN
style="COLOR: #0000cc">)</SPAN><SPAN
style="COLOR: #0000cc">;</SPAN></FONT></SPAN></CODE></P></TD></TR></TBODY></TABLE></P>
<P><FONT face=新宋体>fifo：要操作的缓冲区结构体指针；</FONT></P>
<P><FONT face=新宋体>函数返回缓冲区实际已有的数据字节数，内部实现十分简单，就是in
- out；</FONT></P>
<P><FONT face=新宋体><FONT color=#0000ff>返回值</FONT>
为缓冲区已有的数据字节数。</FONT></P>
<P><FONT face=新宋体>（5）清空缓冲区</FONT>
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style="MARGIN: 5px; LINE-HEIGHT: 150%"><CODE><SPAN
style="COLOR: #000000"><FONT face=新宋体><SPAN
style="COLOR: #0000ff">void</SPAN>
__kfifo_reset<SPAN
style="COLOR: #0000cc">(</SPAN><SPAN
style="COLOR: #0000ff">struct</SPAN> kfifo <SPAN
style="COLOR: #0000cc">*</SPAN>fifo<SPAN
style="COLOR: #0000cc">)</SPAN><SPAN
style="COLOR: #0000cc">;</SPAN><BR><SPAN
style="COLOR: #0000ff">void</SPAN>
kfifo_reset<SPAN
style="COLOR: #0000cc">(</SPAN><SPAN
style="COLOR: #0000ff">struct</SPAN> kfifo <SPAN
style="COLOR: #0000cc">*</SPAN>fifo<SPAN
style="COLOR: #0000cc">)</SPAN><SPAN
style="COLOR: #0000cc">;</SPAN></FONT></SPAN></CODE></P></TD></TR></TBODY></TABLE></P>
<P><FONT face=新宋体>内部实现十分简单，就是in = out =
0。</FONT></P>
<P><FONT face=新宋体>（6）使用结束，释放缓冲区。</FONT>
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<P
style="MARGIN: 5px; LINE-HEIGHT: 150%"><CODE><SPAN
style="COLOR: #000000"><FONT face=新宋体><SPAN
style="COLOR: #0000ff">void</SPAN>
kfifo_free<SPAN
style="COLOR: #0000cc">(</SPAN><SPAN
style="COLOR: #0000ff">struct</SPAN> kfifo <SPAN
style="COLOR: #0000cc">*</SPAN>fifo<SPAN
style="COLOR: #0000cc">)</SPAN><SPAN
style="COLOR: #0000cc">;</SPAN></FONT></SPAN></CODE></P></TD></TR></TBODY></TABLE></P>
<P><FONT face=新宋体>所有的<SPAN lang=en-US><FONT
face=宋体>kfifo</FONT></SPAN></FONT><FONT
face="Courier New">提供的循环缓冲的函数就是这些。在理解内部实现原理的基础上才能更好的使用它，所以<FONT
color=#0000ff><STRONG>再次建议阅读源码，因为源码很简单，但是很精巧。</STRONG></FONT>
<HR id=null>
</FONT>
<P></P>
<P><FONT face=新宋体 color=#0000ff
size=4><STRONG>ARM9开发板实验</STRONG></FONT></P>
<P><STRONG><FONT face=新宋体 color=#0000ff>实验模块源码：<A
href="http://blogimg.chinaunix.net/blog/upfile2/071210215938.gz"
target=_blank><FONT face="Courier New"
size=4>scull-kfifo</FONT></A></FONT></STRONG></P>
<P><STRONG><FONT face=新宋体 color=#0000ff>测试程序源码：<A
href="http://blogimg.chinaunix.net/blog/upfile2/071210215949.gz"
target=_blank><FONT face="Courier New"
size=4>scull-kfifo-test</FONT></A></FONT></STRONG></P>
<P><STRONG><FONT color=#0000ff size=3><FONT
face=新宋体>实验现象：</FONT>
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<P
style="MARGIN: 5px; LINE-HEIGHT: 150%"><CODE><SPAN
style="COLOR: #000000"><FONT face=新宋体><SPAN
style="COLOR: #0000cc">[</SPAN>Tekkaman2440@SBC2440V4<SPAN
style="COLOR: #0000cc">]</SPAN><SPAN
style="COLOR: #0000cc">#</SPAN>cd <SPAN
style="COLOR: #0000cc">/</SPAN>lib<SPAN
style="COLOR: #0000cc">/</SPAN>modules<SPAN
style="COLOR: #0000cc">/</SPAN><BR><SPAN
style="COLOR: #0000cc">[</SPAN>Tekkaman2440@SBC2440V4<SPAN
style="COLOR: #0000cc">]</SPAN><SPAN
style="COLOR: #0000cc">#</SPAN>insmod
scull_kfifo<SPAN
style="COLOR: #0000cc">.</SPAN>ko<BR><SPAN
style="COLOR: #0000cc">[</SPAN>Tekkaman2440@SBC2440V4<SPAN
style="COLOR: #0000cc">]</SPAN><SPAN
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