📄 028_bad_inode_c.html

📁 重读linux 2.4.2o所写的笔记
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      <pre>2007-3-16</pre>
      <pre>   <span lang=zh-cn>当系统发现一个文件的inode有错误的时候，不是返回一个NULL指针，而是返回一个bad_inode.此inode的所有操作函数都返回-EIO.<br>此模块的主要对外接口是</span></pre>
      <pre><font color=#0000ff>/*<br> * When a filesystem is unable to read an inode due to an I/O error in<br> * its read_inode() function, it can call make_bad_inode() to return a<br> * set of stubs which will return EIO errors as required. <br> *<br> * We only need to do limited initialisation: all other fields are<br> * preinitialised to zero automatically.<br> */<br> </font></pre>
      <pre><font color=#0000ff>/**<br> *	make_bad_inode - mark an inode bad due to an I/O error<br> *	@inode: Inode to mark bad<br> *<br> *	When an inode cannot be read due to a media or remote network<br> *	failure this function makes the inode "bad" and causes I/O operations<br> *	on it to fail from this point on.<br> */</font>
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      <pre>void <b><font color=#008080>make_bad_inode</font></b>(struct inode * inode) <br>{<br>	inode-&gt;i_mode = S_IFREG;<br>	inode-&gt;i_atime = inode-&gt;i_mtime = inode-&gt;i_ctime = CURRENT_TIME;<br>	inode-&gt;i_op = &amp;bad_inode_ops;	<br>	inode-&gt;i_fop = &amp;bad_file_ops;	<br>}</pre>
      <pre><font color=#0000ff>/*<br> * This tests whether an inode has been flagged as bad. The test uses<br> * &amp;bad_inode_ops to cover the case of invalidated inodes as well as<br> * those created by make_bad_inode() above.<br> */<br> </font></pre>
      <pre><font color=#0000ff>/**<br> *	is_bad_inode - is an inode errored<br> *	@inode: inode to test<br> *<br> *	Returns true if the inode in question has been marked as bad.<br> */<br> </font></pre>
      <pre>int <font color=#008080><b>is_bad_inode</b></font>(struct inode * inode) <br>{<br>	return (inode-&gt;i_op == &amp;bad_inode_ops);	<br>}</pre>
      <pre>   这是个很好的例子，证名文件操作函数来自于对应的inode。so simple。唯独<font color=#008080><b>bad_follow_link</b></font>需要一些操作：</pre>
      <pre><font color=#0000ff>/*<br>* The follow_link operation is special: it must behave as a no-op<br>* so that a bad root inode can at least be unmounted. To do this<br>* we must dput() the base and return the dentry with a dget().<br>*/</font>
static int <font color=#008080><b>bad_follow_link</b></font>(struct dentry *dent, struct nameidata *nd)<br>{<br>dput(nd-&gt;dentry);<br>nd-&gt;dentry = dget(dent);<br>return 0;<br>}</pre>
      <pre><span lang=zh-cn>   可以想象，当初为了能让bad inode可以unmout，这里进行过艰苦的调试。可惜，到后来的版本中，不能unmout bad inode的情况依<br>然存在。这个函数又被删除。看看path_walk,当inode-&gt;fllow_link 为非指针的时候，inode被认为是一个link。不必深究了，这里要做<br>的很简单，只要没有什么问题即可。只是要关注一下bad inode 的umount问题。</span></pre>
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      <pre>   <br></pre>
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