1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>sb_start_write</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="Linux Filesystems API"><link rel="up" href="vfs.html#the_filesystem_types" title="The Filesystem types"><link rel="prev" href="API-sb-end-intwrite.html" title="sb_end_intwrite"><link rel="next" href="API-sb-start-pagefault.html" title="sb_start_pagefault"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"><span class="phrase">sb_start_write</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="API-sb-end-intwrite.html">Prev</a>&#160;</td><th width="60%" align="center">The Filesystem types</th><td width="20%" align="right">&#160;<a accesskey="n" href="API-sb-start-pagefault.html">Next</a></td></tr></table><hr></div><div class="refentry"><a name="API-sb-start-write"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>sb_start_write &#8212; 
2     get write access to a superblock
3 </p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void <b class="fsfunc">sb_start_write </b>(</code></td><td>struct super_block * <var class="pdparam">sb</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer">&#160;</div></div></div><div class="refsect1"><a name="idp1099075940"></a><h2>Arguments</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>sb</code></em></span></dt><dd><p>
4     the super we write to
5    </p></dd></dl></div></div><div class="refsect1"><a name="idp1099077500"></a><h2>Description</h2><p>
6   When a process wants to write data or metadata to a file system (i.e. dirty
7   a page or an inode), it should embed the operation in a <code class="function">sb_start_write</code> -
8   <code class="function">sb_end_write</code> pair to get exclusion against file system freezing. This
9   function increments number of writers preventing freezing. If the file
10   system is already frozen, the function waits until the file system is
11   thawed.
12   </p><p>
13
14   Since freeze protection behaves as a lock, users have to preserve
15   ordering of freeze protection and other filesystem locks. Generally,
16   freeze protection should be the outermost lock. In particular, we have:
17   </p><p>
18
19   sb_start_write
20   -&gt; i_mutex			(write path, truncate, directory ops, ...)
21   -&gt; s_umount		(freeze_super, thaw_super)
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