1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>blk_init_queue</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="The Linux Kernel API"><link rel="up" href="blkdev.html" title="Chapter&#160;14.&#160;Block Devices"><link rel="prev" href="API-blk-cleanup-queue.html" title="blk_cleanup_queue"><link rel="next" href="API-blk-make-request.html" title="blk_make_request"></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">blk_init_queue</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="API-blk-cleanup-queue.html">Prev</a>&#160;</td><th width="60%" align="center">Chapter&#160;14.&#160;Block Devices</th><td width="20%" align="right">&#160;<a accesskey="n" href="API-blk-make-request.html">Next</a></td></tr></table><hr></div><div class="refentry"><a name="API-blk-init-queue"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>blk_init_queue &#8212; 
2     prepare a request queue for use with a block device
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">struct request_queue * <b class="fsfunc">blk_init_queue </b>(</code></td><td>request_fn_proc * <var class="pdparam">rfn</var>, </td></tr><tr><td>&#160;</td><td>spinlock_t * <var class="pdparam">lock</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer">&#160;</div></div></div><div class="refsect1"><a name="idp1127861860"></a><h2>Arguments</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>rfn</code></em></span></dt><dd><p>
4     The function to be called to process requests that have been
5     placed on the queue.
6    </p></dd><dt><span class="term"><em class="parameter"><code>lock</code></em></span></dt><dd><p>
7     Request queue spin lock
8    </p></dd></dl></div></div><div class="refsect1"><a name="idp1127864548"></a><h2>Description</h2><p>
9   If a block device wishes to use the standard request handling procedures,
10   which sorts requests and coalesces adjacent requests, then it must
11   call <code class="function">blk_init_queue</code>.  The function <em class="parameter"><code>rfn</code></em> will be called when there
12   are requests on the queue that need to be processed.  If the device
13   supports plugging, then <em class="parameter"><code>rfn</code></em> may not be called immediately when requests
14   are available on the queue, but may be called at some time later instead.
15   Plugged queues are generally unplugged when a buffer belonging to one
16   of the requests on the queue is needed, or due to memory pressure.
17   </p><p>
18
19   <em class="parameter"><code>rfn</code></em> is not required, or even expected, to remove all requests off the
20   queue, but only as many as it can handle at a time.  If it does leave
21   requests on the queue, it is responsible for arranging that the requests
22   get dealt with eventually.
23   </p><p>
24
25   The queue spin lock must be held while manipulating the requests on the
26   request queue; this lock will be taken also from interrupt context, so irq
27   disabling is needed for it.
28   </p><p>
29
30   Function returns a pointer to the initialized request queue, or <code class="constant">NULL</code> if
31   it didn't succeed.
32</p></div><div class="refsect1"><a name="idp1127868244"></a><h2>Note</h2><p>
33   <code class="function">blk_init_queue</code> must be paired with a <code class="function">blk_cleanup_queue</code> call
34   when the block device is deactivated (such as at module unload).
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