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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>blk_lld_busy</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="The Linux Kernel API" /><link rel="up" href="ch14.html" title="Chapter 14. Block Devices" /><link rel="prev" href="re528.html" title="__blk_end_request_err" /><link rel="next" href="re530.html" title="blk_rq_unprep_clone" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"><span>blk_lld_busy</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="re528.html">Prev</a> </td><th width="60%" align="center">Chapter 14. Block Devices</th><td width="20%" align="right"> <a accesskey="n" href="re530.html">Next</a></td></tr></table><hr /></div><div class="refentry" title="blk_lld_busy"><a id="API-blk-lld-busy"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>blk_lld_busy —
Check if underlying low-level drivers of a device are busy
</p></div><div class="refsynopsisdiv" title="Synopsis"><h2>Synopsis</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">int <b class="fsfunc">blk_lld_busy </b>(</code></td><td>struct request_queue * <var class="pdparam">q</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1" title="Arguments"><a id="id3031859"></a><h2>Arguments</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>q</code></em></span></dt><dd><p>
the queue of the device being checked
</p></dd></dl></div></div><div class="refsect1" title="Description"><a id="id3031886"></a><h2>Description</h2><p>
Check if underlying low-level drivers of a device are busy.
If the drivers want to export their busy state, they must set own
exporting function using <code class="function">blk_queue_lld_busy</code> first.
</p><p>
Basically, this function is used only by request stacking drivers
to stop dispatching requests to underlying devices when underlying
devices are busy. This behavior helps more I/O merging on the queue
of the request stacking driver and prevents I/O throughput regression
on burst I/O load.
</p></div><div class="refsect1" title="Return"><a id="id3031912"></a><h2>Return</h2><p>
0 - Not busy (The request stacking driver should dispatch request)
1 - Busy (The request stacking driver should stop dispatching request)
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