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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_rq_check_limits</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="re512.html" title="submit_bio" /><link rel="next" href="re514.html" title="blk_insert_cloned_request" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"><span>blk_rq_check_limits</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="re512.html">Prev</a> </td><th width="60%" align="center">Chapter 14. Block Devices</th><td width="20%" align="right"> <a accesskey="n" href="re514.html">Next</a></td></tr></table><hr /></div><div class="refentry" title="blk_rq_check_limits"><a id="API-blk-rq-check-limits"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>blk_rq_check_limits —
Helper function to check a request for the queue limit
</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_rq_check_limits </b>(</code></td><td>struct request_queue * <var class="pdparam">q</var>, </td></tr><tr><td> </td><td>struct request * <var class="pdparam">rq</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1" title="Arguments"><a id="id3029208"></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
</p></dd><dt><span class="term"><em class="parameter"><code>rq</code></em></span></dt><dd><p>
the request being checked
</p></dd></dl></div></div><div class="refsect1" title="Description"><a id="id3029251"></a><h2>Description</h2><p>
<em class="parameter"><code>rq</code></em> may have been made based on weaker limitations of upper-level queues
in request stacking drivers, and it may violate the limitation of <em class="parameter"><code>q</code></em>.
Since the block layer and the underlying device driver trust <em class="parameter"><code>rq</code></em>
after it is inserted to <em class="parameter"><code>q</code></em>, it should be checked against <em class="parameter"><code>q</code></em> before
the insertion using this generic function.
</p><p>
This function should also be useful for request stacking drivers
in some cases below, so export this fuction.
Request stacking drivers like request-based dm may change the queue
limits while requests are in the queue (e.g. dm's table swapping).
Such request stacking drivers should check those requests agaist
the new queue limits again when they dispatch those requests,
although such checkings are also done against the old queue limits
when submitting requests.
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