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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>bio_alloc_bioset</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="other_functions.html" title="Other Functions" /><link rel="prev" href="API-bio-reset.html" title="bio_reset" /><link rel="next" href="API-bio-put.html" title="bio_put" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"><span class="phrase">bio_alloc_bioset</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="API-bio-reset.html">Prev</a>&#160;</td><th width="60%" align="center">Other Functions</th><td width="20%" align="right">&#160;<a accesskey="n" href="API-bio-put.html">Next</a></td></tr></table><hr /></div><div class="refentry"><a id="API-bio-alloc-bioset"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>bio_alloc_bioset &#8212; 
     allocate a bio for I/O
 </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 bio * <strong class="fsfunc">bio_alloc_bioset </strong>(</code></td><td>gfp_t <var class="pdparam">gfp_mask</var>, </td></tr><tr><td>&#160;</td><td>int <var class="pdparam">nr_iovecs</var>, </td></tr><tr><td>&#160;</td><td>struct bio_set * <var class="pdparam">bs</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer">&#160;</div></div></div><div class="refsect1"><a id="idm139881795126288"></a><h2>Arguments</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>gfp_mask</code></em></span></dt><dd><p>
     the GFP_ mask given to the slab allocator
    </p></dd><dt><span class="term"><em class="parameter"><code>nr_iovecs</code></em></span></dt><dd><p>
     number of iovecs to pre-allocate
    </p></dd><dt><span class="term"><em class="parameter"><code>bs</code></em></span></dt><dd><p>
     the bio_set to allocate from.
    </p></dd></dl></div></div><div class="refsect1"><a id="idm139881795119424"></a><h2>Description</h2><p>
   If <em class="parameter"><code>bs</code></em> is NULL, uses <code class="function">kmalloc</code> to allocate the bio; else the allocation is
   backed by the <em class="parameter"><code>bs</code></em>'s mempool.
   </p><p>

   When <em class="parameter"><code>bs</code></em> is not NULL, if <code class="constant">__GFP_WAIT</code> is set then bio_alloc will always be
   able to allocate a bio. This is due to the mempool guarantees. To make this
   work, callers must never allocate more than 1 bio at a time from this pool.
   Callers that need to allocate more than 1 bio must always submit the
   previously allocated bio for IO before attempting to allocate a new one.
   Failure to do so can cause deadlocks under memory pressure.
   </p><p>

   Note that when running under <code class="function">generic_make_request</code> (i.e. any block
   driver), bios are not submitted until after you return - see the code in
   <code class="function">generic_make_request</code> that converts recursion into iteration, to prevent
   stack overflows.
   </p><p>

   This would normally mean allocating multiple bios under
   <code class="function">generic_make_request</code> would be susceptible to deadlocks, but we have
   deadlock avoidance code that resubmits any blocked bios from a rescuer
   thread.
   </p><p>

   However, we do not guarantee forward progress for allocations from other
   mempools. Doing multiple allocations from the same mempool under
   <code class="function">generic_make_request</code> should be avoided - instead, use bio_set's front_pad
   for per bio allocations.
</p></div><div class="refsect1"><a id="idm139881795110656"></a><h2>RETURNS</h2><p>
   Pointer to new bio on success, NULL on failure.
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