1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>ioctl VIDIOC_REQBUFS</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="LINUX MEDIA INFRASTRUCTURE API"><link rel="up" href="user-func.html" title="Appendix A. Function Reference"><link rel="prev" href="vidioc-querystd.html" title="ioctl VIDIOC_QUERYSTD"><link rel="next" href="vidioc-s-hw-freq-seek.html" title="ioctl VIDIOC_S_HW_FREQ_SEEK"></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">ioctl VIDIOC_REQBUFS</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="vidioc-querystd.html">Prev</a> </td><th width="60%" align="center">Appendix A. Function Reference</th><td width="20%" align="right"> <a accesskey="n" href="vidioc-s-hw-freq-seek.html">Next</a></td></tr></table><hr></div><div class="refentry"><a name="vidioc-reqbufs"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>VIDIOC_REQBUFS — Initiate Memory Mapping or User Pointer 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">int <b class="fsfunc">ioctl</b>(</code></td><td>int <var class="pdparam">fd</var>, </td></tr><tr><td> </td><td>int <var class="pdparam">request</var>, </td></tr><tr><td> </td><td>struct v4l2_requestbuffers *<var class="pdparam">argp</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a name="idp1116223540"></a><h2>Arguments</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>fd</code></em></span></dt><dd><p>File descriptor returned by <a class="link" href="func-open.html" title="V4L2 open()"><code class="function">open()</code></a>.</p></dd><dt><span class="term"><em class="parameter"><code>request</code></em></span></dt><dd><p>VIDIOC_REQBUFS</p></dd><dt><span class="term"><em class="parameter"><code>argp</code></em></span></dt><dd><p></p></dd></dl></div></div><div class="refsect1"><a name="idp1116227628"></a><h2>Description</h2><p>This ioctl is used to initiate <a class="link" href="mmap.html" title="Streaming I/O (Memory Mapping)">memory mapped</a>, 2<a class="link" href="userp.html" title="Streaming I/O (User Pointers)">user pointer</a> or <a class="link" href="dmabuf.html" title="Streaming I/O (DMA buffer importing)">DMABUF</a> based I/O. Memory mapped buffers are located in 3device memory and must be allocated with this ioctl before they can be mapped 4into the application's address space. User buffers are allocated by 5applications themselves, and this ioctl is merely used to switch the driver 6into user pointer I/O mode and to setup some internal structures. 7Similarly, DMABUF buffers are allocated by applications through a device 8driver, and this ioctl only configures the driver into DMABUF I/O mode without 9performing any direct allocation.</p><p>To allocate device buffers applications initialize all fields of the 10<span class="structname">v4l2_requestbuffers</span> structure. They set the 11<em class="structfield"><code>type</code></em> field to the respective stream or buffer type, 12the <em class="structfield"><code>count</code></em> field to the desired number of buffers, 13<em class="structfield"><code>memory</code></em> must be set to the requested I/O method and 14the <em class="structfield"><code>reserved</code></em> array must be zeroed. When the ioctl is 15called with a pointer to this structure the driver will attempt to allocate the 16requested number of buffers and it stores the actual number allocated in the 17<em class="structfield"><code>count</code></em> field. It can be smaller than the number 18requested, even zero, when the driver runs out of free memory. A larger number 19is also possible when the driver requires more buffers to function correctly. 20For example video output requires at least two buffers, one displayed and one 21filled by the application.</p><p>When the I/O method is not supported the ioctl 22returns an <span class="errorcode">EINVAL</span> error code.</p><p>Applications can call <code class="constant">VIDIOC_REQBUFS</code> 23again to change the number of buffers, however this cannot succeed 24when any buffers are still mapped. A <em class="structfield"><code>count</code></em> 25value of zero frees all buffers, after aborting or finishing any DMA 26in progress, an implicit <a class="link" href="vidioc-streamon.html" title="ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF"><code class="constant">VIDIOC_STREAMOFF</code></a>. </p><div class="table"><a name="v4l2-requestbuffers"></a><p class="title"><b>Table A.100. struct <span class="structname">v4l2_requestbuffers</span></b></p><div class="table-contents"><table summary="struct v4l2_requestbuffers" width="100%" border="0"><colgroup><col class="c1"><col class="c2"><col class="c3"></colgroup><tbody valign="top"><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>count</code></em></td><td valign="top">The number of buffers requested or granted.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>type</code></em></td><td valign="top">Type of the stream or buffers, this is the same 27as the struct <a class="link" href="vidioc-g-fmt.html#v4l2-format" title="Table A.72. struct v4l2_format">v4l2_format</a> <em class="structfield"><code>type</code></em> field. See <a class="xref" href="buffer.html#v4l2-buf-type" title="Table 3.3. enum v4l2_buf_type">Table 3.3, “enum v4l2_buf_type”</a> for valid values.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>memory</code></em></td><td valign="top">Applications set this field to 28<code class="constant">V4L2_MEMORY_MMAP</code>, 29<code class="constant">V4L2_MEMORY_DMABUF</code> or 30<code class="constant">V4L2_MEMORY_USERPTR</code>. See <a class="xref" href="buffer.html#v4l2-memory" title="Table 3.5. enum v4l2_memory">Table 3.5, “enum v4l2_memory”</a>.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>reserved</code></em>[2]</td><td valign="top">A place holder for future extensions. This array should 31be zeroed by applications.</td></tr></tbody></table></div></div><br class="table-break"></div><div class="refsect1"><a name="idp1116275444"></a><h2>Return Value</h2><p>On success <span class="returnvalue">0</span> is returned, on error <span class="returnvalue">-1</span> and the <code class="varname">errno</code> variable is set appropriately. The generic error codes are described at the <a class="link" href="gen_errors.html#gen-errors" title="Table 19.1. Generic error codes">Generic Error Codes</a> chapter.</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><span class="errorcode">EINVAL</span></span></dt><dd><p>The buffer type (<em class="structfield"><code>type</code></em> field) or the 32requested I/O method (<em class="structfield"><code>memory</code></em>) is not 33supported.</p></dd></dl></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="vidioc-querystd.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="user-func.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="vidioc-s-hw-freq-seek.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">ioctl VIDIOC_QUERYSTD </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> ioctl VIDIOC_S_HW_FREQ_SEEK</td></tr></table></div></body></html> 34