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-<refentry id="vidioc-reqbufs">
- <refmeta>
- <refentrytitle>ioctl VIDIOC_REQBUFS</refentrytitle>
- &manvol;
- </refmeta>
-
- <refnamediv>
- <refname>VIDIOC_REQBUFS</refname>
- <refpurpose>Initiate Memory Mapping or User Pointer I/O</refpurpose>
- </refnamediv>
-
- <refsynopsisdiv>
- <funcsynopsis>
- <funcprototype>
- <funcdef>int <function>ioctl</function></funcdef>
- <paramdef>int <parameter>fd</parameter></paramdef>
- <paramdef>int <parameter>request</parameter></paramdef>
- <paramdef>struct v4l2_requestbuffers *<parameter>argp</parameter></paramdef>
- </funcprototype>
- </funcsynopsis>
- </refsynopsisdiv>
-
- <refsect1>
- <title>Arguments</title>
-
- <variablelist>
- <varlistentry>
- <term><parameter>fd</parameter></term>
- <listitem>
- <para>&fd;</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><parameter>request</parameter></term>
- <listitem>
- <para>VIDIOC_REQBUFS</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><parameter>argp</parameter></term>
- <listitem>
- <para></para>
- </listitem>
- </varlistentry>
- </variablelist>
- </refsect1>
-
- <refsect1>
- <title>Description</title>
-
- <para>This ioctl is used to initiate <link linkend="mmap">memory
-mapped</link> or <link linkend="userp">user pointer</link>
-I/O. Memory mapped buffers are located in device memory and must be
-allocated with this ioctl before they can be mapped into the
-application's address space. User buffers are allocated by
-applications themselves, and this ioctl is merely used to switch the
-driver into user pointer I/O mode and to setup some internal structures.</para>
-
- <para>To allocate device buffers applications initialize all
-fields of the <structname>v4l2_requestbuffers</structname> structure.
-They set the <structfield>type</structfield> field to the respective
-stream or buffer type, the <structfield>count</structfield> field to
-the desired number of buffers, <structfield>memory</structfield>
-must be set to the requested I/O method and the <structfield>reserved</structfield> array
-must be zeroed. When the ioctl
-is called with a pointer to this structure the driver will attempt to allocate
-the requested number of buffers and it stores the actual number
-allocated in the <structfield>count</structfield> field. It can be
-smaller than the number requested, even zero, when the driver runs out
-of free memory. A larger number is also possible when the driver requires
-more buffers to function correctly. For example video output requires at least two buffers,
-one displayed and one filled by the application.</para>
- <para>When the I/O method is not supported the ioctl
-returns an &EINVAL;.</para>
-
- <para>Applications can call <constant>VIDIOC_REQBUFS</constant>
-again to change the number of buffers, however this cannot succeed
-when any buffers are still mapped. A <structfield>count</structfield>
-value of zero frees all buffers, after aborting or finishing any DMA
-in progress, an implicit &VIDIOC-STREAMOFF;. <!-- mhs: I see no
-reason why munmap()ping one or even all buffers must imply
-streamoff.--></para>
-
- <table pgwide="1" frame="none" id="v4l2-requestbuffers">
- <title>struct <structname>v4l2_requestbuffers</structname></title>
- <tgroup cols="3">
- &cs-str;
- <tbody valign="top">
- <row>
- <entry>__u32</entry>
- <entry><structfield>count</structfield></entry>
- <entry>The number of buffers requested or granted.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>type</structfield></entry>
- <entry>Type of the stream or buffers, this is the same
-as the &v4l2-format; <structfield>type</structfield> field. See <xref
- linkend="v4l2-buf-type" /> for valid values.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>memory</structfield></entry>
- <entry>Applications set this field to
-<constant>V4L2_MEMORY_MMAP</constant> or
-<constant>V4L2_MEMORY_USERPTR</constant>. See <xref linkend="v4l2-memory"
-/>.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>reserved</structfield>[2]</entry>
- <entry>A place holder for future extensions and custom
-(driver defined) buffer types <constant>V4L2_BUF_TYPE_PRIVATE</constant> and
-higher. This array should be zeroed by applications.</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
- </refsect1>
-
- <refsect1>
- &return-value;
-
- <variablelist>
- <varlistentry>
- <term><errorcode>EINVAL</errorcode></term>
- <listitem>
- <para>The buffer type (<structfield>type</structfield> field) or the
-requested I/O method (<structfield>memory</structfield>) is not
-supported.</para>
- </listitem>
- </varlistentry>
- </variablelist>
- </refsect1>
-</refentry>