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+<refentry id="vidioc-create-bufs">
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+ <refmeta>
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+ <refentrytitle>ioctl VIDIOC_CREATE_BUFS</refentrytitle>
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+ &manvol;
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+ </refmeta>
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+
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+ <refnamediv>
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+ <refname>VIDIOC_CREATE_BUFS</refname>
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+ <refpurpose>Create buffers for Memory Mapped or User Pointer I/O</refpurpose>
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+ </refnamediv>
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+
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+ <refsynopsisdiv>
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+ <funcsynopsis>
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+ <funcprototype>
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+ <funcdef>int <function>ioctl</function></funcdef>
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+ <paramdef>int <parameter>fd</parameter></paramdef>
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+ <paramdef>int <parameter>request</parameter></paramdef>
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+ <paramdef>struct v4l2_create_buffers *<parameter>argp</parameter></paramdef>
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+ </funcprototype>
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+ </funcsynopsis>
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+ </refsynopsisdiv>
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+
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+ <refsect1>
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+ <title>Arguments</title>
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+
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+ <variablelist>
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+ <varlistentry>
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+ <term><parameter>fd</parameter></term>
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+ <listitem>
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+ <para>&fd;</para>
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+ </listitem>
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+ </varlistentry>
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+ <varlistentry>
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+ <term><parameter>request</parameter></term>
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+ <listitem>
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+ <para>VIDIOC_CREATE_BUFS</para>
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+ </listitem>
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+ </varlistentry>
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+ <varlistentry>
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+ <term><parameter>argp</parameter></term>
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+ <listitem>
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+ <para></para>
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+ </listitem>
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+ </varlistentry>
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+ </variablelist>
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+ </refsect1>
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+
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+ <refsect1>
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+ <title>Description</title>
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+
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+ <para>This ioctl is used to create buffers for <link linkend="mmap">memory
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+mapped</link> or <link linkend="userp">user pointer</link>
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+I/O. It can be used as an alternative or in addition to the
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+<constant>VIDIOC_REQBUFS</constant> ioctl, when a tighter control over buffers
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+is required. This ioctl can be called multiple times to create buffers of
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+different sizes.</para>
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+
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+ <para>To allocate device buffers applications initialize relevant fields of
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+the <structname>v4l2_create_buffers</structname> structure. They set the
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+<structfield>type</structfield> field in the
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+<structname>v4l2_format</structname> structure, embedded in this
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+structure, to the respective stream or buffer type.
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+<structfield>count</structfield> must be set to the number of required buffers.
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+<structfield>memory</structfield> specifies the required I/O method. The
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+<structfield>format</structfield> field shall typically be filled in using
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+either the <constant>VIDIOC_TRY_FMT</constant> or
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+<constant>VIDIOC_G_FMT</constant> ioctl(). Additionally, applications can adjust
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+<structfield>sizeimage</structfield> fields to fit their specific needs. The
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+<structfield>reserved</structfield> array must be zeroed.</para>
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+
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+ <para>When the ioctl is called with a pointer to this structure the driver
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+will attempt to allocate up to the requested number of buffers and store the
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+actual number allocated and the starting index in the
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+<structfield>count</structfield> and the <structfield>index</structfield> fields
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+respectively. On return <structfield>count</structfield> can be smaller than
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+the number requested. The driver may also increase buffer sizes if required,
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+however, it will not update <structfield>sizeimage</structfield> field values.
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+The user has to use <constant>VIDIOC_QUERYBUF</constant> to retrieve that
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+information.</para>
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+
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+ <table pgwide="1" frame="none" id="v4l2-create-buffers">
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+ <title>struct <structname>v4l2_create_buffers</structname></title>
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+ <tgroup cols="3">
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+ &cs-str;
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+ <tbody valign="top">
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+ <row>
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+ <entry>__u32</entry>
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+ <entry><structfield>index</structfield></entry>
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+ <entry>The starting buffer index, returned by the driver.</entry>
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+ </row>
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+ <row>
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+ <entry>__u32</entry>
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+ <entry><structfield>count</structfield></entry>
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+ <entry>The number of buffers requested or granted.</entry>
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+ </row>
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+ <row>
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+ <entry>&v4l2-memory;</entry>
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+ <entry><structfield>memory</structfield></entry>
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+ <entry>Applications set this field to
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+<constant>V4L2_MEMORY_MMAP</constant> or
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+<constant>V4L2_MEMORY_USERPTR</constant>.</entry>
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+ </row>
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+ <row>
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+ <entry>&v4l2-format;</entry>
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+ <entry><structfield>format</structfield></entry>
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+ <entry>Filled in by the application, preserved by the driver.</entry>
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+ </row>
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+ <row>
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+ <entry>__u32</entry>
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+ <entry><structfield>reserved</structfield>[8]</entry>
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+ <entry>A place holder for future extensions.</entry>
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+ </row>
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+ </tbody>
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+ </tgroup>
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+ </table>
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+ </refsect1>
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+
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+ <refsect1>
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+ &return-value;
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+
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+ <variablelist>
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+ <varlistentry>
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+ <term><errorcode>ENOMEM</errorcode></term>
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+ <listitem>
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+ <para>No memory to allocate buffers for <link linkend="mmap">memory
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+mapped</link> I/O.</para>
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+ </listitem>
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+ </varlistentry>
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+ <varlistentry>
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+ <term><errorcode>EINVAL</errorcode></term>
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+ <listitem>
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+ <para>The buffer type (<structfield>type</structfield> field) or the
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+requested I/O method (<structfield>memory</structfield>) is not
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+supported.</para>
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+ </listitem>
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+ </varlistentry>
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+ </variablelist>
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+ </refsect1>
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+</refentry>
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Guennadi Liakhovetski