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<refentry id="vidioc-prepare-buf">
<refmeta>
<refentrytitle>ioctl VIDIOC_PREPARE_BUF</refentrytitle>
&manvol;
</refmeta>
<refnamediv>
<refname>VIDIOC_PREPARE_BUF</refname>
<refpurpose>Prepare a buffer for 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_buffer *<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_PREPARE_BUF</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>argp</parameter></term>
<listitem>
<para></para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Description</title>
<para>Applications can optionally call the
<constant>VIDIOC_PREPARE_BUF</constant> ioctl to pass ownership of the buffer
to the driver before actually enqueuing it, using the
<constant>VIDIOC_QBUF</constant> ioctl, and to prepare it for future I/O.
Such preparations may include cache invalidation or cleaning. Performing them
in advance saves time during the actual I/O. In case such cache operations are
not required, the application can use one of
<constant>V4L2_BUF_FLAG_NO_CACHE_INVALIDATE</constant> and
<constant>V4L2_BUF_FLAG_NO_CACHE_CLEAN</constant> flags to skip the respective
step.</para>
<para>The <structname>v4l2_buffer</structname> structure is
specified in <xref linkend="buffer" />.</para>
</refsect1>
<refsect1>
&return-value;
<variablelist>
<varlistentry>
<term><errorcode>EBUSY</errorcode></term>
<listitem>
<para>File I/O is in progress.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><errorcode>EINVAL</errorcode></term>
<listitem>
<para>The buffer <structfield>type</structfield> is not
supported, or the <structfield>index</structfield> is out of bounds,
or no buffers have been allocated yet, or the
<structfield>userptr</structfield> or
<structfield>length</structfield> are invalid.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
</refentry>
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