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