140 lines
4.6 KiB
XML
140 lines
4.6 KiB
XML
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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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<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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<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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<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_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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<refsect1>
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<title>Description</title>
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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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<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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<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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<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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<refsect1>
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&return-value;
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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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