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- <refentry id="vidioc-create-bufs">
- <refmeta>
- <refentrytitle>ioctl VIDIOC_CREATE_BUFS</refentrytitle>
- &manvol;
- </refmeta>
- <refnamediv>
- <refname>VIDIOC_CREATE_BUFS</refname>
- <refpurpose>Create buffers for Memory Mapped or User Pointer or DMA Buffer
- 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_create_buffers *<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_CREATE_BUFS</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><parameter>argp</parameter></term>
- <listitem>
- <para></para>
- </listitem>
- </varlistentry>
- </variablelist>
- </refsect1>
- <refsect1>
- <title>Description</title>
- <note>
- <title>Experimental</title>
- <para>This is an <link linkend="experimental"> experimental </link>
- interface and may change in the future.</para>
- </note>
- <para>This ioctl is used to create buffers for <link linkend="mmap">memory
- mapped</link> or <link linkend="userp">user pointer</link> or <link
- linkend="dmabuf">DMA buffer</link> I/O. It can be used as an alternative or in
- addition to the <constant>VIDIOC_REQBUFS</constant> ioctl, when a tighter
- control over buffers is required. This ioctl can be called multiple times to
- create buffers of different sizes.</para>
- <para>To allocate the device buffers applications must initialize the
- relevant fields of the <structname>v4l2_create_buffers</structname> structure.
- The <structfield>count</structfield> field must be set to the number of
- requested buffers, the <structfield>memory</structfield> field specifies the
- requested I/O method and the <structfield>reserved</structfield> array must be
- zeroed.</para>
- <para>The <structfield>format</structfield> field specifies the image format
- that the buffers must be able to handle. The application has to fill in this
- &v4l2-format;. Usually this will be done using the
- <constant>VIDIOC_TRY_FMT</constant> or <constant>VIDIOC_G_FMT</constant> ioctl()
- to ensure that the requested format is supported by the driver. Unsupported
- formats will result in an error.</para>
- <para>The buffers created by this ioctl will have as minimum size the size
- defined by the <structfield>format.pix.sizeimage</structfield> field. If the
- <structfield>format.pix.sizeimage</structfield> field is less than the minimum
- required for the given format, then <structfield>sizeimage</structfield> will be
- increased by the driver to that minimum to allocate the buffers. If it is
- larger, then the value will be used as-is. The same applies to the
- <structfield>sizeimage</structfield> field of the
- <structname>v4l2_plane_pix_format</structname> structure in the case of
- multiplanar formats.</para>
- <para>When the ioctl is called with a pointer to this structure the driver
- will attempt to allocate up to the requested number of buffers and store the
- actual number allocated and the starting index in the
- <structfield>count</structfield> and the <structfield>index</structfield> fields
- respectively. On return <structfield>count</structfield> can be smaller than
- the number requested. The driver may also increase buffer sizes if required,
- however, it will not update <structfield>sizeimage</structfield> field values.
- The user has to use <constant>VIDIOC_QUERYBUF</constant> to retrieve that
- information.</para>
- <table pgwide="1" frame="none" id="v4l2-create-buffers">
- <title>struct <structname>v4l2_create_buffers</structname></title>
- <tgroup cols="3">
- &cs-str;
- <tbody valign="top">
- <row>
- <entry>__u32</entry>
- <entry><structfield>index</structfield></entry>
- <entry>The starting buffer index, returned by the driver.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>count</structfield></entry>
- <entry>The number of buffers requested or granted. If count == 0, then
- <constant>VIDIOC_CREATE_BUFS</constant> will set <structfield>index</structfield>
- to the current number of created buffers, and it will check the validity of
- <structfield>memory</structfield> and <structfield>format.type</structfield>.
- If those are invalid -1 is returned and errno is set to &EINVAL;,
- otherwise <constant>VIDIOC_CREATE_BUFS</constant> returns 0. It will
- never set errno to &EBUSY; in this particular case.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>memory</structfield></entry>
- <entry>Applications set this field to
- <constant>V4L2_MEMORY_MMAP</constant>,
- <constant>V4L2_MEMORY_DMABUF</constant> or
- <constant>V4L2_MEMORY_USERPTR</constant>. See <xref linkend="v4l2-memory"
- /></entry>
- </row>
- <row>
- <entry>&v4l2-format;</entry>
- <entry><structfield>format</structfield></entry>
- <entry>Filled in by the application, preserved by the driver.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>reserved</structfield>[8]</entry>
- <entry>A place holder for future extensions. Drivers and applications
- must set the array to zero.</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
- </refsect1>
- <refsect1>
- &return-value;
- <variablelist>
- <varlistentry>
- <term><errorcode>ENOMEM</errorcode></term>
- <listitem>
- <para>No memory to allocate buffers for <link linkend="mmap">memory
- mapped</link> I/O.</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><errorcode>EINVAL</errorcode></term>
- <listitem>
- <para>The buffer type (<structfield>format.type</structfield> field),
- requested I/O method (<structfield>memory</structfield>) or format
- (<structfield>format</structfield> field) is not valid.</para>
- </listitem>
- </varlistentry>
- </variablelist>
- </refsect1>
- </refentry>
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