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authorAnton Arapov <anton@redhat.com>2012-04-16 10:05:28 +0200
committerAnton Arapov <anton@redhat.com>2012-04-16 10:05:28 +0200
commitb4b6116a13633898cf868f2f103c96a90c4c20f8 (patch)
tree93d1b7e2cfcdf473d8d4ff3ad141fa864f8491f6 /Documentation/DocBook/media/v4l/vidioc-create-bufs.xml
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fedora kernel: d9aad82f3319f3cfd1aebc01234254ef0c37ad84v3.3.2-1
Signed-off-by: Anton Arapov <anton@redhat.com>
Diffstat (limited to 'Documentation/DocBook/media/v4l/vidioc-create-bufs.xml')
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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 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>
+
+ <para>This ioctl is used to create buffers for <link linkend="mmap">memory
+mapped</link> or <link linkend="userp">user pointer</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 device buffers applications initialize relevant fields of
+the <structname>v4l2_create_buffers</structname> structure. They set the
+<structfield>type</structfield> field in the
+<structname>v4l2_format</structname> structure, embedded in this
+structure, to the respective stream or buffer type.
+<structfield>count</structfield> must be set to the number of required buffers.
+<structfield>memory</structfield> specifies the required I/O method. The
+<structfield>format</structfield> field shall typically be filled in using
+either the <constant>VIDIOC_TRY_FMT</constant> or
+<constant>VIDIOC_G_FMT</constant> ioctl(). Additionally, applications can adjust
+<structfield>sizeimage</structfield> fields to fit their specific needs. The
+<structfield>reserved</structfield> array must be zeroed.</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.</entry>
+ </row>
+ <row>
+ <entry>&v4l2-memory;</entry>
+ <entry><structfield>memory</structfield></entry>
+ <entry>Applications set this field to
+<constant>V4L2_MEMORY_MMAP</constant> or
+<constant>V4L2_MEMORY_USERPTR</constant>.</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.</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>type</structfield> field) or the
+requested I/O method (<structfield>memory</structfield>) is not
+supported.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+</refentry>