9583183acb
The field 'reserved' was not tagged as a 'structfield' as it should. This made the text a bit confusing. Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
150 lines
5 KiB
XML
150 lines
5 KiB
XML
<refentry id="vidioc-reqbufs">
|
|
<refmeta>
|
|
<refentrytitle>ioctl VIDIOC_REQBUFS</refentrytitle>
|
|
&manvol;
|
|
</refmeta>
|
|
|
|
<refnamediv>
|
|
<refname>VIDIOC_REQBUFS</refname>
|
|
<refpurpose>Initiate Memory Mapping 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_requestbuffers *<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_REQBUFS</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 initiate <link linkend="mmap">memory
|
|
mapped</link> or <link linkend="userp">user pointer</link>
|
|
I/O. Memory mapped buffers are located in device memory and must be
|
|
allocated with this ioctl before they can be mapped into the
|
|
application's address space. User buffers are allocated by
|
|
applications themselves, and this ioctl is merely used to switch the
|
|
driver into user pointer I/O mode and to setup some internal structures.</para>
|
|
|
|
<para>To allocate device buffers applications initialize all
|
|
fields of the <structname>v4l2_requestbuffers</structname> structure.
|
|
They set the <structfield>type</structfield> field to the respective
|
|
stream or buffer type, the <structfield>count</structfield> field to
|
|
the desired number of buffers, <structfield>memory</structfield>
|
|
must be set to the requested I/O method and the <structfield>reserved</structfield> array
|
|
must be zeroed. When the ioctl
|
|
is called with a pointer to this structure the driver will attempt to allocate
|
|
the requested number of buffers and it stores the actual number
|
|
allocated in the <structfield>count</structfield> field. It can be
|
|
smaller than the number requested, even zero, when the driver runs out
|
|
of free memory. A larger number is also possible when the driver requires
|
|
more buffers to function correctly. For example video output requires at least two buffers,
|
|
one displayed and one filled by the application.</para>
|
|
<para>When the I/O method is not supported the ioctl
|
|
returns an &EINVAL;.</para>
|
|
|
|
<para>Applications can call <constant>VIDIOC_REQBUFS</constant>
|
|
again to change the number of buffers, however this cannot succeed
|
|
when any buffers are still mapped. A <structfield>count</structfield>
|
|
value of zero frees all buffers, after aborting or finishing any DMA
|
|
in progress, an implicit &VIDIOC-STREAMOFF;. <!-- mhs: I see no
|
|
reason why munmap()ping one or even all buffers must imply
|
|
streamoff.--></para>
|
|
|
|
<table pgwide="1" frame="none" id="v4l2-requestbuffers">
|
|
<title>struct <structname>v4l2_requestbuffers</structname></title>
|
|
<tgroup cols="3">
|
|
&cs-str;
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry>__u32</entry>
|
|
<entry><structfield>count</structfield></entry>
|
|
<entry>The number of buffers requested or granted.</entry>
|
|
</row>
|
|
<row>
|
|
<entry>&v4l2-buf-type;</entry>
|
|
<entry><structfield>type</structfield></entry>
|
|
<entry>Type of the stream or buffers, this is the same
|
|
as the &v4l2-format; <structfield>type</structfield> field. See <xref
|
|
linkend="v4l2-buf-type" /> for valid values.</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>__u32</entry>
|
|
<entry><structfield>reserved</structfield>[2]</entry>
|
|
<entry>A place holder for future extensions and custom
|
|
(driver defined) buffer types <constant>V4L2_BUF_TYPE_PRIVATE</constant> and
|
|
higher. This array should be zeroed by applications.</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
&return-value;
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><errorcode>EBUSY</errorcode></term>
|
|
<listitem>
|
|
<para>The driver supports multiple opens and I/O is already
|
|
in progress, or reallocation of buffers was attempted although one or
|
|
more are still mapped.</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>
|
|
|
|
<!--
|
|
Local Variables:
|
|
mode: sgml
|
|
sgml-parent-document: "v4l2.sgml"
|
|
indent-tabs-mode: nil
|
|
End:
|
|
-->
|