path: root/Documentation/DocBook/v4l/vidioc-querycap.xml

<refentry id="vidioc-querycap">
  <refmeta>
    <refentrytitle>ioctl VIDIOC_QUERYCAP</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>VIDIOC_QUERYCAP</refname>
    <refpurpose>Query device capabilities</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_capability *<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_QUERYCAP</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para></para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para>All V4L2 devices support the
<constant>VIDIOC_QUERYCAP</constant> ioctl. It is used to identify
kernel devices compatible with this specification and to obtain
information about driver and hardware capabilities. The ioctl takes a
pointer to a &v4l2-capability; which is filled by the driver. When the
driver is not compatible with this specification the ioctl returns an
&EINVAL;.</para>

    <table pgwide="1" frame="none" id="v4l2-capability">
      <title>struct <structname>v4l2_capability</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u8</entry>
	    <entry><structfield>driver</structfield>[16]</entry>
	    <entry><para>Name of the driver, a unique NUL-terminated
ASCII string. For example: "bttv". Driver specific applications can
use this information to verify the driver identity. It is also useful
to work around known bugs, or to identify drivers in error reports.
The driver version is stored in the <structfield>version</structfield>
field.</para><para>Storing strings in fixed sized arrays is bad
practice but unavoidable here. Drivers and applications should take
precautions to never read or write beyond the end of the array and to
make sure the strings are properly NUL-terminated.</para></entry>
	  </row>
	  <row>
	    <entry>__u8</entry>
	    <entry><structfield>card</structfield>[32]</entry>
	    <entry>Name of the device, a NUL-terminated ASCII string.
For example: "Yoyodyne TV/FM". One driver may support different brands
or models of video hardware. This information is intended for users,
for example in a menu of available devices. Since multiple TV cards of
the same brand may be installed which are supported by the same
driver, this name should be combined with the character device file
name (&eg; <filename>/dev/video2</filename>) or the
<structfield>bus_info</structfield> string to avoid
ambiguities.</entry>
	  </row>
	  <row>
	    <entry>__u8</entry>
	    <entry><structfield>bus_info</structfield>[32]</entry>
	    <entry>Location of the device in the system, a
NUL-terminated ASCII string. For example: "PCI Slot 4". This
information is intended for users, to distinguish multiple
identical devices. If no such information is available the field may
simply count the devices controlled by the driver, or contain the
empty string (<structfield>bus_info</structfield>[0] = 0).<!-- XXX pci_dev->slot_name example --></entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>version</structfield></entry>
	    <entry><para>Version number of the driver. Together with
the <structfield>driver</structfield> field this identifies a
particular driver. The version number is formatted using the
<constant>KERNEL_VERSION()</constant> macro:</para></entry>
	  </row>
	  <row>
	    <entry spanname="hspan"><para>
<programlisting>
#define KERNEL_VERSION(a,b,c) (((a) &lt;&lt; 16) + ((b) &lt;&lt; 8) + (c))

__u32 version = KERNEL_VERSION(0, 8, 1);

printf ("Version: %u.%u.%u\n",
	(version &gt;&gt; 16) &amp; 0xFF,
	(version &gt;&gt; 8) &amp; 0xFF,
	 version &amp; 0xFF);
</programlisting></para></entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>capabilities</structfield></entry>
	    <entry>Device capabilities, see <xref
		linkend="device-capabilities" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved</structfield>[4]</entry>
	    <entry>Reserved for future extensions. Drivers must set
this array to zero.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="device-capabilities">
      <title>Device Capabilities Flags</title>
      <tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_CAP_VIDEO_CAPTURE</constant></entry>
	    <entry>0x00000001</entry>
	    <entry>The device supports the <link
linkend="capture">Video Capture</link> interface.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_VIDEO_OUTPUT</constant></entry>
	    <entry>0x00000002</entry>
	    <entry>The device supports the <link
linkend="output">Video Output</link> interface.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_VIDEO_OVERLAY</constant></entry>
	    <entry>0x00000004</entry>
	    <entry>The device supports the <link
linkend="overlay">Video Overlay</link> interface. A video overlay device
typically stores captured images directly in the video memory of a
graphics card, with hardware clipping and scaling.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_VBI_CAPTURE</constant></entry>
	    <entry>0x00000010</entry>
	    <entry>The device supports the <link linkend="raw-vbi">Raw
VBI Capture</link> interface, providing Teletext and Closed Caption
data.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_VBI_OUTPUT</constant></entry>
	    <entry>0x00000020</entry>
	    <entry>The device supports the <link linkend="raw-vbi">Raw VBI Output</link> interface.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_SLICED_VBI_CAPTURE</constant></entry>
	    <entry>0x00000040</entry>
	    <entry>The device supports the <link linkend="sliced">Sliced VBI Capture</link> interface.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_SLICED_VBI_OUTPUT</constant></entry>
	    <entry>0x00000080</entry>
	    <entry>The device supports the <link linkend="sliced">Sliced VBI Output</link> interface.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_RDS_CAPTURE</constant></entry>
	    <entry>0x00000100</entry>
	    <entry>The device supports the <link linkend="rds">RDS</link> interface.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_VIDEO_OUTPUT_OVERLAY</constant></entry>
	    <entry>0x00000200</entry>
	    <entry>The device supports the <link linkend="osd">Video
Output Overlay</link> (OSD) interface. Unlike the <wordasword>Video
Overlay</wordasword> interface, this is a secondary function of video
output devices and overlays an image onto an outgoing video signal.
When the driver sets this flag, it must clear the
<constant>V4L2_CAP_VIDEO_OVERLAY</constant> flag and vice
versa.<footnote><para>The &v4l2-framebuffer; lacks an
&v4l2-buf-type; field, therefore the type of overlay is implied by the
driver capabilities.</para></footnote></entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_HW_FREQ_SEEK</constant></entry>
	    <entry>0x00000400</entry>
	    <entry>The device supports the &VIDIOC-S-HW-FREQ-SEEK; ioctl for
hardware frequency seeking.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_TUNER</constant></entry>
	    <entry>0x00010000</entry>
	    <entry>The device has some sort of tuner to
receive RF-modulated video signals. For more information about
tuner programming see
<xref linkend="tuner" />.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_AUDIO</constant></entry>
	    <entry>0x00020000</entry>
	    <entry>The device has audio inputs or outputs. It may or
may not support audio recording or playback, in PCM or compressed
formats. PCM audio support must be implemented as ALSA or OSS
interface. For more information on audio inputs and outputs see <xref
		linkend="audio" />.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_RADIO</constant></entry>
	    <entry>0x00040000</entry>
	    <entry>This is a radio receiver.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_MODULATOR</constant></entry>
	    <entry>0x00080000</entry>
	    <entry>The device has some sort of modulator to
emit RF-modulated video/audio signals. For more information about
modulator programming see
<xref linkend="tuner" />.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_READWRITE</constant></entry>
	    <entry>0x01000000</entry>
	    <entry>The device supports the <link
linkend="rw">read()</link> and/or <link linkend="rw">write()</link>
I/O methods.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_ASYNCIO</constant></entry>
	    <entry>0x02000000</entry>
	    <entry>The device supports the <link
linkend="async">asynchronous</link> I/O methods.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CAP_STREAMING</constant></entry>
	    <entry>0x04000000</entry>
	    <entry>The device supports the <link
linkend="mmap">streaming</link> I/O method.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>
  </refsect1>

  <refsect1>
    &return-value;

    <variablelist>
      <varlistentry>
	<term><errorcode>EINVAL</errorcode></term>
	<listitem>
	  <para>The device is not compatible with this
specification.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>

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