Documentation/DocBook/v4l/vidioc-querycap.xml

   1 <refentry id="vidioc-querycap">
   2   <refmeta>
   3     <refentrytitle>ioctl VIDIOC_QUERYCAP</refentrytitle>
   4     &manvol;
   5   </refmeta>
   6
   7   <refnamediv>
   8     <refname>VIDIOC_QUERYCAP</refname>
   9     <refpurpose>Query device capabilities</refpurpose>
  10   </refnamediv>
  11
  12   <refsynopsisdiv>
  13     <funcsynopsis>
  14       <funcprototype>
  15         <funcdef>int <function>ioctl</function></funcdef>
  16         <paramdef>int <parameter>fd</parameter></paramdef>
  17         <paramdef>int <parameter>request</parameter></paramdef>
  18         <paramdef>struct v4l2_capability *<parameter>argp</parameter></paramdef>
  19       </funcprototype>
  20     </funcsynopsis>
  21   </refsynopsisdiv>
  22
  23   <refsect1>
  24     <title>Arguments</title>
  25
  26     <variablelist>
  27       <varlistentry>
  28         <term><parameter>fd</parameter></term>
  29         <listitem>
  30           <para>&fd;</para>
  31         </listitem>
  32       </varlistentry>
  33       <varlistentry>
  34         <term><parameter>request</parameter></term>
  35         <listitem>
  36           <para>VIDIOC_QUERYCAP</para>
  37         </listitem>
  38       </varlistentry>
  39       <varlistentry>
  40         <term><parameter>argp</parameter></term>
  41         <listitem>
  42           <para></para>
  43         </listitem>
  44       </varlistentry>
  45     </variablelist>
  46   </refsect1>
  47
  48   <refsect1>
  49     <title>Description</title>
  50
  51     <para>All V4L2 devices support the
  52 <constant>VIDIOC_QUERYCAP</constant> ioctl. It is used to identify
  53 kernel devices compatible with this specification and to obtain
  54 information about driver and hardware capabilities. The ioctl takes a
  55 pointer to a &v4l2-capability; which is filled by the driver. When the
  56 driver is not compatible with this specification the ioctl returns an
  57 &EINVAL;.</para>
  58
  59     <table pgwide="1" frame="none" id="v4l2-capability">
  60       <title>struct <structname>v4l2_capability</structname></title>
  61       <tgroup cols="3">
  62         &cs-str;
  63         <tbody valign="top">
  64           <row>
  65             <entry>__u8</entry>
  66             <entry><structfield>driver</structfield>[16]</entry>
  67             <entry><para>Name of the driver, a unique NUL-terminated
  68 ASCII string. For example: "bttv". Driver specific applications can
  69 use this information to verify the driver identity. It is also useful
  70 to work around known bugs, or to identify drivers in error reports.
  71 The driver version is stored in the <structfield>version</structfield>
  72 field.</para><para>Storing strings in fixed sized arrays is bad
  73 practice but unavoidable here. Drivers and applications should take
  74 precautions to never read or write beyond the end of the array and to
  75 make sure the strings are properly NUL-terminated.</para></entry>
  76           </row>
  77           <row>
  78             <entry>__u8</entry>
  79             <entry><structfield>card</structfield>[32]</entry>
  80             <entry>Name of the device, a NUL-terminated ASCII string.
  81 For example: "Yoyodyne TV/FM". One driver may support different brands
  82 or models of video hardware. This information is intended for users,
  83 for example in a menu of available devices. Since multiple TV cards of
  84 the same brand may be installed which are supported by the same
  85 driver, this name should be combined with the character device file
  86 name (&eg; <filename>/dev/video2</filename>) or the
  87 <structfield>bus_info</structfield> string to avoid
  88 ambiguities.</entry>
  89           </row>
  90           <row>
  91             <entry>__u8</entry>
  92             <entry><structfield>bus_info</structfield>[32]</entry>
  93             <entry>Location of the device in the system, a
  94 NUL-terminated ASCII string. For example: "PCI Slot 4". This
  95 information is intended for users, to distinguish multiple
  96 identical devices. If no such information is available the field may
  97 simply count the devices controlled by the driver, or contain the
  98 empty string (<structfield>bus_info</structfield>[0] = 0).<!-- XXX pci_dev->slot_name example --></entry>
  99           </row>
 100           <row>
 101             <entry>__u32</entry>
 102             <entry><structfield>version</structfield></entry>
 103             <entry><para>Version number of the driver. Together with
 104 the <structfield>driver</structfield> field this identifies a
 105 particular driver. The version number is formatted using the
 106 <constant>KERNEL_VERSION()</constant> macro:</para></entry>
 107           </row>
 108           <row>
 109             <entry spanname="hspan"><para>
 110 <programlisting>
 111 #define KERNEL_VERSION(a,b,c) (((a) &lt;&lt; 16) + ((b) &lt;&lt; 8) + (c))
 112
 113 __u32 version = KERNEL_VERSION(0, 8, 1);
 114
 115 printf ("Version: %u.%u.%u\n",
 116         (version &gt;&gt; 16) &amp; 0xFF,
 117         (version &gt;&gt; 8) &amp; 0xFF,
 118          version &amp; 0xFF);
 119 </programlisting></para></entry>
 120           </row>
 121           <row>
 122             <entry>__u32</entry>
 123             <entry><structfield>capabilities</structfield></entry>
 124             <entry>Device capabilities, see <xref
 125                 linkend="device-capabilities" />.</entry>
 126           </row>
 127           <row>
 128             <entry>__u32</entry>
 129             <entry><structfield>reserved</structfield>[4]</entry>
 130             <entry>Reserved for future extensions. Drivers must set
 131 this array to zero.</entry>
 132           </row>
 133         </tbody>
 134       </tgroup>
 135     </table>
 136
 137     <table pgwide="1" frame="none" id="device-capabilities">
 138       <title>Device Capabilities Flags</title>
 139       <tgroup cols="3">
 140         &cs-def;
 141         <tbody valign="top">
 142           <row>
 143             <entry><constant>V4L2_CAP_VIDEO_CAPTURE</constant></entry>
 144             <entry>0x00000001</entry>
 145             <entry>The device supports the <link
 146 linkend="capture">Video Capture</link> interface.</entry>
 147           </row>
 148           <row>
 149             <entry><constant>V4L2_CAP_VIDEO_OUTPUT</constant></entry>
 150             <entry>0x00000002</entry>
 151             <entry>The device supports the <link
 152 linkend="output">Video Output</link> interface.</entry>
 153           </row>
 154           <row>
 155             <entry><constant>V4L2_CAP_VIDEO_OVERLAY</constant></entry>
 156             <entry>0x00000004</entry>
 157             <entry>The device supports the <link
 158 linkend="overlay">Video Overlay</link> interface. A video overlay device
 159 typically stores captured images directly in the video memory of a
 160 graphics card, with hardware clipping and scaling.</entry>
 161           </row>
 162           <row>
 163             <entry><constant>V4L2_CAP_VBI_CAPTURE</constant></entry>
 164             <entry>0x00000010</entry>
 165             <entry>The device supports the <link linkend="raw-vbi">Raw
 166 VBI Capture</link> interface, providing Teletext and Closed Caption
 167 data.</entry>
 168           </row>
 169           <row>
 170             <entry><constant>V4L2_CAP_VBI_OUTPUT</constant></entry>
 171             <entry>0x00000020</entry>
 172             <entry>The device supports the <link linkend="raw-vbi">Raw VBI Output</link> interface.</entry>
 173           </row>
 174           <row>
 175             <entry><constant>V4L2_CAP_SLICED_VBI_CAPTURE</constant></entry>
 176             <entry>0x00000040</entry>
 177             <entry>The device supports the <link linkend="sliced">Sliced VBI Capture</link> interface.</entry>
 178           </row>
 179           <row>
 180             <entry><constant>V4L2_CAP_SLICED_VBI_OUTPUT</constant></entry>
 181             <entry>0x00000080</entry>
 182             <entry>The device supports the <link linkend="sliced">Sliced VBI Output</link> interface.</entry>
 183           </row>
 184           <row>
 185             <entry><constant>V4L2_CAP_RDS_CAPTURE</constant></entry>
 186             <entry>0x00000100</entry>
 187             <entry>The device supports the <link linkend="rds">RDS</link> interface.</entry>
 188           </row>
 189           <row>
 190             <entry><constant>V4L2_CAP_VIDEO_OUTPUT_OVERLAY</constant></entry>
 191             <entry>0x00000200</entry>
 192             <entry>The device supports the <link linkend="osd">Video
 193 Output Overlay</link> (OSD) interface. Unlike the <wordasword>Video
 194 Overlay</wordasword> interface, this is a secondary function of video
 195 output devices and overlays an image onto an outgoing video signal.
 196 When the driver sets this flag, it must clear the
 197 <constant>V4L2_CAP_VIDEO_OVERLAY</constant> flag and vice
 198 versa.<footnote><para>The &v4l2-framebuffer; lacks an
 199 &v4l2-buf-type; field, therefore the type of overlay is implied by the
 200 driver capabilities.</para></footnote></entry>
 201           </row>
 202           <row>
 203             <entry><constant>V4L2_CAP_HW_FREQ_SEEK</constant></entry>
 204             <entry>0x00000400</entry>
 205             <entry>The device supports the &VIDIOC-S-HW-FREQ-SEEK; ioctl for
 206 hardware frequency seeking.</entry>
 207           </row>
 208           <row>
 209             <entry><constant>V4L2_CAP_TUNER</constant></entry>
 210             <entry>0x00010000</entry>
 211             <entry>The device has some sort of tuner to
 212 receive RF-modulated video signals. For more information about
 213 tuner programming see
 214 <xref linkend="tuner" />.</entry>
 215           </row>
 216           <row>
 217             <entry><constant>V4L2_CAP_AUDIO</constant></entry>
 218             <entry>0x00020000</entry>
 219             <entry>The device has audio inputs or outputs. It may or
 220 may not support audio recording or playback, in PCM or compressed
 221 formats. PCM audio support must be implemented as ALSA or OSS
 222 interface. For more information on audio inputs and outputs see <xref
 223                 linkend="audio" />.</entry>
 224           </row>
 225           <row>
 226             <entry><constant>V4L2_CAP_RADIO</constant></entry>
 227             <entry>0x00040000</entry>
 228             <entry>This is a radio receiver.</entry>
 229           </row>
 230           <row>
 231             <entry><constant>V4L2_CAP_MODULATOR</constant></entry>
 232             <entry>0x00080000</entry>
 233             <entry>The device has some sort of modulator to
 234 emit RF-modulated video/audio signals. For more information about
 235 modulator programming see
 236 <xref linkend="tuner" />.</entry>
 237           </row>
 238           <row>
 239             <entry><constant>V4L2_CAP_READWRITE</constant></entry>
 240             <entry>0x01000000</entry>
 241             <entry>The device supports the <link
 242 linkend="rw">read()</link> and/or <link linkend="rw">write()</link>
 243 I/O methods.</entry>
 244           </row>
 245           <row>
 246             <entry><constant>V4L2_CAP_ASYNCIO</constant></entry>
 247             <entry>0x02000000</entry>
 248             <entry>The device supports the <link
 249 linkend="async">asynchronous</link> I/O methods.</entry>
 250           </row>
 251           <row>
 252             <entry><constant>V4L2_CAP_STREAMING</constant></entry>
 253             <entry>0x04000000</entry>
 254             <entry>The device supports the <link
 255 linkend="mmap">streaming</link> I/O method.</entry>
 256           </row>
 257         </tbody>
 258       </tgroup>
 259     </table>
 260   </refsect1>
 261
 262   <refsect1>
 263     &return-value;
 264
 265     <variablelist>
 266       <varlistentry>
 267         <term><errorcode>EINVAL</errorcode></term>
 268         <listitem>
 269           <para>The device is not compatible with this
 270 specification.</para>
 271         </listitem>
 272       </varlistentry>
 273     </variablelist>
 274   </refsect1>
 275 </refentry>
 276
 277 <!--
 278 Local Variables:
 279 mode: sgml
 280 sgml-parent-document: "v4l2.sgml"
 281 indent-tabs-mode: nil
 282 End:
 283 -->
 284