Documentation/DocBook/media/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.</para>
  71 <para>Storing strings in fixed sized arrays is bad
  72 practice but unavoidable here. Drivers and applications should take
  73 precautions to never read or write beyond the end of the array and to
  74 make sure the strings are properly NUL-terminated.</para></entry>
  75           </row>
  76           <row>
  77             <entry>__u8</entry>
  78             <entry><structfield>card</structfield>[32]</entry>
  79             <entry>Name of the device, a NUL-terminated ASCII string.
  80 For example: "Yoyodyne TV/FM". One driver may support different brands
  81 or models of video hardware. This information is intended for users,
  82 for example in a menu of available devices. Since multiple TV cards of
  83 the same brand may be installed which are supported by the same
  84 driver, this name should be combined with the character device file
  85 name (&eg; <filename>/dev/video2</filename>) or the
  86 <structfield>bus_info</structfield> string to avoid
  87 ambiguities.</entry>
  88           </row>
  89           <row>
  90             <entry>__u8</entry>
  91             <entry><structfield>bus_info</structfield>[32]</entry>
  92             <entry>Location of the device in the system, a
  93 NUL-terminated ASCII string. For example: "PCI Slot 4". This
  94 information is intended for users, to distinguish multiple
  95 identical devices. If no such information is available the field may
  96 simply count the devices controlled by the driver, or contain the
  97 empty string (<structfield>bus_info</structfield>[0] = 0).<!-- XXX pci_dev->slot_name example --></entry>
  98           </row>
  99           <row>
 100             <entry>__u32</entry>
 101             <entry><structfield>version</structfield></entry>
 102             <entry><para>Version number of the driver.</para>
 103 <para>Starting on kernel 3.1, the version reported is provided per
 104 V4L2 subsystem, following the same Kernel numberation scheme. However, it
 105 should not always return the same version as the kernel, if, for example,
 106 an stable or distribution-modified kernel uses the V4L2 stack from a
 107 newer kernel.</para>
 108 <para>The version number is formatted using the
 109 <constant>KERNEL_VERSION()</constant> macro:</para></entry>
 110           </row>
 111           <row>
 112             <entry spanname="hspan"><para>
 113 <programlisting>
 114 #define KERNEL_VERSION(a,b,c) (((a) &lt;&lt; 16) + ((b) &lt;&lt; 8) + (c))
 115
 116 __u32 version = KERNEL_VERSION(0, 8, 1);
 117
 118 printf ("Version: %u.%u.%u\n",
 119         (version &gt;&gt; 16) &amp; 0xFF,
 120         (version &gt;&gt; 8) &amp; 0xFF,
 121          version &amp; 0xFF);
 122 </programlisting></para></entry>
 123           </row>
 124           <row>
 125             <entry>__u32</entry>
 126             <entry><structfield>capabilities</structfield></entry>
 127             <entry>Available capabilities of the physical device as a whole, see <xref
 128                 linkend="device-capabilities" />. The same physical device can export
 129                 multiple devices in /dev (e.g. /dev/videoX, /dev/vbiY and /dev/radioZ).
 130                 The <structfield>capabilities</structfield> field should contain a union
 131                 of all capabilities available around the several V4L2 devices exported
 132                 to userspace.
 133                 For all those devices the <structfield>capabilities</structfield> field
 134                 returns the same set of capabilities. This allows applications to open
 135                 just one of the devices (typically the video device) and discover whether
 136                 video, vbi and/or radio are also supported.
 137             </entry>
 138           </row>
 139           <row>
 140             <entry>__u32</entry>
 141             <entry><structfield>device_caps</structfield></entry>
 142             <entry>Device capabilities of the opened device, see <xref
 143                 linkend="device-capabilities" />. Should contain the available capabilities
 144                 of that specific device node. So, for example, <structfield>device_caps</structfield>
 145                 of a radio device will only contain radio related capabilities and
 146                 no video or vbi capabilities. This field is only set if the <structfield>capabilities</structfield>
 147                 field contains the <constant>V4L2_CAP_DEVICE_CAPS</constant> capability.
 148                 Only the <structfield>capabilities</structfield> field can have the
 149                 <constant>V4L2_CAP_DEVICE_CAPS</constant> capability, <structfield>device_caps</structfield>
 150                 will never set <constant>V4L2_CAP_DEVICE_CAPS</constant>.
 151             </entry>
 152           </row>
 153           <row>
 154             <entry>__u32</entry>
 155             <entry><structfield>reserved</structfield>[3]</entry>
 156             <entry>Reserved for future extensions. Drivers must set
 157 this array to zero.</entry>
 158           </row>
 159         </tbody>
 160       </tgroup>
 161     </table>
 162
 163     <table pgwide="1" frame="none" id="device-capabilities">
 164       <title>Device Capabilities Flags</title>
 165       <tgroup cols="3">
 166         &cs-def;
 167         <tbody valign="top">
 168           <row>
 169             <entry><constant>V4L2_CAP_VIDEO_CAPTURE</constant></entry>
 170             <entry>0x00000001</entry>
 171             <entry>The device supports the single-planar API through the <link
 172 linkend="capture">Video Capture</link> interface.</entry>
 173           </row>
 174           <row>
 175             <entry><constant>V4L2_CAP_VIDEO_CAPTURE_MPLANE</constant></entry>
 176             <entry>0x00001000</entry>
 177             <entry>The device supports the
 178             <link linkend="planar-apis">multi-planar API</link> through the
 179             <link linkend="capture">Video Capture</link> interface.</entry>
 180           </row>
 181           <row>
 182             <entry><constant>V4L2_CAP_VIDEO_OUTPUT</constant></entry>
 183             <entry>0x00000002</entry>
 184             <entry>The device supports the single-planar API through the <link
 185 linkend="output">Video Output</link> interface.</entry>
 186           </row>
 187           <row>
 188             <entry><constant>V4L2_CAP_VIDEO_OUTPUT_MPLANE</constant></entry>
 189             <entry>0x00002000</entry>
 190             <entry>The device supports the
 191             <link linkend="planar-apis">multi-planar API</link> through the
 192             <link linkend="output">Video Output</link> interface.</entry>
 193           </row>
 194           <row>
 195             <entry><constant>V4L2_CAP_VIDEO_OVERLAY</constant></entry>
 196             <entry>0x00000004</entry>
 197             <entry>The device supports the <link
 198 linkend="overlay">Video Overlay</link> interface. A video overlay device
 199 typically stores captured images directly in the video memory of a
 200 graphics card, with hardware clipping and scaling.</entry>
 201           </row>
 202           <row>
 203             <entry><constant>V4L2_CAP_VBI_CAPTURE</constant></entry>
 204             <entry>0x00000010</entry>
 205             <entry>The device supports the <link linkend="raw-vbi">Raw
 206 VBI Capture</link> interface, providing Teletext and Closed Caption
 207 data.</entry>
 208           </row>
 209           <row>
 210             <entry><constant>V4L2_CAP_VBI_OUTPUT</constant></entry>
 211             <entry>0x00000020</entry>
 212             <entry>The device supports the <link linkend="raw-vbi">Raw VBI Output</link> interface.</entry>
 213           </row>
 214           <row>
 215             <entry><constant>V4L2_CAP_SLICED_VBI_CAPTURE</constant></entry>
 216             <entry>0x00000040</entry>
 217             <entry>The device supports the <link linkend="sliced">Sliced VBI Capture</link> interface.</entry>
 218           </row>
 219           <row>
 220             <entry><constant>V4L2_CAP_SLICED_VBI_OUTPUT</constant></entry>
 221             <entry>0x00000080</entry>
 222             <entry>The device supports the <link linkend="sliced">Sliced VBI Output</link> interface.</entry>
 223           </row>
 224           <row>
 225             <entry><constant>V4L2_CAP_RDS_CAPTURE</constant></entry>
 226             <entry>0x00000100</entry>
 227             <entry>The device supports the <link linkend="rds">RDS</link> capture interface.</entry>
 228           </row>
 229           <row>
 230             <entry><constant>V4L2_CAP_VIDEO_OUTPUT_OVERLAY</constant></entry>
 231             <entry>0x00000200</entry>
 232             <entry>The device supports the <link linkend="osd">Video
 233 Output Overlay</link> (OSD) interface. Unlike the <wordasword>Video
 234 Overlay</wordasword> interface, this is a secondary function of video
 235 output devices and overlays an image onto an outgoing video signal.
 236 When the driver sets this flag, it must clear the
 237 <constant>V4L2_CAP_VIDEO_OVERLAY</constant> flag and vice
 238 versa.<footnote><para>The &v4l2-framebuffer; lacks an
 239 &v4l2-buf-type; field, therefore the type of overlay is implied by the
 240 driver capabilities.</para></footnote></entry>
 241           </row>
 242           <row>
 243             <entry><constant>V4L2_CAP_HW_FREQ_SEEK</constant></entry>
 244             <entry>0x00000400</entry>
 245             <entry>The device supports the &VIDIOC-S-HW-FREQ-SEEK; ioctl for
 246 hardware frequency seeking.</entry>
 247           </row>
 248           <row>
 249             <entry><constant>V4L2_CAP_RDS_OUTPUT</constant></entry>
 250             <entry>0x00000800</entry>
 251             <entry>The device supports the <link linkend="rds">RDS</link> output interface.</entry>
 252           </row>
 253           <row>
 254             <entry><constant>V4L2_CAP_TUNER</constant></entry>
 255             <entry>0x00010000</entry>
 256             <entry>The device has some sort of tuner to
 257 receive RF-modulated video signals. For more information about
 258 tuner programming see
 259 <xref linkend="tuner" />.</entry>
 260           </row>
 261           <row>
 262             <entry><constant>V4L2_CAP_AUDIO</constant></entry>
 263             <entry>0x00020000</entry>
 264             <entry>The device has audio inputs or outputs. It may or
 265 may not support audio recording or playback, in PCM or compressed
 266 formats. PCM audio support must be implemented as ALSA or OSS
 267 interface. For more information on audio inputs and outputs see <xref
 268                 linkend="audio" />.</entry>
 269           </row>
 270           <row>
 271             <entry><constant>V4L2_CAP_RADIO</constant></entry>
 272             <entry>0x00040000</entry>
 273             <entry>This is a radio receiver.</entry>
 274           </row>
 275           <row>
 276             <entry><constant>V4L2_CAP_MODULATOR</constant></entry>
 277             <entry>0x00080000</entry>
 278             <entry>The device has some sort of modulator to
 279 emit RF-modulated video/audio signals. For more information about
 280 modulator programming see
 281 <xref linkend="tuner" />.</entry>
 282           </row>
 283           <row>
 284             <entry><constant>V4L2_CAP_READWRITE</constant></entry>
 285             <entry>0x01000000</entry>
 286             <entry>The device supports the <link
 287 linkend="rw">read()</link> and/or <link linkend="rw">write()</link>
 288 I/O methods.</entry>
 289           </row>
 290           <row>
 291             <entry><constant>V4L2_CAP_ASYNCIO</constant></entry>
 292             <entry>0x02000000</entry>
 293             <entry>The device supports the <link
 294 linkend="async">asynchronous</link> I/O methods.</entry>
 295           </row>
 296           <row>
 297             <entry><constant>V4L2_CAP_STREAMING</constant></entry>
 298             <entry>0x04000000</entry>
 299             <entry>The device supports the <link
 300 linkend="mmap">streaming</link> I/O method.</entry>
 301           </row>
 302           <row>
 303             <entry><constant>V4L2_CAP_DEVICE_CAPS</constant></entry>
 304             <entry>0x80000000</entry>
 305             <entry>The driver fills the <structfield>device_caps</structfield>
 306             field. This capability can only appear in the <structfield>capabilities</structfield>
 307             field and never in the <structfield>device_caps</structfield> field.</entry>
 308           </row>
 309         </tbody>
 310       </tgroup>
 311     </table>
 312   </refsect1>
 313
 314   <refsect1>
 315     &return-value;
 316   </refsect1>
 317 </refentry>