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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
53kernel devices compatible with this specification and to obtain
54information about driver and hardware capabilities. The ioctl takes a
55pointer to a &v4l2-capability; which is filled by the driver. When the
56driver 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
68ASCII string. For example: "bttv". Driver specific applications can
69use this information to verify the driver identity. It is also useful
70to work around known bugs, or to identify drivers in error reports.</para>
71<para>Storing strings in fixed sized arrays is bad
72practice but unavoidable here. Drivers and applications should take
73precautions to never read or write beyond the end of the array and to
74make 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.
80For example: "Yoyodyne TV/FM". One driver may support different brands
81or models of video hardware. This information is intended for users,
82for example in a menu of available devices. Since multiple TV cards of
83the same brand may be installed which are supported by the same
84driver, this name should be combined with the character device file
85name (&eg; <filename>/dev/video2</filename>) or the
86<structfield>bus_info</structfield> string to avoid
87ambiguities.</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
93NUL-terminated ASCII string. For example: "PCI Slot 4". This
94information is intended for users, to distinguish multiple
95identical devices. If no such information is available the field may
96simply count the devices controlled by the driver, or contain the
97empty 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
104V4L2 subsystem, following the same Kernel numberation scheme. However, it
105should not always return the same version as the kernel, if, for example,
106an stable or distribution-modified kernel uses the V4L2 stack from a
107newer 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
118printf ("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>Device capabilities, see <xref
128 linkend="device-capabilities" />.</entry>
129 </row>
130 <row>
131 <entry>__u32</entry>
132 <entry><structfield>reserved</structfield>[4]</entry>
133 <entry>Reserved for future extensions. Drivers must set
134this array to zero.</entry>
135 </row>
136 </tbody>
137 </tgroup>
138 </table>
139
140 <table pgwide="1" frame="none" id="device-capabilities">
141 <title>Device Capabilities Flags</title>
142 <tgroup cols="3">
143 &cs-def;
144 <tbody valign="top">
145 <row>
146 <entry><constant>V4L2_CAP_VIDEO_CAPTURE</constant></entry>
147 <entry>0x00000001</entry>
148 <entry>The device supports the single-planar API through the <link
149linkend="capture">Video Capture</link> interface.</entry>
150 </row>
151 <row>
152 <entry><constant>V4L2_CAP_VIDEO_CAPTURE_MPLANE</constant></entry>
153 <entry>0x00001000</entry>
154 <entry>The device supports the
155 <link linkend="planar-apis">multi-planar API</link> through the
156 <link linkend="capture">Video Capture</link> interface.</entry>
157 </row>
158 <row>
159 <entry><constant>V4L2_CAP_VIDEO_OUTPUT</constant></entry>
160 <entry>0x00000002</entry>
161 <entry>The device supports the single-planar API through the <link
162linkend="output">Video Output</link> interface.</entry>
163 </row>
164 <row>
165 <entry><constant>V4L2_CAP_VIDEO_OUTPUT_MPLANE</constant></entry>
166 <entry>0x00002000</entry>
167 <entry>The device supports the
168 <link linkend="planar-apis">multi-planar API</link> through the
169 <link linkend="output">Video Output</link> interface.</entry>
170 </row>
171 <row>
172 <entry><constant>V4L2_CAP_VIDEO_OVERLAY</constant></entry>
173 <entry>0x00000004</entry>
174 <entry>The device supports the <link
175linkend="overlay">Video Overlay</link> interface. A video overlay device
176typically stores captured images directly in the video memory of a
177graphics card, with hardware clipping and scaling.</entry>
178 </row>
179 <row>
180 <entry><constant>V4L2_CAP_VBI_CAPTURE</constant></entry>
181 <entry>0x00000010</entry>
182 <entry>The device supports the <link linkend="raw-vbi">Raw
183VBI Capture</link> interface, providing Teletext and Closed Caption
184data.</entry>
185 </row>
186 <row>
187 <entry><constant>V4L2_CAP_VBI_OUTPUT</constant></entry>
188 <entry>0x00000020</entry>
189 <entry>The device supports the <link linkend="raw-vbi">Raw VBI Output</link> interface.</entry>
190 </row>
191 <row>
192 <entry><constant>V4L2_CAP_SLICED_VBI_CAPTURE</constant></entry>
193 <entry>0x00000040</entry>
194 <entry>The device supports the <link linkend="sliced">Sliced VBI Capture</link> interface.</entry>
195 </row>
196 <row>
197 <entry><constant>V4L2_CAP_SLICED_VBI_OUTPUT</constant></entry>
198 <entry>0x00000080</entry>
199 <entry>The device supports the <link linkend="sliced">Sliced VBI Output</link> interface.</entry>
200 </row>
201 <row>
202 <entry><constant>V4L2_CAP_RDS_CAPTURE</constant></entry>
203 <entry>0x00000100</entry>
204 <entry>The device supports the <link linkend="rds">RDS</link> capture interface.</entry>
205 </row>
206 <row>
207 <entry><constant>V4L2_CAP_VIDEO_OUTPUT_OVERLAY</constant></entry>
208 <entry>0x00000200</entry>
209 <entry>The device supports the <link linkend="osd">Video
210Output Overlay</link> (OSD) interface. Unlike the <wordasword>Video
211Overlay</wordasword> interface, this is a secondary function of video
212output devices and overlays an image onto an outgoing video signal.
213When the driver sets this flag, it must clear the
214<constant>V4L2_CAP_VIDEO_OVERLAY</constant> flag and vice
215versa.<footnote><para>The &v4l2-framebuffer; lacks an
216&v4l2-buf-type; field, therefore the type of overlay is implied by the
217driver capabilities.</para></footnote></entry>
218 </row>
219 <row>
220 <entry><constant>V4L2_CAP_HW_FREQ_SEEK</constant></entry>
221 <entry>0x00000400</entry>
222 <entry>The device supports the &VIDIOC-S-HW-FREQ-SEEK; ioctl for
223hardware frequency seeking.</entry>
224 </row>
225 <row>
226 <entry><constant>V4L2_CAP_RDS_OUTPUT</constant></entry>
227 <entry>0x00000800</entry>
228 <entry>The device supports the <link linkend="rds">RDS</link> output interface.</entry>
229 </row>
230 <row>
231 <entry><constant>V4L2_CAP_TUNER</constant></entry>
232 <entry>0x00010000</entry>
233 <entry>The device has some sort of tuner to
234receive RF-modulated video signals. For more information about
235tuner programming see
236<xref linkend="tuner" />.</entry>
237 </row>
238 <row>
239 <entry><constant>V4L2_CAP_AUDIO</constant></entry>
240 <entry>0x00020000</entry>
241 <entry>The device has audio inputs or outputs. It may or
242may not support audio recording or playback, in PCM or compressed
243formats. PCM audio support must be implemented as ALSA or OSS
244interface. For more information on audio inputs and outputs see <xref
245 linkend="audio" />.</entry>
246 </row>
247 <row>
248 <entry><constant>V4L2_CAP_RADIO</constant></entry>
249 <entry>0x00040000</entry>
250 <entry>This is a radio receiver.</entry>
251 </row>
252 <row>
253 <entry><constant>V4L2_CAP_MODULATOR</constant></entry>
254 <entry>0x00080000</entry>
255 <entry>The device has some sort of modulator to
256emit RF-modulated video/audio signals. For more information about
257modulator programming see
258<xref linkend="tuner" />.</entry>
259 </row>
260 <row>
261 <entry><constant>V4L2_CAP_READWRITE</constant></entry>
262 <entry>0x01000000</entry>
263 <entry>The device supports the <link
264linkend="rw">read()</link> and/or <link linkend="rw">write()</link>
265I/O methods.</entry>
266 </row>
267 <row>
268 <entry><constant>V4L2_CAP_ASYNCIO</constant></entry>
269 <entry>0x02000000</entry>
270 <entry>The device supports the <link
271linkend="async">asynchronous</link> I/O methods.</entry>
272 </row>
273 <row>
274 <entry><constant>V4L2_CAP_STREAMING</constant></entry>
275 <entry>0x04000000</entry>
276 <entry>The device supports the <link
277linkend="mmap">streaming</link> I/O method.</entry>
278 </row>
279 </tbody>
280 </tgroup>
281 </table>
282 </refsect1>
283
284 <refsect1>
285 &return-value;
286 </refsect1>
287</refentry>
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