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Based on kernel version 3.13. Page generated on 2014-01-20 22:02 EST.

1	<refentry id="vidioc-queryctrl">
2	  <refmeta>
3	    <refentrytitle>ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU</refentrytitle>
4	    &manvol;
5	  </refmeta>
6	
7	  <refnamediv>
8	    <refname>VIDIOC_QUERYCTRL</refname>
9	    <refname>VIDIOC_QUERYMENU</refname>
10	    <refpurpose>Enumerate controls and menu control items</refpurpose>
11	  </refnamediv>
12	
13	  <refsynopsisdiv>
14	    <funcsynopsis>
15	      <funcprototype>
16		<funcdef>int <function>ioctl</function></funcdef>
17		<paramdef>int <parameter>fd</parameter></paramdef>
18		<paramdef>int <parameter>request</parameter></paramdef>
19		<paramdef>struct v4l2_queryctrl *<parameter>argp</parameter></paramdef>
20	      </funcprototype>
21	    </funcsynopsis>
22	    <funcsynopsis>
23	      <funcprototype>
24		<funcdef>int <function>ioctl</function></funcdef>
25		<paramdef>int <parameter>fd</parameter></paramdef>
26		<paramdef>int <parameter>request</parameter></paramdef>
27		<paramdef>struct v4l2_querymenu *<parameter>argp</parameter></paramdef>
28	      </funcprototype>
29	    </funcsynopsis>
30	  </refsynopsisdiv>
31	
32	  <refsect1>
33	    <title>Arguments</title>
34	
35	    <variablelist>
36	      <varlistentry>
37		<term><parameter>fd</parameter></term>
38		<listitem>
39		  <para>&fd;</para>
40		</listitem>
41	      </varlistentry>
42	      <varlistentry>
43		<term><parameter>request</parameter></term>
44		<listitem>
45		  <para>VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU</para>
46		</listitem>
47	      </varlistentry>
48	      <varlistentry>
49		<term><parameter>argp</parameter></term>
50		<listitem>
51		  <para></para>
52		</listitem>
53	      </varlistentry>
54	    </variablelist>
55	  </refsect1>
56	
57	  <refsect1>
58	    <title>Description</title>
59	
60	    <para>To query the attributes of a control applications set the
61	<structfield>id</structfield> field of a &v4l2-queryctrl; and call the
62	<constant>VIDIOC_QUERYCTRL</constant> ioctl with a pointer to this
63	structure. The driver fills the rest of the structure or returns an
64	&EINVAL; when the <structfield>id</structfield> is invalid.</para>
65	
66	    <para>It is possible to enumerate controls by calling
67	<constant>VIDIOC_QUERYCTRL</constant> with successive
68	<structfield>id</structfield> values starting from
69	<constant>V4L2_CID_BASE</constant> up to and exclusive
70	<constant>V4L2_CID_BASE_LASTP1</constant>. Drivers may return
71	<errorcode>EINVAL</errorcode> if a control in this range is not
72	supported. Further applications can enumerate private controls, which
73	are not defined in this specification, by starting at
74	<constant>V4L2_CID_PRIVATE_BASE</constant> and incrementing
75	<structfield>id</structfield> until the driver returns
76	<errorcode>EINVAL</errorcode>.</para>
77	
78	    <para>In both cases, when the driver sets the
79	<constant>V4L2_CTRL_FLAG_DISABLED</constant> flag in the
80	<structfield>flags</structfield> field this control is permanently
81	disabled and should be ignored by the application.<footnote>
82		<para><constant>V4L2_CTRL_FLAG_DISABLED</constant> was
83	intended for two purposes: Drivers can skip predefined controls not
84	supported by the hardware (although returning EINVAL would do as
85	well), or disable predefined and private controls after hardware
86	detection without the trouble of reordering control arrays and indices
87	(EINVAL cannot be used to skip private controls because it would
88	prematurely end the enumeration).</para></footnote></para>
89	
90	    <para>When the application ORs <structfield>id</structfield> with
91	<constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> the driver returns the
92	next supported control, or <errorcode>EINVAL</errorcode> if there is
93	none. Drivers which do not support this flag yet always return
94	<errorcode>EINVAL</errorcode>.</para>
95	
96	    <para>Additional information is required for menu controls: the
97	names of the menu items. To query them applications set the
98	<structfield>id</structfield> and <structfield>index</structfield>
99	fields of &v4l2-querymenu; and call the
100	<constant>VIDIOC_QUERYMENU</constant> ioctl with a pointer to this
101	structure. The driver fills the rest of the structure or returns an
102	&EINVAL; when the <structfield>id</structfield> or
103	<structfield>index</structfield> is invalid. Menu items are enumerated
104	by calling <constant>VIDIOC_QUERYMENU</constant> with successive
105	<structfield>index</structfield> values from &v4l2-queryctrl;
106	<structfield>minimum</structfield> to
107	<structfield>maximum</structfield>, inclusive. Note that it is possible
108	for <constant>VIDIOC_QUERYMENU</constant> to return an &EINVAL; for some
109	indices between <structfield>minimum</structfield> and <structfield>maximum</structfield>.
110	In that case that particular menu item is not supported by this driver. Also note that
111	the <structfield>minimum</structfield> value is not necessarily 0.</para>
112	
113	    <para>See also the examples in <xref linkend="control" />.</para>
114	
115	    <table pgwide="1" frame="none" id="v4l2-queryctrl">
116	      <title>struct <structname>v4l2_queryctrl</structname></title>
117	      <tgroup cols="3">
118		&cs-str;
119		<tbody valign="top">
120		  <row>
121		    <entry>__u32</entry>
122		    <entry><structfield>id</structfield></entry>
123		    <entry>Identifies the control, set by the application. See
124	<xref linkend="control-id" /> for predefined IDs. When the ID is ORed
125	with V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and returns
126	the first control with a higher ID. Drivers which do not support this
127	flag yet always return an &EINVAL;.</entry>
128		  </row>
129		  <row>
130		    <entry>__u32</entry>
131		    <entry><structfield>type</structfield></entry>
132		    <entry>Type of control, see <xref
133			linkend="v4l2-ctrl-type" />.</entry>
134		  </row>
135		  <row>
136		    <entry>__u8</entry>
137		    <entry><structfield>name</structfield>[32]</entry>
138		    <entry>Name of the control, a NUL-terminated ASCII
139	string. This information is intended for the user.</entry>
140		  </row>
141		  <row>
142		    <entry>__s32</entry>
143		    <entry><structfield>minimum</structfield></entry>
144		    <entry>Minimum value, inclusive. This field gives a lower
145	bound for <constant>V4L2_CTRL_TYPE_INTEGER</constant> controls and the
146	lowest valid index for <constant>V4L2_CTRL_TYPE_MENU</constant> controls.
147	For <constant>V4L2_CTRL_TYPE_STRING</constant> controls the minimum value
148	gives the minimum length of the string. This length <emphasis>does not include the terminating
149	zero</emphasis>. It may not be valid for any other type of control, including
150	<constant>V4L2_CTRL_TYPE_INTEGER64</constant> controls. Note that this is a
151	signed value.</entry>
152		  </row>
153		  <row>
154		    <entry>__s32</entry>
155		    <entry><structfield>maximum</structfield></entry>
156		    <entry>Maximum value, inclusive. This field gives an upper
157	bound for <constant>V4L2_CTRL_TYPE_INTEGER</constant> controls and the
158	highest valid index for <constant>V4L2_CTRL_TYPE_MENU</constant>
159	controls. For <constant>V4L2_CTRL_TYPE_BITMASK</constant> controls it is the
160	set of usable bits.
161	For <constant>V4L2_CTRL_TYPE_STRING</constant> controls the maximum value
162	gives the maximum length of the string. This length <emphasis>does not include the terminating
163	zero</emphasis>. It may not be valid for any other type of control, including
164	<constant>V4L2_CTRL_TYPE_INTEGER64</constant> controls. Note that this is a
165	signed value.</entry>
166		  </row>
167		  <row>
168		    <entry>__s32</entry>
169		    <entry><structfield>step</structfield></entry>
170		    <entry><para>This field gives a step size for
171	<constant>V4L2_CTRL_TYPE_INTEGER</constant> controls. For
172	<constant>V4L2_CTRL_TYPE_STRING</constant> controls this field refers to
173	the string length that has to be a multiple of this step size.
174	It may not be valid for any other type of control, including
175	<constant>V4L2_CTRL_TYPE_INTEGER64</constant>
176	controls.</para><para>Generally drivers should not scale hardware
177	control values. It may be necessary for example when the
178	<structfield>name</structfield> or <structfield>id</structfield> imply
179	a particular unit and the hardware actually accepts only multiples of
180	said unit. If so, drivers must take care values are properly rounded
181	when scaling, such that errors will not accumulate on repeated
182	read-write cycles.</para><para>This field gives the smallest change of
183	an integer control actually affecting hardware. Often the information
184	is needed when the user can change controls by keyboard or GUI
185	buttons, rather than a slider. When for example a hardware register
186	accepts values 0-511 and the driver reports 0-65535, step should be
187	128.</para><para>Note that although signed, the step value is supposed to
188	be always positive.</para></entry>
189		  </row>
190		  <row>
191		    <entry>__s32</entry>
192		    <entry><structfield>default_value</structfield></entry>
193		    <entry>The default value of a
194	<constant>V4L2_CTRL_TYPE_INTEGER</constant>,
195	<constant>_BOOLEAN</constant> or <constant>_MENU</constant> control.
196	Not valid for other types of controls. Drivers reset controls only
197	when the driver is loaded, not later, in particular not when the
198	func-open; is called.</entry>
199		  </row>
200		  <row>
201		    <entry>__u32</entry>
202		    <entry><structfield>flags</structfield></entry>
203		    <entry>Control flags, see <xref
204			linkend="control-flags" />.</entry>
205		  </row>
206		  <row>
207		    <entry>__u32</entry>
208		    <entry><structfield>reserved</structfield>[2]</entry>
209		    <entry>Reserved for future extensions. Drivers must set
210	the array to zero.</entry>
211		  </row>
212		</tbody>
213	      </tgroup>
214	    </table>
215	
216	    <table pgwide="1" frame="none" id="v4l2-querymenu">
217	      <title>struct <structname>v4l2_querymenu</structname></title>
218	      <tgroup cols="4">
219		&cs-str;
220		<tbody valign="top">
221		  <row>
222		    <entry>__u32</entry>
223		    <entry></entry>
224		    <entry><structfield>id</structfield></entry>
225		    <entry>Identifies the control, set by the application
226	from the respective &v4l2-queryctrl;
227	<structfield>id</structfield>.</entry>
228		  </row>
229		  <row>
230		    <entry>__u32</entry>
231		    <entry></entry>
232		    <entry><structfield>index</structfield></entry>
233		    <entry>Index of the menu item, starting at zero, set by
234		    the application.</entry>
235		  </row>
236		  <row>
237		    <entry>union</entry>
238		    <entry></entry>
239		    <entry></entry>
240		    <entry></entry>
241		  </row>
242		  <row>
243		    <entry></entry>
244		    <entry>__u8</entry>
245		    <entry><structfield>name</structfield>[32]</entry>
246		    <entry>Name of the menu item, a NUL-terminated ASCII
247	string. This information is intended for the user. This field is valid
248	for <constant>V4L2_CTRL_FLAG_MENU</constant> type controls.</entry>
249		  </row>
250		  <row>
251		    <entry></entry>
252		    <entry>__s64</entry>
253		    <entry><structfield>value</structfield></entry>
254		    <entry>
255	              Value of the integer menu item. This field is valid for
256	              <constant>V4L2_CTRL_FLAG_INTEGER_MENU</constant> type
257	              controls.
258	            </entry>
259		  </row>
260		  <row>
261		    <entry>__u32</entry>
262		    <entry></entry>
263		    <entry><structfield>reserved</structfield></entry>
264		    <entry>Reserved for future extensions. Drivers must set
265	the array to zero.</entry>
266		  </row>
267		</tbody>
268	      </tgroup>
269	    </table>
270	
271	    <table pgwide="1" frame="none" id="v4l2-ctrl-type">
272	      <title>enum v4l2_ctrl_type</title>
273	      <tgroup cols="5" align="left">
274		<colspec colwidth="30*" />
275		<colspec colwidth="5*" align="center" />
276		<colspec colwidth="5*" align="center" />
277		<colspec colwidth="5*" align="center" />
278		<colspec colwidth="55*" />
279		<thead>
280		  <row>
281		    <entry>Type</entry>
282		    <entry><structfield>minimum</structfield></entry>
283		    <entry><structfield>step</structfield></entry>
284		    <entry><structfield>maximum</structfield></entry>
285		    <entry>Description</entry>
286		  </row>
287		</thead>
288		<tbody valign="top">
289		  <row>
290		    <entry><constant>V4L2_CTRL_TYPE_INTEGER</constant></entry>
291		    <entry>any</entry>
292		    <entry>any</entry>
293		    <entry>any</entry>
294		    <entry>An integer-valued control ranging from minimum to
295	maximum inclusive. The step value indicates the increment between
296	values which are actually different on the hardware.</entry>
297		  </row>
298		  <row>
299		    <entry><constant>V4L2_CTRL_TYPE_BOOLEAN</constant></entry>
300		    <entry>0</entry>
301		    <entry>1</entry>
302		    <entry>1</entry>
303		    <entry>A boolean-valued control. Zero corresponds to
304	"disabled", and one means "enabled".</entry>
305		  </row>
306		  <row>
307		    <entry><constant>V4L2_CTRL_TYPE_MENU</constant></entry>
308		    <entry>&ge; 0</entry>
309		    <entry>1</entry>
310		    <entry>N-1</entry>
311		    <entry>The control has a menu of N choices. The names of
312	the menu items can be enumerated with the
313	<constant>VIDIOC_QUERYMENU</constant> ioctl.</entry>
314		  </row>
315		  <row>
316		    <entry><constant>V4L2_CTRL_TYPE_INTEGER_MENU</constant></entry>
317		    <entry>&ge; 0</entry>
318		    <entry>1</entry>
319		    <entry>N-1</entry>
320		    <entry>
321	              The control has a menu of N choices. The values of the
322	              menu items can be enumerated with the
323	              <constant>VIDIOC_QUERYMENU</constant> ioctl. This is
324	              similar to <constant>V4L2_CTRL_TYPE_MENU</constant>
325	              except that instead of strings, the menu items are
326	              signed 64-bit integers.
327	            </entry>
328		  </row>
329		  <row>
330		    <entry><constant>V4L2_CTRL_TYPE_BITMASK</constant></entry>
331		    <entry>0</entry>
332		    <entry>n/a</entry>
333		    <entry>any</entry>
334		    <entry>A bitmask field. The maximum value is the set of bits that can
335	be used, all other bits are to be 0. The maximum value is interpreted as a __u32,
336	allowing the use of bit 31 in the bitmask.</entry>
337		  </row>
338		  <row>
339		    <entry><constant>V4L2_CTRL_TYPE_BUTTON</constant></entry>
340		    <entry>0</entry>
341		    <entry>0</entry>
342		    <entry>0</entry>
343		    <entry>A control which performs an action when set.
344	Drivers must ignore the value passed with
345	<constant>VIDIOC_S_CTRL</constant> and return an &EINVAL; on a
346	<constant>VIDIOC_G_CTRL</constant> attempt.</entry>
347		  </row>
348		  <row>
349		    <entry><constant>V4L2_CTRL_TYPE_INTEGER64</constant></entry>
350		    <entry>n/a</entry>
351		    <entry>n/a</entry>
352		    <entry>n/a</entry>
353		    <entry>A 64-bit integer valued control. Minimum, maximum
354	and step size cannot be queried.</entry>
355		  </row>
356		  <row>
357		    <entry><constant>V4L2_CTRL_TYPE_STRING</constant></entry>
358		    <entry>&ge; 0</entry>
359		    <entry>&ge; 1</entry>
360		    <entry>&ge; 0</entry>
361		    <entry>The minimum and maximum string lengths. The step size
362	means that the string must be (minimum + N * step) characters long for
363	N &ge; 0. These lengths do not include the terminating zero, so in order to
364	pass a string of length 8 to &VIDIOC-S-EXT-CTRLS; you need to set the
365	<structfield>size</structfield> field of &v4l2-ext-control; to 9. For &VIDIOC-G-EXT-CTRLS; you can
366	set the <structfield>size</structfield> field to <structfield>maximum</structfield> + 1.
367	Which character encoding is used will depend on the string control itself and
368	should be part of the control documentation.</entry>
369		  </row>
370		  <row>
371		    <entry><constant>V4L2_CTRL_TYPE_CTRL_CLASS</constant></entry>
372		    <entry>n/a</entry>
373		    <entry>n/a</entry>
374		    <entry>n/a</entry>
375		    <entry>This is not a control. When
376	<constant>VIDIOC_QUERYCTRL</constant> is called with a control ID
377	equal to a control class code (see <xref linkend="ctrl-class" />) + 1, the
378	ioctl returns the name of the control class and this control type.
379	Older drivers which do not support this feature return an
380	&EINVAL;.</entry>
381		  </row>
382		</tbody>
383	      </tgroup>
384	    </table>
385	
386	    <table pgwide="1" frame="none" id="control-flags">
387	      <title>Control Flags</title>
388	      <tgroup cols="3">
389		&cs-def;
390		<tbody valign="top">
391		  <row>
392		    <entry><constant>V4L2_CTRL_FLAG_DISABLED</constant></entry>
393		    <entry>0x0001</entry>
394		    <entry>This control is permanently disabled and should be
395	ignored by the application. Any attempt to change the control will
396	result in an &EINVAL;.</entry>
397		  </row>
398		  <row>
399		    <entry><constant>V4L2_CTRL_FLAG_GRABBED</constant></entry>
400		    <entry>0x0002</entry>
401		    <entry>This control is temporarily unchangeable, for
402	example because another application took over control of the
403	respective resource. Such controls may be displayed specially in a
404	user interface. Attempts to change the control may result in an
405	&EBUSY;.</entry>
406		  </row>
407		  <row>
408		    <entry><constant>V4L2_CTRL_FLAG_READ_ONLY</constant></entry>
409		    <entry>0x0004</entry>
410		    <entry>This control is permanently readable only. Any
411	attempt to change the control will result in an &EINVAL;.</entry>
412		  </row>
413		  <row>
414		    <entry><constant>V4L2_CTRL_FLAG_UPDATE</constant></entry>
415		    <entry>0x0008</entry>
416		    <entry>A hint that changing this control may affect the
417	value of other controls within the same control class. Applications
418	should update their user interface accordingly.</entry>
419		  </row>
420		  <row>
421		    <entry><constant>V4L2_CTRL_FLAG_INACTIVE</constant></entry>
422		    <entry>0x0010</entry>
423		    <entry>This control is not applicable to the current
424	configuration and should be displayed accordingly in a user interface.
425	For example the flag may be set on a MPEG audio level 2 bitrate
426	control when MPEG audio encoding level 1 was selected with another
427	control.</entry>
428		  </row>
429		  <row>
430		    <entry><constant>V4L2_CTRL_FLAG_SLIDER</constant></entry>
431		    <entry>0x0020</entry>
432		    <entry>A hint that this control is best represented as a
433	slider-like element in a user interface.</entry>
434		  </row>
435		  <row>
436		    <entry><constant>V4L2_CTRL_FLAG_WRITE_ONLY</constant></entry>
437		    <entry>0x0040</entry>
438		    <entry>This control is permanently writable only. Any
439	attempt to read the control will result in an &EACCES; error code. This
440	flag is typically present for relative controls or action controls where
441	writing a value will cause the device to carry out a given action
442	(&eg; motor control) but no meaningful value can be returned.</entry>
443		  </row>
444		  <row>
445		    <entry><constant>V4L2_CTRL_FLAG_VOLATILE</constant></entry>
446		    <entry>0x0080</entry>
447		    <entry>This control is volatile, which means that the value of the control
448	changes continuously. A typical example would be the current gain value if the device
449	is in auto-gain mode. In such a case the hardware calculates the gain value based on
450	the lighting conditions which can change over time. Note that setting a new value for
451	a volatile control will have no effect. The new value will just be ignored.</entry>
452		  </row>
453		</tbody>
454	      </tgroup>
455	    </table>
456	  </refsect1>
457	
458	  <refsect1>
459	    &return-value;
460	
461	    <variablelist>
462	      <varlistentry>
463		<term><errorcode>EINVAL</errorcode></term>
464		<listitem>
465		  <para>The &v4l2-queryctrl; <structfield>id</structfield>
466	is invalid. The &v4l2-querymenu; <structfield>id</structfield> is
467	invalid or <structfield>index</structfield> is out of range (less than
468	<structfield>minimum</structfield> or greater than <structfield>maximum</structfield>)
469	or this particular menu item is not supported by the driver.</para>
470		</listitem>
471	      </varlistentry>
472	      <varlistentry>
473		<term><errorcode>EACCES</errorcode></term>
474		<listitem>
475		  <para>An attempt was made to read a write-only control.</para>
476		</listitem>
477	      </varlistentry>
478	    </variablelist>
479	  </refsect1>
480	</refentry>
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