1<refentry id="vidioc-g-ext-ctrls">
2  <refmeta>
3    <refentrytitle>ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,
4VIDIOC_TRY_EXT_CTRLS</refentrytitle>
5    &manvol;
6  </refmeta>
7
8  <refnamediv>
9    <refname>VIDIOC_G_EXT_CTRLS</refname>
10    <refname>VIDIOC_S_EXT_CTRLS</refname>
11    <refname>VIDIOC_TRY_EXT_CTRLS</refname>
12    <refpurpose>Get or set the value of several controls, try control
13values</refpurpose>
14  </refnamediv>
15
16  <refsynopsisdiv>
17    <funcsynopsis>
18      <funcprototype>
19	<funcdef>int <function>ioctl</function></funcdef>
20	<paramdef>int <parameter>fd</parameter></paramdef>
21	<paramdef>int <parameter>request</parameter></paramdef>
22	<paramdef>struct v4l2_ext_controls
23*<parameter>argp</parameter></paramdef>
24      </funcprototype>
25    </funcsynopsis>
26  </refsynopsisdiv>
27
28  <refsect1>
29    <title>Arguments</title>
30
31    <variablelist>
32      <varlistentry>
33	<term><parameter>fd</parameter></term>
34	<listitem>
35	  <para>&fd;</para>
36	</listitem>
37      </varlistentry>
38      <varlistentry>
39	<term><parameter>request</parameter></term>
40	<listitem>
41	  <para>VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,
42VIDIOC_TRY_EXT_CTRLS</para>
43	</listitem>
44      </varlistentry>
45      <varlistentry>
46	<term><parameter>argp</parameter></term>
47	<listitem>
48	  <para></para>
49	</listitem>
50      </varlistentry>
51    </variablelist>
52  </refsect1>
53
54  <refsect1>
55    <title>Description</title>
56
57    <para>These ioctls allow the caller to get or set multiple
58controls atomically. Control IDs are grouped into control classes (see
59<xref linkend="ctrl-class" />) and all controls in the control array
60must belong to the same control class.</para>
61
62    <para>Applications must always fill in the
63<structfield>count</structfield>,
64<structfield>ctrl_class</structfield>,
65<structfield>controls</structfield> and
66<structfield>reserved</structfield> fields of &v4l2-ext-controls;, and
67initialize the &v4l2-ext-control; array pointed to by the
68<structfield>controls</structfield> fields.</para>
69
70    <para>To get the current value of a set of controls applications
71initialize the <structfield>id</structfield>,
72<structfield>size</structfield> and <structfield>reserved2</structfield> fields
73of each &v4l2-ext-control; and call the
74<constant>VIDIOC_G_EXT_CTRLS</constant> ioctl. String controls controls
75must also set the <structfield>string</structfield> field.</para>
76
77    <para>If the <structfield>size</structfield> is too small to
78receive the control result (only relevant for pointer-type controls
79like strings), then the driver will set <structfield>size</structfield>
80to a valid value and return an &ENOSPC;. You should re-allocate the
81string memory to this new size and try again. It is possible that the
82same issue occurs again if the string has grown in the meantime. It is
83recommended to call &VIDIOC-QUERYCTRL; first and use
84<structfield>maximum</structfield>+1 as the new <structfield>size</structfield>
85value. It is guaranteed that that is sufficient memory.
86</para>
87
88    <para>To change the value of a set of controls applications
89initialize the <structfield>id</structfield>, <structfield>size</structfield>,
90<structfield>reserved2</structfield> and
91<structfield>value/string</structfield> fields of each &v4l2-ext-control; and
92call the <constant>VIDIOC_S_EXT_CTRLS</constant> ioctl. The controls
93will only be set if <emphasis>all</emphasis> control values are
94valid.</para>
95
96    <para>To check if a set of controls have correct values applications
97initialize the <structfield>id</structfield>, <structfield>size</structfield>,
98<structfield>reserved2</structfield> and
99<structfield>value/string</structfield> fields of each &v4l2-ext-control; and
100call the <constant>VIDIOC_TRY_EXT_CTRLS</constant> ioctl. It is up to
101the driver whether wrong values are automatically adjusted to a valid
102value or if an error is returned.</para>
103
104    <para>When the <structfield>id</structfield> or
105<structfield>ctrl_class</structfield> is invalid drivers return an
106&EINVAL;. When the value is out of bounds drivers can choose to take
107the closest valid value or return an &ERANGE;, whatever seems more
108appropriate. In the first case the new value is set in
109&v4l2-ext-control;.</para>
110
111    <para>The driver will only set/get these controls if all control
112values are correct. This prevents the situation where only some of the
113controls were set/get. Only low-level errors (&eg; a failed i2c
114command) can still cause this situation.</para>
115
116    <table pgwide="1" frame="none" id="v4l2-ext-control">
117      <title>struct <structname>v4l2_ext_control</structname></title>
118      <tgroup cols="4">
119	&cs-ustr;
120	<tbody valign="top">
121	  <row>
122	    <entry>__u32</entry>
123	    <entry><structfield>id</structfield></entry>
124	    <entry></entry>
125	    <entry>Identifies the control, set by the
126application.</entry>
127	  </row>
128	  <row>
129	    <entry>__u32</entry>
130	    <entry><structfield>size</structfield></entry>
131	    <entry></entry>
132	    <entry>The total size in bytes of the payload of this
133control. This is normally 0, but for pointer controls this should be
134set to the size of the memory containing the payload, or that will
135receive the payload. If <constant>VIDIOC_G_EXT_CTRLS</constant> finds
136that this value is less than is required to store
137the payload result, then it is set to a value large enough to store the
138payload result and ENOSPC is returned. Note that for string controls
139this <structfield>size</structfield> field should not be confused with the length of the string.
140This field refers to the size of the memory that contains the string.
141The actual <emphasis>length</emphasis> of the string may well be much smaller.
142</entry>
143	  </row>
144	  <row>
145	    <entry>__u32</entry>
146	    <entry><structfield>reserved2</structfield>[1]</entry>
147	    <entry></entry>
148	    <entry>Reserved for future extensions. Drivers and
149applications must set the array to zero.</entry>
150	  </row>
151	  <row>
152	    <entry>union</entry>
153	    <entry>(anonymous)</entry>
154	  </row>
155	  <row>
156	    <entry></entry>
157	    <entry>__s32</entry>
158	    <entry><structfield>value</structfield></entry>
159	    <entry>New value or current value.</entry>
160	  </row>
161	  <row>
162	    <entry></entry>
163	    <entry>__s64</entry>
164	    <entry><structfield>value64</structfield></entry>
165	    <entry>New value or current value.</entry>
166	  </row>
167	  <row>
168	    <entry></entry>
169	    <entry>char *</entry>
170	    <entry><structfield>string</structfield></entry>
171	    <entry>A pointer to a string.</entry>
172	  </row>
173	</tbody>
174      </tgroup>
175    </table>
176
177    <table pgwide="1" frame="none" id="v4l2-ext-controls">
178      <title>struct <structname>v4l2_ext_controls</structname></title>
179      <tgroup cols="3">
180	&cs-str;
181	<tbody valign="top">
182	  <row>
183	    <entry>__u32</entry>
184	    <entry><structfield>ctrl_class</structfield></entry>
185	    <entry>The control class to which all controls belong, see
186<xref linkend="ctrl-class" />. Drivers that use a kernel framework for handling
187controls will also accept a value of 0 here, meaning that the controls can
188belong to any control class. Whether drivers support this can be tested by setting
189<structfield>ctrl_class</structfield> to 0 and calling <constant>VIDIOC_TRY_EXT_CTRLS</constant>
190with a <structfield>count</structfield> of 0. If that succeeds, then the driver
191supports this feature.</entry>
192	  </row>
193	  <row>
194	    <entry>__u32</entry>
195	    <entry><structfield>count</structfield></entry>
196	    <entry>The number of controls in the controls array. May
197also be zero.</entry>
198	  </row>
199	  <row>
200	    <entry>__u32</entry>
201	    <entry><structfield>error_idx</structfield></entry>
202	    <entry>Set by the driver in case of an error. If it is equal
203to <structfield>count</structfield>, then no actual changes were made to
204controls. In other words, the error was not associated with setting a particular
205control. If it is another value, then only the controls up to <structfield>error_idx-1</structfield>
206were modified and control <structfield>error_idx</structfield> is the one that
207caused the error. The <structfield>error_idx</structfield> value is undefined
208if the ioctl returned 0 (success).</entry>
209	  </row>
210	  <row>
211	    <entry>__u32</entry>
212	    <entry><structfield>reserved</structfield>[2]</entry>
213	    <entry>Reserved for future extensions. Drivers and
214applications must set the array to zero.</entry>
215	  </row>
216	  <row>
217	    <entry>&v4l2-ext-control; *</entry>
218	    <entry><structfield>controls</structfield></entry>
219	    <entry>Pointer to an array of
220<structfield>count</structfield> v4l2_ext_control structures. Ignored
221if <structfield>count</structfield> equals zero.</entry>
222	  </row>
223	</tbody>
224      </tgroup>
225    </table>
226
227    <table pgwide="1" frame="none" id="ctrl-class">
228      <title>Control classes</title>
229      <tgroup cols="3">
230	&cs-def;
231	<tbody valign="top">
232	  <row>
233	    <entry><constant>V4L2_CTRL_CLASS_USER</constant></entry>
234	    <entry>0x980000</entry>
235	    <entry>The class containing user controls. These controls
236are described in <xref linkend="control" />. All controls that can be set
237using the &VIDIOC-S-CTRL; and &VIDIOC-G-CTRL; ioctl belong to this
238class.</entry>
239	  </row>
240	  <row>
241	    <entry><constant>V4L2_CTRL_CLASS_MPEG</constant></entry>
242	    <entry>0x990000</entry>
243	    <entry>The class containing MPEG compression controls.
244These controls are described in <xref
245		linkend="mpeg-controls" />.</entry>
246	  </row>
247	  <row>
248	    <entry><constant>V4L2_CTRL_CLASS_CAMERA</constant></entry>
249	    <entry>0x9a0000</entry>
250	    <entry>The class containing camera controls.
251These controls are described in <xref
252		linkend="camera-controls" />.</entry>
253	  </row>
254	  <row>
255	    <entry><constant>V4L2_CTRL_CLASS_FM_TX</constant></entry>
256	    <entry>0x9b0000</entry>
257	    <entry>The class containing FM Transmitter (FM TX) controls.
258These controls are described in <xref
259		linkend="fm-tx-controls" />.</entry>
260	  </row>
261	  <row>
262	    <entry><constant>V4L2_CTRL_CLASS_FLASH</constant></entry>
263	    <entry>0x9c0000</entry>
264	    <entry>The class containing flash device controls.
265These controls are described in <xref
266		linkend="flash-controls" />.</entry>
267	  </row>
268	</tbody>
269      </tgroup>
270    </table>
271
272  </refsect1>
273
274  <refsect1>
275    &return-value;
276
277    <variablelist>
278      <varlistentry>
279	<term><errorcode>EINVAL</errorcode></term>
280	<listitem>
281	  <para>The &v4l2-ext-control; <structfield>id</structfield>
282is invalid or the &v4l2-ext-controls;
283<structfield>ctrl_class</structfield> is invalid. This error code is
284also returned by the <constant>VIDIOC_S_EXT_CTRLS</constant> and
285<constant>VIDIOC_TRY_EXT_CTRLS</constant> ioctls if two or more
286control values are in conflict.</para>
287	</listitem>
288      </varlistentry>
289      <varlistentry>
290	<term><errorcode>ERANGE</errorcode></term>
291	<listitem>
292	  <para>The &v4l2-ext-control; <structfield>value</structfield>
293is out of bounds.</para>
294	</listitem>
295      </varlistentry>
296      <varlistentry>
297	<term><errorcode>EBUSY</errorcode></term>
298	<listitem>
299	  <para>The control is temporarily not changeable, possibly
300because another applications took over control of the device function
301this control belongs to.</para>
302	</listitem>
303      </varlistentry>
304      <varlistentry>
305	<term><errorcode>ENOSPC</errorcode></term>
306	<listitem>
307	  <para>The space reserved for the control's payload is insufficient.
308The field <structfield>size</structfield> is set to a value that is enough
309to store the payload and this error code is returned.</para>
310	</listitem>
311      </varlistentry>
312      <varlistentry>
313	<term><errorcode>EACCES</errorcode></term>
314	<listitem>
315	  <para>Attempt to try or set a read-only control or to get a
316	  write-only control.</para>
317	</listitem>
318      </varlistentry>
319    </variablelist>
320  </refsect1>
321</refentry>
322
323