1 <refentry id=
"vidioc-g-ext-ctrls">
3 <refentrytitle>ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,
4 VIDIOC_TRY_EXT_CTRLS
</refentrytitle>
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
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>
29 <title>Arguments
</title>
33 <term><parameter>fd
</parameter></term>
39 <term><parameter>request
</parameter></term>
41 <para>VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,
42 VIDIOC_TRY_EXT_CTRLS
</para>
46 <term><parameter>argp
</parameter></term>
55 <title>Description
</title>
57 <para>These ioctls allow the caller to get or set multiple
58 controls atomically. Control IDs are grouped into control classes (see
59 <xref linkend=
"ctrl-class" />) and all controls in the control array
60 must belong to the same control class.
</para>
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
67 initialize the &v4l2-ext-control; array pointed to by the
68 <structfield>controls
</structfield> fields.
</para>
70 <para>To get the current value of a set of controls applications
71 initialize the
<structfield>id
</structfield>,
72 <structfield>size
</structfield> and
<structfield>reserved2
</structfield> fields
73 of each &v4l2-ext-control; and call the
74 <constant>VIDIOC_G_EXT_CTRLS
</constant> ioctl. String controls controls
75 must also set the
<structfield>string
</structfield> field.
</para>
77 <para>If the
<structfield>size
</structfield> is too small to
78 receive the control result (only relevant for pointer-type controls
79 like strings), then the driver will set
<structfield>size
</structfield>
80 to a valid value and return an
&ENOSPC;. You should re-allocate the
81 string memory to this new size and try again. It is possible that the
82 same issue occurs again if the string has grown in the meantime. It is
83 recommended to call &VIDIOC-QUERYCTRL; first and use
84 <structfield>maximum
</structfield>+
1 as the new
<structfield>size
</structfield>
85 value. It is guaranteed that that is sufficient memory.
88 <para>To change the value of a set of controls applications
89 initialize the
<structfield>id
</structfield>,
<structfield>size
</structfield>,
90 <structfield>reserved2
</structfield> and
91 <structfield>value/string
</structfield> fields of each &v4l2-ext-control; and
92 call the
<constant>VIDIOC_S_EXT_CTRLS
</constant> ioctl. The controls
93 will only be set if
<emphasis>all
</emphasis> control values are
96 <para>To check if a set of controls have correct values applications
97 initialize the
<structfield>id
</structfield>,
<structfield>size
</structfield>,
98 <structfield>reserved2
</structfield> and
99 <structfield>value/string
</structfield> fields of each &v4l2-ext-control; and
100 call the
<constant>VIDIOC_TRY_EXT_CTRLS
</constant> ioctl. It is up to
101 the driver whether wrong values are automatically adjusted to a valid
102 value or if an error is returned.
</para>
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
107 the closest valid value or return an
&ERANGE;, whatever seems more
108 appropriate. In the first case the new value is set in
109 &v4l2-ext-control;.
</para>
111 <para>The driver will only set/get these controls if all control
112 values are correct. This prevents the situation where only some of the
113 controls were set/get. Only low-level errors (
⪚ a failed i2c
114 command) can still cause this situation.
</para>
116 <table pgwide=
"1" frame=
"none" id=
"v4l2-ext-control">
117 <title>struct
<structname>v4l2_ext_control
</structname></title>
123 <entry><structfield>id
</structfield></entry>
125 <entry>Identifies the control, set by the
130 <entry><structfield>size
</structfield></entry>
132 <entry>The total size in bytes of the payload of this
133 control. This is normally
0, but for pointer controls this should be
134 set to the size of the memory containing the payload, or that will
135 receive the payload. If
<constant>VIDIOC_G_EXT_CTRLS
</constant> finds
136 that this value is less than is required to store
137 the payload result, then it is set to a value large enough to store the
138 payload result and ENOSPC is returned. Note that for string controls
139 this
<structfield>size
</structfield> field should not be confused with the length of the string.
140 This field refers to the size of the memory that contains the string.
141 The actual
<emphasis>length
</emphasis> of the string may well be much smaller.
146 <entry><structfield>reserved2
</structfield>[
1]
</entry>
148 <entry>Reserved for future extensions. Drivers and
149 applications must set the array to zero.
</entry>
153 <entry>(anonymous)
</entry>
158 <entry><structfield>value
</structfield></entry>
159 <entry>New value or current value.
</entry>
164 <entry><structfield>value64
</structfield></entry>
165 <entry>New value or current value.
</entry>
169 <entry>char *
</entry>
170 <entry><structfield>string
</structfield></entry>
171 <entry>A pointer to a string.
</entry>
177 <table pgwide=
"1" frame=
"none" id=
"v4l2-ext-controls">
178 <title>struct
<structname>v4l2_ext_controls
</structname></title>
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
187 controls will also accept a value of
0 here, meaning that the controls can
188 belong 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>
190 with a
<structfield>count
</structfield> of
0. If that succeeds, then the driver
191 supports this feature.
</entry>
195 <entry><structfield>count
</structfield></entry>
196 <entry>The number of controls in the controls array. May
197 also be zero.
</entry>
201 <entry><structfield>error_idx
</structfield></entry>
202 <entry>Set by the driver in case of an error. If it is equal
203 to
<structfield>count
</structfield>, then no actual changes were made to
204 controls. In other words, the error was not associated with setting a particular
205 control. If it is another value, then only the controls up to
<structfield>error_idx-
1</structfield>
206 were modified and control
<structfield>error_idx
</structfield> is the one that
207 caused the error. The
<structfield>error_idx
</structfield> value is undefined
208 if the ioctl returned
0 (success).
</entry>
212 <entry><structfield>reserved
</structfield>[
2]
</entry>
213 <entry>Reserved for future extensions. Drivers and
214 applications must set the array to zero.
</entry>
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
221 if
<structfield>count
</structfield> equals zero.
</entry>
227 <table pgwide=
"1" frame=
"none" id=
"ctrl-class">
228 <title>Control classes
</title>
233 <entry><constant>V4L2_CTRL_CLASS_USER
</constant></entry>
234 <entry>0x980000</entry>
235 <entry>The class containing user controls. These controls
236 are described in
<xref linkend=
"control" />. All controls that can be set
237 using the &VIDIOC-S-CTRL; and &VIDIOC-G-CTRL; ioctl belong to this
241 <entry><constant>V4L2_CTRL_CLASS_MPEG
</constant></entry>
242 <entry>0x990000</entry>
243 <entry>The class containing MPEG compression controls.
244 These controls are described in
<xref
245 linkend=
"mpeg-controls" />.
</entry>
248 <entry><constant>V4L2_CTRL_CLASS_CAMERA
</constant></entry>
249 <entry>0x9a0000</entry>
250 <entry>The class containing camera controls.
251 These controls are described in
<xref
252 linkend=
"camera-controls" />.
</entry>
255 <entry><constant>V4L2_CTRL_CLASS_FM_TX
</constant></entry>
256 <entry>0x9b0000</entry>
257 <entry>The class containing FM Transmitter (FM TX) controls.
258 These controls are described in
<xref
259 linkend=
"fm-tx-controls" />.
</entry>
262 <entry><constant>V4L2_CTRL_CLASS_FLASH
</constant></entry>
263 <entry>0x9c0000</entry>
264 <entry>The class containing flash device controls.
265 These controls are described in
<xref
266 linkend=
"flash-controls" />.
</entry>
279 <term><errorcode>EINVAL
</errorcode></term>
281 <para>The &v4l2-ext-control;
<structfield>id
</structfield>
282 is invalid or the &v4l2-ext-controls;
283 <structfield>ctrl_class
</structfield> is invalid. This error code is
284 also returned by the
<constant>VIDIOC_S_EXT_CTRLS
</constant> and
285 <constant>VIDIOC_TRY_EXT_CTRLS
</constant> ioctls if two or more
286 control values are in conflict.
</para>
290 <term><errorcode>ERANGE
</errorcode></term>
292 <para>The &v4l2-ext-control;
<structfield>value
</structfield>
293 is out of bounds.
</para>
297 <term><errorcode>EBUSY
</errorcode></term>
299 <para>The control is temporarily not changeable, possibly
300 because another applications took over control of the device function
301 this control belongs to.
</para>
305 <term><errorcode>ENOSPC
</errorcode></term>
307 <para>The space reserved for the control's payload is insufficient.
308 The field
<structfield>size
</structfield> is set to a value that is enough
309 to store the payload and this error code is returned.
</para>
313 <term><errorcode>EACCES
</errorcode></term>
315 <para>Attempt to try or set a read-only control or to get a
316 write-only control.
</para>