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1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_G_CTRL: |
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4 | |
5 | ********************************** | |
6 | ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL | |
7 | ********************************** | |
8 | ||
15e7d615 | 9 | Name |
586027ce | 10 | ==== |
5377d91f | 11 | |
586027ce | 12 | VIDIOC_G_CTRL - VIDIOC_S_CTRL - Get or set the value of a control |
5377d91f | 13 | |
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14 | |
15 | Synopsis | |
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16 | ======== |
17 | ||
b7e67f6c | 18 | .. cpp:function:: int ioctl( int fd, int request, struct v4l2_control *argp ) |
5377d91f | 19 | |
586027ce | 20 | |
15e7d615 | 21 | Arguments |
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22 | ========= |
23 | ||
24 | ``fd`` | |
25 | File descriptor returned by :ref:`open() <func-open>`. | |
26 | ||
27 | ``request`` | |
28 | VIDIOC_G_CTRL, VIDIOC_S_CTRL | |
29 | ||
30 | ``argp`` | |
31 | ||
32 | ||
15e7d615 | 33 | Description |
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34 | =========== |
35 | ||
36 | To get the current value of a control applications initialize the ``id`` | |
acf309a2 | 37 | field of a struct :ref:`struct v4l2_control <v4l2-control>` and call the |
4e03cb76 | 38 | :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl with a pointer to this structure. To change the |
5377d91f | 39 | value of a control applications initialize the ``id`` and ``value`` |
acf309a2 | 40 | fields of a struct :ref:`struct v4l2_control <v4l2-control>` and call the |
2212ff25 | 41 | :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctl. |
5377d91f | 42 | |
cdb4af0f | 43 | When the ``id`` is invalid drivers return an ``EINVAL`` error code. When the |
5377d91f | 44 | ``value`` is out of bounds drivers can choose to take the closest valid |
cdb4af0f | 45 | value or return an ``ERANGE`` error code, whatever seems more appropriate. |
2212ff25 | 46 | However, :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` is a write-only ioctl, it does not return the |
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47 | actual new value. If the ``value`` is inappropriate for the control |
48 | (e.g. if it refers to an unsupported menu index of a menu control), then | |
49 | EINVAL error code is returned as well. | |
50 | ||
51 | These ioctls work only with user controls. For other control classes the | |
4e03cb76 | 52 | :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`, |
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53 | :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` or |
54 | :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` must be used. | |
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55 | |
56 | ||
57 | .. _v4l2-control: | |
58 | ||
59 | .. flat-table:: struct v4l2_control | |
60 | :header-rows: 0 | |
61 | :stub-columns: 0 | |
62 | :widths: 1 1 2 | |
63 | ||
64 | ||
65 | - .. row 1 | |
66 | ||
67 | - __u32 | |
68 | ||
69 | - ``id`` | |
70 | ||
71 | - Identifies the control, set by the application. | |
72 | ||
73 | - .. row 2 | |
74 | ||
75 | - __s32 | |
76 | ||
77 | - ``value`` | |
78 | ||
79 | - New value or current value. | |
80 | ||
81 | ||
15e7d615 | 82 | Return Value |
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83 | ============ |
84 | ||
85 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
86 | appropriately. The generic error codes are described at the | |
87 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
88 | ||
89 | EINVAL | |
90 | The struct :ref:`v4l2_control <v4l2-control>` ``id`` is invalid | |
91 | or the ``value`` is inappropriate for the given control (i.e. if a | |
92 | menu item is selected that is not supported by the driver according | |
af4a4d0d | 93 | to :ref:`VIDIOC_QUERYMENU <VIDIOC_QUERYCTRL>`). |
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94 | |
95 | ERANGE | |
96 | The struct :ref:`v4l2_control <v4l2-control>` ``value`` is out of | |
97 | bounds. | |
98 | ||
99 | EBUSY | |
100 | The control is temporarily not changeable, possibly because another | |
101 | applications took over control of the device function this control | |
102 | belongs to. | |
103 | ||
104 | EACCES | |
105 | Attempt to set a read-only control or to get a write-only control. |