doc/spec/r10104.htm

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>Video for Linux Two API Specification: Revision 0.24</TH
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><H1
><A
NAME="VIDIOC-G-CTRL"
></A
>ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN10108"
></A
><H2
>Name</H2
>VIDIOC_G_CTRL, VIDIOC_S_CTRL&nbsp;--&nbsp;Get or set the value of a control</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN10112"
></A
><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><P
></P
><A
NAME="AEN10113"
></A
><P
><CODE
><CODE
CLASS="FUNCDEF"
>int ioctl</CODE
>(int fd, int request, struct v4l2_control
*argp);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN10123"
></A
><H2
>Arguments</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><CODE
CLASS="PARAMETER"
>fd</CODE
></DT
><DD
><P
>File descriptor returned by <A
HREF="r14090.htm"
><CODE
CLASS="FUNCTION"
>open()</CODE
></A
>.</P
></DD
><DT
><CODE
CLASS="PARAMETER"
>request</CODE
></DT
><DD
><P
>VIDIOC_G_CTRL, VIDIOC_S_CTRL</P
></DD
><DT
><CODE
CLASS="PARAMETER"
>argp</CODE
></DT
><DD
><P
></P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN10143"
></A
><H2
>Description</H2
><P
>To get the current value of a control applications
initialize the <CODE
CLASS="STRUCTFIELD"
>id</CODE
> field of a struct
<CODE
CLASS="STRUCTNAME"
>v4l2_control</CODE
> and call the
<CODE
CLASS="CONSTANT"
>VIDIOC_G_CTRL</CODE
> ioctl with a pointer to this
structure. To change the value of a control applications initialize
the <CODE
CLASS="STRUCTFIELD"
>id</CODE
> and <CODE
CLASS="STRUCTFIELD"
>value</CODE
>
fields of a struct <CODE
CLASS="STRUCTNAME"
>v4l2_control</CODE
> and call the
<CODE
CLASS="CONSTANT"
>VIDIOC_S_CTRL</CODE
> ioctl.</P
><P
>When the <CODE
CLASS="STRUCTFIELD"
>id</CODE
> is invalid drivers
return an <SPAN
CLASS="ERRORCODE"
>EINVAL</SPAN
> error code. When the <CODE
CLASS="STRUCTFIELD"
>value</CODE
> is out
of bounds drivers can choose to take the closest valid value or return
an <SPAN
CLASS="ERRORCODE"
>ERANGE</SPAN
> error code, whatever seems more appropriate. However,
<CODE
CLASS="CONSTANT"
>VIDIOC_S_CTRL</CODE
> is a write-only ioctl, it does not
return the actual new value.</P
><P
>These ioctls work only with user controls. For other
control classes the <A
HREF="r10386.htm"
><CODE
CLASS="CONSTANT"
>VIDIOC_G_EXT_CTRLS</CODE
></A
>, <A
HREF="r10386.htm"
><CODE
CLASS="CONSTANT"
>VIDIOC_S_EXT_CTRLS</CODE
></A
> or
<A
HREF="r10386.htm"
><CODE
CLASS="CONSTANT"
>VIDIOC_TRY_EXT_CTRLS</CODE
></A
> must be used.</P
><DIV
CLASS="TABLE"
><A
NAME="V4L2-CONTROL"
></A
><P
><B
>Table 1. struct <CODE
CLASS="STRUCTNAME"
>v4l2_control</CODE
></B
></P
><TABLE
BORDER="0"
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><COL
WIDTH="25%"
TITLE="C1"><COL
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TITLE="C2"><COL
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TITLE="C3"><TBODY
VALIGN="TOP"
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>id</CODE
></TD
><TD
>Identifies the control, set by the
application.</TD
></TR
><TR
><TD
>__s32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>value</CODE
></TD
><TD
>New value or current value.</TD
></TR
></TBODY
></TABLE
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN10185"
></A
><H2
>Return Value</H2
><P
>On success <SPAN
CLASS="RETURNVALUE"
>0</SPAN
> is returned, on error <SPAN
CLASS="RETURNVALUE"
>-1</SPAN
> and the <CODE
CLASS="VARNAME"
>errno</CODE
> variable is set appropriately:</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><SPAN
CLASS="ERRORCODE"
>EINVAL</SPAN
></DT
><DD
><P
>The struct&nbsp;<A
HREF="r10104.htm#V4L2-CONTROL"
>v4l2_control</A
> <CODE
CLASS="STRUCTFIELD"
>id</CODE
> is
invalid.</P
></DD
><DT
><SPAN
CLASS="ERRORCODE"
>ERANGE</SPAN
></DT
><DD
><P
>The struct&nbsp;<A
HREF="r10104.htm#V4L2-CONTROL"
>v4l2_control</A
> <CODE
CLASS="STRUCTFIELD"
>value</CODE
>
is out of bounds.</P
></DD
><DT
><SPAN
CLASS="ERRORCODE"
>EBUSY</SPAN
></DT
><DD
><P
>The control is temporarily not changeable, possibly
because another applications took over control of the device function
this control belongs to.</P
></DD
></DL
></DIV
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