doc/spec/r11946.htm

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>ioctl VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY</TITLE
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>Video for Linux Two API Specification: Revision 0.24</TH
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><H1
><A
NAME="VIDIOC-G-PRIORITY"
></A
>ioctl VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN11950"
></A
><H2
>Name</H2
>VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY&nbsp;--&nbsp;Query or request the access priority associated with a
file descriptor</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN11954"
></A
><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><P
></P
><A
NAME="AEN11955"
></A
><P
><CODE
><CODE
CLASS="FUNCDEF"
>int ioctl</CODE
>(int fd, int request, enum v4l2_priority *argp);</CODE
></P
><P
></P
></DIV
><DIV
CLASS="FUNCSYNOPSIS"
><P
></P
><A
NAME="AEN11965"
></A
><P
><CODE
><CODE
CLASS="FUNCDEF"
>int ioctl</CODE
>(int fd, int request, const enum v4l2_priority *argp);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN11975"
></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_PRIORITY, VIDIOC_S_PRIORITY</P
></DD
><DT
><CODE
CLASS="PARAMETER"
>argp</CODE
></DT
><DD
><P
>Pointer to an enum v4l2_priority type.</P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN11995"
></A
><H2
>Description</H2
><P
>To query the current access priority
applications call the <CODE
CLASS="CONSTANT"
>VIDIOC_G_PRIORITY</CODE
> ioctl
with a pointer to an enum v4l2_priority variable where the driver stores
the current priority.</P
><P
>To request an access priority applications store the
desired priority in an enum v4l2_priority variable and call
<CODE
CLASS="CONSTANT"
>VIDIOC_S_PRIORITY</CODE
> ioctl with a pointer to this
variable.</P
><DIV
CLASS="TABLE"
><A
NAME="V4L2-PRIORITY"
></A
><P
><B
>Table 1. enum v4l2_priority</B
></P
><TABLE
BORDER="0"
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TITLE="C1"><COL
WIDTH="12%"
TITLE="C2"><COL
WIDTH="50%"
TITLE="C3"><TBODY
VALIGN="TOP"
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_PRIORITY_UNSET</CODE
></TD
><TD
>0</TD
><TD
>&nbsp;</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_PRIORITY_BACKGROUND</CODE
></TD
><TD
>1</TD
><TD
>Lowest priority, usually applications running in
background, for example monitoring VBI transmissions. A proxy
application running in user space will be necessary if multiple
applications want to read from a device at this priority.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_PRIORITY_INTERACTIVE</CODE
></TD
><TD
>2</TD
><TD
>&nbsp;</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_PRIORITY_DEFAULT</CODE
></TD
><TD
>2</TD
><TD
>Medium priority, usually applications started and
interactively controlled by the user. For example TV viewers, Teletext
browsers, or just "panel" applications to change the channel or video
controls. This is the default priority unless an application requests
another.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_PRIORITY_RECORD</CODE
></TD
><TD
>3</TD
><TD
>Highest priority. Only one file descriptor can have
this priority, it blocks any other fd from changing device properties.
Usually applications which must not be interrupted, like video
recording.</TD
></TR
></TBODY
></TABLE
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN12034"
></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 requested priority value is invalid, or the
driver does not support access priorities.</P
></DD
><DT
><SPAN
CLASS="ERRORCODE"
>EBUSY</SPAN
></DT
><DD
><P
>Another application already requested higher
priority.</P
></DD
></DL
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