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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 -- 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 |
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| ></DIV |
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| CLASS="REFSECT1" |
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| NAME="AEN11975" |
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| ><H2 |
| >Arguments</H2 |
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| ><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 |
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| ><TR |
| ><TD |
| ><CODE |
| CLASS="CONSTANT" |
| >V4L2_PRIORITY_UNSET</CODE |
| ></TD |
| ><TD |
| >0</TD |
| ><TD |
| > </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 |
| > </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 |
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| 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 |
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