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| >Video for Linux Two API Specification: Revision 0.24</TH |
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| ><H1 |
| ><A |
| NAME="VIDIOC-QUERYBUF" |
| ></A |
| >ioctl VIDIOC_QUERYBUF</H1 |
| ><DIV |
| CLASS="REFNAMEDIV" |
| ><A |
| NAME="AEN13026" |
| ></A |
| ><H2 |
| >Name</H2 |
| >VIDIOC_QUERYBUF -- Query the status of a buffer</DIV |
| ><DIV |
| CLASS="REFSYNOPSISDIV" |
| ><A |
| NAME="AEN13029" |
| ></A |
| ><H2 |
| >Synopsis</H2 |
| ><DIV |
| CLASS="FUNCSYNOPSIS" |
| ><P |
| ></P |
| ><A |
| NAME="AEN13030" |
| ></A |
| ><P |
| ><CODE |
| ><CODE |
| CLASS="FUNCDEF" |
| >int ioctl</CODE |
| >(int fd, int request, struct v4l2_buffer *argp);</CODE |
| ></P |
| ><P |
| ></P |
| ></DIV |
| ></DIV |
| ><DIV |
| CLASS="REFSECT1" |
| ><A |
| NAME="AEN13040" |
| ></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_QUERYBUF</P |
| ></DD |
| ><DT |
| ><CODE |
| CLASS="PARAMETER" |
| >argp</CODE |
| ></DT |
| ><DD |
| ><P |
| ></P |
| ></DD |
| ></DL |
| ></DIV |
| ></DIV |
| ><DIV |
| CLASS="REFSECT1" |
| ><A |
| NAME="AEN13060" |
| ></A |
| ><H2 |
| >Description</H2 |
| ><P |
| >This ioctl is part of the <A |
| HREF="x5791.htm" |
| >memory |
| mapping</A |
| > I/O method. It can be used to query the status of a |
| buffer at any time after buffers have been allocated with the |
| <A |
| HREF="r13696.htm" |
| ><CODE |
| CLASS="CONSTANT" |
| >VIDIOC_REQBUFS</CODE |
| ></A |
| > ioctl.</P |
| ><P |
| >Applications set the <CODE |
| CLASS="STRUCTFIELD" |
| >type</CODE |
| > field |
| of a struct <A |
| HREF="x5953.htm#V4L2-BUFFER" |
| >v4l2_buffer</A |
| > to the same buffer type as previously |
| struct <A |
| HREF="r10944.htm#V4L2-FORMAT" |
| >v4l2_format</A |
| > <CODE |
| CLASS="STRUCTFIELD" |
| >type</CODE |
| > and struct <A |
| HREF="r13696.htm#V4L2-REQUESTBUFFERS" |
| >v4l2_requestbuffers</A |
| > |
| <CODE |
| CLASS="STRUCTFIELD" |
| >type</CODE |
| >, and the <CODE |
| CLASS="STRUCTFIELD" |
| >index</CODE |
| > |
| field. Valid index numbers range from zero |
| to the number of buffers allocated with <A |
| HREF="r13696.htm" |
| ><CODE |
| CLASS="CONSTANT" |
| >VIDIOC_REQBUFS</CODE |
| ></A |
| > |
| (struct <A |
| HREF="r13696.htm#V4L2-REQUESTBUFFERS" |
| >v4l2_requestbuffers</A |
| > <CODE |
| CLASS="STRUCTFIELD" |
| >count</CODE |
| >) minus one. |
| After calling <CODE |
| CLASS="CONSTANT" |
| >VIDIOC_QUERYBUF</CODE |
| > with a pointer to |
| this structure drivers return an error code or fill the rest of |
| the structure.</P |
| ><P |
| >In the <CODE |
| CLASS="STRUCTFIELD" |
| >flags</CODE |
| > field the |
| <CODE |
| CLASS="CONSTANT" |
| >V4L2_BUF_FLAG_MAPPED</CODE |
| >, |
| <CODE |
| CLASS="CONSTANT" |
| >V4L2_BUF_FLAG_QUEUED</CODE |
| > and |
| <CODE |
| CLASS="CONSTANT" |
| >V4L2_BUF_FLAG_DONE</CODE |
| > flags will be valid. The |
| <CODE |
| CLASS="STRUCTFIELD" |
| >memory</CODE |
| > field will be set to |
| <CODE |
| CLASS="CONSTANT" |
| >V4L2_MEMORY_MMAP</CODE |
| >, the <CODE |
| CLASS="STRUCTFIELD" |
| >m.offset</CODE |
| > |
| contains the offset of the buffer from the start of the device memory, |
| the <CODE |
| CLASS="STRUCTFIELD" |
| >length</CODE |
| > field its size. The driver may |
| or may not set the remaining fields and flags, they are meaningless in |
| this context.</P |
| ><P |
| >The <CODE |
| CLASS="STRUCTNAME" |
| >v4l2_buffer</CODE |
| > structure is |
| specified in <A |
| HREF="x5953.htm" |
| >Section 3.5</A |
| >.</P |
| ></DIV |
| ><DIV |
| CLASS="REFSECT1" |
| ><A |
| NAME="AEN13091" |
| ></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 buffer <CODE |
| CLASS="STRUCTFIELD" |
| >type</CODE |
| > is not |
| supported, or the <CODE |
| CLASS="STRUCTFIELD" |
| >index</CODE |
| > is out of bounds.</P |
| ></DD |
| ></DL |
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