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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
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>ioctl VIDIOC_QUERYBUF</TITLE
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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&nbsp;--&nbsp;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&nbsp;<A
HREF="x5953.htm#V4L2-BUFFER"
>v4l2_buffer</A
> to the same buffer type as previously
struct&nbsp;<A
HREF="r10944.htm#V4L2-FORMAT"
>v4l2_format</A
> <CODE
CLASS="STRUCTFIELD"
>type</CODE
> and struct&nbsp;<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&nbsp;<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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