104 lines
3.1 KiB
XML
104 lines
3.1 KiB
XML
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<refentry id="vidioc-querybuf">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_QUERYBUF</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_QUERYBUF</refname>
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<refpurpose>Query the status of a buffer</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_buffer *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_QUERYBUF</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<para>This ioctl is part of the <link linkend="mmap">memory
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mapping</link> I/O method. It can be used to query the status of a
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buffer at any time after buffers have been allocated with the
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&VIDIOC-REQBUFS; ioctl.</para>
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<para>Applications set the <structfield>type</structfield> field
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of a &v4l2-buffer; to the same buffer type as previously
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&v4l2-format; <structfield>type</structfield> and &v4l2-requestbuffers;
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<structfield>type</structfield>, and the <structfield>index</structfield>
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field. Valid index numbers range from zero
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to the number of buffers allocated with &VIDIOC-REQBUFS;
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(&v4l2-requestbuffers; <structfield>count</structfield>) minus one.
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After calling <constant>VIDIOC_QUERYBUF</constant> with a pointer to
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this structure drivers return an error code or fill the rest of
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the structure.</para>
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<para>In the <structfield>flags</structfield> field the
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<constant>V4L2_BUF_FLAG_MAPPED</constant>,
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<constant>V4L2_BUF_FLAG_QUEUED</constant> and
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<constant>V4L2_BUF_FLAG_DONE</constant> flags will be valid. The
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<structfield>memory</structfield> field will be set to
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<constant>V4L2_MEMORY_MMAP</constant>, the <structfield>m.offset</structfield>
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contains the offset of the buffer from the start of the device memory,
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the <structfield>length</structfield> field its size. The driver may
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or may not set the remaining fields and flags, they are meaningless in
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this context.</para>
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<para>The <structname>v4l2_buffer</structname> structure is
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specified in <xref linkend="buffer" />.</para>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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<para>The buffer <structfield>type</structfield> is not
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supported, or the <structfield>index</structfield> is out of bounds.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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</refentry>
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<!--
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Local Variables:
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mode: sgml
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sgml-parent-document: "v4l2.sgml"
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indent-tabs-mode: nil
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End:
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-->
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