1<refentry id="vidioc-querybuf"> 2 <refmeta> 3 <refentrytitle>ioctl VIDIOC_QUERYBUF</refentrytitle> 4 &manvol; 5 </refmeta> 6 7 <refnamediv> 8 <refname>VIDIOC_QUERYBUF</refname> 9 <refpurpose>Query the status of a buffer</refpurpose> 10 </refnamediv> 11 12 <refsynopsisdiv> 13 <funcsynopsis> 14 <funcprototype> 15 <funcdef>int <function>ioctl</function></funcdef> 16 <paramdef>int <parameter>fd</parameter></paramdef> 17 <paramdef>int <parameter>request</parameter></paramdef> 18 <paramdef>struct v4l2_buffer *<parameter>argp</parameter></paramdef> 19 </funcprototype> 20 </funcsynopsis> 21 </refsynopsisdiv> 22 23 <refsect1> 24 <title>Arguments</title> 25 26 <variablelist> 27 <varlistentry> 28 <term><parameter>fd</parameter></term> 29 <listitem> 30 <para>&fd;</para> 31 </listitem> 32 </varlistentry> 33 <varlistentry> 34 <term><parameter>request</parameter></term> 35 <listitem> 36 <para>VIDIOC_QUERYBUF</para> 37 </listitem> 38 </varlistentry> 39 <varlistentry> 40 <term><parameter>argp</parameter></term> 41 <listitem> 42 <para></para> 43 </listitem> 44 </varlistentry> 45 </variablelist> 46 </refsect1> 47 48 <refsect1> 49 <title>Description</title> 50 51 <para>This ioctl is part of the <link linkend="mmap">memory 52mapping</link> I/O method. It can be used to query the status of a 53buffer at any time after buffers have been allocated with the 54&VIDIOC-REQBUFS; ioctl.</para> 55 56 <para>Applications set the <structfield>type</structfield> field 57 of a &v4l2-buffer; to the same buffer type as was previously used with 58&v4l2-format; <structfield>type</structfield> and &v4l2-requestbuffers; 59<structfield>type</structfield>, and the <structfield>index</structfield> 60 field. Valid index numbers range from zero 61to the number of buffers allocated with &VIDIOC-REQBUFS; 62 (&v4l2-requestbuffers; <structfield>count</structfield>) minus one. 63The <structfield>reserved</structfield> field should to set to 0. 64After calling <constant>VIDIOC_QUERYBUF</constant> with a pointer to 65 this structure drivers return an error code or fill the rest of 66the structure.</para> 67 68 <para>In the <structfield>flags</structfield> field the 69<constant>V4L2_BUF_FLAG_MAPPED</constant>, 70<constant>V4L2_BUF_FLAG_QUEUED</constant> and 71<constant>V4L2_BUF_FLAG_DONE</constant> flags will be valid. The 72<structfield>memory</structfield> field will be set to the current 73I/O method, the <structfield>m.offset</structfield> 74contains the offset of the buffer from the start of the device memory, 75the <structfield>length</structfield> field its size. The driver may 76or may not set the remaining fields and flags, they are meaningless in 77this context.</para> 78 79 <para>The <structname>v4l2_buffer</structname> structure is 80 specified in <xref linkend="buffer" />.</para> 81 </refsect1> 82 83 <refsect1> 84 &return-value; 85 86 <variablelist> 87 <varlistentry> 88 <term><errorcode>EINVAL</errorcode></term> 89 <listitem> 90 <para>The buffer <structfield>type</structfield> is not 91supported, or the <structfield>index</structfield> is out of bounds.</para> 92 </listitem> 93 </varlistentry> 94 </variablelist> 95 </refsect1> 96</refentry> 97 98<!-- 99Local Variables: 100mode: sgml 101sgml-parent-document: "v4l2.sgml" 102indent-tabs-mode: nil 103End: 104--> 105