Based on kernel version 4.7.2. Page generated on 2016-08-22 22:45 EST.
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">streaming 52 </link> I/O method. It can be used to query the status of a 53 buffer 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 61 to the number of buffers allocated with &VIDIOC-REQBUFS; 62 (&v4l2-requestbuffers; <structfield>count</structfield>) minus one. 63 The <structfield>reserved</structfield> and <structfield>reserved2 </structfield> 64 fields must be set to 0. 65 When using the <link linkend="planar-apis">multi-planar API</link>, the 66 <structfield>m.planes</structfield> field must contain a userspace pointer to an 67 array of &v4l2-plane; and the <structfield>length</structfield> field has 68 to be set to the number of elements in that array. 69 After calling <constant>VIDIOC_QUERYBUF</constant> with a pointer to 70 this structure drivers return an error code or fill the rest of 71 the structure.</para> 72 73 <para>In the <structfield>flags</structfield> field the 74 <constant>V4L2_BUF_FLAG_MAPPED</constant>, 75 <constant>V4L2_BUF_FLAG_PREPARED</constant>, 76 <constant>V4L2_BUF_FLAG_QUEUED</constant> and 77 <constant>V4L2_BUF_FLAG_DONE</constant> flags will be valid. The 78 <structfield>memory</structfield> field will be set to the current 79 I/O method. For the single-planar API, the <structfield>m.offset</structfield> 80 contains the offset of the buffer from the start of the device memory, 81 the <structfield>length</structfield> field its size. For the multi-planar API, 82 fields <structfield>m.mem_offset</structfield> and 83 <structfield>length</structfield> in the <structfield>m.planes</structfield> 84 array elements will be used instead and the <structfield>length</structfield> 85 field of &v4l2-buffer; is set to the number of filled-in array elements. 86 The driver may or may not set the remaining fields and flags, they are 87 meaningless in this context.</para> 88 89 <para>The <structname>v4l2_buffer</structname> structure is 90 specified in <xref linkend="buffer" />.</para> 91 </refsect1> 92 93 <refsect1> 94 &return-value; 95 96 <variablelist> 97 <varlistentry> 98 <term><errorcode>EINVAL</errorcode></term> 99 <listitem> 100 <para>The buffer <structfield>type</structfield> is not 101 supported, or the <structfield>index</structfield> is out of bounds.</para> 102 </listitem> 103 </varlistentry> 104 </variablelist> 105 </refsect1> 106 </refentry>
