Documentation/DocBook/media/v4l/vidioc-querybuf.xml

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