Documentation/media/uapi/v4l/vidioc-expbuf.rst

   1 .. -*- coding: utf-8; mode: rst -*-
   2
   3 .. _VIDIOC_EXPBUF:
   4
   5 *******************
   6 ioctl VIDIOC_EXPBUF
   7 *******************
   8
   9 Name
  10 ====
  11
  12 VIDIOC_EXPBUF - Export a buffer as a DMABUF file descriptor.
  13
  14
  15 Synopsis
  16 ========
  17
  18 .. c:function:: int ioctl( int fd, VIDIOC_EXPBUF, struct v4l2_exportbuffer *argp )
  19     :name: VIDIOC_EXPBUF
  20
  21
  22 Arguments
  23 =========
  24
  25 ``fd``
  26     File descriptor returned by :ref:`open() <func-open>`.
  27
  28 ``argp``
  29
  30
  31 Description
  32 ===========
  33
  34 This ioctl is an extension to the :ref:`memory mapping <mmap>` I/O
  35 method, therefore it is available only for ``V4L2_MEMORY_MMAP`` buffers.
  36 It can be used to export a buffer as a DMABUF file at any time after
  37 buffers have been allocated with the
  38 :ref:`VIDIOC_REQBUFS` ioctl.
  39
  40 To export a buffer, applications fill struct
  41 :c:type:`v4l2_exportbuffer`. The ``type`` field is
  42 set to the same buffer type as was previously used with struct
  43 :c:type:`v4l2_requestbuffers` ``type``.
  44 Applications must also set the ``index`` field. Valid index numbers
  45 range from zero to the number of buffers allocated with
  46 :ref:`VIDIOC_REQBUFS` (struct
  47 :c:type:`v4l2_requestbuffers` ``count``) minus
  48 one. For the multi-planar API, applications set the ``plane`` field to
  49 the index of the plane to be exported. Valid planes range from zero to
  50 the maximal number of valid planes for the currently active format. For
  51 the single-planar API, applications must set ``plane`` to zero.
  52 Additional flags may be posted in the ``flags`` field. Refer to a manual
  53 for open() for details. Currently only O_CLOEXEC, O_RDONLY, O_WRONLY,
  54 and O_RDWR are supported. All other fields must be set to zero. In the
  55 case of multi-planar API, every plane is exported separately using
  56 multiple :ref:`VIDIOC_EXPBUF` calls.
  57
  58 After calling :ref:`VIDIOC_EXPBUF` the ``fd`` field will be set by a
  59 driver. This is a DMABUF file descriptor. The application may pass it to
  60 other DMABUF-aware devices. Refer to :ref:`DMABUF importing <dmabuf>`
  61 for details about importing DMABUF files into V4L2 nodes. It is
  62 recommended to close a DMABUF file when it is no longer used to allow
  63 the associated memory to be reclaimed.
  64
  65
  66 Examples
  67 ========
  68
  69
  70 .. code-block:: c
  71
  72     int buffer_export(int v4lfd, enum v4l2_buf_type bt, int index, int *dmafd)
  73     {
  74         struct v4l2_exportbuffer expbuf;
  75
  76         memset(&expbuf, 0, sizeof(expbuf));
  77         expbuf.type = bt;
  78         expbuf.index = index;
  79         if (ioctl(v4lfd, VIDIOC_EXPBUF, &expbuf) == -1) {
  80             perror("VIDIOC_EXPBUF");
  81             return -1;
  82         }
  83
  84         *dmafd = expbuf.fd;
  85
  86         return 0;
  87     }
  88
  89
  90 .. code-block:: c
  91
  92     int buffer_export_mp(int v4lfd, enum v4l2_buf_type bt, int index,
  93         int dmafd[], int n_planes)
  94     {
  95         int i;
  96
  97         for (i = 0; i < n_planes; ++i) {
  98             struct v4l2_exportbuffer expbuf;
  99
 100             memset(&expbuf, 0, sizeof(expbuf));
 101             expbuf.type = bt;
 102             expbuf.index = index;
 103             expbuf.plane = i;
 104             if (ioctl(v4lfd, VIDIOC_EXPBUF, &expbuf) == -1) {
 105                 perror("VIDIOC_EXPBUF");
 106                 while (i)
 107                     close(dmafd[--i]);
 108                 return -1;
 109             }
 110             dmafd[i] = expbuf.fd;
 111         }
 112
 113         return 0;
 114     }
 115
 116
 117 .. c:type:: v4l2_exportbuffer
 118
 119 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
 120
 121 .. flat-table:: struct v4l2_exportbuffer
 122     :header-rows:  0
 123     :stub-columns: 0
 124     :widths:       1 1 2
 125
 126
 127     -  .. row 1
 128
 129        -  __u32
 130
 131        -  ``type``
 132
 133        -  Type of the buffer, same as struct
 134           :c:type:`v4l2_format` ``type`` or struct
 135           :c:type:`v4l2_requestbuffers` ``type``, set
 136           by the application. See :c:type:`v4l2_buf_type`
 137
 138     -  .. row 2
 139
 140        -  __u32
 141
 142        -  ``index``
 143
 144        -  Number of the buffer, set by the application. This field is only
 145           used for :ref:`memory mapping <mmap>` I/O and can range from
 146           zero to the number of buffers allocated with the
 147           :ref:`VIDIOC_REQBUFS` and/or
 148           :ref:`VIDIOC_CREATE_BUFS` ioctls.
 149
 150     -  .. row 3
 151
 152        -  __u32
 153
 154        -  ``plane``
 155
 156        -  Index of the plane to be exported when using the multi-planar API.
 157           Otherwise this value must be set to zero.
 158
 159     -  .. row 4
 160
 161        -  __u32
 162
 163        -  ``flags``
 164
 165        -  Flags for the newly created file, currently only ``O_CLOEXEC``,
 166           ``O_RDONLY``, ``O_WRONLY``, and ``O_RDWR`` are supported, refer to
 167           the manual of open() for more details.
 168
 169     -  .. row 5
 170
 171        -  __s32
 172
 173        -  ``fd``
 174
 175        -  The DMABUF file descriptor associated with a buffer. Set by the
 176           driver.
 177
 178     -  .. row 6
 179
 180        -  __u32
 181
 182        -  ``reserved[11]``
 183
 184        -  Reserved field for future use. Drivers and applications must set
 185           the array to zero.
 186
 187
 188 Return Value
 189 ============
 190
 191 On success 0 is returned, on error -1 and the ``errno`` variable is set
 192 appropriately. The generic error codes are described at the
 193 :ref:`Generic Error Codes <gen-errors>` chapter.
 194
 195 EINVAL
 196     A queue is not in MMAP mode or DMABUF exporting is not supported or
 197     ``flags`` or ``type`` or ``index`` or ``plane`` fields are invalid.