vidioc-expbuf.rst

  1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
  2.. c:namespace:: V4L
  3
  4.. _VIDIOC_EXPBUF:
  5
  6*******************
  7ioctl VIDIOC_EXPBUF
  8*******************
  9
 10Name
 11====
 12
 13VIDIOC_EXPBUF - Export a buffer as a DMABUF file descriptor.
 14
 15Synopsis
 16========
 17
 18.. c:macro:: VIDIOC_EXPBUF
 19
 20``int ioctl(int fd, VIDIOC_EXPBUF, struct v4l2_exportbuffer *argp)``
 21
 22Arguments
 23=========
 24
 25``fd``
 26    File descriptor returned by :c:func:`open()`.
 27
 28``argp``
 29    Pointer to struct :c:type:`v4l2_exportbuffer`.
 30
 31Description
 32===========
 33
 34This ioctl is an extension to the :ref:`memory mapping <mmap>` I/O
 35method, therefore it is available only for ``V4L2_MEMORY_MMAP`` buffers.
 36It can be used to export a buffer as a DMABUF file at any time after
 37buffers have been allocated with the
 38:ref:`VIDIOC_REQBUFS` ioctl.
 39
 40To export a buffer, applications fill struct
 41:c:type:`v4l2_exportbuffer`. The ``type`` field is
 42set to the same buffer type as was previously used with struct
 43:c:type:`v4l2_requestbuffers` ``type``.
 44Applications must also set the ``index`` field. Valid index numbers
 45range from zero to the number of buffers allocated with
 46:ref:`VIDIOC_REQBUFS` (struct
 47:c:type:`v4l2_requestbuffers` ``count``) minus
 48one. For the multi-planar API, applications set the ``plane`` field to
 49the index of the plane to be exported. Valid planes range from zero to
 50the maximal number of valid planes for the currently active format. For
 51the single-planar API, applications must set ``plane`` to zero.
 52Additional flags may be posted in the ``flags`` field. Refer to a manual
 53for open() for details. Currently only O_CLOEXEC, O_RDONLY, O_WRONLY,
 54and O_RDWR are supported. All other fields must be set to zero. In the
 55case of multi-planar API, every plane is exported separately using
 56multiple :ref:`VIDIOC_EXPBUF` calls.
 57
 58After calling :ref:`VIDIOC_EXPBUF` the ``fd`` field will be set by a
 59driver. This is a DMABUF file descriptor. The application may pass it to
 60other DMABUF-aware devices. Refer to :ref:`DMABUF importing <dmabuf>`
 61for details about importing DMABUF files into V4L2 nodes. It is
 62recommended to close a DMABUF file when it is no longer used to allow
 63the associated memory to be reclaimed.
 64
 65Examples
 66========
 67
 68.. code-block:: c
 69
 70    int buffer_export(int v4lfd, enum v4l2_buf_type bt, int index, int *dmafd)
 71    {
 72	struct v4l2_exportbuffer expbuf;
 73
 74	memset(&expbuf, 0, sizeof(expbuf));
 75	expbuf.type = bt;
 76	expbuf.index = index;
 77	if (ioctl(v4lfd, VIDIOC_EXPBUF, &expbuf) == -1) {
 78	    perror("VIDIOC_EXPBUF");
 79	    return -1;
 80	}
 81
 82	*dmafd = expbuf.fd;
 83
 84	return 0;
 85    }
 86
 87.. code-block:: c
 88
 89    int buffer_export_mp(int v4lfd, enum v4l2_buf_type bt, int index,
 90	int dmafd[], int n_planes)
 91    {
 92	int i;
 93
 94	for (i = 0; i < n_planes; ++i) {
 95	    struct v4l2_exportbuffer expbuf;
 96
 97	    memset(&expbuf, 0, sizeof(expbuf));
 98	    expbuf.type = bt;
 99	    expbuf.index = index;
100	    expbuf.plane = i;
101	    if (ioctl(v4lfd, VIDIOC_EXPBUF, &expbuf) == -1) {
102		perror("VIDIOC_EXPBUF");
103		while (i)
104		    close(dmafd[--i]);
105		return -1;
106	    }
107	    dmafd[i] = expbuf.fd;
108	}
109
110	return 0;
111    }
112
113.. c:type:: v4l2_exportbuffer
114
115.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
116
117.. flat-table:: struct v4l2_exportbuffer
118    :header-rows:  0
119    :stub-columns: 0
120    :widths:       1 1 2
121
122    * - __u32
123      - ``type``
124      - Type of the buffer, same as struct
125	:c:type:`v4l2_format` ``type`` or struct
126	:c:type:`v4l2_requestbuffers` ``type``, set
127	by the application. See :c:type:`v4l2_buf_type`
128    * - __u32
129      - ``index``
130      - Number of the buffer, set by the application. This field is only
131	used for :ref:`memory mapping <mmap>` I/O and can range from
132	zero to the number of buffers allocated with the
133	:ref:`VIDIOC_REQBUFS` and/or
134	:ref:`VIDIOC_CREATE_BUFS` ioctls.
135    * - __u32
136      - ``plane``
137      - Index of the plane to be exported when using the multi-planar API.
138	Otherwise this value must be set to zero.
139    * - __u32
140      - ``flags``
141      - Flags for the newly created file, currently only ``O_CLOEXEC``,
142	``O_RDONLY``, ``O_WRONLY``, and ``O_RDWR`` are supported, refer to
143	the manual of open() for more details.
144    * - __s32
145      - ``fd``
146      - The DMABUF file descriptor associated with a buffer. Set by the
147	driver.
148    * - __u32
149      - ``reserved[11]``
150      - Reserved field for future use. Drivers and applications must set
151	the array to zero.
152
153Return Value
154============
155
156On success 0 is returned, on error -1 and the ``errno`` variable is set
157appropriately. The generic error codes are described at the
158:ref:`Generic Error Codes <gen-errors>` chapter.
159
160EINVAL
161    A queue is not in MMAP mode or DMABUF exporting is not supported or
162    ``flags`` or ``type`` or ``index`` or ``plane`` fields are invalid.