1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2
3.. _VIDIOC_EXPBUF:
4
5*******************
6ioctl VIDIOC_EXPBUF
7*******************
8
9Name
10====
11
12VIDIOC_EXPBUF - Export a buffer as a DMABUF file descriptor.
13
14
15Synopsis
16========
17
18.. c:function:: int ioctl( int fd, VIDIOC_EXPBUF, struct v4l2_exportbuffer *argp )
19    :name: VIDIOC_EXPBUF
20
21
22Arguments
23=========
24
25``fd``
26    File descriptor returned by :ref:`open() <func-open>`.
27
28``argp``
29    Pointer to struct :c:type:`v4l2_exportbuffer`.
30
31
32Description
33===========
34
35This ioctl is an extension to the :ref:`memory mapping <mmap>` I/O
36method, therefore it is available only for ``V4L2_MEMORY_MMAP`` buffers.
37It can be used to export a buffer as a DMABUF file at any time after
38buffers have been allocated with the
39:ref:`VIDIOC_REQBUFS` ioctl.
40
41To export a buffer, applications fill struct
42:c:type:`v4l2_exportbuffer`. The ``type`` field is
43set to the same buffer type as was previously used with struct
44:c:type:`v4l2_requestbuffers` ``type``.
45Applications must also set the ``index`` field. Valid index numbers
46range from zero to the number of buffers allocated with
47:ref:`VIDIOC_REQBUFS` (struct
48:c:type:`v4l2_requestbuffers` ``count``) minus
49one. For the multi-planar API, applications set the ``plane`` field to
50the index of the plane to be exported. Valid planes range from zero to
51the maximal number of valid planes for the currently active format. For
52the single-planar API, applications must set ``plane`` to zero.
53Additional flags may be posted in the ``flags`` field. Refer to a manual
54for open() for details. Currently only O_CLOEXEC, O_RDONLY, O_WRONLY,
55and O_RDWR are supported. All other fields must be set to zero. In the
56case of multi-planar API, every plane is exported separately using
57multiple :ref:`VIDIOC_EXPBUF` calls.
58
59After calling :ref:`VIDIOC_EXPBUF` the ``fd`` field will be set by a
60driver. This is a DMABUF file descriptor. The application may pass it to
61other DMABUF-aware devices. Refer to :ref:`DMABUF importing <dmabuf>`
62for details about importing DMABUF files into V4L2 nodes. It is
63recommended to close a DMABUF file when it is no longer used to allow
64the associated memory to be reclaimed.
65
66
67Examples
68========
69
70
71.. code-block:: c
72
73    int buffer_export(int v4lfd, enum v4l2_buf_type bt, int index, int *dmafd)
74    {
75	struct v4l2_exportbuffer expbuf;
76
77	memset(&expbuf, 0, sizeof(expbuf));
78	expbuf.type = bt;
79	expbuf.index = index;
80	if (ioctl(v4lfd, VIDIOC_EXPBUF, &expbuf) == -1) {
81	    perror("VIDIOC_EXPBUF");
82	    return -1;
83	}
84
85	*dmafd = expbuf.fd;
86
87	return 0;
88    }
89
90
91.. code-block:: c
92
93    int buffer_export_mp(int v4lfd, enum v4l2_buf_type bt, int index,
94	int dmafd[], int n_planes)
95    {
96	int i;
97
98	for (i = 0; i < n_planes; ++i) {
99	    struct v4l2_exportbuffer expbuf;
100
101	    memset(&expbuf, 0, sizeof(expbuf));
102	    expbuf.type = bt;
103	    expbuf.index = index;
104	    expbuf.plane = i;
105	    if (ioctl(v4lfd, VIDIOC_EXPBUF, &expbuf) == -1) {
106		perror("VIDIOC_EXPBUF");
107		while (i)
108		    close(dmafd[--i]);
109		return -1;
110	    }
111	    dmafd[i] = expbuf.fd;
112	}
113
114	return 0;
115    }
116
117
118.. c:type:: v4l2_exportbuffer
119
120.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
121
122.. flat-table:: struct v4l2_exportbuffer
123    :header-rows:  0
124    :stub-columns: 0
125    :widths:       1 1 2
126
127    * - __u32
128      - ``type``
129      - Type of the buffer, same as struct
130	:c:type:`v4l2_format` ``type`` or struct
131	:c:type:`v4l2_requestbuffers` ``type``, set
132	by the application. See :c:type:`v4l2_buf_type`
133    * - __u32
134      - ``index``
135      - Number of the buffer, set by the application. This field is only
136	used for :ref:`memory mapping <mmap>` I/O and can range from
137	zero to the number of buffers allocated with the
138	:ref:`VIDIOC_REQBUFS` and/or
139	:ref:`VIDIOC_CREATE_BUFS` ioctls.
140    * - __u32
141      - ``plane``
142      - Index of the plane to be exported when using the multi-planar API.
143	Otherwise this value must be set to zero.
144    * - __u32
145      - ``flags``
146      - Flags for the newly created file, currently only ``O_CLOEXEC``,
147	``O_RDONLY``, ``O_WRONLY``, and ``O_RDWR`` are supported, refer to
148	the manual of open() for more details.
149    * - __s32
150      - ``fd``
151      - The DMABUF file descriptor associated with a buffer. Set by the
152	driver.
153    * - __u32
154      - ``reserved[11]``
155      - Reserved field for future use. Drivers and applications must set
156	the array to zero.
157
158
159Return Value
160============
161
162On success 0 is returned, on error -1 and the ``errno`` variable is set
163appropriately. The generic error codes are described at the
164:ref:`Generic Error Codes <gen-errors>` chapter.
165
166EINVAL
167    A queue is not in MMAP mode or DMABUF exporting is not supported or
168    ``flags`` or ``type`` or ``index`` or ``plane`` fields are invalid.
169